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SIMULIA Tosca Structure Documentation 8.1
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SIMULIA Tosca Structure
SIMULIA Tosca Structure
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SIMULIA Tosca Structure
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SIMULIA Tosca Structure
Table of Contents SIMULIA Tosca Structure Documentation 8.1 General Remarks
0-i
Volume I
Start Manual
1
Preface
1-3
Getting Started with Tosca ANSA environment
1-5
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Version 8.1.0 Rev. 1 - 05.2014
1.1 User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6 1.1.1 General Buttons toolbar 1.1.1.1 FOCUS panel 1.1.1.2 VISIBILITY panel 1.1.2 Database and selection windows 1.1.3 Task Manager window 1.1.4 Input of an existing parameter file 1.1.5 Saving task and saving database 1.1.6 Highlighting 1.1.7 Input and output using Task Manager 1.1.8 Input and output using the main menu 1.1.9 Modules Buttons window 1.1.10 Selecting and deselecting the geometric objects 1.1.10.1 Selecting single objects 1.1.10.2 Box selection 1.1.10.3 Polygon area selection 1.1.11 View control 1.1.11.1 Rotating 1.1.11.2 Translating 1.1.11.3 Zooming 1.1.11.4 Faster view selection 1.1.11.5 Function keys related to view control 1.1.12 Keys facilitating input in dialogs
1-8 1-9 1-10 1-11 1-13 1-14 1-15 1-15 1-18 1-19 1-20 1-20 1-21 1-21 1-22 1-23 1-23 1-24 1-24 1-24 1-25 1-25
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1.1.13 Managing Groups 1.1.13.1 SET HELP window 1.1.13.2 Selection of objects in group selection mode 1.1.13.3 List of Tosca Structure commands with groups 1.1.14 Configuration of Tosca ANSA environment
1-26 1-26 1-27 1-30 1-31
1.2.1 1.2.2 1.2.3 1.2.4 1.2.5
1.2.6
1.2.7 1.2.8 1.2.9
1.2.10
What is Topology Optimization? The Model Optimization Task Step by Step Manual: Summary Preprocessing 1.2.5.1 Choice of the optimization type 1.2.5.2 Loading the input model file 1.2.5.3 Choice of the design area 1.2.5.4 Choice of the design constraints 1.2.5.5 Choice of the objective function 1.2.5.6 Choice of the constraints 1.2.5.7 Saving Tosca Structure parameter file Start Optimization 1.2.6.1 Start Tosca Structure 1.2.6.2 Logging and monitoring Postprocessing Report Generation Result Transfer and Validation Run (Smooth) 1.2.9.1 Generating smooth surface 1.2.9.2 Modifying the surface using RECONSTRUCT 1.2.9.3 Remeshing the model 1.2.9.4 Saving the resulting model in solver format 1.2.9.5 Running the solver with the new model 1.2.9.6 Saving the resulting model in solver format (alternative) 1.2.9.7 Running the solver with the new model (alternative) Result Discussion
1-33 1-34 1-37 1-37 1-38 1-38 1-39 1-40 1-43 1-45 1-46 1-47 1-48 1-48 1-48 1-48 1-50 1-55 1-55 1-57 1-58 1-59 1-60 1-60 1-61 1-61
1.3 Shape Optimization with Tosca ANSA environment . . . . . . . . . . . 1-67 1.3.1 1.3.2 1.3.3 1.3.4 1.3.5
0 - vi
What is Shape Optimization? The Model Optimization Task Step by Step Manual: Summary Preprocessing 1.3.5.1 Choice of the optimization type 1.3.5.2 Loading the input model file 1.3.5.3 Selection of mesh smoothing elements 1.3.5.4 Choice of design area 1.3.5.5 Choice of design variable constraint 1.3.5.6 Choice of the objective function 1.3.5.7 Saving Tosca Structure parameter file
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1.2 Topology Optimization with Tosca ANSA environment . . . . . . . . . 1-33
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1.3.6 Node Displacement Check (Check Inputs) 1.3.7 Start Optimization 1.3.7.1 Start Tosca Structure 1.3.7.2 Logging and monitoring 1.3.7.3 Viewing the results in the optimized model 1.3.8 Postprocessing 1.3.9 Report Generation 1.3.10 Result transfer (Smooth) 1.3.10.1 Generating smooth surface 1.3.11 Result Discussion 1.3.12 Extensions 1.3.12.1 Design variable constraints 1.3.12.2 Define a volume constraint 1.3.12.3 Redefine the global stop condition 1.3.12.4 Selecting mesh smooth elements automatically 1.3.13 Troubleshooting 1.3.13.1 Suggestions in case of mesh problems
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1.4 Bead Optimization with Tosca ANSA environment . . . . . . . . . . . 1-113 1.4.1 What is Bead Optimization? 1.4.1.1 Tosca Structure.bead 1.4.2 The Model 1.4.3 Optimization Task 1.4.4 Step by Step Manual: Summary 1.4.5 Preprocessing 1.4.5.1 Choice of the optimization type 1.4.5.2 Loading the input model file 1.4.5.3 Choice of design area 1.4.5.4 Choice of the objective function 1.4.5.5 Choice of the constraint 1.4.5.6 Optimization settings 1.4.5.7 Saving Tosca Structure parameter file 1.4.6 Node Displacement Check (Check Inputs) 1.4.7 Start Optimization 1.4.7.1 Start Tosca Structure 1.4.7.2 Logging and monitoring 1.4.7.3 Viewing the results in the optimized model 1.4.8 Postprocessing 1.4.9 Report Generation 1.4.10 Result Transfer (Smooth) 1.4.10.1 Generating smooth surface 1.4.11 Result Discussion
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1.5 Sizing with Tosca ANSA environment . . . . . . . . . . . . . . . . . . . . . 1-145 1.5.1 What is Sizing Optimization?
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1.5.2 1.5.3 1.5.4 1.5.5
1.5.6
1.5.7 1.5.8 1.5.9
2
Model 1-146 Optimization Task 1-148 Step by Step Manual: Summary 1-149 Preprocessing 1-150 1.5.5.1 Choice of the optimization type 1-150 1.5.5.2 Loading the input model file 1-151 1.5.5.3 Choice of design area 1-152 1.5.5.4 Choice of thickness bounds (design variable constraint)1-155 1.5.5.5 Optional: Cluster groups 1-157 1.5.5.6 Choice of the objective function 1-157 1.5.5.7 Choice of the constraint 1-159 1.5.5.8 Saving Tosca Structure parameter file 1-159 Start Optimization 1-160 1.5.6.1 Start Tosca Structure 1-160 1.5.6.2 Logging and monitoring 1-160 Postprocessing 1-161 Report Generation 1-162 Result Discussion 1-167
Getting Started with Tosca Structure.gui
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2.1.1 Requirements, Settings and Program Start 2.1.2 Tosca Structure.pre 2.1.2.1 Overview 2.1.2.2 Creating, modifying and saving parameter files 2.1.2.3 Defining optimization tasks 2.1.2.4 Simplifications for the user 2.1.3 Starting the Optimization 2.1.4 Tosca Structure.smooth 2.1.5 Visualization with Tosca Structure.view 2.1.6 Postprocessing (Tosca Structure.report)
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2.2 Topology Optimization with Tosca Structure.gui . . . . . . . . . . . . . 1-189 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5
0 - viii
What is Topology Optimization? The Model Optimization Task Step by Step Manual: Summary Preprocessing 2.2.5.1 Starting Tosca Structure Preprocessor 2.2.5.2 Loading the input model file 2.2.5.3 Group creation (Nastran users only) 2.2.5.4 Define the design area 2.2.5.5 Choice of the design variable constraints 2.2.5.6 Definition of design responses 2.2.5.7 Choice of the objective function
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2.2.6 2.2.7 2.2.8 2.2.9
2.2.10
2.2.5.8 Choice of the constraints 2.2.5.9 Definition of the optimization task 2.2.5.10 Saving Tosca Structure parameter file Start Optimization Postprocessing Report Generation Result Transfer and Validation Run 2.2.9.1 Surface generation using Tosca Structure.smooth. 2.2.9.2 Processing the optimized structure Result Discussion
1-203 1-204 1-206 1-206 1-208 1-210 1-215 1-216 1-217 1-218
2.3 Shape Optimization with Tosca Structure.gui . . . . . . . . . . . . . . . 1-223 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5
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2.3.6
2.3.7 2.3.8 2.3.9 2.3.10 2.3.11 2.3.12
2.3.13
What is Shape Optimization? The Model Optimization Task Step by Step Manual: Summary Preprocessing 2.3.5.1 Starting Tosca Structure Preprocessor 2.3.5.2 Loading the input model file 2.3.5.3 Group creation (Nastran users only) 2.3.5.4 Select design area 2.3.5.5 Definition of design responses 2.3.5.6 Choice of the design variable constraint 2.3.5.7 Choice of the objective function 2.3.5.8 Select mesh smoothing elements 2.3.5.9 Definition of the optimization task 2.3.5.10 Define a stop condition 2.3.5.11 Saving Tosca Structure parameter file Check Inputs 2.3.6.1 TEST_SHAPE 2.3.6.2 Starting the test optimization 2.3.6.3 Viewing the test results Start Optimization Postprocessing Report Generation Result Transfer Result Discussion Extensions 2.3.12.1 Design variable constraints 2.3.12.2 Define a volume constraint 2.3.12.3 Updating the optimization task 2.3.12.4 Redefine the global stop condition 2.3.12.5 Selecting mesh smooth elements automatically Troubleshooting
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2.3.13.1 How to workaround mesh problems?
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2.4 Bead Optimization with Tosca Structure.gui . . . . . . . . . . . . . . . . 1-271 2.4.1 What is Bead Optimization? 2.4.1.1 Tosca Structure.bead 2.4.2 Model 2.4.3 Optimization Task 2.4.4 Step by Step Manual: Summary 2.4.5 Preprocessing 2.4.5.1 Starting Tosca Structure Preprocessor 2.4.5.2 Loading the input model file 2.4.5.3 Group creation (Nastran users only) 2.4.5.4 Select design area 2.4.5.5 Definition of design responses 2.4.5.6 Choice of the objective function 2.4.5.7 Create bead height constraint 2.4.5.8 Definition of the optimization task 2.4.5.9 Optimization settings 2.4.5.10 Saving Tosca Structure parameter file 2.4.6 Check Inputs 2.4.6.1 TEST_BEAD 2.4.6.2 Starting the test optimization 2.4.6.3 Viewing test results 2.4.7 Start Optimization 2.4.8 Postprocessing 2.4.8.1 Result Transfer 2.4.9 Report Generation 2.4.10 Result Discussion 2.4.10.1 Logging and monitoring
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2.5.1 2.5.2 2.5.3 2.5.4 2.5.5
What is Sizing Optimization? 1-305 Model 1-306 Optimization Task 1-308 Step by Step Manual: Summary 1-309 Preprocessing 1-310 2.5.5.1 Starting Tosca Structure Preprocessor 1-310 2.5.5.2 Loading the input model file 1-311 2.5.5.3 Define the design area 1-311 2.5.5.4 Choice of thickness bounds (design variable constraint)1-313 2.5.5.5 Optional: Cluster groups 1-314 2.5.5.6 Definition of design responses 1-315 2.5.5.7 Choice of the objective function 1-318 2.5.5.8 Choice of the constraints 1-319 2.5.5.9 Definition of the optimization task 1-320 2.5.5.10 Saving Tosca Structure parameter file 1-322 2.5.6 Start Optimization 1-322 0-x
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2.5 Sizing Optimization with Tosca Structure.gui. . . . . . . . . . . . . . . . 1-305
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2.5.7 Postprocessing 2.5.8 Report Generation 2.5.9 Result Discussion
3
Getting Started with Tosca Extension for ANSYS/WB
1-324 1-326 1-332
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3.1 User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-335 3.1.1 Buttons 3.1.2 Handling Tips
1-337 1-339
3.2 Topology Optimization with Tosca Extension for ANSYS/WB. . . 1-347 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6
The model Loading the Extension Example files Preparing the model Optimization preprocessing Postprocessing 3.2.6.1 Optimization result view options 3.2.6.2 Iteration Animation 3.2.7 Validation Run 3.2.8 Troubleshooting
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3.3 Shape Optimization with Tosca Extension for ANSYS/WB . . . . . 1-371
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3.3.1 3.3.2 3.3.3 3.3.4 3.3.5 3.3.6
The model Loading the extension Example files Preparing the model Optimization preprocessing Postprocessing 3.3.6.1 Optimization result view options 3.3.6.2 Iteration Animation 3.3.7 Troubleshooting
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Volume II
User Manual
1
Preface
2-3
Overview of Tosca Structure
2-5
1.1 The Tosca Structure Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5 1.1.1 Abaqus CAE
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1.1.2 1.1.3 1.1.4 1.1.5 1.1.6 1.1.7 1.1.8
Tosca ANSA environment Tosca Structure.gui Tosca Extension for ANSYS/WB Tosca Structure optimization modules Tosca Structure.report Tosca Structure.view Tosca Structure.smooth
2-6 2-6 2-6 2-7 2-7 2-7 2-7
1.2 Overview of the Optimization Process . . . . . . . . . . . . . . . . . . . . . . . 2-8 1.2.1 1.2.2 1.2.3 1.2.4 1.2.5 1.2.6
Planning Preprocessing: Model generation Check Run Optimization Loop Postprocessing: Evaluation of Optimization results Result Transfer and Validation Run
2-8 2-8 2-9 2-9 2-10 2-10
1.3 Workflow for Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11
2
Working with Tosca Structure
2-13
2.1 Working with Tosca ANSA environment . . . . . . . . . . . . . . . . . . . . 2-13 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5
Preprocessing Check Run Start Optimization Postprocessing Result Transfer and Validation Run
2-14 2-15 2-16 2-16 2-16
2.2.1 2.2.2 2.2.3 2.2.4 2.2.5
Preprocessing Check Run Start Optimization Postprocessing Result Transfer and Validation Run
2-18 2-19 2-19 2-20 2-21
2.3 Working with Tosca Extension for ANSYS/Workbench . . . . . . . . . 2-22 2.3.1 2.3.2 2.3.3 2.3.4
Preprocessing Start Optimization Postprocessing Result Transfer and Validation Run
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2.4 Working with Tosca Structure in the Command Shell . . . . . . . . . . 2-26 2.4.1 2.4.2 2.4.3 2.4.4 2.4.5
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Logging in command shell Preprocessing Check Run Start optimization Postprocessing
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2.2 Working with the Graphical User Interface Tosca Structure.gui . . 2-17
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2.4.6 Result Transfer
3
The Model
2-29
2-31
3.1 Models for Optimization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-31 3.1.1 3.1.2 3.1.3 3.1.4
Models for topology optimization Models for shape optimization Models for bead optimization Models for sizing
2-31 2-32 2-32 2-33
3.2 Optimizable Element Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-33 3.3 Preprocessing FE Models for Optimization . . . . . . . . . . . . . . . . . . 2-34 3.3.1 Abaqus/CAE 3.3.2 Preprocessing with ANSYS/Prep7 3.3.2.1 Generation of the finite element input file 3.3.2.2 Load cases 3.3.2.3 Check of the batch input file 3.3.2.4 Generation of groups 3.3.3 Preprocessing with ANSYS Workbench 3.3.3.1 Export of finite element input model 3.3.3.2 Generation of groups 3.3.3.3 Suitable meshes for topology optimization
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3.4 Loading FE Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-41
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3.4.1 3.4.2 3.4.3 3.4.4 3.4.5 3.4.6 3.4.7
Analysis Files for Optimization (FEM_INPUT) LIFE_FILE TEMPERATURE_FILE ADD_FILE COPY_FILE Special FEM_INPUT-commands Options for loading FE Data (OPTIONS) 3.4.7.1 Loading displacement restrictions 3.4.7.2 Identifying surface nodes for shape optimization
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3.5 Include Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-47 3.6 Group Definition (GROUP_DEF, GROUP_AUTO_DEF) . . . . . . . . . . 2-47 3.6.1 3.6.2 3.6.3 3.6.4 3.6.5
Default predefined groups Group definition in Tosca ANSA environment Group definition in Tosca Extension for ANSYS/WB Manual group definition in Tosca Structure.gui Automatic node group definition (GROUP_AUTO_DEF)
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3.7 Selection of Objects in Tosca Structure.gui. . . . . . . . . . . . . . . . . . 2-53 3.8 Coordinate Systems (CS_DEF) . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-59 3.8.1 Definition by three nodes
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3.8.2 Definition by coordinates of three points 3.8.3 Definition by origin and rotation angles 3.8.4 General remarks about coordinate systems
2-63 2-66 2-67
3.9 Solids (Geometric Primitives). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-68 3.9.1 Definition in Tosca ANSA environment 3.9.2 Definition in Tosca Structure.gui
4
Terms for Optimization
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4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-71 4.1.1 Mathematical formulation
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4.2 Objective Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-72 4.2.1 Overview 4.2.2 Minimization or maximization of an objective function 4.2.3 Multidisciplinary objectives (minmax formulation)
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4.4.1 Compliance (Stiffness Optimization) 4.4.1.1 Compliance example 4.4.2 Energy stiffness measure 4.4.2.1 Example for energy stiffness measure 4.4.3 Displacement and rotation 4.4.3.1 Example of a displacement design response 4.4.4 Reaction force 4.4.4.1 Example of reaction force design response 4.4.5 Internal force 4.4.5.1 Example internal force 4.4.6 Eigenfrequency 4.4.6.1 Eigenvalue example 4.4.6.2 Mode tracking 4.4.7 Equivalent stress 4.4.8 Stress in topology optimization 4.4.8.1 Example: Stresses in objective function 4.4.8.2 Example: Stresses in constraint definition 4.4.9 Center of gravity 4.4.10 Moment of inertia 4.4.11 Volume 4.4.11.1 Volume design response example 4.4.12 Weight 4.4.12.1 Example of a weight design response 4.4.13 DENSITY_MEASURE 4.4.14 Bead height
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4.5 Combined Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-143 0 - xiv
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4.3 Constraints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-79 4.4 Design Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-83
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4.5.1 Group operations for design responses 2-144 4.5.1.1 Group Operations for Stresses 2-145 4.5.1.2 Group Operations for Stiffness 2-145 4.5.1.3 Group Operations for Displacements 2-146 4.5.1.4 Group operations for reaction forces/moments 2-152 4.5.1.5 Group Operations for Internal Forces 2-156 4.5.2 Load case combination and selection 2-160 4.5.2.1 Load case specification (LC_SET) 2-160 4.5.2.2 Selection criteria for load cases (LC_SEL) 2-164 4.5.3 Design response combination 2-165 4.5.3.1 Combined responses in sensitivity based optimization 2-167 4.5.3.2 Combining design responses (Tosca ANSA environment)2-171 4.5.3.3 Combining displacements and rotations 2-174 4.5.3.4 Combining reaction forces and internal forces 2-175 4.5.3.5 Combining absolute values of responses 2-176 4.5.3.6 Controller based combined terms 2-176 4.5.3.7 Other operators for controller based shape optimization2-178
4.6 Logging and Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-178
5
Topology Optimization
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5.1 General Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-179 5.2 The Optimization Task. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-180 5.2.1 Controller versus sensitivity based topology optimization 5.2.2 How to create the optimization model
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5.3 Design Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-186 5.3.1 Design variables 2-186 5.3.1.1 Results from previous runs as initial material distribution2-188 5.3.2 Manufacturing conditions and geometrical restrictions 2-189 5.3.2.1 Frozen areas 2-190 5.3.2.2 Prevention of undercuts in the model 2-192 5.3.2.3 Tightness constraint for the resulting structure 2-199 5.3.2.4 Stamping restriction 2-203 5.3.2.5 Minimum truss thickness (minimum member size) 2-203 5.3.2.6 Maximum truss thickness (maximum member size) 2-207 5.3.2.7 Symmetry conditions 2-210 5.3.2.8 Combination of manufacturing restrictions 2-215 5.3.2.9 Tips on defining restrictions with Tosca Structure.gui 2-216
5.4 Objective Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-217 5.4.1 Overview 5.4.2 Minimization or maximization of an objective 5.4.3 Multidisciplinary objective (minmax formulation)
2-217 2-217 2-219
5.5 Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-220 5.5.1 Multiple material constraints and constitutive laws
2-223
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5.6 Typical Tasks for Static Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 2-226 5.6.1 5.6.2 5.6.3 5.6.4 5.6.5 5.6.6 5.6.7
Minimizing compliance under volume constraint Minimizing displacement/rotation under volume constraint Constraint for difference between two displacements Minimization of a reaction or internal force Minimization of the volume under displacement constraint Minimize the maximum stress with volume constraint Minimize the material volume with stress constraint
2-226 2-228 2-235 2-240 2-250 2-254 2-256
5.7 Typical Optimization Tasks for Modal Analysis . . . . . . . . . . . . . . 2-257 5.7.1 5.7.2 5.7.3 5.7.4
Maximization of the first eigenfrequencies Maximizing the eigenfrequency of a certain eigenmode Maximization of the band gap Constraining an eigenfrequency
2-258 2-262 2-267 2-270
5.8 Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-273 5.8.1 Parameters for standard linear static topology optimization 5.8.1.1 Increments of volume modification (SPEED) 5.8.1.2 Volume reduction in first iteration (START_DELETE) 5.8.1.3 Tips on speed control 5.8.1.4 Relation between relative density and stiffness 5.8.2 Settings for the general sensitivity based optimization 5.8.2.1 Mode tracking 5.8.2.2 Initial values of density 5.8.2.3 Removing soft elements for increasing performance 5.8.2.4 Limits for design variables and changes 5.8.2.5 Update strategy of the method of moving asymptotes 5.8.2.6 Settings of the mesh filter 5.8.2.7 FILTER_TYPE 5.8.2.8 Material interpolation
2-273 2-273 2-274 2-274 2-274 2-276 2-276 2-278 2-279 2-285 2-286 2-287 2-288 2-289
5.9.1 Convergence Criteria 5.9.1.1 Stop criterion: change in objective function 5.9.1.2 Stop criterion: change in element densities 5.9.1.3 Start iteration for convergence check 5.9.2 Global Stop Criterion (Number of iterations)
2-292 2-293 2-293 2-294 2-294
5.10 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-295
6
Shape Optimization
2-297
6.1 General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-297 6.1.1 Theoretical background
2-298
6.2 The Optimization Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-298 6.2.1 How to create the optimization model
2-298
6.3 Design Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-301 0 - xvi
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5.9 Stop Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-292
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SIMULIA Tosca Structure
6.3.1 Design variables (DV_SHAPE) 2-302 6.3.2 Mesh smoothing (MESH_SMOOTH) 2-305 6.3.2.1 Element group for mesh smoothing 2-306 6.3.2.2 Fixation of free surface nodes (FREE_SF) 2-309 6.3.2.3 Fixation of the MESH_SMOOTH area boundary 2-311 6.3.2.4 Automatic MESH_SMOOTH area (MS_LAYER) 2-311 6.3.2.5 Convergence of the smoothed mesh (LEVEL_CONV) 2-312 6.3.2.6 Enforcing restrictions (LEVEL_DVCON) 2-313 6.3.2.7 Quality control and improvement (LEVEL_QUAL) 2-313 6.3.2.8 Quality criteria of the solver (SOLVER_CHECK) 2-316 6.3.2.9 Correction of distorted elements (CORRECT_ELEMENTS) 2317 6.3.2.10 Mesh smooth strategy (STRATEGY) 2-318 6.3.2.11 Definition in Tosca ANSA environment 2-319 6.3.3 Restrictions (DVCON_SHAPE) 2-320 6.3.3.1 Node group for design variable constraints 2-322 6.3.3.2 Restricting the amount of displacement 2-323 6.3.3.3 Minimum or maximum member size 2-324 6.3.3.4 Displacement check against solids (CHECK_SOLID) 2-326 6.3.3.5 Penetration check (CHECK_ELGR, PENETRATION_CHECK) 2-328 6.3.3.6 Restricting displacement directions (CHECK_BC, CHECK_DOF) 2-329 6.3.3.7 Restricting displacement to a slide surface 2-330 6.3.3.8 Assigning link/coupling conditions (CHECK_LINK) 2-333 6.3.3.9 Definition in Tosca ANSA environment 2-334 6.3.3.10 Definition in Tosca Structure.gui 2-334 6.3.3.11 Command syntax 2-334 6.3.4 Link and coupling conditions (LINK_SHAPE) 2-336 6.3.4.1 Determining the master node (MASTER) 2-338 6.3.4.2 Displacement of the client nodes (CLIENT) 2-340 6.3.4.3 Plane symmetry (PLANE_SYM) 2-342 6.3.4.4 Plane symmetry for non-symmetric meshes (SURF_PLANE_SYM) 2-343 6.3.4.5 Cyclic symmetry for non-symmetric meshes (SURF_CYCLIC_SYM) 2-344 6.3.4.6 Cyclic-plane symmetry combination (SURF_CYCLIC_PLANE_SYM) 2-345 6.3.4.7 Point symmetry (POINT_SYM) 2-347 6.3.4.8 Rotational symmetry (ROTATION_SYM) 2-348 6.3.4.9 Coupling displacement coordinates (VECTOR) 2-349 6.3.4.10 Coupling displacement direction (DIRECTION) 2-350 6.3.4.11 Coupling amount of displacement (LENGTH) 2-351 6.3.4.12 Coupling coordinates in the FE displacement coordinate system (DISP_CS) 2-352 6.3.4.13 Stampable surface (SURF_STAMP) 2-352
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6.3.4.14 Turnable surface (SURF_TURN) 6.3.4.15 Drillable surface (SURF_DRILL) 6.3.4.16 Demoldable surface (SURF_DEMOLD) 6.3.4.17 Command examples
2-353 2-354 2-354 2-357
6.4 Objective Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-358 6.4.1 Overview 6.4.2 Reference stress 6.4.3 Objective function terms
2-358 2-359 2-360
6.5 Constraints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-362 6.5.1 Volume constraint 6.5.2 Weight constraint
2-362 2-364
6.6 Typical Optimization Tasks for Static Analysis . . . . . . . . . . . . . . 2-364 6.6.1 Minimization of maximum equivalent stress 6.6.2 Notch optimization with fixed reference value 6.6.3 Notch relief with variable reference value
2-364 2-367 2-369
6.7 Advanced Tosca Structure.shape Optimizations . . . . . . . . . . . . . 2-371 6.7.1 Highly nonlinear shape optimization 6.7.2 Minimization of contact pressure
2-371 2-373
6.8 Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-376 6.8.1 6.8.2 6.8.3 6.8.4 6.8.5 6.8.6
Scale of displacement (SCALE) Treatment of the midside nodes (MID_NODES) Curvature based modification of optimization displacements Filter function for the optimization displacements (FILTER) Updating the optimization displacement vectors (VECTOR) Control of the amount of optimization displacement (DISP)
2-377 2-378 2-379 2-380 2-382 2-383
6.9.1 6.9.2 6.9.3 6.9.4
General Test run (CHECK_INPUTS) in Tosca ANSA environment Test run in Tosca Structure.gui Command syntax
2-383 2-384 2-385 2-385
6.10 Morphing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-387 6.10.1 General 6.10.1.1 Morphing areas 6.10.1.2 Morphing displacement 6.10.1.3 Morphing task 6.10.2 Morphing in Tosca ANSA environment 6.10.3 Morphing in Tosca Structure.gui 6.10.4 Command Syntax 6.10.5 Postprocessing 6.10.6 Evaluation
2-388 2-389 2-392 2-393 2-395 2-396 2-396 2-398 2-399
6.11 Stop Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-399 0 - xviii
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6.11.1 6.11.2 6.11.3 6.11.4 6.11.5
Global Stop Condition Local Stop Condition Stop Condition in Tosca ANSA environment Stop Condition in Tosca Structure.gui Examples
2-400 2-400 2-401 2-402 2-403
6.12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-404
7
Bead Optimization
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7.1 General Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-405 7.2 The Optimization Task. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-406 7.2.1 7.2.2 7.2.3 7.2.4
Controller based bead optimization Sensitivity based bead optimization Differences between bead optimization algorithms How to create the optimization model
2-407 2-408 2-408 2-413
7.3 Design Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-416 7.3.1 Design variables (DV_BEAD) 2-416 7.3.2 Restrictions (DVCON_BEAD) 2-418 7.3.2.1 General 2-418 7.3.2.2 Restricting the absolute displacement 2-420 7.3.2.3 Displacement check against solids (CHECK_SOLID) 2-422 7.3.2.4 Displacement check against elements (CHECK_ELGR)2-423 7.3.2.5 Restricting the direction of displacement 2-424 7.3.2.6 Symmetry conditions (CHECK_LINK) 2-425 7.3.2.7 Example LINK_BEAD 2-426
7.4 Objective Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-428 7.4.1 Overview
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7.5 Typical Optimization Tasks for Linear Static Analysis . . . . . . . . . 2-430 7.5.1 Maximize stiffness with controller based algorithm 2-430 7.5.1.1 Combining static load cases (controller based algorithm)2-431 7.5.2 Linear static sensitivity based optimization 2-432 7.5.2.1 Minimize compliance 2-432
7.6 Typical Optimization Tasks for Modal Analysis . . . . . . . . . . . . . . 2-433 7.6.1 Maximization of the lowest natural frequency (controller) 7.6.2 Sensitivity based eigenvalue optimization 7.6.2.1 Maximize the first natural mode (first eigenvalue) 7.6.2.2 Maximize a range of modes 7.6.2.3 Maximize a certain mode 7.6.2.4 Adjust eigenvalue 7.6.2.5 Maximize band gaps
2-433 2-434 2-434 2-435 2-437 2-438 2-439
7.7 Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-440 7.8 Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-441
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7.8.1 Parameters for controller based bead optimization 2-444 7.8.1.1 Scaling of displacements (SCALE) 2-445 7.8.1.2 Update of optimization displacement vectors (VECTOR)2-445 7.8.1.3 Bead width (BEAD_WIDTH) 2-445 7.8.1.4 Number of iterations (BEAD_ITER) 2-446 7.8.1.5 Penalty conditions (BEAD_MIN_STRESS and BEAD_MAX_MEMBRANE) 2-446 7.8.1.6 Mesh enhancing parameters (CURV_SMOOTH and BEAD_NODE_SMOOTH) 2-448 7.8.2 Optimization parameters (sensitivity based bead optimization) 2-449 7.8.2.1 Filtering (FILTER_RADIUS) 2-449 7.8.2.2 MMA parameters 2-449 7.8.2.3 Optimization parameters for mode tracking 2-450 7.8.2.4 Optimization parameters for frequency response 2-450
7.9 7.10 7.11 7.12
8
Check run (TEST_BEAD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stop Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special Remarks Using Sensitivity Based Algorithm . . . . . . . . . . References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sizing Optimization
2-451 2-455 2-456 2-458
2-459
8.1 General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-459 8.2 The Optimization Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-460 8.2.1 How to create the optimization model
2-461
8.3.1 Design variables 8.3.2 Manufacturing conditions and geometrical restrictions 8.3.2.1 Frozen areas 8.3.2.2 Shell thickness bounds 8.3.2.3 Cluster groups 8.3.2.4 Width control (minimum cluster width) 8.3.2.5 Definition of symmetry conditions 8.3.2.6 Tips on defining restrictions
2-463 2-465 2-466 2-467 2-469 2-471 2-473 2-476
8.4 Objective Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-477 8.4.1 Overview 8.4.2 Minimization or maximization of an objective 8.4.3 Multidisciplinary objective (minmax formulation)
2-477 2-477 2-479
8.5 Constraints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-481 8.6 Typical Tasks for Static Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 2-483 8.6.1 Minimizing mass with stiffness restrictionst
2-483
8.7 Typical Optimization Tasks for Modal Analysis . . . . . . . . . . . . . . 2-486 8.7.1 Maximization of the first eigenfrequencies 8.7.2 Maximizing the torsional modal eigenfrequency 0 - xx
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8.8 Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-495 8.8.1 8.8.2 8.8.3 8.8.4
Mode tracking Update strategy of the method of moving asymptotes Settings of the mesh filter FILTER_TYPE
2-495 2-497 2-498 2-499
8.9 Stop Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-499 8.9.1 Convergence Criteria 8.9.1.1 Stop criterion: change in objective function 8.9.1.2 Stop criterion: change in element thickness 8.9.1.3 Start iteration for convergence check 8.9.2 Global Stop Criterion (Number of iterations)
9
Result Transfer and Validation Run
2-499 2-500 2-500 2-501 2-501
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9.1 Tosca Structure.smooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-505
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9.1.1 Starting Tosca Structure.smooth (Tosca ANSA environment) 9.1.2 Starting Tosca Structure.smooth (Tosca Structure.gui) 9.1.3 Starting Tosca Structure.smooth (Tosca Extension for ANSYS/ Workbench)2-508 9.1.4 Defining the parameters for Tosca Structure.smooth 9.1.5 Processing results of topology optimization 9.1.6 Processing results from shape or bead optimization 9.1.7 Isosurface and smoothing parameters 9.1.8 Reduction parameters 9.1.9 Output parameters 9.1.10 Slices through 3D models and border of 2D models 9.1.11 Processing of groups 9.1.12 Volume control 9.1.13 Correction of defects in topology optimization results 9.1.14 Troubleshooting
2-506 2-507
2-510 2-516 2-519 2-520 2-525 2-529 2-533 2-536 2-538 2-540 2-542
9.2 Validation Run in Tosca ANSA environment . . . . . . . . . . . . . . . . 2-544 9.2.1 9.2.2 9.2.3 9.2.4
BATCH_RECONSTRUCT and MANUAL_RECONSTRUCT SOLID_MESH Generating the model for validation run Starting the validation run
2-545 2-549 2-549 2-552
9.3 Validation Run in Tosca Extension for ANSYS/Workbench . . . . 2-553 9.4 Workarounds Using Other Environments . . . . . . . . . . . . . . . . . . 2-561 9.5 Result Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-562 9.5.1 Result transfer to CATIA RSO module 9.5.2 Result transfer to NX
2-562 2-562
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10 Postprocessing of Optimization Results
2-565
10.1 Generation of Postprocessing Data . . . . . . . . . . . . . . . . . . . . . . . 2-565 10.1.1 Tosca Structure.report in Tosca ANSA environment 2-566 10.1.2 Tosca Structure.report in Tosca Structure.gui 2-568 10.1.3 Tosca Structure.report in Tosca Extension for ANSYS/Workbench 2571 10.1.4 Starting Tosca Structure.report in Commandline 2-573 10.1.5 Standard Reports 2-574 10.1.5.1 Tosca Structure.topology results 2-574 10.1.5.2 Tosca Structure.shape results 2-575 10.1.5.3 Tosca Structure.bead results 2-577 10.1.5.4 Tosca Structure.sizing results 2-577 10.1.5.5 Morphing results 2-578 10.1.5.6 Sensitivity plots 2-579
10.2 Tosca Structure.view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-580 10.2.1 10.2.2 10.2.3 10.2.4 10.2.5 10.2.6 10.2.7 10.2.8 10.2.9
Starting and using Tosca Structure.view User Interface Tosca Structure.view Model and group visualization Visualization of topology optimization results Visualization of shape optimization results Visualization of bead optimization results Visualization of sizing results Visualization of morphing results VTFX PlugIn for Office applications and Webbrowser 10.2.9.1 Prerequisites and installation 10.2.9.2 Embedding the PlugIn into PowerPoint 10.2.10Integrating VTFX files in internet pages 10.2.11Limitations of the PlugIn
2-580 2-582 2-588 2-591 2-592 2-594 2-595 2-596 2-596 2-596 2-597 2-599 2-600
10.3.1 Optimization result view options 10.3.2 Iteration Animation 10.3.3 Result files
2-600 2-602 2-603
10.4 Tosca Structure Report Builder. . . . . . . . . . . . . . . . . . . . . . . . . . 2-603 10.4.1 Capturing Data for the Report 10.4.2 Report generation 10.4.3 Add-Ins for Tosca Structure Report Builder 10.4.3.1 Add-in for MS Word 10.4.3.2 Add-in for MS Powerpoint 10.4.3.3 Templates
2-604 2-606 2-607 2-608 2-609 2-610
10.5 Toolbox for Postprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-611 10.5.1 Numerical variables (VARIABLE) 10.5.2 Logical variables (LOGICAL) 0 - xxii
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10.3 Postprocessing with Tosca Extension for ANSYS/Workbench . . 2-600
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10.5.3 Stop conditions (STOP) 10.5.4 User defined output files (USER_FILE) 10.5.4.1 Tabular output 10.5.4.2 Modification file for CATIA RSO module 10.5.4.3 Modification file for NX 10.5.4.4 ONF output
11 Solver Specific Features
2-613 2-615 2-616 2-616 2-617 2-618
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11.1 Abaqus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-622 11.1.1 11.1.2 11.1.3 11.1.4 11.1.5 11.1.6 11.1.7 11.1.8 11.1.9
Files and formats Supported element types Node and Element Groups Coordinate Systems Materials and Properties Analysis Types Loads and Boundary Conditions Remarks for sensitivity based optimizations Nonsupported Features (Cards/Keywords...)
2-622 2-624 2-630 2-632 2-632 2-635 2-637 2-638 2-639
11.2 ANSYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-639 11.2.1 11.2.2 11.2.3 11.2.4 11.2.5 11.2.6 11.2.7 11.2.8
Files and Formats Supported Element Types Node and Element Groups Coordinate Systems Materials and Properties Analysis Types Loads and Boundary Conditions Remarks for sensitivity based optimizations
2-640 2-642 2-644 2-645 2-645 2-647 2-649 2-649
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11.3 Marc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-652 11.3.1 11.3.2 11.3.3 11.3.4 11.3.5 11.3.6 11.3.7 11.3.8
Files and Formats Supported Element Types Coordinate Systems Materials and Properties Analysis Types Loads and Boundary Conditions Remarks for sensitivity based optimizations Frequency spectrum
2-652 2-653 2-657 2-657 2-657 2-658 2-658 2-659
11.4 MSC Nastran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-659 11.4.1 Files and Formats 11.4.2 Supported Element Types 11.4.3 Coordinate Systems
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11.4.4 11.4.5 11.4.6 11.4.7 11.4.8
Materials and Properties Analysis Types Loads and Boundary Conditions Remarks for sensitivity based optimizations Frequency spectrum
2-663 2-663 2-666 2-667 2-668
11.5 PERMAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-668 11.5.1 Files and Formats 11.5.2 Supported Element Types 11.5.3 Node and Element Groups 11.5.4 Coordinate Systems 11.5.5 Materials and Properties 11.5.6 Analysis Types 11.5.7 Loads and Boundary Conditions 11.5.8 Remarks for sensitivity based optimizations 11.5.9 PERMAS Configuration for use with Tosca Structure 11.5.10Nonsupported Features (Cards/Keywords...) 11.5.11Frequency spectrum
2-669 2-670 2-673 2-674 2-674 2-674 2-675 2-676 2-676 2-676 2-677
11.6.1 Supported durability solvers 11.6.2 Workflow 11.6.2.1 Preprocessing 11.6.2.2 Optimization loop 11.6.2.3 Definition of the optimization task 11.6.2.4 Start of the optimization 11.6.2.5 Postprocessing 11.6.3 FEMFAT 11.6.3.1 General 11.6.4 fe-safe 11.6.5 ONF 11.6.5.1 General
12 Tosca Structure Control
2-677 2-678 2-678 2-679 2-679 2-680 2-682 2-682 2-682 2-685 2-687 2-687
2-689
12.1 Program Sequence and Data Flow of Tosca Structure . . . . . . . . 2-689 12.2 Starting Tosca Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-691 12.2.1 List of command line options 12.2.1.1 Deprecated command line options 12.2.2 General 12.2.3 Logging 12.2.3.1 TOSCA.OUT 12.2.3.2 Special logfiles 12.2.3.3 Viewing TOSCA.OUT using Tosca ANSA environment 12.2.3.4 Viewing TOSCA.OUT using Tosca Structure.gui
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11.6 Shape Optimization Based on a Durability Analysis . . . . . . . . . . 2-677
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12.2.3.5 Viewing TOSCA.OUT using Tosca Extension for ANSYS/WB2700 12.2.3.6 Changing logging using the command shell 2-701 12.2.3.7 Tips and tricks viewing TOSCA.OUT 2-701 12.2.4 Solver interface 2-703 12.2.5 Durability interface 2-703 12.2.6 Tosca Structure.report run 2-703 12.2.6.1 Configuring default Tosca Structure.report run 2-704 12.2.7 Automatic Tosca Structure.smooth run 2-704 12.2.7.1 Configuring default Tosca Structure.smooth run 2-705 12.2.8 Testing the optimization process 2-705 12.2.8.1 Test level 1 2-705 12.2.8.2 Test level 2 2-706 12.2.8.3 Test level 3 2-707 12.2.8.4 Test level 4 2-708 12.2.9 Restart modes 2-709 12.2.9.1 Requirements for a restart 2-709 12.2.9.2 Restart process 2-709 12.2.10Online help 2-710 12.2.11Sequential temperature analysis 2-711 12.2.12Arbitrary analysis sequence 2-711
12.3 Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-712 12.3.1 Configuration files 12.3.2 Environment variables
2-712 2-714
12.4 Script Entry Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-715 12.4.1 Adding files to the working directory
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12.5 Optimization Preprocessing (TOSCA_PREP) . . . . . . . . . . . . . . . 2-719
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12.6 Solver Run. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-720 12.7 Optimization Module (TOSCA_OPT). . . . . . . . . . . . . . . . . . . . . . 2-720 12.7.1 RES2VTM 12.7.2 TOSCA_OPT 12.7.3 FEM_MODIF
2-721 2-721 2-721
12.8 Completion of the Optimization Process . . . . . . . . . . . . . . . . . . . 2-721 12.8.1 Directories and files after the completion of optimization
13 Troubleshooting
2-721
2-723
13.1 Errors During Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-723 13.2 Determining the Point of Program Termination . . . . . . . . . . . . . . 2-724
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13.3 Program Abort at the Start of the Optimization . . . . . . . . . . . . . . 2-728 13.3.1 Check of program installation and paths 13.3.2 Analysis files not found
2-728 2-730
13.4 Program Abort in TOSCA_PREP. . . . . . . . . . . . . . . . . . . . . . . . . 2-731 13.5 Program Abort During FE Analysis . . . . . . . . . . . . . . . . . . . . . . . 2-733 13.5.1 Error in the analysis model 13.5.2 Error with the solver license 13.5.3 Incorrect solver settings
2-733 2-735 2-735
13.6 Program Abort in the Optimization Module . . . . . . . . . . . . . . . . . 2-735 13.6.1 FE model of the next iteration is not calculated 13.6.2 Insufficient disk space
2-735 2-737
13.7 Tosca ANSA environment Specific Tips . . . . . . . . . . . . . . . . . . . 2-737
14 Appendix
2-741
14.1 Additional Tosca Structure optimization modules . . . . . . . . . . . . 2-741 14.1.1 Tosca Structure.durability 14.1.2 Tosca Structure.nonlinear 14.1.3 Tosca Structure.morph
2-741 2-741 2-742
14.2 Limits of Tosca Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-743 14.3 Predefined Output Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-744
Volume III CONFIG CONSTRAINT CONTOURPLOT CS_DEF DRESP DVCON_AUTO_SHAPE DVCON_BEAD DVCON_SHAPE DVCON_SIZING DVCON_TOPO DV_BEAD DV_SHAPE DV_SIZING 0 - xxvi
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DV_TOPO FEM_INPUT GROUP_AUTO_DEF GROUP_DEF GROUP_IMPORT INCLUDE LINK_BEAD LINK_SHAPE LINK_SIZING LINK_TOPO LIST LIST, info LOGICAL MESH_SMOOTH MORPH MORPH_AREA OBJ_FUNC OPTIMIZE OPTIONS OPT_PARAM REPORT SELECT SF_IDENT SMOOTH SOLID STOP TEST_BEAD TEST_SHAPE USER_FILE VARIABLE
3-70 3-72 3-75 3-78 3-81 3-82 3-83 3-84 3-95 3-97 3-100 3-106 3-107 3-109 3-115 3-117 3-118 3-120 3-123 3-129 3-143 3-146 3-153 3-154 3-162 3-163 3-166 3-168 3-170 3-178
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Volume IV
Examples Manual
1
Preface
4-3
Topology Optimization
4-5
1.1 Example overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 1.2 Airbeam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6 1.2.1 1.2.2 1.2.3 1.2.4 1.2.5 1.2.6
Model Optimization Task Procedure: Summary Procedure in Detail: Tosca ANSA environment Procedure in Detail: Tosca Structure.gui Results
4-6 4-6 4-7 4-7 4-7 4-10
1.3 Picker_arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11 1.3.1 1.3.2 1.3.3 1.3.4 1.3.5 1.3.6
Model Optimization Task Procedure: Summary Procedure in Detail: Tosca ANSA environment Procedure in Detail: Tosca Structure.gui Optimization results
4-11 4-11 4-11 4-12 4-13 4-15
1.4 Crane Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15 1.4.1 Procedure: Summary 1.4.2 Procedure in Detail: Tosca ANSA environment 1.4.3 Procedure in Detail: Tosca Structure.gui
4-18 4-18 4-19
1.5.1 Procedure: Summary 1.5.2 Procedure in Detail: Tosca ANSA environment 1.5.3 Procedure in Detail: Tosca Structure.gui
4-22 4-22 4-23
1.6 Minimum und Maximum Member Size (plate_min_max) . . . . . . . . 4-26 1.6.1 Procedure: Summary 1.6.2 Procedure in Detail: Tosca ANSA environment 1.6.3 Procedure in Detail: Tosca Structure.gui
2
Sensitivity Based Topology Optimization
4-26 4-27 4-28
4-31
2.1 Example overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31 2.2 Crane hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-32 2.2.1 Procedure: Summary 2.2.2 Procedure in detail: Tosca ANSA environment
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1.5 Beam with Symmetry Restrictions (airbeam_sym) . . . . . . . . . . . . 4-21
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2.2.3 Procedure in detail: Tosca Structure.gui 2.2.4 Optimization results
4-37 4-40
2.3 Symmetric Plate (plate_sym_freq) . . . . . . . . . . . . . . . . . . . . . . . . 4-44 2.3.1 2.3.2 2.3.3 2.3.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-45 4-45 4-46 4-49
2.4 Bonnet with Minmax Formulation . . . . . . . . . . . . . . . . . . . . . . . . . 4-50 2.4.1 2.4.2 2.4.3 2.4.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-50 4-51 4-51 4-53
2.5 Crankshaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-56 2.5.1 2.5.2 2.5.3 2.5.4 2.5.5
The model Optimization task Optimization task definition in Tosca ANSA environment Optimization task definition in Tosca Structure.gui Result discussion and validation run
4-56 4-57 4-57 4-59 4-62
2.6 Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-64 2.6.1 Procedure: Summary 2.6.2 Procedure in detail: Tosca ANSA environment 2.6.3 Procedure in detail: Tosca Structure.gui
4-66 4-66 4-67
2.7 Internal Forces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-68 2.7.1 2.7.2 2.7.3 2.7.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results when considering force constraints
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2.8 Temperature Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-78 2.8.1 2.8.2 2.8.3 2.8.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-79 4-79 4-80 4-83
2.9 Stress Constraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-84 2.9.1 2.9.2 2.9.3 2.9.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-84 4-85 4-86 4-88
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3
Shape Optimization
4-89
3.1 Example overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-89 3.2 Holeplate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-91 3.2.1 3.2.2 3.2.3 3.2.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-92 4-92 4-93 4-94
3.3 Two Hole (Relief Notch) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-94 3.3.1 3.3.2 3.3.3 3.3.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-95 4-96 4-96 4-97
3.4 Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-98 3.4.1 3.4.2 3.4.3 3.4.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-98 4-99 4-99 4-103
3.5 Carrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-103 3.5.1 3.5.2 3.5.3 3.5.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-104 4-104 4-105 4-108
3.6 Carrier_stamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-108 Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization result
4-110 4-111 4-111 4-112
3.7 Shaft_turn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-112 3.7.1 Procedure: Summary 3.7.2 Procedure in detail: Tosca ANSA environment 3.7.3 Procedure in detail: Tosca Structure.gui
4-114 4-115 4-116
3.8 Shaft_drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-117 3.8.1 Procedure: Summary 3.8.2 Procedure in detail: Tosca ANSA environment 3.8.3 Procedure in detail: Tosca Structure.gui
4-118 4-119 4-120
3.9 Clip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-122 3.9.1 3.9.2 3.9.3 3.9.4 0 - xxx
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
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3.10 Rim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-127 3.10.1 3.10.2 3.10.3 3.10.4 3.10.5
The model Optimization task Procedure in Detail: Tosca ANSA environment Procedure in Detail: Tosca Structure.gui Result discussion
4-128 4-128 4-128 4-132 4-134
3.11 Threehole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-135 3.11.1 3.11.2 3.11.3 3.11.4
Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
4-136 4-136 4-136 4-137
3.12 Hub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-138 3.12.1 3.12.2 3.12.3 3.12.4 3.12.5
4
The model Procedure: Summary Procedure in detail: Tosca ANSA environment Procedure in detail: Tosca Structure.gui Optimization results
Bead Optimization
4-139 4-140 4-140 4-141 4-143
4-147
4.1 Example overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-147 4.2 Plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-148 4.2.1 Procedure: Summary 4.2.2 Procedure in Detail: Tosca ANSA environment 4.2.3 Procedure in Detail: Tosca Structure.gui
4-149 4-149 4-150
4.3 Hood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-152
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4.3.1 4.3.2 4.3.3 4.3.4
Procedure: Summary Procedure in Detail: Tosca ANSA environment Procedure in Detail: Tosca Structure.gui Optimization results
4-153 4-153 4-154 4-157
4.4 Hood_eig and Hood_eig_sens . . . . . . . . . . . . . . . . . . . . . . . . . . 4-157 4.4.1 4.4.2 4.4.3 4.4.4
4.5
5
Eigenfrequency optimization with Tosca Structure.bead Eigenfrequency optimization using controller algorithm Eigenfrequency optimization using sensitivity algorithm Discussion of differences
4-157 4-158 4-160 4-162
Holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-164
Sizing
4-169
5.1 Examples overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-169 5.2 Beam2D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-170
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5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.2.6
Model Optimization Task Procedure: Summary Procedure in Detail: Tosca ANSA environment Procedure in Detail: Tosca Structure.gui Results
4-170 4-171 4-171 4-171 4-173 4-176
5.3 Beam with Symmetry Restrictions (beam_sym) . . . . . . . . . . . . . 4-177 5.3.1 5.3.2 5.3.3 5.3.4
6
Procedure: Summary Procedure in Detail: Tosca ANSA environment Procedure in Detail: Tosca Structure.gui Optimization results
Shape Optimization in Combination with Durability Analysis
4-178 4-178 4-179 4-181
4-183
6.1 Holeplate_dam: Femfat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-184 6.2 Holeplate_dam: fe-safe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-186
7
Morphing
4-189
7.1 Crane hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-189 Procedure: Summary Procedure in Detail: Tosca ANSA environment Procedure in Detail: Tosca Structure.gui Optimization results
4-191 4-191 4-198 4-200
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SIMULIA Tosca Structure General Remarks
General Remarks Documentation Manuals Tosca Structure documentation is contained in the following manuals: • Getting Started with Tosca Structure (volume 1) • User Manual (volume 2) • Commands Manual (volume 3) • Examples Manual (volume 4) • Installation Manual
Description of Manuals A short description and comment of the content of each manual is given below: Getting Started Manual (volume 1) This manual gives a compact introduction to Tosca Structure and the work with the frontends Tosca ANSA environment, Tosca Structure.gui and Tosca Extension for ANSYS/Workbench. The set-up, running and evalution of typical optimization tasks for each type of optimization are explained in detail. Thus in particular new users are able to find an access to Tosca Structure quickly and efficiently whereas experienced users can look up detailed descriptions of specific work steps.
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User Manual (volume 2) The main usage of the Tosca Structure functionalities are explained here along with entry of the control instructions required to generate an optimization model. A description of the individual command syntax is not given, only how they work and interact with each other. The Commands Manual lists a full description of the command syntax. The User Manual is divided into various parts: firstly, the user receives an overview of the program procedures and the program modules. Requirements for optimizable finite element models are described. Next a detailed explanation of the functionalities for topology, shape, bead and sizing optimization is given. Visualization and postprocessing possibilities are also shown. Finally, a description of additional tools and examples of control records for topology, shape, bead and sizing optimization is presented.
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Commands Manual (volume 3) The Commands Manual is the lexicon of Tosca Structure.topology, Tosca Structure.shape, Tosca Structure.bead and Tosca Structure.sizing. The lexicon contains a complete description of all commands used. Each command and its syntax is listed in alphabetical order with an explanation. Cross-references on how to use other commands are also listed here. Most commands are listed with an entry example. How to use the main functionalities is explained in the Users Manual. Examples Manual (volume 4) The examples provided with the installation are described in more detail in this manual. Not only does this aid in creating a better understanding of the problems involved in finding a solution, but also gives an understanding of the obtained solutions to the problems.
Reference to Spelling Used in the Manuals To differentiate between command names, parameters, fixed and open parameter values, several different styles of fonts are used as highlighted in the examples below: • Command names and parameter labels are always written in capital letters. • Fixed options used for switching parameters are written in capital letters and are also emphasized where necessary. • Names selected by the user are written in small letters.
• Names which are addressed in detail in the text or which have a special meaning in context are written in bold letters. • Chosen values are marked in square brackets. • Tosca ANSA environment buttons and functions are denoted in Courier New. • Tosca Structure commands and parameters are either linked to the corresponding commands manual entry or denoted in Courier New. • If an action (normally right mouse click) or choice is required, brackets [] are used.
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• Names which refer to a predefined ID are written in small, cursive letters.
SIMULIA Tosca Structure General Remarks
Examples for Tosca Structure commands: GROUP_DEF ID_NAME TYPE FORMAT
=design_elements--> user name =ELEM--> given option =SELECTED--> given option
END_ DV_TOPO ID_NAME EL_GROUP
= dv_design_elements--> user name = design_elements--> reference to a group
END_ STOP ID_NAME ITER_MAX
= stop_condition--> user name = --> chosen value
END_
Examples for Tosca ANSA environment functions: PRE-PROCESSING| SHAPE_OPTIMIZATION_CONTROLLER | DESIGN_AREA | [EDIT] In the task manager choose (evtl. open / expand) Folder PRE-PROCESSING, subfolder SHAPE_OPTIMIZATION_CONTROLLER, subfolder DESIGN_AREA, right mouse click and choose EDIT.
The entire content of the documentation is available as context sensitive online help directly accessible from Tosca Structure.gui or the windows start menu. Further, a printable pdf document can be found under the filename: $tosca/docu/tosca_structure_v810.pdf
The online documentation supports hypertext functions, therefore the navigation through the various manuals is easy and fast. Acrobat Reader from Adobe or another pdf reader is needed to visualize the pdf document. The reader is available at the internet address http:// www.adobe.com.
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Documentation and Introduction to Optimization
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Volume I
Start Manual
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SIMULIA Tosca Structure
SIMULIA Tosca Structure Preface
Preface
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This manual demonstrates how to work with the structural optimization package Tosca Structure. In the chapters chapter 1 Getting Started with Tosca ANSA environment, chapter 2 Getting Started with Tosca Structure.gui and chapter 3 Getting Started with Tosca Extension for ANSYS/WB, it is explained how these three different front ends can be used in order to define, start and process the optimization task. The following tutorials demonstrate for all front ends how to set up, run and evaluate typical topology, shape, bead and sizing optimization tasks. The step by step explanation contained in the tutorials enables a user inexperienced with Tosca Structure to set up a simple optimization task. No emphasis has been placed on details about the single optimization settings. These details are covered in vol.2 User Manual and vol.3 Commands Manual.
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SIMULIA Tosca Structure Getting Started with Tosca ANSA
1
Getting Started with Tosca ANSA environment Tosca ANSA environment is used in order to define an optimization task for Tosca Structure based on an existing finite element input deck. The finite element model, including the loads and boundary conditions, is loaded into Tosca ANSA environment, so that the user is able to examine the model in detail. Then, the optimization task is defined by the user step by step. The geometric information represented in Tosca ANSA environment enables the interactive group selection as well as other actions that facilitate the definition of optimization task. Then, the optimization in Tosca Structure is started from within Tosca ANSA environment using the original finite element model and the optimization task definition. The results of optimization are used in order to create a postprocessing model or a model for validation run; the processed optimization results can be saved in a format suitable for CAD transfer.
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Please note: The current version of Tosca ANSA environment does not yet support sizing optimization.
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SIMULIA Tosca Structure User Interface
1.1 User Interface
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SIMULIA Tosca Structure Getting Started with Tosca ANSA
The position of different toolbars is configurable. In order to show or hide a specific toolbar or window, use the corresponding command in the menu items Windows, Containers and Tools : The most important toolbars and windows are the following: • Modules Buttons: provides the access to optimization task related information defined using Task Manager; it is necessary to use this window for several commands (e.g., definition of a new coordinate system) that are not supported in Task Manager. • General Buttons: manages the representation of geometry, including the visibility of elements and nodes; • Ansa Info: window for logging, warnings and errors; • Settings: configuration dialog;
• Task Manager: represents Tosca Structure tasks;
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• Database: represents the contents of the finite element model in a structured form;
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SIMULIA Tosca Structure User Interface
Certain windows and toolbars can also be shown or hidden using Windows toolbar: Task manager
Includes
Properties
Materials
Sets
Database
Mesh Parameters
1.1.1
General Buttons toolbar The buttons on General Buttons toolbar define the visualization parameters and serve for the selection or deselection of geometric objects as well as some other geometric operations. Each button corresponds to a command with a certain name; this name is shown in the tool tip for the button.
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Measure
SIMULIA Tosca Structure Getting Started with Tosca ANSA
1.1.1.1 FOCUS panel This panel represents the commands in TOPO>FOCUS group: OR: select the elements that remain visible (hide the remaining ones). AND: select the elements, then their neighbors will become visible. NOT: select the elements to be hidden.
!NOT: select entities that will remain visible. The selected entities temporary (during selection) are excluded from the visible area and as soon as the middle mouse is pressed (selections' termination) they -and only them- remain visible (invert operation). ALL: makes all geometric objects visible.
INVERT: shows hidden objects while hiding shown objects.
LOCK: saves the current view so that ALL command returns to this view.
PEEL: hides one layer of outer elements.
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NEAR: Logical operation that brings to visible all the nearby items of selected entities, according to a specified tolerance value.
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NEIGHB: makes one layer of neighbor elements (or all connected elements) visible.
1.1.1.2 VISIBILITY panel This panel represents the commands in TOPO>VISIB group: WIRE: defines if the grid is to be shown; note that the grid is hidden at some point when the model is zoomed out. SHADOW: defines if the shaded faces are to be shown. HIDDEN: an alternative to SHADOW: shows the faces colored black. FE-Mod.: makes the elements visible or hidden.
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GRIDs: makes the nodes visible or hidden.
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Draw Mode: defines how the model is to be colored: according to the type of geometric object (ENT), property ID of elements (PID), material ID of elements (MID) or another element-related value.
Database and selection windows Database window represents the information from the finite element model as well as the commands defined in Task Manager (Tosca Structure item). Next to some items, there is a checkbox that defines if the contents of the item is shown or hidden. Double clicking an item in Database opens the selection window (in the figure, the element selection window is shown).
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1.1.2
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That allows the user to inspect the single objects. While the selection window is active, the corresponding objects can be selected by clicking on the model; e.g., this is a quick way to retrieve the ID of an element or node. In this selection window, it is also possible to edit, copy or delete selected entries. Using Modify command from the context menu, it is possible to set a certain property of all selected items (e.g., PID for elements) to a chosen value.
The buttons of the selection window provide the following functionality: sets the selection to the objects that were selected previously; sets the selection to the objects that were selected next; updates the list in the selection window; turns the highlighting of selected objects on or off;
sets the active filter or opens the filter definition window; unsets the current filter. defines the properties to be displayed in columns. list of all action items actual entity is highlighted and the only selectable
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the text field serves for the selection of objects by their IDs, other properties (e.g. property ID) or with the help of filters;
SIMULIA Tosca Structure Getting Started with Tosca ANSA
1.1.3
Task Manager window Task Manager represents the topology optimization task and allows the user to start the optimization in Tosca Structure as well as to perform the actions that follow the optimization. The information is displayed in a tree form; the user interacts with it by creating new items and running the commands in context menu for specific items.
The marked button expands the tree making all items show. A new Tosca Structure task is created by a command in Tasks | Tosca Structure task | ... group that corresponds to the desired optimization type; this command produces a new top level item as well as the uninitialized children items for each part of the process. calls Update command for the current item (see below);
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attempts to call Update commands for all items and thus run all actions; turns on or off the highlighting of the group associated with the active item. The context menu for an item in Task Manager (e.g., START_OPTIMIZATION | RUN as shown in the figure) contains the following commands: Edit: opens the dialog for editing the parameters for the item or data associated with it. Delete: removes the item and all its subitems. Change: if the item is checked (as indicated in the checkbox next to it), it gets unchecked so that Update command can be applied to it again.
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Update: for the items associated with some action (as in the example, with the start of the optimization), this action is performed and the item is marked as checked in case of success. Calling Update for an item automatically invokes this command for all unchecked items that the current item depends upon. View: for the items associated with groups, the group is shown (View | Show), hidden (View | Hide) or shown alone (View | Show Only). Edit Comments: opens the window for editing the comments for the item. Disable: marks the item as disabled, so that its name is shown struckthrough and all actions proceed as if the item were not present. A disabled item is returned to normal state by Enable command in context menu. Set Break: sets the breakpoint to the item, so that, once this item is reached while calling Update for another item (or with "update all" button), the user is given the choice to either stop the actions or continue. For some items, the subitems can be created using New | ... command of the context menu. All items can be renamed: to do this, click an already selected item once and wait until its text becomes editable. Note that, in some cases, the name of the item is important because it defines some file name (or a part of it).
1.1.4
Input of an existing parameter file
All standard parameters are added to the task manager, advanced parameters will only appear in the database list. Remarks 1. When importing an existing Tosca Structure parameter file, the output item for the name of the parameter file and the job directory is named Output by default and not automatically after the name of the imported parameter file.
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In order to load an existing parameter file into Tosca ANSA environment, select File | Input | Tosca Structure:
SIMULIA Tosca Structure Getting Started with Tosca ANSA
2. In case the parameter file contains commands not recognized by Tosca ANSA environment, e.g. CONFIG block, those commands are stored as comments in the Tosca ANSA environment database in Output | Edit Comments. The commands are automatically added to the parameter file on output. If needed, the commands can be edited directly in Output | Edit Comments.
1.1.5
Saving task and saving database There are two possibilities to save: You can save the task only, or you save the whole database If you want to save the task only press Tasks | Save Task in Task Manager. You save only the task settings, not the model related content and results. For example, if you did the optimization of a model and you want to smooth it another day, it is not enough to save the task, because you have to run the optimization step again.
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If you want to save the complete database, which also includes the task, press File | Save As. The file size is much bigger than that of the task, of course, but you can access the model and all existing results.
1.1.6
Highlighting There are two possibilities of highlighting: You can use the highlighting button or you can put a checkmark at several groups in database window. highlighting button: switch the highlighting on and off With the highlight button in the Task Manager you can, for example, check the demolding direction or other task definitions: Mark the corresponding defini-
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tion and switch the highlight on. Direction definitions are shown as arrows in the graphic window and the design group is marked in color.
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Another important feature of highlighting is to visualize properties, grids, elements and so on, listed in the database. Doubleclick at the corresponding topic, property in this case, and a new window opens. Now you can highlight one or more definitions of the topic by using the corrsponding button.
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The same highlight button can also be found in selection windows like SET, for example. So it is possible to check definitions of sets like frozen or design areas.
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By using checkmarks in the database, you are able to switch on or off the visibility of database parameters like forces or boundary conditions, for example:
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1.1.7
Input and output using Task Manager In order to load a finite element model into Tosca ANSA environment and use it for the definition of an optimization task, create a Tosca Structure task first using a command in Tasks | Tosca Structure task | ... group. Then, apply Edit command on MODEL_LINK item and choose the solver corresponding to your model (unless the correct solver is already chosen).
Both the model file name and the directory can be changed; however, keep in mind that the file name and the directory should lead to the model not only during the loading of the model but also after that. The directory where the model is located is recognized as the working directory for Tosca ANSA environment, and the job directory of Tosca Structure will be created in it. Therefore, in order for Tosca Structure to access the model, it should be located in the working directory. Note that Tosca Structure always starts with the initial finite element model as supplied by the user, and all modifications done in Tosca ANSA environment (e.g., deleting elements) will not influence the optimization but might affect the processing of optimization results. Therefore, it is recommended not to modify the input model prior to the optimization. As the working directory stored in PRE-PROCESSING item, a relative path can be used; it can even be set to "./" indicating that the working directory is the current directory. However, this path is relative to the directory Tosca ANSA environment is started from, and not the path of the workspace. In order to avoid confusion, it is recommended to define the workspace by an absolute path. A reason to use a relative path might be that the workspace and the model are expected to be moved from one location to another; in this case,
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When Edit command is applied on FILE item, the open file dialog is shown. Once a file is chosen, the item gets the file name as its text, and the directory of the file is stored in PRE-PROCESSING item. Then, load the model using Update command on what was previously FILE item.
SIMULIA Tosca Structure Getting Started with Tosca ANSA
use the relative path but take care concerning the directory where Tosca ANSA environment is started from. There is no quick way to unload an already loaded model; the only solution is to delete all relevant entries in Database manually. However, this is rarely needed since the model is unloaded at the moment when another model is selected using Edit command of FILE item. The job directory for Tosca Structure where all intermediate files as well as optimization results are stored is named after Tosca Structure parameter file that contains the optimization task. The name of this file equals Output.par by default; it can be modified by renaming the item Output that represents the Tosca Structure parameter file.
The parameter file as well as the job directory for Tosca Structure are created in the working directory that is specified in PRE-PROCESSING item. The actions after the optimization require the files stored in Tosca Structure job directory, mostly from the subdirectories SAVE.onf and TOSCA_POST. See for the details on log files created by Tosca Structure.
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1.1.8
Input and output using the main menu Using File | Input | command from the main menu, a finite element model is loaded into Tosca ANSA environment but is not used for the definition of an optimization task or any further actions, except that SOLID_MESH attempts to remesh it alongside the result of RECONSTRUCT. For most applications, loading of an external model is not needed, however it might serve as a workaround in certain situations. At any moment, the current geometry together with the defined loads, boundary conditions, etc., can be saved in a solver format by File | Output | menu command. Still, it is recommended to use the command VALIDATION_OUTPUT described in in details, in order to make sure that the saving is done at appropriate moment. The output (as well as input) in VRML format is supported; however, the output in IGES format using File | Output CAD | IGES v5.1 does not work.
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1.1.9
Modules Buttons window In Modules Buttons window, the optimization task related information that is later written to Tosca Structure parameter file is edited. For most applications, the optimization task can be defined using Task Manager alone; however, the advanced actions such as definition of a new coordinate system or selection of another MESH_SMOOTH command, can only be done using the commands in Modules Buttons window. The names of buttons as well as the names of dialog fields follow the command names from Tosca Structure parameter file.
1.1.10 Selecting and deselecting the geometric objects
A click with the middle mouse button confirms the selection or terminates the current action. Using the right mouse button, the selected objects are deselected.
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The selection of geometric objects (elements, nodes, etc.) is done using the left mouse button.
SIMULIA Tosca Structure Getting Started with Tosca ANSA
1.1.10.1 Selecting single objects
To select, click the left mouse button on an object or close to it. Selected objects become highlighted. Repeat for multiple selections. In order to deselect an object, click it with the right mouse button. Double clicking an object selects its neighbors. The selection is confirmed with the middle mouse button. In case that the selection window is active (see the previous section), the properties window will open for the first selected object.
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1.1.10.2 Box selection
Multiple geometric objects are selected by drawing a frame with the mouse while holding the left mouse button. A frame with the right mouse button pressed deselects the objects that lie inside it. Note that it is possible to select nodes while they are hidden, but not hidden elements.
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1.1.10.3 Polygon area selection
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Set the first node of polygon by clicking a point with the left mouse button (or, for deselection, with the right mouse button) while holding Shift key. Then set the consequent nodes by clicking the points with the mouse (holding Shift key is not necessary), and finally click the middle mouse button to end the selection. Then, the polygon will close and the objects located inside it will be selected (or deselected).
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1.1.11 View control 1.1.11.1 Rotating Moving the mouse while holding Ctrl key and the left mouse button rotates the view around an axis that is perpendicular to the mouse track and lies on the screen plane. The rotation axis goes through the closest shown node or the closest point of a shown element, with respect to the point where the mouse has been clicked for the first time.
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Moving the mouse while holding Ctrl key and the right mouse button rotates the view in plane. The center of rotation is the rotation pole is the closest shown node or the closest point of a shown element, with respect to the point where the mouse has been clicked for the first time.
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1.1.11.2 Translating Moving the mouse while holding Ctrl key and the right mouse button translates the view.
1.1.11.3 Zooming By moving the mouse while holding Ctrl key and left and middle mouse buttons simultaneously, the view is zoomed in or out according to the direction the mouse is moved (see the figure). A simpler alternative is to use the mouse wheel; the zooming center is always the center of the visible area. Yet another possibility is to use the keys F7 (zoom in) and F8 (zoom out): then, the zooming center is the current mouse position.
The modification of a view is faster when both Ctrl and Shift keys are pressed, as certain items are not drawn during movement.
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1.1.11.4 Faster view selection
SIMULIA Tosca Structure Getting Started with Tosca ANSA
1.1.11.5 Function keys related to view control
1.1.12 Keys facilitating input in dialogs
If a text input field requires a group name, then the window SET HELP is opened when "?" key is pressed inside the text field.
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The list of all keys supported by an input text field in some dialog and the description of the field are shown in its tool tip:
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Double clicking an item in this window inserts the group name in the text field and closes SET HELP window. See the next section for more information about this window as well as about the definition of new groups.
If a field requires a node or element ID, then pressing F1 key closes the window temporarily and waits until the user selects a node or element from the current view. Then, the window reappears and the ID of the selected object is inserted in the text field. Pressing F2 key opens the options dialog for the node or element with the ID from the text field. With F7 key, the current view is zoomed in at the node or element with the selected ID. When F3 key is pressed in any text input field, the window A_PARAMETERs is opened in which the user defined parameters can be defined and then selected. Later, changing the value of a parameter is reflected in all text fields where this parameter is used. The parameters can be assigned to numerical or literal values.
1.1.13 Managing Groups 1.1.13.1 SET HELP window
To make this window appear, do one of the following: • apply Edit command on GROUPS item in Task Manager • press "?" key in a text field that requires the input of a group name (e.g., the dialog DV_TOPO opened by Edit command applied on DESIGN_AREA item in Task Manager) 1 - 26 Start Manual
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For the group management, the window SET HELP is used:
SIMULIA Tosca Structure Getting Started with Tosca ANSA
• double clicking the item SET in Database window opens the selection window for groups that is basically equivalent to SET HELP window In this window, the groups loaded from the input model as well as the new groups defined in Tosca ANSA environment are represented. Although only the new groups are written to Tosca Structure parameter file, the optimization task may contain references to already defined groups as well, When SET HELP window is active, clicking an element or a node of the model highlights all groups that this element or node belongs to. The button Highlight turns on or off the highlighting of the selected group.
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The command NEW creates a new group and starts the group selection mode described in the next section. When the group selection ends, the group properties window titled S E T [SET] is shown.
This window is also opened by Edit command applied on an item in SET HELP window. In this dialog, the name of the group is specified as well as other properties that normally need not be modified.
1.1.13.2 Selection of objects in group selection mode To start the selection mode for an already existing group, apply the command Modify Contents on the group item. Note that in SET HELP window opened by "?" key, this command is named MODIFY. To start the selection mode with a new group, press the button NEW in SET HELP window; in group selection window, you need to choose the command New from the popup menu to create a new empty group, and then to apply the command Modify Contents.
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When the selection mode starts, Database window title changes to Modifying SET: (ID: ), reflecting the name of the group and its ID, as well as the selection window for the objects of current type (GRID in the figure below) appears: In the column In SET of Database window, the red number next to an item shows how many objects of this type belong to the group. The highlighted item in Database shows what objects are currently being selected. In order to change the type of selected objects (e.g., from nodes to elements), highlight the corresponding line (e.g., ELEMENT) by clicking the item once. If you have selected some objects of wrong type by mistake, you need to deselect them first and then change the type of selected objects, since otherwise a mixed group will be produced.
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The selection or deselection of objects with desired IDs can be done in the selection window. See for details on the selection window.
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Selection of nodes or elements is done by drawing a frame with the left mouse button pressed:
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Note that, in this example, Database item GRID is highlighted, therefore the nodes will be selected. The selection window is also titled GRID. To change the type of objects being selected, click the corresponding Database item.
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Once the mouse button is released, the selected nodes appear:
The number of selected nodes is shown in red in Database column In SET. In the selection window, the IDs of selected nodes are highlighted. If needed, the selection can be expanded or decreased; refer to for details. The selection is confirmed with the click by the middle mouse button.
The specification of groups is necessary for several items: • Design Variables • Design Responses for Objective Function Terms • Design Responses for Constraints • Manufacturing Constraints • Tabular Output
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1.1.13.3 List of Tosca Structure commands with groups
SIMULIA Tosca Structure Getting Started with Tosca ANSA
1.1.14 Configuration of Tosca ANSA environment The options of Tosca ANSA environment are edited in the dialog opened by Windows | Options... menu command:
Tosca ANSA environment: Options dialog.
The settings edited in this dialog are divided into two types: general settings (TOSCA.defaults file) and GUI settings (TOSCA.xml file). On start of Tosca ANSA environment, both files are first read from the directory config located in the installation directory; then, the same files are searched for in .BETA directory located in your home directory; if found, these files are loaded and the settings defined in them override the ones read previously. Please refer to for the details about Tosca Structure configuration.
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Fig. 1
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1.2
Topology Optimization with Tosca ANSA environment
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At the beginning of the conventional design process the design engineer defines the shape and the topology of new components using the experience and the results gained from the forerunner. This results in an evolution process which might lead to an optimum design after some iterations and a long period of time. Nowadays it is necessary to shorten the development process of new components. Therefore tools are necessary that replace the natural evolution process by an automatic procedure. With Tosca Structure it is possible to carry out topology and shape optimization in the CAE environment.
1.2.1
What is Topology Optimization? Topology optimization is a tool to generate a design proposal and is often used within the concept finding for a new component. Starting with the design area which is the maximum allowed area for the component and with the boundary conditions, such as loads, fixtures and manufacturing conditions the optimization system will determine a new material distribution by removing material from the design area. This design proposal fulfills all mechanical requirements and represents a weight-optimal design proposal. For the optimization the following constraints and objectives can be realized:
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SIMULIA Tosca Structure Topology Optimization with Tosca ANSA environment
• stiffness (compliance and displacements) • eigenfrequencies • internal and reaction forces • weight, volume • center of gravity • moment of inertia In addition a number of manufacturing constraints can be applied so that the design proposal can be produced with casting, stamping. For this casting constraints, member size constraints, freezing and symmetry and coupling constraints can be defined. As result the optimization system creates a design proposal with the information where the material has to be positioned. This design proposal has to be interpreted and has to be used for the more detailed analysis. For supporting this step Tosca Structure supports the generation of a verification model within Tosca ANSA environment. This means a new model based on the results of the topology optimization can be created easily without the necessity of applying the loads and boundary conditions to the verification model. All loadcases and boundary conditions of the optimization model are transferred automatically to the verification model. With the results of the verification run it is possible to perform a normal FE postprocessing step within the postprocessing environement suitable for your solver or a CAD model can be generated which then can be transferred back to your CAD system.
The Model The component to be used within the tutorial represents a control arm for a car and is found in the Tosca Structure installation directory () according to your FE-solver () : //examples/topo/control_arm The model is loaded with one loadcase consisting of two fixtures in the upper left and right areas and is loaded with one load in the lower bearing area. The
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1.2.2
SIMULIA Tosca Structure
original design is the realized design which has to be strengthened by the optimization.
Design Area
Fig. 2
Existing design of a control arm with the design area
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The model for the topology optimization was modified in such a way that the inner areas of the component are filled with elements to create a design area where the optimization system can remove or rearrange elements for getting a better mechanical behavior of a component with a lower weight with the same mechanical behavior . The start model for the optimization represents a design of a control arm for a car. The component has to be manufactured by forging and consists of aluminum. The red areas of the component are not free for the optimization
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Fig. 3
Loads of the model
The fixture is realized with spring elements on the right upper side. The springs represent a rubber bearing. The left bearing is fixed in all three translation degrees of freedom, but is able to rotate about the x-axis. As loading a force is applied in the center of the lower bearing. Due to symmetry reasons only one half of the model is meshed so the symmetry plane is fixed in z-direction for ensuring the symmetry condition.
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because they are used for the fixtures and for the load application. One red area is used for the mounting of a sensor for the headlight range adjustment.
SIMULIA Tosca Structure
1.2.3
Optimization Task The optimization task is to find a structure with the maximum stiffness for the component with a volume or weight restriction. This represents the most common standard optimization task for the topology optimization. The value to be optimized is the compliance which is the reciprocal value of the stiffness. The compliance is represented as the sum of the strain energy of the complete model. This value has to be minimized. The constraint is the weight or volume constraint which is defined to be 70% of the initial volume/weight of the structure. As manufacturing constraint a casting/forging constraint has to be defined. The idea of the constraint is to ensure that the created structure of the topology optimization has no undercuts and can be demolded (or removed from the forging die).
1.2.4
Step by Step Manual: Summary Preprocessing 1. Create Tosca Structure task: Tasks | Tosca Structure Task | TOPO_CONTROLLER command of Task Manager 2. Input file: PRE_PROCESSING | MODEL_LINK | FILE 3. Design area: PRE_PROCESSING | TOPOLOGY_OPTIMIZATION_CONTROLLER | DESIGN_AREA 4. Design constraints: PRE_PROCESSING | TOPOLOGY_OPTIMIZATION_CONTROLLER | DESIGN_AREA | DV_CONSTRAINTS
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5. Objective function: PRE_PROCESSING | TOPOLOGY_OPTIMIZATION_CONTROLLER | OBJ_FUNC_ITEM_1 6. Constraints: PRE_PROCESSING | TOPOLOGY_OPTIMIZATION_CONTROLLER | CONSTRAINTS 7. Saving Tosca Structure parameter file: PRE_PROCESSING | TOPOLOGY_OPTIMIZATION_CONTROLLER | Output Start optimization 8. Running Tosca Structure: START_OPTIMIZATION | RUN Postprocessing 9. Viewing the intermediate results: POST-PROCESSING | GENERATE_REPORT_FILE
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Result transfer and validation run 10.Smooth surface: SMOOTH | SMOOTH_INSTANCE | RUN_SMOOTH 11.Modified surface: SMOOTH | SMOOTH_INSTANCE | VALIDATE | BATCH_RECONSTRUCT 12.Remeshing: SMOOTH | SMOOTH_INSTANCE | VALIDATE | SOLID_MESH 13.Saving the result: SMOOTH | SMOOTH_INSTANCE | VALIDATE | VALIDATION_OUTPUT 14.Running the solver: SMOOTH | SMOOTH_INSTANCE | VALIDATE | VALIDATION_RUN Please note that Tosca Structure 7.0 or higher is required in order to complete the optimization task. With previous versions of Tosca Structure some changes may be necessary to achieve the same results.
1.2.5
Preprocessing
1.2.5.1 Choice of the optimization type
2. In Task Manager, select Tasks | Tosca Structure TASK | TOPO_CONTROLLER.
3. In Task Manager, press the expand-button.
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1. If Task Manager panel is hidden, click the button to make it appear in the left side of ANSA window.
SIMULIA Tosca Structure
1.2.5.2 Loading the input model file 1. Right click the item MODEL_LINK in Task Manager and select Edit or double click the item MODEL_LINK.
2. In the window titled MODEL LINK, choose as WORKING DECK the solver that matches your input file (MSC Nastran in this example) and click OK. Note that the steps 1 and2 are not needed if the correct solver is already chosen in MODEL_LINK.
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3. Right click FILE item in Task Manager and select Edit or double click FILE.
4. In the Open dialog, choose the input file and click Open. The items FILE and PRE-PROCESSING in Task Manager get renamed: the file name is used as the name of FILE item, while the directory of the file is appended to PRE_PROCESSING item name.
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5. Right click the item named after the file you have just chosen and select Update. The input file is loaded and the model is shown in the main window.
1.2.5.3 Choice of the design area In topology optimization, the design area denotes the set of elements that may be removed during the optimization, in contrast to the frozen areas that remain unchanged. 1. Right click the item DESIGN_AREA in Task Manager and select Edit or double click DESIGN_AREA.
3. Activate the text field with the title GROUP_DEF and press "?" key.
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2. In the DV_TOPO window, choose GROUP_DEF from the dropdown list below EL_GROUP.
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4. The SET HELP window opens. Click the "Actions"-button in the toolbar or right click in the empty space and select New. The window titled Modifying SET: Untitled (Id:1) appears in the right part of the screen. 5. In this window, click ELEMENT item once in order to highlight it. Now, the elements of the model can be chosen using the mouse.
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6. First, select the whole model by enclosing it in a frame made with the left mouse button pressed. Note that you may move, rotate in plane, rotate in space or zoom the model using CTRL + middle mouse button, CRTL + right mouse button, CTRL + left mouse button and CTRL + mouse wheel resp.
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7. Deselect the 4 parts shown in the figure by moving the mouse with the right mouse button pressed. It is recommended to rotate the model in plane and zoom in and out to make the selection more accurately. Click with the middle mouse button to confirm the selection and to proceed to SET window.
9. In SET HELP window, double click the name of the group you have just created to assign the group to your design variable selection. The window will then close. 10. Click OK in DV_TOPO window.
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8. Enter the desired group name (my_design_group in this example) in Name field. You may also proceed with the default group name and click OK.
SIMULIA Tosca Structure
11. If you want to check your group selection switch on the highlight button in Task Manager and click Design Area under TOPOLGY_OPTIMIZATION. Your group definition will be marked in color in the model.
1.2.5.4 Choice of the design constraints Design constraints introduce restrictions on the shape of the optimized model. In addition to the demolding constraint discussed below, other types of design constraints such as symmetry and member size restrictions are supported by Tosca Structure. 1. Right click DV_CONSTRAINTS item under DESIGN_AREA and Select New | DEMOLD_CONTROL.
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2. In DEMOLD_CONTROL window, choose GROUP_DEF from the dropdown list below EL_GROUP
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3. Activate the text field with the title GROUP_DEF and press "?" key.
4. In the SET HELP window, double click my_design_group item. The window will then close.
6. In DEMOLD_CONTROL window, enter the values 0, 0, 1 in the fields PULL_DIR_1, PULL_DIR_2 and PULL_DIR_3. These values are the components of the pull direction needed for the definition of the demolding constraint. Click OK.
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5. Repeat the last 3 steps for CHECK_GROUP. Now, the same element set my_design_group is used in both EL_GROUP and CHECK_GROUP fields
SIMULIA Tosca Structure
7. Check the demold direction by clicking DEMOLD_CONTROL and switching on highlight button. The arrow shows the demold direction and the coloured area shows that part of the model for which the restriction is applied (my_design_group in this case).
1.2.5.5 Choice of the objective function The objective function will be minimized or maximized by Tosca Structure, depending on the settings.
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1. Right click COMPLIANCE item under OBJ_FUNC_ITEM_1 and select EDIT or double click COMPLIANCE.
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2. Click OK without any change.
3. Right click OBJ_FUNC_ITEM_1 item and select Edit or double click OBJ_FUNC_ITEM_1.
4. Set TARGET field to the correct value MIN and click OK. Note that although no changes are needed since TARGET field has already set to the correct value MIN, this step is required in order to proceed.
Constraints are equations or inequations that are maintained by Tosca Structure during the optimization. 1. Right click VOLUME_CONSTRAINT item under CONSTRAINTS and select EDIT or double click VOLUME_CONSTRAINT.
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1.2.5.6 Choice of the constraints
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2. Enter 0.7 in the field VALUE and click OK.
1.2.5.7 Saving Tosca Structure parameter file The Tosca Structure parameter file contains commands which define all settings for the optimization task.
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1. Right click Output item. Select Update. The parameter file Output.par for Tosca Structure is written at this point. The file is saved in the same directory where the input model is located. The optimization with Tosca Structure will also start in this directory.
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1.2.6
Start Optimization
1.2.6.1 Start Tosca Structure 1. Right click RUN item under START_OPTIMIZATION. Select Update. Tosca Structure will start in background. Wait until it finishes. Then close the TOSCA Job and the OPTIMIZATION_RUN window to continue.
1.2.6.2 Logging and monitoring To see the optimization history (the values of objective function and constraints for each iteration), open the file optimization_report.csv with Microsoft Excel or a text editor. Tosca Structure log file TOSCA.OUT from TOSCA_POST directory contains this information too, along with the warnings and errors if available.
Postprocessing Using Tosca Structure.report, the intermediate results of topology optimization, namely the densities of individual elements, can be visualized. This subsection is optional. 1. Right click TOPO_MAT item under GENERATE_REPORT_FILE. Select Update. The generated VTFX file containing the original (nonsmoothed) optimization result will open in Tosca Structure.view.
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1.2.7
SIMULIA Tosca Structure
3. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. Close the Tosca Structure.view, the TOSCA_POST and the TOSCA Job window in order to proceed.
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2. If you’ve just generated the report file and want to view the VTFX file again right click VTF_VISUALIZATION item under GENERATE_POST_FILE and select View.
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1.2.8
Report Generation 1. Open your VTFX file again by clicking GENERATE_POST_FILE | VTF_VISUALIZATION and select View.
2. Under View | Viewports you can select up to four viewports in different positions. Choose two viewports: You see the relative material distribution of your model on the left side of the split window. The right side is still empty.
4. To move both views synchronously select View | Synchronous Navigation.
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3. Select Original model in the Table of Cases and drag it onto the right side of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1.
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5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
7. A new window opens: Enter an appropriate description, select Image as Situation type and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
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6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation.
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8. In GLView Report Builder window click File | Save Repository as to save the actual situations to a file.
9. Switch to Tosca Structure.view window. Repeat step 6 and 7, but select 3D model as situation type for capturing.
10. In the Tosca Structure Report Builder window both siutations are listed. By rightclicking at the situation you can delete it or change the order.
12. The last setting is used for capturing, thus the smoothed optimization result is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the smoothed optimization result (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at step 6 and 7, if necessary, and do not forget to activate the window).
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11. Switch back to Tosca Structure.view window. Now, select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation.
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14. In Tosca Structure.view doubleclick at CONSTRAINT_NORM in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder. 15. Repeat step 13 with the same plot and capture it using situation type Table. 16. Repeat steps 12,13 and 14 with the objective function (OBJ_FUNC in the Table of Cases).
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17. Now there should be 8 entrys in the Situations window. Doubleclick at the third entry, which is the smoothed optimization result as 3D model to deactivate this situation for the transfer.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx in \report\Templates. Select an output file name. Choose the media type which mainly determines how 3d information is included into the report (3D plugin for interactive animated results, video for animated (but static) results and image only for screenshots). Click OK.
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18. Transfer these situation into a powerpoint document by clicking File | Create PowerPointReport.
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20. A PowerPoint file is created. The order of figures and tables is determined by the template. 21. For tranferring into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with the internet explorer, you can choose Video and image as Media type for other browsers.
1.2.9
Result Transfer and Validation Run (Smooth) After the optimization an automatic validation run enables quality checks of the result. An approved result must then be transferred into the product development process. To this end, the new design proposal must be available for import and further processing in CAD systems.
Tosca Structure.smooth generates the surface of the material remaining after the topology optimization and improves the surface quality. 1. Right click RUN_SMOOTH item under SMOOTH_INSTANCE and select Edit or double click RUN_SMOOTH.
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1.2.9.1 Generating smooth surface
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2. In SMOOTH RUN PARAMETERS window, choose the output formats for the result transfer (e.g., STL or IGES) if needed; click OK
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3. Right click RUN_SMOOTH item under SMOOTH and select Update. Tosca Structure.smooth will start in background. When finished, the generated triangular surface is loaded and shown in place of the initial model; see next figure
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1.2.9.2 Modifying the surface using RECONSTRUCT
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1. Right click BATCH_RECONSTRUCT item under VALIDATE and select Edit or double click BATCH_RECONSTRUCT.
2. Check the check button Preview and the check button Freeze SPC Nodes, uncheck the check button Automatic feature line recognition at SMOOTH_CUT_ELEMENTS area and click OK.
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3. Right click BATCH_RECONSTRUCT item and select Update. BATCH_RECONSTRUCT generates a new, more regular triangular surface that can be used for the remeshing of the volume with tetrahedra.
1.2.9.3 Remeshing the model
2. Some time after SOLID_MESH starts, the window PROPERTIES will appear. Double click the first (and only) line in the list, then it will close and SOLID_MESH will resume. When it finishes, a new tetrahedral mesh will appear in addition to the triangular surface.
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1. Right click SOLID_MESH under VALIDATE and select Update.
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1.2.9.4 Saving the resulting model in solver format Please note, in some cases (ANSYS workbench models) the standard way may not work, as ANSA does not support some specific solver settings. In this case continue with chapter 1.2.9.6 Saving the resulting model in solver format (alternative) 1. Right click VALIDATION_OUTPUT item and select Edit or double click VALIDATION_OUTPUT.
3. Choose the file name for the output model to be saved in the format of the solver you use and click Save. In the Output Parameters window click Ok. 4. Right click the item with the chosen file name under VALIDATE and select Update.
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2. In the Output Parameters window click Browse....Depending on your solver format, several additional settings can be made.
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1.2.9.5 Running the solver with the new model 1. Right click VALIDATION_RUN and select Update. Then, the solver will start in the same folder where the output file has been saved.
1.2.9.6 Saving the resulting model in solver format (alternative) 1. Right click VALIDATION_OUTPUT and select Disable.
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2. Right click VALIDATE and select New | MODIFICATION_FILES.
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3. Choose the file name for the output model to be saved in .onf format and click Save. 4. Right click the item with the chosen file name under VALIDATE and select Update.
5. Tosca Structure modification willstart in background. After finishing, the newverification file in the format of the solver you usecan be found in the location specified in the previous step. The file name will be the same asthe one of the .onf file defined in the previous step.
1.2.9.7 Running the solver with the new model (alternative) 1. After creating a verification file using the MODIFICATION_FILE option, the execution of the solver job from Tosca ANSA environment is not possible. Please use your solver specific environment for starting and postprocessing the verification job.
The topology optimization created a new design proposal for the control arm component. The result of the topology optimization has to be discussed in several ways. First of all the optimization result has to be checked. This can be done with viewing the convergence plot and with checking TOSCA.OUT file for warnings and errors. If there is a critical error during the optimization the optimization loop will be stopped. In other cases (if some results are missing) the optimization system will continue but the result may be not sufficient. Second the resulting model and the finite element analysis of the model has to be checked if the displacements, the stresses and all other finite element related information are suitable.
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1.2.10 Result Discussion
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Initial model (complete model with 70% of material homogeneously distributed)
Result
Strain Energy Table 1
1645850
Final model
425093.5
Result comparison
Fig. 4
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Von Mises stresses of optimized structure
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For this optimization task the stresses are in the same range compared to the initial model but the stiffness of the structure is higher and the material amount necessary for the structure is lower. The values to be compared are the volume or weight of the structure and the sum of the strain energy. The strain energy is the measure for the compliance which is the reciprocal value of the stiffness.
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Fig. 5
Optimization result represented after data reduction: IGES surfaces for CAD transfer
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After checking the results the remaining structure can be passed to the design department as a CAD model to be used as design proposal for the fine tuning of the design. If the stresses within the component are not below the allowed range the shape optimization of Tosca Structure (Tosca Structure.shape) will be able to remove the stress peaks so that the component will be suitable from the mechanical point of view.
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The results can be transferred as surfaces in STL format or IGES format. Another way to transfer less data is to export the results as slices.
Optimization result represented as slices
For sharing the result and the animation with colleagues or partners the VTFX format is a comfortable way. This result format is able to contain a full 3D animated model with the optimization history. The model can be rotated and zoomed during the animation. The viewer is available for free for different
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Fig. 6
SIMULIA Tosca Structure
platforms and there is also a possibilty to include the files into HTML-pages and into Powerpoint presentations.
Material distribution after topology optimization
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Fig. 7
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Topology Optimization with Tosca ANSA environment
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1.3
Shape Optimization with Tosca ANSA environment
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Shape optimization allows specific detail improvements of existing designs. Through shape optimization the surface geometry of a given model is modified automatically to avoid material failure and increase durability or comfort.
1.3.1
What is Shape Optimization? Shape optimization is mostly used at the end of the design process when the general layout of a component is more or less fixed and only minor changes and improvements are allowed. Typically, the objective function is to minimize stress concentrations. Based on the results of a stress analysis modifications of the surface geometry of a component are performed until the required stress level is reached. This process is usually carried out manually by trialand-error. Tosca Structure.shape allows an automatization of this improvement process. The surface geometry of a given FE model is modified iteratively based on the FE results, such that the required optimization target is reached. The start
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model is taken from an existing design, which should be improved, or from a previous topology optimization. Tosca Structure.shape enables you to perform the following tasks • Minimization of the equivalent stress • Maximization of selected natural frequencies • Specification of a volume constraint • Surface-based manufacturing constraints for casting, forging, stamping, extrusion and drilling • Minimum and maximum member size • Symmetry constraints • Specification of design domain restrictions by FE-meshes • Mesh adjustment and mesh smoothing in each optimization cycle • Additional functionalities like optimization using durability results are available with Tosca Structure.durability • Additional functionalities like optimization using nonlinear results or for the optimization of contact areas are available with Tosca Structure.nonlinear
1.3.2
The Model
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The component optimized in this tutorial is a connecting rod (conrod) and is found in the Tosca Structure installation directory (): //examples/shape/conrod The model is built with an autogenerated tetrahedron mesh symmetric to the xz and yz plane. The mesh quality is medium/poor with average element
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De sig n
are a
edge of ~ 2 mm. Outer dimensions: 180 x 84 x 24 mm. Allowed design and mesh smooth area are shown in Fig. 8.
Mesh smooth area
Fig. 8
Connecting rod (conrod) with design and mesh smooth area
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Loaded nodes are connected with MPCs to the inner side of the conrod mounts. Nodes in the big eye nodes on the inner radius (crankshaft bearing) are fixed in all three coordinate directions. There are five loadcases realized in the model (see Fig. 9): Loadcase 1: Centrifugal force (a in Fig. 9), 15000 N applied in z-direction Screw fixation Loadcase 2: Gas pressure (b in Fig. 9), 25000 N applied in negative z-direction Fixation in nodes of big eye Loadcase 3: Bending about the x-axis Fixation in nodes of big eye
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Loadcase 4: Bending moment about the y-axis Fixation in nodes of big eye Loadcase 5: Torsion about the z-axis. Fixation in nodes of big eye
a
Fig. 9
1.3.3
Loads and boundary conditions of the model conrod: (a) centrifugal force, right: force caused by gas pressure (b), bending and torsion about x-, y- and z-axis.
Optimization Task The goal is to reduce stress peaks on the surface of the component with small changes at the surface of the component. Thus the optimization task is to minimize the maximum stresses of the loadcases on the connecting rod,
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b
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see Fig. 9. The design area is shown in Fig. 8 and consists of the surface nodes of the area in the inner rectangle.
1.3.4
Step by Step Manual: Summary Preprocessing 1. Create Tosca Structure task: Tasks -> Tosca Structure Task -> SHAPE_CONTROLLER command of Task Manager 2. Input file: PRE_PROCESSING | MODEL_LINK | FILE 3. Design area: PRE_PROCESSING | SHAPE_OPTIMIZATION_CONTROLLER | DESIGN_AREA 4. Design variable constraint: PRE_PROCESSING | SHAPE_OPTIMIZATION_CONTROLLER | DESIGN_AREA | DV_CONSTRAINTS | DOF_CONTROL 5. Mesh smoothing options: PRE_PROCESSING | SHAPE_OPTIMIZATION_CONTROLLER | DESIGN_AREA | MESH_SMOOTH 6. Objective function type: PRE_PROCESSING | SHAPE_OPTIMIZATION_CONTROLLER | OBJ_FUNC_ITEM_1 7. Objective function term: PRE_PROCESSING | SHAPE_OPTIMIZATION_CONTROLLER | OBJ_FUNC_ITEM_1 | EQUIVALENT_STRESS 8. Saving Tosca Structure parameter file: PRE_PROCESSING | SHAPE_OPTIMIZATION_CONTROLLER | Output
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Node displacement check (Check Inputs) 9. Using test displacements: CHECK_INPUTS | TEST_SHAPE_CHECK | TEST_SHAPE Start optimization 10.Running Tosca Structure: START_OPTIMIZATION | RUN Postprocessing 11.Viewing the intermediate results: POST-PROCESSING | GENERATE_REPORT_FILE
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Result transfer (Smooth) 12.Smooth surface, output for result transfer: SMOOTH | SMOOTH_INSTANCE | RUN_SMOOTH Please note that Tosca Structure 7.0 or higher is required in order to complete the optimization task. With previous versions of Tosca Structure some changes may be necessary to achieve the same results.
1.3.5
Preprocessing
1.3.5.1 Choice of the optimization type 1. If Task Manager panel is hidden, click the button to make it appear in the left side of ANSA window.
3. In Task Manager, press the expand-button.
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2. In Task Manager, select Tasks | Tosca Structure TASK | SHAPE_CONTROLLER.
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1.3.5.2 Loading the input model file 1. Right click the item MODEL_LINK in Task Manager and select Edit or double click MODEL_LINK.
2. In the window titled MODEL LINK, choose as WORKING DECK the solver that matches your input file (MSC Nastran in this example) and click OK. Note that the steps 1 and 2 are not needed if the correct solver is already chosen in MODEL_LINK.
4. In the Open dialog, choose the input file and click Open. The items FILE and PREPROCESSING in Task Manager get renamed: the file name is used as the name of FILE item, while the directory of the file is appended to PRE_PROCESSING item name.
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3. Right click FILE item in Task Manager and select Edit or double click FILE.
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5. Right click the item named after the file you have just chosen and select Update. The input file is loaded and the model is shown in the main window.
1.3.5.3 Selection of mesh smoothing elements During the shape optimization, the displacement of surface nodes usually leads to distorted elements unless mesh smoothing is performed. Therefore, it is required to select the elements that can be modified during the mesh smoothing. The general rule is to select the elements at the nodes of the design area, plus several layers of elements towards the inside of the model. Usually, selecting too many elements in mesh smoothing area does not cause any problems except that the calculation time increases.
1. In this case for defining a group for mesh smoothing the easiest way is to reduce the model view to the mesh tightening area first and to define the element group afterwards. So press the NOT button.
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Note that there is an automated method of selection of mesh smoothing elements: see chapter 1.3.12.4 Selecting mesh smooth elements automatically. Still, the manual method is recommended.
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3. Save this view by clicking the dropdown menu next to the Lock button and select Store Lock. Enter a name, for example MESH_SMOOTH, and press Enter 4. Now this view is saved and can be selected by Lock dropdown menu | MANAGE LOCKs.
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2. If needed, bring the model to the view shown in the figure by pressing F2 key and select the faces of the part shown in the left figure by enclosing them in a frame drawn with the mouse while holding the left mouse button. The enframed part disappears. Then select the faces of the part shown in the right figure.
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5. The view can be shown by right clicking the chosen name | Show only.
6. To see the whole model again, make sure that the Lock button is not activated and the view is unlocked. To deactivate click once the Lock button. 7. Then press the ALL button. The whole model will appear. 8. Select your predefined view (key button | MANAGE LOCKs, then rightclick on mesh_smoothing_elements | Show only) and right click the item MESH_SMOOTH under DESIGN_AREA in Task Manager and select Edit or double click MESH_SMOOTH.
10. Activate the text field with the title GROUP_DEF and press "?" key.
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9. Choose GROUP_DEF in the dropdown list below EL_GROUP.
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11. The SET HELP window opens. Click the "Actions"-button in the toolbar or right click in the space with the group list and select New. The window titled Modifying SET: Untitled (Id:1) appears in the right part of the screen. 12. In this window, activate SOLID and deactivate all others under ELEMENT item. If necessary, click once again at SOLID item to highlight it. Now, the solids of the model can be chosen using the mouse.
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13. Select all faces of the part by enclosing them in a frame drawn with the mouse while holding the left mouse button. Click with the middle mouse button to confirm the selection and to proceed to SET window.
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14. Enter the desired group name (mesh_smooth in this example) in SET window. You may also proceed with the default group name.
15. In SET HELP window, double click the name of the group you have just created. The window will then close.
Remark to mesh smoothing If you wish to examine the influence of MESH_SMOOTH on the optimization result, you may run the optimization (as described below) with following settings and compare the results: • MESH_SMOOTH disabled by using Disable command on MESH_SMOOTH item; ALL_ELEMENTS is chosen as the group in EL_GROUP field of MESH_SMOOTH dialog.
1.3.5.4 Choice of design area In shape optimization, the design area denotes the set of nodes that may be displaced during the optimization, in contrast to the frozen areas that remain unchanged.
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16. Click OK in MESH_SMOOTH window.
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1. Right click the item DESIGN_AREA in Task Manager and select Edit or double click DESIGN_AREA. 2. In the appeared DV_SHAPE window, choose GROUP_DEF from the dropdown list below ND_GROUP. The process of selecting a group is similar to one used for defining the mesh smooth area.
4. The SET HELP window opens. Click the "Actions"-button in the toolbar or right click in the empty space and select New. The window titled Modifying SET: Untitled (Id:1) appears in the right part of the screen.
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3. Activate the text field with the title GROUP_DEF and press "?" key.
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5. In this window, click SOLIDFACET item once in order to highlight it. Now, the surface faces of the model can be chosen using the mouse.
6. Activate the Feature Area button with an angle of 40°. So all surfaces which are linked with an angle equal or less of 40 degree are selected.
7. Select the surface outside of geometry and neglect the intersection plane and the bushing.
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bushing
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8. As the mesh smooth area should contain more layers than the design area for a smooth transition between optimized and non-optimized part deselect the last three or four layers at each end: If needed, change the viewport by pressing F2 key and deselect the parts by enclosing them in a frame drawn with the mouse while holding the right mouse button.
9. To keep the small eye planar activate the Feature Area button with an angle of 10° and deselect the three layers at the front and the back side.
11. Enter the desired group name (my_design_group in this example) in SET window. You may also proceed with the default group name and click OK.
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10. Confirm your selection (click middle mouse button) and proceed to SET window. Note that although the resulting group consists of faces, it is later transformed into a node group that is then written to the Tosca Structure parameter file.
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12. In SET HELP window, double click the name of the group you have just created. The window will then close.
13. Click OK in DV_SHAPE window.
1.3.5.5 Choice of design variable constraint The interior of the smaller eye of the conrod should not be changed. Therefore the nodes of this area have to be fixed in all directions by a design variable constraint (DOF_CONTROL).
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14. You can check your group selection by clicking Windows | Sets in main menu. In SET window switch on the highlight button. Selected groups will be marked in different colors.
SIMULIA Tosca Structure
1. Right click DV_CONSTRAINTS item and select New | DOF_CONTROL.
2. Choose GROUP_DEF in the dropdown list instead of ALL_NODE. Activate the text field with the title GROUP_DEF and press "?" key.
3. The SET HELP window opens. Click the "Actions"-button in the toolbar or right click in the empty space and select New. The window titled Modifying SET: Untitled (Id:1) appears in the right part of the screen.
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4. Activate the Feature Area button with an angle of 10°.
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5. Make sure, that SOLIDFACET is highlighted in Modifying SET window and select the two inner layers of the eye at the front and back side (see left figure) and the bushing. Confirm the selection with the middle mouse button and proceed to SET window. Enter a name and click ok. 6. In SET HELP window doubleclick at the new group. Select FIXED at the fields DOF_1, DOF_2 and DOF_3.
Remark: 1. As an alternative it is possible to define a second DOF control at the hidden outer surface. Then the reduction of the upper half of the conrod eye is not necessary and the whole small eye can be added to the mesh smooth area. The second DOF control is necessary as the outer surface of the upper half of the eye should also remain unchanged.
In the example, the min-max formulation of the objective function is used in order to minimize the maximal value of von Mises stress over all nodes of the design area and over two loadcases. A separate design response of EQUIVALENT_STRESS type is created for each loadcase, therefore the steps 1-8 have to be done five times. 1. Right click OBJ_FUNC_ITEM_1 item and select New | EQUIVALENT_STRESS.
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1.3.5.6 Choice of the objective function
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2. Choose GROUP_DEF in the dropdown list instead of ALL_NODES.
3. Activate the text field with the title GROUP_DEF and press "?" key. In this case, no new group should be defined since the design area group is already selected. Therefore, the window SET HELP that appears when "?" key is pressed is only needed for the selection of the group name, that may also be inserted manually.
5. Select SIG_MISES in the field TYPE of OBJFUNC_TERM dialog.
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4. Double click the name of the design area group (my_design_group in this example). The window SET HELP then closes.
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6. In OBJFUNC_TERM window, set the value of LC_SET field to "(ALL,1)". Alternatively, select the appropriate values of APPROACH and LOADCASE fields (ALL and 1, resp.) after clicking MORE in the dialog LC_SET that opens when "?" key is pressed in LC_SET field. Click OK. 7. Repeat the steps 1-6 four times in order to create the design responses for the other loadcases. In step 6, enter "(ALL,2)", "(ALL,3)" and so on instead of "(ALL,1)" in order to specify the other loadcases for the design response. Finally you have five objective function items. For better handling and control of the results we recommend to create one DRESP for each loadcase. This allows for more detailed postprocessing and eventually different weighting of the loadcases in the objective function. 8. Right click OBJ_FUNC_ITEM_1 item and select Edit or double click OBJ_FUNC_ITEM_1.
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9. Select MINMAX as the value of TARGET field and click OK.
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1.3.5.7 Saving Tosca Structure parameter file The Tosca Structure parameter file contains commands which define all settings for the optimization task. 1. Right click Output item and select Update. The parameter file Output.par for Tosca Structure is written at this point. The file is saved in the same directory where the input model is located. The optimization with Tosca Structure will also start in this directory. Note that you may change the parameter file name (and, thus, the working directory that is named after it) by clicking twice on Output item.
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1.3.6
Node Displacement Check (Check Inputs) Using CHECK_INPUTS item, the change of the geometry caused by sample optimization displacements is examined. This test reveals possible problems with the definition of the design area and the mesh smoothing area, as well as checks if the syntax of the parameter file is correct. Also, by viewing the geometry after the test displacements in VTFX format, the user is able to see if the real optimization displacements are likely to result in distorted elements or violate some other requirements. This check is optional; it has no effect on further actions. However, it is recommended in most cases since it requires much less calculation time than the entire shape optimization. In case that the design restrictions are defined, they are also enforced during CHECK_INPUTS operation, and thus it can be checked if they are defined correctly.
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1. Right click CHECK_INPUTS item and select New | TEST_SHAPE_CHECK. If the CHECK_INPUTS item is missing rightclick TOSCA Structure Task | New | CHECK_INPUTS. 2. Right click TEST_SHAPE_CHECK item and select New | TEST_SHAPE.
3. In the opened TEST_SHAPE dialog, enter 3 in the field DISPLACEMENT; this is the maximal test displacement value.
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4. Enter 3 in the field INCREMENT; this is the number of iterations in which the displacement is increased from 0 to the maximal value.
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5. Optionally, select SHRINK instead of GROW in DIRECTION field; this changes the direction of displacements (towards the inside or towards the outside). Click OK.
6. Right click TEST_SHAPE_1 item and select Update. Wait until Tosca Structure finishes. Close the TOSCA Job and the TOSCA_TEST window to continue.
8. Right click VTF_VISUALIZATION item and select View. Tosca Structure.view window opens.
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7. Right click TEST_SHAPE_CHECK item and select New | VTF_VISUALIZATION.
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9. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. You can change between SHAPE_DISP and SHAPE_CTRL by doubleclicking on the corresponding case in the Table of Cases window or by selecting it in the dropdown menu. Examine the model with test displacements and close Tosca Structure.view window in order to proceed with Tosca ANSA environment.Please note: as no FE-Analysis is performed, there are no CTRL_INPUT results available. 10. In the animation appearing after the test run it should be quite easy to check:
• Is the optimization direction (nodal movement) in the correct direction?
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• Are the design nodes (moving nodes) correctly defined?
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1.3.7
Start Optimization
1.3.7.1 Start Tosca Structure 1. Right click RUN item under START_OPTIMIZATION and select Update. Tosca Structure will start in background. Wait until it finishes and then close TOSCA Job and OPTIMIZATION_RUN window in order to proceed.
1.3.7.2 Logging and monitoring To see the optimization history (the values of objective function and constraints for each iteration), open the file optimization_report.csv with Microsoft Excel or a text editor. Tosca Structure log file TOSCA.OUT from TOSCA_POST directory contains this information too, along with the warnings and errors if available.
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1.3.7.3 Viewing the results in the optimized model The results produced by the solver in the last iteration are saved in the directory SAVE., where is the extension corresponding to the solver (in this example, the directory are SAVE.f06 and SAVE.op2). Since the model with the optimized geometry is used in the last iteration, a generation of a new model for validation run (as in topology optimization) is not needed.
1.3.8
Postprocessing Using Tosca Structure.report, the geometry after the shape optimization as well as the values of controller input (von Mises stress in the example) can be visualized. This subsection is optional.
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1. Right click SHAPE_CTRL item under GENERATE_REPORT_FILE and select Edit or double click GENERATE_REPORT_FILE.
3. Right click SHAPE_DISP item under GENERATE_REPORT_FILE and select Update. The generated VTFX file containing the original (nonsmoothed) optimization result will open in Tosca Structure.view. 4. If you’ve just generated the report file and want to view the VTFX file again right click VTF_VISUALIZATION item under GENERATE_REPORT_FILE and select View.
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2. In the opened CONTOUR_PLOT PARAMETERS dialog, choose NODAL DISPLACEMENTS (SHAPE) from the dropdown list in TYPE_PROPERTY field. Alternatively, SHAPE CONTROLLER INPUT can be chosen: then, the fringe plot (i.e., the color of the surface) will reflect the controller input values (von Mises stress in the example) and not the optimization displacement values. Click OK.
SIMULIA Tosca Structure
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5. In Case Panel choose your result case, either a 3D animation of an optimization plot or a result plot. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. Close the Tosca Structure.view, the TOSCA_POST and the TOSCA Job window in order to proceed.
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1.3.9
Report Generation 1. Open your VTFX file again by clicking GENERATE_POST_FILE | VTF_VISUALIZATION and select View.
2. View | Viewports allows to select up to four viewports in different positions. Choose two viewports: You see the relative material distribution of your model on the left side of the split window. The right side is still empty.
4. To move both views synchronously select View | Synchronous Navigation.
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3. Select Case 2 in the Table of Cases and drag it onto the right part of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1.
SIMULIA Tosca Structure
6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation.
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5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
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7. A new window opens: Enter an appropriate description, select Image as Situation type and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
8. In GLView Report Builder window click File | Save Repository as to save your captured situations to a file. If you close the Tosca Structure Report Builder window, you can continue by opening your saved repository.
10. In Tosca Structure Report Builder window both model siutationsare listed. By rightclicking at the situation you can delete it or change the order.
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9. Switch back to Tosca Structure.view window. Repeat steps 6 and 7, but select 3D model as situation type for capturing.
SIMULIA Tosca Structure
11. Switch back to Tosca Structure.view window. Now, select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation. 12. The last setting is kept for capturing, thus, the original model is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the original model (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at steps 6 and 7, if necessary, and do not forget to activate the window). 14. In Tosca Structure.view doubleclick at VARIABLE | DRESP values in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder.
16. Repeat steps 13, 14 and 15 with the objective function (OBJ_FUNC in the Table of Cases).
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15. Repeat step 13 with the same plot captured as Table.
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17. Now there should be 8 entrys in the Situations window. Doubleclick at the third entry, which is the original model as 3D model to deactivate this situation for the transfer. The same effect is given by rightclicking and selecting Deactivate.
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18. Transfer these situations into a powerpoint document by clicking File | Create PowerPointReport.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx under \report\Templates. Select a file location and the media type. Click OK.
20. A PowerPoint file is created. The order of figures and tables is determined by the template.
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21. For tranferring into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with the internet explorer, you can choose Video and image as Media type for other browsers.
1.3.10 Result transfer (Smooth) Tosca Structure.smooth is used in order to extract the surface of the optimized geometry and to save it in a desired format. IGES and STL output formats as well as the output of slices in IGES format are supported.
1.3.10.1 Generating smooth surface
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1. Right click RUN_SMOOTH item under SMOOTH_INSTANCE and select Edit or double click RUN_SMOOTH.
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2. Make sure that TASK is set to SURFACE and choose the output formats you need for CAD transfer (STL and IGES1 in this example); refer to vol.2 chapter 9.1.9, Output parameters for the differences between different IGES formats and the description of other formats. If the output of slices is desired, check slices checkbox and then fill in the fields SLICE_NUMBER (number of section planes), SLICE_NORMAL (normal direction of section planes) and SLICE_FORMAT (choice between polygon or spline slices). Refer to vol.2 chapter 9.1.10, Slices through 3D models and border of 2D models for more information. Click OK.
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3. Right click RUN_SMOOTH item under SMOOTH and select Update.
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Besides the new geometry loaded into Tosca ANSA environment, the results of Tosca Structure.smooth (by default saved in TOSCA_POST subdirectory of your working directory (named Output by default)) might include: • VTFX file for visualization (SMOOTH_INSTANCE.vtfx); • STL file with the optimized geometry (SMOOTH_INSTANCE.stl); • IGES file with the optimized geometry (SMOOTH_INSTANCE.igs);
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4. Tosca Structure.smooth will start in background. When finished, close the TOSCA Job and the TOSCA_SMOOTH windows. The generated triangular surface is loaded and shown in place of the initial model.
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• IGES file with slices in one direction (SMOOTH_INSTANCE_slices.igs): see the next figure.
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1.3.11 Result Discussion The result, depending on the used solver, should be similar to Fig. 10.
Stress reduction in the design area from 197 MPa to 134 MPa in 5 iterations (see chapter 1.3.12.3 Redefine the global stop condition)
In Fig. 10 the stress reduction is clearly seen. The maximal stress has been decreased about 32%. The remaining stress concentration in Fig. 10 can not be removed because further nodal optimization displacement would lead to inacceptable element quality. A solution would be to remesh the two areas or the whole part and to restart the optimization.
1.3.12 Extensions 1.3.12.1 Design variable constraints There may be different manufacturing constraints for the conrod. Assume that it is produced by casting and therefore must comply to the following requirements: 1. be demoldable;
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Fig. 10
SIMULIA Tosca Structure
2. be symmetric to x-z-plane. These requirements can be realized in different ways in Tosca Structure.shape. In the following only one of these ways is described in detail, some alternatives will be discussed at the end of the chapter. Casting Constraint
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1. Add new definitions to your optimization task: rightclick at PRE-PROCESSING | SHAPE_OPTIMIZATION_CONT ROLLER | DESIGN_AREA | DV_CONSTRAINTSand select New | DEMOLD_CONTROL for a new casting constraint.
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2. Define settings for the casting constraint. Set your demolding direction (DEMOLD_DIR_1 to DEMOLD_DIR_3 fields) to (1, 0, 0). Define a new group of solidfacets consisting the exterior of the positive half in x-axisdirection. It’s important to avoid intersection! Set ND_GROUP and CHECK_GROUP fields to your new node group (e.g. SURF_DEMOLD_POS). Repeat this step with the negative part and the demolding direction (-1,0,0).
Symmetry to x-z-plane
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3. Define symmetry (PREPROCESSING | SHAPE_OPTIMIZATION_CONT ROLLER | DV_CONSTRAINTS | New | SYMMETRY_CONTROL) for all design nodes. The normal vector for the symmetry plane should be in y-direction and a point in the plane defined by x and y both being zero. Note, mesh also has to be symmetric.
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1.3.12.2 Define a volume constraint By visual observation the FE-model seems to gain weight. This may not be a desired effect. One way to prevent this is to define a volume constraint.
2. Set MAGNITUDE to REL (relative volume)and enter 1.0 in VALUE field. Click OK.
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1. In PRE-PROCESSING | SHAPE_OPTIMIZATION_CONT ROLLER |CONSTRAINTS item, select New | VOLUME_CONSTRAINT.
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1.3.12.3 Redefine the global stop condition Although the very efficient shape optimization often does a really good job in only 5 iterations a few percent more may be gained by letting the optimizer run a little longer. The simplest way to do this is to change the maximum number of iterations. 1. In PRE-PROCESSING | SHAPE_OPTIMIZATION | GLOBAL_STOP_CONDITION item, choose Edit or double click GLOBAL_STOP_CONDITION. 2. Set maximal number of iterations, ITER_MAX, to 10. Click OK.
1.3.12.4 Selecting mesh smooth elements automatically
1. Try it out using Edit command on SHAPE_OPTIMIZATION_CONT ROLLER | DESIGN_AREA | MESH_SMOOTH item or double click MESH_SMOOTH.
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Tosca Structure.shape has a built in function to select a number of layers of elements away from the design nodes.
SIMULIA Tosca Structure
2. Select MS_LAYER in EL_GROUP field. In ND_GROUP field, choose the design area group. Set the value of LAYERS field (the number of mesh smooth layers) to 5 and click OK. Observe the difference in the geometry after the optimization, especially the inner surface of of the holes of the conrod. Remark
2. The default if no MESH_SMOOTH command is defined is 6 layers from the design nodes. For the current model and the design area in Fig. 8, the mesh smooth group becomes too large and the optimization stops after several iterations because of a bad mesh.
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1. Compared to the description in chapter 1.3.5.3 Selection of mesh smoothing elements, the automatic definition of the mesh smoothing elements is a quick but not always optimal option. The problems that can occur are many especially. In real life applications, the automatic method may lead to many problems. In this example, the nodes on the inner surface of the the holes (where the connection elements are) are also displaced, although this is not desired. Therefore, we emphasize that selecting the mesh smoothing element group manually can often save time in the long run.
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1.3.13 Troubleshooting
Fig. 11
Error message of optimization run. The solver run (Abaqus in this example) was not successful.
1.3.13.1 Suggestions in case of mesh problems The best solution is of course to remesh, but this may be a time consuming task. The second best solution is to check the solver log file and find out which elements are causing the problems. Look these elements up in your preprocessor. If you only have a few problematic elements at the edge of the mesh smoothing area, try to remove these problematic elements from the mesh smoothing area.
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In most cases, the problems during shape optimization are related to the mesh problems, causing the optimization to stop.
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A good mesh for shape optimization does not always mean a high quality calculation mesh. Avoid using mesh refinement on the surface and instead mesh a little coarser than usual and uniformly.
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Shape Optimization with Tosca ANSA environment
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1.4
Bead Optimization with Tosca ANSA environment Bead optimization is a way to enhance shell structures without adding more mass to the structure. The beads can easily be added in the stamping process which makes bead a low weight and cost neutral alternative to enhance a sheet-metal structure.
1.4.1
What is Bead Optimization?
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The easiest way to understand bead optimization is a simple example every mechanical engineer will intuitively understand.
a) Fig. 12
b)
Simple plate in bending with loading and supports (a) and an optimal bead (b). The maximal displacement of (a) is 6.6 mm and (b) is 0.25 mm
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In Fig. 12, a simple flat plate in bending is shown. It is evident that the solution in Fig. 12 (b) has a much greater stiffness than the original flat plate in Fig. 12 (a). Regarding the simple example in Fig. 12 a couple of comments must be made:
bead height
bead width Fig. 13
Bead height and bead width
• The bead height (see Fig. 13) has the most significant effect on the stiffness of the plate structure. Usually, the greater the bead height the greater the stiffness. But, the bead height is usually controlled by manufacturing capabilities, i.e. how deep one can draw a bead with your available tools.
Increasing stiffness Fig. 14
Bead layouts for simple geometries with a uniform pressure load. From Oehler and Weber: "Steife Blech- und Kunststoffkonstruktionen", Springer-Verlag GmbH (1972)
For more complex loads or dynamic problems, i.e. eigenvalue or frequency response, the optimal bead layout is not intuitive anymore (see Fig. 14).
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• The bead width (see Fig. 13) has an effect on the possible designs. As seen in Fig. 14 a small or a large bead width is not necessarily related to the stiffness of the sheet structure. Tosca Structure.bead default values usually suffice, but if an optimal solution is sought you must try more bead widths.
SIMULIA Tosca Structure
Thus, an easy way to find a good bead pattern is to use Tosca Structure.bead.
1.4.1.1 Tosca Structure.bead Tosca Structure.bead is the Tosca Structure module for bead optimization. Two bead optimization algorithms have been implemented: • Controller based bead optimization (BEAD_CONTROLLER) • Sensitivity based bead optimization (BEAD_SENSITIVITY) In general the controller algorithm is much faster than the sensitivity algorithm, but lacks handling of complex design responses such as frequency response or combined responses. The controller algorithm leads to very easy interpretable beads. The bead patterns of the sensitivity algorithm can be more difficult to interpret, but the results are often superior to the controller results, especially for dynamic problems. For the optimization the following constraints and objectives can be realized: • stiffness (compliance and displacements*) • eigenfrequencies * Only sensitivity based algorithm allows these constraints and objectives The following presents a start guide for Tosca Structure.bead. The purpose is to show how simple it is to set up a bead optimization problem in Tosca ANSA environment. For more background knowledge about bead optimization, differences between the two algorithms and other advanced settings in Tosca Structure.bead please consult the user manual. This guide is restricted to showing the controller based bead algorithm.
The Model Model information: A model of an oilpan is found in the Tosca Structure installation directory () according to your FE-solver () :
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//examples/bead/oil_pan
z
y
x Fig. 15
FE-model of an oilpan: a typical automotive sheet metal part.
• Dimensions: Length (z-direction): ~ 500 mm width (x-direction): ~ 305 mm, depth (y-direction): ~42 mm, thickness: 1.3 mm
• Mesh: Average element edge length: ~ 7 mm, mostly linear quads and a few trias. • Initial 1st eigenvalue: 179 Hz • Boundary conditions are for simplicity crude full supports on the edges of the oilpan. Real life boundary condition could be obtained by using the full body-in-white model of a car which would also run with Tosca Structure - of course with unreasonable runtimes for this simple introduction.
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• The element normals of the shell elements are in the negative y-direction.
y x Fig. 16
1.4.3
Design area
Optimization Task Maximize the natural (1st) eigenfrequency of the oil pan using controller based algorithm. The maximal bead height is 5 mm and the bead direction must be in the positive y-direction, see Fig. 15. Note that, with some minor modifications, the same task can be solved using the sensitivity-based bead optimization. However, for this example, the controller-based algorithm is chosen because it leads to shorter optimization time.
1.4.4
Step by Step Manual: Summary Preprocessing 1. Create Tosca Structure task: Tasks -> Tosca Structure Task -> BEAD_CONTROLLER command of Task Manager
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2. Input file: PRE_PROCESSING | MODEL_LINK | FILE 3. Design area: PRE_PROCESSING | BEAD_OPTIMIZATION_CONTROLLER | DESIGN_AREA 4. Constraint on nodes with boundary conditions: PRE_PROCESSING | BEAD_OPTIMIZATION_CONTROLLER | DESIGN_AREA | DV_CONSTRAINTS | CHECK_BC 5. Objective function: PRE_PROCESSING | BEAD_OPTIMIZATION_CONTROLLER | OBJ_FUNC_ITEM_1 6. Objective function term: PRE_PROCESSING | BEAD_OPTIMIZATION_CONTROLLER | OBJ_FUNC_ITEM_1 | EIGENFREQUENCY
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7. Bead height constraint: PRE_PROCESSING | BEAD_OPTIMIZATION_CONTROLLER | CONSTRAINT | BEAD_HEIGHT_CONSTRAINT 8. Saving Tosca Structure parameter file: PRE_PROCESSING | BEAD_OPTIMIZATION_CONTROLLER | Output Node displacement check (Check Inputs) 9. Using test displacements: CHECK_INPUTS | TEST_BEAD_CHECK | TEST_BEAD Start optimization 10.Running Tosca Structure: START_OPTIMIZATION | RUN Postprocessing 11.Viewing the intermediate results:POST-PROCESSING | GENERATE_REPORT_FILE Result transfer and validation run (Smooth) 12.Smooth surface: SMOOTH | SMOOTH_INSTANCE | RUN_SMOOTH 13.Modified surface: SMOOTH | SMOOTH_INSTANCE | VALIDATE | BATCH_RECONSTRUCT 14.Saving the result: SMOOTH | SMOOTH_INSTANCE | VALIDATE | VALIDATION_OUTPUT
Please note that Tosca Structure 7.0 or higher is required in order to complete the optimization task. With previous versions of Tosca Structure some changes may be necessary to achieve the same results.
1.4.5
Preprocessing
1.4.5.1 Choice of the optimization type 1. If Task Manager panel is hidden, click the button to make it appear in the left side of ANSA window.
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15.Running the solver: SMOOTH | SMOOTH_INSTANCE | VALIDATE | VALIDATION_RUN
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2. In Task Manager, select Tasks | Tosca Structure TASK | BEAD_CONTROLLER.
3. In Task Manager, press the Expand-button.
1.4.5.2 Loading the input model file
2. In the window titled MODEL LINK, chooseas WORKING DECK the solver that matches your input file (MSC Nastran in this example) and click OK. Note that the steps 1 and 2 are not needed if the correct solver is already chosen in MODEL_LINK.
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1. Right click the item MODEL_LINK in Task Manager and select Edit or double click MODEL_LINK.
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3. Right click FILE item in Task Manager and select Edit or double click FILE.
4. In the Open dialog, choose the input file and click Open. The items FILE and PREPROCESSING in Task Manager get renamed: the file name is used as the name of FILE item, while the directory of the file is appended to PRE_PROCESSING item name.
1.4.5.3 Choice of design area In bead optimization, the design area denotes the set of nodes that may be displaced during the optimization, in contrast to the frozen areas that remain unchanged.
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5. Right click the item named after the file you have just chosen and select Update. The input file is loaded and the model is shown in the main window.
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1. Right click the item DESIGN_AREA in Task Manager and select Edit or double click DESIGN_AREA.
2. In the appeared DV_BEAD window, choose GROUP_DEF from the dropdown list below ND_GROUP.
4. The SET HELP window opens. Click the "Actions"-button in the toolbar or right click in the empty space and select New. The window titled Modifying SET: Untitled (Id:1) appears in the right part of the screen.
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3. Activate the text field with the title GROUP_DEF and press "?" key.
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5. In this window, click GRID item once in order to highlight it. Now, the nodes of the model can be chosen using the mouse.
6. If needed, bring the model to the view shown in the figure by pressing F1 key. Then, enclose all nodes but those that belong to the outer rim in a frame drawn with the mouse while holding the left mouse button. Make sure that the nodes on the upper flat surface are not selected. Click with the middle mouse button to confirm the selection and to proceed to SET window.
8. In SET HELP window, double click the name of the group you have just created. The window will then close.
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7. Enter the desired group name (my_design_group in this example) in SET window. You may also proceed with the default group name and click OK.
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9. Click OK in DV_BEAD window.
1.4.5.4 Choice of the objective function In the example, the objective function that is to be maximized is the first eigenvalue.
2. In OBJFUNC_TERM window, set the value of LC_SET field to "(MODAL,All,1)". Alternatively, select the appropriate values of APPROACH, LOADCASE and SUBSTEP fields of the dialog LC_SET that opens when "?" key is pressed in LC_SET field and click OK.
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1. Right click OBJ_FUNC_ITEM_1 item and select New | EIGENFREQUENCY.
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3. Right click OBJ_FUNC_ITEM_1 item and select Edit or double click OBJ_FUNC_ITEM_1.
4. Select MAX as the value of TARGET field and click OK.
1.4.5.5 Choice of the constraint The constraint is necessary in order to put the limits for optimization displacements.
2. In CONSTRAINT_ITEM window, select ABS in the dropdown list MAGNITUDE and set the value of VALUE field to 5.
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1. Right click CONSTRAINTS item and select New | BEAD_HEIGHT_CONSTRAINT.
SIMULIA Tosca Structure
3. Select GROUP_DEF instead of ALL_NODES in GROUP_DEF dropdown list.
4. Activate the text field with the title GROUP_DEF and press "?" key. In this case, no new group should be defined since the design area group is already selected. Therefore, the window GROUP_DEF HELP that appears when "?" key is pressed is only needed for the selection of the group name, that may also be inserted manually.
6. Click OK.
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5. Double click the name of the design area group (my_design_group in this example). The window SET HELP then closes.
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1.4.5.6 Optimization settings 1. Right click BEAD_OPTIMIZATION_CONTR OLLER itemabd select New | SETTINGS.
2. In the opened OPT_PARAM window, set the value of SCALE field to -1. This changes the displacement direction of nodes in the design area. Click OK.
The Tosca Structure parameter file contains commands which define all settings for the optimization task.
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1.4.5.7 Saving Tosca Structure parameter file
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3. Right click Output item and select Update. The parameter file Output.par for Tosca Structure is written at this point. The file is saved in the same directory where the input model is located. The optimization with Tosca Structure will also start in this directory. Note that you may change the parameter file name (and, thus, the working directory that is named after it) by clicking twice on Output item.
Node Displacement Check (Check Inputs) Using CHECK_INPUTS item, the change of the geometry caused by sample optimization displacements is examined. This test reveals possible problems with the definition of the design area as well as checks if the syntax of the parameter file is correct. Also, by viewing the geometry after the test displacements in VTFX format, the user is able to see if the real optimization displacements are likely to result in distorted elements or violate some other requirements. This check is optional; it has no effect on further actions. However, it is recommended in most cases since it usually requires much less calculation time than the entire bead optimization. In case that design restrictions are defined, they are also enforced during CHECK_INPUTS operation, and thus it can be checked if they are defined correctly. 1. Right click CHECK_INPUTS item and select New | TEST_BEAD_CHECK.
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2. Right click TEST_BEAD_CHECK item and select New | TEST_BEAD.
3. In the opened TEST_SHAPE dialog, enter 3 in the field DISPLACEMENT; this is the maximal test displacement value.
5. Make sure that the value in DIRECTION field is GROW and click OK.
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4. Enter 3 in the field INCREMENT; this is the number of iterations in which the displacement is increased from 0 to the maximal value.
SIMULIA Tosca Structure
6. Right click TEST_BEAD_1 item and select Update. Wait until Tosca Structure finishes and close TOSCA Job and TOSCA_TEST window to continue.
7. Right click TEST_BEAD_CHECK item and select New | VTF_VISUALIZATION.
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8. Right click VTF_VISUALIZATION item and select View. Tosca Structure.view window opens.
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9. The animation starts and stops by clicking on the start forward/ backward, pause and stop symbol in the task menu. Examine the model with test displacements and close Tosca Structure.view window in order to proceed with Tosca ANSA environment.
1.4.7
Start Optimization
1. Right click RUN item under START_OPTIMIZATION and select Update. Tosca Structure will start in background. Wait until it finishes and then close TOSCA Job and OPTIMIZATION_RUN window in order to proceed.
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1.4.7.1 Start Tosca Structure
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1.4.7.2 Logging and monitoring To see the optimization history (the values of objective function and constraints for each iteration), open the file optimization_report.csv with Microsoft Excel or a text editor. Tosca Structure log file TOSCA.OUT from TOSCA_POST directory contains this information too, along with the warnings and errors if available. The default bead width is proportional to the average element length; in this example, the average element lengths equals 7 while the bead width is 45; both values are found in TOSCA.OUT file.
1.4.7.3 Viewing the results in the optimized model The results produced by the solver in the last iteration are saved in the directory SAVE., where is the extension corresponding to the solver (in this example, the directory are SAVE.f06 and SAVE.op2). Since the model with the optimized geometry is used in the last iteration, a generation of a new model for validation run (as in topology optimization) is not needed.
1.4.8
Postprocessing Using Tosca Structure.report, the geometry after the bead optimization as well as the values of controller input can be visualized. This subsection is optional.
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1. Right click BEAD_DISP item under GENERATE_REPORT_FILE and select Edit or double click BEAD_DISP.
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2. In the opened CONTOUR_PLOT PARAMETERS dialog, choose NODAL DISPLACEMENT (BEAD) from the dropdown list in TYPE_PROPERTY field. Alternatively, BEAD CONTROLLER INPUT can be chosen: then, the fringe plot (i.e., the color of the surface) will reflect the controller input values and not the optimization displacement values. Click OK.
4. If you’ve just generated the report file and want to view the VTFX file again right click VTF_VISUALIZATION item under GENERATE_REPORT_FILE and select View.
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3. Right click BEAD_DISP item under GENERATE_REPORT_FILE and select Update. The generated VTFX file containing the original (nonsmoothed) optimization result will open in Tosca Structure.view.
SIMULIA Tosca Structure
5. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. Close the Tosca Structure.view, the TOSCA_POST and the TOSCA Job window in order to proceed.
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6. Click POST-PROCESSING | Update.
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1.4.9
Report Generation 1. Open your VTFX file: GENERATE_POST_FILE | VTF_VISUALIZATION > View.
2. With View | Viewports you can select up to four viewports in different positions. Choose two viewports: You see the relative material distribution of your model in the left side of the split window. The right part is still empty.
4. To move both views synchronously select View | Synchronous Navigation.
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3. Select Case 2 in the Table of Cases and drag it onto the right part of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1.
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6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation.
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5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
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7. A new window opens: Enter an appropriate description, select Image as Situation type and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
8. In GLView Report Builder window click File | Save Repository as to save the situations to a file. If you close the Tosca Structure Report Builder window, you can go on by opening your saved repository.
10. In the Tosca Structure Report Builder window now both siutations are listed. By rightclicking at the situation you can delete it.
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9. Go back to Tosca Structure.view window. Repeat step 6 and 7, but select 3D model as Situation type for capturing.
SIMULIA Tosca Structure
11. Now, in Tosca Structure.view window select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation. 12. The last settings are kept for capturing, thus the original model is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the original model (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at step 6 and 7, if necessary, and do not forget to activate the window). 14. In Tosca Structure.view doubleclick at CONSTRAINT_NORM in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder.
16. Repeat steps 12,13 and 14 with the objective function (OBJ_FUNC in the Table of Cases).
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15. Repeat step 13 to capture the same plot as Table.
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17. Now there should be 8 entrys in the Situations window. Doubleclick at the third entry, which is the original model as 3D model to deactivate this situation for the transfer. The situation name is shown without number in italic. The same effect is achieved by rightclicking and selecting Deactivate.
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18. Transfer the active situations into a powerpoint document by clicking File | Create PowerPointReport.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx in \report\Templates. Select your output file name and the media type (3D plugin for interactive and animated 3D data, videos and image for animations and image only for screenshots of all situations). Click OK.
20. A PowerPoint file is created. The order of figures and tables is determined by the template.
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21. For tranferring into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with the internet explorer, you can choose Video and image as Media type for other browsers.
1.4.10 Result Transfer (Smooth) 1.4.10.1 Generating smooth surface Tosca Structure.smooth is used in order to extract the surface of the optimized geometry and to save it in a desired format. IGES and STL output formats are supported. 1. Right click RUN_SMOOTH item under SMOOTH_INSTANCE and select Edit or double click RUN_SMOOTH.
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2. Make sure that TASK is set to SURFACE.
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3. Choose the output formats you need for CAD transfer (STL and IGES in this example); refer for the differences between different IGES formats and the description of other formats and click OK.
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4. Right click RUN_SMOOTH item under SMOOTH and select Update. Tosca Structure.smooth will start in background. When finished, the generated triangular surface is loaded and shown in place of the initial model; see next figure.
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5. Tosca Structure.smooth will start in background. When finished, close the TOSCA Job and the TOSCA_SMOOTH windows. The generated triangular surface is loaded and shown in place of the initial model.
Besides the new geometry loaded into Tosca ANSA environment, the results of Tosca Structure.smooth (by default saved in TOSCA_POST subdirectory of your working directory (named Output by default)) might include: • VTFX file for visualization (SMOOTH_INSTANCE.vtfx); • STL file with the optimized geometry (SMOOTH_INSTANCE.stl);
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• IGES file with the optimized geometry (SMOOTH_INSTANCE.igs).
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1.4.11 Result Discussion When the bead optimization with Tosca Structure is finished, the result (depending on solver) should be similar to Fig. 17.
a)
Optimization displacement result plots from controller based bead optimization where a) has default bead width and b) has bead width 30.0 mm. The eigenvalues are (a) 356 Hz and (b) 385 Hz, which is an increase of 99% and 115%, respectively.
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Fig. 17
b)
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1.5
Sizing with Tosca ANSA environment At the beginning of the conventional design process, the design engineer often defines new components using the experience and the results gained from existing designs. This results in an evolution process that might require several manual design iterations and a long process development time. Optimization tools provide the engineer with an automatic procedure to develop fundamentally new designs and shorten the development process. For sheet metal structures ideal sheet thicknesses according to the existing load and boundary conditions have to be derived. With Tosca Structure, it is possible to carry out sizing optimization in the existing CAE environment. Within this process shell thicknesses are calculated automatically to obtain optimal sheet metal structures.
Fig. 18
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1.5.1
Sizing for chassis components
What is Sizing Optimization? Sizing is a tool to optimize sheet metal components through modification of sheet thicknesses. It is mostly applied at a later stage of the development process when the general layout of a component (i.e. the topology) is more or less fixed. Starting with the design area (which represents the sheet structures to be modified) and with the boundary conditions, such as loads, fixtures and manufacturing conditions, the optimization system will determine a new thickness distribution by modification of the shell thicknesses in the design area. This design proposal should fulfill all mechanical requirements and often represents a weight-optimal design proposal. Sizing with Tosca Structure allows changes for each single shell element in the model as well as clustering of thicknesses, i.e. simultaneous modification of shell thicknesses for specific areas. For the optimization, the following constraints and objectives can be applied:
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• stiffness (compliance and displacements); • eigenfrequencies; • internal and reaction forces; • weight, volume; • center of gravity; • moment of inertia. In addition, a number of manufacturing constraints can be applied ensuring that the design proposal can be produced. Different constraints like, e.g., symmetry constraints can be defined. As result, the optimization creates a design proposal with new shell thicknesses. This design proposal can then be transferred back to your CAD system.
1.5.2
Model The component to be used within the tutorial represents a holder for a gear shift control and is found in the Tosca Structure installation directory () according to your FE-solver () (available for Abaqus and ANSYS): //examples/sizing/holder
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The model is meshed with linear homogenous shell elements with an initial thickness of 3.5. There are two loadcases defined. The first one is a bending loadcase with a load Fx =-2500N at node 5 and the second one is a torsional moment Mx =
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80000 Nmm at node 5. Further, all drill holes are fixed in all directions (cf. Fig. 19).
Fig. 19
Original design of a holder with loads and design area (yellow)
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The design area consists of the elements in the interior of the structure, colored yellow in Fig. 19 . The elements of the design area are combined to a group design_all which can later be used for the optimization. For further
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Fig. 20
1.5.3
Clustering groups (from left to right): Horizontal clustering groups named DES_HOR1 (on the top) till DES_HOR12, vertical clustering groups named DES_VER1 (left group) till DES_VER6 and circular clustering groups named DES_RING1 (outer ring) till DES_RING3.
Optimization Task The optimization task is to find a structure with maximum stiffness for the component for both static load cases. Additionally, a volume constraint of maximum 100 % of the initial volume should be considered. The value to be optimized is the compliance which is the reciprocal value of the stiffness. The compliance is represented as the sum of the strain energy of the complete model. This value has to be minimized. The value for the first constraint is calculated from the sum of the volumes of all elements.The first eigenmode is derived from a modal analysis.
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tasks using clustering this design domain is split into several subgroups as described below:
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The shell thicknesses should vary between an absolute value of 0.1 and 3.0. Four variants of the optimization can be performed: • Free sizing (i.e. the shell thicknesses of all design elements can be modified independently) • Clustering with horizontal areas (the design area is split horizontally into several areas in which the shell size will vary simultaneously) • Clustering with vertical areas (the design area is split vertically) • Clustering with "circular" areas (the design area is split into several "round" areas) - this cluster variant is motivated by the result of the free sizing.
1.5.4
Step by Step Manual: Summary Preprocessing 1. Create Tosca Structure task: Tasks -> Tosca Structure Task -> SIZING command of Task Manager 2. Input file: PRE_PROCESSING | MODEL_LINK | FILE 3. Design area: PRE_PROCESSING | SIZING_OPTIMIZATION | DESIGN_AREA 4. Constraint on shell thickness: PRE_PROCESSING | SIZING_OPTIMIZATION | DESIGN_AREA | DV_CONSTRAINTS | THICKNESS_BOUNDS
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6. Objective function: PRE_PROCESSING | SIZING_OPTIMIZATION | OBJ_FUNC_ITEM_1
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5. Optional: Clustergroup definition: PRE_PROCESSING | SIZING_OPTIMIZATION | DESIGN_AREA | DV_CONSTRAINTS | CLUSTER_GROUPS
9. Volume constraint terms: PRE_PROCESSING | SIZING_OPTIMIZATION | CONSTRAINTS | VOLUME_CONSTRAINT
7. Objective function terms: PRE_PROCESSING | SIZING_OPTIMIZATION | OBJ_FUNC_ITEM_1 | COMPLIANCE 8. Volume constraint: PRE_PROCESSING | SIZING_OPTIMIZATION | CONSTRAINTS
10.Saving Tosca Structure parameter file: PRE_PROCESSING | SIZING_OPTIMIZATION | Output
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Start optimization 11.Running Tosca Structure: START_OPTIMIZATION | RUN Postprocessing 12.Viewing the intermediate results:POST-PROCESSING | GENERATE_REPORT_FILE Please note that Tosca Structure 8.0 or higher is required in order to complete the optimization task.
1.5.5
Preprocessing In the following detailed description the setup of a typical sizing optimization task with Tosca ANSA environment is shown.
1.5.5.1 Choice of the optimization type 1. If Task Manager panel is hidden, click the button to make it appear in the left side of ANSA window.
3. In Task Manager, press the Expand-button.
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2. In Task Manager, select Tasks | Tosca Structure TASK | SIZING.
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1.5.5.2 Loading the input model file 1. Right click the item MODEL_LINK in Task Manager and select Edit or double click MODEL_LINK.
2. In the window titled MODEL LINK, choose as WORKING DECK the solver that matches your input file (Abaqus in this example) and click OK. Note that the steps 1 and 2 are not needed if the correct solver is already chosen in MODEL_LINK.
4. In the Open dialog, choose the input file holder. and click Open.
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3. Right click FILE item in Task Manager and select Edit or double click FILE.
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5. Right click the item named after the file you have just chosen (holder.) and select Update. The input file is loaded and the model is shown in the main window.
1.5.5.3 Choice of design area In sizing optimization, the design area denotes the set of elements that may be changed (whose thicknesses are modified) during the optimization. A subset can be defined as frozen areas which will remain unchanged. 1. Right click the item DESIGN_AREA in Task Manager and select Edit or double click DESIGN_AREA.
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2. In the DV_SIZING window, choose GROUP_DEF from the dropdown list below EL_GROUP.
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3. Activate the text field with the title GROUP_DEF and press "?" key.
4. The SET HELP window opens. Choose your predefined group DESIGN_ALL from the list of predefined groups.
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5. Double click to assign this group to your design area definition. Click OK.
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6. FE model with the highlighted DESIGN_AREA.
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1.5.5.4 Choice of thickness bounds (design variable constraint) Design variable constraints introduce restrictions on the shape of the optimized model. Besides the shell thickness constraint discussed below, other types of design constraints such as symmetry and minimum member size restrictions are supported by Tosca Structure. 1. Right click DV_CONSTRAINTS item under DESIGN_AREA and Select New | THICKNESS_BOUNDS.
2. In THICKNESS_BOUNDS window, choose GROUP_DEF from the dropdown list below EL_GROUP
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3. Activate the text field with the title GROUP_DEF and press "?" key.
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4. In the SET HELP window, double click DESIGN_ALL item. The window will then close and assign the chosen group to the design variable constraint.
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5. For defining a thickness restriction for the selected element group define a lower and upper bound of 0.1 and 3.0 respectively in the corresponding fields. Select Magnitude = ABS for absolute magnitude.
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1.5.5.5 Optional: Cluster groups It is always recommended to perform a first sizing optimization without too much additional constraints to use the maximum design flexibility for the optimization. Influenced by a first design proposal, clustering may be introduced. With Clustering, certain areas of the model are grouped such that they get a common shell thickness during the optimization. Clustered areas may later be manufactured by sheets of constant thickness. An example is the optimization of an assembled sheet structure like a car body, where each sheet has one thickness. 1. Right click DV_CONSTRAINTS item under DESIGN_AREA and Select New | CLUSTER_GROUPS.
3. For horizontal clustering choose the groups DES_HOR1 till DES_HOR12, for vertical clustering choose the groups DES_VER1 till DES_VER6 and for circular clustering choose the groupsDES_RING1 till DES_RING3 as shown in Fig. 20. Please note: for each cluster group one single DV_CONSTRAINT definition is required.
1.5.5.6 Choice of the objective function In the example, the maximum compliance of both loadcases is to be minimized.
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2. In CLUSTER_GROUPS window, choose GROUP_DEF from the dropdown list below EL_GROUP. Type "?" to access the list of predefined groups.
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1. Right click OBJ_FUNC_ITEM_1 item and select New | COMPLIANCE.
2. In OBJFUNC_TERM window, set the value of LC_SET field to "(STATIC,1,,)". Alternatively, select the appropriate values of APPROACH, LOADCASE and SUBSTEP fields of the dialog LC_SET that opens when "?" key is pressed in LC_SET field and click OK.
3. Repeat steps 1-2 for the second load case.
5. Select MIN as the value of TARGET field and click OK.
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4. Right click OBJ_FUNC_ITEM_1 item and select Edit or double click OBJ_FUNC_ITEM_1.
SIMULIA Tosca Structure
1.5.5.7 Choice of the constraint Constraints are equations or inequations that are maintained by Tosca Structure during the optimization. 1. Right click CONSTRAINT item and select NEW, then select VOLUME_CONSTRAINT.
1.5.5.8 Saving Tosca Structure parameter file The Tosca Structure parameter file contains commands which define all settings for the optimization task.
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2. Enter 1.0 in the field VALUE and click OK.
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1. Right click Output item. Select Update. The parameter file Output.par for Tosca Structure is written at this point. The file is saved in the same directory where the input model is located. The optimization with Tosca Structure will also start in this directory.
1.5.6
Start Optimization The following chapters describe how to start the optimization with an illustrated step-by-step instruction.
1. Right click RUN item under START_OPTIMIZATION. Select Update. Tosca Structure will start in background. Wait until it finishes. Then close the TOSCA Job and the OPTIMIZATION_RUN window to continue.
1.5.6.2 Logging and monitoring To see the optimization history (the values of objective function and constraints for each iteration), open the file optimization_report.csv with Microsoft Excel or a text editor. Tosca Structure log file TOSCA.OUT from TOSCA_POST directory contains this information too, along with the warnings and errors if available.
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1.5.6.1 Start Tosca Structure
SIMULIA Tosca Structure
1.5.7
Postprocessing Using Tosca Structure.report, the intermediate results of sizing optimization, namely the thicknesses of element shells, can be visualized. This subsection is optional. 1. Right click SIZING_THICKNESS item under GENERATE_REPORT_FILE. Select Update. A VTFX file containing the optimization results will be generated.
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2. To view the VTFX file right click VTF_VISUALIZATION item under GENERATE_POST_FILE and select View.
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3. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. Close the Tosca Structure.view, the TOSCA_POST and the TOSCA Job window in order to proceed.
1.5.8
Report Generation 1. Open your VTFX file: GENERATE_POST_FILE | VTF_VISUALIZATION > View.
3. Select Case 2 in the Table of Cases and drag it onto the right part of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1. 4. To move both views synchronously select View | Synchronous Navigation.
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2. Under View | Viewports you can select up to four viewports in different positions. Choose two viewports: You see the element thickness distribution of your model on the left side of the split window. The right side is still empty.
SIMULIA Tosca Structure
5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
7. A new window opens: Enter an appropriate description, select Image as Situation type for capturing and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
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6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation.
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8. In GLView Report Builder window click File | Save Repository as to save the chosen situations to a file. If you close the Tosca Structure Report Builder window, you can continue by opening your saved repository. 9. Switch back to Tosca Structure.view window. Repeat steps 6 and 7, but select 3D model as situation type for capturing.
11. Switch back to Tosca Structure.view window. Now, select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation. 12. The last setting is used for capturing, thus, the smoothed optimization result is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the optimization result ELEMENT_DELTA_THICKNESS (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at step 6 and 7, if necessary, and do not forget to activate the window).
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10. In Tosca Structure Report Builder window both model situations are now listed. By rightclicking at the situation you can delete it or change the order.
SIMULIA Tosca Structure
14. In Tosca Structure.view doubleclick at CONSTRAINT_NORM in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder. 15. Repeat step 13 with the same plot as Table. 16. Repeat step 12,13 and 14 with the objective function (OBJ_FUNC in the Table of Cases).
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17. Now there should be 8 entries in the Situations window. Doubleclick at one entry to deactivate this situation for the transfer. The same effect is given by rightclicking and selecting Deactivate.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx under \report\Templates. Select a file location and the media type. Click OK.
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18. Transfer these situations into a powerpoint document by clicking File | Create PowerPointReport.
SIMULIA Tosca Structure
20. A PowerPoint file is created. The order of figures and tables is determined by the template. 21. For transferring into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with Internet Eplorer, you can choose Video and image as Media type for other browsers.
1.5.9
Result Discussion
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A free sizing optimization without additional restrictions leads (naturally) to the best results, in this case a reduction of the maximum displacement by 45%. An optimization with clustering (circular in this case), required by manufacturing, still leads to an improvement of 30%. In the figure below (Fig. 21) the displacement results are shown:
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Displacement magnitude: initial model, optimization result without clustering and with circular clustering (top to bottom)
Fig. 22 and Fig. 23 show the shell thickness in the design area for different cases: The differences in the results of the optimization without clustering and
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Fig. 21
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with the several kinds of clustering are obvious. Furthermore, the result of optimization with vertical clustering indicates the unsymmetric load.
Fig. 22
Optimization results: Final shell thickness in the design area without clustering (left) and with horizontal clustering (right)
Fig. 23
Optimization results: Final shell thickness in the design area with vertical clustering (left) and with circular clustering (right)
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Sizing with Tosca ANSA environment
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2
Getting Started with Tosca Structure.gui Tosca Structure.gui simplifies the work process of Tosca Structure for the user. The graphical user interface supports the user with defining the optimization task (Tosca Structure.pre), starting the optimization in Tosca Structure, calculating iso surfaces, data smoothing and reduction (Tosca Structure.smooth) and preparing results for FE postprocessors (Tosca Structure.report).
Fig. 24
2.1
Tosca Structure.gui: graphical user interface of Tosca Structure
User interface
2.1.1
Requirements, Settings and Program Start Tosca Structure.gui is a platform-independent Jar archive. An html browser and Adobe Acrobat Reader to view the documentation should be installed to simplify the handling of the program. Further, a vrml plugin (not provided with Tosca Structure) or a vtfx plugin (for download see http://www.fe-design.de/ tosca/toscaview.html) must be installed to visualize vrml or vtfx files in html pages.
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Tosca Structure.gui is the classical user interface for the definition, start and postprocessing of Tosca Structure optimization tasks.
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Tosca Structure.gui is started by calling the jar files tosca_gui.jar. When using Unix, type tosca_gui in a command line. For Windows, Tosca Structure.gui can be found in the Start Menu.
Tosca Structure.gui: Settings
In order to gain the most from all program functionalities a few default settings may need to be made. The window “Edit Configuration“ shows the paths of the external programs used by Tosca Structure.gui, the Tosca Structure installation directory (Tosca StructureHome) and extensions of the solver files. The paths are set to standard paths during installation. Using the button "Reset to Defaults" the paths are read from the Tosca Structure configuration and entered on the screen. The settings are saved (button “Save“) in a file toscagui##.ini (## = current Tosca Structure version) in the user directory (and in the user profile). This file also serves as a configuration file for Tosca Structure.pre. Should there be deviations in the paths from standard during installation of the modules, some paths may need to be set individually.
2.1.2
Tosca Structure.pre The optimization task is defined using Tosca Structure.pre and the settings are stored in a parameter file. A predefined parameter file can be loaded into Tosca Structure.pre (File -> open) and is then available for any desired modifications or the optimization task can be defined from scratch. The optimiza-
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Fig. 25
SIMULIA Tosca Structure Getting Started with Tosca Structure.gui
tion task can either be created by a wizard or by defining the individual commands.
Fig. 26
Tosca Structure.pre: Defining the optimization task
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2.1.2.1 Overview The graphical user interface of Tosca Structure.pre consists of a menu, a toolbar, a status line and a split inner frame. The left frame shows the entire parameter file in text format, compact format or tree format. The compact format only shows command types and the ID name of each command. By "Opening" the command the complete definition is shown. Using the text view (text format in left frame) of the parameter file, a double click on a command opens the corresponding command template in the right frame. In the tree format, commands can be edited by simply clicking on an entry in the tree. Commands of the same type are grouped in the tree view. The order of the commands corresponds to the best sequence for creating a new parameter file. In the right frame, a selected command can be created or modified in a command template.
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The toolbar provides buttons to move commands, save and open parameter files, undo and redo buttons and a help button that opens the Tosca Structure help file.
Fig. 27
Interface of Tosca Structure.pre
2.1.2.2 Creating, modifying and saving parameter files Creating a new parameter file
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The menu item File/New File creates a new (empty) parameter file. There is no difference between the creation of a parameter file for a bead, topo or shape optimization task.
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The new parameter file contains only a standard header and the final EXIT command.
Fig. 28
Creating or opening a parameter file
The menu item File/Open can open an existing parameter file. The parameter file can be selected in a file dialog. If the parameter file contains FEM_INPUT or GROUP_IMPORT definitions, the corresponding files will automatically be scanned for group definitions. These groups are available whenever a group can be selected by a command. The content of these groups can not be modified. Nastran bdf files do not contain any group definitions, therefore this feature is not available for Nastran files. Saving a parameter file The parameter file can be saved by pressing the save button in the toolbar or in the file menu.
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Reading an existing parameter file
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Switching between text, tree and compact view The buttons in the lower left corner of the interface allow the user to switch between text view, compact view and tree view of the parameter file (similar to the tree structure in previous Tosca Structure versions)
Fig. 29
Different views of the parameterfile
Quitting the program If the parameter file has been modified, and the application is ended by File/Exit or if a new file is opened or created the user will be warned by a message box:
Fig. 30
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The text version is editable when no command is opened in the command editor in the right frame. All copy & paste functionalities that are available in Windows or Unix are accessible. The tree view gives the best overview over the commands of the groups. For each type of commands a folder is shown. Any new defined command is added to the folder of its type in the tree structure. The tree view is not directly editable, therefore commands have to be edited in the corresponding command templates. The compact view allows the user to "open" commands to display the complete definition of a single command. This view is not editable, therefore commands have to be edited in the command editor.
SIMULIA Tosca Structure Getting Started with Tosca Structure.gui
2.1.2.3 Defining optimization tasks Procedure A right-click in the left frame (parameter file) opens a context menu with the most common commands: This context menu also represents a guideline for defining an optimization task that sequentially can be processed. Specific commands are labeled according to the optimization type (bead (B), shape (S), topology (T)). Add commands A new command can be created either by selecting the corresponding item in the context menu or using the command menu:
Adding a new command using the command menu
A template will open in the right frame where parameters for the commands can be set. A basic syntax check is performed when creating a new command. By pressing the button "Create" the command is inserted into the parameter file. The position of the command in the parameter file is deter-
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Fig. 31
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mined by Tosca Structure.pre. Afterwards, the commands can be modified in the parameter file.
Referencing previously defined commands
Objects defined by previous commands can be referenced in other commands by choosing them in the selection boxes (see Fig. 32). The solver input files that are specified in the READ or GROUP_IMPORT commands will be scanned for definitions of element and node groups. These groups can be referenced by various commands too (see vol.1 chapter 2.1.2.4). Modifying commands If an existing command should be changed, it has to be selected in the parameter file. The command is opened with an appropriate template in the right frame where the parameters can be changed. The changes are accepted by pressing the button "Modify". To copy a command it first has to be selected in the parameter file view (left frame). The id name of the command must now be changed in the command editor. By pressing "Create" the command is inserted as a copy of the original command. It is essential to change the id name of the command, because two commands of the same type must not have identical id names.
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Fig. 32
SIMULIA Tosca Structure Getting Started with Tosca Structure.gui
When using the text view for editing the parameter file, commands can be copied with copy & paste, but the id name has to be modified manually afterwards!
Fig. 33
Modify and copy commands
Some commands are only allowed once in the parameter file (e.g. FEM_INPUT) and can not be copied.
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Deleting commands The button "Delete" removes the selected command from the parameter file. Arrangement of the commands The arrangement of the individual commands in the parameter file is arbitrary. Only if a command references another command, the referenced command has to be defined before. New commands will be added automatically to the parameter file in a suitable position. Comments Comments can be added anywhere in the parameter file (even inside of commands). Commands are not available as a command, but have to be inserted
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manually in the text view of the parameter file. Comment lines always start with an ’!’. Existing comments can be loaded and edited in a command template. INCLUDE commands An INCLUDE statement inserts Tosca Structure commands from another file into the current parameter file. A file can be selected in a file selection box by Add Include from the menu "Edit" and from the context menu, respectfully. INCLUDE-commands are always by default inserted at the end of the parameter file. Therefore, it has to be moved manually to the desired position. Adding free text Tosca Structure.pre does not support all available commands (e.g. SELECT). These commands can be added as free text. There is no command item for free text. However, free text can just be added into the text view of the parameter file.
2.1.2.4 Simplifications for the user Tosca Structure.pre offers some direct possibilities to select common features or to reference previously defined objects.
If other objects have to be referenced in a command (e.g. when combining constraint, objective function and design variables to a complete optimization task with the command "OPTIMIZE") the appropriate objects are supplied in a selection list. Groups that are defined in the solver input files are extracted and can be referenced by other commands (this feature is only available for Abaqus, Marc, ANSYS and PERMAS). The format of the input file is detected automatically by the file extension. Tosca Structure uses by default the common file extensions of the solvers. Default values can be changed in the preferences menu of Tosca Structure.gui. Extensions of default solvers in Tosca Structure.gui: • NastranSuffix = nas; bdf • AbaqusSuffix = inp • ANSYSSuffix = ans; cdb • PERMASSuffix = uci • MarcSuffix = dat Standard Design Responses The compilation of design responses is needed for defining the objective function and the constraint. The compilation is quite simple when using one of the following standard design responses: 1 - 180 Start Manual
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Selection lists of predefined objects
SIMULIA Tosca Structure Getting Started with Tosca Structure.gui
• First natural frequency: used for defining the objective function in shape and topology optimization • Maximum absolute displacement: can be used as a constraint in topology optimization • Maximum von Mises stress: used to define the objective function in shape optimization • Sum of Strain Energy: can be used to define the objective function in topology optimization • Volume (Shape): total volume of the model; which can be used to define constraints in shape optimization • Volume (Topology): relative volume of the model; which defines volume constraints in topology optimization • Bead height: used for defining the constraint in bead optimization.
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By selecting one of these standards all parameters in the design response template will automatically be set. Eventually, the group chosen for the calculation of the design response has to be changed. Afterwards, the command just has to be inserted into the parameter file.
Fig. 34
Standard Design Response
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Wizard New parameter files can be generated using a wizard. The wizard is available in the menu File/TOSCA.wizard or by pressing the "New" button in the toolbar.
Fig. 35
Tosca Structure.wizard
When finishing the wizard, a parameter file with all absolutely required definitions is created. Afterwards, the parameter file can be modified as usual. The wizard is limited to the following topics: • selection of optimization type (Topo, Shape, Bead)
• definition of design area • geometrical restrictions (frozen area, casting restrictions) • definition of an objective function • specification of a constraint (if available) • optimization parameters (speed)
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• choice of model file (solver input file)
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• output requests
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Fig. 36
Tosca Structure.wizard: some steps
Design nodes and elements are defined by an element or a node group. If the groups are available in the solver input file, they can be selected in the wizard. Alternatively, a new group can be defined as an element or node list. After completing the wizard, the commands can be modified or new commands can be added as usual.
2.1.3
Starting the Optimization Optimization with Tosca Structure.bead, Tosca Structure.shape or Tosca Structure.topology can be started on the "Start Tosca Structure" screen in
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Fig. 37
Tosca Structure: Starting optimization from Tosca Structure.gui
When pressing the button "Abort", the current optimization aborts. To resume the optimization has to be started again with the option "-restart". A small queueing system is available in the template "Start Tosca Structure". It can be used to start multiple Tosca Structure jobs successively on your
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Tosca Structure.gui. The job name of the optimization job (chosen by a parameter file), the start directory and if necessary the name of the FE solver are defined here. Further (optional) settings can be made using the menu "additional Parameters". After starting the optimization, information about the optimization process is given in the output window. When calling tosca using a command line vol.2 chapter 2.4, Working with Tosca Structure in the Command Shell, this control information is transferred directly into the command window. More detailed information regarding the output information for the optimization process can be found in the Tosca Structure User Manual (vol.2 chapter 12, Tosca Structure Control).
SIMULIA Tosca Structure Getting Started with Tosca Structure.gui
local computer. If a Tosca Structure job is already running and a new job is started, the new job will automatically be added to the queue.
Fig. 38
Add a job to the queue
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By the button "Edit queue" it is possible to display the status of the queue. All optimization jobs that will be started after the current job are listed here. Each individual job can be moved or deleted. If the current optimization is aborted, the optimization stops and the queue is paused. Meaning that no new optimization is started until the pause mode is ended.
Fig. 39
2.1.4
Editing the queue
Tosca Structure.smooth Tosca Structure.smooth prepares the optimization result for transfer into a CAD-system or FE-preprocessor. The Tosca Structure.gui window Tosca Structure.smooth enables you to enter parameters to perform and control sur-
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face or isosurface calculation for an optimization result, smoothing and data reduction. The results from Tosca Structure.smooth can be displayed by Tosca Structure.view.
Fig. 40
2.1.5
Tosca Structure.smooth: Input parameters via Tosca Structure.gui
Visualization with Tosca Structure.view
2.1.6
Postprocessing (Tosca Structure.report) The module Tosca Structure.report allows a preparation for postprocessing of the optimization results. Animation sequences for Tosca Structure.view
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Tosca Structure.view can display animations of the optimization results. Start Tosca Structure.gui using the button View Report of Tosca Structure.smooth or Tosca Structure.report screen in Tosca Structure.gui. Besides Tosca Structure.view a plug-in for MS Internet explorer, MS PowerPoint and MS Word is available. Thus, it is possible to create interactive presentations inside MS Office documents.
SIMULIA Tosca Structure Getting Started with Tosca Structure.gui
including plots of optimization relevant values (objective, constraint) can be created.
Tosca Structure.report: Preparation of the optimization results for postprocessing
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Fig. 41
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SIMULIA Tosca Structure User interface
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2.2
Topology Optimization with Tosca Structure.gui
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At the beginning of the conventional design process the design engineer defines the shape and the topology of new components using the experience and the results gained from the forerunner. These results in an evolution process which might lead to an optimum design after some iterations and a long period of time. Nowadays it is necessary to shorten the development process of new components. Therefore tools are necessary that replace the natural evolution process by an automatic procedure. With Tosca Structure it is possible to carry out topology and shape optimization in the CAE environment.
2.2.1
What is Topology Optimization? Topology optimization is a tool to generate a design proposal and is often used within the concept finding for a new component. Starting with the design area which is the maximum allowed area for the component and with the boundary conditions, such as loads, fixtures and manufacturing conditions the optimization system will determine a new material distribution by removing material from the design area. This design proposal fulfills all mechanical requirements and represents a weight-optimal design proposal. For the optimization the following constraints and objectives can be realized:
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• stiffness (compliance and displacements) • eigenfrequencies • internal and reaction forces • weight, volume • center of gravity • moment of inertia In addition a number of manufacturing constraints can be applied so that the design proposal can be produced with casting, stamping. For this casting constraints, member size constraints, freezing and symmetry and coupling constraints can be defined. As result the optimization system creates a design proposal with the information where the material has to be positioned. This design proposal has to be interpreted and has to be used for the more detailed analysis. For supporting this step the Tosca Structure system supports the generation of a verification model within Tosca ANSA environment. This means a new model based on the results of the topology optimization can be created easily without the necessity of applying the loads and boundary conditions to the verification model. All loadcases and boundary conditions of the optimization model are transferred automatically to the verification model. With the results of the verification run it is possible to perform a normal FE postprocessing step within the postprocessing environment suitable for your solver or a CAD model can be generated which then can be transferred back to your CAD system.
The Model The component to be used within the tutorial represents a control arm for a car and is found in the Tosca Structure installation directory () according to your FE-solver () : //examples/topo/control_arm
The model is loaded with one loadcase consisting of two fixtures in the upper left and right areas and is loaded with one load in the lower bearing area. The
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2.2.2
SIMULIA Tosca Structure
original design is the realized design which has to be strengthened by the optimization.
Design Area
Existing design of a control arm with the design area
The model for the topology optimization was modified in such a way that the inner areas of the component are filled with elements to create a design area where the optimization system can remove or rearrange elements for getting a better mechanical behavior of a component with a lower weight. The start model for the optimization represents a design of a control arm for a car. The component has to be manufactured by forging and consists of aluminum. The red areas of the component are not free for the optimization because they are used for the fixtures and for the load application. One red area is used for the mounting of a sensor for the headlight range adjustment.
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Fig. 42
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Fig. 43
Loads of the model
The fixture is realized with spring elements on the right upper red area. The springs represent a rubber bearing. The left bearing is fixed in all three translation degrees of freedom, but is able to rotate about the x-axis. As loading a force is applied in the center of the lower bearing. Due to symmetry reasons only one half of the model is meshed so the symmetry plane is fixed in z-direction for ensuring the symmetry condition.
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Topology Optimization with Tosca Structure.gui
SIMULIA Tosca Structure
2.2.3
Optimization Task The optimization task is to find a structure with the maximum stiffness for the component with a volume or weight restriction. This represents the most common standard optimization task for the topology optimization. The value to be optimized is the compliance which is the reciprocal value of the stiffness. The compliance is represented as the sum of the strain energy of the complete model. This value has to be minimized. The constraint is the weight or volume constraint which is defined to be 70% of the initial volume/weight of the structure. As manufacturing constraint a casting/forging constraint has to be defined. The idea of the constraint is to ensure that the created structure of the topology optimization has no undercuts and can be demolded (or removed from the forging die).
2.2.4
Step by Step Manual: Summary If you have never worked with Tosca Structure.gui before you should skip this summary and go directly to the detailed description. If you do have some experience with Tosca Structure.gui you can try to generate your parameter file just using the recipe summary. Did you get it all right? Preprocessing 1. Starting Tosca Structure preprocessor: Tosca Structure.pre | Tree 2. Input file: Tosca Structure.pre | FEM_INPUT 3. Define Group (Nastran users only): Tosca Structure.pre | GROUP_DEF | Read Nastran Set
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4. Design area: Tosca Structure.pre | DV_TOPO 5. Design constraints: Tosca Structure.pre | DVCON_TOPO | Cast 6. Design Responses: Tosca Structure.pre | DRESP 7. Objective function: Tosca Structure.pre | OBJ_FUNC | Minimize 8. Constraints: Tosca Structure.pre | CONSTRAINT 9. Define optimization task: Tosca Structure.pre | OPTIMIZE 10.Saving Tosca Structure parameter file: Tosca Structure.pre | FILE | Save As Start Optimization 11.Running Tosca Structure: Start Tosca Structure | Start
TOSCA
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Postprocessing 12.Generating material distibution file: Tosca Structure.report | Generate Report Result Transfer and Validation Run 13.Generating smooth surfaces: Tosca Structure.smooth | Start Smoothing Performing a complete validation run as well as generating the whole setup for a validation run is not possible automatically using Tosca Structure.gui. Nevertheless, different output formats for the optimized structure are supported as basis for validation models. However, further preprocessing (manual addition of loads and boundary conditions) is required by the user in order to generate a FE model using the optimized structure. Please note that Tosca Structure 7.0 or higher is required in order to complete the optimization task. With previous versions of Tosca Structure some changes may be necessary to achieve the same results.
2.2.5
Preprocessing
1. Tosca Structure.gui starts and the Tosca Structure.pre module is displayed. Left click on the Tree button to change the view of the optimization task structure on the left side to tree mode. 1 - 194 Start Manual
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2.2.5.1 Starting Tosca Structure Preprocessor
SIMULIA Tosca Structure
2.2.5.2 Loading the input model file 1. Select the item FEM_INPUT from the optimization task tree. The FEM_INPUT menu appears on the right.
2. In the Input Files area, click Add to select the model for the optimization. The Open dialog appears.
4. Left click on Create to add the item MY_INPUT_FILES to the optimization task tree.
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3. In the Open dialog, choose the FE model for your solver (control_arm. where is the extension your FEsolver uses.) and press Open. The model name with its full path appears in the The finite element input files field.
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2.2.5.3 Group creation (Nastran users only) The following part is important only for Nastran users. If your input file matches any other solver supported by Tosca Structure please skip this chapter and continue with the definition of the design area. For any other solver the groups for topology optimization are included in the solver input files and transferred in Tosca Structure via the FEM_INPUT command. 1. Select the item GROUP_DEF from the optimization task tree. The GROUP_DEF menu appears to the right.
2. Type a proper name for the group in the field ID_NAME, DESIGN_ELEMENTS for example, and activate the radio button Element next to Type to specify the group type.
4. In the Open dialog, choose the file control_arm_groups.bdf which contains the element set needed for the topology optimization and press Open. The Select Nastran Set dialog appears where the content of the file control_arm_groups.bdf is listed.
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3. Click Read Nastran Set to select the existing group. The Open dialog appears.
SIMULIA Tosca Structure
5. In the Select Nastran Set dialog, select 1 from the Set Number dropdown list if not already selected and press Ok. The selected Nastran set transferred to the Data field in the GROUP_DEF menu.
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6. Click Create to add the item DESIGN_ELEMENTS to the optimization task tree.
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2.2.5.4 Define the design area In topology optimization, the design area denotes the set of elements that may be removed during the optimization, in contrast to the frozen areas that remain unchanged. 1. Select the item DV_TOPO from the optimization task tree. The DV_TOPO menu appears on the right.
2. Choose the group DESIGN_ELEMENTS from the dropdown list next to EL_GROUP and click Create to add the item MY_DV_TOPO to the optimization task tree.
2.2.5.5 Choice of the design variable constraints
1. Select the item DVCON_TOPO from the optimization task tree. The DVCON_TOPO menu appears on the right.
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Design variable constraints introduce restrictions on the shape of the optimized model. Besides the demolding constraint discussed below, other types of design constraints such as symmetry and member size restrictions are supported by Tosca Structure.
SIMULIA Tosca Structure
2. Type a proper name in the field ID_NAME, for example DVCON_CAST, and select DESIGN_ELEMENTS from the dropdown list next to Element Group. The constraint will now be applied to all elements of the selected group. Please note that the ID_NAME is a special mark of any component of the optimization task. The ID_NAME must be unique for each component. Using the ID_NAME you can select between different components of the same type during the optimization setup. If no other component of the same type appear in the optimization task, the change of the ID_NAME is optional and the Tosca Structure default ID_NAME can be used.
4. Choose DESIGN_ELEMENTS from the Check Group dropdown list to define the check group for the cast restriction and click Create to add the item DVCON_CAST to the optimization task tree.
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3. For defining a cast restriction for the selected element group activate the radio button Cast and define the pull direction vector by typing in the values 0,0,1 in the fields next to Pull Direction. Make sure the global coordinate system CS_0 is selected in the field next to Pull_CS.
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2.2.5.6 Definition of design responses In order to specify optimization target and constraints you must first define design responses. The design responses are assigned to output parameters from the FE analysis. In this example design responses for the volume and the strain energy will be needed. 1. Select the item DRESP from the optimization task tree. The DRESP menu appears on the right.
3. Choose ALL_ELEMENTS from the Element/Elementgroup dropdown list and set the Group Operator to Sum to build the sum of the volumes of each element in the model. Thus the whole volume of the structure is determined. Click Create to add the design response DRESP_VOLUME to the optimization task tree. 4. Repeat step 1 to define another design response.
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2. Type a proper name in the field ID_NAME, for example DRESP_VOLUME, and choose the type VOLUME in the field Type of the Base category.
SIMULIA Tosca Structure
5. Type a ID_NAME for the new design response, for example DRESP_STRAIN_ENERGY, in the corresponding field and choose Stress/Strain from the Category dropdown list and in the Type field choose the type STRAIN_ENERGY.
6. Activate the Element/Elementgroup radio button and select ALL_ELEMENTS from the Element/Elemtgroup dropdown list.
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7. Set the Group Operator to Sum and click Create to add the design response DRESP_STRAIN_ENERGY to the optimization task tree.
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2.2.5.7 Choice of the objective function The objective function will be minimized or maximized by Tosca Structure, depending on the settings. 1. Select the item OBJ_FUNC from the optimization task tree. The OBJ_FUNC menu appears on the right.
2. Click Add Dresp to select a design response for the objective function. The Select Design Responses dialog appears.
4. Select the radio button Minimize next to Target and click Create to add the item MY_OBJ_FUNC to the optimization task tree.
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3. In the Select Design Responses dialog, activate the design response DRESP_STRAIN_ENERGY and press Ok. The window closes and the selected design response appears in the field.
SIMULIA Tosca Structure
2.2.5.8 Choice of the constraints Constraints are equations or inequations that are maintained by Tosca Structure during the optimization. 1. Select the item CONSTRAINT from the optimization task tree. The CONSTRAINT menu appears on the right.
2. Type a proper name in the field ID_NAME, for example VOLUME_CONSTRAINT, and choose the design response DRESP_VOLUME from the Design Response dropdown list.
4. Select the equality radio button next to Constraint Type, thus the target volume for the optimization is set to exactly 70 percent of the original volume, and click Create to add the item VOLUME_CONSTRAINT to the optimization task tree.
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3. Select the radio button Relative next to Type to set the constraint type and push the slider to 70 or type the value in the field manually.
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2.2.5.9 Definition of the optimization task 1. Select the item OPTIMIZE from the optimization task tree. The OPTIMIZE menu appears on the right.
2. Select TOPO_CONTROLLER from the Strategy dropdown list to choose the optimization strategy. Design area and objective function are selected automatically.
4. In the Select Design Variable Constraints dialog, activate the design variable constraint DVCON_CAST and press Ok. The DVCON_CAST item appears in the DV Constraints field. 5. Click Add next to the Constraints field to add the constraints to the optimization task. The Select Constraints dialog appears.
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3. Click Add next to the DV Constraints field to add the design variable constraints to the optimization task. The Select Design Variable Constraints dialog appears.
SIMULIA Tosca Structure
6. Activate the constraint VOLUME_CONSTRAINT and press Ok. The VOLUME_CONSTRAINT item appears in the Constraints field.
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7. Click Create to add the item MY_OPTIMIZATION_TASK to the optimization task tree.
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2.2.5.10 Saving Tosca Structure parameter file The Tosca Structure parameter file contains ASCII commands which define all settings for the optimization task. 1. Select File from the main menu and pick Save As from the File dropdown list. The Save As dialog appears.
2. In the Save As dialog choose a name for the optimization task, enter the filename in the field below and press Save As. The file automatically receives the extension .par and becomes the parameter file for Tosca Structure.
Start Optimization 1. Switch to the Start TOSCA Structure module from the Module dropdown list in the upper right corner.
2. Choose all from the Type dropdown list . This option includes a preprocessing test and the optimization run.
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2.2.6
SIMULIA Tosca Structure
3. Select the solver of your choice from the Solver dropdown list.
4. Click Start TOSCA to start the optimization. Status information about the optimization run is displayed in the field below.
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5. After approx. 15 design cycles the optimization run is finished and the status TOSCA job finished is displayed.
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2.2.7
Postprocessing Viewing the intermediate results using Tosca Structure.report. Using Tosca Structure.report, the intermediate results of topology optimization, namely the densities of individual elements, can be visualized. 1. Switch to the Tosca Structure.report module from the Module dropdown list in the upper right corner.
3. To see every design cycle click in the field below Iter (concerning the result Controller Input) and select All from the Iter dropdown menu (default). Repeat this for the result Material Distribution (second field below Iter). 4. Click Generate Report to start the generation of the result file. Status information about the file generation is displayed in the field below.
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2. Select the results by activating the buttons to the left of the Results Controller Input and Material Distribution. A standard report is available in the directory | TOSCA_POST after each optimization which can be visualized using Tosca Structure.view.
SIMULIA Tosca Structure
5. When the file generation is completed a message about the successful job ending is displayed in the status field.
6. Click View Report to view the material distribution in the optimized structure. The Open dialog appears.
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7. In the open dialog select the generated .vtfx file and press Open. Tosca Structure.view starts.
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8. The Animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. The described example is generated using the FE solver MSC Nastran. Please note that slight differencies in the optimized design are possible for the different solvers. However the design conception remains the same.
2.2.8
Report Generation 1. Click View Report to view the material distribution in the optimized structure. The Open dialog appears. Open your vtfx file.
3. Select Case 2 in the Table of Cases and drag it onto the right part of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1. 4. To move both views synchronously select View | Synchronous Navigation.
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2. Under View | Viewports you can select up to four viewports in different positions. Choose two viewports: You see the relative material distribution of your model on the left side of the split window. The right side is still empty.
SIMULIA Tosca Structure
5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
7. A new window opens: Enter an appropriate description, select Image as Situation type for capturing and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
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6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation.
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8. In GLView Report Builder window click File | Save Repository as to save the chosen situations to a file. If you close the Tosca Structure Report Builder window, you can continue by opening your saved repository. 9. Switch back to Tosca Structure.view window. Repeat steps 6 and 7, but select 3D model as situation type for capturing.
11. Switch back to Tosca Structure.view window. Now, select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation. 12. The last setting is used for capturing, thus, the smoothed optimization result is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the smoothed optimization result (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at step 6 and 7, if necessary, and do not forget to activate the window).
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10. In Tosca Structure Report Builder window both model siutations are now listed. By rightclicking at the situation you can delete it or change the order.
SIMULIA Tosca Structure
14. In Tosca Structure.view doubleclick at CONSTRAINT_NORM in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder. 15. Repeat step 13 with the same plot as Table. 16. Repeat step 12,13 and 14 with the objective function (OBJ_FUNC in the Table of Cases).
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17. Now there should be 8 entrys in the Situations window. Doubleclick at the third entry, which is the smoothed optimization result as 3D model to deactivate this situation for the transfer. The same effect is given by rightclicking and selecting Deactivate.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx under \report\Templates. Select a file location and the media type. Click OK.
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18. Transfer these situation into a powerpoint document by clicking File | Create PowerPointReport.
SIMULIA Tosca Structure
20. A PowerPoint file is created. The order of figures and tables is determined by the template. 21. For tranferring into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with the internet explorer, you can choose Video and image as Media type for other browsers.
2.2.9
Result Transfer and Validation Run
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After the optimization an automatic validation run enables quality checks of the result. An approved result must then be transferred into the product development process. To this end, the new design proposal must be available for import and further processing in CAD systems.
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2.2.9.1 Surface generation using Tosca Structure.smooth. Tosca Structure.smooth generates the surface of the material remaining after the topology optimization and improves the surface quality. 1. Switch to the Tosca Structure.smooth module from the Module dropdown list in the upper right corner. 2. In the Tosca Structure.smooth module click Select Job. The Open dialog appears.
3. In the Open dialog, select the Tosca Structure parameter file and press Open.
5. When the file generation is completed the message Program finished is displayed in the status field.
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4. Click Start Smoothing (keep the default configuration). Status information about the file generation is displayed in the field below.
SIMULIA Tosca Structure
6. Click View Result to view the material distribution in the optimized structure. The Open dialog appears.
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7. In the Open dialog, select the corresponding .vtfx file and press Open. Tosca Structure.view starts.
2.2.9.2 Processing the optimized structure Using Tosca Structure.gui a complete reconstruction of the model with the new design is not possible. Therefore some additional steps are required which should be performed manually by the user. However Tosca Struc-
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ture.gui offers several opportunities to generate a design model using Tosca Structure.smooth as a base for further processing by the user. Different output formats for the smooth surface can be chosen. For example geometry surfaces can be created using the stl or igs format. In this case the geometry can be loaded in a CAD tool for further handling or in a FE preprocessor for generating a new mesh. Using solver output format (bdf, inp, cdb, etc.) Tosca Structure.smooth automatically generates a mesh on the smooth structure in the corresponding solver format. However the boundary conditions for the FE analysis must be generated manually by the user.
The topology optimization created a new design proposal for the control arm component. The result of the topology optimization has to be discussed in several ways. First of all the optimization result has to be checked. This can be done with viewing the convergence plot and with checking the TOSCA.OUT file for warnings and errors. If there is a critical error during the optimization the optimization loop will be stopped. In other cases (if some results are missing) the optimization system will continue but the result may be not sufficient. Second the resulting model and the finite element analysis of the model has to be checked if the displacements, the stresses and all other finite element related information are suitable. Initial model (complete model with 70% of material homogeneously distributed)
Result
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Result comparison
Final model
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2.2.10 Result Discussion
SIMULIA Tosca Structure
Fig. 44
von Mises stresses of optimized structure
After checking the results the remaining structure can be passed to the design department as a CAD model to be used as design proposal for the fine tuning of the design. If the stresses within the component are not below the allowed range the shape optimization of Tosca Structure (Tosca Struc-
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For this optimization task the stresses are in the same range compared to the initial model but the stiffness of the structure is higher and the material amount necessary for the structure is lower. The values to be compared are the volume or weight of the structure and the sum of the strain energy. The strain energy is the measure for the compliance which is the reciprocal value of the stiffness
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Fig. 45
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Optimization result represented after data reduction: IGES surfaces for CAD transfer
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ture.shape) will be able to remove the stress peaks so that the component will be suitable from the mechanical point of view.
SIMULIA Tosca Structure
The results can be transferred as surfaces in STL format or IGES format. Another way to transfer less data is to export the results as slices.
Optimization result represented as slices
For sharing the result and the animation with colleagues or partners the VTFX format is comfatable way. This result format is able to contain a full 3D animated model with the optimization history. The model can be rotated and zoomed during the animation. The viewer is available for free for different
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Fig. 46
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platforms and there is also a possibility to include the files into HTML-pages and into Powerpoint presentations.
Material distribution after topology optimization
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2.3
Shape Optimization with Tosca Structure.gui Shape optimization allows specific detail improvements of existing designs. Through shape optimization the surface geometry of a given model is modified automatically to avoid material failure and increase durability or comfort.
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2.3.1
What is Shape Optimization? Shape optimization is mostly used at the end of the design process when the general layout of a component is more or less fixed and only minor changes and improvements are allowed. Typically, the objective function is to minimize stress concentrations. Based on the results of a stress analysis modifications of the surface geometry of a component are performed until the required stress level is reached. This process is usually carried out manually by trialand-error. Tosca Structure.shape allows an automatization of this improvement process. The surface geometry of a given FE model is modified iteratively based on the FE results, such that the required optimization target is reached. The start
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model is taken from an existing design, which should be improved, or from a previous topology optimization. Tosca Structure.shape enables you to perform the following tasks • Minimization of the equivalent stress • Maximization of selected natural frequencies • Specification of a volume constraint • Surface-based manufacturing constraints for casting, forging, stamping, extrusion and drilling • Minimum and maximum member size • Symmetry constraints • Specification of design domain restrictions by FE-meshes • Mesh adjustment and mesh smoothing in each optimization cycle • Additional functionalities like optimization using durability results are available with Tosca Structure.durability • Additional functionalities like optimization using nonlinear results or for the optimization of contact areas are available with Tosca Structure.nonlinear
2.3.2
The Model
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The component optimized in this tutorial is a connecting rod (conrod) and is found in the Tosca Structure installation directory (): //examples/shape/conrod The model is built with an autogenerated tetrahedron mesh symmetric to the xz and yz plane. The mesh quality is medium/poor with average element
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De sig n
are a
edge of ~ 2 mm. Outer dimensions: 180 x 84 x 24 mm. Allowed design and mesh smooth area are shown in Fig. 48.
Mesh smooth area
Fig. 48
Connecting rod (conrod) with design and mesh smooth area
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Loaded nodes are connected with MPCs to the inner side of the conrod mounts. Nodes in the big eye nodes on the inner radius (crankshaft bearing) are fixed in all three coordinate directions. There are five loadcases realized in the model (see Fig. 49): Loadcase 1: Centrifugal force (a in Fig. 49), 15000 N applied in z-direction Screw fixation Loadcase 2: Gas pressure (b in Fig. 49), 25000 N applied in negative z-direction Fixation in nodes of big eye Loadcase 3: Bending about the x-axis Fixation in nodes of big eye
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Loadcase 4: Bending moment about the y-axis Fixation in nodes of big eye Loadcase 5: Torsion about the z-axis. Fixation in nodes of big eye
a
Fig. 49
2.3.3
Loads and boundary conditions of the model conrod: (a) centrifugal force, right: force caused by gas pressure (b), bending and torsion about x-, y- and z-axis.
Optimization Task The goal is to reduce stress peaks on the surface of the component with small changes at the surface of the component. Thus the optimization task is to minimize the maximum stresses of the loadcases on the connecting rod, see Fig. 49. The design area is shown in Fig. 48 and consists of the surface nodes of the area in the inner rectangle.
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b
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2.3.4
Step by Step Manual: Summary If you have never worked with Tosca Structure.gui before you should skip this summary and go directly to the detailed description. If you do have some experience with Tosca Structure.gui you can try to generate your parameter file just using the recipe summary. Did you get it all right? Preprocessing 1. Starting Tosca Structure preprocessor: Tosca Structure.pre | Tree 2. Input file: Tosca Structure.pre | FEM_INPUT 3. Define group (Nastran users only): Tosca Structure.pre | GROUP_DEF | Read Nastran Set 4. Design area: Tosca Structure.pre | DV_SHAPE 5. Design variable constraint: Tosca Structure.pre | DVCON_SHAPE | Check_DOF 6. Design responses: Tosca Structure.pre | DRESP | Add LC 7. Objective function: Tosca Structure.pre | OBJ_FUNC | Minmax 8. Mesh smooth: Tosca Structure.pre | MESH_SMOOTH 9. Define optimization task: Tosca Structure.pre | OPTIMIZE 10.Global stop condition: Tosca Structure.pre | STOP 11.Saving Tosca Structure parameter file: Tosca Structure.pre | FILE | Save As Check Inputs
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12.Setting up test optimization: Tosca Structure.pre | TEST_SHAPE 13.Running test optimization: Start Tosca Structure | test1 | Start TOSCA 14.Viewing test results: Tosca Structure.report | Generate Report Start Optimization 15.Running Tosca Structure: Start Tosca Structure | all | Start TOSCA Postprocessing 16.Generating result displacement file: Tosca Structure.report | Generate Report
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Result Transfer 17.Generating CAD output: Tosca Structure.smooth | igs | Start Smoothing Extensions 18.Link Conditions: Tosca Structure.pre | LINK_SHAPE | SURFACE_DEMOLD 19.Design Variable Constraints: Tosca Structure.pre | DVCON_SHAPE | Link Condition 20.Design Responses: Tosca Structure.pre | DRESP 21.Constraints: Tosca Structure.pre | CONSTRAINT 22.Mesh Smooth: Tosca Structure.pre | MESH_SMOOTH 23.Global Stop Condition: Tosca Structure.pre | STOP
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Please note that Tosca Structure 7.0 or higher is required in order to complete the optimization task. With previous versions of Tosca Structure
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some changes may be necessary to achieve the same results.
2.3.5
Preprocessing
2.3.5.1 Starting Tosca Structure Preprocessor
1. Tosca Structure.gui starts and the Tosca Structure.pre module is displayed. Left click on the Tree button to change the view of the optimization task structure on the left side to tree mode.
1. Select the item FEM_INPUT from the optimization task tree. The FEM_INPUT menu appears on the right.
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2.3.5.2 Loading the input model file
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2. In the Input Files area, click Add to select the model for the optimization. The Open dialog appears.
3. In the Open dialog, select the FE model for your solver (conrod. where is the extension your FE-solver uses.) and press Open. The model name with its full path appears in the field The finite element input files.
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4. Left click on Create to add the item MY_INPUT_FILES to the optimization task tree.
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2.3.5.3 Group creation (Nastran users only) The following part is important only for Nastran users. If your input file matches any other solver supported by Tosca Structure please skip this chapter and continue with the definition of the design area. For any other solver the groups for shape optimization are included in the solver input files and transferred in Tosca Structure via the FEM_INPUT command. 1. Select the item GROUP_DEF from the optimization task tree. The GROUP_DEF menu appears on the right.
2. Type a proper name for the group in the field ID_NAME, for example DESIGN_NODES, and activate the radio button Node next to Type to specify the group type.
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3. Click Read Nastran Set to select the existing group. The Open dialog appears.
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4. In the Open dialog, select the file conrod_groups.bdf which contains the sets needed for the shape optimization and press Open. The Select Nastran Set dialog appears where the content of the file groups.bdf is listed.
5. In the Select Nastran Set dialog, select 1 from the Set Number dropdown list and press Ok. The selected Nastran set is transferred to the Data field in the GROUP_DEF menu.
6. Click Create to add the group DESIGN_NODES to the optimization task tree.
8. Type a proper name for the group in the field ID_NAME, for example MESH_SMOOTH_ELEMENTS, and activate the radio button Element next to Type. 9. Repeat step 3 and 4 selecting once again the file groups.bdf.
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7. Now repeat step 1 in order to create another group.
SIMULIA Tosca Structure
10. In the Select Nastran Set dialog, select 2 from the Set Number dropdown list and press Ok. The selected NASTRAN set is transferred to the Data field in the GROUP_DEF menu.
11. Click Create to add the group MESH_SMOOTH_ELEMENTS to the optimization task tree.
12. Repeat these steps from 1 to 6 with set number 3 to create a group FIXED_NODES.
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13. Still two groups are necessary for a further step in this example (see chapter 2.3.12 Extensions). So repeat all steps from 1 to 6 twice again to create two more node groups. Name the first group SURF_DEMOLD_POS and select the NASTRAN set number 4 in the Select Nastran Set dialog. Choose the name SURF_DEMOLD_NEG for the second node group and select the Nastran set number 5 in the Select Nastran Set dialog.
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2.3.5.4 Select design area 1. Select the item DV_SHAPE from the optimization task tree. The DV_SHAPE menu appears on the right.
2. Select the group DESIGN_NODES from the ND_GROUP dropdown list.
3. Click Create to add the item MY_DV_SHAPE to the optimization task tree.
In order to specify optimization target and constraints you must first define design responses. The design responses are assigned to output parameters from the FE analysis. In this example design responses for the von Mises stress for both loadcases will be needed. 1. Select the item DRESP from the optimization task tree. The DRESP menu appears on the right.
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2.3.5.5 Definition of design responses
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2. Type a proper name in the field ID_NAME, for example DRESP_MISES_LC1.
3. Select Stress/Strain from the Category dropdown list and select in the Type field the type SIG_MISES
4. Select the group DESIGN_NODES from the Node/Nodegroup dropdown list and set the Group operator to Max.
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5. Click Add LC to select the load case for the design response. The Select Loadcase dialog appears.
6. In the Select Loadcase dialog, enter 1 instead of All in the Loadcase Number field and press Ok. The new entry appears in the Loadcase Selection field.
7. Click Create to add the item DRESP_MISES_LC1 to the optimization task tree.
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8. Repeat all steps from 1 to 7 four times again to create four other design responses for von Mises stress. Name the design response DRESP_MISES_LC2, DRESP_MISES_LC3 and so on and select the loadcase number 2, 3, 4 and 5 in the Select Loadcase dialog.
2.3.5.6 Choice of the design variable constraint As the mesh smooth area also contains elements which should not be changed a DOF control has to be implemented which fixes the nodes of this area in all directions. 1. Select the item DVCON_SHAPE from the optimization task tree. The DVCON_SHAPE menu appears on the right. 2. Enter an appropriate name and select FIXED_NODES as ND_GROUP.
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3. Activate the CHECK DOF field and DOF 1, DOF 2 and DOF 3. Click OK.
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2.3.5.7 Choice of the objective function The objective function will be minimized or maximized by Tosca Structure, depending on the settings. 1. Select the item OBJ_FUNC from the optimization task tree. The OBJ_FUNC menu appears on the right.
2. Click Add Dresp to select a design response for the objective function. The Select Design Responses dialog appears.
4. Activate the radio button MinMax next to Target to minimize the maximal von Mises stress and click Create to add the item MY_OBJ_FUNC to the optimization task tree.
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3. In the Select Design Responses dialog, activate both design responses and press Ok. The window closes and the selected design responses appear in the field.
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2.3.5.8 Select mesh smoothing elements 1. From the Command menu select MESH_SMOOTH. The MESH_SMOOTH menu appears on the right.
2. Activate the radio button EL_GROUP and select the element group MESH_SMOOTH_ELEMENTS from the dropdown list.
3. Leave all default settings unchanged and click Create to add the item MY_MESH_SMOOTH to the optimization task tree.
1. Select the item OPTIMIZE from the optimization task tree. The OPTIMIZE menu appears on the right.
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2.3.5.9 Definition of the optimization task
SIMULIA Tosca Structure
2. Select SHAPE_CONTROLLER from the Strategy dropdown list to choose the optimization strategy. Design area and objective function are selected automatically.
3. Click Add next to DV Constraints.
4. Activate the DVCON_DOF_CONTROL button and press Ok.
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5. Select MY_MESH_SMOOTH from the Mesh Smooth dropdown list and click Create to add the item MY_OPTIMIZATION_TASK to the optimization task tree.
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2.3.5.10 Define a stop condition 1. Select the item STOP from the optimization task tree. The STOP menu appears on the right.
2. Activate the Maximum number of iterations radio button and change the iteration number to 5. Click Create to add the item MY_STOP to the optimization task tree.
2.3.5.11 Saving Tosca Structure parameter file The Tosca Structure parameter file contains ASCII commands which define all settings for the optimization task.
2. In the Save As dialog enter the filename and press Save As. The file automatic receives the extension .par and becomes the parameter file for Tosca Structure.
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1. Select File from the main menu and pick Save As from the File dropdown list. The Save As dialog appears.
SIMULIA Tosca Structure
2.3.6
Check Inputs Before starting an eventually long running optimization task you should always check if your definitions make sense and are complete. Missing settings may require a complete rerun of your optimization.
2.3.6.1 TEST_SHAPE The command TEST_SHAPE creates a simple optimization displacement on all your design nodes. Then you can see if everything works as you imagined it. 1. From the Command menu select TEST_SHAPE. The TEST_SHAPE menu appears on the right.
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2. Select the direction entry GROW, set the displacement amount to 3 (mm) and enter 3 to specify the number of increments for the test displacement.
3. Click Create to add the item TEST_SHAPE to the optimization task tree.
4. Click Save to save the changes in the parameter file.
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2.3.6.2 Starting the test optimization 1. Switch to the Start TOSCA Structure module from the Module dropdown list in the upper right corner.
2. Select the optimization type test1 from the Type dropdown list (this option includes a preprocessing test and the test optimization run) and select the solver of your choice from the Solver dropdown list 3. Click Start TOSCA to start the test optimization. Status information about the optimization run is displayed in the field below.
2.3.6.3 Viewing the test results 1. Switch to the Tosca Structure.report module from the Module dropdown list in the upper right corner.
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4. After 3 increments the test optimization run is finished and the status TOSCA job finished is displayed.
SIMULIA Tosca Structure
2. Select the results by activating the buttons to the left of the Results Optimization Displacements and Opt. Displacement Values. A standard report is available in the directory | TOSCA_POST after each optimization which can be visualized using Tosca Structure.view.
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3. To see the Optimization Displacements and the Opt. Displacement Values for every design cycle click in the field below Iter (concerning the result Optimization Displacements) and select All from the Iter dropdown menu (default). Repeat this for the result Opt. Displacement Values (second field below Iter). 4. Click Generate Report to start the generation of the result file. Status information about the file generation is displayed in the field below.
5. When the file generation is completed a message about the successful job ending is displayed in the status field.
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6. Click View Report to view the test displacements. The Open dialog appears.
8. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. You can change between SHAPE_DISP and SHAPE_CTRL by doubleclicking on the corresponding case in the Table of Cases window or by selecting it in the dropdown menu. Examine the model with test displacements and close Tosca Structure.view window in order to proceed with Tosca ANSA environment. Please note: as no FE-Analysis is performed, there are no CTRL_INPUT results available.
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7. In the open dialog select the generated .vtfx file and press Open. Tosca Structure.view starts.
SIMULIA Tosca Structure
9. In the animation appearing after the test run it should be quite easy to check: • Are the design nodes (moving nodes) correctly defined?
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• Is the optimization direction (nodal movement) in the correct direction?
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2.3.7
Start Optimization 1. Switch back to the Start TOSCA Structure module from the Module dropdown list in the upper right corner.
2. Change the optimization type to all from the dropdown list next to Type.
This will cause the sequential start of both the test run and the real optimization. In order to skip the test run you can go to the Tosca Structure.pre module and delete the TEST_SHAPE item from the optimization task.
4. After 5 design cycles the optimization run is finished and the status TOSCA job finished is displayed.
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3. Click Start TOSCA to start the optimization. Status information about the optimization run is displayed in the field below.
SIMULIA Tosca Structure
2.3.8
Postprocessing 1. Switch again to the Tosca Structure.report module from the Module dropdown list in the upper right corner.
2. Activate the button next to Controller Input and deactivate all other buttons to view only the optimization results under consideration of the optimized parameters (in this case von Mises stress).
To view also the changes in the shape of the structure with the amounts of the nodal displacements of the design nodes, activate also the button next to Optimization Displacements or next to Opt. Displacements Value.
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3. Click in the field of column Iter and row Controller Input and select in the Iter drop-down menu All to view all cycles of the optimization. 4. In the row of Controller Input you can optionally enter 0 in the column Fringe(min) and 150 in the column Fringe(max). (Doubleclick in the corresponding field for editation.) 5. Click Generate Report to start the generation of the result file. Status information about the file generation is displayed in the field below.
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6. When the file generation is completed a message about the successful job ending is displayed in the status field.
7. Click View Report to view the test displacements. The Open dialog appears.
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8. In the open dialog select the generated .vtfx file and press Open. Tosca Structure.view starts.
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9. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. The described example is generated using the FE solver MSC Nastran. Please note that slight differencies in the optimized design are possible for the different solvers. However the design conception remains the same.
2.3.9
Report Generation 1. Click View Report to view the material distribution in the optimized structure. The Open dialog appears. Open your vtfx file.
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2. View | Viewports allows to select up to four viewports in different positions. Choose two viewports: You see the relative material distribution of your model on the left side of the split window. The right side is still empty. 3. Select Case 2 in the Table of Cases and drag it onto the right part of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1.
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4. To move both views synchronously select View | Synchronous Navigation.
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6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation.
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5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
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7. A new window opens: Enter an appropriate description, select Image as Situation type and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
8. In GLView Report Builder window click File | Save Repository as to save your captured situations to a file. If you close the Tosca Structure Report Builder window, you can continue by opening your saved repository.
10. In Tosca Structure Report Builder window both model siutationsare listed. By rightclicking at the situation you can delete it or change the order.
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9. Switch back to Tosca Structure.view window. Repeat steps 6 and 7, but select 3D model as situation type for capturing.
SIMULIA Tosca Structure
11. Switch back to Tosca Structure.view window. Now, select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation. 12. The last setting is kept for capturing, thus, the original model is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the original model (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at steps 6 and 7, if necessary, and do not forget to activate the window). 14. In Tosca Structure.view doubleclick at VARIABLE | DRESP values in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder.
16. Repeat steps 13, 14 and 15 with the objective function (OBJ_FUNC in the Table of Cases).
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15. Repeat step 13 with the same plot captured as Table.
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17. Now there should be 8 entrys in the Situations window. Doubleclick at the third entry, which is the original model as 3D model to deactivate this situation for the transfer. The same effect is given by rightclicking and selecting Deactivate.
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18. Transfer these situations into a powerpoint document by clicking File | Create PowerPointReport.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx under \report\Templates. Select a file location and the media type. Click OK.
20. A PowerPoint file is created. The order of figures and tables is determined by the template.
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21. For transfer into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with the internet explorer, you can choose Video and image as Media type for other browsers.
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2.3.10 Result Transfer Valid optimization results need to be transferred back into the design process. To this end the modified model has to be written in a format which can be read by CAD programs to be used as draft for modifications of the existing design. To this end a Tosca Structure.smooth run will write the modified surface of the optimized model to STL or iges, for example. 1. Switch to the Tosca Structure.smooth module from the Module dropdown list in the upper right corner.
2. Click Select Job. The Open dialog appears.
4. Click the button with the three dots at the right of Optimization results to load them. The Open dialog appears.
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3. In the Open dialog, select the Tosca Structure parameter file and press Open.
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5. In the Open dialog, go to the SAVE.onf directory and select the the file SHAPE_00x.onf, where x represents the last design cycle of the bead optimization. In this case, select the file SHAPE_005.onf and press Open. The selected file with its whole path appears in the field next to Optimization Results. 6. Select the option Create Surface + Optimization displacements (Shape and Bead optimization) from the Task dropdown list. 7. Select a CAD output format, for example .igs or .stl and deactivate the format .vtf.
9. When the file generation is completed the message Program finished is displayed in the status field. Click View Result and navigate in the Open window to your smooth results in your job directory in the subdirectory TOSCA_POST. For CAD transfer IGES-SLICES can be used. Continue with the following steps to create IGES-SLICES using Tosca Structure.smooth: 10. Activate the checkbox Additional Parameters. Additional fields are displayed.
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8. Click Start Smoothing. Status information about the file generation is displayed in the field below.
SIMULIA Tosca Structure
11. Select Slices (3D) from dropdown list next to Slices.
12. Select igs_curves from the Format dropdown list.
13. Change the number of slices to 60 and enter the normal vector 0,0,1 to specify the slices orientation.
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14. Click Start Tosca Structure.smooth. After Tosca Structure is finished click View Result and navigate in the Open window to your smooth results in your job directory in the subdirectory TOSCA_POST.
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2.3.11 Result Discussion The result, depending on the used solver, should be similar to Fig. 50.
Stress reduction in the design area from 197 MPa to 134 MPa in 5 iterations (see chapter 2.3.12.4 Redefine the global stop condition)
In Fig. 50 the stress reduction is clearly seen. The maximal stress is minimized with around 32%. The staying stress concentrations in Fig. 50 can not be removed because of the element quality prohibits futher nodal optimization displacement. A solution would be to remesh the two areas or the whole part and restart the optimization.
2.3.12 Extensions 2.3.12.1 Design variable constraints There may be different manufacturing constraints for the conrod. Let’s assume that in the production it is cast and must therefore:
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Fig. 50
SIMULIA Tosca Structure
1. be demoldable; 2. be symmetric to x-z-plane. These requirements can be realized in different ways in Tosca Structure.shape. In the following only one of these ways is described in detail, some alternatives will be discussed at the end of the chapter. Casting Constraint 1. Go back to the Tosca Structure.pre module. If neccessary load again your parameter file. From the Command menu select LINK_SHAPE. The LINK_SHAPE menu appears on the right.
3. Select the global carthesian coordinate system CS_0 from the Coordinate System dropdown list and enter the vector 1,0,0 in the fields next to DEMOLD_DIR to set the demold direction.
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2. Type a proper name in the field ID_NAME, for example LINK_CAST_POS, and select SURF_DEMOLD from the Client dropdown list to specify a cast restriction.
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4. Select the group SURF_DEMOLD_POS as check group for the link condition and click Create to add the item LINK_CAST to the optimization task tree. How to create the groups for Nastran is explained in chapter 2.3.5.3 Group creation (Nastran users only). 5. Select the item DVCON_SHAPE from the optimization task structure tree. The DVCON_SHAPE menu appears on the right.
7. Select the link condition LINK_CAST_POS from the Link Condition dropdown list and click Create to add the item DVCON_CAST_POS to the optimization task tree. Now the setup has to be repeated to create a casting constraint for the other half of the design area in the negative direction. Repeat all steps from 1 to 12 to create the new casting constraint. Name the link condition LINK_CAST_NEG, enter the vector -1,0,0 for the opposite pull direction and select the group SURF_DEMOLD_NEG as check group. Choose the name DVCON_CAST_NEG for the new DVCON_SHAPE definition. Select the node group SURF_DEMOLD_NEG in the ND_GROUP field and coose the new link condition LINK_CAST_NEG in the Link Condition field. Leave all other settings from the described steps unchanged. 1 - 262 Start Manual
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6. Type a proper name in the field ID_NAME, for example DVCON_CAST_POS, and select the node group SURF_DEMOLD_POS from the ND_GROUP dropdown list.
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Symmetry to x-z-plane
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8. Define symmetry for all design nodes with a symmetry plane normal to the y-axis through the point (0,0,100). First define a Cartesian coordinate system with origin in point (0,0,100). Then define plane symmetry using LINK_SHAPE: The symmetry plane contains the origin of the referenced coordinate system and the normal vector is defined by CLIENT_DIR. Third, reference LINK_SHAPE in DVCON_SHAPE for all design nodes.
2.3.12.2 Define a volume constraint By visual observation the FE-model seems to gain weight. This may not be a desired effect. One way to prevent this is to define a volume constraint.Define a design response for the volume 1. Select the item DRESP from the optimization task stree. The DRESP menu appears on the right.
3. Select ALL_ELEMENTS from the dropdown list next to Element/Elementgroup and choose Sum from the Group Operator dropdown list. Thus the sum of the volumes of each element in the model is built and the whole volume of the structure is determined.
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2. Type a proper name in the field ID_NAME, for example DRESP_VOLUME, and select in the Type field of the Base category the type VOLUME.
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4. Click Create to add the design response DRESP_VOLUME to the optimization task tree.
Define the volume constraint 1. Select the item CONSTRAINT from the optimization task tree. The CONSTRAINT menu appears on the right.
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2. Type a proper name in the field ID_NAME, for example VOLUME_CONSTRAINT, and select the design response DRESP_VOLUME at the Design Response dropdown list.
3. Select the radio button Relative next to Type to set the constraint type and push the slider to 100 or type the value in the field manually. 4. Activate the equality radio button next to Constraint Type, thus the original volume will remain unchanged, and click Create to add the item VOLUME_CONSTRAINT to the optimization task tree.
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2.3.12.3 Updating the optimization task 1. Select the item MY_OPTIMIZATION_TASK from the optimization task tree. The OPTIMIZE menu appears on the right.
2. Click Add next to the DV Constraints field to add the design variable constraints to the optimization task. The Select Design Variable Constraints dialog appears.
4. Click Add next to the Constraints field to add the constraints to the optimization task. The Select Constraints dialog appears.
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3. In the Select Design Variable Constraints dialog, activate all design variable constraints and press Ok. The items appear in the DV Constraints field.
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5. In the Select Constraints dialog, activate the only defined constraint VOLUME_CONSTRAINT and press Ok. The VOLUME_CONSTRAINT item appears in the Constraints field. 6. Click Modify to activate the changes and to exit the OPTIMIZE menu.
Although the very efficient shape optimization often does a really good job in only 5 iterations a few percent more may be gained by letting the optimizer run a little longer. The simplest way to do this is to change the maximum number of iterations. The change of the global stop condition is described in vol.2 chapter 6.11.1, Global Stop Condition. Modify the item MY_STOP and change the iteration number to 10.
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2.3.12.4 Redefine the global stop condition
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2.3.12.5 Selecting mesh smooth elements automatically 1. Select the item MY_MESH_SMOOTH from the optimization task tree. The MESH_SMOOTH menu appears on the right.
2. Activate the radio button ND_GROUP, Layer, select the group DESIGN_NODES from the ND_GROUP, Layer dropdown list and change the number of layers for mesh smooth to 5.
3. Click Modify to activate the changes and to exit the MESH_SMOOTH menu. Run the optimization. What happens? Check the inside of the holes of the conrod. Have nodes moved there? Why?
1. This automatic definition of the mesh smoothing elements should only be used as the lazy option compared to the description in chapter 2.3.5.8 Select mesh smoothing elements. The problems that can occur are many especially for real life applications. In this case the nodes on the inner surface of the holes (where the connection elements are) are also moved, which is not wanted. Therefore, we emphasize that selecting the MESH_SMOOTH element group manually can often save time in the long run. 2. If no MESH_SMOOTH command is defined per default 6 adjacent layers of elements are added to the MESH_SMOOTH group starting from the design nodes. For the current model and the design area in Fig. 48 the mesh smooth group becomes too large - and optimization stops within a couple of iterations because of a bad mesh.
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Remark:
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2.3.13 Troubleshooting Shape optimization is often seen as a difficult optimization type which is in most cases related to the mesh problems that may arise during optimization. This can cause the optimization to stop.
2.3.13.1 How to workaround mesh problems?
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The best solution is of course to remesh, but this may be a time consuming task. The second best solution is to check the solver log file and find out which elements are causing the problems. Look these elements up in your preprocessor. If you only have a few problematic elements at the edge of the MESH_SMOOTH area, try to remove these problematic elements from the MESH_SMOOTH area. A good mesh for shape optimization is not always equal to a high quality calculation mesh. Avoid using mesh refinement on the surface and rather mesh a little coarser than usual and uniformly.
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Shape Optimization with Tosca Structure.gui
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2.4
Bead Optimization with Tosca Structure.gui Bead optimization is a way to enhance shell structures without adding more mass to the structure. The beads can easily be added in the stamping process which makes bead a low weight and cost neutral alternative to enhance a sheet-metal structure.
2.4.1
What is Bead Optimization?
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The easiest way to understand bead optimization is a simple example every mechanical engineer will intuitively understand.
a) Fig. 51
b)
Simple plate in bending with loading and supports (a) and an optimalbead (b). The maximal displacement of (a) is 6.6 mm and (b) is 0.25 mm
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In Fig. 51 is a simple flat plate in bending shown. It is evident that the solution in Fig. 51 (b) has a much greater stiffness than the original flat plate in Fig. 51 (a). Regarding the simple example in Fig. 51 a couple of comments must be made:
bead height
Fig. 52
bead width Bead height and bead width
• The bead height (see Fig. 52) has the most significant effect on the stiffness of the plate structure. Usually, the greater the bead height the greater the stiffness. But, the bead height is usually controlled by manufactoring capabilities i.e. how deep can you draw a bead with your available tools.
Increasing stiffness Fig. 53
Bead layouts for simple geometries with a uniform pressure load. From Oehler and Weber: "Steife Blech- und Kunststoffkonstruktionen", Springer-Verlag GmbH (1972)
For more complex loads or dynamic problems i.e. eigenvalue or frequency response, the optimal bead layout is not intuitive anymore (see Fig. 53). 1 - 272 Start Manual
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• The bead width (see Fig. 52) has an effect on the possible designs. As seen in Fig. 53 a small or a large bead width is not necessarily related to the stiffness of the sheet structure. The Tosca Structure.bead default values usually suffice, but if an optimal solution is saught you must try more bead widths.
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Thus, an easy way to find a good bead pattern is to use Tosca Structure.bead.
2.4.1.1 Tosca Structure.bead Tosca Structure.bead is the Tosca Structure module for bead optimization. Two bead optimization algorithms has been implemented: • Controller based bead optimization (BEAD_CONTROLLER) • Sensitivity based bead optimization (BEAD_SENSITITY) In general the controller algorithm is much faster than the sensitivity algorithm, but lacks handling of complex design responses such as frequency response or combined responses. The controller algorithm leads to very easy interpretable beads. The bead patterns of the sensitivity algorithm can be more difficult to interpret, but the results are often superior to the controller results, especially for dynamic problems. For the optimization the following constraints and objectives can be realized: • stiffness (compliance and displacements*) • eigenfrequencies * Only sensitivity based algorithm allows these constraints and objectives The following presents a start guide for Tosca Structure.bead. The purpose is to show how simple it is to set up a bead optimization problem in Tosca ANSA environment. For more background knowledge about bead optimization, differences between the two algorithms and other advanced settings in Tosca Structure.bead please consult the users manual. This guide is restricted to showing the controller based bead algorithm.
Model Model information: A model of an oilpan is found in the Tosca Structure installation directory () according to your FE-solver () :
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//examples/bead/oil_pan
z
y
x Fig. 54
FE-model of an oilpan - a typical automotive sheet metal part.
• Dimensions: length (z-direction): ~ 500 mm width (x-direction): ~ 305 mm, depth (y-direction): ~42 mm, thickness: 1.3 mm.
• Mesh: Average element edge lenght: ~ 7 mm, mostly linear quads and a few trias. • Initial 1st eigenvalue: 179 Hz • Boundary conditions are for simplicity crude full supports on the edges of the oilpan. Real life boundary condition could be obtained by using the full body-in-white model of a car which would also run with Tosca Structure - of course with unreasonable runtimes for this simple introduction.
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• The element normals of the shell elements are in the negative y-direction
y x Fig. 55
2.4.3
Design area
Optimization Task Task 1: Maximize the natural (1st) eigenfrequency of the oil pan using controller based algorithm. The maximum bead height is 5 mm and the bead direction must be in the positive y-direction, see Fig. 54. Prerequisites • Tosca ANSA environment Basics - read and understood • FE-model oil_pan_tosca_env. for your solver
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2.4.4
Step by Step Manual: Summary If you have never worked with Tosca Structure.gui before you should skip this summary and go directly to the detailed description. If you do have some experience with Tosca Structure.gui you can try to generate your parameter file just using the recipe summary. Did you get it all right? Preprocessing 1. Starting Tosca Structure preprocessor: Tosca Structure.pre | Tree 2. Input file: Tosca Structure.pre | FEM_INPUT 3. Define Group (Nastran users only): Tosca Structure.pre | GROUP_DEF | Read Nastran Set 4. Design area: Tosca Structure.pre | DV_BEAD 5. Design Responses: Tosca Structure.pre | DRESP 6. Objective function: Tosca Structure.pre | OBJ_FUNC | Maximize
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7. Constraints: Tosca Structure.pre | CONSTRAINT 8. Define optimization Task: Tosca Structure.pre | OPTIMIZE 9. Saving Tosca Structure parameter file: Tosca Structure.pre | FILE | Save As Check Inputs 10.Setting up test optimization: Tosca Structure.pre | TEST_BEAD 11.Running test optimization: Start Tosca Structure | test1 | Start TOSCA 12.Viewing test results: Tosca Structure.report | Generate Report Start Optimization 13.Running Tosca Structure: Start Tosca Structure | all | Start TOSCA Postprocessing 14.Generating result displacement file: Tosca Structure.report | Generate Report Result Transfer 15.Generating CAD output: Tosca Structure.smooth | igs | Start Smoothing
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Please note that Tosca Structure 7.0or higher is required in order to complete the optimization task. With previous versions of Tosca Structure some changes may be necessary to achieve the same results.
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2.4.5
Preprocessing
2.4.5.1 Starting Tosca Structure Preprocessor
1. Tosca Structure.gui starts and the Tosca Structure.pre module is displayed. Left click on the Tree button to change the view of the optimization task structure on the left side to tree mode.
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2.4.5.2 Loading the input model file 2. Select the item FEM_INPUT from the optimization task tree. The FEM_INPUT menu appears on the right.
3. In the area Input Files, click Add to select the model for the optimization. The Open dialog appears.
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4. In the Open dialog, choose the FE model for your solver (oil_pan. where is the extension your FE-solver uses.) and press Open. The model name with its full path appears in the field The finite element input files.
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5. Left click on Create to add the item MY_INPUT_FILES to the optimization task tree.
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2.4.5.3 Group creation (Nastran users only) The following part is important only for Nastran users. If your input file matches any other solver supported by Tosca Structure please skip this chapter and continue with the definition of the design area. For any other solver the groups for topology optimization are included in the solver input files and transferred in Tosca Structure via the FEM_INPUT command. 1. Select the item GROUP_DEF from the optimization task tree. The GROUP_DEF menu appears on the right.
2. Type a proper name for the group in the field ID_NAME, DESIGN_NODES for example, and click the radio button Node next to Type to specify the group type.
4. In the Open dialog, choose the file groups.bdf which contains the sets needed for the bead optimization and press Open. The Select Nastran Set dialog appears where the content of the file groups.bdf is listed.
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3. Click Read Nastran Set to select the existing group. The Open dialog appears.
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5. In the Select Nastran Set dialog, select 1 from the Set Number dropdown list and press Ok. The selected Nastran set is transferred to the Data field in the GROUP_DEF menu.
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6. Click Create to add the item DESIGN_NODES to the optimization task tree.
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2.4.5.4 Select design area 1. Select the item DV_BEAD from the optimization task tree. The DV_BEAD menu appears on the right.
2. Choose the group DESIGN_NODES from the dropdown list next to ND_GROUP and click Create to add the item MY_DV_BEAD to the optimization task tree.
2.4.5.5 Definition of design responses In order to specify optimization target and constraints you must first define design responses. The design responses are assigned to output parameters from the FE analysis. In this example design responses for the bead height and the first eigenfrequency will be needed.
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1. Select the item DRESP from the optimization task tree. The DRESP menu appears on the right.
2. Type a proper name in the field ID_NAME, for example DRESP_BEAD_HEIGHT, and choose the type BEAD_HEIGHT in the field Type of the category Base.
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3. Select the group DESIGN_NODES from the Node/Nodegroup dropdown list, make sure the Group Operator is set to Max and click Create to add the item DRESP_BEAD_HEIGHT to the optimization task tree. 4. Repeat step 1 to create a new design response and name it DRESP_EIGEN_1.
6. In the Select Loadcase dialog, select MODAL as Analysis Type and enter the value 1 instead of All in the Eigenmode/Substep field and click Ok. The new entry appears in the Loadcase Selection field.
7. Click Create to add the item DRESP_EIGEN_1 to the optimization task tree.
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5. Select DYN_FREQ instead of BEAD_HEIGHT in the Type field of the category Base and click Add LC to assign the design response to the first eigenfrequency. The Select Loadcase dialog appears.
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2.4.5.6 Choice of the objective function The objective function will be minimized or maximized by Tosca Structure, depending on the settings. 1. Select the item OBJ_FUNC from the optimization task tree. The OBJ_FUNC menu appears on the right.
2. Click Add Dresp to select a design response for the objective function. The Select Design Responses dialog appears.
4. Select the radio button Maximize in the Target area to maximize the first eigenvalue and click Create to add the item MY_OBJ_FUNC to the optimization task tree.
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3. In the Select Design Responses dialog, activate the design response DRESP_EIGEN_1 and press Ok. The dialog closes and the selected design response appears in the field.
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2.4.5.7 Create bead height constraint 1. Select the item CONSTRAINT from the optimization task tree. The CONSTRAINT menu appears to the right.
2. Type a proper name in the field ID_NAME, for example BEAD_HEIGHT_CONSTRAINT, and choose the design response DRESP_BEAD_HEIGHT from the Design Response dropdown list. 3. Select the radio button Absolute in the Type area to set the constraint type, enter the value 5 in the Absolute field to set the maximum height for the beads and make sure the Constraint Type is set to equality
2.4.5.8 Definition of the optimization task 1. Select the item OPTIMIZE from the optimization task tree. The OPTIMIZE menu appears to the right.
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4. Click Create to add the item BEAD_HEIGHT_CONSTRAINT to the optimization task tree.
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2. Select BEAD_CONTROLLER from the Strategy dropdown list to choose the optimization strategy. Design area and objective function are selected automatically.
3. Click Add next to the Constraints field to add constraints to the optimization task. The Select Constraints dialog appears.
4. In the Select Constraints dialog, activate the constraint BEAD_HEIGHT_CONSTRAINT and press Ok. The BEAD_HEIGHT_CONSTRAINT item appears in the Constraints field.
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5. Click Create to add the item MY_OPTIMIZATION_TASK to the optimization task tree.
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2.4.5.9 Optimization settings The optimization direction of the controller algorithm can be changed in the optimization settings. 1. Select OPT_PARAM in the Command menu to open the optimization settings. The OPT_PARAM menu appears on the right.
2. Enter the value -1 in the Scale field to reverse the optimization direction. For bead optimizations the numeric value has no influence, only the sign of the value. 3. Optionally you can change the bead width by typing a new value in the BEAD_WIDTH field. For now use the default value by leaving the field empty. The default value will be written in the file TOSCA.OUT in the TOSCA_POST directory after the optimization is finished.
2.4.5.10 Saving Tosca Structure parameter file The Tosca Structure parameter file contains ASCII commands which define all settings for the optimization task.
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4. Click Create to add the item MY_PARAMETERS to the optimization task tree.
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1. Select File from the main menu and pick Save As from the File dropdown list. The Save As dialog appears.
2. In the Save As dialog, choose a name for the optimization task, enter the filename in the field below and press Save As. The file automatic receives the extension .par and becomes the parameter file for Tosca Structure.
2.4.6
Check Inputs
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Before starting an eventually long running optimization task you should always check if your definitions make sense and are complete. Missing settings may require a complete rerun of your optimization.
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2.4.6.1 TEST_BEAD The command TEST_BEAD creates a simple optimization displacement on all your design nodes. Then you can see if everything works as you imagined it. 1. From the Command menu select TEST_BEAD. The TEST_BEAD menu appears on the right.
2. Leave the default Direction entry GROW, set the displacement amount to 5 (mm) and enter 5 to specify the number of increments for the test displacement.
3. Click Create to add the item TEST_SHAPE to the optimization task tree.
2.4.6.2 Starting the test optimization 1. Switch to the Start TOSCA Structure module from the Module dropdown list in the upper right corner.
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4. Click Save to save the changes in the parameter file.
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2. Switch the optimization type to test1 from the Type dropdown list (this option includes a preprocessing test and the test optimization run) and select the solver of your choice from the Solver dropdown list. 3. Click Start TOSCA to start the test optimization. Status information about the optimization run is displayed in the field below.
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4. After 5 increments the test optimization run is finished and the status TOSCA job finished is displayed.
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2.4.6.3 Viewing test results 1. Switch to the Tosca Structure.report module from the Module dropdown list in the upper right corner of the Tosca Structure.gui 2. Activate the two buttons under Result Name at Result Selection. A standard report is available in the directory | TOSCA_POST after each optimization which can be visualized using Tosca Structure.view.
4. Click Generate Report to start the generation of the result file. Status information about the file generation is displayed in the field below.
5. When the file generation is completed a message about the successful job ending is displayed in the status field.
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3. To see the Optimization Displacements and the Opt. Displacement Values for every design cycle click in the field below Iter (concerning the result Optimization Displacements) and select All from the Iter dropdown menu (default). Repeat this for the result Opt. Displacement Values (second field below Iter).
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6. Click View Report to view the test displacements. The Open dialog appears.
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7. In the open dialog select the generated .vtfx file and press Open. Tosca Structure.view starts.
8. Click to the start and stop button to animate the test result.
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In the animation appearing after the test run it should be quite easy to check: • Are the design nodes (moving nodes) correctly defined?
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• Is the optimization direction (nodal movement) in the correct direction i.e. positive y-direction?
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2.4.7
Start Optimization 1. Close Tosca Structure.view and switch back to the Start TOSCA Structure module from the Module dropdown list in the upper right corner. 2. Change the optimization type to all from the dropdown list next to Type. This will cause the sequential start of both the test run and the real optimization.
In order to skip the test run you can go to the Tosca Structure.pre module and delete the TEST_BEAD item from the optimization task. 3. Click Start TOSCA to start the optimization. Status information about the optimization run is displayed in the field below.
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4. After 3 design cycles the optimization run is finished and the status TOSCA job finished is displayed.
2.4.8
Postprocessing 1. Switch again to the Tosca Structure.report module from the Module dropdown list in the upper right corner.
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2. Activate the buttons next to Optimization Displacements and Opt. Displacement Values and deactivate all other buttons.
3. Click Generate Report to start the generation of the result file. Status information about the file generation is displayed in the field below. 4. When the file generation is completed a message about the successful job ending is displayed in the status field. 5. Click View Report to view the test displacements. The Open dialog appears.
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6. In the open dialog select the generated .vtfx file and press Open. Tosca Structure.view starts.
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7. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. The described example is generated using the FE solver MSC Nastran. Please note that slight differencies in the optimized design are possible for the different solvers. However the design conception remains the same.
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2.4.8.1 Result Transfer Valid optimization results need to be transferred back into the design process. To this end the modified model has to be written in a format which can be read by CAD programs to be used as draft for modifications of the existing design. To this end a Tosca Structure.smooth run will write the modified surface of the optimized model to e.g. - STL or iges. 1. Switch to the Tosca Structure.smooth module from the Module dropdown list in the upper right corner. 2. Click Select Job. The Open dialog appears.
4. Click the button with the three dots at the right of Optimization results to load them. The Open dialog appears.
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3. In the Open dialog, select the Tosca Structure parameter file and press Open.
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5. In the Open dialog, go to the SAVE.onf directory and select the the file BEAD_00x.onf, where x represents the last design cycle of the bead optimization. In this case, select the file BEAD_003.onf and press Open. The selected file with its whole path appears in the field next to Optimization Results. 6. Select the task Create Surface + Optimization displacements (Shape and Bead optimization) from the Task dropdown list.
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7. Activate a button with a CAD output format, for example .igs or .stl and deactivate all other buttons. 8. Click Start Smoothing. After Tosca Structure is finished click View Result and navigate in the Open window to your smooth results in your job directory in the subdirectory TOSCA_POST.
2.4.9
Report Generation 1. Open your VTFX file by clicking View Result.
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2. With View | Viewports you can select up to four viewports in different positions. Choose two viewports: You see the relative material distribution of your model in the left side of the split window. The right part is still empty. 3. Select Case 2 in the Table of Cases and drag it onto the right part of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1.
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4. To move both views synchronously select View | Synchronous Navigation.
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6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation.
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5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
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7. A new window opens: Enter an appropriate description, select Image as Situation type and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
8. In GLView Report Builder window click File | Save Repository as to save the situations to a file. If you close the Tosca Structure Report Builder window, you can go on by opening your saved repository.
10. In the Tosca Structure Report Builder window now both siutations are listed. By rightclicking at the situation you can delete it.
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9. Go back to Tosca Structure.view window. Repeat step 6 and 7, but select 3D model as Situation type for capturing.
SIMULIA Tosca Structure
11. Now, in Tosca Structure.view window select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation. 12. The last settings are kept for capturing, thus the original model is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the original model (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at step 6 and 7, if necessary, and do not forget to activate the window). 14. In Tosca Structure.view doubleclick at CONSTRAINT_NORM in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder.
16. Repeat steps 12,13 and 14 with the objective function (OBJ_FUNC in the Table of Cases).
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15. Repeat step 13 to capture the same plot as Table.
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17. Now there should be 8 entrys in the Situations window. Doubleclick at the third entry, which is the original model as 3D model to deactivate this situation for the transfer. The situation name is shown without number in italic. The same effect is achieved by rightclicking and selecting Deactivate.
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18. Transfer the active situations into a powerpoint document by clicking File | Create PowerPointReport.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx in \report\Templates. Select your output file name and the media type (3D plugin for interactive and animated 3D data, videos and image for animations and image only for screenshots of all situations). Click OK.
20. A PowerPoint file is created. The order of figures and tables is determined by the template.
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21. For tranferring into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with the internet explorer, you can choose Video and image as Media type for other browsers.
2.4.10 Result Discussion When Tosca Structure is done the result (depending on solver) should be similar to Fig. 56.
a)
Optimization displacement result plots from controller based bead optimization where a) has default bead width and b) has bead width 30.0 mm. The eigenvalues are (a) 356 Hz and (b) 385 Hz, which is an increase of 99% and 115%, respectively.
2.4.10.1 Logging and monitoring The history of the optimization can either be followed in Tosca Structure’s logfile TOSCA.OUT or in the optimization_report.csv-file. The default bead width is determined from the average element edge length in design area. In the logfile TOSCA.OUT is the average element edge length found to be 8.3 mm and the BEAD_WIDTH 53.0 mm (see log file TOSCA.OUT).
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Fig. 56
b)
SIMULIA Tosca Structure
2.5
Sizing Optimization with Tosca Structure.gui At the beginning of the conventional design process, the design engineer often defines new components using the experience and the results gained from existing designs. This results in an evolution process that might require several manual design iterations and a long process development time. Optimization tools provide the engineer with an automatic procedure to develop fundamentally new designs and shorten the development process. For sheet metal structures ideal sheet thicknesses according to the existing load and boundary conditions have to be derived. With Tosca Structure, it is possible to carry out sizing optimization in the existing CAE environment. Within this process shell thicknesses are calculated automatically to obtain optimal sheet metal structures.
Fig. 57
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2.5.1
Sizing for chassis components
What is Sizing Optimization? Sizing is a tool to optimize sheet metal components through modification of sheet thicknesses. It is mostly applied at a later stage of the development process when the general layout of a component (i.e. the topology) is more or less fixed. Starting with the design area (which represents the sheet structures to be modified) and with the boundary conditions, such as loads, fixtures and manufacturing conditions, the optimization system will determine a new thickness distribution by modification of the shell thicknesses in the design area. This design proposal should fulfill all mechanical requirements and often represents a weight-optimal design proposal. Sizing with Tosca Structure allows changes for each single shell element in the model as well as clustering of thicknesses, i.e. simultaneous modification of shell thicknesses for specific areas. For the optimization, the following constraints and objectives can be applied:
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• stiffness (compliance and displacements); • eigenfrequencies; • internal and reaction forces; • weight, volume; • center of gravity; • moment of inertia. In addition, a number of manufacturing constraints can be applied ensuring that the design proposal can be produced. Different constraints like, e.g., symmetry constraints can be defined. As result, the optimization creates a design proposal with new shell thicknesses. This design proposal can then be transferred back to your CAD system.
2.5.2
Model The component to be used within the tutorial represents a holder for a gear shift control and is found in the Tosca Structure installation directory () according to your FE-solver () (available for Abaqus and ANSYS): //examples/sizing/holder
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The model is meshed with linear homogenous shell elements with an initial thickness of 3.5. There are two loadcases defined. The first one is a bending loadcase with a load Fx =-2500N at node 5 and the second one is a torsional moment Mx = 80000Nmm at node 5. Further, all drill holes are fixed in all directions (cf. Fig. 58)
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Fig. 58
Original design of a holder with loads and design area (yellow coloured)
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The design area consists of the elements in the interior of the structure, colored yellow in Fig. 58 . The elements of the design area are combined to a group design_all which can later be used for the optimization. For further
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Fig. 59
2.5.3
Clustering groups:Horizontal clustering groups named DES_HOR1 (on the top) until DES_HOR12 on the left, vertical clustering groups named DES_VER1 (left group) until DES_VER6 in the middle and cicular clustering groups named DES_RING1 (outer ring) until DES_RING3 on the right.
Optimization Task The optimization task is to find a structure with maximum stiffness for the component for both static load cases. Additionally, a weight constraint of maximum 100 % of the initial weight should be considered. The value to be optimized is the compliance which is the reciprocal value of the stiffness. The compliance is represented as the sum of the strain energy of the complete model. This value has to be minimized. The value for the first constraint is calculated from the sum of the volumes of all elements.The first eigenmode is derived from a modal analysis.
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tasks using clustering this design domain is split into several subgroups as described below:
SIMULIA Tosca Structure
The shell thicknesses should vary between an absolute value of 0.1 and 3.0. Four variants of the optimization can be performed: • Free sizing (i.e. the shell thicknesses of all design elements can be modified independently) • Clustering with horizontal areas (the design area is split horizontally into several areas in which the shell size will vary simultaneously) • Clustering with vertical areas (the design area is split vertically) • Clustering with "circular" areas (the design area is split into several "round" areas) - this cluster variant is motivated by the result of the free sizing.
2.5.4
Step by Step Manual: Summary If you have never worked with Tosca Structure.gui before you should skip this summary and go directly to the detailed description. If you do have some experience with Tosca Structure.gui you can try to generate your parameter file just using the recipe summary. Did you get it all right? Preprocessing 1. Starting Tosca Structure preprocessor: Tosca Structure.pre | Tree 2. Input file: Tosca Structure.pre | FEM_INPUT 3. Design area: Tosca Structure.pre | DV_SIZING 4. Design variable constraints: Tosca Structure.pre | DVCON_SIZING 5. Design Responses: Tosca Structure.pre | DRESP
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6. Objective function: Tosca Structure.pre | OBJ_FUNC | Minimize 7. Constraints: Tosca Structure.pre | CONSTRAINT 8. Define optimization Task: Tosca Structure.pre | OPTIMIZE 9. Saving Tosca Structure parameter file: Tosca Structure.pre | FILE | Save As Start Optimization 10.Running Tosca Structure: Start Tosca Structure | all | Start TOSCA
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Postprocessing 11.Generating result displacement file: Tosca Structure.report | Generate Report Please note that Tosca Structure 8.0 or higher is required in order to complete the optimization task.
2.5.5
Preprocessing In the following detailed description the setup of a typical sizing optimization task with Tosca Structure.gui is shown.
1. Tosca Structure.gui starts and the Tosca Structure.pre module is displayed. Left click on the Tree button to change the view of the optimization task structure on the left side to tree mode.
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2.5.5.1 Starting Tosca Structure Preprocessor
SIMULIA Tosca Structure
2.5.5.2 Loading the input model file 1. Select the item FEM_INPUT from the optimization task tree. The FEM_INPUT menu appears on the right.
2. In the Input Files area, click Add to select the model for the optimization. The Open dialog appears.
3. In the Open dialog, choose the FE model for your solver (holder. where is the extension your FE-solver uses.) and press Open. The model name with its full path appears in the The finite element input files field.
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4. Left click on Create to add the item MY_INPUT_FILES to the optimization task tree.
2.5.5.3 Define the design area In sizing optimization, the design area denotes the set of elements that may be changed (whose thicknesses are modified) during the optimization. A subset can be defined as frozen areas which will remain unchanged.
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1. Select the item DV_SIZING from the optimization task tree. The DV_SIZING menu appears on the right.
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2. Choose the group DESIGN_ALL from the dropdown list next to EL_GROUP and click Create to add the item MY_DV_SIZING to the optimization task tree.
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2.5.5.4 Choice of thickness bounds (design variable constraint) Design variable constraints introduce restrictions on the shape of the optimized model. Besides the shell thickness constraint discussed below, other types of design constraints such as symmetry and minimum member size restrictions are supported by Tosca Structure. 1. Select the item DVCON_SIZING from the optimization task tree. The DVCON_SIZING menu appears on the right.
2. Select DESIGN_ALL from the dropdown list next to Element Group. The constraint will now be applied to all elements of the selected group.
3. For defining a thickness restriction for the selected element group activate the radio button Thickness Bounds and define a lower and upper bound of 0.1 and 3.0 respectively in the corresponding fields. Select Magnitude = ABS for absolute magnitude.
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Please note that the ID_NAME is a special mark of any component of the optimization task. The ID_NAME must be unique for each component. Using the ID_NAME you can select between different components of the same type during the optimization setup. If no other component of the same type appears in the optimization task, the change of the ID_NAME is optional and the Tosca Structure default ID_NAME can be used.
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2.5.5.5 Optional: Cluster groups It is always recommended to perform a first sizing optimization without too much additional constraints to use the maximum design flexibility for the optimization. Influenced by a first design proposal clustering may be introduced. With Clustering, certain areas of the model are grouped such that they get a common shell thickness during the optimization. Clustered areas may later be manufactured by sheets of constant thickness. An example is the optimization of an assembled sheet structure like a car body in white, where each sheet has one thickness. 1. Select the item DVCON_SIZING from the optimization task tree. The DVCON_SIZING menu appears on the right.
3. For horizontal clustering choose the groups DES_HOR1 till DES_HOR12, for vertical clustering choose the groups DES_VER1 till DES_VER6 and for circular clustering choose the groupsDES_RING1 till DES_RING3 as shown in Fig. 59
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2. Type a proper name in the field ID_NAME, for example DVCON_CLUSTER_GROUPS. Activate the radio button CLUSTER_GROUPS and Select all element groups for which elements the thicknesses shall remain the same.
SIMULIA Tosca Structure
2.5.5.6 Definition of design responses In order to specify optimization target and constraints you must first define design responses. The design responses are assigned to output parameters from the FE analysis. In this example design responses for the volume and the strain energy will be needed. 1. Select the item DRESP from the optimization task tree. The DRESP menu appears on the right.
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2. Type a proper name in the field ID_NAME, for example DRESP_VOLUME, and choose the type VOLUME in the field Type of the Base category.
3. Choose DESIGN_ALL from the Element/Elementgroup dropdown list and set the Group Operator to Sum to build the sum of the volumes of each element in the model. Thus the whole volume of the structure is determined. Click Create to add the design response DRESP_VOLUME to the optimization task tree. 4. Repeat step 1 to define another design response.
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5. Type a ID_NAME for the new design response, for example DRESP_STRAIN_ENERGY_1, in the corresponding field and choose Stress/Strain from the Category dropdown list and in the Type field choose the type STRAIN_ENERGY.
6. Activate the Element/Elementgroup radio button and select ALL_ELEMENTS from the Element/Elemtgroup dropdown list. 7. Set the Group Operator to Sum.
9. In the Select Loadcase dialog, choose Static as Analysis Type and enter 1 as Loadcase Number. Click OK: The new entry appears in the Loadcase Selection field.
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8. Click Add LC to selct the load case for the design response. The Select Loadcase dialog appears.
SIMULIA Tosca Structure
10. Click Create to add the design response DRESP_STRAIN_ENERGY_1 to the optimization task tree.
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11. Repeat steps 4-10 to define a second design response for the strain energy of load case 2.
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2.5.5.7 Choice of the objective function The objective function will be minimized or maximized by Tosca Structure, depending on the settings. 1. Select the item OBJ_FUNC from the optimization task tree. The OBJ_FUNC menu appears on the right.
2. Click Add Dresp to select a design response for the objective function. The Select Design Responses dialog appears.
4. Select the radio button MinMax next to Target and click Create to add the item MY_OBJ_FUNC to the optimization task tree.
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3. In the Select Design Responses dialog, activate the design responses DRESP_STRAIN_ENERGY_1 and DRESP_STRAIN_ENERGY_2 and press Ok. The window closes and the selected design responses appear in the field.
SIMULIA Tosca Structure
2.5.5.8 Choice of the constraints Constraints are equations or inequations that are maintained by Tosca Structure during the optimization. 1. Select the item CONSTRAINT from the optimization task tree. The CONSTRAINT menu appears on the right.
2. Type a proper name in the field ID_NAME, for example VOLUME_CONSTRAINT, and choose the design response DRESP_VOLUME from the Design Response dropdown list.
4. Select the less or equal radio button next to Constraint Type, thus the target volume for the optimization is restricted by 100 percent of the original volume, and click Create to add the item VOLUME_CONSTRAINT to the optimization task tree.
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3. Select the radio button Relative next to Type to set the constraint type and push the slider to 100 or type the value in the field manually.
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2.5.5.9 Definition of the optimization task 1. Select the item OPTIMIZE from the optimization task tree. The OPTIMIZE menu appears on the right.
2. Select SIZING_SENSITIVITY from the Strategy dropdown list to choose the optimization strategy. Design area and objective function are selected automatically.
4. In the Select Design Variable Constraints dialog, activate the design variable constraints DVCON_SIZING and DVCON_CLUSTER and press Ok. The corresponding items appear in the DV Constraints field. 5. Click Add next to the Constraints field to add the constraints to the optimization task. The Select Constraints dialog appears.
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3. Click Add next to the DV Constraints field to add the design variable constraints to the optimization task. The Select Design Variable Constraints dialog appears.
SIMULIA Tosca Structure
6. Activate VOLUME_CONSTRAINT and press Ok. The corresponding items appear in the Constraints field.
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7. Click Create to add the item MY_OPTIMIZATION_TASK to the optimization task tree.
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2.5.5.10 Saving Tosca Structure parameter file The Tosca Structure parameter file contains ASCII commands which define all settings for the optimization task. 1. Select File from the main menu and pick Save As from the File dropdown list. The Save As dialog appears.
2. In the Save As dialog choose a name for the optimization task, enter the filename in the field below and press Save As. The file automatically receives the extension .par and becomes the parameter file for Tosca Structure.
Start Optimization 1. Switch to the Start TOSCA Structure module from the Module dropdown list in the upper right corner. 2. Choose all from the Type dropdown list . This option includes a preprocessing test and the optimization run.
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2.5.6
SIMULIA Tosca Structure
3. Select the solver (Abaqus or ANSYS) of your choice from the Solver dropdown list.
4. Click Start TOSCA to start the optimization. Status information about the optimization run is displayed in the field below.
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5. After approx. 15 design cycles the optimization run is finished and the status TOSCA job finished is displayed.
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2.5.7
Postprocessing Viewing the intermediate results using Tosca Structure.report. Using Tosca Structure.report, the intermediate results of sizing optimization, namely the thicknesses of element shells, can be visualized. 1. Switch to the Tosca Structure.report module from the Module dropdown list in the upper right corner.
3. To see every design cycle click in the field below Iter (concerning the result ELEMENT_THICKNESS) and select All from the Iter dropdown menu (default). Repeat this for the result ELEMENT_DELTA_ THICKNESS (second field below Iter).
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2. Select the results by activating the buttons to the left of the Results ELEMENT_THICKNESS and ELEMENT_DELTA_ THICKNESS. A standard report is available in the directory | TOSCA_POST after each optimization which can be visualized using Tosca Structure.view.
SIMULIA Tosca Structure
4. Click Generate Report to start the generation of the result file. Status information about the file generation is displayed in the field below.
5. When the file generation is completed a message about the successful job ending is displayed in the status field.
6. Click View Report to view the material distribution in the optimized structure. The Open dialog appears.
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7. In the open dialog select the generated .vtfx file and press Open. Tosca Structure.view starts.
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8. The animation starts and stops by clicking on the start forward/backward, pause and stop symbol in the task menu. The described example is generated using the FE solver Abaqus. Please note that slight differencies in the optimized design are possible for the different solvers. However the design conception remains the same.
2.5.8
Report Generation
2. Under View | Viewports you can select up to four viewports in different positions. Choose two viewports: You see the element thickness distribution of your model on the left side of the split window. The right side is still empty.
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1. Click View Report to view the material distribution in the optimized structure. The Open dialog appears. Open your vtfx file.
SIMULIA Tosca Structure
3. Select Case 2 in the Table of Cases and drag it onto the right part of the window. Another possibility is to rightclick at case two and select Assign Case In View | View 1.
5. Click at the left model: Now, this model is activated and its frame becomes green. Choose the last iteration step by using the Step Backward button and move both views synchronously in an appropriate position (hold Ctrl and the appropriate mouse button while moving the mouse).
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4. To move both views synchronously select View | Synchronous Navigation.
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6. To generate a report activate the left window and click Capture active view in the quick access toolbar or select File | Capture Situation. 7. A new window opens: Enter an appropriate description, select Image as Situation type for capturing and press OK. A new window named GLview Report Builder opens. Keep this window open till the end of this chapter!
9. Switch back to Tosca Structure.view window. Repeat steps 6 and 7, but select 3D model as situation type for capturing.
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8. In GLView Report Builder window click File | Save Repository as to save the chosen situations to a file. If you close the Tosca Structure Report Builder window, you can continue by opening your saved repository.
SIMULIA Tosca Structure
10. In Tosca Structure Report Builder window both model siutations are now listed. By rightclicking at the situation you can delete it or change the order. 11. Switch back to Tosca Structure.view window. Now, select the right window and click Quick Capture active view in the quick access toolbar or select File | Quick Capture Situation. 12. The last setting is used for capturing, thus, the smoothed optimization result is loaded as 3D model into the Tosca Structure Report Builder. 13. Load the optimization result ELEMENT_DELTA_THICKNESS (right window in Tosca Structure.view) as image into the Tosca Structure Report Builder. (Look at step 6 and 7, if necessary, and do not forget to activate the window).
15. Repeat step 13 with the same plot as Table. 16. Repeat step 12,13 and 14 with the objective function (OBJ_FUNC in the Table of Cases).
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14. In Tosca Structure.view doubleclick at CONSTRAINT_NORM in the Table of Cases. This case cannot be displayed with another viewport. By selecting Capture Situation or Capture active view load the plot as Image into the Tosca Structure Report Builder.
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17. Now there should be 8 entrys in the Situations window. Doubleclick at one entry to deactivate this situation for the transfer. The same effect is given by rightclicking and selecting Deactivate.
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18. Transfer these situation into a powerpoint document by clicking File | Create PowerPointReport.
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19. For template selection click Browse and select TOSCA_Structure_PowerPoint_Template_GenericTags.pptx under \report\Templates. Select a file location and the media type. Click OK.
20. A PowerPoint file is created. The order of figures and tables is determined by the template.
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21. For tranferring into a word file use Create WordReport and the template TOSCA_Structure_Word_Template_GenericTags.docx, for a HTML file Create HTMLReport and the template TOSCA_Structure_HTML_Template_GenericTags.html. As the vtfx plug-in only works in combination with the internet explorer, you can choose Video and image as Media type for other browsers.
2.5.9
Result Discussion
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A free sizing optimization without additional restrictions leads (naturally) to the best results, in this case a reduction of the maximum displacement by 45%. An optimization with clustering (circular in this case), required by manufacturing, still leads to an improvement of 30%. In the figure below (Fig. 60) the displacement results are shown:
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Displacement magnitude: initial model, optimization result without clustering and with circular clustering (top to bottom)
Fig. 61 and Fig. 62 show the shell thickness in the design area for different cases: The differences in the results of the optimization without clustering and
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Fig. 60
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Fig. 61
Optimization results: Final shell thickness in the design area without clustering (left) and with horizontal clustering (right)
Fig. 62
Optimization results: Final shell thickness in the design area with vertical clustering (left) and with circular clustering (right)
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with the several kinds of clustering are obvious. Furthermore, the result of optimization with vertical clustering indicates the unsymmetric load.
SIMULIA Tosca Structure Getting Started with Tosca Extension for
3
Getting Started with Tosca Extension for ANSYS/WB Tosca Extension for ANSYS/Workbench allows the integration of Tosca Structure.topology and Tosca Structure.shape in ANSYS Workbench. Tosca Extension for ANSYS/Workbench is not supported for bead and sizing optimization yet. Tosca Structure.topology and Tosca Structure.shape is treated like every other system in the Project Schematic and sources its Geometry, Model and Load/Boundary Conditions input data via connection to other systems within the Project Schematic. The optimization and all its available options will be set up in the Mechanical Application. Once every wished option is selected the optimization run can be started. The resulting model of this iterative optimization run is visualized and can be used for further postprocessing such as a complete validation run.
3.1
User Interface
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The entire optimization from model creating to the last step of the optimization takes place in three main windows / applications. The main window, the ANSYS Workbench with its Project Schematic collects all parts of a project in a graphically clear manner. Every subsystem or template is listed and connections between the single systems are visible.
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Fig. 63
ANSYS Workbench overview. The Project Schematic shows the used systems / templates
Fig. 64
Design Modeler is Workbench’s default CAD application
Fig. 65
Mechanical is a FEA graphical user interface. It is included as an application in Workbench, too
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User Interface
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Fig. 66
3.1.1
Tree Outline (left) and Details View (right)
Buttons
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The relevant buttons for the use of the Tosca Extension for ANSYS/Workbench can be found in the upper toolbar of the Mechanical application. All optimization options, controls and conditions will be inserted with these buttons.
Under this point, buttons can be found to set a design area or define different manufacturing restrictions. Defines the part of the geometry that has to be optimized. Defines parts that have to be left out of the optimization.
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Inserts direction for pulling out the model of a casting mold. Is able to avoid material accumulation in certain areas or to set a minimum size / circumference for bars. Adds different kinds of symmetry for the topology optimization.
Under this point, buttons can be found to set a design area or define different manufacturing restrictions. These buttons are only applicable for TOSCA Structure.shape Defines the part of the geometry that has to be optimized. The area for mesh smoothing is also defined here in order to prevent a bad quality mesh. Different design variable constraints to limit or influence the nodal movement of the design nodes during the optimization can be defined.
Constraints and Objective Functions for the optimization can be chosen Defines the kind of system output.
Inserts values for a design response to converge to. Generates Tosca Input Files (parameterfile, FE-Input-Deck) and saves them to a user defined directory for external solve.
Here you can add result options. Shows the result of the topology optimization (relative densities).
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Minimizes or maximizes a certain design response.
SIMULIA Tosca Structure Getting Started with Tosca Extension for
Adds a smoothed surface model of the optimization result. Smooth Result is needed for the Valudation Run. Imports external solved results.
After an optimization run an optional validation run can be performed. Starts the validation run. Imports Contact Definitions into the Validation System.
3.1.2
Handling Tips • If there are for example optimization options inserted in the Tree Outline and you want them to be ignored during an optimization run, the Suppress / Unsuppress buttons work with Tosca Extension for ANSYS/Workbench as well as with any other system in ANSYS Workbench.
• Tosca Extension for ANSYS/Workbench creates certain files into different directories. In general it is possible and sometimes recommandable to look up TOSCA’s parameter-file or several report files to get an overview or to find mistakes that influence the optimization. To find these files efficiently, use the right click option on headlines in the Tree Outline and choose Open Solver Files Directory.
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• It is often mandatory to apply the concerned geometry for an optimization option like Frozen area for example. Make always sure that the correct selection button is activated as well as the Select Mode (Single / Box).
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• Using Tosca Extension for ANSYS/Workbench it is often required to apply a part of the geometry to an optimization option. Instead of selecting a certain geometry for different occasions over and over again by hand, it is also possible to create a Named Selection beforehand. This selection can be chosen later and applied as Geometry much easier. A second advantage of Named Selections is that in the .par-file a selection will be named after your selection’s labeling instead of a list of nodes or elements. The .par-file (or other files) becomes more comfortable to read. Therefore define a Named Selection for example in Design Modeler by clicking Tools | Named Selection. It will be listed in the Tree Outline. Rename it (F2 button) in order to find and use it later with ease.
The Named Selection is listed from now on in the Tree Outline of the Mechanical application. (A Named Selection can also be defined directly in Mechanical)
Use it later when for example defining a force. Instead of choosing the geometry by hand, you can now simply change the Scoping Method to Named Selection and find yours in the list. • When using multiple shared Analysis Systems for the Optimization, they can be used again for the Validation Run. Since they are copies of the ini-
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The concerned geometry has to be defined.
SIMULIA Tosca Structure Getting Started with Tosca Extension for
tial systems, they can’t be shared anymore. You have to reassign faces for the boundary conditions for each system again. Alternatively it’s possible to use multiple steps in one analysis instead of multiple systems.
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• Tosca Extension for ANSYS/WB needs to know the path of the Tosca Installation (Tosca Bin Dir). If you use the Extension for the first time, you have to specify the path in Mechanical in Analysis Settings | Tosca Bin folder (ends with "...\bin"). When clicking Solve to start the first Optimization, the entered path will be saved and used again in your future projects. If you want to change the path again, declare a new one in the analysis settings. Clicking Solve will save it again as default path.
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• It is possible to edit the parameterfile manually before starting the Optimization. Go to the Analysis Settings and set Edit PAR before calling Tosca to Yes. Set up your Optimization and click on Solve. The parameter-file and FE-InputFile will be generated and then the solve process will be paused. The par-file will be selected in a new Explorer Window and can be edited.
• If you just want to set up the optimization and run it on another machine or cluster, it is possible to generate the needed input files (parameter-file and FE input deck) using Tosca Extension for ANSYS/WB. Set up the whole optimization (FE-Mesh, Boundary Conditions, Design Area, Design Responses, Objective Function, Constraint, etc.) within the extension, select Tosca in the Tree Outline and then click on Optimization | Write out PAR-File. Choose or create the desired export folder in the pop up window and click OK.
• In addition to watch the Optimization Status in the Command Shell, the more detailed solver output (TOSCA.OUT) can be displayed in Workbench after or during the optimization. Therefore, select Tosca’s Solution 1 - 342 Start Manual
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After saving your changes, go back to Mechanical. There is a message which informs about the paused process. Click OK to continue the Optimization with the edited par-file.
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Information in the Tree Outline. The Tosca Loglevel can be changed in the Analysis Settings before starting the optimization.
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• The captions of all Tosca "loads" (Design Area, Design Response etc.) in the Tree Outline of Mechanical will be reused in the Tosca parameter-file. Rename these objects (F2-button) to avoid missunderstandings in Workbench and to facilitate the readability of the parameter-file.
Attention: Do not name your items manually with a blank followed by a number
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("DRESP 3 Volume"). Workbench will slice the caption internally ("DRESP"). Use underlines or omit the blank ("DRESP_3_Volume" or "DRESP3Volume") to avoid this behavior. • It’s possible to display a Demold and Symmetry Plane. Go to the Demold or Symmetry Control in the Tree Outline and choose a Coordinate System and Demold Direction/Symmetry Axis. The Show Plane option is used to show (Yes) or hide (No) the plane. The diameter of the displayed disc depends on the size of the Bounding Box of your assembly.
The second option Center | Origin of Coordinate System uses the origin of the selected CS.
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For the center of the displayed disc there are two possible settings. Center | Projected Center of Assembly is the default setting. The center of the disc depends on the center of the assembly (unsupressed parts).
SIMULIA Tosca Structure Getting Started with Tosca Extension for
• To have a better understanding of your optimization setup, the Frozen Area Elements, which will be excluded from the optimization, can be displayed in Workbench. Select the Frozen Area in the Tree Outline. In Detail’s View, set Show Frozen Elements to Yes. The display will be updated automatically if you change this setting or the geometry selection. Remark: This view is not recommended, if Frozen Area is a Body. The selected faces are colored blue, the elements are green. With the default viewing option, you can’t see the elements, since they are inside the part.
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Select Wireframe in the upper ANSYS toolbar, to hide the faces of the part and show the Frozen Elements.
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Additionally to the Wireframe view, the Show Mesh option in the upper toolbar might be useful.
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• If you run an optimization, change some settings and want to start a second optimization, there might occur an error. Before starting the new optimization, it’s recommended to delete the existing files (Tree Outline | Solution | Clear Generated Data) and close and reopen the Mechanical application.
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3.2
Topology Optimization with Tosca Extension for ANSYS/WB This little instruction should help to get in touch with the Tosca Extension for ANSYS/Workbench. Some guided clicks should provide a first overview, setting up an optimization example.
3.2.1
The model
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A car’s control arm is used as an example. A control arm is a part of a car’s independent wheel suspension and supports against occuring cross forces. That means on the one hand that it is a mass-produced component, so any material and cost reduction pays off. On the other hand every weight reduction in cars is welcome in general because dynamic characteristics increase and less mass has to be accelerated and slowed.
Fig. 67
3.2.2
This model shows an example of a topology optimization with Tosca Extension for ANSYS/Workbench
Loading the Extension In order to load the extension, open the Extension Manager by clicking Extensions | Manage Extensions.
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Check the box for the current Tosca Extension for ANSYS/Workbench (8.1.0). The extension is loaded immediately; close the Extensions Manager and wait for the Busy icon in the down left corner of the screen to disappear.
Fig. 68
Use the Extension Manager to load Tosca Extension for ANSYS/Workbench
3.2.3
Example files Dependent on where you want to start the procedure, you can choose one of the following files. You find all necessary files in the directory \ansys\TS_Ext_for_WB\examples\topo\. 1. Start from scratch using the provided control_arm.stp geometry file. Continue at chapter 3.2.4 Preparing the model. 2. Start the project with an imported geometry file. Use the ANSYS Workbench project archive control_arm.wbpz. Continue at chapter 3.2.4 Preparing the model, step 15. 3. Start the project with an imported geometry file and defined boundary conditions. Use the ANSYS Workbench project archive control_arm_bc.wbpz. Continue at chapter 3.2.5 Optimization preprocessing.
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If you save a project and the extension is used, it is loaded automatically the next time the project will be opened.
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3.2.4
Preparing the model At first, the task has to be set up. Then the model is loaded into ANSYS Workbench and loads and boundary conditions are added, using the different applications in ANSYS Workbench. Make sure the extension is loaded (See chapter Loading the Extension). 1. Add a Static Structural system to the Project Schematic by dragging the corresponding template onto the Project Schematic surface. 2. Right click on the Geometry cell in order to import the provided model "control_arm.stp".
4. The imported geometry is listed in the Tree Outline. The yellow lightning symbolizes that the import is not finished yet. Click on Generate to execute the import of the control arm model.
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3. Double-click Geometry in order to open the application Design Modeler. Select mm as unit and confirm.
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5. In order to create an isolated part of the geometry that can be used as Design Area to be optimized later, slice the geometry. Activate the XYPlane in the Tree Outline and click New Sketch.
6. The button Look at Face/ Plane/Sketch will turn the activated plane if necessary. 7. Click the tab Sketching to open the sketching toolbar. Add geometry to mark the areas of the model that are not to be changed during the optimization. Be careful with overlapping geometry which causes an error. Trim (Modify | Trim) if necessary.
9. Click Extrude.
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8. Make sure that the marked areas are defined correctly.
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10. If Extrude is clicked immediately after having sketched, the correct sketch will be highlighted as Geometry. If not, choose the correct sketch. Click Apply. 11. Choose Slice Material as Operation.
12. Click Generate. Different body colors mark the different parts; the transparency indicates the parts as Frozen. Unfrozen geometries in contact would be combined to a single body automatically.
14. It is recommended in general to save the project from time to time. Therefore use the button Save or Save as in the upper toolbar of ANSYS Workbench. 15. Double-click the Model cell in order to open the Mechanical application.
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13. Close DesignModeler.
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16. Check if units are defined correctly (Metric - mm, kg, N).
18. Assign the entire geometry (5 Bodies). Enter 5 (mm) as Element Size. A click on Update creates a tetrahedral (automatic) mesh.
19. It is possible to display the generated mesh of the model. Either use the Show Mesh button in the upper toolbar or click on the Mesh folder in the Tree Outline.
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17. Activate Mesh in the Tree Outline by clicking on it once. That makes appear the concerned buttons in the upper toolbar. Mesh control | Sizing adds a mesh sizing operation.
SIMULIA Tosca Structure
20. Activate Model in the Tree Outline. Click on the Symmetry button. 21. Right click the inserted Symmetry unit in the Tree Outline, choose Insert | Symmetry Region.
22. Apply the control arm’s mid plane as Geometry by holding CTRL while selecting the different faces (make sure Face Selection is activated, see chapter "Handling Tips").
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23. Select Z Axis as Symmetry Normal.
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24. Activate the Static Structural in the Tree Outline. 25. Add a load to the Tree Outline with the button Loads | Force. Make sure the selection option Face ist activated.
27. In the definition, change Define By from Vector to Components and enter 7071 N as X Component and -7071 N as Y Component magnitude.
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26. As Geometry choose the inner face of the lower drill-hole; click Apply.
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28. Add an Elastic Support by clicking Supports | Elastic Support on the outer face of the upper anchor.
29. Select the outer face with the face selection tool.
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30. Enter 10 N/mm³ as Foundation Stiffness.
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31. Select the upper bearing’s inner face.
32. Add a Remote Displacement.
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33. In the corresponding Details View, set the X Coordinate to 25.65 mm, and the Y and Z Coordinate to 0 mm. Within the DefinitionGroup, change all Components from Free to 0, except for the Rotation X.
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34. Activate Solution in the Tree Outline. Click on Stress | Equivalent (von-Mises) to add a stress analysis as result output. Make sure all five bodies are selected for the analysis. A stress analysis is set up. Click Solve to execute the analysis. 35. Save the project.
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3.2.5
Optimization preprocessing Now that the calculation put out all the requested solutions, an optimization task can be set up. It is not mandatory to solve any stresses or strains before the optimization. Loads and boundary conditions are enough. It is recommended though, since it can be checked whether the analysis is correctly set up or not. 36. Close the Mechanical application and continue working in the Project Schematic. Now use a TOSCA Structure.topology system.
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37. Drag a TOSCA Structure.topology template onto the Model cell of the existing Static Structural in the Project Schematic. This way both systems are connected on the level of the Model and the TOSCA Structure.topology draws on the generated data of the Static Structural system. Important: If you connect the systems otherwise, the TOSCA Structure.topology is not able to perform correctly. Mechanical needs to be closed when you connect the systems.
39. For the TOSCA Structure.topology | Analysis settings in the Tree Outline, choose Controller as Strategy in the Details View. Auto Frozen is not needed, set it to Off. If you use Tosca Extension for ANSYS/WB for the first time, you have to define the TOSCA bin folder ("...\Tosca80\bin"). Otherwise the solver does not start. After you set a path, and solved the first project, your future projects will use this path by default.
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38. Double-click the Setup cell on the TOSCA Structure.topology in order to open the Mechanical application.
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40. Add the options for the optimization run. The area to be optimized is defined with a Topology | Design Area.
41. Insert the Design Area in the TOSCA Structure.topology in the Tree Outline. 42. Apply the main area as Geometry (1 Body).
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43. Add a Demold Control.
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44. Select the Global Coordinate System as Coordinate System and Z as direction. Therefore make sure the resulting vector equals (0, 0, 1). Remark: Use the Show all Coordinate Systems button (upper ANSYS toolbar) to facilitate the definition of the Demold Direction. The displayed disc shows the Demold Direction.
46. Add the first of two Design Responses via Optimization | Design Response.
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45. Select the main part of the geometry as Geometry and CheckGroup.
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47. In the corresponding Details View select Volume as Response Type and choose the same geometry as in Design Area as Geometry (1 Body). 48. Rename the Design Response to "Dresp_Vol"; click on it once in the Tree Outline and then use the F2 button. 49. Add the second of the two Design Responses. 50. Select Stress/Strain as Category. Again, select the main area as Geometry and choose All as Load Case. Rename the design response to "Dresp_Stren".
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51. Add an Objective Function by clicking Optimization | Objective Function. 52. Choose Minimize sum as Target.
53. Click on Tabular Data in the Details View window, create a new table; select Dresp_Stren as Design Response. Click Apply.
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54. Add a Constraint to the optimization task by clicking on Optimization | Constraint. 55. Select Dresp_Vol as Design Response and 0.7 as Value.
56. Click the toolbar button Results and add an Optimization Result and a Smooth Result.
For more information about the smooth options, see the Tosca Structure Documentation.
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57. For the Smooth Result, choose 0,1 as Iso Value.
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58. Click Solve to start the optimization. Save the project.
3.2.6
Postprocessing The Tosca Extension for ANSYS/Workbench offers in the Mechanical application some visualization options. The optimization result can be displayed in different ways, single iterations can be showed, too.
3.2.6.1 Optimization result view options To display a topology optimization result correctly in the Mechanical application, make sure that the correct Geometry option in the upper toolbar is activated. leads to
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Geometry view option
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With the option Capped IsoSurfaces it depends on the elements’ relative density whether they are displayed or not. This limit density (elements above or below are displayed) is adjustable.
With IsoSurfaces activated, no result will be displayed.
The Graph window in the Mechanical application provides an overview of the optimization steps. It’s either possible to have a look at each single iteration or to show even a little animation from the beginning until the end of the optimization run. To display a single iteration step, select it with the left mouse button, then right click | Retrieve this result. For a little animation it is possible to use a Play and Stop button or regulate animation speed. All the needed buttons can be found in the Graph window.
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3.2.6.2 Iteration Animation
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3.2.7
Validation Run As continuation after an optimization and smoothing run, a validation run can be performed. The smoothed model describes the surface of the optimization result. Based on this resulting model, a solid three dimensional model is reconstructed which can be loaded with the original forces and supported with the original boundary conditions. The validation run can only be executed after a smoothing run.
The Project Schematic after the Validation looks like shown on the left.
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59. Click Validation | Run to start the Validation. The procedure might take a few minutes and is finished as soon as the new Validation System is opened automatically.
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61. Begin with the Symmetry Condition. Reselect the mid plane faces and apply it as Geometry of the Symmetry Region.
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60. Forces, boundary conditions and other options, too, have to be reassigned.
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62. As Geometry of the Force, reassign the inner face of the lower drill-hole.
63. Select the Elastic Support in the Tree Outline and choose the corresponding face(s) as Geometry. Remark: It’s possible, that the initial face is split into several small pieces. Select all of them to recreate this boundary condition.
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64. Reassign the face of the Remote Displacement.
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3.2.8
Troubleshooting Wrong connection in Project Schematic Make sure the Tosca Optimizer has all the input it needs: Engineering Data, Geometry, Model. Loads cannot be specified in a standalone TOSCA Structure.topology system. Optimization strategy The controller based algorithm is developed to solve a volume contraint / stiffness maximization. For problems involving Displacement or Membersize Control for example, a sensivity based algorithm is needed. At the same time, controller based algorithm solutions work with equality constraints while the sensivity based algorithm handles unequality constraints like greater or less than a certain value.
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65. When all options are reassigned to the model, click Solve.
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To receive appropriate solutions, approximately 15 design cycles / iterations are needed for the controller strategy and 35-45 cycles for sensitivity strategy (see, e.g., vol.2 chapter 5.2.1, Controller versus sensitivity based topology optimization). Otherwise the solver will not converge.
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Topology Optimization with Tosca Extension for ANSYS/WB
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3.3
Shape Optimization with Tosca Extension for ANSYS/WB This little instruction should help to get in touch with the shape optimization module in the Tosca Extension for ANSYS/Workbench. Some guided clicks should provide a first overview, setting up an optimization example.
3.3.1
The model
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A connecting rod (conrod) is used as an example. A conrod is a part of a car's reciprocating piston engine and is used to turn the reciprocating motion of the piston into rotating motion. This means that high stress levels in the component generally lead to a premature failure of the component since it is used in many different load cycles. If the stress peaks in the conrod can be reduced, this also means that the life of the component prior to failure can be extended.
Fig. 69
This model shows an example of a shape optimization with Tosca Extension for ANSYS/Workbench
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In the FE-Model of the conrod loaded nodes are connected with MPCs to the inner side of the conrod mounts. Nodes on the inner radius of the big eye (crankshaft bearing) are fixed in all three coordinate directions. There are five loadcases realized in the model (see Fig. 2): Loadcase 1: Centrifugal force (a in Fig. 2), 15000 N applied in z-direction Screw fixation Loadcase 2: Gas pressure (b in Fig. 2), 25000 N applied in negative z-direction Fixation in nodes of big eye Loadcase 3: Bending about the x-axis, 1000 N applied in negative x-direction Fixation in nodes of big eye Loadcase 4: Bending moment about the y-axis (-10000Nmm) Fixation in nodes of big eye Loadcase 5:
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Torsion about the z-axis (10000Nmm) Fixation in nodes of big eye
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Loads and boundary conditions of the conrod model: left: (A) centrifugal force, (B) and (C) screw fixation right: force caused by gas pressure (A), bending and torsion about x-, y- and z-axis (C), (D) and (E). Fixation in nodes of big eye (B).
For simplicity reasons only loadcase 2 will be described in depth in this manual as this is the most dominant loadcase causing the highest stresses. An optional ANSYS Workbench project archive exists in which all five loadcases are predefined.
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Fig. 70
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3.3.2
Loading the extension In order to load the extension, open the Extension Manager by clicking Extensions | Manage Extensions. Check the box for the current Tosca Extension for ANSYS/Workbench (8.1.0). The extension is loaded immediately; close the Extensions Manager and wait for the Busy icon in the down left corner of the screen to disappear.
Use the Extension Manager to load Tosca Extension for ANSYS/Workbench
If you save a project and the extension is used, it is loaded automatically the next time the project will be opened.
3.3.3
Example files Dependent on where you want to start the procedure, you can choose one of the following files. You find all necessary files in the directory \ansys\TS_Ext_for_WB\examples\shape\. 1. Start from scratch using the provided control_arm.stp geometry file. Continue at chapter 3.3.4 Preparing the model.
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2. Start the project with an imported geometry file. Use the ANSYS Workbench project archive control_arm.wbpz. Continue at chapter 3.3.4 Preparing the model, step 15. 3. Start the project with an imported geometry file and defined boundary conditions. Use the ANSYS Workbench project archive control_arm_bc.wbpz. Continue at chapter 3.3.5 Optimization preprocessing.
3.3.4
Preparing the model At first, the task has to be set up. Then the model is loaded into ANSYS Workbench and loads and boundary conditions are added, using the different applications in ANSYS Workbench. Make sure the extension is loaded (See chapter Loading the Extension). 1. Add a Static Structural system to the Project Schematic by dragging the corresponding template onto the Project Schematic surface.
3. Double-click Geometry in order to open the application Design Modeler. Select mm as unit and confirm.
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2. Right click on the Geometry cell in order to import the provided model "conrod.stp".
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4. The imported geometry is listed in the Tree Outline. The yellow lightning symbolizes that the import is not finished yet. Click on Generate to execute the import of the conrod model.
5. In order to create an isolated part of the geometry that can be used as Design Area to be optimized later, slice the geometry. Activate the XYPlane in the Tree Outline and click New Sketch.
7. Click the tab Sketching to open the sketching toolbar. Add geometry to mark the areas of the model that are not to be changed during the optimization. Be careful with overlapping geometry which causes an error. Trim (Modify | Trim) if necessary.
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6. The button Look at Face/ Plane/Sketch will turn the activated plane if necessary.
SIMULIA Tosca Structure
8. Make sure that the marked areas are defined correctly. The area should encompass the lower half of the small eye to the area above the big eye where the conrod starts to widen up.
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9. Click Extrude. 10. If Extrude is clicked immediately after having sketched, the correct sketch will be highlighted as Geometry. If not, choose the correct sketch. Click Apply. 11. Choose Slice Material as Operation.
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13. Select all three bodies in the Tree Outline and click on Form New Part from the context menu. This causes the conrod to be treated as a single part in Mechanical later, but the single bodies are still selectable. This is especially desirable since the mesh will be continuous. 14. Close DesignModeler.
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12. Click Generate. Different body colors mark the different parts; the transparency indicates the parts as Frozen. Unfrozen geometries in contact would be combined to a single body automatically.
SIMULIA Tosca Structure
15. It is recommended in general to save the project from time to time. Therefore use the button Save or Save as in the upper toolbar of ANSYS Workbench. 16. Double-click the Model cell in order to open the Mechanical application.
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17. Check if units are defined correctly (Metric - mm, kg, N).
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18. Activate Mesh in the Tree Outline by clicking on it once. That makes appear the concerned buttons in the upper toolbar. Mesh control | Sizing adds a mesh sizing operation.
20. The upper half of the small eye will most likely not be meshed with tetrahedral elements like the other two bodies. In order to achieve a homogenous mesh, the upper half of the small eye needs to be meshed with tetrahedrals manually. Mesh control | Method adds an Automatic method. Assign the entire geometry (3 Bodies). Change the Method to Tetrahedrons. 21. A click on Update creates an automatically generated tetrahedral mesh.
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19. Assign the entire geometry (3 Bodies). Enter 2 (mm) as Element Size. A click on Update creates a tetrahedral (automatic) mesh.
SIMULIA Tosca Structure
22. It is possible to display the generated mesh of the model. Either use the Show Mesh button in the upper toolbar or click on the Mesh folder in the Tree Outline. 23. Activate the Static Structural in the Tree Outline.
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24. Add a load to the Tree Outline with the button Loads | Remote Force. Make sure the selection option Face ist activated.
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25. As Geometry choose the inner faces of the conrod mount (the small eye) by holding CTRL while selecting the different faces (make sure Face Selection is activated, see chapter 3.1.2 Handling Tips); click Apply.
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26. In the definition, change Define By from Vector to Components and enter -25000 N as Z Component magnitude.
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27. Add a Displacement by clicking Supports | Displacement on the inner face of the big eye.
28. Select the inner face of the big eye with the face selection tool. Click Apply.
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29. Within the Definition Group, change all Components from Free to 0.
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30. Activate Solution in the Tree Outline. Click on Stress | Equivalent (von-Mises) to add a stress analysis as result output. Make sure all five bodies are selected for the analysis. A stress analysis is set up. Click Solve to execute the analysis.
3.3.5
Optimization preprocessing Now that the calculation put out all the requested solutions, an optimization task can be set up. It is not mandatory to solve any stresses before the optimization. Loads and boundary conditions are enough. It is recommended though, since it can be checked whether the analysis is correctly set up or not.
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31. Save the project.
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32. Close the Mechanical application and continue working in the Project Schematic. Now use a TOSCA Structure.shape system.
34. Double-click the Setup cell on the TOSCA Structure.shape in order to open the Mechanical application.
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33. Drag a TOSCA Structure.shape template onto the Model cell of the existing Static Structural in the Project Schematic. This way both systems are connected on the level of the Model and the TOSCA Structure.shape draws on the generated data of the Static Structural system. Important: If you connect the systems otherwise, the TOSCA Structure.shape is not able to perform correctly. Mechanical needs to be closed when you connect the systems.
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35. In the TOSCA Structure.shape | Analysis settings in the Tree Outline the default settings do not have to be changed. If you use Tosca Extension for ANSYS/WB for the first time, you have to define the TOSCA bin folder ("...\Tosca81\bin"). Otherwise the solver does not start. After you set a path, and solved the first project, your future projects will use this path by default. 36. Add the options for the optimization run. The area to be optimized is defined with a Shape | Shape Design Area.
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37. Select the Design Area in TOSCA Structure.shape in the Tree Outline.
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38. Apply the the surfaces of the main area as Design Variables. The design area (design variables) always has to be a subset of the mesh smooth area. Thus only surfaces on the main body are allowed to be selected. Make sure that the interior of the small eye are not selected (indicated by the eclipse). Click Apply.
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39. Click in the Geometry field of the Mesh Smooth area. This will define the body which will be considered during the optimization.
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40. Select the center body as the Geometry of the Mesh Smooth area Make sure that Body/Element Selection is activated. Click Apply.
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41. In order to make sure that the functional area of the small eye isn’t moved during the mesh smooth it has to be fixed. Add a Shape | DV Constraints Shape.
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42. In the corresponding Details View select the lower half of the small eye and the adjacent outer surface as Geometry. Make sure that the outer surfaces on both sides are selected.
44. Add the Design Response via Optimization | Design Response.
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43. Select CHECK_DOF as Constraint Type and choose the Global Coordinate as System Coordinate System. Change Check_dof1, Check_dof2 and Check_dof3 to Fix. This will fix the nodal movement in all directions during the mesh smooth.
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45. Select Stress/Strain as Category and SIG_Mises as Response Type. Choose the same geometry as in Design Area as Geometry and select All as Load Case. Rename the Design Response to "Dresp_Stress"; click on it once in the Tree Outline and then use the F2 button. 46. Add an Objective Function by clicking Optimization | Objective Function. 47. Choose Minimize sum as Target.
49. Click the toolbar button Results and add a Controller Input.
50. Click Solve to start the optimization. Save the project.
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48. Click on Tabular Data in the Details View window, create a new table; select Dresp_Stress as Design Response. Click Apply.
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3.3.6
Postprocessing The Tosca Extension for ANSYS/Workbench offers some visualization options in the Mechanical application. The optimization result can be displayed in different ways, single iterations can also be shown.
3.3.6.1 Optimization result view options
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To display the stress results of a shape optimization in the Mechanical application, the created Controller Input has to be selected. This will display the resulting stresses and optimized shape of the component. Alternatively it is also possible to display the nodal displacement for each iteration in order to determine to what extent each node is moved during the optimization. Right click on Solution in the Tree Outline and then Insert | Deformation | Total. Please note that this does NOT refer to the total deformation of the component subject to the different loadcases of the static structural analysis..
Besides the total nodal displacement, the directional nodal displacement can be visualized as well. Right click on Solution in the Tree Outline and then Insert | Deformation | Directional if you wish to visualize the directional results.
3.3.6.2 Iteration Animation The Graph window in the Mechanical application provides an overview of the optimization steps. It is either possible to have a look at each single iteration or to show an animation of the course of the optimization run. This can be done for Controller Input (stresses) as well for the nodal displacements. To display a single iteration step, select it with the left mouse button, then right click | Retrieve this result. For an animation it is possible to
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use a Play and Stop button or regulate animation speed. All required buttons can be found in the Graph window. .
3.3.7
Troubleshooting Wrong connection in Project Schematic
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Make sure the Tosca Optimizer has all the input it needs: Engineering Data, Geometry, Model. Loads cannot be specified in a standalone TOSCA Structure.shape system.
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Volume II
User Manual
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SIMULIA Tosca Structure
SIMULIA Tosca Structure Preface
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Preface The User Manual is the standard reference describing the available functionalities of all Tosca Structure modules. chapter 1 Overview of Tosca Structure gives a brief overview of Tosca Structure. This includes a short description of each module (chapter 1.1 The Tosca Structure Modules), the chronological sequence of the optimization process with Tosca Structure (chapter 1.2 Overview of the Optimization Process) and a diagram (chapter 1.3 Workflow for Optimization) showing the step-by-step process of the optimization with useful links to the documentation. The chapter 2 Working with Tosca Structure shows how each module can be started with or without a graphical user interface. The contents of these two sections together with the manual vol.1 Start Manual give a sufficient description to understand the process for a “standard” topology, shape and bead optimization. A more detailed description of the optimization process with the relevant data flow can be found in chapter 12 Tosca Structure Control. The chapter 3 The Model explains requirements for the optimization model. It shows how the link between finite element model and optimization task is established and how further model specifications like group or coordinate system definition can be made. chapter 4 Terms for Optimization explains terms required for the optimization (objective and constraint) and their definition using the several front ends. It further lists design responses (e.g. analysis results) allowed for the definition of optimization targets and constraints. A more detailed description of the functionalities available for topology optimization (chapter 5 Topology Optimization), shape optimization (chapter 6 Shape Optimization), bead optimization (chapter 7 Bead Optimization) and sizing optimization (chapter 8 Sizing Optimization) discusses e.g. manufacturing constraints and typical optimizations tasks. Each command is described only in the context of its functionality with other commands. A more detailed description of the command syntax can be found in volume 3: Commands Manual. The next chapter (chapter 9 Result Transfer and Validation Run) describes how optimization results can be transferred to CAD for further processing of the optimization results and how a validation run can be set up. The possibilities available for analyzing the optimization results are shown in chapter 10 Postprocessing of Optimization Results. The different solver-specific functionalities are described in chapter 11 Solver Specific Features including shape optimization taking into account the lifetime of a component. chapter 12 Tosca Structure Control shows the program flow of Tosca Structure in detail as well as configuration of the program and file structure of optimization results. The chapter 13 Troubleshooting describes troubleshooting in case of unwanted or premature termination of the program.
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The Appendix chapter 14 Appendix summarizes the possibilities that are provided by Tosca Structure modules for specific functionalitites. It further lists the program limits and predefined macros.
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SIMULIA Tosca Structure Overview of Tosca Structure
1
Overview of Tosca Structure Tosca Structure is a modular system for non-parametric structural optimization. Topology, shape, bead and sizing optimization of FE models can be performed with Tosca Structure for design of lightweight, rigid and durable components and systems. A parameterization of the model is not needed. Topology optimization determines an optimum design proposal starting with a given maximum design domain. In Shape optimization, the components surface is modified to reduce local stress or damage peaks. Bead optimization is used to determine the optimum location and orientation of bead stiffeners for sheet metal components. With Tosca Structure.bead, the static stiffness and the vibration behavior can be improved. Sizing optimization derives optimal thicknesses for a shell structure to, e.g., increase stiffness or reduce vibrations. Structural optimization with Tosca Structure is an iterative process. The structural response of the component is calculated in each design cycle with an external FE solver. The user can work with his favorite solver in his favorite pre- and postprocessing environment and does not need additional training in a new CAE environment. Working with Tosca ANSA environment this link is even closer and allows the complete setup, start and validation of an optimization task with one front end. A closed development process can be achieved by the interaction of the components of Tosca Structure from the first concept to the optimized geometry in the CAD system.
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1.1
The Tosca Structure Modules The optimization system Tosca Structure consists of several modules supporting the user with his optimization process. Different front ends are available to set up the process: the Tosca ANSA environment and Tosca Structure.gui. Further, topology optimization tasks can be processed entirely within ANSYS Wokbench. All front ends interact with several Tosca Structure modules for definition of the optimization task, running the optimization process, result transfer, visualization and postprocessing. However, it is not necessary to work with a graphical user interface for carrying out an optimization. Working in the command shell is described in more detail in chapter 2.4 Working with Tosca Structure in the Command Shell.
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1.1.1
Abaqus CAE Abaqus CAE allows users to setup and perform topology, shape or sizing optimization tasks with Tosca Structure fully integrated into Abaqus CAE. Optimization results can be visualized in the visualization module of CAE. For details about the Tosca integration in Abaqus/CAE, Tosca for Abaqus, see the Abaqus manuals provided with your Abaqus installation. All other graphical user interfaces are treated within this documentation.
1.1.2
Tosca ANSA environment Tosca ANSA environment is a powerful front end. The graphical user interface supports the complete workflow for optimization setup, optimization, result transfer and validation run. A task manager guides the user through the process. For details about the Tosca ANSA environment see vol.1 chapter 1, Getting Started with Tosca ANSA environment and vol.2 chapter 2.1, Working with Tosca ANSA environment.
1.1.3
Tosca Structure.gui
1.1.4
Tosca Extension for ANSYS/WB Tosca Extension for ANSYS/WB allows ANSYS/Workbench users to setup and perform topology and shape optimization tasks with Tosca Structure fully integrated into ANSYS/WB. Optimization results can be visualized in the Mechanical applications within Workbench. Validation runs are also included. For details about the Tosca Extension for ANSYS/WB see vol.1 chapter 3, Getting Started with Tosca Extension for ANSYS/WB, vol.1 chapter 3.2, Topology Optimization with Tosca Extension for ANSYS/WB and vol.1 chapter 3.3, Shape Optimization with Tosca Extension for ANSYS/WB.
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Tosca Structure.gui is the graphical user interface where other modules of the optimization system can be started. Tosca Structure.gui includes the module Tosca Structure.pre for interactive input of optimization parameters. For details about Tosca Structure.gui see vol.1 chapter 2, Getting Started with Tosca Structure.gui and vol.2 chapter 2.2, Working with the Graphical User Interface Tosca Structure.gui. Tosca Structure.gui can be used as alternative to Tosca ANSA environment.
SIMULIA Tosca Structure Overview of Tosca Structure
1.1.5
Tosca Structure optimization modules The modules Tosca Structure.topology, Tosca Structure.shape, Tosca Structure.bead and Tosca Structure.sizing form the actual optimization kernel of Tosca Structure. Tosca Structure controls the start of data preprocessing, the optimization and the FE solver run (see vol.2 chapter 12, Tosca Structure Control). For specific functionalities, further modules are available (see vol.2 chapter 14.1, Additional Tosca Structure optimization modules).
1.1.6
Tosca Structure.report Tosca Structure.report automatically generates vtfx reports for quick navigation through the results of the optimization. It contains important graphical information of the model and optimization results as well as tables of the process of significant values to be stored in an archive.
1.1.7
Tosca Structure.view Tosca Structure.view is an efficient viewer for fast visualization of optimization results and reports generated by Tosca Structure.report. For presentation purposes a plug-in for Microsoft PowerPoint is available (see vol.2 chapter 10.2, Tosca Structure.view). Further, an integrated report generator transfers Tosca Structure optimization results to MS Office and html documents.
Tosca Structure.smooth Tosca Structure.smooth prepares the optimization results for import into a CAD system or FE-preprocessor or a remeshing for a validation run (see vol.2 chapter 9.1, Tosca Structure.smooth). This validation run is performed automatically using Tosca ANSA environment.
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1.1.8
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1.2
Overview of the Optimization Process Each optimization requires several steps independent of the optimization type (see Fig. 1).
OPTIMIZATION STEPS
PLANNING
PREPROCESSING
CHECK RUN
OPTIMIZATION LOOP
POSTPROCESSING
VALIDATION RUN Fig. 1
Planning The optimization and simulation tasks should be carefully thought out and formulated before beginning the optimization. All requirements like the optimization target, the necessary restrictions and the acceptable volume of the whole project should be considered.
1.2.2
Preprocessing: Model generation All requirements from the planning step have to be considered for the generation of the simulation model. In order to avoid unnecessary tasks, it is important that the relevant information for the analysis and optimization is carefully considered before starting. Model generation covers the following:
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1.2.1
Steps in the optimization
SIMULIA Tosca Structure Overview of Tosca Structure
• Creating the analysis model (if not yet created) in the FE preprocessor. It contains all data that is important for the FE analysis. Normally no special specifications for the optimization are required in the FE model. However, some definitions (e.g. definition of groups) in the FE model may help to simplify the optimization process. Using Tosca ANSA environment groups can be defined graphically when the optimization task is set up (see e.g. vol.1 chapter 1.1.13, Managing Groups). The functionalities available for the applied solver and the relevant preprocessor are depicted in vol.2 chapter 10, Postprocessing of Optimization Results. The model properties are described in more detail in vol.2 chapter 3, The Model. • Combination of the optimization model The optimization model consists of the analysis data (compiled in one or more analysis models) and the settings for the optimization task. The definition of the optimization task in Tosca Structure can be performed using Tosca ANSA environment or Tosca Structure.gui. All specifications for the optimization task are stored in a parameter file. The specifications and data necessary for an optimization can be found in chapter 5 Topology Optimization (topology optimization), chapter 6 Shape Optimization (shape optimization), chapter 7 Bead Optimization (bead optimization) and chapter 8 Sizing Optimization (sizing optimization).
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1.2.3
Check Run The check run should be performed before starting the optimization to avoid wrong or missing definitions for the optimization task. Using Tosca ANSA environment (see vol.2 chapter 2.1.2, Check Run) this step is included in the task manager. With Tosca Structure.gui the check run is a normal optimization run with special settings (vol.2 chapter 2.2.2, Check Run).
1.2.4
Optimization Loop The optimization can be started in Tosca ANSA environment (see vol.2 chapter 2.1.3), using Tosca Structure.gui (see vol.2 chapter 2.2.3) or Tosca Extension for ANSYS/Workbench (see vol.2 chapter 2.3.2) or by calling Tosca Structure in a command shell (see vol.2 chapter 2.4.4). Tosca Structure first starts a preprocessing step to check the definitions and write the complete optimization model to the database. Then the optimization loop runs until the stop criteria defined by the user is reached.
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1.2.5
Postprocessing: Evaluation of Optimization results After the optimization is completed, Tosca Structure.report can be called for data preparation with respect to postprocessing. During the optimization process the optimization results can be combined to animated sequences which can be visualized by Tosca Structure.view (see vol.2 chapter 10.2, Tosca Structure.view). Further, the process of specific optimization values like terms for the objective or constraints can be visualized in graphs and tables. All this postprocessing data can be combined in vtfx archives.
1.2.6
Result Transfer and Validation Run
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Valid optimization results have to be further processed in the design process. Tosca Structure.smooth can be used to prepare the optimization results for a transfer to a CAD system or FE-Preprocessor. Further, smoothed topology optimization results can be remeshed and a validation run can be performed. The task manager in Tosca ANSA environment supports this feature in an automated way (vol.2 chapter 9.2, Validation Run in Tosca ANSA environment). In other environments validation runs require a minimal amount of manual model adaptation (vol.2 chapter 9.4, Workarounds Using Other Environments).
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1.3
Workflow for Optimization FE-Model creation
Preprocessing Tosca ANSA environment Tosca Structure.pre
Check Run
Start Optimization
Tips on FE-Model vol.2 chapter 3.1 and vol.2 chapter 3.3
Definition of optimization task: vol.2 chapter 5, Topology Optimization, vol.2 chapter 6, Shape Optimization, vol.2 chapter 7, Bead Optimization, vol.2 chapter 8, Sizing Optimization.
vol.2 chapter 6.9, Check run (TEST_SHAPE), vol.2 chapter 7.9, Check run (TEST_BEAD) vol.2 chapter 2.1.3 Tosca ANSA environment, vol.2 chapter 2.2.3 Tosca Structure.gui, vol.2 chapter 2.3.2 Tosca Extension for ANSYS/ WB, vol.2 chapter 2.4.4 Command Shell,
vol.2 chapter 12.2, Starting Tosca Structure If model doesn’t run see vol.2
chapter 13 Postprocessing
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Tosca Structure.report Tosca Structure.view
Preparation of data for postprocessing see vol.2 chapter 10.1 Visualization and animation of optimization results see vol.2 chapter
10.2
Result Transfer to CAD Validation Tosca Structure.smooth Tosca ANSA environment
Preparation of data for CAD see vol.2 chapter 9.1 Validation run see vol.2 chapter 9.2
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Optimization process with links to documentation
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Fig. 2
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2
Working with Tosca Structure In this chapter, the general workflow with Tosca Structure is described. More details and practical examples can be found in vol.1 Start Manual. Prior to starting Tosca Structure a FE model must exist of the part that needs to be optimized. The model has to be analyzed at least once and the results checked. In chapter 3.1 Models for Optimization tips on model building for the required type of optimization are listed. How much the definition of the optimization problem can be simplified through entries made in the FE preprocessor is described in chapter 10 Postprocessing of Optimization Results for the relevant preprocessor. It is recommended to control the whole optimization workflow using Tosca ANSA environment that allows visual control of your component and geometric definitions or the classical Tosca Structure.gui. All steps of the optimization process (but not FE modeling and postprocessing) can be accessed from Tosca Structure.gui. Access to Tosca Structure from the command shell is described in chapter 2.4 Working with Tosca Structure in the Command Shell.
2.1
Working with Tosca ANSA environment Tosca ANSA environment provides the user with a workflow oriented tool to implement the complete optimization process. The graphical user interface supports • function based definition of the optimization task (preprocessing) • check run to review completeness and correctness of the definitions • start of the optimization
• result transfer for CAD and postprocessors • validation run for optimization results.
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• visual postprocessing with Tosca Structure.view
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Fig. 3
Optimization Task in Tosca ANSA environment
One big advantage over the classical workflow with Tosca Structure.gui is the possibility to perform geometric definitions (like design variable constraints or group selection) interactively. Further, consistency checks and updates of all dependencies are performed for each step. At the end of a topology optimization the modified model with all boundary conditions and load cases can be prepared automatically for the validation run. Tosca ANSA environment can be started with the command tosca_ansa_env in a TOSCA command shell. The start script can be found in \bin\tosca_ansa_env.
2.1.1
Preprocessing
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The preprocessing step in Tosca ANSA environment is used to set up the complete optimization task which can then be stored in a parameter file. Thereby a new function based approach is applied such that the user no longer needs to care about dependencies or single commands. The task man-
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ager tree view shows a logical sequence of definitions necessary for the optimization task.
Fig. 4
Preprocessing in Tosca ANSA environment
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First the link to the model has to be established. After loading the linked model can be used for interactive definitions of groups or constraints on design variables. Then optimization type dependent items for the optimization task can be defined and are grouped into folders according to their context. A detailed description of the setup of the optimization task can be found in vol.1 chapter 1.2, Topology Optimization with Tosca ANSA environment, vol.1 chapter 1.3, Shape Optimization with Tosca ANSA environment and vol.1 chapter 1.4, Bead Optimization with Tosca ANSA environment.
2.1.2
Check Run Once the optimization task is completely defined, a check run should be made. Tosca Structure then performs a complete syntax check of the optimization task to ensure a valid definition. Test runs for shape and bead optimization can be added to the CHECK INPUTS folder which will apply hypothetic optimization displacements to the model to enable the user to check restrictions etc. visually. The test results can be visualized (VTF_VISUALIZATION) using Tosca Structure.view.
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2.1.3
Start Optimization The optimization task defined in the task manager tree can now be started by simply updating the RUN item in the task manager tree. Eventually required settings can be entered in an editor window. When starting the optimization, all dependencies are actualized automatically. It is possible to deactivate definitions in the tree which are then skipped for the optimization run.
2.1.4
Postprocessing After the successful completion of the optimization run, the results have to be carefully checked. In the postprocessing step of your optimization task you can prepare your optimization results for a visual check with Tosca Structure.view (see chapter 10.1.3 Tosca Structure.report in Tosca Extension for ANSYS/Workbench andchapter 10.2 Tosca Structure.view) which can be directly accessed from the task manager (item VTF_VISUALIZATION). The user can navigate through the several steps of the iterations to visualize the changes in the model for one or more optimization relevant values. Further, graphs of specific optimization terms like, e.g., values of the objective or constraints, can be added to the vtfx visualization archive. Additionally Tosca Structure.view provides you with a plug-in for MS PowerPoint to create interactive presentations including your optimization results (see chapter 10.2.9 VTFX PlugIn for Office applications and Webbrowser).
Result Transfer and Validation Run For topology optimization, a validation of the optimized model is needed to be able to evaluate the responses without the void material in the simulation. Tosca Structure.smooth creates smooth surfaces of the area with remaining material (SMOOTH_RUN). The results from Tosca Structure.smooth can be displayed by Tosca Structure.view (VTF_VISUALIZATION).
Fig. 5
Smoothing and Visualization inTosca ANSA environment
Then the smoothed structure can be prepared for a validation run (VALIDATE) by performing a reconstruct step to improve the quality of the surface
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SIMULIA Tosca Structure Working with Tosca Structure
mesh, batch creation of a solid mesh and output of the optimized model in your solver format. All loads and boundary conditions of the design space model are transferred automatically to the new mesh. Finally, the finite element analysis (VALIDATION_RUN) can be started to evaluate stresses and displacements.
Fig. 6
Result Transfer and Validation Run inTosca ANSA environment
Satisfying optimization results can now be prepared by Tosca Structure.smooth for transfer into a CAD-system for further treatment in the design process (Create a new SMOOTH_INSTANCE with suitable output format). A more detailed description of this process and possible settings can be found in vol.2 chapter 9.1, Tosca Structure.smooth.
2.2
Working with the Graphical User Interface Tosca Structure.gui
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Tosca Structure.gui simplifies the work process of Tosca Structure for the user. The graphical user interface enables the following tasks to be completed: defining the optimization task (Tosca Structure.pre), starting the optimization in Tosca Structure, calculating iso surfaces, data smoothing and
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SIMULIA Tosca Structure Working with the Graphical User Interface Tosca Structure.gui
reduction (Tosca Structure.smooth), preparing results for postprocessing (Tosca Structure.report) and viewing them (Tosca Structure.view).
Fig. 7
Graphical user interface of Tosca Structure in Tosca Structure.gui
Tosca Structure.gui can be started with the command tosca_gui in a TOSCA command shell. The start script can be found in \bin\tosca_gui.
Preprocessing Tosca Structure.pre is used to define the settings for the optimization task which are then stored in a parameter file. The optimization task can either be created by a wizard, by defining the individual commands or by modifying an existing parameter file. A tree view with a logical sequence of the commands supports the user in the definition. For details about the use of Tosca Structure.pre and tips for the user refer to vol.1 chapter 2, Getting Started with Tosca Structure.gui. The parameters for
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SIMULIA Tosca Structure Working with Tosca Structure
the optimization commands and their syntax are described in detail in vol.3 Commands Manual.
Fig. 8
2.2.2
Defining the optimization task at Tosca Structure.pre
Check Run Once the optimization task is completely defined, a check run should be made. Tosca Structure then performs a complete syntax check of the optimization task to ensure a valid definition. Eventually some test runs for shape (see vol.2 chapter 6.9, Check run (TEST_SHAPE)) and bead optimization (see vol.2 chapter 7.9, Check run (TEST_BEAD)) are made which will apply hypothetic optimization displacements to the model to enable the user to check restrictions etc. visually (e.g. using Tosca Structure.view).
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2.2.3
Start Optimization Optimization with Tosca Structure.bead, Tosca Structure.shape or Tosca Structure.topology can be started on the "Start Tosca Structure" screen in Tosca Structure.gui. The job name of the optimization job (chosen by a parameter file), the start directory and if necessary the name of the FE solver are defined here. Further (optional) settings can be made using the menu "additional Parameters". A protocol window, convergence plots and a small queuing system are available to support the user in his work. For more details about the optimization
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SIMULIA Tosca Structure Working with the Graphical User Interface Tosca Structure.gui
start refer to vol.1 chapter 2.1.3, Starting the Optimization and vol.2 chapter 12.2, Starting Tosca Structure.
Fig. 9
Postprocessing The module Tosca Structure.report allows a preparation of the optimization results for postprocessing by Tosca Structure.view (see more chapter 10.1 Generation of Postprocessing Data). The user can navigate through the several steps of the iterations to visualize the changes in the model for one or more optimization relevant values. Further, graphs of specific optimization terms like, e.g., values of the objective or constraints, can be added to the vtfx visualization archive. Tosca Structure.view provides you with a plug-in for MS PowerPoint to create interactive presentations including your optimization
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2.2.4
Starting optimization from Tosca Structure.gui
SIMULIA Tosca Structure Working with Tosca Structure
results (see more chapter 10.2.9 VTFX PlugIn for Office applications and Webbrowser).
Fig. 10
Result Transfer and Validation Run Tosca Structure.smooth prepares the optimization result for transfer into a CAD-system for further treatment in the design process or into your FE-preprocessor for preparation of a validation run. Further, the results from Tosca Structure.smooth can be displayed by Tosca Structure.view and added to vtfx visualization archives. In the Tosca Structure.smooth window just choose your task to perform (surface or isosurface calculation), select your job (corresponding parameter file) and eventually enter more parameters to control
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2.2.5
Preparation of the optimization results for FE postprocessing at Tosca Structure.report
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SIMULIA Tosca Structure Working with Tosca Extension for ANSYS/Workbench
smoothing and data reduction and output formats (additional information see vol.2 chapter 9.1, Tosca Structure.smooth).
Fig. 11
2.3
Input parameters via Tosca Structure.gui at Tosca Structure.smooth
Working with Tosca Extension for ANSYS/ Workbench Tosca Extension for ANSYS/Workbench provides the ANSYS/WB user with a workflow oriented tool to implement and perform a complete topology and shape optimization process. The graphical user interface supports • function based definition of the optimization task (preprocessing)
• visual postprocessing within ANSYS/WB • result transfer for CAD and postprocessors • validation run for optimization results.
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• start of the optimization
SIMULIA Tosca Structure Working with Tosca Structure
Fig. 12
Optimization Task in Tosca Extension for ANSYS/WB
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One big advantage over the classical workflow with Tosca Structure.gui is the possibility to perform geometric definitions (like design variable constraints or group selection) interactively. At the end of a topology optimization the modified model with all boundary conditions and load cases can be prepared for the validation run. Tosca Extension for ANSYS/WB is fully included into ANSYS/WB.
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SIMULIA Tosca Structure Working with Tosca Extension for ANSYS/Workbench
2.3.1
Preprocessing The preprocessing step in Tosca Extension for ANSYS/WB is used to set up the complete optimization task which can then be stored in a parameter file. The Tree Outline lists all definitions that are made for the optimization task.
Preprocessing in Tosca Extension for ANSYS/WB
Before starting an optimization setup, an FE-analysis has to be set up first. Then, after loading the extension, all definitions, design variables constraints, etc. are added to the same Mechanical application. A detailed description of the setup of the optimization task can be found in vol.1 chapter 3, Getting Started with Tosca Extension for ANSYS/WB
2.3.2
Start Optimization The optimization task defined in the Tree Outline can now be started by clicking Solve. It is possible to deactivate single definitions by suppressing them in the Tree Outline. These definitions are then skipped for the optimization run.
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Fig. 13
SIMULIA Tosca Structure Working with Tosca Structure
2.3.3
Postprocessing After the successful completion of the optimization run, the results have to be carefully checked. The Tosca Extension for ANSYS/Workbench offers in the Mechanical application some visualization options (see chapter 10.3 Postprocessing with Tosca Extension for ANSYS/Workbench). Futher, a standard vtfx report for visualization with Tosca Structure.view is available in your jobname directory.
2.3.4
Result Transfer and Validation Run
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For topology optimization, a validation of the optimized model is needed to be able to evaluate the responses without the void material in the simulation. Tosca Structure.smooth creates smoothed surfaces of the area with remaining material. The results from Tosca Structure.smooth are displayed directly in the Mechanical application of ANSYS/WB.
Fig. 14
Visualization of smoothed model in Mechanical
Then the smoothed structure can be prepared for a validation run. During the two validation steps the smoothed surface model - which serves only for visu-
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SIMULIA Tosca Structure Working with Tosca Structure in the Command Shell
alization purposes - is reconstructed to first a shell model and eventually a solid model. This solid model can be used in an FE-analysis again.
Fig. 15
Result Transfer and Validation Run in Tosca Extension for ANSYS/WB
2.4
Working with Tosca Structure in the Command Shell For remote calculations or work with queuing systems it may become necessary to call Tosca Structure modules in batch mode from a command shell. Please ensure that the Tosca Structure variable is known (e.g. by using a Tosca Structure command shell on Windows) when working without a graphical user interface. This chapter gives only a brief overview of the basic process and the individual commands. More detailed information regarding the optimization process can be found in (vol.2 chapter 12, Tosca Structure Control). A quick and very short help is printed using the command: tosca810 --help
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Satisfying optimization results can now be prepared by Tosca Structure.smooth for transfer into a CAD-system for further treatment in the design process (Choose suitable output format). A more detailed description of this process and possible settings can be found in vol.2 chapter 9.1, Tosca Structure.smooth.
SIMULIA Tosca Structure Working with Tosca Structure
2.4.1
Logging in command shell Logging is always done to /TOSCA.OUT-file. The following levels can be used. - WARNING (not recommended) Only WARNINGs and ERRORs are printed - NOTICE Default output to STDOUT. Only the most important logging - INFO Default output to logfile TOSCA.OUT - DEBUG Very verbose output, mostly for support - TRACE (not recommended) Extremely verbose, major performance los, only for developers To change log level to logfile TOSCA.OUT use the command line parameter: tosca810
--loglevel ...
To increase the amount of output to the command shell set the parameter: tosca810 --loglevel_stdout
Note that --loglevel must be equal or more verbose than --loglevel_stdout. Example: 1. Increase log level to INFO on the command shell and DEBUG output into the logfile TOSCA.OUT tosca810 --loglevel_stdout INFO --loglevel DEBUG ...
2. More information about logging see chapter 12.2.3 Logging
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2.4.2
Preprocessing Once the FE model has been completed and checked, the optimization task must be defined. The parameter files containing these definitions can be created with an editor. This is only recommended when single commands in an existing parameter file need to be modified. Groups and coordinate systems can be defined in the FE-model to simplify the creation of the optimization task. A more detailed description of the command syntax for parameter files can be found in vol.3 Commands Manual. Tosca ANSA environment can be started with the command tosca_ansa_env, Tosca Structure.gui can be started with the command tosca_gui in a TOSCA command shell. Tosca Extension for ANSYS/Workbench can be started from within ANSYS/Workbench. The start script can be found in \bin\tosca_ansa_env or in \bin\tosca_gui.
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2.4.3
Check Run Before starting the optimization, the FE model (jobname.ext) and the parameter file (jobname.par) must already exist in the work directory. As part of a routine check, the FE model should be analyzed and evaluated. Consequently, a test run has to be completed and checked with respect to the optimization task before beginning the optimization. tosca810 jobname --solver solvername --type test1 (see vol.2 chapter 12.2.8, Testing the optimization process). It is worthwhile to make different test runs depending on the optimization task. Once the test run is completed, a visual check of the definition of the optimization task can follow.
2.4.4
Start optimization Starting the optimization with the standard settings is done with the command tosca810 jobname --solver solvername Further command line options are described in chapter 12.2 Starting Tosca Structure.
Postprocessing Tosca Structure.report allows the preparation of optimization results for postprocessing using Tosca Structure.view. The optimization results are written by Tosca Structure in a neutral format (ONF). A converting module allows the creation of a report file containing visualization sequences and graphs for specific results. Automatic generation of a visual post processing file can be done with the command line option report, e.g.: tosca810 jobname --report The above automatically call Tosca Structure.report which generates a vtfxfile in the directory TOSCA_POST after a successful optimization. More details regarding postprocessing can be found in chapter 10.1 Generation of Postprocessing Data. The vtfx-file can be viewed in Tosca Structure.view which allows visualization of the optimization results by an animation over the iterations of the optimization. The sequences can be created with Tosca Structure.smooth or Tosca Structure.report. Call Tosca Structure.view with the command line: tosca810 --view jobname/TOSCA_POST/
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2.4.6
Result Transfer Tosca Structure.smooth allows the preparation for the transfer of the optimization results into the design process (for more details see chapter 9.1 Tosca Structure.smooth). Tosca Structure.smooth is called up in a command shell with the command tosca810 jobname --smooth More details regarding postprocessing can be found in chapter 9 Result Transfer and Validation Run. The vtfx-file can be viewed in Tosca Structure.view which allows visualization of the optimization results by an animation over the iterations of the optimization.
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tosca810 --view jobname/TOSCA_POST/
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SIMULIA Tosca Structure The Model
3
The Model Each optimization task is based on one or more finite element analysis models. These models form the basis for the optimization, i.e. contain the nodes or elements to be changed and the loads and boundary conditions for the calculation of important terms for the optimization (see vol.2 chapter 4, Terms for Optimization). Further, node and element groups or coordinate systems in the analysis files are available for further definitions in the optimization task. Additional files may contain objects for the definition of constraints or provide supplementary analysis results to be considered in the optimization. This chapter deals with requirements for optimizable models and discusses the loading of models. Further, the definition of groups and coordinate systems in your optimization environment is explained.
3.1
Models for Optimization
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When defining a model for analyzing, the selection and definition of the loads and boundary conditions should be constructed with special consideration because an incorrectly defined or forgotten load or support may have a very pronounced effect on the result of the optimized structure. The basic characteristics of the analysis model that can be optimized are described in detail in vol.2 chapter 11, Solver Specific Features (optimizable element types, number of load cases and permitted boundary conditions, types of analysis, nonlinearities, etc.) and in vol.2 chapter 14.2, Limits of Tosca Structure. Remark One single finite element can consist of several laminates which is especially common for shell elements to specify e.g. several cross sections, materials etc. In Tosca Structure, this is called a "ply". Currently Tosca Structure supports only one single ply for each element and stops with an error message if elements with multiple plies are found.
3.1.1
Models for topology optimization Topology optimization determines the optimized material distribution in a given space for achieving an optimized design. Based on the external loads and boundary conditions, Tosca Structure.topology determines the optimum material distribution in the design space. The topology optimization creates holes and perforations that extensively alters the shape of the component. Alternatively, an existing component can be optimized whereby the topology optimization rearranges the material distribution of the component.
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SIMULIA Tosca Structure Models for Optimization
The available design space must exist as a FE model. The resolution of the designed structures depends strongly on the selected discretization. A fine mesh produces a structure with a higher resolution than a coarse mesh. On the other hand, it will also substantially increase the processing time required. A compromise between structural resolution and processing time needs to be found.
3.1.2
Models for shape optimization
3.1.3
Models for bead optimization The design area for a bead optimization must be a shell type of structure i.e. shell or plate elements. The mesh should be uniform in element size. The element size should be chosen such that 6 elements covers the wanted bead width. It is recommended to use linear elements, but not necessary.
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In shape optimization, the boundaries or surfaces of a component are modified. At first the optimizer calculates the new coordinates of the design nodes on the component surface based on the stress condition and then adjusts the remaining FE mesh accordingly. The calculation of the new coordinates of the nodes is not based on geometrical parameters, but rather on each individual coordinate for the nodes. Generally, every FE model can serve as a basis for shape optimization. The mesh must be of such quality that the analysis results from the FE mesh remain essentially unaffected. To assure this, most FE preprocessors have checking routines. The user must define an adequate mesh density for a subsequent optimization, i.e., high stress gradients should not be present within an element. The mesh density must be set correctly in order to achieve smooth contours. For example, smooth contours cannot be expected when a 90 degree curve is meshed by only three elements. The finer the mesh density, the closer the contour will be to optimum. Tosca Structure.shape features an integrated efficient smoothing mesh algorithm. It is capable of adjusting the FE mesh to the optimized displacement of the design nodes without re-meshing. It is possible that the FE model will collapse when there is a large optimized displacement of the design nodes due to a poor mesh. This can be avoided by setting the mesh to an adequate density.
SIMULIA Tosca Structure The Model
3.1.4
Models for sizing The design area for a sizing optimization must be a shell type of structure i.e. shell or plate elements. The shell thicknesses of the most typical modeling shell elements are supported as design variables. The mesh should be uniform in element size. Only single layered shells are supported. Contact in the design area is also allowed. Geometrical non-linearities ae not supported. Constitutive non-linear modeling is only allowed outside the design area (e.g. a non-linear spring).
3.2
Optimizable Element Types In general, Tosca Structure allows all element types listed in Table 1 in the optimization area. Details concerning specific element definitions for the several solvers are listed in chapter 11 Solver Specific Features. Some design responses are not allowed for all element types. This can be found in the coresponding paragraphs of chapter 4 Terms for Optimization.
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Tosca Structure Element Type
Topological Description
PLANE_QUAD_4
Four-node 2D plate element
PLANE_QUAD_8
Eight-node 2D plate element
PLANE_TRIANG_3
Three-node 2D plate element
PLANE_TRIANG_6
Six-node 2D plate element
SHELL_QUAD_4
Four-node 3D shell element
SHELL_QUAD_8
Eight-node 3D shell element
SHELL_TRIANG_3
Three-node 3D shell element
SHELL_TRIANG_6
Six-node 3D shell element
SOLID_BRICK_8
Eight-node 3D solid element
SOLID_BRICK_20
Twenty-node 3D solid element
SOLID_TETRA_4
Four-node 3D solid element
SOLID_TETRA_10
Ten-node 3D solid element
SOLID_PYRAM_5
Five-node 3D solid element
SOLID_PYRAM_13
Thirteen-node 3D solid element
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Tosca Structure Element Type SOLID_PENTA_6
Six-node 3D solid element
SOLID_PENTA_15
Fifteen-node 3D solid element
Fig. 16
Optimizable element types
Optimizable element types *supported with Tosca Structure 7.3 for controller based optimization for ANSYS
Preprocessing FE Models for Optimization Preprocessing of a finite element analysis may be performed in various preprocessing systems. To be able to use Tosca Structure in a familiar environment, Tosca Structure offers several preprocessing interfaces.
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Table 1
3.3
Topological Description
SIMULIA Tosca Structure The Model
The finite element model may be generated in every finite element preprocessor that can generate an input model for the supported finite element solvers. Simplifications for the formulation of the optimization task (such as groups, different properties, ...) may also be defined in many FE preprocessing systems that are not mentioned below (e.g. Hypermesh). The optimization preprocessing of Tosca Structure is mainly based on group information. Using Tosca ANSA environment, group definition can be made by graphical selection of nodes and elements or already in the FE-preprocessor. Using Tosca Structure.gui, all necessary information such as design nodes or frozen elements should be defined as groups in the FE-preprocessor. These groups may be read by Tosca Structure.pre and then be referenced in the further definitions of the parameter file.
3.3.1
Abaqus/CAE The analysis model for the optimization procedure may be generated in the standard way in Abaqus/CAE. All groups that are necessary for the optimization should be generated in Abaqus/CAE. Currently, the use of parts and assemblies in the Abaqus input file is not supported by Tosca Structure. It is recommended to configure Abaqus/CAE such that no parts & assemblies are written. To achieve this, the following parameter must be set in the configuration file abaqus_v6.env: cae_no_parts_input_file=ON Alternatively before writing the input deck, right click on the model in the Model Database, select "Edit Attributes..." and activate "Do not use parts and assemblies in input files".
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3.3.2
Preprocessing with ANSYS/Prep7 The analysis model for the optimization with Tosca Structure and ANSYS can be generated in /PREP7 in the standard way. For the batch processing of ANSYS the ANSYS CDB, inp and dat format can be used. An ANSYS CDB file contains the complete finite element information without the solution strategy (/SOLU). The solution strategy has to be added manually by the user.
3.3.2.1 Generation of the finite element input file The CDB File is generated in ANSYS/PREP/ with the following command: CDWRITE, OPTION, FNAME, EXT, DIR, FNAMEI, EXTI, FMAT
The option DB has to be used to ensure that the complete finite element information is written into the file. The file name (Fname) and the extension (Ext)
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have also to be specified. In the examples of the Tosca Structure installation, the extension "cdb" is used. A complete command for the generation of a CDB file looks as follows: CDWRITE, DB, HOLEPLATE, ANS
This file does not contain the solution strategy.
3.3.2.2 Load cases If only one load case should be calculated, the load case information is already included in the CDB file. In this case only the solution strategy has to be added: /SOLU SOLVE FINISH
If multiple load cases are used, the load cases can be stored in load case files (file.s01, file.s02, ...). These files are generated using the following command: LSWRITE, LSNUM
The solution strategy for multiple load cases has to be added to the CDB file: /SOLU LSREAD, 1 SOLVE LSREAD, 2 SOLVE ...
3.3.2.3 Check of the batch input file To check if the CDB file is running correctly in batch mode, an analysis should be started on the command line before starting the optimization with Tosca Structure. Using the ANSYS 14.5 solver, the command line looks as follows: • Windows ANSYS145 -B -I [INPUT FILE] -O [OUTPUT FILE] -P[PRODUCTVAR]
• Unix ANSYS145 -P -P[PRODUCTVAR] < [INPUT FILE] > [OUTPUT FILE]
Errors are reported to the *.err file. In case of errors, the input file must be modified.
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FINISH
SIMULIA Tosca Structure The Model
3.3.2.4 Generation of groups The node and element groups (assemblies and components) are generated using the "component manager" or with the following commands: CM, CNAME, ENTITY CMGRP, ANAME, CNAM1, CNAM2, CNAM3, CNAM4, CNAM5, CNAM6, CNAM7, CNAM8
These components or assemblies are treated as node and element groups in Tosca Structure. These groups are extracted from the cdb file and are accessible via the group name in the optimization preprocessor. If node and element groups are generated with the same name, the groups get the suffix "_NODE" and "_ELEM" during the import in order to keep the group names unique.
3.3.3
Preprocessing with ANSYS Workbench Topology optimization with Tosca Structure is available fully integrated into ANSYS/Workbench. ANSYS/Workbench can further be used to set up models for shape and bead optimization or the further processing with Tosca ANSA environment or Tosca Structure.gui.
3.3.3.1 Export of finite element input model
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Topology optimization with Tosca Structure is available fully integrated into ANSYS/Workbench. Nevertheless, for shape and bead optimization respectively, the ANSYS Workbench *.wbpj simulation database cannot be directly used in combination with Tosca Structure. Before starting the Tosca Structure optimization, a CDB, dat or inp file has to be exported from the Workbench.
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SIMULIA Tosca Structure Preprocessing FE Models for Optimization
For the export of a CDB File, the corresponding solution has to be activated first. If the solution is active, Write ANSYS Input command can be selected from the Tools menu.
Activate "Solution"
"Tools" | "Write ANSYS Input File" Fig. 17
Generation of ANSYS CDB Files
Enter .cdb Fig. 18
Switch to "All Files(*.*)"
File name specification with *.cdb extension
3.3.3.2 Generation of groups In ANSYS Workbench, groups/components are generated dependent on the selected geometric entities. If a volume is selected, all finite elements of the volume are selected to an element group. If area, line or point entities are
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For the selection of the filename in the ANSYS Workbench File Export, the file extension can be specified: to prevent the standard Extension *.inp from being used during export, one should switch to ALL FILES in the output file dialog and specify the *.cdb extension manually.
SIMULIA Tosca Structure The Model
selected in the workbench, the connected nodes are selected to a node group.
Fig. 19
Selection of element and node groups in ANSYS Workbench
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With ANSYS version 14.0 and later, node groups can also be defined independent of hte geometry using Select Geometry | Select Mesh (Activate "show Mesh" before). The name specified for the component in ANSYS Workbench is output to the CDB file and may be used to reference the groups in the definition of the Tosca Structure optimization task.
Fig. 20
Definition of group names in ANSYS Workbench
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3.3.3.3 Suitable meshes for topology optimization In general, ANSYS Workbench provides suitable meshes for topology optimization. For topology optimization, the mesh should be homogeneous in order to be able to represent the inner surfaces during the redistribution of the material. Nevertheless, if the homogenity of the mesh needs to be improved, in ANSYS Workbench this can be achieved using the Patch Independent meshing algorithm.
Choose "Method": Tetrahedron "Algorithm": Patch Independent
Choose linear element formulation
Define min. and max. element size in a small range Patch Independent meshing algorithm in ANSYS Workbench
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Fig. 21
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If the minimum and maximum element sizes are chosen in a small range, a homogeneous mesh is generated inside the volumetric parts, which is more suitable for a topology optimization task.
Fig. 22
3.4
Mesh for topology optimization
Loading FE Data All FE models used for the optimization can be loaded using the MODEL_LINK folder in the task tree of Tosca ANSA environment or the FEM_INPUT command in Tosca Structure.gui. Here, several models can be linked to your optimization task:
• The ADD_FILE item refers to analysis files which may contain additional geometry for definition of geometric constraints. • The COPY_FILE item allows to copy files to the working directory. • The LIFE_FILE item refers to an analysis model for a durability solver.
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• The FILE item refers to analysis files with always the same geometry (node and element structure) which describe the design space.
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• The TEMPERATURE_FILE item refers to an analysis model for a temperature solver run.
Fig. 23
Analysis Files for Optimization (FEM_INPUT) Optimization with Tosca Structure always refers to one or more analysis files which provide the design space and necessary values for the optimization as results of a finite element analysis run. A single finite element file or several finite element files are referenced in the item FILE in the command FEM_INPUT or the folder MODEL_LINK in Tosca ANSA environment. However, all finite element files should have the same number of elements, nodes, material properties, element groups, nodes groups etc. The only difference allowed between the different input finite element files is that the analysis types can vary. The analysis type can either be linear static, non-linear static, modal eigenfrequency or frequency response analysis. The FEM_INPUT command is applied for reading the finite element files in the following way: FEM_INPUT ID_NAME FILE FILE FILE ...
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= = = =
id_read_files fe_file_name_1 fe_file_name_2 fe_file_name_3
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3.4.1
Loading data by MODEL_LINK in Tosca ANSA environment (left) and FEM_INPUT command in Tosca Structure.gui (right)
SIMULIA Tosca Structure The Model
END_
Working with Tosca ANSA environment, all three files can be entered into the MODEL_LINK folder in a similar way. The possibilities available to the user for loading the analysis model when creating the optimization model depend on the chosen solver (see vol.2 chapter 10 and vol.2 chapter 11) and the option set (volume 3: OPTIONS). The model data is loaded using an internal interface. After reading the model, the following FE objects are available for further reference in the optimization task: • Node groups • Element groups • Nodes • Elements • Coordinate systems • Materials • Properties • Element types • Boundary conditions (depending on the OPTIONS)
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• Load cases Analysis results used as terms for objective or constraint, so called design responses (DRESP), are built by referring the load case numbers for the desired responses. The load cases in the first file (fe_file_name_1) are numbered using the original load case numbers used in the finite element file. The load cases in the second file (fe_file_name_2) are numbered using the original load case numbers used in the finite element file plus 10.000. The load cases in the third file (fe_file_name_3) are numbered using the original load case numbers used in the finite element file plus 20.000 and etc. E.g. the load cases 1, 3 and 4 in the first finite element file have the numbers 1, 3 and 4 in the parameter file, the load cases 1, 3 and 4 in the second finite element file have the numbers 10001, 10003 and 10004 in the parameter file, the load cases 1, 3 and 4 in the third finite element file have the numbers 20001, 20003 and 20004 in the parameter file and etc. In vol.2 chapter 11 the different allowed analysis types for the specific solvers are described. Furthermore, vol.2 chapter 4.5.2.1 describes how the load case numbers for the different finite element solvers are applied in the design response definitions (DRESP). This is especially important for the finite element input decks using no numbers when defining load cases. For the finite element solvers using no numbers the general rule is that the load cases
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SIMULIA Tosca Structure Loading FE Data
have the numbers according to the order within they are defined. Meaning that the load case number one will always have the load number of one for Tosca Structure etc. Remarks 1. A model link can only be made once for an optimization task, i.e. the command FEM_INPUT can only be used once in a parameter file. 2. Several analysis files can be added, i.e. the item FILE can be repeated several times. The first file in the list of files will be handled as master file, which means that the configuration of the finite element model will be read from this file. The second and all later referenced files will be used to perform a finite element calculation. The model in these files has to be identical to the original FE model. The files will be modified during the optimization.
3.4.2
LIFE_FILE Is used to define input files for the durability solver (life_solver). Please see vol.2 chapter 11.6, Shape Optimization Based on a Durability Analysis.
TEMPERATURE_FILE This parameter allows Abaqus users to specify an Abaqus input file for a sequential temperature analysis. First, a temperature calculation is carried out, of which the results are used as boundary conditions for the following finite element calculation. The input file, which is used for the temperature calculation, can be specified using the TEMPERATURE_FILE command. All model changes due to the optimization are also changed to the temperature model.
3.4.4
ADD_FILE In certain circumstances it is useful to define additional nodes and elements in the optimization model that are not required in the FE analysis. In this case, it is practical to write the additional nodes and elements in a separate file. This file can be read using the item ADD_FILE in the MODEL_LINK folder in Tosca ANSA environment or the FEM_INPUT definition in Tosca Structure.gui. For example, these additionally loaded elements can be used to define restriction areas of any form. To simplify the selection of the elements in the
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SIMULIA Tosca Structure The Model
parameter file, it is recommended to assign these elements with specific element properties, which can be used as selection criteria. Remarks 1. The item ADD_FILE can be repeated several times. All nodes and elements stored in the file referenced with this item are not available for the optimization. This item can be used for the specification of neighbouring elements for the definition of manufacturing constraints. 2. Tosca Structure can not manage double numbers. The user should be aware of this and be sure that there is no conflict of numbers during file loading (e.g. elements with identical numbers in the different files in the MODEL_LINK or FEM_INPUT command).
3.4.5
COPY_FILE The COPY_FILE command is the easiest way to copy a file into the working directory of Tosca Structure. This could be an extra configuration file for your FE-solver or another file that has no direct influence on Tosca Structure. The item may be repeated several times. Example: If the file my_copy_file should be present in the working directory, e.g. because it is required by the user’s solver or for use in a script call, it could be copied as follows: FEM_INPUT
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ID_NAME FILE COPY_FILE END_
3.4.6
= OPTIMIZATION_MODEL = holeplate.bdf = my_copy_file
Special FEM_INPUT-commands The special extra commands: FILE_SOLVER_EXE, FILE_CMDLINE, FILE_ADD_CALL, LIFE_FILE_SOLVER_EXE, LIFE_FILE_CMDLINE, LIFE_FILE_ADD_CALL, DEPENDENT_FILE are all related to the last FILE or LIFE_FILE command. These are only be used in very advanced setups and should normaly be avoided.
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3.4.7
Options for loading FE Data (OPTIONS) The default settings for loading the FE data can be changed with the OPTIONS command: the settings influence, for example, the loading of the boundary conditions, the identification of the model surface and the loading of the FE results. The loading options refer to the command FEM_INPUT (see vol.2 chapter 3.4) and must be specified before loading the FE data. Using Tosca Structure.gui the OPTIONS command is available in the command drop down menu. In Tosca ANSA environment the command can be entered using the modules menu. A list of all possible parameters can be found in volume 3: Commands Manual.
3.4.7.1 Loading displacement restrictions When the model is loaded with the FEM_INPUT command all existing nodes, elements, material properties, coordinate systems and essential element properties are read from the FE input file. Forces, pressures and other loads are not required by the optimization model and therefore not loaded. By default fixed nodes are not loaded. Using the READ_BC = ALL option in the command OPTIONS, all fixed nodes are loaded directly as node displacement restrictions for the optimization model. This option is activated with the command: OPTIONS READ_BC
= ALL
END_
1. For some solver interfaces it is also possible to directly enter a number to specify which fixed nodes are loaded as optimization boundary conditions. This proves especially useful when the optimization boundary conditions are defined as an additional load case in the FE model. The exact function of this load option depends on the different interfaces (see vol.2 chapter 10). 2. Fixed nodes can also be defined in the parameter file with the command DVCON_SHAPE. However, defining fixed nodes in the FE model is more efficient. 3. Only fixed nodes with a translation equal to zero in the one, two or three direction according to the coordinate systems of the nodes can be loaded from the FE input in the optimization model. Constraint displacements not equal to zero are not loaded.
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SIMULIA Tosca Structure The Model
3.4.7.2 Identifying surface nodes for shape optimization The identification of surface nodes is necessary for shape optimization. During the optimization preprocessing the surface nodes are automatically identified when the design variables are defined (DV_SHAPE). The surface nodes can already be identified when reading the analysis model, such that a selection of the surface nodes is possible for the definition of groups. When using the parameter READ_SF_IDENT = ON in the OPTIONS command all surface nodes are identified and can be used for further definitions. In certain cases problems can occur in the surface node recognition for the whole model. In these cases, only the elements should be selected which are meant to be assigned with the surface nodes. For example, if shells lie on the surface of solid elements, only the free boundary of the shell is identified as being a surface. In this case the solid elements have to be selected (command SELECT) and their surface nodes have to be identified with the command SF_IDENT. The command SF_IDENT can only be used once. This command is not available using Tosca ANSA environment and must be entered manually in Tosca Structure.gui.
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3.5
Include Files The parameter files can consist of several parts which can be encapsulated in separate files. These files are referenced in the actual parameter file (jobname.par) with the command INCLUDE. This is useful in cases where the file is too large due to long selection lists used to define groups. The user can save these group definitions in a separate file and link this with INCLUDE at the relevant position. A second command INCLUDE can be used also in the included file. The INCLUDE files are searched for in the given directory. Should no directory be entered, a search is made in the current working directory or the subdirectory macros of the Tosca Structure installation directory. Please Note: The command INCLUDE is not required for your work with Tosca ANSA environment and thus is not available there.
3.6
Group Definition (GROUP_DEF, GROUP_AUTO_DEF) The definition of groups is a very important function in Tosca Structure. For example, if one or more nodes should be assigned a specific attribute (e.g. a restriction), the nodes are first assembled in an object “node group”. Then the attribute is assigned to the object “node group”.
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SIMULIA Tosca Structure Group Definition (GROUP_DEF, GROUP_AUTO_DEF)
In Tosca Structure two different types of groups exist: node groups and element groups. Groups can be defined manually using selection of objects or using lists in Tosca Structure.gui or can be defined using graphical selection in Tosca ANSA environment. Further, automatic node group definition is available to define groups following specific geometric patterns like, e.g., on surfaces of revolution. All groups from the FE input file(s) linked to the optimization task are also available for definitions in Tosca Structure. Groups are uniquely defined and addressed with their user-defined names (character string). The use of an identical name for a node group and an element group is not permitted.
Default predefined groups The system automatically creates a node group named ALL_NODES and an element group named ALL_ELEMENTS. All nodes and elements respectively that have been loaded with the first file in the FEM_INPUT command are contained in these groups. However, nodes (or elements) loaded from all other files are not contained in the ALL_NODES (ALL_ELEMENTS) group. If a topology optimization is performed, the element group NON_DESIGN is also generated. This group contains all elements that have not been defined as design elements. The NON_DESIGN group must be visualized together with the HARD element group to be able to view the entire structure of the optimized design in the postprocessing system. The groups defined in the FE input model are also loaded by Tosca Structure and therefore can be referenced in the same way as the groups defined in the parameter file. The names of the groups imported from the input model remain unchanged, with the following exceptions: - if a node group (NSET) and an element group (ELSET) have the same names in an Abaqus input model, they get the suffices _NODE and _ELEM respectively. See vol.2 chapter 11.1.3 for details. - if the Abaqus input file contains more than one instance of the same part, the group names are modified as described in vol.2 chapter 11.1.1.
3.6.2
Group definition in Tosca ANSA environment Groups are usually defined in Tosca ANSA environment right when they are needed in some item of Task Manager (e.g., DV_TOPO). All groups from the FE input model are also available in the group selection windows. To create a new group, click the Action button and select New. In a dialog that lists all groups, select the nodes or elements you choose for the group and confirm the selection with a middle mouse button click.For details of group selection refer to vol.1 chapter 1.1.13, Managing Groups.
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3.6.3
Group definition in Tosca Extension for ANSYS/WB Groups are usually defined in Tosca Extension for ANSYS/WB right when it is needed for some item of the optimization task (e.g., DV_TOPO). It is recommended to define named selections in advance for later use in the definition of, e.g., design area or responses for objective and constraint. For examples see vol.1 chapter 3.2.5, Optimization preprocessing.
3.6.4
Manual group definition in Tosca Structure.gui In Tosca Structure.gui node and element groups can be defined manually using lists of node IDs or element IDs in the GROUP_DEF command: GROUP_DEF ID_NAME = ndgr_name TYPE = NODE FORMAT = LIST LIST_BEGIN 1,2,5,3000,...
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END_
Changing the TYPE to ELEM assembles the elements with the numbers listed into the group. Further, a list of materials or properties can be specified using the LIST_MAT or LIST_PROP entry for FORMAT to combine all nodes or elements related to the listed materials or properties. In Combination with the command SELECT,... (see volume 3: SELECT or vol.2 chapter 3.7, Selection of Objects in Tosca Structure.gui) more complex group definitions are possible. To this end, the nodes (or elements) to be included in the group must first be selected according to their numbers, geometric position, belonging to a certain area etc., sometimes using several SELECT commands sequentially in order to collect specific nodes or elements in the selection list. Subsequently, the group is defined with GROUP_DEF. A typical command sequence appears as follows: SELECT,NODE,S,... GROUP_DEF ID_NAME TYPE FORMAT
= ndgr_name = NODE = SELECTED
END_
The group is given an unique user defined name.
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SIMULIA Tosca Structure Group Definition (GROUP_DEF, GROUP_AUTO_DEF)
3.6.5
Automatic node group definition (GROUP_AUTO_DEF) Apart from the definition of individual node groups, several node groups can be defined automatically using the GROUP_AUTO_DEF command. The GROUP_AUTO_DEF command is available from the modules button menu in Tosca ANSA environment or the command menu in Tosca Structure.gui. This feature is especially important in relation to function based node coupling. For example, if the rotation symmetry of a shaft shoulder loaded with a bending moment should be maintained during optimization, it is necessary to couple all nodes of the circumference. This involves a large number of node groups and node couplings. (For examples see vol.4 chapter 3.4, Shaft or vol.4 chapter 3.5, Carrier). Starting with a parent group that has been previously defined by the user, the GROUP_AUTO_DEF command can be used to automatically define child groups (children). Employing various methods, search areas are established originating at every node of the parent group. All nodes located within a search area are “captured” and collected in a child group. Thereby, only those nodes that are currently in the selection list “NODES” are considered. Per default, all nodes are selected at the beginning. (Thus, if no SELECT command is activated, all existing nodes are considered. You can "preselect" a certain area using SELECT to restrict automatic group definition to this area, see chapter 3.7 Selection of Objects in Tosca Structure.gui). Child groups are labeled with the name of the parent group and a numerical index. For example, if child groups are formed from a node group titled “parent” which contains 4 nodes, the four children groups are named “parent_1”, “parent_2”, “parent_3” and “parent_4”. Various procedures can be used to define a search area.
GROUP_AUTO_DEF ND_GROUP ... SEARCH_TYPE .... END_
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1. Specification of a continuous search area (SEARCH_TYPE = CONTINUOUS): All nodes located within the search area that are currently selected by the node selection list are assembled and assigned to a child group:
SIMULIA Tosca Structure The Model
dir Direction -Snap Tolerance 2*Snap Tolerance
Search Area
Not Grouped
Member of Parent Group
Fig. 24
+Snap Tolerance
Length
Continuous search area
2. Specification of a search area divided into discrete sections (SEARCH_TYPE = DISCRETE): All nodes located within the discrete sections that are currently selected by the node selection list are assembled in child groups: GROUP_AUTO_DEF ND_GROUP ... SEARCH_TYPE ....
= parent_group = DISCRETE
END_
dir Direction
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Discrete Length
2*Tolereance 2
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Search-Length Discrete Length
Discrete Length
2*Tolerance 1 Member of Parent Group
Fig. 25
Not Grouped Search Area
Discrete area search
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3. Search in various local coordinate systems (SEARCH_TYPE = CS_MULTI): The coordinates of the individual nodes in the parent group are determined in relation to a specified coordinate system. All selected nodes with matching coordinates in relation to specified search coordinate system are assembled in child groups together with the corresponding parent node: GROUP_AUTO_DEF ND_GROUP ... SEARCH_TYPE ....
= parent_group = CS_MULTI
END_
Y1 CS 1
Yparent
X1
CSparent
Xparent Y2
X2
X 1 in CS 1 = X 2 in CS 2 = X parent in CS parent Y 1 in CS 1 = Y 2 in CS 2 = Y parent in CS parent Fig. 26
Multiple coordinate systems in the AUTO_GROUP command
Remarks 1. Only currently active (selected) nodes are considered for the definition of children groups when using GROUP_AUTO_DEF. Per default, all nodes are selected at the beginning of the optimization. If - for specific reasons only a subset of nodes was active (selected) and if nowall nodes should be considered for the children group definition, then all nodes must be activated (again) using SELECT, NODE, ALL before the GROUP_AUTO_DEF 2 - 52 User Manual
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SIMULIA Tosca Structure The Model
command is executed (see also chapter 3.7 Selection of Objects in Tosca Structure.gui).
3.7
Selection of Objects in Tosca Structure.gui The command SELECT provides the user with powerful possibilities to select objects, in particular nodes and elements, without using graphical interaction. The SELECT command can be entered into the parameter file using a text editor or the text view in Tosca Structure.gui. Due to the advanced graphical selection possibilities in Tosca ANSA environment, the SELECT command is not required and thus not supported in this front end. Most of the FE objects and Tosca Structure objects can be selected with the SELECT command in the parameter file. Nodes and elements are selected by addressing certain attributes. Selection of nodes and elements can be used to define node and element groups. These can be used as optimization groups. Object lists In Tosca Structure a list is created for most object types. At the beginning each object list is loaded with all the data that is read in by the FE interface, e.g., the list of elements contains all elements from the first input file linked to the optimization task. When an object is selected, the selected object is added to the corresponding list. Selection lists can be used as selection criteria (Fig. 27). The following types of objects have their own lists and can be selected using the command SELECT: • Coordinate Systems (CS) • Elements (ELEM)
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• Element groups (ELGR) • Nodes (NODE) • Node groups (NDGR) • Element types (ETYPE, see Table 1) • Element properties (EPROP) • Materials (MAT) • Solids (SOLID) Selection types Every SELECT command refers to one object type.The user must define whether the selected objects should be added to the existing object list (ADD)
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or removed (UNSELECT) or whether the selection list should be reset (SELECT). Additionally, it is possible to keep only the actually selected objects of an existing selection list (RESELECT). All objects of the corresponding type can be registered in the selection list (ALL) or the selection list can be emptied (NONE). It is also possible to invert (INVERT) the content of the selection list. Depending on the selection type, existing selection lists can be extended or varied (Table 2):
Shortcut
Type
Description
S
Select
Initialization and New Selection.
R
Reselect
Selection of a subset from a selection list.
A
Add
Add objects to current selection list.
U
Unselect
Remove objects from current selection list.
ALL
Select all
Select all objects of the object type.
Select none
Empty selection list.
Invert
Invert: Reverse selected and non-selected objects of the object type.
NONE INV
Selection types in Tosca Structure
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Table 2
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MAT
ETYP
EPROP
ELGR
ELEM
NODES: ND_ALL ND_ANY
LAYER
SOLID
ELEM
Restrict
NODE
Location
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Surface
Design
List
A
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NDGR
A
B
Selection for list A with selection criterion active list B.
A
Selection for list A from all entities A.
C
Property C
A
Fig. 27
Selection for list A from entities A with property C.
Selection lists and selection criteria
Selection criteria Almost all objects can be added to a selection list using numbers or names. For nodes and elements a variety of selection criteria exists (Table 3). For example, it is possible to select elements by their element property or mate-
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rial number defined in the analysis file. Thus element and node numbers do not have to be explicitly known by the user. Selection lists are useful tools that help the user to quickly define element and node lists. Selection lists are required for group definitions. .
X
ELGR
X
NDGR
X
ETYP
X X
MAT
X
SOLID
EPROP
ETYP
NDGR
ELGR
X
X
X
NODE
X
ELEM
X
Table 3
CS
NR.
EPRO P
SOLID
CS
MAT
Selection lists
NAME
Selection criteria
X
X X
X
X
Selection lists and selection criteria
The following example serves to illustrate the effect of the selection commands. Each step is accompanied by a description of how the selection lists change. The aim of this detailed example is to select a node group by list entries for which various assignments are applied (e.g. nodes to elements, element to element properties). The following steps are taken: • Direct selection of elements by specifying the element numbers (in the example: elements 1, 3, 5). • Selection of elements using element properties (in the example: element properties 3 and 5). • Selection of the nodes associated with the actually selected elements. Step 1: Select element numbers directly: 2 - 56 User Manual
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Elements can be selected directly by entering the element number: SELECT, ELEM, S, ELEM, 1, 5, 2
- By specifying the list name “ELEM”, the element list is addressed. The selection operator “S” initializes the element list (SELECT). The element numbers are directly specified as selection criterion (elements 1 to 5 with increments of 2). The elements 1, 3 and 5 are selected directly with their numbers and written into the element list. All other lists remain unchanged.
List ELEM Table 4
List entries 1, 3, 5
Selection example (step1)
Step 2: Element Selection using Element Properties The element list should be extended to include elements with the properties 3 or 5. • First, the element properties 3 and 5 are added to the element property list. It is also possible to use increments. SELECT, EPROP, S, EPROP, 3,5,2
- The EPROP list is addressed. The selection operator “S” initializes the element property list. The ELEM list remains unchanged:
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List
List entries
ELEM
1, 3, 5
EPROP
3, 5
Table 5
Selection example (step2)
• Now all elements with element properties that are currently in the element property list should be added to the already existing element list. SELECT, ELEM, A, EPROP
- The element list is addressed. The operator “A” (ADD) adds elements to the existing element list where the added elements have properties that are specified in the element property list:
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List
List entries
ELEM
1, 3, 5;and all elements with the element properties 3 and 5
EPROP
3, 5
Table 6
Selection example (step 3)
Step 3: Select Nodes In this step all nodes that belong to the selected elements are added to the node list. The element list is used as a selection criterion for nodes: SELECT, NODE, S, ELEM
- The node list is addressed and initialized. All nodes of the elements currently in the element list are included in the node list:
List
List entries
ELEM
1, 3, 5; and all elements with the element properties 3 and 5
EPROP
3, 5
NODES
all nodes of the elements in the element list
Table 7
Selection example (step 4)
Remarks 1. To use the selection possibilities for element types, materials and coordinates in Tosca Structure, all quantities must previously be defined and assigned in the FE analysis file. 2. Upon loading the analysis model, all loaded objects (nodes, elements, coordinate systems, materials, element types, element properties) are written into the corresponding lists. Initially, the lists “SOLID”, “ELGR” and “NDGR” are empty.
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Selection of elements by their material numbers or element types can be also be carried out this way (vol.2 chapter 10).
SIMULIA Tosca Structure The Model
3.8
Coordinate Systems (CS_DEF) In certain situations, the definition of solids and displacement directions requires the coordinate systems that differ from those defined in the FE model. Cartesian and cylindrical coordinate systems defined in the FE model are accessible in Tosca Structure and can be referenced in the parameter file by their names. For details and exceptions refer to chapter 11.1.4 Coordinate Systems (Abaqus), chapter 11.2.4 Coordinate Systems (ANSYS), chapter 11.3.3 Coordinate Systems (Marc), chapter 11.4.3 Coordinate Systems (MSC Nastran) and chapter 11.5.4 Coordinate Systems (PERMAS). Additionally, the command CS_DEF of Tosca Structure parameter file defines the coordinate systems using either the IDs of existing nodes, or coordinates and rotation angles (if needed). Each coordinate system has an ID_NAME value (editable by the user) that is then used in order to reference the coordinate system. In Tosca ANSA environment, the list of defined coordinate systems opens when the item COORD of the database is clicked twice:
Viewing the coordinate systems in Tosca ANSA environment
The selection window (the right window in Fig. 28) allows the user to create, edit or delete coordinate systems. An alternative way is to use the buttons in CS_DEF group of Modules Buttons window. The button INFO opens the list of defined coordinate systems that is basically equivalent to the selection window. The names of the buttons that create new coordinate systems depend on the selected solver; they are described below in details.
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Fig. 28
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In Tosca Structure.gui, a new coordinate system is created by Command | CS_DEF main menu command of Tosca Structure.pre screen:
Fig. 29
Definition of coordinate systems in Tosca Structure.gui
Note that the definition of a coordinate system in Tosca ANSA environment, in case that the coordinates are used, follows the guidelines of some solver (mostly Nastran) and is different from one used in Tosca Structure.gui. During the output of the parameter file, Tosca ANSA environment converts the coordinate systems to the format supported by Tosca Structure. In case of coordinate systems defined using nodes, the definitions are basically the same.
Definition by three nodes In Tosca ANSA environment, the button corresponding to the creation of a new coordinate system using three nodes is called CORD1 (Nastran), NODE (Abaqus) or CS (ANSYS); in the latter case, only Cartesian coordinate systems are supported; in the other two cases, the type of the coordinate system is chosen in the drop down list.
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SIMULIA Tosca Structure The Model
Coordinate system type Cartesian
Cylindrical
Spherical
solver Abaqus
CS_DEF button label
COORD database
Z RECTANGULAR
ORIENTATION_NODES_R
RECTANGULAR
ORIENTATION_NODES_DYN
Nastran
CORD1R
CORD_NODES_R
ANSYS
CS
LOCAL_NODES_DYN
Abaqus
CYLINDRICAL
ORIENTATION_NODES_C
Nastran
CORD1C
CORD_NODES_C
ANSYS
not supported
not supported
Abaqus
SPHERICAL
ORIENTATION_NODES_S
Nastran
CORD1S
CORD_NODES_S
ANSYS
not supported
not supported
In each case, after the command is chosen, the user selects three nodes from the model that are used as follows: • the first node is the origin;
• the axis that follows after the first one (i.e., Y- or X-axis) lies in the plane defined by the three nodes, perpendicular to the first axis and closer to the direction from the origin to the third node;
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• the direction from the origin to the second node is the direction of the first axis that is X-axis (in case of NODES | RECTANGULAR (Abaqus), CS (ANSYS) or ..._NODES_DYN (in selection window)) or Z-axis (otherwise);
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SIMULIA Tosca Structure Coordinate Systems (CS_DEF)
• the last axis is perpendicular to the first and the second one, forming a positively oriented basis.
Fig. 30
Definition of coordinate systems using three nodes in Tosca ANSA environment and in Tosca Structure.gui
In Tosca Structure.gui, the IDs of nodes should be entered in the corresponding fields, and also the fields Axis (x-axis or z-axis) and Plane (xy-plane or xz-plane) should be specified. Then, the first chosen node (Node ID of Origin field) is the origin, the second node (Node on Axis field) defines the axis (specified in Axis field) as described above, and the third node (Node in Plane field) is needed to define the plane according to Plane field. Example A Cartesian coordinate system with the label, CS_12, should be defined by the three nodes 101, 102 and 103. Node 101 is located at the origin of CS_12, node 102 is on Z axis and node 103 is in XZ plane:
ID_NAME CS_TYPE DEF_TYPE CS_AXIS NODE_ORIGIN NODE_AXIS NODE_PLANE
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= = = = = = =
CS_12 RECTANGULAR NODE Z_XZ 101 102 103
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SIMULIA Tosca Structure The Model
END_
z 102
103 CS_12
y
101 x Fig. 31
3.8.2
Definition of a coordinate system by three nodes
Definition by coordinates of three points
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Instead of choosing three existing points, the coordinates of three arbitrary points, plus, optionally, one rotation angle can be used in order to define a coordinate system in Tosca ANSA environment. In Tosca Structure.gui, this mode of coordinate system definition is not supported; see the next subsection.
Fig. 32
Definition of coordinate systems using coordinates in Tosca ANSA environment
The commands creating the coordinate systems are found under the buttons CORD2 (Nastran), CORD (Abaqus) or LOCAL (ANSYS), as well as in the context menu command New of the selection window for the coordinate systems:
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SIMULIA Tosca Structure Coordinate Systems (CS_DEF)
Coordinate system type
solver
Cartesian
Abaqus
Cylindrical
Spherical
CS_DEF button label
COORD database
RECTANGULAR
ORIENTATION_R
OFFSET TO NODES
ORIENTATION_OFFSET_TO_ NODES
Nastran
CORD2R
CORD_R
ANSYS
RECTANGULAR
LOCAL_R
Abaqus
CYLINDRICAL
ORIENTATION_C
Nastran
CORD2C
CORD_C
ANSYS
CYLINDRICAL
LOCAL_C
Abaqus
SPHERICAL
ORIENTATION_S
Nastran
CORD2S
CORD_S
ANSYS
SPHERICAL
LOCAL_S
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After a command is chosen, the user should select three points from the model. If a point close to an edge is clicked, the middle point of the edge is chosen; otherwise, if the point is close to a node, this node is chosen. Please take care not to select the edges in case you need the nodes. To do this, choose a point between the edges going from the node you wish to choose, sufficiently close to the node but not to any edge.
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When all three nodes are chosen, the following dialog appears:
Fig. 33
Definition of coordinate systems using coordinates in Tosca ANSA environment
This window contains the coordinates of the nodes that have just been chosen (A1..A3, B1..B3, C1..C3 fields). This coordinates may be modified; moreover, if it is needed to define the coordinate system using some points that not necessarily coincide with nodes or middle points of edges, the easiest way is to create a coordinate system using any three points and then to set the correct values in the fields of this dialog window. The three points are used as follows: • the first point (A1, A2, A3) is the origin; • the direction from the origin to the second point (B1, B2, B3) is the direction of Z-axis;
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• X-axis lies in the plane defined by the three nodes, perpendicular to Z-axis and closer to the direction from the origin to the third point (C1, C2, C3); • Y-axis is perpendicular to the other two, forming a positively oriented basis. The field RID defines the reference coordinate system (by default, it is set to 0 indicating the global coordinate system). Pressing "?" key in this field opens the list of all defined coordinate systems. The values in A1..C3 fields are interpreted as the points with the corresponding coordinates with respect to the coordinate system that has ID equal to RID field, with RID = 0 corresponding to the global coordinate system. Choosing Abaqus or ANSYS as the solver allows (but not requires) the specification of one rotation angle using "rotation axis" field: choosing an axis (1 to 3, i.e., X to Z) in this field and then an angle in degrees in "rotation angle" field leads to the rotation of the new coordinate system around the specified axis (the "new" one, i.e., calculated basing on the chosen points).
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3.8.3
Definition by origin and rotation angles In Tosca Structure.gui, instead of using three points with given coordinates, the origin and the rotation angles around the three axes are used in order to define a coordinate system. This is done using Local radio button (this is equivalent to setting DEF_TYPE = LOCAL in CS_DEF command):
Fig. 34
Definition of coordinate systems using an origin point and three rotation angles in Tosca Structure.gui
Then, the coordinates of the origin (with respect to the coordinate system specified in Reference CS field) and the three rotation angles are to be chosen. The directions of the axes of the coordinate system are constructed in the following manner: • first, the axes X, Y, Z of the reference coordinate system are taken; • then, the axes are rotated around Z-axis by the first angle in Rotation fields (labeled with 3): axes X’, Y’, Z’ = Z are produced;
• finally, these axes are rotated around X’’ by the third angle (field labeled with 1): axes X’’’ = X’’, Y’’’, Z’’’ are produced that give the directions for the coordinate system axes. All rotations are performed in positive (counter-clockwise) directions; the values of the angles are in degrees. Examples A Cartesian coordinate system with the name CS_14 should be defined relative to the global Cartesian coordinate system CS_0. The point of origin of the new coordinate system should have the coordinates (30, 20, 0). Then, a cylindrical coordinate system CS_15 should be defined relative to CS_14 with the origin at the point (60, 5, 0). CS_15 should be rotated 15° around Z axis: The result coordinate system CS_15 defines a cylindrical coordinate system with origin (90,25,0) with respect to the global Cartesian coordinate system CS_0. The polar axis through the new origin is rotated by 15° around the z-
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• the resulting axes are rotated around Y’ by the second angle (field labeled with 2): axes X’’, Y’’ = Y’, Z’’ are produced;
SIMULIA Tosca Structure The Model
axis. The longitudinal axis is parallel to the original z-axis through the new origin: CS_DEF ID_NAME CS_TYPE DEF_TYPE CS_REF ORIGIN_123 ROTATION_321
= = = = = =
CS_14 RECTANGULAR
LOCAL CS_0 30,20,0 0,0,0
END_
CS_DEF ID_NAME CS_TYPE DEF_TYPE CS_REF ORIGIN_123 ROTATION_321
= = = = = =
CS_15 CYLINDRICAL
LOCAL CS_14 60,5,0 15,0,0
END_
y y CS_15 z
15
x
5
CS_14 20
60
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z CS_0
Fig. 35
3.8.4
30
x
Definition of coordinate systems using the origin and the rotation angles
General remarks about coordinate systems 1. When coordinate systems are loaded via the FE interface, their numbers are treated as names (character strings) in Tosca Structure. For example, the coordinate system 15 (number) in the FE system is defined in Tosca Structure as a coordinate system with the name “15”.
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SIMULIA Tosca Structure Solids (Geometric Primitives)
2. In Tosca Structure the following coordinate system is defined globally and can be addressed at any time: CS_0: Global Cartesian coordinate system 3. A coordinate system defined in Tosca ANSA environment will only be written to the parameter file if it is used for some reason, e.g., as the value of PULL_CS field of DEMOLD_CONTROL dialog. 4. Default name of a coordinate system that is defined in Tosca ANSA environment when using ANSYS solver is "Anonymous CS" (without any index). When defining more than one such coordinate system, their names should be modified so that they are unique.
3.9
Solids (Geometric Primitives)
Fig. 36
3.9.1
Geometric primitives (SOLIDs) in Tosca ANSA environment
Definition in Tosca ANSA environment In Tosca ANSA environment, in order to define a CHECK_SOLID design constraint, call New | CHECK_SOLID command on the item DV_CONSTRAINTS in Task Manager. In the dialog that appears, only the node group for which the relations are checked is specified. Then, one needs to define one or more
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In some applications, it is required that the nodes stay in a certain region, or, conversely, are not allowed to enter a certain region during the shape or bead optimization. In Tosca Structure, such regions can be defined by geometric primitives: in two dimensions, rectangles, circles or circular segments; in three dimensions, bricks, cylinders and cylinder segments are supported. The type of the geometric primitive depends on the coordinate system it is defined with. In the figure, the cylindrical segment 0 ≤ r ≤ 10 , 0 ≤ ϕ ≤ 90 , 5 ≤ z ≤ 10 in the cylindrical coordinate system C2 and the cube 5 ≤ x ≤ 10 , 5 ≤ y ≤ 10 , 5 ≤ z ≤ 10 in the Cartesian coordinate system R1 are shown, as represented in Tosca ANSA environment:
SIMULIA Tosca Structure The Model
SOLIDs using New | SOLID command on the created CHECK_SOLID item that opens the following dialog:
Fig. 37
Geometric primitives (SOLIDs) in Tosca ANSA environment
The field SOLID_PROP defines how the geometric primitive is to be used: • NEUTRAL: has no effect; • VARIATION: defines the allowed region for the nodes in the node group; • RESTRICTED: defines the prohibited region for the nodes in the node group.
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Choosing CS_DEF in CS field and pressing "?" key in CS_DEF field opens the list of all defined coordinate systems. The fields VAL_1_MIN, VAL_1_MAX,.., VAL_3_MAX define the extents of the geometric primitive in each coordinate. For Cartesian coordinate systems, the coordinates are x, y and z; for cylindrical coordinate systems, they are r, phi and z. The list of all defined SOLIDs is opened by the button SOLID in RESTRICTION panel of Modules Buttons in Tosca ANSA environment.
3.9.2
Definition in Tosca Structure.gui The main menu command Command | SOLID in Tosca Structure.pre screen of Tosca Structure.gui creates a new geometric primitive. This command opens the window where the type of the geometric primitive (Neutral, Varia-
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SIMULIA Tosca Structure Solids (Geometric Primitives)
tion or Restricted), the coordinate system and the extents of the geometric primitive in each coordinate are edited. See the previous subsection for more information about these fields. The field ID_NAME defines the name of the geometric primitive, so that it can be referenced in the DVCON_SHAPEcommand (see vol.2 chapter 6.3.3).
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Remarks Another usage of geometric primitives in Tosca Structure is in SELECT command. In this case, the nodes that lie inside a geometric primitive defined using a SOLID command are selected. Node selection in solids is independent of the mesh density of the FE model, only depending of geometric dimensions. This selection method is more complicated than other methods but is highly recommended for models with varying mesh density.
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SIMULIA Tosca Structure Terms for Optimization
4
Terms for Optimization In this chapter typical optimization definitions are explained. What are your targets? What are your restrictions? Which values define your targets and restrictions?
Overview To optimize anything you need to know what to optimize. Do you want to minimize stresses? Or maximize all eigenvalues? The two above statements are too unclear for defining an optimization. Therefore, we usually reduce the “what” to well defined terms, say: Minimize the maximal nodal stresses of load case 1 and 2, or maximize the sum of the first 5 eigenvalues. The goal or objective of an optimization is usually called the objective function (OBJ_FUNC), e.g. when you want to minimize or maximize some well defined terms. You may also want to enforce certain values, for example a displacement of a given node must not exceed a certain value. This would be defined through a CONSTRAINT. In Tosca Structure the objective function depends upon at least one term or more, whereas a constraint always depends on exactly one term. These terms or responses are in Tosca Structure called design responses or DRESP. DRESP’s are the fundamental definitions of the optimization problem. In Tosca ANSA environment the DRESP’s are available under the OBJ_FUNC_ITEM_1 item and the CONSTRAINTS item. Most DRESP definitions depend on a node or element group, but not all e.g. eigenfrequencies (DRESP, TYPE=DYN_FREQ). This node or element group may also consist of one single item, say one node, e.g. displacement in Xdirection of a node (DRESP, TYPE=DISP_X). The optimization problem is summarized in the OPTIMIZE command and the dependencies can be visualized in following way:
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4.1.1
Mathematical formulation An optimization problem can be stated as:
min ( Φ ( U ( x ), x ) ) s.t. Ψ i ( U ( x ), x ) ≤ 0 s.t.
gi ( x ) ≤ 0
where Φ is the objective function (OBJ_FUNC) which depends on the state variables, U, as well as on the design variables x (DV_BEAD, DV_SHAPE or DV_TOPO). The problem may be constrained by the constraints ψ i (volume 3: CONSTRAINT), and may have the design variable constraints g i (DVCON_BEAD, DVCON_SHAPE or DVCON_TOPO). Note, that maximizing the objective is the same as minimizing – Φ . For minimization (MIN) or maximization (MAX) the objective function consists of a sum of design responses ( ϕ i ). Each design response can be given a ref weight ( w i ) and a reference value ( ϕ i ). By minimizing or maximizing the objective one gets the formulations: N
ref Φ = min w ( ϕ ( ( U ( x ), x ) ) ) – ϕ i ) i=1 i i N
ref Φ = max w ( ϕ ( ( U ( x ), x ) ) ) – ϕ i ) i=1 i i
Another important optimization formulation is to minimize the maximum design response, the so-called MIN-MAX-formulation: ref
s.t.
Ψ i ( U ( x ), x ) ≤ 0
s.t.
gi ( x ) ≤ 0
The MINMAX formulation should always be used for controller based optimization. For sensitivity based optimization MIN or MAX are prefered because they tend to converge better and faster. Note remark in next section regarding default reference value and shape optimization.
4.2
Objective Function The objective function defines the values to be maximized or minimized during optimization. This function may depend analysis results, geometric values or combinations of those.
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Φ = minmax { w i ( ϕ i ( U ( x ), x ) – ϕ i ) }
SIMULIA Tosca Structure Terms for Optimization
4.2.1
Overview The objective function depends upon results of the finite element analysis such as compliance, displacements, stresses, reaction forces, internal forces, eigenfrequencies or properties of the finite element model such asmaterial volume or nodal positions. These results are combined to scalar values using the so called ’design responses’. Initially, one or several responses for the objective function have to be defined using the command DRESP. These responses are then added to the objective: DRESP (scalar value) DRESP (scalar value) DRESP (scalar value) ...................... Fig. 38
OBJ_FUNC
MIN (scalar values) MAX (scalar values) MINMAX (scalar values)
Defining an objective function
Weight and reference values can be applied in the combination using the command OBJ_FUNC. OBJ_FUNC ID_NAME DRESP DRESP DRESP DRESP ... TARGET
= = = = =
... id_name_1, id_name_2, id_name_3, id_name_4,
WEIGHT, WEIGHT, WEIGHT, WEIGHT,
REFERENCE REFERENCE REFERENCE REFERENCE
= MIN | MAX | MINMAX
The ID_NAME of the OBJ_FUNC must be referenced in the OPTIMIZE command to activate the objective function. The WEIGHT and REFERENCE values are optional. The default weighting ref factor is w i = 1 and the default reference value is ϕ i = 0 , except for controller based shape optimization, see Remark. See also equations in chapter 4.1.1 Mathematical formulation. Because of the default values the user has not to define WEIGHT and REFERENCE for the most common optimization formulations. The command TARGET can be set to MIN, MAX or MINMAX indicating if the objective function is minimized or maximized or a min-max formulation is used.
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END_
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In logfile TOSCA.OUT the object function value can be monitored: --------------------------------------------------------------------of OBJ_FUNC_TERM Value Weight Reference | --------------------------------------------------------------------DRESP_MAX_MISES1 161.820 1.00000 92.8566 DRESP_MAX_MISES2 80.9101 1.00000 92.8566 --------------------------------------------------------------------of OBJ_FUNC (based on objective function terms): 68.9636
In above example the total objective function Φ =68.9636. Each DRESP ϕ 1 = DRESP_MAX_MISES1 = 161.820 and ϕ 2 = DRESP_MAX_MISES2 = 80.9101. Also the above shows the weight and reference value of each term. These values can also be found in two extra log-files, optimization_report.csv and optimization_status_all.csv. The first file only lists DRESPs that are included in the optimization task as objective function or constraint. The latter lists all DRESPs defined in the parameter file. Example: Example optimization_report.csv imported into a spread sheet:
ref
ti = wi ( ϕi – ϕi ) If constraints are defined in optimization task these are also included in optimization_report.csv and optimization_status_all.csv. Remark 1. For controller based shape optimization (chapter 6 Shape Optimization) ref the reference value ( ϕ i ) has a special meaning. The reference value is the value around which Tosca Structure homogenizes the stress around. ref Thus, a value ϕ i = 0 usually does not make sense and Tosca Struc-
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In above example first the total objective function Φ is listed for each iteration as MINIMIZE_MAX_MISES. The objective function is always the first colomn. Then each DRESP in the ϕ 1 = DRESP_MAX_MISES1 and ϕ 2 = DRESP_MAX_MISES2 is listed as OBJ_FUNC_DRESP:DRESP_MAX_MISES1 and OBJ_FUNC_DRESP: DRESP_MAX_MISES2. After each DRESP the terms are listed: OBJ_FUNC_TERM:DRESP_MAX_MISES1 and OBJ_FUNC_TERM: DRESP_MAX_MISES2. The terms include weight and reference value and are given as:
SIMULIA Tosca Structure Terms for Optimization
ref
ture calculates a default reference value if REFERENCE ( ϕ i ) is unset. The reference calculated can be seen in TOSCA.OUT --------------------------------------------------------------------of OBJ_FUNC_TERM Value Weight Reference | --------------------------------------------------------------------DRESP_MAX_MISES 92.5353 1.00000 87.4261 ---------------------------------------------------------------------
2. Also, for controller based shape optimization the user must either set all REFERENCE-values or none at all (automatic reference value calculation). 3. Please note that the reference value for the MINMAX function differs from the above definition by eigenfrequency optimization for the sensitivity based algorithm, see for example chapter 7.6.2.5 Maximize band gaps. 4. Please note that the reference value for von Mises stresses in topology optimization differs from the above definition (see also vol.2 chapter 4: Reference stress for objective function). The design responses (DRESP) listed in OPTIMZE will be summed up taking into account the individual weighting and reference values (see also chapter 4.1.1 Mathematical formulation) if TARGET is set to MIN or MAX. A min-max formulation is applied if TARGET is set to MINMAX. Then the design responses (DRESP) are dealt with individually in a multidisciplinary optimization taking into account the individual weighting and reference values.
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4.2.2
Minimization or maximization of an objective function This section deals with the minimization or maximization of the objective function. Then the optimization formulation consists of an objective function and a set of constraints as shown in the first equation of chapter 4.1.1 Mathematical formulation. In vol.2 chapter 5.4, vol.2 chapter 6.4 and vol.2 chapter 7.4 is described which response types are allowed in the objective functions for topology, shape and bead optimization and how they can be combined. In vol.2 chapter 5.5, vol.2 chapter 6.5 and vol.2 chapter 7.7 is described which response types are allowed as constraints and how these are added to the constraints. The objective can be minimized or maximized using the MIN and MAX in the TARGET parameter of the OBJECTIVE command, respectively. In these cases the values for the objective function defined by the DRESPs are summed up. E.g., if the objective should be minimized (or maximimized): OBJ_FUNC
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SIMULIA Tosca Structure Objective Function
ID_NAME DRESP DRESP ... TARGET
= ... = ... = ... = MIN (or MAX)
END_
where the DRESP definitions are referring to the desired responses for the objective function using the ID name of the defined responses. The defined responses which should be minimized (or maximized) have to be valid design responses (see chapter 4.4 Design Responses).
4.2.3
Multidisciplinary objectives (minmax formulation) This section deals with the minimization of the maximum term referenced in the objective function. In this case the value of the objective function is generated with a maximum function over a set of terms defined by Design Responses. In chapter 4.4 Design Responses is described which response types are allowed in the objective and how they can be combined (see also chapter 4.1.1 Mathematical formulation). If the maximum objective term should be minimized, the definition is as follows: OBJ_FUNC = ... = ... = ... = MINMAX
END_
where the DRESP definitions are referring to the desired design responses for the objective function using the ID name of the defined responses. The defined responses that should be minimized have to be valid design responses (see also chapter 4.4 Design Responses).
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ID_NAME DRESP DRESP ... TARGET
SIMULIA Tosca Structure Terms for Optimization
Definition in Tosca ANSA environment Tosca ANSA environment only allows design responses to be defined within either an objective function (OBJ_FUNC) or within the CONSTRAINT object.
Fig. 39
Definition of the minimization of the objective function.
Fig. 40
Definition of the design responses for the objective function.
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In addition to the target definition for the objective function definition, the user also has to define the design responses for the objective function combined by the target. These terms then will be minimized or maximized.
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SIMULIA Tosca Structure Objective Function
Definition in Tosca Structure.gui For the definition of the objective function within Tosca Structure.gui, the design responses that should be minimized or maximized have to be defined previously. Please refer to the chapter vol.2 chapter 4.4 and vol.2 chapter 4.5.
Fig. 41
Defining the objective function using a previously defined design response.
Definition in Tosca Extension for ANSYS/Workbench
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In Tosca Extension for ANSYS/WB an objective function has to be added to the project using the corresponding button. A design response has to be
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defined beforehand and can be referenced within the objective function. Choose whether you want the design response to be minized or maximized.
Fig. 42
Constraints Normally, optimization tasks have some restrictions. These restrictions limit the values of the design responses or linear combinations of the design responses. If the constraint is not fulfilled the optimization result is not feasible. Tosca Structure allows inequality constraints in all sensitivity based algorithms. Equality constraints are only allowed in the controller based approaches. This means that the item EQ_VALUE defining the equality value may only be used for controller based optimization. LE_VALUE and GE_VALUE are to be used for the upper and lower values of constraints in sensitivity based optimization algorithms. An equality constraint is given as (see also vol.2 chapter 4.1.1, Mathematical formulation):
Ψ = ϕ
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Add and define an objective function and select a previously defined design response
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where ϕ is the value of the design response. Inequality constraints are given as (see also chapter 4.1.1 Mathematical formulation):
Ψ≤ϕ Ψ≥ϕ
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The can be defined as ABS or REL, short for absolute or relative value of the design response in the constraint. When using the relative value the design response is normalized with respect to the initial value of the design response (design response value of optimization iteration 0).
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Definition in Tosca ANSA environment
Fig. 43
Definition of the constraint using the related design response.
For the definition of a constraint within the Tosca Structure.gui the design response which should be constraint has to be defined previously. Please
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refer to vol.2 chapter 4.4 and vol.2 chapter 4.5.
Fig. 44
Defining a constraint with a previously defined design response.
Definition in Tosca Extension for ANSYS/Workbench In Tosca Extension for ANSYS/WB add a constraint to the project by clicking on Optimization | Constraint. Within this constraint, choose a previously defined design response and set the other desired settings.
Add and set up a constraint using a previously defined design response
Tosca Structure Parameter file: A constraint definition is given as: CONSTRAINT ID_NAME DRESP MAGNITUDE EQ_VALUE LE_VALUE GE_VALUE END_
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Fig. 45
SIMULIA Tosca Structure Terms for Optimization
The must be referenced in the OPTIMIZE command for the constraint to be activated. Only one of the constraint items EQ_VALUE, LE_VALUE and GE_VALUE may be defined. They define the constraint value Ψ.
Fig. 46
Normalized output of constraint in Tosca Structure.view
Remark
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1. In the above plot CONSTRAINT_NORM are all constraints plottet, normalized. CONSTRAINT_NORM is a special normalization so all fullfiled constraints are < 1.0. This also applies to GE_EQUAL constraints.
4.4
Design Responses Most design responses are only available for certain analysis types. Others are independent of the analysis type because they are directly linked to the geometry of the FE-model. Each design response represents one scalar value which can be extracted from the model information (like the volume) or from the FE-results. All design responses always consist of one single scalar value. So although you reference a node or element group in the DRESP definition, Tosca Structure will use a group operator (GROUP_OPER) to either use the maximal
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(MAX), minimal (MIN) or sum of the values (SUM) to combine the responses to a single value. (see also chapter 4.5.1 Group operations for design responses) Although Tosca Structure can handle more load cases within one design response, it is best practice to use one design response for each load case. This is done with the item LC_SET: LC_SET = , ,
If more load cases or sub-steps are referenced in the LC_SET item the maximum (MAX) or minimum (MIN) value will be used within the design response, depending on the setting of load case selection (LC_SEL). If LC_SEL is not set explicitly, a default value is used according to the type of the design response. Using Tosca Structure.gui LC_SEL no longer needs to be defined manually. Again, this is done to obtain exactly one single value. See also chapter 4.5.2.1 Load case specification (LC_SET). Command in parameter file: DRESP ID_NAME DEF_TYPE TYPE VAR_OPER UPDATE GROUP_OPER EL_GROUP ND_GROUP ELEM NODE LC_SET LC_SEL
= = = = = = = = = = = =
..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .....
Most entries have default values. See definition of a design response (DRESP) in the commands manual for more information.
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Definition in Tosca ANSA environment Tosca ANSA environment admits design responses to be defined within an objective function (OBJ_FUNC) and within a CONSTRAINT.
Fig. 47
Possible categories of design responses for sensitivity based topology optimization. The number of possibilities varies with respect to optimization type.
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Allowed objective functions and constraints are shown in the Tosca ANSA environment, see Fig. 47.
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Definition in Tosca Structure.gui:
a)
b)
Fig. 48
Defining design responses in Tosca Structure.gui. a) Apply Template to access the simplest and most used optimization responses. b) The category selector is used to switch between the main categories of the design responses.
Add a design response to the project by clicking Optimization | Design Response. Then choose Category and Response Type and the other settings.
Fig. 49
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Add a design response to the project and define the desired settings
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Definition in Tosca Extension for ANSYS/Workbench
SIMULIA Tosca Structure Terms for Optimization
4.4.1
Compliance (Stiffness Optimization) c =
STRAIN_ENERGY
uT Ku
Analysis types: Static linear or non-linear analysis
Ku = F where K may be linear or non-linear
TOPO OBJ_FUNC CONSTRAINT Table 8
SHAPE
BEAD
SIZING
C*,S*
C,S
S
S*
S
S
Compliance (C = controller, S = sensitivity) * Topology optimization allows nonlinearities as well as temperature loading
Compliance has a large popularity within scientific publications, and compliance is of large importance in engineering applications even though the expression may not be widely known outside the optimization community. Compliance may be expressed as the overall flexibility or “softness” of a structure given by the sum of elastic or strain energy in a structure. Thus, compliance can be seen as a stiffness measure or more correctly the reciprocal of stiffness. To maximize the global stiffness we therefore minimize compliance. Compliance is defined in Tosca Structure by the sum of strain energy of all elements.
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Remarks: 1. In certain cases including prescribed displacements or thermal fields "minimizing compliance" will result in a stiff structure. If a load case is driven by prescribed displacements or a thermal field the elastic energy / compliance will only decrease if the structure is made softer. If only prescribed displacements are present without external loading, the strain energy should be maximized to obtain optimal results:
R ⋅ u∗ max -------------- 2 with R=reaction force and u* = nodal prescribed displacements. If both external loading and prescribed displacements are present, a new energy stiffness measure is introduced (see chapter 4.4.2 Energy stiffness
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measure). The "standard" strain energy does not lead to optimal results:
P ⋅u R ⋅ u∗ ---------+ -------------2 2 with P=external loading and u = corresponding nodal deflections of the loaded nodes. 2. Compliance is equal to the overall strain energy. Therefore the strain energy for all elements is required. Any other element group is not allowed, because in such cases the optimization problems are not self-adjoint. 3. If no LC_SET is specified (no load case is selected from the existing load cases) Tosca Structure will always read the last sub-step for each load case in case of non-linear loading.
4.4.1.1 Compliance example We want to minimize compliance (maximize stiffness) of a structure with respect to the 2nd load case in our finite element input deck.
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Definition in Tosca ANSA environment Tosca ANSA environment only admits design responses to be defined below either OBJ_FUNC_ITEM_1 item or CONSTRAINTS item.
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1. In the context menu of OBJ_FUNC_ITEM_1, choose Edit. In OBJ_FUNC_ITEM dialog choose TARGET = MIN, because the compliance is to be minimized in order to maximize the stiffness.
Fig. 50
Choosing compliance as objective function in Tosca ANSA environment
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2. Apply New | COMPLIANCE command on OBJ_FUNC_ITEM_1. In the OBJ_FUNC_TERM dialog, press "?" key in LC_SET field. In the LC_SET dialog click MORE and enter the load case number (2 for the second load case) in the second text field of the appeared line.
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Definition in Tosca Structure.gui 1. Choose Command | DRESP. Click Apply Template and choose Sum of Strain Energy.
Fig. 51
Defining compliance design response using Tosca Structure.gui
2. To choose load case click Add LC. In the field Load case number enter 2.
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3. Choose Command | OBJ_FUNC.
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4. Click Add Dresp and choose the previously defined design response for compliance.
Fig. 52
Choosing DRESP for compliance as objective function in Tosca Structure.gui
Definition in Tosca Extension for ANSYS/Workbench
Fig. 53
Add and define a design response
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In order to minimize the compliance using Tosca Extension for ANSYS/WB, add a design response at first and choose Stress/Strain as Category and Strain Energy as Response Type. In addition, select the desired Load Cases.
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When done, add an objective function to the project. Select Minimize sum as Target and select the previously defined design response in a new tab.
Fig. 54
Add an objective function to the project and select the design response for a minimization
Tosca Structure Parameter file:
OBJ_FUNC ID_NAME DRESP TARGET END_
4.4.2
= = = = = =
compliance STRAIN_ENERGY SYSTEM STATIC,2, ALL_ELEMENTS SUM
= MY_OBJ_FUNC = compliance = MIN
Energy stiffness measure ENERGY_STIFF_MEASURE
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c = P ⋅ u – R ⋅ u∗
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DRESP ID_NAME TYPE DEF_TYPE LC_SET EL_GROUP GROUP_OPER END_
SIMULIA Tosca Structure Terms for Optimization
Analysis types: Static linear or non-linear analysis TOPO
SHAPE
BEAD
SIZING
OBJ_FUNC
S
S
CONSTRAINT
S
S
Table 9
Energy stiffness measure (C = controller, S = sensitivity)
ENERGY_STIFF_MEASURE describes a new stiffness measure (without physical meaning) for simultaneous handling of external loading and prescribed displacement in stiffness optimization. For stiffness optimization of structures with only external loading the strain energy should be minimized (see chapter 4.4.1 Compliance (Stiffness Optimization)):
P⋅u min ---------- 2 where P is the external loading and u is the corresponding nodal deflections of the loaded nodes. If a load case is driven by prescribed displacements the elastic energy / compliance will only decrease if the structure is made softer. If only prescribed displacements are present without external loading, the strain energy should be maximized to obtain optimal results:
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R ⋅ u∗ max -------------- 2
where u* are the nodal prescribed displacements being different from zero and R are the corresponding nodal reaction forces. The physical strain energy with both external load and prescribed displacements is described as follows but may not lead to optimal stiffness results:
P ⋅ u R ⋅ u∗ θ = ---------- + -------------2 2 The new stiffness measure (ENERGY_STIFF_MEASURE) combines the first two approaches in the following optimization formulation :
P ⋅ u R ⋅ u∗ min ---------- – -------------- 2 2
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Remarks: 1. Energy stiffness measure should always be minimized (TARGET = MIN) in the objective function independent upon external loading, prescribed displacement and thermal loading. This requires less user effort compared to total strain energy ! 2. Energy stiffness measure should always be applied to ALL_ELEMENTS. 3. Thermal loading is allowed as long the thermal loading is independent upon material distribution 4. Energy stiffness measure can also be applied in a min-max optimization formulation (TARGET = MINMAX). 5. The energy stiffness measure is also allowed in constraints. 6. If only external loading is present in a given loadcase then the energy stiffness measure (TYPE = ENERGY_STIFF_MEASURE) is equal to the total strain energy (TYPE = STRAIN_ENERGY) also called the compliance. 7. If only prescribed displacements are present in a given loadcase then the energy stiffness measure (TYPE = ENERGY_STIFF_MEASURE) is equal to the minus total strain energy (TYPE = STRAIN_ENERGY) also called the compliance. 8. If both external loading and prescribed displacements are present in a given loadcase then the energy stiffness measure (TYPE = ENERGY_STIFF_MEASURE) is not equal to the total strain energy (TYPE = STRAIN_ENERGY). 9. The energy stiffness measure is not a physical energy measure!
11.Thermal loading is not supported. 12.Mass dependent loading (e.g. gravity) is not supported.
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10.The energy stiffness measure is not available for the controller based optimization strategy.
SIMULIA Tosca Structure Terms for Optimization
4.4.2.1
Example for energy stiffness measure Maximize the stiffness by minimizing the energy stiffness measure subject to a mass constraint of 35 %. Varying prescribed displacements are assigned.
Fig. 55
Minimize energy stiffness measure for varying prescribed displacements.
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Definition in Tosca ANSA environment Not yet supported by Tosca ANSA environment.
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Definition in Tosca Structure.gui 1. Choose Command | DRESP. Choose Type | ENERGY_STIFF_MEASURE. Select ALL_ELEMENTS in dropdown menu Elementgroup.
Fig. 56
Defining compliance design response using Tosca Structure.gui
2. To choose load case click Add LC. In the field Load case number enter 2.
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3. Choose Command | OBJ_FUNC.
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4. Click Add Dresp and choose the previously defined design response for energy stiffness measure.
Fig. 57
Choosing DRESP for compliance as objective function in Tosca Structure.gui
Tosca Structure Parameter file: DRESP ID_NAME DEF_TYPE TYPE EL_GROUP GROUP_OPER
= = = = =
... SYSTEM ENERGY_STIFF_MEASURE ALL_ELEMENTS SUM
END_
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4.4.3
Displacement and rotation DISP_X, DISP_Y, DISP_Z
ui
ROT_X, ROT_Y,ROT_Z
θi
DISP_X_ABS, DISP_Y_ABS, DISP_Z_ABS
u i2
DISP_ABS
u x2 + u y2 + u z2
Analysis types: Static linear or non-linear analysis*
Ku = F where K may be linear or non-linear.
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TOPO
SHAPE
BEAD
SIZING
OBJ_FUNC
S*
S
S
CONSTRAINT
S*
S
S
Table 10
Displacements and rotations (C = controller, S = sensitivity) * Nonlinear analysis allowed
Displacements and rotations are the primary variables in the FEM solution. They are also very often the main interest of the FEM-analyst, e.g. the maximal displacement. Displacements and rotations should be defined using a nodal id, although node groups may also be referenced. Large node groups can lead to major performance issues, see chapter 4.5.1 Group operations for design responses. Displacements and rotations can also be referenced in a local coordinate system. See also chapter 4.5 Combined Terms. Remark 1. It is always strongly recommended that the user defines design elements attached to nodes used in displacement definitions or reaction definitions (DRESP) as frozen elements. This stabilizes the optimization iterations and often leads to a significant lower number of optimization iterations.
4.4.3.1 Example of a displacement design response
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The absolute displacement of node 10 in local coordinate system CS_1 is to be minimized.
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Definition in Tosca ANSA environment Apply New | Displacement command on OBJ_FUNC_ITEM_1.
Choosing displacement as objective function.
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Fig. 58
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Definition in Tosca Structure.gui
Fig. 59
Choosing displacement as design response
Definition in Tosca Extension for ANSYS/Workbench
Fig. 60
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Add and define a design response for displacement
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In Tosca Extension for ANSYS/WB an objective function containing a displacement has to be set up in two steps. At first, add and define a design response containing the displacement. Therefore add a design respone to the project, choose Displacement as Category and Absolute as Response Type.
SIMULIA Tosca Structure Terms for Optimization
In order to select the node: activate a nodal selection first by clicking Show mesh and Select mesh. Then select the desired node graphically.
Fig. 61
Activate nodal selection
Then call this design response in an objective function. In order to set up a minization function, add an objective function to the project, select Minimize sum as Target, and choose the previously defined design response in a new tab.
Fig. 62
Set up an objective function for a minization
Command in parameter file The resulting command in the Tosca Structure parameter file is then:
ID_NAME TYPE CS_REF DEF_TYPE LC_SET NODE END_
= = = = = =
disp_x_abs DISP_X_ABS CS_1 SYSTEM STATIC, 2, 10
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DRESP
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4.4.4
Reaction force REACTION_FORCE_ABS
F =
REACTION_FORCE_X, REACTION_FORCE_Y, REACTION_FORCE_Z
F =
Ke ui Ke ui
REACTION_FORCE_X_ABS, REACTION_FORCE_Y_ABS, REACTION_FORCE_Z_ABS
F =
Ke ui
REACTION_MOMENT_ABS
F =
REACTION_MOMENT_X, REACTION_MOMENT_Y, REACTION_MOMENT_Z
F =
Ke ui Ke ui
REACTION_MOMENT_X_ABS, REACTION_MOMENT_Y_ABS, REACTION_MOMENT_Z_ABS
F =
Ke ui
Where e are the elements connected to the nodes i on supported DOFs. Analysis types: Static linear or non-linear analysis
TOPO
SHAPE
BEAD
SIZING
OBJ_FUNC
S
S
S
CONSTRAINT
S
S
S
Table 11
Reaction forces (C = controller, S = sensitivity)
The reaction forces and the reaction moments can only be defined as a DRESP (design response) in the sensitivity based bead and topology optimization. Remarks 1. A reference coordinate system (CS_REF) cannot be used for the reaction force responses defined using REACTION_FORCE_ABS and REACTION_MOMENT_ABS. 2. The reaction force, reaction moment, internal force and/or internal moment in a given DOF of a node applied in the optimization formulation has to 2 - 102 User Manual
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Ku = F where K may be linear or non-linear.
SIMULIA Tosca Structure Terms for Optimization
have stiffness in the DOF direction similar to the DOF direction of the reaction force or internal force used in the optimization formulation. Meaning that at least one of the elements surrounding the node has to have stiffness in the DOF direction similar to the reaction force or internal force direction applied in the optimization formulation. Hence, this criterion is also physical meaningful since a structure having no stiffness in a given direction will always have zero reaction force in this direction. 3. Differences between reaction forces can be defined using group operations. 4. Examples for combinations of reaction forces can be found in chapter 4.5.1.4 Group operations for reaction forces/moments.
4.4.4.1 Example of reaction force design response Define a reaction force in Y-direction (REACTION_FORCE_Y) of the global coordinate system (CS_0) of node 112072. Definition in Tosca ANSA environment REACTION_FORCE on OBJ_FUNC_ITEM_1 or CONST-
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Apply New | STRAINTS item.
Fig. 63
Defining the reaction force as constraint (choose magnitude =ABS)
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Definition in Tosca Structure.gui
Fig. 64
Defining the reaction force as design response
Definition in Tosca Extension for ANSYS/Workbench
Fig. 65
Reaction force design response setup
Command in parameter file The resulting command in the Tosca Structure parameter file yields: DRESP ID_NAME DEF_TYPE TYPE
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= my_reac = SYSTEM = REACTION_FORCE_Y
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In order to set up a reaction force design response in Tosca Extension for ANSYS/WB, add a design response to the project. Set the Category to Reaction Force/Moment and the Response Type to Y.
SIMULIA Tosca Structure Terms for Optimization
NODE LC_SET GROUP_OPER CS_REF END_
4.4.5
= = = =
112072 ALL,2,All Max CS_0
Internal force INTERNAL_FORCE_ABS
F =
INTERNAL_FORCE_X, INTERNAL_FORCE_Y, INTERNAL_FORCE_Z
F =
Ke ui Ke ui
INTERNAL_FORCE_X_ABS, INTERNAL_FORCE_Y_ABS, INTERNAL_FORCE_Z_ABS
F =
Ke ui
INTERNAL_MOMENT_ABS
F =
INTERNAL_MOMENT_X, INTERNAL_MOMENT_Y, INTERNAL_MOMENT_Z
F =
Ke ui Ke ui
INTERNAL_MOMENT_X_ABS, INTERNAL_MOMENT_Y_ABS, INTERNAL_MOMENT_Z_ABS
F =
Ke ui
For the elements e attached to the nodes i.
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Analysis types: Static linear or non-linear analysis
Ku = F where K may be linear or non-linear . TOPO
SHAPE
BEAD
SIZING
OBJ_FUNC
S
S
S
CONSTRAINT
S
S
S
Table 12
Internal forces (C = controller, S = sensitivity)
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The internal forces and the internal moments can be defined as a DRESP (design response) in the sensitivity based bead and topology optimization. The internal forces as DRESPs are supported for Abaqus, ANSYS, Marc, MSC Nastran.
a)
b)
Fig. 66
Internal forces are defined through node(s) and element(s). a) Defining the internal axial forces of a bar/beam using one node and one element. b) Defining the internal axial forces of a continuum element by summing up the forces in axial direction using a node group and element group.
As previously shown the internal forces are defined by nodes and elements. Meaning that the design response is defined in the following way:
ID_NAME DEF_TYPE TYPE CS_DEF GROUP_OPER ND_GROUP NODE EL_GROUP ELEM LC_SET
= = = = = = = = = =
..... SYSTEM ..... ..... MAX or .....or .....or .....or .....or .....
SUM use the use the use the use the
NODE-definition ND_GROUP-definition ELEM-definition ELEM_GROUP-definition
END_
Remarks 1. The reaction force, reaction moment, internal force and/or internal moment in a given DOF of a node applied in the optimization formulation has to 2 - 106 User Manual
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DRESP
SIMULIA Tosca Structure Terms for Optimization
have stiffness in the DOF direction similar to the DOF direction of the reaction force or internal force used in the optimization formulation. Meaning that at least one of the elements surrounding the node has to have stiffness in the DOF direction similar to the reaction force or internal force direction applied in the optimization formulation. Hence, this criterion is also physical meaningful since a structure having no stiffness in a given direction will always have zero reaction force in this direction. 2. Internal forces are only supported for elements having node numbers. If the element is not defined by nodes (e.g. some weld element) then the internal forces of this element can not be applied in the optimization. 3. Both node(s) and element(s) always have to be defined for internal forces. 4. See also the tables of supported element types (chapter 11 Solver Specific Features) for a list of elements which can be used for internal forces. 5. A reference coordinate system (CS_REF) can not be used for the internal force responses defined using INTERNAL_FORCE_ABS and INTERNAL_MOMENT_ABS. 6. Internal forces are supported for Abaqus, ANSYS, Marc and MSC Nastran. 7. Internal forces are not supported for PERMAS. 8. Examples for combinations of internal forces can be found in chapter 4.5.1.5 Group Operations for Internal Forces.
Define the sum of internal forces in the Y-direction (INTERNAL_FORCE_Y) of the global coordinate system (CS_0) of node group ND_INTERNAL_GROUP_LEFT connected to the element group EL_INTERNAL_GROUP_LEFT.
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4.4.5.1 Example internal force
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Definition in Tosca ANSA environment Apply New | INTERNAL_FORCE on OBJ_FUNC_ITEM_1 or CONSTRAINTS item.
Defining internal forces as constraint
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Fig. 67
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Definition in Tosca Structure.gui
Fig. 68
Defining internal forces as design response
Definition in Tosca Extension for ANSYS/Workbench Tosca Extension for ANSYS/WB does not support this Tosca Structure feature at the moment. Command in parameter file The resulting command in the Tosca Structure parameter file is:
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DRESP ID_NAME DEF_TYPE TYPE EL_GROUP ND_GROUP LC_SET GROUP_OPER CS_REF END_
4.4.6
= = = = = = = =
internal_force_response SYSTEM INTERNAL_FORCE_Y EL_INTERNAL_GROUP ND_INTERNAL_GROUP ALL,1,All Sum CS_0
Eigenfrequency DYN_FREQ
fj
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DYN_FREQ_KREISSEL
– kf j 1 – --- ln e , k j 30 by default k = ---------f min
Analysis types: Modal analysis 2 2
( 4π f M – K )ϕ = 0
TOPO
SHAPE
BEAD
SIZING
OBJ_FUNC
S*
C, S*
S*
CONSTRAINT
S*
S*
S*
Table 13
Eigenvalues (C = controller, S = sensitivity) *Note that Kreisselmaier-Steinhauser formulation is only allowed in objective function
Eigenvalues are the simplest dynamic responses in structural mechanics. Typical optimization tasks for modal analysis would be to: 1. Maximize the first eigenfrequency (first natural mode) 2. Constrain an eigenfrequency to be higher or lower than a given value
4. Bandgap optimization: Force modes away from a certain frequency Only the first eigenvalue optimization task (1.) is allowed by all optimization types. The other definitions, 2.-4., are only possible with sensitivity based optimization. It is recommended to use the Kreisselmaier-Steinhauser formulation when maximizing the first eigenfrequencies (especially for multiple eigenfrequencies) given by
– kf j 30 1 – --- ln e , by default k = --------- f min k j
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3. Maximize or minimize an eigenfrequency at a certain mode
SIMULIA Tosca Structure Terms for Optimization
The Kreisselmaier-Steinhauser formulation is defined by DYN_FREQ_KREISSEL in the design response. For this design response mode tracking is not needed. For the other optimization tasks mode tracking is often necessary because the modes and thereby the eigenfrequencies may switch during the optimization.
4.4.6.1 Eigenvalue example Define the Kreisselmaier-Steinhauser formulation for the first 5 eigenvalues of the first load case. Definition in Tosca ANSA environment 1. Apply New | EIGENFREQUENCY on OBJ_FUNC_ITEM_1 or CONSTRAINTS item.
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2. In the LC_SET field enter a question mark "?".
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3. Click MORE 5 times and enter sub-steps 1 to 5 and click OK.
?
Maximizing the first five eigenfrequencies using the Kreisselmaier-Steinhauser formulation. www.3ds.com/tosca Version Version 8.1.0 8.1.0 Rev. 1Rev. - 05.2014 1 - 05.2014
Fig. 69
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Definition in Tosca Structure.gui
Fig. 70
Defining the Kreisselmaier-Steinhauser formulation as design response
Definition in Tosca Extension for ANSYS/Workbench
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Add a design response to the project, select Eigenfrequency as Category and DYN_FREQ_KREISSEL as Response Type. In order to select the desired five eigenfrequencies, select Manual as Load Case Selection, chose Modal as Analysis and set Step to 5.
Fig. 71
Design response definition and corresponding Load Case table
Command in parameter file The resulting command in the Tosca Structure parameter file is then: DRESP ID_NAME TYPE DEF_TYPE LC_SET
= = = =
freq_kreissel DYN_FREQ_KREISSEL SYSTEM MODAL,ALL,1-5
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LC_SEL END_
= MIN
4.4.6.2 Mode tracking Mode tracking is available in the sensitivity based optimization and defined using three optimization parameters (OPT_PARAM):
Mode tracking is activated using the optimization parameter MODETRACKING= ON. The second item in MODETRACKING defines the node group which is used for the mode tracking. The node group can improve performance when the node group is small. If no node group is defined all nodes in the model will be applied as default. This is reasonable for small to medium sized finite element models. By default the mode tracking applies for 5 modes. This can be changed by the item MODENUMBERS = . This number should not be set too high otherwise the CPU-time might have a significant increase. Using the parameter MODETRACK_REFERENCE for the Modal Assurance Criterion (MAC) allows the user to define the reference modes applied when tracking the modes during the optimization iterations. If the parameter MODETRACK_REFERENCE is set to INITIAL then the reference modes are set to be the modes of the initial optimization iteration throughout the entire optimization history. If the parameter MODETRACK_REFERENCE is set to PREVIOUS then the reference modes are always set to be the modes of the previous optimization iteration. Typically, setting MODETRACK_REFERENCE to INITIAL is the most consistent comparison in the modetracking. However, some initial modes may change significantly or completely disappear during the optimization iterations and thereby, the INITIAL comparison may fail. When INITIAL as setting for MODETRACK_REFERENCE is failing then the only option is to apply PREVIOUS even though the comparison might not be so consistent as INITIAL.
4.4.7
Equivalent stress SIG_1
σ1
SIG_2
σ2
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MODETRACKING =, MODENUMBERS = MODETRACK_REFERENCE =INITIAL | PREVIOUS
SIMULIA Tosca Structure Terms for Optimization
SIG_3
σ3
SIG_11
σ 11
SIG_22
σ 22
SIG_33
σ 33
SIG_12
σ 12
SIG_23
σ 23
SIG_13
σ 13
SIG_ABS_123
max ( σ 1 , σ 2 , σ 3 )
SIG_ABS_3
σ3
SIG_MISES
SIG_TRESCA
1--2 2 2 { ( σ1 – σ2 ) + ( σ2 – σ3 ) + ( σ1 – σ3 ) } 2 max ( σ 1 – σ 2 , σ 2 – σ 3 , σ 3 – σ 1 )
SIG_BELTRAMI SIG_GALILEI SIG_KUHN SIG_MARIOTTE
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SIG_SANDEL 2
2
2
[ σ1 + σ2 + σ3 1---
2–ν 2 – 2ν -----------------2- ( σ 1 σ 2 + σ 2 σ 3 + σ 1 σ 3 ) ] 1 + 2ν SIG_SAUTER
n
n
n
σ1 – σ2 + σ2 – σ3 + σ3 – σ1
n
SIG_DRUCKER_PRAGER STRAIN_ENERGY
1 T c = --- u Ku 2
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STRAIN_ENERGY_ DENSITY
1 T c = ------- u Ku 2V
DAMAGE_LC
user / program dependent
DAMAGE
user / program dependent
Contact and strain meassures
SIG_CONTACT_SHEAR
p
SIG_CONTACT_ SHEAR_X
τ1
SIG_CONTACT_ SHEAR_Y
τ2
SIG_CONTACT_TOTAL STRAIN_ELASTIC
2
2
2
2
τ1 + τ2
2
p + τ1 + τ2
2 2 2 2 - ( εe ) + ( εe ) + ( εe ) -11 22 33 3 2 2 2 +2 ( ε e ) + ( ε e ) + ( ε e ) 12 13 23
STRAIN_PLASTIC
1--2
2 2 2 2 - ( εp ) + ( εp ) + ( εp ) -11 22 33 3 2 2 2 +2 ( ε p ) + ( ε p ) + ( ε p ) 12 13 23
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STRAIN_TOTAL
2 2 2 2 - [ ε 11 + ε 22 + ε 33 -3 2 2 2 +2 ( ε 12 + ε 13 + ε 23 ) ]
ABQ_ND_PEEQ
1--2
PEEQ, see Abaqus documentation
Analysis types: Any analysis type with stress output or fatigue result
TOPO OBJ_FUNC
SHAPE
BEAD
SIZING
C
CONSTRAINT
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Table 14
Equivalent stress (C = controller, S = sensitivity)
The equivalent stresses are the main input for the shape optimization controller algorithm. All values, whether nodal, from gauss points or elements, are interpolated to the nodes. Equivalent stress is only allowed in the objective function by controller based shape optimization. Typical optimization tasks: 1. Minimize maximal von Mises stress (see vol.2 chapter 6.6.1, Minimization of maximum equivalent stress) 2. Minimize maximal damage (fatigue analysis) 3. Minimize contact pressure in a contact region (see vol.2 chapter 6.7.2, Minimization of contact pressure) Equivalent stresses are always read for ALL_NODES to give the user the most appropriate output. This will give some warnings for nodes which do not
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have any equivalent stress values, e.g., nodes on elements which are not in contact when evaluating SIG_CONTACT_... . Remark: Plastic strain values (TYPE = STRAIN_PLASTIC) are calculated by Tosca Structure and may differ slightly from your solver results.
4.4.8
Stress in topology optimization
2
( σ vMises ) SIG_TOPO_MISES = Max -------------------------2 ⋅ σ y ( f ( ρ i )σ y ) The σ vMises is the elemental centroidal von Mises stress, σ y is the reference stress and f ( ρ i ) is a factor for interpolating the stresses of the elements having intermediate densities (given by the topology optimization, see vol.2 chapter 4: Stress interpolation). Only von Mises stress can be applied in topology optimization. Analysis type: Static linear and non-linear (contact) analysis (no geometrical and material non-linearities in element group) TOPO OBJ_FUNC
S
CONSTRAINT
S
BEAD
SIZING
Weighted centroidal von Mises stress for topology optimization (C = controller, S = sensitivity)
Remarks Stress applied in topology optimization cannot directly be compared to the von Mises stress given as output from the finite element solver. Only for solid elements ( ρ = 1 ) the von Mises stresses given by Tosca Structure stresses is equal to the von Mises stresses as output from the FE-solver (see vol.2 chapter 4: Stress interpolation). Please note: Topology optimization using stresses as DRESP is implemented as a prerelease feature at Tosca Structure version 7.2.0. Consequently, this newly developed feature may not yet be applied to all possible practical scenarios. Thus, we appreciate your feedback since this feature is still under development.
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Table 15
SHAPE
SIMULIA Tosca Structure Terms for Optimization
Stress calculation The von Mises stress is calculated in the elemental centroid for avoiding stress singularities which might be present in the initial model or appear in the non-smoothed topology optimized structures. singular stresses
Fig. 72
Singular stresses caused by the initial model (left) and by a nonsmooth topology optimized structure (right)
Reference stress for objective function The reference stress σ ref is defined in the objective function command or will be automatically calculated by Tosca Structure for the objective function. A reference stress for the objective function terms can be directly defined as OBJ_FUNC ID_NAME = OBJ_FUNCTION_ID DRESP = DRESP_ID_1,, DRESP = DRESP_ID_2,, ........... TARGET = MIN END_
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where and correspond to σ ref . The reference stress values should not be chosen too low as this might cause numerical singularities. This corresponds to 2 2 ( σ vMises ) ( σ vMises ) + α Min α 1 Max -----------------------------Max ------------------------------- 2 ( f ( ρ i )σ ref 1 ) 2 ( f ( ρ i )σ ref 2 ) 2
If the user does not define a reference stress in the objective function command then Tosca Structure automatically determines a reference stress, which is generated in the initial optimization iteration and is written to TOSCA.OUT. Constraint value A limitation on the stresses can be formed for a DRESP of type SIG_TOPO_MISES used in a constraint definition with the LE_VALUE parameter:
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CONSTRAINT ID_NAME DRESP MAGNITUDE LE_VALUE
= = = =
STRESS_CONSTRAINT DRESP_STRESS_ID ABS
END_
This corresponds to restricting the weighted centroidal von Mises stress by the constraint value stress_constraint= σ con : 2
( σ vMises ) Max -----------------------------2- ⋅ σ con ≤ σ con ( f ( ρ i )σ con )
Remarks 1. σ ref is equal to the reference value when the DRESP defined by SIG_TOPO_MISES is applied in the objective function. The reference stress σ ref can be changed by modifying the reference value in the objective. 2. σ con is equal to LE_VALUE (or GE_VALUE) when the DRESP defined by SIG_TOPO_MISES is applied in a constraint. 3. A DRESP being TYPE = SIG_TOPO_MISES can only be applied once in the objective function or as constraint!. 4. Note that a reference stress or constrained stress which is too low might cause numerical singularities.
The factor f ( ρ i ) describes a function for the interpolation of stresses depending of the density ρ i of the element i. The interpolation is needed because during the topology optimization the densities of the elements are modified and can have a minimum value close to zero. Stress values calculated by the solver for transition or soft elements (i.e. elements with low density) have no real physical meaning for the stresses and must be weighted by a factor to allow for a successful optimization convergence.
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Stress interpolation
SIMULIA Tosca Structure Terms for Optimization
. Different densities of several elements during topology optimization
Void
Initial Fig. 73
Optimized
Densities of elements during the optimization: Initial equal density of all elements (bottom left), modified densities during the topology optimization iterations (top) and final density values for the optimized model (bottom right)
The stress interpolation for intermediate densities is similar to the stiffness material interpolation and can be illustrated as
Thus, the stress measure SIG_TOPO_MISES applied in topology optimization cannot be directly compared to the von Mises stresses seen as output from the finite element solver. Only for solid elements ( ρ = 1 ) the
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E ( ρi ) ------------- ∼ f ( ρ i ) E0
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SIG_TOPO_MISES corresponds to the von Mises stresses calculated by the FE-solver. Solid elements:
Von Mises stress = constraint stress:
2
2
( σ vMises ) σ vMises f ( ρ i = 1 ) = 1 -------------------------2 = ------------------( f ( ρ i )σ y ) σ y2 2
σ vMises -------------------- = 1 DRESP = σ vMises = σ con 2 σ con
Element group The element group for the stress measure can consist of both design and non-design elements. Frequently, the initial model for the optimization contains non-physical modeling around loaded nodes and boundary conditions, respectively. The user should avoid including stresses from stress singularities caused by external loaded nodes or by boundary conditions. These singularities are eliminated by excluding these elements from the group used for calculating the DRESP.
The user should exclude elements with loaded nodes and boundary conditions to avoid stress singularities.
Supported element types Supported element types are 3D standard continuum elements which are shown in Fig. 16: • Hexahedral 8 and 20 node elements • Tetrahedral 4 (not recommended!) and 10 node elements • Pentahedron 6 and 15 nodes elements All linear isotropic materials are supported for the elements in the element group. Anisotropic and non-linear materials both inside and outside the design domain (DV_TOPO) are only supported if the stresses of these materials are not a part of the element group applied for calculation of the DRESP of TYPE = SIG_TOPO_MISES.
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Fig. 74
SIMULIA Tosca Structure Terms for Optimization
Pyramidal 5 and 13 node elements as well as shell elements are not supported. Remark: 1. Shear and volume locking in the finite element yield wrong results not only in the finite element analysis but can also cause optimization convergence problems when such stress responses are included in the optimization formulation. Especially, the linear 4 node tetrahedral elements should be avoided. Instead it is recommended to use the quadratic10 node tetrahedral element or the linear 8 node hexahedral element. Loadcases Several loadcases can be defined for the stress measure. Static linear analysis is supported. For static non-linear analysis only contact is supported. Thus, geometrical non-linearities (like large deformation) and non-linear materials are not supported.
4.4.8.1 Example: Stresses in objective function We want to minimize the maximum von Mises stress. For a typical optimization task see chapter 5.6.6 Minimize the maximum stress with volume constraint. Definition in Tosca ANSA environment
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Not yet available with Tosca ANSA environment 13.2.x. Stresses as design responses are only supported for ANSA version 13.3.0 and later.
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Definition in Tosca Structure.gui
Fig. 75
Design response SIG_TOPO_MISES
Definition in Tosca Extension for ANSYS/Workbench
Fig. 76
Design response using SIG_Topo_Mises
Command in Parameter file The design response for stresses for topology optimization is defined as follows: DRESP ID_NAME TYPE DEF_TYPE EL_GROUP LC_SET END_
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= = = = =
TOPO_STRESS_DESIGN_ELEMENTS SIG_TOPO_MISES SYSTEM
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Add a design response to the project first, then chose Stress/Strain as Category and SIG_Topo_Mises as Response Type.
SIMULIA Tosca Structure Terms for Optimization
The design response for stresses is applied in the objective function as the following: OBJ_FUNC ID_NAME = OBJ_FUNCTION_ID DRESP = SIG_TOPO_MISES,, ........... TARGET = MIN END_
4.4.8.2 Example: Stresses in constraint definition Define a constraint on the Maximum von Mises stress. For a typical optimization task see chapter 5.6.7 Minimize the material volume with stress constraint. Definition in Tosca ANSA environment Not yet available with Tosca ANSA environment 13.2.x. Stresses as design responses are only supported for ANSA version 13.3.0 and later.
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Definition in Tosca Structure.gui
Fig. 77
Design response SIG_TOPO_MISES
Definition in Tosca Extension for ANSYS/Workbench Set up a design response first with Stress/Strain as Category and SIG_Topo_Mises as Response Type. Then add a constraint to the project
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and select the perviously defined von Mises stress design response, set Type to Absolute, Category to Less or equal and set the desired value.
Fig. 78
Using SIG_Topo_Mises design response in a constraint
Command in Parameter file The design response for stresses for topology optimization is defined as the following: DRESP ID_NAME TYPE DEF_TYPE EL_GROUP LC_SET
= = = = =
TOPO_STRESS_DESIGN_ELEMENTS SIG_TOPO_MISES SYSTEM
END_
The constraint is then defined as: CONSTRAINT = = = =
STRESS_CONSTRAINT TOPO_STRESS_DESIGN_ELEMENTS ABS
END_
Remarks 1. Each design response definition of type SIG_TOPO_MISES may only be applied once in either the objective or constraint definition. If stresses should be considered both in constraint or the objective (or several stresses should be combined) for each use one separate design response has to be defined. 2. Different optimization settings (STRESS_DRESP_OPT = ON) are applied for updating the design variables (=relative densities) when DRESP is TYPE = SIG_TOPO_MISES.
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ID_NAME DRESP MAGNITUDE LE_VALUE
SIMULIA Tosca Structure Terms for Optimization
When the stresses are applied as design response (DRESP) in a topology optimization formulation the following default settings are modified: • The move limit (DENSITY_MOVE = 0.10 in OPT_PARAM) on the design variables is decreased from 0.25 to 0.10. • The maximal number of optimization iterations (ITER_MAX = 80 in STOP) is increased from 50 to 80. 3. The default settings are overwritten by setting STRESS_DRESP_OPT=OFF, e.g. OPT_PARAM ...... STRESS_DRESP_OPT = OFF DENSITY_MOVE = 0.15 DENSITY_UPDATE = CONSERVATIVE ...... END_
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4.4.9
Center of gravity CENTER_GRAVITY_X
ρx dV x G = ---------------- ρ dV
CENTER_GRAVITY_Y
ρy dV y G = ---------------- ρ dV
CENTER_GRAVITY_Z
ρxz dV z G = ------------------- ρ dV
Analysis independent design response
TOPO OBJ_FUNC
S
SHAPE
BEAD
SIZING
S
S
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TOPO CONSTRAINT Table 16
S
SHAPE
BEAD
SIZING
S
S
Center of gravity (C = controller, S = sensitivity)
Fig. 79
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The center of gravity and the moments of inertia can be calculated in the global coordinate system or/and a user defined local Cartesian coordinate system. The calculation in the local coordinate system involves both a translation of the origin and a rotation of the coordinate system.
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The center of gravity for the three directions is defined by CENTER_GRAVITY_X, CENTER_GRAVITY_Y and CENTER_GRAVITY_Z, respectively. The center of gravity and the moments of inertia can be defined as a DRESP (design response) and as a VARIABLE in the sensitivity based topology, bead and sizing optimization. For shape optimization the center of gravity and the moments of inertia can only be defined as a VARIABLE which means that the values can only be used for output or control purposes. Both the center of gravity and the moments of inertia can be defined as a design response for the entire structure or for a part of the entire structure, e.g. some specific components. This is done using the command EL_GROUP. The center of gravity and the moments of inertia are per default calculated in the global coordinate system. However, the user has the option to calculate the center of gravity and the moments of inertia in a local coordinate system. The local coordinate system is defined in the design response using the command CS_REF. For the calculation of the center of gravity both the directions and origin of the local coordinate system is used as reference whereas for the moments of inertia the directions of the axes of the local coordinate system is applied, see figure Fig. 79. The global coordinate system is applied if no local coordinate system is defined in the design response (DRESP). The volume for which the center of gravity is calculated is defined using EL_GROUP.
SIMULIA Tosca Structure Terms for Optimization
Remarks 1. Only elements of the element group (EL_GROUP) listed in the tables of supported element types (chapter 11 Solver Specific Features) will be applied in the calculation of center of gravity. 2. The physical density defined in finite element input deck will be used in the calculation for the center of gravity. 3. The moments of inertia for shell and membrane elements are calculated as true 3D elements in Tosca Structure using the thickness defined in the properties of the shell and membrane elements in the finite element deck. Some finite element solvers and postprocessors calculate the moments of inertia for shell and membrane elements as 2D elements without thickness. 4. The physical density defined in finite element input deck will be used in the calculation for the center of gravity and in the calculation for the moments of inertia. 5. Internally, Tosca Structure calculates the center of gravity and the moments of inertia using more digits than can be observed in the finite element input deck. A slight difference (
The way the quality values are determined can be outlined as follows: • QUAD planes (QUAD elements, lateral planes of HEXA and PENTA elements): - Optimum angle is 90°-> quality=1. - Angle smaller or equal to QUAD_LOW_ANGLE -> quality=0. - Angle greater or equal to QUAD_HIGH_ANGLE -> quality=0. • TRIA surfaces (TRIA elements, lateral surfaces of TETRA and PENTA elements): - Optimum angle is 60° -> quality=1. - Angle smaller or equal to TRIA_LOW_ANGLE -> quality=0. - Angle greater or equal to TRIA_HIGH_ANGLE -> quality=0. 2 - 314 User Manual
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END_
SIMULIA Tosca Structure Shape Optimization
• TETRA elements: - Optimum aspect ratio is 1.33 -> quality=1. - Aspect ratio smaller or equal to TETRA_LOW_ASPECT -> quality=0. - Aspect ratio greater or equal to TETRA_HIGH_ASPECT -> quality=0. Remarks 1. With LEVEL_QUAL=NOT no element quality is calculated and the interval limits are not required. 2. The default values are practical and usually do not need to be changed. Changing the interval limits usually only leads to a slight change in the mesh quality. 3. The value for QUAD_LOW_ANGLE must lie between 0° and 89°. The value for QUAD_HIGH_ANGLE must lie between 91° and 180°. The value for TRIA_LOW_ANGLE must lie between 0° and 59°. The value for TRIA_HIGH_ANGLE must lie between 61° and 180°. The value for TETRA_LOW_ASPECT must lie between 0.00177 and 1.30. The value for TETRA_HIGH_ASPECT must lie between 1.36 and 999. 4. Determination of the local quality in the MESH_SMOOTH is decoupled from the global quality determination that is activated for the entire model with the READ_ELEM_QUALITY parameter of the OPTIONS command. Output of the global quality values can be made through the Patran interface or the parameter LIST, ELEM, QUAL (see volume 3: LIST). The local quality values of MESH_SMOOTH cannot be accessed by the user.
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Poor quality elements A list of the elements that are rated as poor quality by MESH_SMOOTH with an internal quality value of zero can be made as an output. To do so, set the QUAL_LIST=YES parameter. The default setting is QUAL_LIST=NO, no list of poor quality elements is printed out. MESH_SMOOTH ... QUAL_LIST
= NO
END_
Remark 5. The list of poor quality elements can only be printed for LEVEL_QUAL=LOW, MEDIUM or HIGH. No element qualities are calculated with LEVEL_QUAL=NOT and poor elements cannot be identified.
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6.3.2.8 Quality criteria of the solver (SOLVER_CHECK) In shape optimization there is a danger that the desired optimum cannot be achieved with the specified mesh which is continually adjusted to changing conditions. This means that the mesh is a component that should be restricted in the optimization job. Usually, the quality of the mesh decreases with an increase in the number of design cycles. The program for the finite element analysis may abort as a result. Some quality criteria for elements are checked in the finite element analysis program. If the solver identifies elements that are too poor in quality, the finite elements analysis is aborted. This has the disadvantage that no analysis results for the subsequent design cycle are then available in Tosca Structure and therefore, the optimization must be aborted (error message due to lack of results data instead of error message due to poor mesh quality, for more see vol.2 chapter 13.6.1, FE model of the next iteration is not calculated). Using the option SOLVER_CHECK=YES (default is NO) the user has the possibility, to check some finite element solver quality criteria in the Tosca Structure optimization module before the actual finite elements analysis. The quality criteria Q4TAPER, Q4SKEW, T3SKEW and TETRAAR are checked. The poorest values and the corresponding elements are logged to the output file. The default values in Tosca Structure can be changed by the user using the options Q4TAPER, Q4SKEW, T3SKEW and TETRAAR. The option SOLVER_STOP=YES (default is NO) causes a regular program stop in the Tosca Structure optimization module when one of the quality criteria is violated. This means that the subsequent finite elements analysis, which would be canceled without results data, is no longer carried out. This setting has the advantage that an optimization stop is easier to understand for the user who is saved from having to check the finite element solver results files for the source of the error.
... SOLVER_CHECK Q4TAPER Q4SKEW T3SKEW TETRAAR SOLVER_STOP
= = = = = =
YES YES
END_
Remarks 1. The allowed value limit for the element quality should be set identically in Tosca Structure and the finite element solver. 2. The option SOLVER_STOP=YES is only active when SOLVER_CHECK=YES is also set. This means that the regular program
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stop due to poor mesh quality can only be carried out if the mesh quality is checked. 3. The optimization in Tosca Structure stops when the SOLVER_STOP condition is fulfilled or stops when reaching the global condition STOP, ITER_MAX (STOP) which set the maximum number of allowed iterations (design cycles).
6.3.2.9 Correction of distorted elements (CORRECT_ELEMENTS) In some cases the program for the finite element analysis aborts due to bad element quality (inverted element or aspect ratio too big) some time during the optimization and thus prevents Tosca Structure from performing the optimization task. Very often only a few elements cause this trouble and the desired optimum is only slightly affected when modifiying the concerned elements in order to gain a better mesh quality.
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Fig. 184 Correction of distorted elements: a) original element, b) optimized element with bad aspect ratio (d), c) corrected element (good aspect ratio) For tetrahedral and hexahedral elements this can be activated with the CORRECT_ELEMENTS = YES option (default, use NO to disable). For hexahedral elements and tetrahedral elements with bad element quality, it is tried to correct the element CE_CORRECTION_LOOPS times by multiplying the optimization displacements with CE_CORRECTION_FACTOR (default is 0.5). If the element is still in a poor state it depends on CE_FAIL_ACTION what is done next: If CE_FAIL_ACTION = RESET is set (default), the optimization displacement is set to zero. If CE_FAIL_ACTION is set to CONTINUE the element is left as it is (with the risk that the solver will abort). MESH_SMOOTH ... TETRAAR = CORRECT_ELEMENTS=YES | NO
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CE_CORRECTION_LOOPS= CE_CORRECTION_FACTOR= (0.5) CE_FAIL_ACTION = RESET | CONTINUE END_
Remarks 1. The element quality for tetrahedral elements with four nodes is determined by calculating the aspect ratio. Use the TETRAAR setting to influence the quality detection. 2. The element quality for quadratic tetrahedral elements and for hexahedral elements is determined by calculating the Jacobian. If it is negativ the element needs to get corrected. 3. To make sure that the solver will not fail due to bad element quality, the TETRAAR quality criteria should be set a little bit lesser than in the solver. 4. This option is only working with tetrahedral, hexahedral and pyramid elements (with or without midnotes). 5. The modified elements are saved to a group with name ’CORRECTED_ELEMENTS_’. 6. When used during TEST_SHAPE with more than one increment only the group of the last increment step is saved.
The mesh smooth strategy is defined by the parameter STRATEGY. By default, STRATEGY = CONSTRAINED_LAPLACIAN, and the default mesh smoothing method is used. If, instead, STRATEGY = LOCAL_GRADIENT is chosen, the optimization-based mesh smoothing algorithm is used. In each iteration, it identifies the elements with the worst element quality and improves them by displacing the nodes. For relatively small models (less than 1000 nodes in the mesh smooth area), the method usually results in meshes with elements having the optimal shape; the measure of the optimality is roughly the ratio of the element volume (area for shell elements) to the corresponding power of its diameter. For larger models, the iterations tend to stop before the optimal mesh quality is reached since otherwise the calculation time becomes too large. In this case, the changes might only affect the elements with the worst element quality. The nodes on the surface are displaced as well, though their displacements are chosen to be parallel to the surface. It guarantees that the overall geometry remains mostly unchanged by the algorithm. Note that LEVEL_CONV and LEVEL_DVCON parameters are not used if STRATEGY = LOCAL_GRADIENT is specified.
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6.3.2.10 Mesh smooth strategy (STRATEGY)
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6.3.2.11 Definition in Tosca ANSA environment In Tosca ANSA environment, mesh smooth areas are defined below the item DESIGN_AREA in Task Manager. In MESH_SMOOTH dialog the element group for the mesh smooth area is chosen and further settings are defined. It is opened by New | MESH_SMOOTH command on DESIGN_AREA item (if MESH_SMOOTH item did not exist before) or Edit command on an already existing MESH_SMOOTH item. .
Fig. 185 Definition of a mesh smooth area (MESH_SMOOTH) in Tosca ANSA environment Definition in Tosca Structure.gui
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In Tosca Structure.gui, mesh smooth areas are defined in the MESH_SMOOTH command of Tosca Structure.pre screen where the element group for the mesh smooth area can be chosen and further settings be defined.
Fig. 186 Definition of a mesh smooth area (MESH_SMOOTH) in Tosca Structure.gui Command syntax Each MESH_SMOOTH definition has a name (ID_NAME parameter) and references a previously defined element group (EL_GROUP parameter). The name is required in order to subsequently activate the MESH_SMOOTH definition when specifying the optimization job (see OPTIMIZE command). The area for the mesh smoothing is specified by the element group. These two
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declarations are mandatory. A typical MESH_SMOOTH command appears as follows: MESH_SMOOTH ID_NAME EL_GROUP ...
= mesh_smooth_name = elem_group_name
END_
All other declarations are optional and are used for additional specifications in the MESH_SMOOTH definition by the user. Remarks 1. The recommended procedure is to define MESH_SMOOTH area immediately after defining the design area (see DV_SHAPE command) since the two areas are assigned to one another. 2. The MESH_SMOOTH definition must be activated by reference in the OPTIMIZE command. Non-activated definitions have no influence in the optimization. The reference in the OPTIMIZE command assigns the design area (see DV_SHAPE command) and the area for mesh smoothing (see MESH_SMOOTH command) to one another. 3. It is recommended to define MESH_SMOOTH before the DVCON_SHAPE entries (see vol.2 chapter 6.3.3) or a volume constraint (see vol.2 chapter 6.5.1). This enables the system-defined MESH_SMOOTH node group to then be used for the DVCON_SHAPE definitions or the user/systemdefined MESH_SMOOTH element group to be used for the definition of the volume constraint.
Restrictions (DVCON_SHAPE) For shape optimization, restrictions are defined as boundary conditions that limit the potential area of the node displacement. A design variable constraint is a restriction that directly affects the individual design variables, i.e., the individual design nodes. Since the nodes in the mesh smoothing area (see volume 3: MESH_SMOOTH) can be interpreted as second order design nodes, there is also the possibility to apply the restrictions (to a limited degree) to the nodes of the mesh smoothing area. Compared to geometrical optimization based on a few parameters, Tosca Structure.shape allows every design node to be displaced ‘independently’ from other design nodes. To meet functional and manufacturing requirements, it is usually necessary to limit the solution area and therefore the independence of the design nodes. Unrestricted shape optimization can produce trivial results. For example, if the shape of a shaft shoulder under axial tensile stress is optimized without restricting the design nodes, a smooth beam will arise that will not be able to
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fulfill the original function. To achieve the best results the rule: “As much flexibility as possible, as few restrictions as necessary!” should be followed. The possible restrictions are the specification of an allowed displacement area by limiting the directional amount of optimization displacement and the specification of variation and frozen areas. It is also possible to influence the allowed displacement direction by limiting the displacement to specific coordinate directions. In addition, the optimization displacement of a node can be made dependent on the optimization displacement of another node. The definition of the design variable constraints for shape optimization is done with the DVCON_SHAPE command. The following restrictions are available for shape optimization: • Restriction of the amount of displacement (see vol.2 chapter 6.3.3.2) • Maximum and minimum member size (see vol.2 chapter 6.3.3.3) • Displacement check against solids (see vol.2 chapter 6.3.3.4) • Displacement check against elements of an element group (see vol.2 chapter 6.3.3.5) • Restriction of the displacement direction (see vol.2 chapter 6.3.3.6) • Restricting the displacement to a slide surface (see vol.2 chapter 6.3.3.7)
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• Assignment of a coupling condition (see vol.2 chapter 6.3.3.8)
Fig. 187 Design variable constraints available in Tosca ANSA environment (left) and Tosca Structure.gui
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Remarks 1. Some of the design variable constraints for shape optimization can be interpreted as side constraints or bounds (design variable boundaries) in the same way these terms are used in standard optimization nomenclature. 2. Some of the design variable constraints for shape optimization relate not only to the design variable itself but also to the corresponding optimization displacement vectors (or the design coordinates). The term ‘design variable constraint’ in this case should be interpreted in a more general sense. 3. In contrast to the DVCON_SHAPE parameter, which has a direct effect on the individual design variables, the CONSTRAINT parameter defines a constraint for the optimization job that affects the functional relationships of several design variables (e.g. volume constraint). 4. The activated DVCON_SHAPE entries are executed in the order in which they are referenced in the OPTIMIZE command or defined in Tosca ANSA environment. The individual DVCON_SHAPE entries are checked independent of one another, i.e., a DVCON_SHAPE entry always overrides the preceding DVCON_SHAPE entry. If mutually independent restrictions are declared all restrictions are observed. If mutually dependent restrictions are declared the user must select an order of execution that is logical and specific for the problem.
This section only contained a general overview of the command forms without going into detail about the exact syntax and operations of the individual restrictions. In the following sections the individual restrictions are described in more detail.
6.3.3.1 Node group for design variable constraints The area to which restrictions are applied to is defined by a node group. This node group must contain only design nodes or nodes in the mesh smooth area. Remarks 1. The restrictions are checked only for the corner nodes of the node group (ND_GROUP parameter). If mid-side nodes are contained in the node group they are subsequently placed in between the neighboring corner nodes. 2 - 322 User Manual
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5. The restricted nodes are checked at the beginning and the execution stops if the defined constraint is not fulfilled (CHECK_SLIDE, CHECK_LINK). This behavior can be switched off with the parameter FEASIBLE_START=NO. But for example if the surface described node group is not stampable and this check is switched off the restriction enforces the stampable surface.
SIMULIA Tosca Structure Shape Optimization
Therefore, for mid-side nodes, it is not possible to guarantee adherence to the restrictions; a small amount of deviation may occur. 2. It is important to ensure that the only node groups referenced in the DVCON_SHAPE definitions are those whose nodes are contained in the MESH_SMOOTH area.
6.3.3.2 Restricting the amount of displacement It is possible to specify a maximum allowed absolute optimization displacement for each node in relation to the starting geometry. This involves differentiating between growth (node is moved outwards) and shrinkage (node is moved inwards). This function can be used, for example, in the optimization of mold parts that require a specific minimum and maximum wall thickness to allow the component to be cast. The parameters CHECK_GROW CHECK_SHRINK
= =
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specify a maximum amount of displacement allowed in the growth direction and a maximum amount of displacement allowed in the shrink direction. Both values must be positive and can be set in the GROW/SHRINK_CONTROL menu of Tosca ANSA environment or the Displacement fields in Tosca Structure.gui. Fig. 188 provides a graphic illustration of the allowed displacement area.
Fig. 188 Specification of an upper and lower displacement limit relative to the start contour
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Remark 1. The CHECK_GROW and CHECK_SHRINK restrictions can only be defined for surface nodes since only surface nodes exhibit a growth or shrinkage direction. If inner nodes are contained in the node group (ND_GROUP parameter), the DVCON_SHAPE definition will be rejected.
6.3.3.3 Minimum or maximum member size
Fig. 189 Minimum member size with radius = 3.0 (thickness = 6.0 for TAE) A typical parameter set for the member size restriction is of the following form: DVCON_SHAPE ID_NAME ND_GROUP CHECK_MAX_MEM CHECK_MIN_MEM CHECK_NDGR TOLERANCE DVCON_SHAPE
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For the definition of minimum member size a radius is specified, such that normal to the surface of the model a minimum thickness of 2*radius must be achieved. If optimization displacements break this restriction they will be readapted according to the selected master criterion. If the structure is smaller in certain regions from the very first, only growth is permitted in these areas unless the areas fit the condition. CHECK_MAX_MEM works analogously. In Tosca ANSA environment, the settings are edited in MEMBERSIZE_CONTROL dialog.
SIMULIA Tosca Structure Shape Optimization
Technically the implementation is based on the surface of the finite elements of the design nodes. The member size is calculated as the distance between a node and the intersection point in negative normal direction to an element surface. If no element surface is intersected the member size is ignored for this node. The ND_GROUP parameter specifies the node group that is modified by the algorithm. This group should be a subset of the meshsmooth area. The distance of the nodes in this group is tested against the node group specified by CHECK_NDGR. This is an optional parameter and set by default to . This option is useful if the member size shall only be tested against certain regions like in Fig. 190. The TOLERANCE parameter is important for intersection tests: If the intersection test for one node misses the border of the slightly, the element faces can be extended by the TOLERANCE value (in absolute units) so that the intersection test succeeds and the desired member size for this node is not ignored. However a too large TOLERANCE value implies the risk of getting incorrect distances. This parameter is optional and the default value is 0.1 * max element length.
ND_GROUP
CHECK_NDGR
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Fig. 190 Example for ND_GROUP and CHECK_NDGR Remark: 1. If you want to ensure the minimum (maximum) member size restriction for a certain region which is not necessarily part of the mesh smooth area, choose all surface nodes of this region as CHECK_NDGR. Areas which alreadfy fulfil your restriction and are not influenced by the optimization can be left out. 2. The minimum member size restriction tends to be non-conservative. This means that the resulting member size is possibly smaller than the desired one. A workaround is to give a higher desired minimum meber size value.
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3. For the same reason, the maximum member size tends to be conservative. 4. If your starting model does not fulfill your desired thickness, the member size restriction is unable to fit the model to these values.
6.3.3.4 Displacement check against solids (CHECK_SOLID) It is possible to define geometric primitives (solids) as a restriction of the node displacements. Geometric primitives are defined using the SOLID parameter. The SOLID command allows the definition of circles, circle segments, ring segments and rectangles in two-dimensional models and cylinders, cylinder segments, tubes, cubes and cube segments in three-dimensional models. There is a differentiation between a variation solid and a restriction solid (variation area or restriction area, see vol.2 chapter 3.9, Solids (Geometric Primitives)). The parameter: CHECK_SOLID = solid_name specifies a solid whose borders may not be penetrated. Fig. 191 provides a graphic illustration. The solid must be defined using the SOLID menu (New | SOLID command on a CHECK_SOLID item found below DV_CONSTRAINTS) in Tosca ANSA environment or with the SOLID command in Tosca Structure.gui before being referenced.
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Fig. 191 Displacement check against a solid
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Fig. 192 CHECK_SOLID definition using Tosca ANSA environment (left) and Tosca Structure.gui
Remarks
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1. The CHECK_SOLID restrictions can be performed for surface nodes as well as for inner nodes. To limit the exterior form of a component, it only makes sense to restrict surface nodes. However, the node displacements in the MESH_SMOOTH area should be limited. 2. Up to six different CHECK_SOLID parameters can be defined in every DVCON_SHAPE command. They are executed in the order of their declaration within the DVCON_SHAPE command. In Tosca ANSA environment this corresponds to the order of the solid entries in the task manager. 3. If the solid is a variation solid, all nodes of the node group in the start model (see ND_GROUP parameter) must be located inside the variation solid. If nodes are located outside the variation solid, the DVCON_SHAPE definition will be rejected. If the solid is a restriction solid, all nodes of the node group in the start model (see ND_GROUP parameter) must be located outside the restriction solid. If nodes are located inside the restriction solid, the DVCON_SHAPE definition will be rejected.
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6.3.3.5 Penetration check (CHECK_ELGR, PENETRATION_CHECK) Element surfaces and lines as well as solid elements can be defined as limiting surfaces, lines or solids in order to check node displacements against any contour. This option offers more flexibility than the check for the absolute amount of displacement or the check against geometric primitives. The limiting surfaces are formed by beam structures in 2D models and by shell structures or solid structures in 3D models. The limiting surfaces are generated in the FE preprocessor and loaded via the interface (MODEL_LINK Folder or FEM_INPUT command, ADD_FILE parameter) in the optimization preprocessor. The parameter CHECK_ELGR = elgr_name can be defined in the CHECK_GROUP field of the PENETRATION_CHECK menu in Tosca ANSA environment or in the Element Group field of Tosca Structure.gui. It specifies an element group whose elements may not be penetrated (contact condition) by the nodes of the node group specified by the ND_GROUP parameter for shell or beam elements. For solid elements, all nodes inside the solids specified by the CHECK_ELGR parameter are frozen and for all nodes outside the penetration into the solid is avoided. Fig. 193 provides a graphic illustration. Activation of the element check represents a collision control. If a node attempts to penetrate an element, the node displacement is scaled back so the effected node remains on the side of the element where it is intended. The element group must be defined with GROUP_DEF or in the analysis file before it can be referenced with CHECK_ELGR. Remarks
Fig. 193 Displacement check against solid and beam elements
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1. CHECK_ELGR restrictions can be performed for surface nodes as well as for inner nodes. To limit the exterior form of a component, it only makes sense to restrict surface nodes. However, the node displacements in the MESH_SMOOTH area should be limited.
SIMULIA Tosca Structure Shape Optimization
2. Up to six CHECK_ELGR parameters can be defined in every DVCON_SHAPE command. They are executed in the order of their declaration within the DVCON_SHAPE command. In Tosca ANSA environment for each group a new PENETRATION_CHECK entry has to be created. 3. To simplify the definition of the contact check it is useful to divide the limiting surfaces by assigning various element property numbers (or materials). This greatly simplifies the selection and assembly of groups in the optimization preprocessor (when using manual selection). 4. The nodes (ND_GROUP parameter) and the elements (CHECK_ELEM parameter) should have a definite minimum distance to ensure that a node must remain on the right element side and the initial model is feasible. 5. For determining penetration by beam elements (without lateral dimension), a hypothetical tolerance area amounting to 1% of the beam length surrounds each beam element. A beam element is considered penetrated when a node is moved into the tolerance area. A node displacement moving alongside the tolerance area is not considered a penetration. 6. If the elements being used in the check are loaded with the ADD_FILE parameter of FEM_INPUT command, attention should be paid that node or element IDs are not used twice since Tosca Structure cannot process duplicated IDs.
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6.3.3.6 Restricting displacement directions (CHECK_BC, CHECK_DOF) In Tosca Structure.shape the displacement direction of the design nodes (optimization displacement vector) is normally determined as the surface normal (see vol.2 chapter 6.8.1). The inner nodes are subsequently recalculated in relation to the displacement of the design nodes determined by the selected mesh smoothing algorithm. However, to meet functional and manufacturing requirements it is often necessary to deviate from the automatically determined displacement direction for design nodes as well as for mesh smoothing nodes. In doing so, every translational degree of freedom can be fixed for any node in a freely defined coordinate system. In this way, a node can be restricted to move on one plane only (fixed to one value) or to move within a displacement vector (fixed to two values). The restriction of all three translational degrees of movement is equivalent to a constraint of the node in the shape optimization. The displacement boundary condition must be unique.In contrast to FE boundary conditions for several load cases, the total of all the supports for all load cases are considered as supports in the optimization. A prescribed node displacement as an optimization boundary condition is also not permitted. Tosca Structure.shape offers the user two possibilities for restricting the displacement directions of nodes.
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Loading the Node Fixations via the Interface from the FE Program The full or partial fixation of nodes is the most common and most important type of restriction; it is practically used in every optimization model. The most efficient method for defining the displacement restrictions in the FE preprocessor is as an extra load case in the analysis model and then load it via the FE interface in the optimization preprocessor. The interface must first be activated with the OPTIONS, BC = ... parameter. In this way all node fixations for the optimization model can be defined in advance in the FE preprocessor. The fixation is always based on the FE displacement coordinate system of the node. The parameter CHECK_BC
= YES
activates the node fixations of the node group (ND_GROUP parameter) that are loaded in the FE model. Fixations that reference nodes not contained in the node groups are not activated. To prevent loaded fixations from being activated enter: CHECK_BC
= NO
Direct definition of the displacement restriction If it is necessary to restrict other displacement directions in addition or at a later stage, this can be accomplished with the CHECK_DOF parameter in the menu DOF_Control (Tosca ANSA environment) or the field DOF (Tosca Structure.gui). This restriction is applied to a node group (defined in the FE File, using group definition or graphically in Tosca ANSA environment). The coordinate system must also be defined or loaded. With the parameter CHECK_DOF = , FIX/FREE, FIX/FREE, FIX/FREE all the displacements of all nodes in the node group selected with ND_GROUP are fixed (FIX) or free (FREE) relative to the specified coordinate directions of the coordinate system . Either FREE or FIX is allowed for each coordinate direction.
1. The restrictions CHECK_BC or CHECK_DOF can be applied to both: surface nodes and inner nodes. 2. The essential difference between CHECK_BC and CHECK_DOF is: CHECK_BC is read in through the FE interface whereas CHECK_DOF is defined in the optimization preprocessor. With CHECK_BC each node generally has its own fixation in its own displacement coordinate system, whereas with CHECK_DOF all nodes of the node group are all fixed in the same coordinate system.
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Remarks
SIMULIA Tosca Structure Shape Optimization
flexibility than restricting the direction of displacement. The limiting surfaces are formed by shell structures. Those surfaces can be generated automatically with a link shape command.
Fig. 194 Master nodes generate the slide surface A master node group is required describing sufficiently the contour of the surface. The following command defines a surface of revolution with rotation axis Z in the global coordinate system:
ID_NAME MASTER CLIENT CLIENT_DIR TOL CS
= = = = = =
surface NDGR, slide_master_ndgr SURF_TURN 0, 0, 1 0.1, 0.1, 0.1 CS_0
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END
Fig. 195 Generated slide surface This slide surface is connected to a node group via a DVCON_SHAPE command: DVCON_SHAPE = slide_restriction = surface = restricted_nodes
END_
Alternatively the limiting surfaces are generated in the FE preprocessor and loaded via the interface (FEM_INPUT command, ADD_FILE parameter) in the optimization preprocessor. With a LINK_SHAPE command LINK_SHAPE ID_NAME MASTER CLIENT TOL CS
END_
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= = = = =
surface NDGR, slide_ndgr FREE_FORM 0.1, 0.1, 0.1 CS_0
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ID_NAME CHECK_SLIDE ND_GROUP
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Here, the node group "slide_ndgr" is used to generate the surface on which the design nodes will be restricted. The CLIENT = FREE_FORM allows for freeform surfaces. Remarks 1. CHECK_SLIDE restrictions can be performed for surface nodes as well as for inner nodes. To limit the exterior form of a component, it only makes sense to restrict surface nodes. The restriction of inner nodes can be undertaken. However, the node displacements in the MESH_SMOOTH area should be limited. 2. To simplify the definition of the contact check it is useful to divide the limiting surfaces by assigning various element property numbers (or materials). This greatly simplifies the selection and assembly of groups in the optimization preprocessor. 3. If the elements being used in the check are loaded with the ADD_FILE parameter of FEM_INPUT command, attention should be paid that node or element IDs are not used twice since Tosca Structure cannot process duplicated IDs.
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6.3.3.8 Assigning link/coupling conditions (CHECK_LINK) A parameter-free optimization is performed for shape optimization in Tosca Structure, i.e., each of the design nodes can be moved independent of the other design nodes. However, in some cases certain restrictions are specified that make it necessary to link or couple design nodes.The design nodes are then no longer allowed to move freely; there is an interdependent relationship between the individual design nodes. This relationship is defined by a link condition. The following are examples of the type of restrictions that might necessitate the activation of link conditions: All design nodes in the start model are located on a cylinder and should also be located on a cylinder (with an altered radius) in the optimized model. Another example: due to a specified punch direction, the design nodes must lie along the punch direction. Yet another example: an originally symmetrical component should still be symmetrical following the optimization despite asymmetric stress. The parameter CHECK_LINK = link_shape_name activates a link condition for the nodes of the node group (ND_GROUP parameter). This link condition must be defined with the LINK_SHAPE parameter and referenced with its unique name (link_shape_name). The possibilities for defining link conditions are numerous and varied. All of the definition options are described in vol.2 chapter 6.3.4. Since it is not necessary to know the link conditions for the basic definition of a shape optimization job, inexperienced
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readers should skip this chapter at this time. This section can be read when the need arises. Remarks 1. An individual link condition can be assigned several times, i.e., an individual link condition can be activated in several DVCON_SHAPE entries for several node groups. 2. Some manufacturing restrictions require the definition of numerous node groups and restrictions. To make this easier, you can automatically generate node groups using the GROUP_AUTO_DEF command and automatically assign link conditions as restrictions using the DVCON_AUTO_SHAPE command. 3. A detailed description of the LINK_SHAPE command is available in vol.2 chapter 6.3.4. 4. In Tosca ANSA environment coupling conditions can be defined using the modules buttons LINK_SHAPE and DVCON_SHAPE.
6.3.3.9 Definition in Tosca ANSA environment In Tosca ANSA environment, design variable constraints are defined below the item DV_CONSTRAINTS of the task manager. The dialog where a node group to be restricted is chosen and further settings are defined is opened by New | command applied on DV_CONSTRAINTS item (if a new design variable constraint is to be created) or by Edit command on an already existing item that corresponds to the design variable constraint.
In Tosca Structure.gui, design variable constraints are defined in the DVCON_SHAPE mask of Tosca Structure.pre where the node group for the restrictions can be chosen and further settings be defined.
6.3.3.11 Command syntax Each DVCON_SHAPE definition has a name (ID_NAME parameter) and references a previously defined node group (ND_GROUP parameter). The name is required to subsequently activate the DVCON_SHAPE definition when specifying the optimization job (see OPTIMIZE command). The node group specifies the node area where the restriction is in effect. The following parameters define the individual restrictions for shape optimization: • CHECK_GROW, CHECK_SHRINK: Restriction of the amount of displacement (see vol.2 chapter 6.3.3.2)
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6.3.3.10 Definition in Tosca Structure.gui
SIMULIA Tosca Structure Shape Optimization
• CHECK_MAX_MEM, CHECK_MIN_MEM: Definition of a maximum and minimum member size (see vol.2 chapter 6.3.3.3) • CHECK_SOLID: Check the displacements against geometric primitive solids (see vol.2 chapter 6.3.3.4) • CHECK_ELGR: Check the displacements against elements of an element group (see vol.2 chapter 6.3.3.5) • CHECK_BC, CHECK_DOF: Restriction of the displacement direction (see vol.2 chapter 6.3.3.6) • CHECK_SLIDE: Restricting the displacement to a slide surface (see vol.2 chapter 6.3.3.7) • CHECK_LINK: Assignment of a coupling condition (see vol.2 chapter 6.3.3.8) A DVCON_SHAPE command using all of the individual restrictions appears as follows:
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DVCON_SHAPE ID_NAME =name_of_dvcon_shape ND_GROUP =name_of_node_group CHECK_GROW = CHECK_SHRINK = CHECK_MAX_MEM = CHECK_MIN_MEM = CHECK_SOLID =name_of_solid CHECK_ELGR =name_of_element_group CHECK_BC =cs_name,[FREE|FIX],[FREE|FIX],[FREE|FIX] CHECK_DOF =[YES|NO] CHECK_SLIDE =name_of_link_shape CHECK_LINK =name_of_link_shape FEASIBLE_START =[YES|NO] END_
Remarks 1. It is possible to define several individual CHECK_* restrictions within a DVCON_SHAPE command. The order of the execution of the individual restrictions within a DVCON_SHAPE command appears as follows: CHECK_GROW/ CHECK_SHRINK, CHECK_MAX_MEM, CHECK_MIN_MEM, CHECK_SOLID, CHECK_ELGR, CHECK_BC, CHECK_DOF, CHECK_SLIDE, CHECK_LINK. The individual restrictions are checked independent of one another, i.e., an individual restriction always overrides the preceding restriction.
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2. It is possible to define several design variable constraints using the DVCON_SHAPE command. Each DVCON_SHAPE definition must have its own unique name. 3. The DVCON_SHAPE definitions must be activated by a reference in the OPTIMIZE command. Non-activated definitions have no influence upon the optimization. The reference in the OPTIMIZE command assigns the design variable constraints, the design area (see DV_SHAPE command) and the area for mesh smoothing (see MESH_SMOOTH command) to one another. Therefore, it is important to ensure that the only node groups referenced in the DVCON_SHAPE definitions are those whose nodes are contained in the MESH_SMOOTH area. 4. The recommended procedure is to define the assigned restrictions immediately after defining the design area (see DV_SHAPE command) and the mesh smoothing area (see MESH_SMOOTH parameter). The systemdefined MESH_SMOOTH node group can then be reused to define the restrictions.
Link and coupling conditions (LINK_SHAPE) Shape optimization involves determining the displacement of each design node in order to homogenize the stress on the surface based on the optimization criteria. The displacement of the neighboring nodes is not coupled, i.e., each of the design nodes can move independent from the other design nodes. For example, during optimization free-form surfaces may develop from flat surfaces. By coupling the design nodes the optimization can maintain the regularity of planes. In order to take into account functional and manufacturing restrictions in shape optimization, certain link conditions can be set with the command LINK_SHAPE. Link conditions are defined using Modules Buttons toolbar of Tosca ANSA environment (click the button LINK_SHAPE on LINK_CONDITIONS panel, then click New) or using the LINK_SHAPE command in Tosca Struc-
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6.3.4
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ture.gui.Using Tosca ANSA environment, link definitions are visualized graphically in the model view.
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Fig. 196 LINK_SHAPE definition in Tosca ANSA environment Each link condition has a name (ID_NAME parameter). A criterion for determining the master node (MASTER parameter) is defined as well as a rule for the displacement of the client nodes (CLIENT parameter). A typical LINK_SHAPE command appears as follows: LINK_SHAPE ID_NAME MASTER CLIENT ...
= name_of_link_shape = ... = ...
END_
Depending on the selected CLIENT parameter, other parameters are also required. In some circumstances a coordinate system (CS parameter) or tolerances (TOL parameter) must be specified. These parameters of a LINK_SHAPE command may appear as follows:
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LINK_SHAPE ... CS TOL
= name_of_coord_system = , ,
END_
In the following subsections the MASTER and CLIENT parameters are described in detail. The CS and TOL parameters are also described when applicable. design nodes
design nodes (coupled)
without node coupling
master node
including node coupling
Fig. 197 Synchronous coupling of design nodes Remarks
2. The definition of coupling conditions can require a great deal of time and effort. In order to be able to estimate the best possible potential of an optimization, one optimizationshould be performed with as few restrictions as possible and only a few coupling conditions at the beginning of a project. 3. Coupling conditions restrict the range of solutions for the system and reduce the optimization potential.
6.3.4.1 Determining the master node (MASTER) The MASTER parameter is used in each definition of a link condition to specify how to determine the master node. This node prescribes the displacement of the nodes affected by the link condition. It can be set explicitly by the user: MASTER = NODE, NODE_NR
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1. Link conditions basically only define a coupling rule without referencing a specific node group. The coupling condition is assigned to a node group after activation with CHECK_LINK in the DVCON_SHAPE command. In Tosca ANSA environment, the link definition can be chosen after typing a "?" in the CHECK_LINK field (click DVCON_SHAPE in RESTRICTIONS panel of Modules Buttons toolbar, then click New so that the window with the design variable constraint settings appears). In Tosca Structure.gui the link condition is assigned in the drop down menu of the DVCON_SHAPE command.
SIMULIA Tosca Structure Shape Optimization
This causes the master displacement to be determined from the same node during the entire optimization. Furthermore the master node may be determined from a master node group. This allows the user to define a components edge to be the master edge for optimization. The algorithm will determine the master node automatically from the master node group. In this case the master node group must contain exactly one node of each link group. MASTER = NDGR,
Another way is to have the system automatically determine the master node according to two different criteria: MASTER = MAX
or MASTER = MIN
In this case, the master node is re-determined in every cycle. When the master node is automatically determined, the critical factor is identifying which node displacement (determined by the stress) for the coupling group is relevant. Principally, there exist four different cases of how the largest and smallest node displacements relate to the reference value within the node group: • Case 1 The stress everywhere is greater than the reference value, i.e., a positive displacement is determined for all design nodes of the coupling group. All design nodes will grow out of the component.
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• Case 2 The stress everywhere is less than the reference value, i.e., for all design nodes of the coupling group a negative displacement is determined. All design nodes will shrink inwards. • Case 3 There are nodes with greater and less stress than the reference value and the absolute shrinkage is greater than the absolute growth (abs(max_neg) > abs(max_pos)). • Case 4 There are nodes with greater and less stress than the reference value and the absolute shrinkage is less than the absolute growth (abs(max_neg) < abs(max_pos)). Case 1
Case 2
Case 3
Case 4
ALL_GROWTH
ALL_SHRINK
MORE_SHRINK
MORE_GROWT H
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max_growth min_growth OBJ_FUNC
max_growth max_growth OBJ_FUNC min_shrink
OBJ_FUNC
max_shrink
max_shrink
OBJ_FUNC max_shrink
lab1 =
Selected Master Displacement Value
MAX
max_growth
min_shrink
max_growth
max_growth
MIN
min_growth
max_shrink
max_shrink
max_shrink
The two criteria MAX and MIN, respectively, select different master nodes corresponding to the selected displacement values: • MAX The MAX-Criterion is the “conservative” option. Here, the maximum growth (as in the cases 1, 3, 4) or the smallest shrinkage (as in case 2) is always used to select the master node. This is the standard criterion for shape optimization. • MIN The MIN-Criterion moves the component surface inward as far as possible. This criterion has to be used when linking conditions are required while optimizing contact surfaces. Remark
2. Older parameters CRIT_1 and CRIT_2 correspond to MAX and MIN respectively. With Tosca Structure 8.1.0 these older definitions are still supported.
6.3.4.2 Displacement of the client nodes (CLIENT) The CLIENTparameter is used in each definition of a link condition to set a rule for determining the displacement of the client nodes based on the displacement of the master node. The client nodes are moved relative to the master node. The following rules can be selected: • Plane symmetry (PLANE_SYM, see chapter 6.3.4.3 Plane symmetry (PLANE_SYM))
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1. CHECK_LINK in the DVCON_SHAPE command assigns the link condition to a node group. For MASTER=NODE, node_nr, the explicitly declared node must not necessarily be contained in the node group. For MASTER=MAX or MASTER= MIN, the master node is always determined from the nodes of the node group.
SIMULIA Tosca Structure Shape Optimization
• Plane symmetry for non-symmetric meshes (SURF_PLANE_SYM, see chapter 6.3.4.4 Plane symmetry for non-symmetric meshes (SURF_PLANE_SYM)) • Cyclic symmetry for non-symmetric meshes (SURF_CYCLIC_ROTATIONAL_SYM, see 6.3.4.5chapter 6.3.4.5 Cyclic symmetry for non-symmetric meshes (SURF_CYCLIC_SYM) ) • Cyclic-plane symmetry combination (SURF_CYCLIC_PLANE_SYM, see chapter 6.3.4.6 Cyclic-plane symmetry combination (SURF_CYCLIC_PLANE_SYM)) • Point symmetry (POINT_SYM, see vol.2 chapter 6: Point symmetry (POINT_SYM)) • Rotational symmetry (ROTATION_SYM, see chapter 6.3.4.8 Rotational symmetry (ROTATION_SYM)) • Coupling of displacement coordinates (VECTOR, see chapter 6.3.4.9 Coupling displacement coordinates (VECTOR)) • Coupling of the displacement direction (DIRECTION, see chapter 6.3.4.10 Coupling displacement direction (DIRECTION)) • Coupling of the amount of displacement (LENGTH, see chapter 6.3.4.11 Coupling amount of displacement (LENGTH)) • Coupling of coordinates in the FE displacement coordinate system (DISP_CS, see chapter 6.3.4.12 Coupling coordinates in the FE displacement coordinate system (DISP_CS))
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• Coupling as stampable surface (SURF_STAMP, see chapter 6.3.4.13 Stampable surface (SURF_STAMP)) • Coupling as turnable surface (SURF_TURN, see chapter 6.3.4.14 Turnable surface (SURF_TURN)) • Coupling as drillable surface (SURF_DRILL, see chapter 6.3.4.15 Drillable surface (SURF_DRILL)) • Coupling as demoldable surface (SURF_DEMOLD, see chapter 6.3.4.16 Demoldable surface (SURF_DEMOLD)) • Defining a free form slide surface (FREE_FORM, see chapter 6.3.3.7 Restricting displacement to a slide surface) The individual rules for determining the client displacements are described in detail in the following chapters..
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6.3.4.3 Plane symmetry (PLANE_SYM) To be able to couple displacements symmetric to a plane, the position and the orientation of the plane must be exactly specified. It is also necessary to specify tolerances in order to identify symmetric nodes. The following four parameters are necessary for the definition of the link condition: CLIENT CLIENT_DIR CS TOL
= = = =
PLANE_SYM , ,
name_of_coord_system , ,
The origin of the coordinate system referenced by CS defines a point on the plane. The direction specified by the CLIENT_DIR parameter defines the normal of the plane. The symmetry of the nodes (assigned by ND_GROUP in the DVCON_SHAPE command) is checked against the symmetry plane. Symmetric nodes are assembled into a symmetry group (normally two symmetric nodes per symmetry group). Then the master node of the symmetry group is determined and the displacements of the client nodes are calculated in such a way that they move symmetrically to the plane of the master node (see Fig. 198). The tolerances are required in order to identify symmetric nodes.Symmetric nodes share equal coordinates in the plane and inversely equal coordinates normal to the plane (and added tolerances). The three tolerance values tol_* are assigned to the three coordinate directions of the coordinate system referenced by CS. Remarks 1. The coordinate system referenced by CS must be a Cartesian coordinate system.
Fig. 198 Symmetric coupling relative to a plane
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2. Only the MASTER=MAX or MASTER=MIN criteria are allowed for determination of the master node.
SIMULIA Tosca Structure Shape Optimization
6.3.4.4 Plane symmetry for non-symmetric meshes (SURF_PLANE_SYM) To be able to couple displacements symmetrically to a plane on not necessarily symmetrically meshed geometries, the position and the orientation of the plane must be specified. The following four parameters are necessary for the definition of the link condition: CLIENT CLIENT_DIR CS TOL
= = = =
SURF_PLANE_SYM , ,
name_of_coord_system tolerance_value
The origin of the coordinate system referenced by CS defines a point on the symmetry plane. The direction specified by the CLIENT_DIR parameter defines the normal of the plane. The tolerance value specified by TOL is used as absolute tolerance in intersection tests and can be used to influence the behaviour on the border of the selected node group. The symmetry of the nodes (assigned by ND_GROUP in the DVCON_SHAPE command) is checked against the symmetry plane. For each node a reference displacement is calculated for its symmetric "counterpart". This counterpart is obtained by reflecting the node at the symmetry plane, i.e. by intersecting a line through the node in plane normal direction with the surface defined by all selected nodes. The reference displacement is obtained by interpolation of the optimization displacements of the adjacent nodes. The tolerance is required to find reference displacements at the border of the selected node group, where it will happen that nodes do not have an opposite face (with respect to the plane definition) and thus no intersection points in plane normal directions can be found. Optional, a strategy to determine node position influence on the result can be chosen: = MAX | MIN
The symmetry is built up by using the maximum (default) or the minimum of the displacement of the selected node (d1 in Fig. 199) and the interpolated displacement of its plane symmetric counter part (reference displacement d2 in Fig. 199).
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node, reflected by symmetry plane
displaced model surface
y displaced node d1
d2
x
z
plane of symmetry
original position of node
Fig. 199 Symmetric coupling relative to a plane Remarks 1. The coordinate system referenced by CS must be a Cartesian coordinate system. 2. Only the MASTER=MAX or MASTER=MIN criteria are allowed for determination of the master node.
This link condition couples nodes in a not necessary symmetric mesh that reoccur in a cyclic manner around a rotational axis. To be able to build up the coupling, a symmetry axis and an angle must be specified. The following six parameters are necessary for the definition of the link condition: CLIENT CLIENT_DIR CS TOL ANGLE CYCLIC_SYM_START
= = = = = =
SURF_CYCLIC_SYM , ,
name_of_coord_system tolerance_value angle_in_degree , ,
The CLIENT_DIR parameter defines the rotational axis and is specified in coordinates of the coordinate system CS. Like for the SURF_PLANE_SYM link condition (chapter 6.3.4.4 Plane symmetry for non-symmetric meshes (SURF_PLANE_SYM)) the TOL parameter is used in intersection tests as
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6.3.4.5 Cyclic symmetry for non-symmetric meshes (SURF_CYCLIC_SYM)
SIMULIA Tosca Structure Shape Optimization
absolute tolerance. The ANGLE divides the area around the axis (CLIENT_DIR) in pieces of equal size that shall be made symmetric. Thus, the angle must be a divisor of 360°. The CYCLIC_SYM_START point defines the starting point for the partitioning (see Fig. 200). Its coordinates are given with reference to the global cartesian coordinate system. It must not lie on the rotational axis. Again, like for the SURF_PLANE_SYM link condition (chapter 6.3.4.4 Plane symmetry for non-symmetric meshes (SURF_PLANE_SYM)) a master strategy might be selected: MASTER
=
MAX | MIN}
Again, the strategy determines if the maximum or the minimum displacement of the linked nodes should be used to return a symmetric result. The link is determined in a similiar way as for plane symmetry: for each node, reference points on the surface with respect to the rotational cyclic symmetry and their interpolated displacements are calculated. The master criterion then influences which optimization displacement will be applied.
axis CYCLIC_SYM_START
Fig. 200 Cyclic coupling relative to a rotational axis
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Remarks 1. The coordinate system referenced by CS must be a Cartesian coordinate system. 2. Only the MASTER=MAX or MASTER=MIN criteria are allowed for determination of the master node. 3. The coordinates of parameter CYCLIC_SYM_START are given with reference to the global cartesian coordinate system.
6.3.4.6 Cyclic-plane symmetry combination (SURF_CYCLIC_PLANE_SYM) This link condition is a combination of cyclic rotational and planar symmetry. (chapter 6.3.4.4 Plane symmetry for non-symmetric meshes (SURF_PLANE_SYM) and chapter 6.3.4.5 Cyclic symmetry for non-symmet-
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ric meshes (SURF_CYCLIC_SYM)). First, the cyclic symmetry is enforced and afterwards the surface is modified to ensure plane symmetry in each segment. The plane for each segment cuts the segment into two halves. The following parameters are necessary for the definition of the link condition: CLIENT CLIENT_DIR CS TOL ANGLE CYCLIC_SYM_START
= = = = = =
SURF_CYCLIC_PLANE_SYM , ,
name_of_coord_system tolerance_value angle in degree , ,
In comparison to the SURF_CYCLIC_SYM case, the CYCLIC_SYM_START point is really important here. As it defines the starting point of the partitioning process, this point directly influences the areas that shall be made plane symmetric. Its coordinates are given with reference to the global cartesian coordinate system.
axis planes of symmetry
CYCLIC_SYM_START
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Fig. 201 Combination of cyclic and plane symmetry
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a)
b)
c)
Fig. 202 Differences of symmetries: a) plane symmetry (SURF_PLANE_SYM), b) cyclic symmetry (SURF_CYCLIC_SYM), c) combination of plane and cyclic symmetry (SURF_CYCLIC_PLANE_SYM)
6.3.4.7 Point symmetry (POINT_SYM) To be able to couple displacements symmetric to a point, the position of the point must be exactly specified. It is also necessary to specify tolerances in order to identify nodes that lie symmetric to one another relative to the point. The following three parameters are necessary for the definition of the link condition:
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CLIENT CS TOL
= POINT_SYM = name_of_coord_system = , ,
The origin of the coordinate system referenced by CS defines the symmetry point. The symmetry of the nodes (assigned by ND_GROUP in the DVCON_SHAPE command) is checked against the symmetry point. Symmetric nodes are assembled into a symmetry group (normally two symmetric nodes per symmetry group). Then the master node of the symmetry group is determined and the displacements of the client nodes are calculated in such a way that they move symmetric to the point of the master node (see Fig. 203). The tolerances are required in order to identify symmetric nodes. Point symmetric nodes share inversely equal coordinates (and added tolerances). The three tolerance values tol_* are assigned to the three coordinate directions of the coordinate system referenced by CS.
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Remarks 1. The coordinate system referenced by CS must be a cartesian coordinate system. 2. Only the MASTER=MAX or MASTER=MIN criteria are allowed for determination of the master node.
Fig. 203 Symmetric coupling relative to a point
6.3.4.8 Rotational symmetry (ROTATION_SYM) To couple displacements rotational symmetric about an axis, the position and the orientation of the axis must be exactly specified. It is also necessary to specify tolerances in order to identify nodes lying rotational symmetric relative to the axis. The mesh of the coupled node group should be rotational symmetric. These parameters are specified as follows: = = = =
ROTATION_SYM ,,
name_of_coord_system , ,
The origin of the coordinate system referenced by CS defines a point on the axis. The direction specified by the CLIENT_DIR parameter defines the axis direction. The symmetry of the nodes assigned by ND_GROUP in the DVCON_SHAPE command is checked against the symmetry axis. Symmetric nodes are assembled into a symmetry group (a simplification of the GROUP_AUTO_DEF command, where these symmetry groups can be build according to cylindrical coordinate systems, in combination with LINK_SHAPE, CLIENT=VECTOR and DVCON_AUTO_SHAPE). Then the master node of the symmetry group is determined and the displacements of
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the client nodes are calculated in such a way that they move rotational symmetric to the axis (see Fig. 204).
Fig. 204 Symmetry groups for rotational symmetric coupling Additionally an angle can be defined to divide the search area into discrete sections. ANGLE = For a detailed description of discrete and continuous node selection see vol.2 chapter 3.6.5, Automatic node group definition (GROUP_AUTO_DEF).
6.3.4.9 Coupling displacement coordinates (VECTOR)
CLIENT CS
= VECTOR = name_of_coord_system
The procedure involves calculating the difference between the current coordinates and start coordinates of the master node in relation to the coordinate systems referenced by CS.Then the start coordinates of the client nodes are calculated in relation to the coordinate system, the difference of the master
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The following two parameters are entered for coupling displacement coordinates:
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node is applied and the current coordinates of the client nodes are determined (see Fig. 205).
Fig. 205 Coupling of displacement coordinates (relative to a Cartesian coordinate system). It is also possible to couple only single displacement coordinates by adding options to the standard form of the CLIENT=VECTOR parameter: CLIENT CS
= VECTOR, ON/OFF, ON/OFF, ON/OFF = name_of_coord_system
Each of the three coordinates can be set to either ON or OFF. Only those displacement coordinates set to ON are coupled. Displacement coordinates set to OFF are not taken into consideration for the coupling. The default setting is VECTOR=ON, ON, ON. Remarks 1. The coordinate system referenced by CS can be a Cartesian coordinate system or a cylindrical or spherical coordinate system.
3. If the coordinate system is cylindrical or spherical, the displacement vectors of the master node and client nodes with respect to the global Cartesian coordinate system can generally differ. Corresponding coordinates are determined in the relevant coordinate system. For example, if a group of moving nodes allocated in a circle have the same radial coordinates in relation to a cylindrical coordinate system and are coupled with respect to this coordinate system, the nodes of the final design will always lie on the same circle.
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2. If the coordinate system is Cartesian, all nodes have the same displacement vector (given the name CLIENT=VECTOR), i.e., all nodes are moved translational like a ‘rigid body’. All nodes have the same displacement direction and the same amount of displacement.
SIMULIA Tosca Structure Shape Optimization
CLIENT CS
= DIRECTION = name_of_coord_system
The procedure is the same as that for CLIENT=VECTOR, but with the difference that the retained displacement vector is rescaled to the original displacement amount of the client nodes (see Fig. 206).
Fig. 206 Coupling of the displacement direction (with reference to a Cartesian coordinate system) Remark 1. See note for CLIENT=VECTOR (see vol.2 chapter 6: Remarks).
6.3.4.11 Coupling amount of displacement (LENGTH) The following parameter is entered for coupling the amount of displacement: CLIENT
= LENGTH
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The procedure is as follows: The amount of displacement of the master node is calculated and the displacement direction of the master node is determined (growth or shrinkage). The displacements of the client nodes are scaled in such a way that the displacement amount of the master node is retained (see Fig. 207).
Fig. 207 Coupling of the amount of displacements
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6.3.4.12 Coupling coordinates in the FE displacement coordinate system (DISP_CS) The following parameter is entered for coupling the coordinates in the FE displacement coordinate system: CLIENT
= DISP_CS
The procedure is as follows: The optimization displacements (coordinates) of the master node with reference to the FE displacement coordinate system are transferred directly into the FE displacement coordinate system of the client nodes. It is also possible to couple only single displacement coordinates by adding parameters to the standard form of the CLIENT=DISP_CS parameter CLIENT
= DISP_CS, ON/OFF, ON/OFF, ON/OFF
Each of the three coordinates can be set to either ON or OFF. Only those displacement coordinates set to ON are coupled. Displacement coordinates set to OFF are not taken into consideration for the coupling. The default setting is DISP_CS=ON, ON, ON. Remarks 1. The FE displacement coordinate system of the coupled nodes must be of the same type, i.e. either Cartesian, cylindrical or spherical. 2. Each node can have its own FE displacement coordinate system. Alternatively, if all nodes have the same FE displacement coordinate system, an identical link condition with CLIENT=VECTOR can be defined.
6.3.4.13 Stampable surface (SURF_STAMP)
CLIENT CLIENT_DIR CS
= SURF_STAMP = ,, = name_of_coord_system
The master nodes are found using the standard master criterion. The stamping surface is defined using the given stamping direction and the cutting edge automatically generated by Tosca Structure. All nodes of the node group are linked to this surface. An additional demolding direction can be included: DEMOLD_DIR
= ,,
The demolding direction has to be orthogonal to the client direction. Therefore Tosca Structure projects the demold vector onto a plane normal to the client direction.
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Maintaining a stampable surface during optimization involves defining a stamping direction. The stamping domain is defined using a node group. The direction defined by the CLIENT_DIR parameter specifies the stamping direction.The link condition is defined using the following parameters:
SIMULIA Tosca Structure Shape Optimization
Remarks 1. This link condition allows the definition of stamping restrictions to arbitrary meshes. No special meshing conditions have to be taken into consideration. 2. It is possible to define stamping restrictions for initial components which are not stampable in the beginning of the optimization procedure. However, this is not recommended because the conditions for stamping are met in the first design cycle. This may lead to large node displacements and a distorted finite element mesh.
6.3.4.14 Turnable surface (SURF_TURN) Maintaining a turnable surface during optimization involves defining a rotation axis. The domain that assures a turnable surface is defined using a node group, i.e. all nodes of the specified surface node group are checked for rotation symmetry in the given rotation axis. The link condition is defined using the following parameters: CLIENT CLIENT_DIR CS
= SURF_TURN = ,, = name_of_coord_system
The direction defined by the CLIENT_DIR and the origin of the coordinate system specify the exact position and direction of the rotation axis. The master nodes are found using the standard master criteria. The turning surface is defined using the given rotation axis and the cutting edge automatically generated by Tosca Structure. All nodes of the node group are linked to this surface.
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Remarks 1. This link condition allows the definition of turning restrictions to arbitrary meshes. No special meshing conditions have to be taken into consideration. 2. The referenced coordinate system must lie exactly on the rotation axis as the algorithm always orientates the surface towards the coordinate system. If non-symmetrical effects occur during optimization, the correct position of the coordinate system has to be checked. 3. It is possible to define turning restrictions for initial components that are not turnable in the beginning of the optimization procedure. However, this is not recommended because the conditions for turning are met in the first design cycle. This may lead to large node displacements and a distorted finite element mesh.
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6.3.4.15 Drillable surface (SURF_DRILL) The drill restriction is a combination of the turning and the demolding restriction. Maintaining a drillable surface during optimization involves defining the drill axis and the drill feed. The drilling domain is defined using a node group, i.e. all nodes of the specified surface node group are checked for drilling in the given drill direction. The link condition is defined using the following parameter: CLIENT CLIENT_DIR CS ANGLE
= = = =
SURF_DRILL ,,
name_of_coord_system (0° < angle < 45°)
The direction defined by the CLIENT_DIR and the origin of the coordinate system specify the exact position and direction of the drill axis, the angle specifies a minimum surface angle. The shape of the drilling surface can be specified with an additional undercut tolerance. The term ‘drilling surface’ in this case should be interpreted in a more general sense. UNDERCUT_TOL
= (>0)
drill direction
Fig. 208 Drilling surface with undercut tolerance Remark 1. See note for CLIENT=SURF_TURN (see vol.2 chapter 6: Remarks).
6.3.4.16 Demoldable surface (SURF_DEMOLD) Defining a demolding or forging restriction involves specifying the manufacturing direction. The area to restrict is defined using a node group of surface nodes. Demolding in the specified direction or forging against this direction is maintained during optimization and undercuts are avoided. The link condition for the demold restriction is defined as follows:
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CLIENT DEMOLD_DIR CS CHECK_GROUP TOL
= = = = =
SURF_DEMOLD ,,
name_of_coord_system name_of_node_group , ,
The direction defined by the DEMOLD_DIR specifies the demolding direction respectively the negative forging direction. All nodes in the node group are checked for undercuts and for demolding against the specified CHECK_GROUP. This group of surface nodes should qualify the cast sufficiently. In the simplest case the group of all surface nodes can be chosen. In Fig. 209 node group 1 describes the demolding area. If the check group contains only node group 1 the undercut is not detected because the check group describes no restricting surface. Only node group 1 and 2 together qualify a surface to detect undercuts reliably.
Fig. 209 Demolding check group In addition, an angle for the surface inclination may be specified using the ANGLE parameter. ANGLE = The undercut tolerance specifies the maximum valid undercut (default = 0):
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UNDERCUT_TOL
=
Remarks 1. It is possible to define demolding restrictions for initial components which are not demoldable at the beginning of the optimization procedure. However, this is not recommended as the conditions for demolding are met in the first design cycle. This may lead to large node displacements and a distorted finite element mesh. 2. No single master nodes need to be determined for demolding restrictions. The master criterion in this case is used to determine a priority rule between nodes in the undercut and overlapping nodes. 3. All SURF_xxx link commands have a parameter called: SURF_PARAM = , which are used to create a spline that
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it may help setting SURF_PARAM. Important is that must be larger than 4 and at least double the size of . Good values are e.g. SURF_PARAM = 12, 4. 4. Another reason for the above error message is that there is not enough nodes in the design area to create the "surface" for the SURF_xxx condition.
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defines the "surface" in the SURF_xxx LINK_SHAPE commands. The values , are integer values and automatically determined by Tosca Structure. In the event of an error like:
SIMULIA Tosca Structure Shape Optimization
5. Default tolerances for all SURF_xxx LINK_SHAPE commands are TOL = 0.01, 0.01, 0.01. If you have a mesh where these values are either very large or very small consider setting them to about 0.25 * element edge length in design area.
6.3.4.17 Command examples This section contains examples of link conditions. Link condition with fixed master node All nodes of the previously defined node group ‘node_rigid’ should have the same displacement with respect to the global Cartesian coordinate system as the design node with the number 46. Node 46 need not be a part of the node group ‘node_rigid’. The link condition should have the name ‘link_rigid’. The link condition is then used in the restriction with the name ‘dvcon_rigid’. LINK_SHAPE ID_NAME MASTER CLIENT CS
= = = =
link_rigid NODE, 46 VECTOR CS_0
END_
DVCON_SHAPE ID_NAME ND_GROUP CHECK_LINK
= dvcon_rigid = node_rigid = link_rigid
END_
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Coupling condition with automatic determination of the master node All nodes of the node group ‘ndgr_left’ should have the same displacement as the node from ‘ndgr_left’ that has the greatest outward displacement. In the same way, all nodes of the node group ‘ndgr_right’ should have the same displacement as the node from ‘ndgr_right’ that has the greatest outward displacement. This requires a link condition and two restrictions. LINK_SHAPE ID_NAME MASTER CLIENT CS
= = = =
link_left_or_right MAX VECTOR CS_0
END_
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DVCON_SHAPE ID_NAME ND_GROUP CHECK_LINK
= dvcon_left = ndgr_left = link_left_or_right
END DVCON_SHAPE ID_NAME ND_GROUP CHECK_LINK
= dvcon_right = ndgr_right = link_left_or_right
END_
In each design cycle the system identifies which nodes in each of the node groups, ‘ndgr_left’ and ‘ndgr_right’, has the greatest positive displacement (in the growth direction). Usually, these are the nodes with the largest stress difference between the effective value and the targeted value. These displacements are then applied to all nodes of the node groups ‘ndgr_left’ and ‘ndgr_right’, respectively. The following command can be used instead of the two individual DVCON_SHAPE commands: DVCON_AUTO_SHAPE ID_NAME = dvcon_* ND_GROUP_FAMILY = ndgr_* CHECK_LINK = link_left_or_right END_
6.4
Objective Function The objective function describes the optimization target. In general, one scalar value (sometimes combined from other scalars) is to be maximized or minimized.
6.4.1
Overview The OBJECTIVE FUNCTION is the function, which value can be maximized or minimized during the optimization. This function depends on the results of the FE analysis combined into design responses (DRESP). Tosca Structure.shape works with a CONTROLLER-based algorithm which homogenizes the stresses with respect to a reference value (see also chapter
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The naming ‘left’ and ‘right’ is determined automatically from the complete name of the node groups and added to the root name of the automatically generated DVCON_SHAPE entries. However, this requires that only these two node groups begin with the name ‘ndgr_’ otherwise other node groups will be taken into consideration.
SIMULIA Tosca Structure Shape Optimization
6.1.1 Theoretical background). For simple optimizations this reference value can be ignored - Tosca Structure.shape will automatically generate a reference value which will be adequate for most cases.
6.4.2
Reference stress You may want to define a reference value yourself. In this case you need to understand how Tosca Structure.shape works. The CONTROLLER-based algorithm is driven by following redesign rule: • Design nodes with stress above the reference value are moved outwards (growth). • Design nodes with stress below the reference value are moved inwards (shrinkage). This produces components with homogenized stress in the design area. So, if you choose a high reference value most design nodes will shrink in order to achieve this value. A low reference value will have the opposite effect. With some practice, a good choice of reference value can be estimated giving the designer an optimal control over the shape optimization. You may also choose the reference value to variable e.g. dependent on a design response. This has a special use by design of relief notches where the reference value is chosen outside the design nodes area. This causes the design nodes to shrink until they have the same stress value as the reference value. This „trick“ can only be done if the design area is relatively close to the area where the reference value is. Otherwise, you will not get the stress dampening effect of a relief notch.
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Remarks: 1. A reference value is NOT the same as a CONSTRAINT! For most real structures, the maximum stress of a converged shape optimization will be some percent larger than the given or the automatically calculated reference stress. 2. Some structures and/or loading situations are not well suited for the CONTROLLER-based algorithm. You must have the correlation between growth in design nodes also minimizes the stresses. - One example is a cantilever beam with a prescribed displacement at its free end. Due to the high stresses at the supports, the beam will become thicker. Because of the prescribed displacement the stresses will be higher in the next iteration. The homogenization works but the stresses will increase because the beam stiffness increases as well.
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- Another example is shape design in contact area: In this case we know that the design rule must be the opposite the normal design rule because growth will cause even greater contact stresses. This can be turned around by using the optimization setting SCALE and set it to a negative value. Now, the shape optimization will shrink by high contact stresses and thus homogenize these to achieve an homogeneous contact.
6.4.3
Objective function terms Tosca Structure.shape allows optimization on different stress hypotheses, strain formulations and damage results (see also chapter 4.4 Design Responses). The most used equivalent stress is von Mises (SIG_MISES). Description
SIG_1 SIG_2 SIG_3
Maximum principal stress 2nd. principal stress Minimum principal stress
SIG_11 SIG_22 SIG_33 SIG_12 SIG_23 SIG_13
Components of stress tensor
SIG_ABS_123
Maximum of the absolute value of the principal stresses
SIG_ABS_3
Absolute value of the minimum principal stress
* The marked design responses are only supported by the Abaqus and ANSYS interface, see vol.2 chapter 11.1, Abaqus and vol.2 chapter 11.2, ANSYS. ** Note that ABQ_ND_PEEQ is the scalar value that Abaqus calculates as PEEQ, which is NOT the same as STRAIN_PLASTIC. ABQ_ND_PEEQ is only available in Abaqus.
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SIG_MISES SIG_TRESCA SIG_BELTRAMI SIG_GALILEI SIG_KUHN SIG_MARIOTTE SIG_SANDEL SIG_SAUTER SIG_DRUCKER_PRAGER SIG_CONTACT_PRESSURE *
von Mises stress hypothesis Tresca stress hypothesis Beltrami stress hypothesis Galilei stress hypothesis Kuhn stress hypothesis Mariotte stress hypothesis Sandel stress hypothesis Sauter stress hypothesis Drucker-Prager stress hypothesis Contact stress pressure
SIG_CONTACT_SHEAR * SIG_CONTACT_SHEAR_X * SIG_CONTACT_SHEAR_Y * SIG_CONTACT_TOTAL *
Total shear contact stress Shear X Contact stress Shear Y Contact stress Total Contact stress
Strain formulations STRAIN_ELASTIC* STRAIN_PLASTIC* STRAIN_TOTAL * STRAIN_ENERGY STRAIN_ENERGY_DENS Solver specific results ABQ_ND_PEEQ ** Damage results
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DAMAGE DAMAGE_LC
Description Elastic Strain Plastic Strain Total Strain (elastic + plastic) Strain energy Strain energy density Description Abaqus PEEQ nodal value
Description Damage value from durability analysis Damage value from durability analysis with loadcase information (mustuse ONF 601)
* The marked design responses are only supported by the Abaqus and ANSYS interface, see vol.2 chapter 11.1, Abaqus and vol.2 chapter 11.2, ANSYS. ** Note that ABQ_ND_PEEQ is the scalar value that Abaqus calculates as PEEQ, which is NOT the same as STRAIN_PLASTIC. ABQ_ND_PEEQ is only available in Abaqus. Remark: ref
1. For controller based shape optimization the reference value ( ϕ i , see chapter 4.1.1 Mathematical formulation) has a special meaning. The reference value is the value around which Tosca Structure homogenizes the ref stress around. Thus, a value ϕ i = 0 usually does not make sense and
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ref
Tosca Structure calculates a default reference value if REFERENCE ( ϕ i ) is unset. The reference calculated can be seen in TOSCA.OUT ----------------------------------------------------------------f OBJ_FUNC_TERM Value Weight Reference | ----------------------------------------------------------------DRESP_MAX_MISES 92.5353 1.00000 87.4261 -----------------------------------------------------------------
2. Also, for controller based shape optimization the user must either set all REFERENCE-values or none at all (automatic reference value calculation).
6.5
Constraints The only allowed constraints for controller based shape optimization are volume and weight constraints.
6.5.1
Volume constraint In order to select volume as the design response, the volume must be requested with TYPE=VOLUME. The individual element volumes of the element group (EL_GROUP parameter) are then added together by the summation parameter (GROUP_OPER=SUM parameter) to achieve the total volume. The volume is a variable independent of the load cases. The design response is labeled with a unique name (ID_NAME parameter) so it can be referenced as a constraint. A typical definition of a design response appears as follows: DRESP = = = = = =
dresp_volume SYSTEM
all_elements VOLUME SUM EVER
END_
Once the volume of an element area has been defined as the design response, the design response must be defined as a constraint using the CONSTRAINT parameter. The value of the equality constraint (EQ_VALUE parameter) is also declared. In addition, the parameter EQ_VALUE is declared as absolute value (MAGNITUDE=ABS) or relative value (MAGNITUDE=REL) in relation to the initial volume. The constraint is labeled with a unique name (ID_NAME parameter) so it can be referenced in an optimization job (see OPTIMIZE command). A typical definition of a constraint appears as follows:
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ID_NAME DEF_TYPE EL_GROUP TYPE GROUP_OPER UPDATE
SIMULIA Tosca Structure Shape Optimization
CONSTRAINT ID_NAME DRESP MAGNITUDE EQ_VALUE
= = = =
volume_constraint
dresp_volume REL 1
END_
Example: The total volume of a element group in the start model is 2000. For the optimized model a total volume of 1800 is requested for the element group. Using absolute values, MAGNITUDE=ABS, EQ_VALUE=1800 must be declared. Using relative values, MAGNITUDE=REL, EQ_VALUE=0.9 must be declared. Remarks 1. The CONSTRAINT definition must be activated by a reference in the OPTIMIZE command. 2. It is highly recommended to choose a volume constraint near the orignal volume, say +/- 5% depending on the mesh quality and size of design area. 3. Tosca Structure.shape will enforce the volume constraint in first design cycle. This may destroy the mesh, esspecially if the volume constraint is far away from the initial volume. If you want to turn off this mechanism and let Tosca Structure.shape iterate for more iteration to achieve volume constraint use OPTIONS. This setting is not recommended as it will simply cause more design cycles before the mesh is corrupted.
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OPTIONS SHAPE_FORCE_VOLUME = OFF END_
4. Maintaining the volume constraint involves an iterative process, i.e. several steps are performed within each design cycle to approximate the volume constraint. Each step in the volume iteration involves executing a complete MESH_SMOOTH algorithm. In order to keep the computing time within limits, it is strongly recommended to select the MESH_SMOOTH area as small as possible and to keep the various levels of the MESH_SMOOTH definition (particularly LEVEL_CONV, LEVEL_DVCON and LEVEL_QUAL) as low as possible! A complex mesh smoothing can result in a significant increase in computing time! 5. It is also recommended to define a volume constraint when using the objective function ‘maximization of the lowest natural frequency’. The user can control the volume increase or decrease by activating this constraint.
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Consequently, it may be possible to achieve a further increase in the frequency.
6.5.2
Weight constraint Weight constraints are defined in exactly the same way as volume constraints (see chapter 6.5.1 Volume constraint). Using this design response a physical target weight can be set explicitly. This is in particular useful when different materials are present in the model. The corresponding design response is defined as follows: DRESP ID_NAME DEF_TYPE EL_GROUP TYPE GROUP_OPER UPDATE
= = = = = =
dresp_volume SYSTEM
all_elements WEIGHT SUM EVER
END_
Once the volume of an element area has been defined, the design response must be referenced in the CONSTRAINT definition.
6.6
Typical Optimization Tasks for Static Analysis The section describes the typical optimization tasks for linear or non-linear static analysis.
Minimization of maximum equivalent stress Probably the most used shape optimization type is a minimization of the maximal von Mises stresses. This task is automated in Tosca Structure so that the user must not care about any reference values. If the default settings cause the geometry to change unwanted in size a volume constraint can be utilized. See also chapter 6.6.2 Notch optimization with fixed reference value. Example: Define a minimum of maximum von Mises stress with a volume constraint.
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6.6.1
SIMULIA Tosca Structure Shape Optimization
Tosca ANSA environment 1. Apply New | EQUIVALENT_STRESS command on OBJ_FUNC item
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2. Apply Edit on OBJ_FUNC item. Set TARGET = MINMAX.
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Commands DRESP ID_NAME DEF_TYPE TYPE ND_GROUP LC_SET LC_SET GROUP_OPER
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= = = = = = =
DRESP_VON_MISES SYSTEM SIG_MISES design_nodes ALL,1,All ALL,2,All Max
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END_ OBJ_FUNC ID_NAME TARGET DRESP
= MY_OBJ_FUNC = MINMAX = DRESP_VON_MISES, ,
END_
6.6.2
Notch optimization with fixed reference value For full control over the Tosca Structure.shape controller the user may prescribe a fixed reference value. This can be used to force the homogenization to around a certain value. Again, it must be stressed that this is not a stress constraint! It is simply a way to gain more influence over the shape controller.
In the shown example Fig. 210 the effect is clearly seen: • A low reference value enforces more growth • A high reference value enforces more shrinkage
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Fig. 210 The hole plate example with a reference value of 70 N/mm and 120 N/mm
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Tosca ANSA environment Apply New | EQUIVALENT_STRESS command on OBJ_FUNC item.
Command OBJ_FUNC ID_NAME TARGET DRESP END_
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= MY_OBJ_FUNC = MINMAX = DRESP_VON_MISES, , 120.
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6.6.3
Notch relief with variable reference value Increasing the stress in one notch can decrease the stress in another near by notch (Neuber’s law of load stress decay). This is typically called a relief notch. This is a very useful tool if you experience too large stresses in an area that you are not allowed to change, but you are allowed to change nearby geometry (the "nearby" is important - the stress decay does not work over great distances but only locally). To understand this type of optimization a simple example is the best explanation:
Fig. 211 Design area and reference nodes for determining the reference stress
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In Fig. 211 is a simple notch shown with a relief notch. The primary notch is not allowed to be changed only the relief notch. The result is shown in Fig. 212 where the stresses at the reference nodes are drastically minimized through the optimized relief notch.
Fig. 212 Optimization result using variable reference value
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Tosca Structure.gui 1. Define a VARIABLE for the reference stress of the reference nodes.
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2. Use this VARIABLE in as reference value in the objective function, OBJ_FUNC.
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Commands VARIABLE ID_NAME DEF_TYPE TYPE ND_GROUP LC_SET LC_SET GROUP_OPER
= = = = = = =
REF_NODE_STRESS SYSTEM SIG_MISES refence_nodes ALL,1,All ALL,2,All Max
= = = = = = =
DRESP_VON_MISES SYSTEM SIG_MISES design_nodes ALL,1,All ALL,2,All Max
END_ DRESP ID_NAME DEF_TYPE TYPE ND_GROUP LC_SET LC_SET GROUP_OPER END_ OBJ_FUNC ID_NAME TARGET DRESP
= MY_OBJ_FUNC = MINMAX = DRESP_VON_MISES, , REF_NODE_STRESS
END_
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6.7
Advanced Tosca Structure.shape Optimizations Tosca Structure.shape is used for the optimization of already detailed designs. Thus, a detailed and realistic analysis model is required for reliable optimization results. Tosca Structure allows optimization in combination of non-linear or contact analysis to avoid error prone model simplifications. This chapter describes these advanced features used for shape optimization.
6.7.1
Highly nonlinear shape optimization For highly non-linear calculations is the stress measure not always a good indicator e.g. a structure under plastic deformations will (for ideal plastic)
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have a large constant stress over the plastic area. For this reason most analysts use a strain measure to inspect these areas. Tosca Structure.shape optimization supports different strain measures for this purpose, currently only supported by Abaqus, see vol.2 chapter 11.1, Abaqus, and ANSYS, see chapter 11.2 ANSYS. Example: Choose TOTAL_STRAIN_ENERGY as design response measure:
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Tosca Structure.gui
Command DRESP
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ID_NAME DEF_TYPE TYPE ND_GROUP LC_SET GROUP_OPER
= = = = = =
MY_DRESP SYSTEM STRAIN_TOTAL design_nodes ALL,1,All Max
END_
6.7.2
Minimization of contact pressure Another special usage of Tosca Structure.shape controller algorithm is the optimization of contact zones. Here it is important to understand that the normal shape optimization must be reversed because growth in a contact zones will result in a higher contact pressure and shrinkage in a lower. This is done by changing the setting SCALE in OPT_PARAM to a negative value, usually a small negative value e.g. -0.001. The Tosca Structure.shape optimization of contact zones only works within the contact zone where small changes in the contact surface usually has a
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big influence on the contact pressure. This is the reason for a small SCALE value. The CONTACT_PRESSURE design responses are currently only supported by Abaqus, see vol.2 chapter 11.1, Abaqus. Tosca ANSA environment 1. Choose TYPE = SIG_CONTACT_PRESSURE
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2. Change the SCALE parameter in the dialog opened by New | SETTINGS command applied on SHAPE_OPTIMIZATION_CONTROLLER item.
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Commands DRESP ID_NAME DEF_TYPE TYPE ND_GROUP LC_SET GROUP_OPER
= = = = = =
MY_DRESP SYSTEM SIG_CONTACT_PRESSURE DESIGN_NODES ALL,1,All Max
END_
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OPT_PARAM ID_NAME OPTIMIZE SCALE
= MY_PARAMETERS = MY_OPTIMIZATION_TASK = -0.001
END_
6.8
Settings
Fig. 213 Optimization settings (OPT_PARAM) in Tosca ANSA environment Each OPT_PARAM command has a unique name (ID_NAME parameter) and references a previously defined optimization job (OPTIMIZE command). The specified parameters only relate to the given optimization task. A typical OPT_PARAM command appears as follows: OPT_PARAM ID_NAME OPTIMIZE ... END_
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= param_for_shape_optimization = shape_optimization
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Shape optimization in Tosca Structure operates with a controller-based method. The controller has been given numerous default settings that deliver satisfying results for a variety of optimization models. Usually, these default settings do not need to be changed by the user. However, using a specific configuration of the controller for a given optimization task can lead to a modified controller response and consequently the optimization procedure can be improved. The user can set several optimization parameters using the OPT_PARAM command and thereby influence the controller response. In Tosca ANSA environment, the settings are available in the task manager (New | SETTINGS command on SHAPE_OPTIMIZATION_CONTROLLER item) or using the OPT_PARAM button in the modules buttons. In Tosca Structure.gui, the settings are defined in OPT_PARAM command.
SIMULIA Tosca Structure Shape Optimization
Six parameters can be set by the user for shape optimization: • Scaling of the allowed amount of displacement • Treatment of the midside nodes during the optimization • Curvature based modification of the optimization movement vector • Filtering of the optimization displacements • Updating of the normal vectors (optimization displacement vector) • Control of the increments according to the allowed displacements Remark 1. The OPT_PARAM command is also used in topology optimization (volume 3: OPT_PARAM). However, the optimization parameters that can be set depend on the type of optimization. The only parameters that can be set here are those allowed for shape optimization.
6.8.1
Scale of displacement (SCALE) The controller provides an automatic increment control of the optimization displacements. An initial increment is first determined based on the mesh of the FE start model. The size of the increment is then automatically adjusted in every design cycle. Usually, the user does not need to modify the increment control manually. The user can increase or decrease the increment using a scaling factor (SCALE parameter):
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... SCALE ...
=
The default setting is SCALE=1.0, i.e. the optimization displacements are applied in increments determined by the controller. If the selected scaling factor has a value greater than one, the increment size determined by the controller will increase correspondingly, i.e. the optimization is accelerated. On the other hand, if the selected scaling factor has a value less than one, the increment size determined by the controller will decrease accordingly, i.e. the optimization is slowed down. Example: With SCALE=2.0 the increment size as determined by the controller is doubled. With SCALE=0.8 the increment size of the controller is reduced to 80% of the initial increment size. The scaling factor can be split in a factor for growth and a factor for shrinkage: ... SCALE ...
= ,
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Remarks 1. It is highly recommended to perform the first optimization run with the default increment size (SCALE=1.0). From evaluating the obtained results, it can be decided if the optimization should be accelerated or slowed down. 2. Increasing the increment size can be useful when several optimization steps in the same direction are performed in the beginning of the optimization and hardly any change in the increment size is observed. Especially, for tight FE meshes with small element edge lengths, the increment size is relatively small which leads to numerous design cycles with relatively small changes in the model in each design cycle. If the selected increment size is too large, the possibility that the optimum will be bypassed exists and the optimization will not converge. In addition, the mesh quality decreases with increasing increment size. In extreme cases individual elements may collapse. 3. Decreasing the increment size is recommended when the start model is close to optimum at the start. A decrease of the increment size can also be helpful when numerous restrictions with link conditions (DVCON_SHAPE with CHECK_ LINK) are contained in the optimization task. A decrease of the increment size can also be of advantage when the mesh quality is poor.
6.8.2
Treatment of the midside nodes (MID_NODES) Only corner nodes (from finite elements) are supported as design nodes. Midside nodes may be included in the design node group but the optimization displacements of the midside nodes of second order elements is interpolated from the optimization displacement of the adjacent corner nodes. The interpolation method can be chosen with the MID_NODES parameter: ... MID_NODES ...
= [ LINEAR | INTERPOLATE ]
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4. With a license for the module Tosca Structure.nonlinear a negative scale factor can be executed. In this case, the calculated nodal displacements are multiplied with the scale factor and the direction of the displacement changed. The controller strategy can be inverted (i.e. high stress = shrinkage, low stress = growth). This functionality allows the optimization of contact surfaces as an example (see chapter 6.7.2 Minimization of contact pressure).
SIMULIA Tosca Structure Shape Optimization
polated from the optimization displacement of the connected corner nodes. If in the initial position the midside node is on the line between the corner nodes there will be no difference between the two methods. But if the edge of the element is bent only with INTERPOLATE the bending can be prevented.
6.8.3
Curvature based modification of optimization displacements The nodal optimization movement vector is modified in areas of high curvature to prevent a collapse of the mesh for large volume changes (CURV_SMOOTH). A bigger radius causes a bigger curvature based modification of the optimization movement vector. (Default=5.0 * element edge lengths; OFF=0.0) = 5.0
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... CURV_SMOOTH ...
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6.8.4
Filter function for the optimization displacements (FILTER) To smooth local peaks of the nodal reference stresses, the item FILTER can be specified to activate a filter function: ... FILTER ...
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= , ,
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Fig. 214 Curvature based modification of the optimization movement vector
SIMULIA Tosca Structure Shape Optimization
The filter is given by: N
i = 1 Φi Bij Φ j = ---------------------------N i = 1 Bij
B ij = ( r j – d ji )
r j = r max e
p
– 0 ,5 ( κ max ⁄ σ )
κ max = max ( n j × n R ) Φ is the filter value for node j. The main filter function (B) decreases with the distance (d) between node i and j. The maximal radius ( rmax ) defines the maximum distance for the nodes i to influence the filter value. The curvature dependency ( r j ) defines a weight function to reduce the radius at higher local surface curvature ( κ max ) approximated by the vector product of the node normal ( n j ) to the neighboring nodes ( n k ). SIGMA ( σ ) and EXPONENT (p) are optional with the default values (0.2 and 1., respectively). The smaller the SIGMA, the larger is the influence of the surface curvature. To avoid this effect, use a large SIGMA value (e.g., 10000). The exponent value defines the weight function which controls the influence depending on the distance from the node. To smooth local peaks of the nodal reference stresses, use the DRESP OPER=FILTER which gives the user the possibility to define filters that correspond to single design responses. Example:
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DRESP ID_NAME DEF_TYPE VAR_OPER VAR_A RADIUS EXPONENT SIGMA
= = = = = = =
DRESP_MISES_FILTERED OPER FILTER DRESP_MAX_MISES 30.0 1.0 1.0
END_
The parameters RADIUS, EXPONENT and SIGMA have the same meaning as in the filtering of nodal displacements. Remark Large values of RADIUS may increase CPU-time.
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6.8.5
Updating the optimization displacement vectors (VECTOR) As explained in section vol.2 chapter 6.3.1 an optimization displacement vector is determined by the optimization algorithm for every design node. This vector graphically corresponds to the outer surface unit normal at the node and indicates the optimization displacement direction. Restrictions influencing the direction (DVCON_SHAPE with CHECK_DOF and CHECK_BC) are included in the calculation of the optimization displacement vectors. The VECTOR parameter enables the user to specify the design cycle in which to determine the optimization displacement vectors: ... VECTOR ...
= [ EVER | FIRST ]
Fig. 215 Fixed and updated optimization displacement vectors
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The default setting is VECTOR=EVER. The optimization displacement vectors are re-determined in every design cycle by the optimization algorithm and consequently adjusted to changed conditions (for example shape of the structure, effective restrictions, mesh quality, etc.). With the setting VECTOR=FIRST, the optimization displacement vectors are calculated only once in the first design cycle and then kept constant in all other cycles. The optimization displacement vectors are not adjusted to changes in conditions during the remaining part of the optimization. Fig. 215 provides an illustration of the two settings. Generally, VECTOR=EVER provides better results since the mesh smoothing algorithm is less restricted and a better mesh can be achieved. However, in certain cases the setting VECTOR=FIRST can be of advantage.
SIMULIA Tosca Structure Shape Optimization
6.8.6
Control of the amount of optimization displacement (DISP) Based on the current FE mesh, an allowed amount of displacement is determined for every design node. This displacement variable limits the amount of the optimization displacement, i.e. optimization displacements that are greater than the allowed displacements are scaled back automatically to the allowed value node by node. This is intended for avoiding the collapse of a neighboring element when having a large optimization displacement of one node. The controller provides automatic increment control of the optimization displacements. The increment size is dependent on the allowed displacements of the design nodes. A decrease of the allowed displacements (a decrease in the quality of the FE mesh) automatically leads to a decrease in the increment size of the controller. The increment size of the controller is automatically adjusted in every design cycle. The DISP parameter enables the user to specify which allowed displacement is to be used in the increment control: ... DISP ...
= [ MINIMUM | AVERAGE ]
DISP=AVERAGE is the mean value of the allowed amount of displacement for the design nodes used in the increment control; DISP=MINIMUM (default) is the smallest value used. The setting DISP=AVERAGE delivers a larger increment size and consequently a faster approximation to the optimum. However, this opens for the possibility that nodes for which only small displacements are allowed move too little causing ‘undesirable corners’ in the design area.
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6.9
Check run (TEST_SHAPE) After the definition of the optimization task, all definitions should be checkedfor completeness and correctness. This can be done using a TEST_SHAPE run which performs a "virtual optimization" with fictitious displacements.
6.9.1
General Before beginning an optimization, it is advisable to check the output file (TOSCA.OUT) of the optimization preprocessors for any possible warnings or errors. If the optimization preprocessing (for more detailed information see vol.2 chapter 12) has been performed without error, the user has the option of carrying out a test run for the shape optimization without a prior FE analysis. This is done by applying pseudo ‘optimization displacements’. This option enables the user to quickly and easily check if the mesh smoothing (see vol.2
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chapter 6.3.2) and the restrictions (see vol.2 chapter 6.3.3) are fully defined and will deliver the desired results. The above procedure is especially recommended for link conditions (see vol.2 chapter 6.3.4). The following are typical questions that such a test run can answer: • Is the design area, i.e., the design nodes, selected correctly? • Is the MESH_SMOOTH area too small or too large? • Is the selected transition area between the design area and the border of the MESH_SMOOTH area in order? • Will all of the restrictions be fulfilled (displacement directions, amount of displacement, contact against solids or elements, link conditions)? • Will any nodes be moved by MESH_SMOOTH although they should not be modified, so that additional restriction of these nodes is needed? The results of the test run are sent to user-defined files that can be subsequently loaded into a suitable postprocessor for evaluation. This allows the test results to be easily displayed and checked. If the results of the test run are not satisfying, the optimization model may need to be modified. The effort required to perform a test run in the optimization preprocessor is much less than the effort required for a complete optimization. Unwanted side effects can make a ‘costly’ and time-consuming optimization useless although the side effects might have been recognized without much effort in a test run.
Test run (CHECK_INPUTS) in Tosca ANSA environment In Tosca ANSA environment the test run is available in the CHECK_INPUTS item of Task Manager. First apply New | TEST_SHAPE_CHECK command on CHECK_INPUTS item, then apply New | TEST_SHAPE command on TEST_SHAPE_CHECK item. The test is performed when Update command is applied on the created TEST_SHAPE item. The results are opened in Tosca Structure.view using the item VTF_VISUALIZATION that is also created
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6.9.2
SIMULIA Tosca Structure Shape Optimization
below TEST_SHAPE_CHECK. For a detailed description please refer to vol.1 chapter , Start Manual.
Fig. 216 CHECK_INPUTS: Definition of a test run for shape optimization
6.9.3
Test run in Tosca Structure.gui In Tosca Structure.gui your test displacements will be defined using the TEST_SHAPE command mask. To start the test run, start Tosca Structure with Type test1. Create your visualization sequence using Tosca Structure.report. For a detailed description please refer to vol.1 chapter 2.3.6.1.
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Fig. 217 Start of a test run for shape optimization in Tosca Structure.gui
6.9.4
Command syntax The test run in the shape optimization is controlled by the TEST_SHAPE command. A test run is always based on a previously defined optimization job that is referenced in the OPTIMIZE command. The format information for the postprocessing is specified with the FORMAT parameter. The name of the file into which the postprocessing data is written is specified with the FILE_NAME parameter. The test displacement in a specified direction (DIRECTION) is applied in a specified number of increments (INCREMENT parameter) until reaching a maximum displacement (DISPLACEMENT parameter). A typical TEST_SHAPE command appears as follows: TEST_SHAPE
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OPTIMIZE
FORMAT DIRECTION DISPLACEMENT INCREMENT
= = ONF FILE_NAME= = [ GROW | SHRINK | RANDOM ] = =
END_
Remarks 1. If all the information entered by the user is correct, the TEST_SHAPE command is executed immediately after it is entered. The command does not have its own name with which it can be referenced and all command data are only temporarily active during the execution of the command. 2. The referencing of a previously defined optimization task (OPTIMIZE command) is mandatory. The test displacements are applied to the design nodes of the optimization job. 3. Specification of a file name (FILE_NAME parameter) is optional. By default the file name TEST_SHAPE is used. An increment number is always attached to the file names (for example, 000, 001, 002 etc.) to enable identification of the results from the various increments. Caution: The automatic creation of the vtfx report requires the use of the default file name "TEST_SHAPE".
5. Because uniform displacements are applied with DIRECTION=GROW or SHRINK, it may occur that LINK_SHAPE conditions will be insufficiently tested due to the fact that LINK_SHAPE conditions (conditional on the uniform displacements) may be fulfilled a priori. If the optimization job contains LINK_SHAPE conditions, it is recommended to apply non-uniform displacements using DIRECTION=RANDOM. This will allow the correct operation of the LINK_SHAPE conditions to be tested. 6. Specification of the maximum amount of displacement (DISPLACEMENT parameter) is optional. If no maximum amount of displacement is specified by the user, then a maximum amount of displacement dependent upon the measurements of the FE mesh will be automatically determined.
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4. Specification of a displacement direction (DIRECTION parameter) is optional. The default setting is GROW. Three possibilities can be selected in specifying the displacement direction: uniform growth of all design nodes in the optimization group outwards (DIRECTION=GROW), uniform shrinkage of all design nodes in the optimization group inwards (DIRECTION=SHRINK) or non-uniform ‘randomly controlled’ displacement of the design nodes in the optimization group (DIRECTION=RANDOM).
SIMULIA Tosca Structure Shape Optimization
7. Specification of a number of increments (INCREMENT parameter) is optional. The default value is INCREMENT=1. If the user specifies 5 increments, for example, 6 results files are generated, whereby the first result file with the file extension ‘000’ represents the initial state. 8. If DIRECTION=RANDOM is selected, it is possible that the design node with the maximum displacement will have a smaller amount of displacement than is specified in the DISPLACEMENT parameter. Here, the maximum specified displacement only represents an upper limit that does not need to be achieved due to the ‘randomly controlled’ distribution of the displacements. Example: The optimization task named shape_optimization should be subjected to a test run. The file names are to have the name test_grow. In the growth direction five displacement increments should be applied with a maximum displacement of 1.5 length units, i.e. the displacements are applied in increments of 0.0, 0.3, 0.6, 0.9, 1.2 and 1.5. TEST_SHAPE OPTIMIZE FILE_NAME DIRECTION DISPLACEMENT INCREMENT
= = = = =
shape_optimization test_grow GROW 1.5 5
END_
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6.10 Morphing With TOSCA Structure.morph it is possible to apply changes to certain areas, so called morph areas, by moving the nodes of these morph areas. This can be used, e.g., to automatically generate several model variants and submit analysis runs for these models. Further it allows to study the simultaneous influence of changes in the morph areas on certain design responses defining the quality of the design. These design responses are normally used to formulate optimization targets and constraints. Based on these quality criteria an optimum start design for a subsequent local shape optimization can be derived. Please note: morphing is a new feature within Tosca Structure implemented to access more optimization potential. At this point not all practical requirements may be considered yet. We appreciate your feedback to continuously improve our user interfaces and workflow.
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6.10.1 General Performing a local shape optimization sometimes does not exploit the complete potential for design improvement. In particular for complex models, when e.g. thermomechanical fatigue is involved, global interactions can be observed. A change in the model geometry, in particular a large wall thickness modification in "less critical" areas, will influence the stiffness and transient temperature distribution in critical areas, but will have no significant influence on the less critical areas. Shape optimization results can thus be improved through start with a design where these global effects are already considered..
Using TOSCA Structure.morph several design variants can be created automatically. With these variants global interactions and influences can be assessed and evaluated prior to a local shape optimization. Thereby a specific design of experiments is performed which modifies the predefined morph areas according to an user defined experiment plan. Morphing is offered as add-on to shape optimization, where "morphed models" are created based on the experiment plan. In each step of the morphing process (each experiment) a constant displacement is applied independently to the nodes of each morph area. The modified (morphed) model is analysed and the requested design responses (i.e. all values required for the optimization task) are evaluated.
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Fig. 218 Interaction between morphing areas and critical areas
SIMULIA Tosca Structure Shape Optimization
The base of the parameter file is a shape optimization task where all nodes in any MORPH_AREA must be part of the design area. MESH_SMOOTH and DVCON_SHAPE commands defined in OPTIMIZE are referenced by MORPH-command and thus used. Objective function and eventually constraint define relevant values for postprocessing and evaluation of the quality of the design. These values will be available e.g. as fringe plots on the several morphing variants.
6.10.1.1 Morphing areas
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A morphing area (MORPH_AREA) is a node group which will be modified independently of other morphing areas during the morphing process. All nodes in one morphing area obtain the same morphing displacement in one morphing step. This may lead to unwanted sharp edges in your structure. Thus, transition zones can be introduced for each morphing area. The transition zone is formed by the nodes of the morphing area which are connected to the border of the morph area by no more edges than specified with the TRANSITION_ZONE command. These nodes will not be displaced by the same constant morphing displacement applied to the rest of the morphing area but will be moved back to an intermediate position to assure a smooth transition between, e.g., two adjacent morphing areas or a morphing area and its surrounding area. .
Fig. 219 Morphing area, morphing displacement and transition zone
Remarks 1. For one optimization several independent (non-intersecting) morphing areas can be defined. 2. All nodes in any MORPH_AREA must be part of the design area.
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3. Each area will be assigned a morphing type. Currently, only NORMAL is supported, where all nodes in the morphing area are moved ("morphed") in node-normal direction. 4. All definitions made for the design variables (design variable constraints and mesh smooth definitions) also apply to morphing areas. Consequently, these definitions are also considered during morphing. Thus, e.g., symmetry definitions may enforce symmetry for symmetric morphing areas even if unsymmetric morphing displacements are applied. Also, mesh smoothing ensures high mesh quality for the morphed models and thus reliable analysis results for evaluation of the model quality. 5. Mesh smoothing in general may not allow for smooth transitions between single morphing areas as all morphing areas are part of one big design area. This can only be ensured if each morphing area is surrounded by some (at least 3-5) layers of nodes which do not belong to morphing areas. If the model contains adjacent morphing areas, use the parameter TRANSITION_ZONE of the MORPH_AREA command instead for smooth results. The size of the transition zone should be in reasonable relation to the size of the morphing area and the morphing displacement (e.g. 10% of the morphing area diameter or twice as large as the morphing displacement).
Fig. 220 Transition zone with 0, 2 and 4 layers
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6. If a morph area with TRANSITION_ZONE>0 is situated close to an edge of the geometry with an angle larger than 60° degree no transition zone is choosen for this edge.
SIMULIA Tosca Structure Shape Optimization
Definition in Tosca ANSA environment For each morphing area add a MORPH_AREA block via right-click on MORPHING folder (added to your optimization task within the Task Manager with right clicking on ‚Tosca Structure Task‘ -> ‚New‘ -> ‚MORPHING). For each MORPH_AREA different properties can be defined. Define a name for your MORPH_AREA, here MORPH_AREA_1, then select GROUP_DEF, under ND_GROUP. In GROUP_DEF, enter a ‚?‘ and select or define a node_group describing the area to morph. Under TYPE, select the direction of the morphing displacements vectors. So far only ‚NORMAL‘ is supported Under TRANSITION_ZONE the number of nodes as transition zone can be entered.
Fig. 222 Morph area properties Definition in Tosca Structure.gui.
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Define the morphing area in the command MORPH_AREA by selecting the corresponding node group (predefined at the command GROUP_DEF) and entering the number of transition zones.
Fig. 223 MORPH_AREA definition in Tosca Structure.gui Command MORPH_AREA ID_NAME = [string] ND_GROUP = [string] TYPE = NORMAL TRANSITION_ZONE =
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[integer] END_
6.10.1.2 Morphing displacement For each step of the morphing process a constant displacement is applied independently to the nodes of each morph area. .
Fig. 224 Morphing displacement The displacements are defined in an external morphing parameter file .csv referenced in the MORPH command. The external file offers easier access from external process automation programs (like ISight or OPTIMUS) and reusabiltiy: Morphing parameter file 0, , ,, … !
2, < MORPH_DISP _1>, < MORPH_DISP _2>, < MORPH_DISP _3>, … 3, < MORPH_DISP _1>, < MORPH_DISP _2>, < MORPH_DISP _3>, … 4, < MORPH_DISP _1>, < MORPH_DISP _2>, < MORPH_DISP _3>, … 5, …
The first line in the morphing parameter file contains the morphing areas involved in the morphing process (referenced MORPH_AREA commands). The order of appearance does not matter, but the commands must have been defined in the parameter file prior to the MORPH command. Each further line describes an experiment. Each morph_disp in a line tells how much the corresponding MORPH_AREA area should be moved.
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1, < MORPH_DISP _1>, < MORPH_DISP _2>, < MORPH_DISP _3>, …
SIMULIA Tosca Structure Shape Optimization
=0.0 means no movement. Negative and positive values are accepted. Example test_morph.csv: 0, ! 1, 2, 3, 4, 5, 6,
Morph2, Morph3, Morph4, Morph1 1.0, 0.0, 0.0, 0.0 0.0, 1.0, 0.0, 0.0 0.0, 0.0, 1.0, 0.0 0.0, 0.0, 0.0, 1.0 1.0, 1.0, 1.0, 1.0 -1.0, -1.0, -1.0, -1.0
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This file describes six morphing steps for four morphing areas Morph2, Morph3, Morph4, Morph1. The first four lines move the nodes of each MORPH_AREA by 1.0 each, starting with Morph2. Line 5 moves the nodes of all areas together by 1.0 outwards, and line 6 moves all nodes inwards. .
Fig. 225 Six morphing steps with 4 different morphing areas
6.10.1.3 Morphing task Using the MORPH command, the single morphing areas (MORPH_AREA) , the morphing parameter file and the optimization task are combined: MORPH ID_NAME OPTIMIZE MORPH_AREA MORPH_AREA MORPH_AREA
= = = = =
[string] [string] [string] [string] …
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MORPH_PARAM_FILE = [string] NUMBER_OF_PARALLEL_JOBS = SMOOTHING = YES|NO [string] END_
The parameter NUMBER_OF_PARALLEL_JOBS defines optionally a number of jobs which can be run in parallel. If omitted or =1, a sequential run will be performed (default). SMOOTHING is another optional parameter that switches off the surface mesh smoothing for the nodes in the morph areas. By default surface smoothing is omitted to gain the exact displacement as specified in the csv-file. However some manufacturing constraint might not work as expected in this case. Definition in Tosca ANSA environment
Fig. 227 Morph command: MORPH_PARAM_FILE and selection of morph areas Definition in Tosca Structure.gui Define the morphing task in the command MORPH by selecting the corresponding optimization task. Morph areas can be entered by clicking the but-
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Add a new MORPH command via right-click on MORPHING folder and adding ‚New‘ -> ‚MORPH’. Link your MORPHING with a valid shape optimization task: click in ‚OPTIMIZE‘ and select via typing ‚?‘ your previously defined shape optimization, here ‚OPTIMIZE_1_SHAPE_OPTIMIZATION_CONTROLLER‘. Select your MORPH_PARAM_FILE csv file describing your morphing task and the combinations of morphing displacements to be executed. Then select the morphing areas. PARALLEL_JOBS and SMOOTHING can be defined optionally.
SIMULIA Tosca Structure Shape Optimization
ton Add and activating the corrsponding areas. Enter a morph parameter file and the number of processors..
Fig. 228 MORPH definition in Tosca Structure.gui
6.10.2 Morphing in Tosca ANSA environment areas on/off.
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Fig. 230 Morph command: PARALLEL_JOBS and SMOOTHING
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After these settings you can run the morph task. Add a ‚RUN_MORPH‘ command via right-click on MORPHING folder.
Fig. 232 Run your defined morph task
6.10.3 Morphing in Tosca Structure.gui
Fig. 233 Start of a morphing run for shape optimization in Tosca Structure.gui
6.10.4 Command Syntax Command example: Please note: a complete shape optimization task is required! FEM_INPUT
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In Tosca Structure.gui your morphing will be defined using the MORPH command mask. To start the morphing run, start Tosca Structure with your parameter file including the morphing commands. Create your visualization sequence using Tosca Structure.report. For an example please refer to vol.4 chapter 7, Morphing.
SIMULIA Tosca Structure Shape Optimization
ID_NAME FILE
= OPTIMIZATION_MODEL = model.ext
END_
DV_SHAPE ID_NAME ND_GROUP areas)
= design_variables = design_nodes (must contain all MORPH_DEF
END_
MORPH_AREA ID_NAME ND_GROUP TYPE
= Morph1 = LEFT_NODES = NORMAL
END_
MORPH_AREA ID_NAME ND_GROUP TYPE
= Morph2 = UPPER_ROUND = NORMAL
END_
MORPH_AREA ID_NAME ND_GROUP TYPE
= Morph3 = LOWER_ROUND = NORMAL
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END_
MORPH_AREA ID_NAME ND_GROUP TYPE
= Morph4 = LOWER = NORMAL
END_
DRESP ID_NAME DEF_TYPE
= DRESP_MAX_MISES = SYSTEM
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TYPE UPDATE ND_GROUP GROUP_OPER
= SIG_MISES = EVER = design_nodes = MAX
END_
OBJ_FUNC ID_NAME DRESP TARGET
= minimize_max_mises = DRESP_MAX_MISES = MIN
END_
OPTIMIZE ID_NAME DV OBJ_FUNC STRATEGY
= = = =
shape_optimization design_variables minimize_max_mises SHAPE_CONTROLLER
END_
STOP ID_NAME ITER_MAX
= global_stop = 5
END_
ID_NAME = tosca_morph OPTIMIZE = shape_optimization MORPH_DEF = Morph1 MORPH_DEF = Morph2 MORPH_DEF = Morph3 MORPH_DEF = Morph4 MORPH_PARAM_FILE = test_morph.csv NUM_PROCS = 1 SMOOTHING = NO END_
6.10.5 Postprocessing Postprocessing shows fringe plots of the typical results shown for the associated optimization task (in shape optimization; controller input for the objective function, as well as optimization displacement) and a table of the requested
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MORPH
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design responses (values of objective, evtl. Constraint) for each morphing step. For an example see vol.4 chapter 7, Morphing. Remark: Pleate note: In general Tosca Structure does not keep all input decks and all solver output files for each design variant. If these should be saved for all design cycles, please change the settings in your configuration file (e.g. tosca_ctrl.cfg) or using the CONFIG parameter in your parameter file: CONFIG set_copy_solver_info_list("ever", "SAVE.${inp_ext}", "${__FE_FILE__}"); add_move_per_iter_list("ever", "SAVE.${res_ext}", "${__FE_MODEL__}.fil"); add_move_per_iter_list("ever", "SAVE.${res_ext}", "${__FE_MODEL__}.odb"); add_move_per_iter_list("ever", "SAVE.msg", "${__FE_MODEL__}.msg"); add_move_per_iter_list("ever", "SAVE.dat", "${__FE_MODEL__}.dat"); add_move_per_iter_list("ever", "SAVE.sta", "${__FE_MODEL__}.sta"); END_
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6.10.6 Evaluation The morphing process can be used for a global indirect optimization to get an improved start model for a subsequent local shape optimization. To this end, the results of the different morphing steps are evaluated. Design responses characterizing the objective and constraint are monitored and the best model is considered. Eventually some more experiments with combined morphing steps are required to get the best improvement in objective and constraint values. The best morphing model can then be optimized by Tosca Structure.shape.
6.11 Stop Condition Generally, it is helpful to formulate a stop condition to check the fulfillment of the optimization task and end the optimization when the minimum (or maximum) has been reached.
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6.11.1 Global Stop Condition The first stop criterion is the maximum number of optimization iterations which is default 50. When the maximum number of optimization iterations is reached the optimization algorithm always stops independent of other criteria. The allowed maximum number of optimization iterations can be increased or decreased by the user. This is done by modifying ITER_MAX in the STOP command STOP ID_NAME ITER_MAX
= global_stop = 5
END_
where ITER_MAX is decreased to 5. A global stop condition should be set for each optimization task to limit the number of design cycles. The optimization algorithm does not have its own stop condition; a stop condition must always be defined by the user. Since a ‘partially optimized model’ can be used as a starting model for a subsequent optimization, it makes sense to calculate first a few design cycles and then to use information from the optimization result to calculate more design cycles with adjusted settings. Remarks: 1. For shape optimization tasks it is sufficient to limit the number of iterations to 5 or 10. In this case it is important to define the stop condition by yourself. Using TAE, the stop condition is predefined already (default=5).
6.11.2 Local Stop Condition The possibilities for local stop conditions might include the following: • If an objective function without a constraint should be minimized (maximized), the value of the objective function of the current design cycle should be smaller (greater) than the value of the objective function for the design in the previous optimization cycle. If this is not the case, the optimization can be ended. • Only relatively small changes in the value of the objective function are to be expected when approaching the optimum. If the relative change in the
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2. The global stop criterion leads to a hard stop of the optimization - independend of a complete convergence of the result. For shape optimization tasks this is no drawback as the optimization task can be continued for some more steps using the input file of the last iteration as start file.
SIMULIA Tosca Structure Shape Optimization
objective function falls below a tolerance limit in one design cycle, the optimization can be considered as completed. • If the norm of the optimization displacements is smaller than a certain tolerance value within one design cycle, the modifications of the model will only be small and the optimization is stopped. This condition has the advantage that it is suitable for optimization jobs with and without constraints. The condition can be equally used without any changes for a variety of objective functions (stress or frequency). Stop conditions can be formulated and combined by linking the VARIABLE definitions with LOGICAL variables. However, experiments have shown that it is usually not worthwhile to define complicated stop conditions for shape optimization. It is often sufficient to limit the maximum number of allowable design cycles as a global stop condition. Also, a compact form of a stop condition is available which enables to compare the actual value of a variable with a value from the first or previous step (parameters MOD_TYPE for the definition of the variable, MOD_OPER for the comparison operator and MOD_REF for the reference value definition). Remark: 1. Please note that the global stop criterion is defined using a STOP command whereas convergence criteria are defined in the optimization settings (OPT_PARAM command).
Per default, a global stop condition limiting the number of design cycles to 5 is defined (visible in the task manager tree). If necessary, the number of design cycles can be changed (Edit command applied on GLOBAL_STOP_CONDITION_1 item). Several local stop conditions can be entered in the task manager (New | STOP_CONDITION command applied on SHAPE_OPTIMIZATION_CONTROLLER item). In the pop up window the parameters described above or in detail in vol.3 Commands Manual can be defined. As this compact form of stop conditions is usually sufficient for opti-
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6.11.3 Stop Condition in Tosca ANSA environment
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mization tasks, more complicated stop conditions including logical variables are not supported by Tosca ANSA environment.
Fig. 234 Local stop condition for shape optimization in Tosca ANSA environment
6.11.4 Stop Condition in Tosca Structure.gui
Fig. 235 Local stop condition for shape optimization in Tosca Structure.gui
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In Tosca Structure.gui, the definition of stop conditions is available in the commands menu. For details about the several parameters refer tovol.3 Commands Manual. More complicated stop conditions like in vol.2 chapter 6: Example 3: can be defined using variables, combining them to logical expressions and referring them in the stop condition.
SIMULIA Tosca Structure Shape Optimization
6.11.5 Examples Example 1: The number of design cycles should be limited to 5 as a global stop condition: STOP ID_NAME ITER_MAX OPTIMIZE
= stop_condition = 5 =
END_
Example 2: The stop condition is fulfilled, if the maximum equivalence stress in the node group ALL_NODES is less than 1% of the maximum equivalence stress of the first iteration. STOP ID_NAME MOD_NDGR MOD_TYPE MOD_OPER MOD_REF OPTIMIZE
= = = = = =
stop_command all_nodes MAX, CTRL_INP_SHAPE LE 0.01, MULT, FIRST run
END_
Example 3: If the sum of the optimization displacements of the design node group in a given design cycle is smaller than 1% of the sum of the optimization displacements in the initial design cycle, the optimization should be stopped:
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VARIABLE ID_NAME DEF_TYPE TYPE ND_GROUP GROUP_OPER UPDATE
= = = = = =
sum_disp SYSTEM SHAPE_MOVE design_nodes SUM EVER
= = = = = =
sum_disp_first SYSTEM SHAPE_MOVE design_nodes SUM FIRST
END_ VARIABLE ID_NAME DEF_TYPE TYPE ND_GROUP GROUP_OPER UPDATE
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END_ VARIABLE ID_NAME DEF_TYPE VALUE
= one_percent = FIX = 0.01
END_ VARIABLE ID_NAME DEF_TYPE VAR_OPER VAR_A VAR_B
= = = = =
sum_disp_first_001 OPER MULT one_percent sum_disp_first
= = = = =
logical_for_stop SYSTEM LT sum_disp sum_disp_first_001
END_ LOGICAL ID_NAME DEF_TYPE OPER VAR_A VAR_B END_ STOP ID_NAME LOGI_NAME OPTIMIZE
= stop_optimization = logical_for_stop =
END_
Meske, R., Sauter, J., and Schnack, E. (2005). Nonparametric gradient-less shape optimization for real-world applications. Structural and Multidisciplinary Optimization. 30:201218, 2005. 10.1007/s00158-0050518-0. Sauter, J. (1992). Applied mathematics and mechanics. ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik. 72(6):T566T614. Schnack, E. (1979). An optimization procedure for stress concentrations by the finite element technique. International Journal for Numerical Methods in Engineering. 14:115124. 2 - 404 User Manual
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6.12 References
SIMULIA Tosca Structure Bead Optimization
7
Bead Optimization Bead optimization is a way to enhance shell structures without adding more mass to the structure. The beads can easily be added in the stamping process which makes beads a low weight and cost neutral alternative to enhance a sheet-metal structures.
7.1
General Information The easiest way to understand bead optimization is a simple example every mechanical engineer will intuitively understand.
a)
b)
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Fig. 236 Simple plate in bending with loading and supports (a) and an optimalbead (b). The maximal displacement of (a) is 6.6 mm and (b) is 0.25 mm In Fig. 236 is a simple flat plate in bending shown. It is evident that the solution in Fig. 236 (b) has a much greater stiffness than the original flat plate in Fig. 236 (a). Regarding the simple example in Fig. 236 a couple of comments must be made:
Bead height
Bead width Fig. 237 Bead height and bead width The bead height (see Fig. 237) has the most significant effect on the stiffness of the plate structure. Usually, the greater the bead height the greater the stiff-
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ness. But, the bead height is usually controlled by manufacturing capabilities i.e how deep can you draw a bead with your available tools. • The bead width (see Fig. 237) has an effect on the possible designs. As seen in Fig. 238 a small or a large bead width is not necessarily related to the stiffness of the sheet structure. The Tosca Structure.bead default values usually suffice, but if an optimal solution is sought you must try more bead widths.
Increasing stiffness Fig. 238 Bead layouts for simple geometries with a uniform pressure load. From Oehler and Weber: "Steife Blech- und Kunststoffkonstruktionen", Springer-Verlag GmbH (1972)
7.2
The Optimization Task Tosca Structure.bead is a module that automatically determines the optimum bead location and orientation for arbitrary shell structures. For this task Tosca Structure provides two algorithms: • Controller based bead optimization (BEAD_CONTROLLER) • Sensitivity based bead optimization (BEAD_SENSITIVITY)
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For more complex loads or dynamic problems i.e. eigenvalue or frequency response, the optimal bead layout is not intuitive anymore (see also Fig. 238). Thus, an easy way to find a good bead pattern is to use Tosca Structure.bead.
SIMULIA Tosca Structure Bead Optimization
7.2.1
Controller based bead optimization The controller based bead optimization (BEAD_CONTROLLER) is based upon a special bending hypothesis developed at IPEK at Karlsruhe University. It determines the orientation of the maximum bending stress or Differential Stress Tensor (DST) for each point in the design domain. Special filters are used to generate the beads along the bending trajectories.
Fig. 239 Distribution of bending stress and scalar fields for bead direction This method has the following advantages: • Solver-independent and sensitivity-independent • mesh-independent • clear results
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• restrictions on the bead form can be included Remark 1. It should be emphasized that bead optimization does NOT always give better mechanical behavior. The design problem must be suited for bead optimization, that is: - Design area should be mainly in bending or a bending mode. The bead algorithm will then increase the moment of inertia which leads to a greater stiffness or eigenfrequency. - Design area should NOT be in a membrane stress state (see also vol.2 chapter 7.8.1.5, Penalty conditions (BEAD_MIN_STRESS and BEAD_MAX_MEMBRANE)). A bead may in this case make the structure softer.
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7.2.2
Sensitivity based bead optimization Sensitivity based bead optimization (BEAD_SENSITIVITY) makes it possible to define very complex optimization tasks. It has been shown in industrial size examples that the method is very powerful and attractive, especially for dynamic problems. The typical problems which can be solved by this algorithm are: • Maximize stiffness (linear static) • Minimize displacement for critical nodes (linear static) • Maximize first eigenvalue (modal) • Maximize a certain eigenvalue (using mode tracking) • Move eigenvalues away from certain frequency (band gap optimization with modal analysis) Remarks 1. The sensitivity based algorithm has no bead filter implemented. This means that the results are not necessarily a distinct bead pattern like the results from the controller algorithm. 2. Design nodes must be connected to elements which are supported by Tosca Structure. See Table 27.
Differences between bead optimization algorithms The user may choose between two bead optimization algorithms in Tosca Structure.bead. The algorithms have different ways to find the solution and their differences will be discussed in this chapter. In the attempt to avoid confusion the following chapters will be marked with either "BEAD_CONTROLLER" or "BEAD_SENSITIVITY" if it is only valid for
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SIMULIA Tosca Structure Bead Optimization
the one algorithm. If the chapter is not marked (like this chapter or e.g. vol.2 chapter 7.3, Design Area) the content applies to both algorithms
a)
b)
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Fig. 240 Bead pattern of maximization of first eigenfrequency using controller (a) vs. sensitivity (b) based algorithm
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a)
Fig. 241 Iteration history for controller (a) and sensitivity (b) based optimization from Fig. 240.
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b)
SIMULIA Tosca Structure Bead Optimization
In Fig. 240 and Fig. 241 is the same optimization task, maximizing first eigenvalue, done by the sensitivity based optimization algorithm and controller based algorithm. Some of the main differences between the two algorithms are listed here: 1. Bead pattern. The controller based algorithm creates nice bead structures because of its bead-filter. Such bead generation is not implemented in the sensitivity based solution, why the results do not show a distinct bead pattern (see Fig. 240). 2. Number of optimization iterations. The controller based algorithm always uses 3 optimization iterations. Whereas for the sensitivity based optimization algorithm usually needs 20 or more iterations to converge (see Fig. 241). 3. Analysis types. The controller based supports all analysis types which produces a stress tensor as output, although it is recommended to only use the algorithm for static analysis. The sensitivity based algorithm supports the responses of: - linear static - linear eigenfrequency - frequency response Note the better results by sensitivity based optimization for dynamic problems, e.g. Fig. 241.
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4. Objective and constraint types. The sensitivity based algorithm can have one objective function and several constraints where the constraints are all inequality constraints. The objective and the constraints can be based upon the compliance, displacements, eigenfrequencies or frequency dependent displacements. Whereas the controller based algorithm has the compliance as objective and the BEAD_HEIGHT as an equality constraint. 5. Supported element types. The sensitivity based algorithm supports only the elements given in Table 27. The controller algorithm supports all plate and shell elements. 6. BEAD_HEIGHT. For sensitivity based algorithm all DRESP which can be used in the object function (OBJ_FUNC) can also be used in the CONSTRAINT definitions. The maximal nodal displacement is in this context not considered a design response but instead a design variable constraint (DVCON_BEAD). DRESP of the type BEAD_HEIGHT is not allowed in sensitivity based algorithm (see volume 3: DRESP). To get a similar optimization displacement in sensitivity based algorithm in a benchmark example against the controller algorithm use: DVCON_BEAD
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ID_NAME ND_GROUP CHECK_GROW CHECK_SHRINK
= = = =
name_of_dvcon_bead
design_nodes 0.0
END_
where the is equal to the bead height defined by the controller input deck. Also note that the sensitivity based algorithm can move the nodes in positive and in negative direction, thus the optimization parameter SCALE has no effect by sensitivity based algorithm. As already stated the following chapters will differ with respect to the two bead optimization algorithms. To make it easier to distinguish which chapter concerns what method we introduce two key words: BEAD_CONTROLLER BEAD_SENSITIVITY These two words reappear in the OPTIMIZE commands item STRATEGY.
Fig. 243 In Tosca Structure.gui the strategy is chosen in the OPTIMIZE command
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Fig. 242 Select the appropriate Tosca Structure Task in Tosca ANSA environment to choose between BEAD_CONTROLLER or BEAD_SENSITIVITY strategies.
SIMULIA Tosca Structure Bead Optimization
7.2.4
How to create the optimization model The following describes the general procedure for the definition of an optimization task. These procedures are supported by the task manager in Tosca ANSA environment (TAE) as well as the command tree in Tosca Structure.pre (GUI) (see vol.1 chapter 1, Getting Started with Tosca ANSA environment, vol.1 chapter 2, Getting Started with Tosca Structure.gui, vol.2 chapter 2, Working with Tosca Structure). The analysis model must be completely defined in advance. Analysis Model 1. Question: Which file(s) contains the FE- model for the optimization? Procedure: Link file(s) to optimization task. TAE: MODEL_LINK | FILE | [EDIT], choose your model file. GUI: Choose your model file in FEM_INPUT Design Area
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2. Question: Which surface area of the FE model should be selected regarding bead optimization? Procedure: Assign node group with surface nodes to design area. TAE: DESIGN_AREA | [EDIT], choose predefined group or select new group. GUI: Choose or define the node group with the surface nodes of the selected design area (GROUP_DEF) and define the design variables (DV_BEAD). 3. Question: Are there nodes in the design area that are subject to certain restrictions? How can these restrictions be described? Procedure: Define design variable constraints for node group. For sensitivity based bead optimization nodes must be constrained in maximum positive and negative displacement. TAE: DESIGN_AREA | DV_CONSTRAINTS | [NEW] | , choose predefined group or select new group for this restriction. If required, define link conditions using modules buttons. GUI: Choose or define node groups with common restrictions (GROUP_DEF). Define the restrictions using DVCON_BEAD. 4. Question: Are there certain symmetry conditions that should be fulfilled? Procedure: Create a symmetry coupling condition. TAE: DESIGN_AREA | DV_CONSTRAINTS | [NEW] | [SYMMETRY_CONTROL]. GUI: Create a LINK_BEAD condition and reference it in a restriction
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command (DVCON_BEAD). LINK_BEAD is not supported by sensitivity based bead optimization. Objective Function 5. Question: Which terms describe the values to be optimized? Should these values be minimized or maximized or otherwise combined? Procedure: Choose terms for optimization (design responses) and target. TAE: OBJ_FUNC_ITEM_1 | [NEW] | , OBJ_FUNC_ITEM_1 | [EDIT] for choice of target (min, max). GUI: Define the design response (DRESP) and assign it to the objective function (OBJ_FUNC). Constraint 6. Question: Which design response describes the constraint? Which value should the constraint have? Procedure: Choose term for constraint and set target value or upper/lower boundary. TAE: CONSTRAINT | [NEW] | . GUI: Define the design response (DRESP) and assign it to the constraint (CONSTRAINT). Optimization Task
8. Question: Are you using controller or sensitivity based optimization strategy? Procedure: Choose corresponding strategy. TAE: Chosen in the beginning with your task (BEAD_OPTIMIZATION_CONTROLLER or BEAD_OPTIMIZATION_SENSITIVITY). GUI: Set the correct value to either BEAD_CONTROLLER or BEAD_SENSITIVITY in OPTIMIZE subcommand STRATEGY. Stop Condition 9. Question: Should the optimization stop after a number of iterations (or certain other conditions)? Procedure: Define a stop condition 2 - 414 User Manual
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7. Question: Are all of the command definitions listed above complete and ready for the optimization job? Procedure: If necessary complete any additional required definitions and prepare the optimization job. TAE: Automatically prepared by task manager. GUI: Reference all definitions above in OPTIMIZE.
SIMULIA Tosca Structure Bead Optimization
TAE: GLOBAL_STOP_CONDITION | [EDIT] and change number of iterations. GUI: STOP. Check Run 10.Question: Would prior testing of the restriction definitions be useful? Procedure: Apply test displacements TAE: BEAD_OPTMIZATION... | [NEW] | TEST_BEAD or CHECK_INPUTS | [NEW] | TEST_BEAD_CHECK. GUI: TEST_BEAD. Completion 11.Question: Has all the required data been specified? Procedure: If yes, finish the definition of the optimization problem and save your definition. TAE: Click twice on OUTPUT and change the jobname. GUI: Save as .par.
Fig. 244 Block structure of bead optimization commands
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The essential commands required for the optimization model in bead optimization are described in the following. The definitions for the optimization job are assembled in a parameter file. The exact syntax of the commands can be looked up in vol.3 Commands Manual. Fig. 244 gives an overview of a standard optimization task and the relation between the several commands. Only commands which are referenced in the OPTIMIZE command will be included in the optimization.
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7.3
Design Area During an optimization, only part of the model may be changed. This part is defined as design area.
7.3.1
Design variables (DV_BEAD) In bead optimization shell models may be modified by moving the nodes perpendicular to the shells. Only nodes which are members of a shell element may be used as design nodes. Nodes for solid elements cannot be design nodes. The design variables for bead optimization are defined using the DV_BEAD command (design variable bead).
Fig. 245 Selecting the design node group in Tosca Structure.gui
Fig. 246 Defining DESIGN_AREA in Tosca ANSA environment. The selected group must consist of nodes. Remark 1. For BEAD_CONTROLLER the nodes are only moved in the positive direction of the shells determined by the element definition in the FE analysis. For BEAD_SENSITIVITY the nodes may move in both the positive (GROW) as well as the negative (SHRINK) normal direction. See Fig. 247 2. If you want to have nodal movement in negative normal direction and using BEAD_CONTROLLER invert the optimization displacement direction by
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?
SIMULIA Tosca Structure Bead Optimization
defining a negative SCALE factor in the OPT_PARAM command. This has no effect for BEAD_SENSITIVITY.
Fig. 247 Optimization displacement direction for bead optimization 3. BEAD_SENSITIVITY is restricted to using only certain shell elements. Please consult Table 27. Valid element types for sensitivity based bead optimization
Abaqus element type
ANSYS element type
Shell elements SHELL_TRIANG_3
S3 S3R STRI3
SHELL_QUAD_4
S4 S4R
SHELL143 SHELL181 SHELL41 SHELL43 SHELL63
SHELL_QUAD_8
S8R
SHELL93
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Valid element types attached to the design nodes for sensitivity based bead optimization
MSC Nastran element type
Marc element type
PERMAS element type
Shell elements SHELL_TRIANG_3
CTRIA3 CTRIAR
SHELL_TRIANG_6
CTRIA6 CTRIAX6
SHELL_QUAD_4
SHELL_QUAD_8 Table 27
7.3.2
138
TRIA3 TRIA3K
CQUAD4 CQUADR CSHEAR
18 139 140
QUAD4
CQUAD8
30 72
Valid elements connected to design nodes for sensitivity based bead optimization.
Restrictions (DVCON_BEAD)
Restrictions in bead optimization can either be defined as boundary conditions that limit the node displacement or as a LINK-condition. The latter is only allowed for controller based bead optimization. A design variable constraint is a restriction that directly affects the individual design variables or the individual design nodes. Possible restrictions are: the specification of an allowable displacement area by limiting the signed absolute displacement and the specification of variation and frozen areas. It is also possible to influence the allowable displacement direction by limiting the displacement to specific coordinate directions. At last it is possible to link the design variables and thereby force them to be optimized in a symmetric way (only controller). The definition of the design variable constraints for bead optimization is done using the DVCON_BEAD command. Remarks 1. Possible restrictions for bead optimization are very similar to the restrictions of shape optimization (see vol.2 chapter 6.3.3, Restrictions
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7.3.2.1 General
SIMULIA Tosca Structure Bead Optimization
(DVCON_SHAPE)). The definition of the CHECK parameters is often identical. 2. Some of the design variable constraints for bead optimization relate not only to the design variable itself but also to the corresponding optimization displacement vectors or the design coordinates. The term ‘design variable constraint’ in this case should be interpreted in a more general way. Restrictions for bead optimization The following individual restrictions can be defined for bead optimization: • CHECK_GROW: Restriction of the absolute displacement in shell normal direction (see vol.2 chapter 7.3.2.2) * • CHECK_SHRINK: Restriction of the absolute displacement opposite the shell normal direction (see vol.2 chapter 7.3.2.2) * • CHECK_SOLID: Check the displacements against geometric primitive solids (see vol.2 chapter 7.3.2.3) • CHECK_ELGR: Check the displacements against elements of an element group (see vol.2 chapter 7.3.2.4) • CHECK_BC, CHECK_DOF: Restriction of the displacement direction (see vol.2 chapter 7.3.2.5) • CHECK_LINK: Assignment of a coupling condition (only BEAD_CONTROLLER)(see vol.2 chapter 7.3.2.6) A DVCON_BEAD command using all of the individual restrictions appears as follows:
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DVCON_BEAD ID_NAME ND_GROUP CHECK_SOLID CHECK_ELGR CHECK_GROW CHECK_SHRINK CHECK_BC CHECK_DOF CHECK_LINK
= = = = = = = = =
name_of_dvcon_bead name_of_node_group name_of_solid name_of_element_group cs_name, FREE/FIX, FREE/FIX, FREE/FIX YES/NO
END_
Remarks 1. Using CHECK_GROW and CHECK_SHRINK is the easiest way to constrain design nodes for sensitivity based optimization. See also chapter 7.3.2.2 Restricting the absolute displacement.
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2. CHECK_SHRINK has no effect on controller algorithm while it only "grows". 3. CHECK_LINK has no effect on sensitivity based algorithm. 4. The restrictions are checked only for the corner nodes of the node group (ND_GROUP parameter). If midside nodes are contained in the node group they are subsequently placed in between the neighboring corner nodes. Therefore, it’s not possible for mid-side nodes to guarantee adherence to the restrictions; a small amount of deviation may occur. 5. It is possible to define several individual CHECK_* restrictions within a DVCON_BEAD command. The order of the execution of the individual restrictions within a DVCON_BEAD command appears as follows: CHECK_GROW, CHECK_SOLID, CHECK_ELGR, CHECK_BC, CHECK_DOF, CHECK_LINK. The individual restrictions are checked independently of each other, i.e. an individual restriction always overrides the previous restriction. 6. The activated DVCON_BEAD entries are executed in the order in which they are referenced in the OPTIMIZE command. The individual DVCON_BEAD entries are checked independently of each other, i.e. a DVCON_BEAD entry always overrides the previous DVCON_BEAD entry. If mutually independent restrictions are declared all restrictions are observed. If mutually dependent restrictions are declared the user must select an order of execution that is logical and specific to the problem.
8. The DVCON_BEAD definitions must be activated by a reference in the OPTIMIZE command. Non-activated definitions have no influence on the optimization. The reference in the OPTIMIZE command assigns the design variable constraints and the design area (see DV_BEAD command) to each other. The recommended procedure is to define the assigned restrictions immediately after defining the design area.
7.3.2.2 Restricting the absolute displacement It is possible to specify a maximum allowable absolute displacement for each node in relation to the starting geometry. The parameters CHECK_GROW
=
CHECK_SHRINK
=
specifies a maximum absolute displacement allowed in the growth direction and in the opposite direction. The values must be positive. 2 - 420 User Manual
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7. It is possible to define several design variable constraints using the DVCON_BEAD command. Each DVCON_BEAD definition must have its own unique name.
SIMULIA Tosca Structure Bead Optimization
In controller based bead optimization the maximum displacement amount of the design nodes is restricted in the constraint of the optimization task (see DRESP type "BEAD_HEIGHT" and volume 3: CONSTRAINT). The definition of an additional restriction by the DVCON_BEAD command allows for the definition of additional restrictions on specified design nodes. For sensitivity based algorithm the DVCON_BEAD are the only restriction on the design nodes optimization displacement and must therefore be defined. If any node in the design area is not restricted Tosca Structure will stop with an error. The easiest way to constrain all design nodes is to this is to use: DVCON_BEAD ID_NAME ND_GROUP CHECK_GROW CHECK_SHRINK
= = = =
MY_DVCON_BEAD DESIGN_NODES 10.0 0.0
END_
The command above is equivalent to define the following BEAD_HEIGHT constraint in the controller based algorithm. CONSTRAINT ID_NAME DRESP EQ_VALUE MAGNITUDE
= = = =
MY_BEAD_HEIGHT_CONSTRAINT BEAD_HEIGHT_DRESP 10.0 ABS
END_
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Realization in Tosca ANSA environment To create a design variable constraint in Tosca ANSA environment select Tosca Structure Task | PRE-PROCESSING | BEAD_OPTIMIZATION_ | DESIGN_AREA | DV_CONSTRAINTS | [New].
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Here is the example just described constraint all design nodes to a maximum growth of 10.0 and no shrink using GROW/SHRINK_CONTROL.
7.3.2.3 Displacement check against solids (CHECK_SOLID) It is possible to define geometric primitives (solids) as a restriction of the node displacements. Geometric primitives are defined using the SOLID parameter. The SOLID parameter allows for the definition of circles, circle segments, ring segments and rectangles in two-dimensional models and cylinders, cylinder segments, tubes, cubes, cube segments in three-dimensional models. There is a differentiation here between a variation solid and a restriction solid (vari-
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Realization in Tosca Structure.gui Example just described constraining all design nodes to a maximum growth of 10.0 and no shrink using DVCON_BEAD.
SIMULIA Tosca Structure Bead Optimization
ation area or restriction area, see vol.2 chapter 3.9, Solids (Geometric Primitives)). The parameter: CHECK_SOLID
= solid_name
specifies a solid whose borders may not be penetrated. The solid must be defined with a SOLID command before being referenced. Remarks 1. Up to six different CHECK_SOLID parameters can be defined in every DVCON_BEAD command. They are executed in the order of their declaration within the DVCON_BEAD command. 2. If the solid is a variation solid, all nodes of the node group in the start model (see ND_GROUP parameter) must be located inside the variation solid. If nodes are located outside the variation solid, the DVCON_BEAD definition will be rejected. If the solid is a restriction solid, all nodes of the node group in the start model must be located outside the restriction solid. If nodes are located inside the restriction solid, the DVCON_BEAD definition will be rejected.
7.3.2.4 Displacement check against elements (CHECK_ELGR) Element surfaces/lines can be defined as limiting surfaces/lines in order to check node displacements against any contour. This option offers more flexibility than the check for the absolute displacement or the check against geometric primitives. The limiting surfaces are formed by beam, shell or solid structures. The limiting surfaces are generated in the FE preprocessor and loaded via the interface (FEM_INPUT) in the optimization preprocessor. The parameter
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CHECK_ELGR
= elgr_name
specifies an element group whose elements may not be penetrated (contact condition) by the nodes of the node group (ND_GROUP parameter). Activation of the element check represents a collision control. If a node attempts to penetrate an element, the node displacement is scaled back so that the affected node remains on the side of the element where it is intended to be. For example, the element group must be defined with GROUP_DEF before it can be referenced with CHECK_ELGR. Remarks 1. Up to six CHECK_ELGR parameters can be defined in every DVCON_BEAD command. They are executed in the order of their declaration within the DVCON_BEAD command.
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2. To simplify the definition of the contact check if it is useful to divide the limiting surfaces by assigning various element property numbers (or materials). This simplifies the selection and assembly of groups in the optimization preprocessor. 3. All nodes of the selected node group are checked against all elements of the element group, elgr_name. To keep the number of control conditions within limits, only those nodes and elements that have the potential for penetration should be checked against one another. The groups should be correspondingly defined. 4. The nodes (ND_GROUP parameter) and the elements (CHECK_ELEM parameter) should have a definite minimum distance in the initial model in order to verify on which side of the element a node must remain. 5. If the elements being used in the check are loaded with the ADD_FILE parameter (FEM_INPUT), care should be taken that node or element IDs are not used twice as Tosca Structure cannot process duplicated IDs.
7.3.2.5 Restricting the direction of displacement In Tosca Structure.bead the displacement direction of the design nodes (optimization displacement vector) is normally determined as the surface normal (see vol.2 chapter 7.8.1.2). A restriction of the displacement direction in bead optimization may be necessary due to two reasons:
2. Some areas in the design domain should not be modified during optimization, e.g. the boundary of the design domain. These areas may be restricted using the CHECK_DOF or CHECK_BC parameters. The displacement boundary condition must be unique. In contrast to FE boundary conditions of several load cases, the total of all supports for all load cases are considered as supports in the optimization. A prescribed node displacement as an optimization boundary condition is also not permitted. Loading Node Fixations via the Interface from the FE Program The full or partial fixation of nodes is the most common and most important type of restriction; it is practically used in every optimization model. The most efficient method for defining the displacement restrictions in the FE preprocessing as an extra load case in the transition model and then to load it via the FE interface in the optimization preprocessor. In order to do this, the interface must first be activated with OPTIONS, READ_BC=.... In this way all node fixations for the optimization model can be defined in advance in the FE 2 - 424 User Manual
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1. Standardly, the displacement direction in bead optimization is determined in the initial model and is not modified during optimization (OPT_PARAM, VECTOR = FIRST). In order to define own displacement directions the original displacement directions may be restricted.
SIMULIA Tosca Structure Bead Optimization
preprocessor. The fixation is always based on the FE displacement coordinate system of the node. The special features of the FE interfaces are described in vol.2 chapter 11. The parameter CHECK_BC
= ALL
activates the node fixations of the node group (ND_GROUP parameter) which are loaded through the FE interface. Fixations that reference nodes not contained in the node groups are not activated. To prevent loaded fixations from being activated enter: CHECK_BC
= NO
Definition of the Displacement Direction by Command The CHECK_DOF parameter can be used to restrict other displacement directions if necessary as an addition or at a later stage. When entering node fixations by command and in contrast to load the node fixations via the FE interface, it is necessary to first compile all nodes that should be assigned a certain attribute to a node group. The coordinate system must also be defined or loaded. With the parameter CHECK_DOF
= cs_name,[FIX|FREE],[FIX|FREE],[FIX|FREE]
all the displacements of all nodes in the node group selected with ND_GROUP are fixed (FIX) or free (FREE) relative to the specified coordinate directions of the coordinate system, cs_name. Either FREE or FIX is allowed for each coordinate direction. Remark
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1. The main difference between CHECK_BC and CHECK_DOF is: CHECK_BC is read in through the FE interface whereas CHECK_DOF is defined in the optimization preprocessor. Generally, with CHECK_BC each node has its own fixation in its own displacement coordinate system, whereas all nodes of the node group are all fixed in the same coordinate system with CHECK_DOF.
7.3.2.6 Symmetry conditions (CHECK_LINK) BEAD_CONTROLLER Symmetry conditions can also be applied in Tosca Structure.bead. A LINKcondition is needed to create a symmetry condition. The types of symmetry supported by Tosca Structure.bead is point, plane and rotational symmetry LINK_BEAD ID_NAME TYPE
CS
= = POINT_SYM PLANE_SYM, AXIS_* ROTATIONAL_SYM, AXIS_* =
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END_
The origin of the coordinate system referenced by the (vol.2 chapter 3.8) is the symmetry point or a point on the symmetry plane, where AXIS_* is the normal to this plane. For rotational symmetry the origin of the coordinate system is a point on the symmetry axis, where AXIS_* gives the direction.
symmetry
Loads
Loads
Fig. 248 An asymmetric load case without (left) and with (right) symmetry condition. Remarks 1. AXIS_* can be AXIS_1, AXIS_2 or AXIS_3 of the chosen coordinate system.
3. The name of the link is referenced in a DVCON_BEAD command using CHECK_LINK=.
7.3.2.7 Example LINK_BEAD Creating a plane symmetry condition about the global coordinate system in the Y-axis for controller based bead optimization. Command syntax LINK_BEAD ID_NAME CS TYPE
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= MY_LINK_BEAD = CS_0 = PLANE_SYM, AXIS_2
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2. Only cartesian coordinate systems can be used for symmetry conditions.
SIMULIA Tosca Structure Bead Optimization
END_ DVCON_BEAD ID_NAME CHECK_BC ND_GROUP CHECK_LINK
= = = =
MY_DVCON_BEAD_SYM NO DESIGN_NODES MY_LINK_BEAD
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END_
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SIMULIA Tosca Structure Objective Function
Realization within the Tosca ANSA environment
7.4
Objective Function The objective function describes the optimization target. In general, one scalar value (sometimes combined from other scalars) is to be maximized or minimized.
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Realization within the Tosca Structure.gui
SIMULIA Tosca Structure Bead Optimization
7.4.1
Overview Bead optimization is mostly used to maximize stiffness of a structure or improve the dynamical properties of a shell structure. As already noted (chapter 7.2.3 Differences between bead optimization algorithms) Tosca Structure.bead has two different optimization approaches. The differences have already been discussed in general. The possible design responses in the objective function is one of the major differences which becomes obvious looking at the following Table 28.
Static analysis
Gravity / Inertia
Frequency response
DISP_ABS
CENTER_GRAVITY_X
FS_ACCEL_X
DISP_X
CENTER_GRAVITY_Y
FS_ACCEL_Y
DISP_X_ABS
CENTER_GRAVITY_Z
FS_ACCEL_Z
DISP_Y
INERTIA_XX
FS_DISP_ABS
DISP_Y_ABS
INERTIA_XY
FS_DISP_X_ABS
DISP_Z
INERTIA_XZ
FS_DISP_Y_ABS
DISP_Z_ABS
INERTIA_YY
FS_DISP_Z_ABS
ROT_X
INERTIA_YZ
FS_VELOCITY_X
ROT_Y
INERTIA_ZZ
FS_VELOCITY_Y
ROT_Z
FS_VELOCITY_Z
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STRAIN_ENERGY*
Modal analysis DYN_FREQ* DYN_FREQ_KREISS EL Table 28
Possible design responses in the objective function for Tosca Structure.bead. All terms are allowed in BEAD_SENSITIVTY, for BEAD_CONTROLLER only the terms marked with a * are allowed
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Remarks: 1. Only design responses marked with * are allowed in controller based algorithm (BEAD_CONTROLLER). 2. BEAD_HEIGHT is not allowed in sensitivity algorithm. Use DVCON_BEAD instead. 3. The Gravity / Inertia design response types are only usable if at least one design response of the other types is used in the objective function or constraints. In the following chapters typical optimization tasks are described which can be solved with Tosca Structure.bead.
7.5
Typical Optimization Tasks for Linear Static Analysis This section deals with the typical optimization tasks for linear static analysis types. Only some very common tasks are described here.
7.5.1
Maximize stiffness with controller based algorithm BEAD_CONTROLLER To maximize stiffness of the structure the compliance - or sum of strain energy - should be minimized. The design response should be defined like the following: ID_NAME TYPE DEF_TYPE UPDATE EL_GROUP GROUP_OPER LC_SET
= = = = = = =
dresp_compliance STRAIN_ENERGY SYSTEM EVER ALL_ELEMENTS SUM Static,1,All
END_
Remarks 1. Compliance is defined as the sum of the energy of all the elements in the FE-model regardless how large your design domain may be. 2. The algorithm is based on element stress tensors. Therefore these must be requested in the FE-analysis, but Tosca Structure for most solvers adds these result request (see Vol.I Chapter 13). 2 - 430 User Manual
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DRESP
SIMULIA Tosca Structure Bead Optimization
Definition of the objective function OBJ_FUNC ID_NAME DRESP TARGET
= minimize_compliance = dresp_compliance = MIN
END_
7.5.1.1 Combining static load cases (controller based algorithm) BEAD_CONTROLLER If more load cases and/or sub-steps are present in the FE-analysis, Tosca Structure.bead will try to combine all these load cases. The "best-practiceway", however, is to define each load case separately in its own DRESP. Thereby one can easily give the load cases different weights in the objective function: OBJ_FUNC ID_NAME DRESP DRESP TARGET
= = = =
minimize_compliance dresp_compliance_1, 0.90 dresp_compliance_2, 1.10 MIN
END_
Here, the first design response is weighted 10% less than the norm, and the second 10% more than the norm. The norm (1.0) is default. Remarks 1. It is highly recommended only to combine linear static load cases! 2. It is recommended to look up the definition of load cases in (DRESP).
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3. Reference value has no effect in controller algorithm. If one DRESP references all load cases: DRESP ID_NAME DEF_TYPE EL_GROUP TYPE GROUP_OPER LC_SET
= = = = = =
dresp_min_compliance SYSTEM ALL_ELEMENTS STRAIN_ENERGY SUM All,All,All
END_
Tosca Structure.bead will try to combine All load cases in the finite element calculation with the weighting of 1.0. Once again, this method is NOT recom-
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mended and the former mentioned method of defining the load cases separately and then combining them in the objective function is emphasized.
7.5.2
Linear static sensitivity based optimization BEAD_SENSITIVITY The sensitivity based bead optimization offers a large range of responses for static analysis. But note that the controller based bead algorithm will often be superior and more effective in pure minimization of compliance designs. Of course, if you need more control of displacements of certain nodes within your model you will be better of using the sensitivity based algorithm.
7.5.2.1 Minimize compliance To minimize the compliance of a shell structure the command structure is similar to the controller based algorithm. Define a compliance design response and reference it in the objective function. DRESP ID_NAME DEF_TYPE EL_GROUP TYPE GROUP_OPER LC_SET
= = = = = =
dresp_compliance SYSTEM ALL_ELEMENTS STRAIN_ENERGY SUM Static,1,All
END_
ID_NAME DRESP TARGET
= min_compliance = dresp_compliance = MIN
END_
Explanation: • A design response with name "dresp_compliance" is defined for the first static load case. Note that the design response is defined using GROUP_OPER = SUM over ALL_ELEMENTS which is also the correct definition because compliance must be equal to the outer work (force x displacement). The compliance design response is minimized (TARGET=MIN) in the object function. Note that no constraint is necessary, but remember to add a DVCON_BEAD which constrains the nodes in positive and negative normal direction.
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OBJ_FUNC
SIMULIA Tosca Structure Bead Optimization
7.6
Typical Optimization Tasks for Modal Analysis This section deals with the typical optimization tasks for modal analysis types. Some very common tasks are described here.
7.6.1
Maximization of the lowest natural frequency (controller) BEAD_CONTROLLER The natural frequency may be optimized by using the maximization the dynamic frequency response. Remark • It should be emphasized that the sensitivity based algorithm (BEAD_SENSITIVITY) is usually superior for this task, see Fig. 241). An example of maximization of first natural eigenfrequency is shown here: DRESP ID_NAME DEF_TYPE TYPE LC_SET
= = = =
dresp_max_eigenfrequency SYSTEM DYN_FREQ Modal,All,1
END_
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OBJ_FUNC ID_NAME DRESP TARGET
= maximize_eigenfrequency = dresp_max_eigenfrequency = MAX
END_
Explanation: • The type of the design response is DYN_FREQ (eigenfrequency). To choose the first eigenfrequency the third argument in the item LC_SET is set to 1. This design responses ID_NAME is referenced in the OBJ_FUNC where it is set to be maximized.
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Remarks 1. To consider for example the second eigenfrequency, the LC_SET parameter has to be set as follows: LC_SET = Modal, All, 2. More information can be found in Commands manual (see volume 3: DRESP). 2. Warning: Do NOT define the third argument in the LC_SET command as All (e.g. LC_SET=Modal,1,all). The algorithm will then try to combine All modes from the modal analysis, which normally will NOT lead to good results for the controller based algorithm.
7.6.2
Sensitivity based eigenvalue optimization BEAD_SENSITIVITY The eigenvalue optimization of the sensitivity based bead optimization has shown to be superior to the controller based algorithm. It’s not only possible to optimize the first eigenfrequency, but following tasks can also be done: • maximize (or minimize) an eigenmode • maximize (or minimize) a range of modes • move a certain eigenmode higher or lower using mode-tracking • maximize band gaps (distance between modes) using the special MINMAX function • force eigenvalue to achieve a certain value
BEAD_SENSITIVITY The definition of a maximization of an eigenvalue problem could be done similar to the controller based bead algorithm. But this is not recommended. In the sensitivity based algorithm we have more control over the modes. A problem you usually want to avoid when optimizing eigenmodes is modeswitching because it destabilizes the optimization algorithm. The typical problem is by maximizing the first eigenmode it may "overtake" the second mode hence, the modes switch place (previous second mode becomes the first mode) and sensitivity algorithm must suddenly take a new mode into consideration. Mode tracking can of course be used (chapter 7.8.2.3 Optimization parameters for mode tracking), but the computationally cheapest way to push the first
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7.6.2.1 Maximize the first natural mode (first eigenvalue)
SIMULIA Tosca Structure Bead Optimization
eigenmode up is to use the Kreissel-Meier Steinhauser formulation (TYPE = DYN_FREQ_KREISSEL):
α ϕ = – --- ln k
N
j = 1 e
– kf j
In the formulation f j is the eigenfrequency, e the base of the natural logarithm and α and k are constants. In the following the formulation will enforce the 5 first modes to keep their sequence. This is usually sufficient to avoid mode switching among the first couple of modes. See also Fig. 241 at iteration 13-14 where modes almost switch, but do not because of this formulation. DRESP ID_NAME DEF_TYPE TYPE LC_SET
= = = =
dresp_eig_kreissel SYSTEM DYN_FREQ_KREISSEL Modal,All,1-5
END_ OBJ_FUNC ID_NAME DRESP TARGET
= max_dresp_eig_kreissel = dresp_eig_kreissel = MAX
END_
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Explanation • The definition above will enforce the 5 first modes to keep their sequence. This is usually sufficient to avoid mode switching among the first couple of modes. The first mode is maximized (TARGET=MAX) until it comes near the higher modes in which case they are being considered as well.
7.6.2.2 Maximize a range of modes BEAD_SENSITIVITY Maximizing a range of modes can be done in following simple way: DRESP ID_NAME DEF_TYPE TYPE LC_SET
= = = =
dresp_eigs_1-5 SYSTEM DYN_FREQ Modal,All,1-5
END_ OBJ_FUNC
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ID_NAME DRESP TARGET
= max_dresp_eigs_1-5 = dresp_eigs _1-5 = MAX
END_
Explanation Here, the 5 first modes are summed in one design response (dresp_eigs_15). This sum is being maximized (TARGET=MAX).This solution often has the pitfall that the higher modes usually are weighted higher than the lower ones. One way to circumvent this is to define a design response for each eigenmode: DRESP ID_NAME DEF_TYPE TYPE LC_SET
= = = =
dresp_eig1 SYSTEM DYN_FREQ Modal,All,1
= = = =
dresp_eig2 SYSTEM DYN_FREQ Modal,All,2
END_ DRESP ID_NAME DEF_TYPE TYPE LC_SET END_ DRESP ID_NAME
= dresp_eig...
OBJ_FUNC ID_NAME DRESP DRESP DRESP DRESP DRESP TARGET
= = = = = = =
max_dresp_eigs_1-5 dresp_eig1, 0.10, 100. dresp_eig2, 0.05, 200. dresp_eig3, 0.04, 250. dresp_eig4, 0.0025,400. dresp_eig5, 0.002, 500. MAX
Hz Hz Hz Hz Hz
END_
Explanation • Here, each of the 5 first modes are multiplied by a weight (reciprocal value of the initial eigenvalue) and then summed and maximized.
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SIMULIA Tosca Structure Bead Optimization
7.6.2.3 Maximize a certain mode BEAD_SENSITIVITY Sometimes it may be sufficient to only have interest for one single mode and at the same time we do not want to regard the other modes. This can be done using mode tracking. DRESP ID_NAME DEF_TYPE TYPE LC_SET
= = = =
dresp_eig2 SYSTEM DYN_FREQ Modal,All,2
END_ OBJ_FUNC ID_NAME DRESP TARGET
= max_ dresp_eig2 = dresp_eig2 = MAX
END_ OPTIMIZE ID_NAME DV STRATEGY OBJ_FUNC
= = = =
opt my_design_nodes BEAD_SENSITIVITY max_ dresp_eig2
= = = =
my_parameters opt ON 10
END_ OPT_PARAM ID_NAME OPTIMIZE MODETRACKING MODENUMBERS
Explanation: • The second mode is chosen to be maximized. The important difference is that mode tracking is activated the optimization parameters (MODETRACKING= ON). Default by mode tracking in Tosca Structure is to take 5 modes into account, but this can be changed by the item MODENUMBERS. This should not be set too high because of computational effort.
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END_
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Fig. 249 Optimization displacements and convergence plots without (a) and with (b) mode tracking
7.6.2.4 Adjust eigenvalue BEAD_SENSITIVITY The opposite of the former approach may also be the case -- that is to force an eigenfrequency to achieve a certain value. This may be realized using constraint functions. ID_NAME DEF_TYPE TYPE LC_SET
= = = =
dresp_eig_2 SYSTEM DYN_FREQ Modal,All,2
END_
OBJ_FUNC ID_NAME DRESP TARGET END_ CONSTRAINT
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= max_dresp_eig_2 = dresp_eig_2 = MAX
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DRESP
SIMULIA Tosca Structure Bead Optimization
ID_NAME DRESP MAGNITUDE LE_VALUE
= = = =
con_dresp_eig_2_le_15Hz dresp_eig_2 ABS 15.
= = = = =
opt my_design_nodes BEAD_SENSITIVITY max_ dresp_eig2 con_dresp_eig_2_le_15Hz
END_ OPTIMIZE ID_NAME DV STRATEGY OBJ_FUNC CONSTRAINT END_
Explanation: • The second eigenmode will be maximized, but because of the constraint it may not become higher than 15. Hz.
7.6.2.5 Maximize band gaps BEAD_SENSITIVITY For dynamic problems it is often problematic to have an eigenvalue at some frequency. This can be done with the special form Tosca Structure handles MINMAX-problems for eigenvalue. Here, the object function Φ for eigenfrequencies by TARGET= MINMAX is given:
1 Φ α -----------------∗ fk – fk
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By minimizing this expression the eigenfrequencies f will be moved away * from the value of f k . With α as a constant the Tosca Structure commands would be: DRESP ID_NAME DEF_TYPE TYPE LC_SET
= = = =
dresp_eig_2 SYSTEM DYN_FREQ Modal,All,2
END_
OBJ_FUNC ID_NAME DRESP TARGET
= move_dresp_eig_2_from_15Hz = dresp_eig_2, 1.0, 15. = MINMAX
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SIMULIA Tosca Structure Constraints
END_
Fig. 250 Convergence of eigenvalues of a bandgap optimization (15 Hz) Explanation: The second eigenmode will be pushed away from 15.0 Hz. The weighting of the design response is simply 1.0. Remark: 1. Flat structures should first have the eigenvalues maximized before doing the band-gap optimization because the optimizer must also be able to move some eigenvalues down.
Constraints The number of constraints allowed for BEAD_SENSITIVITY is almost as vast as the possibilities for object function definition. For BEAD_CONTROLLER the only allowed and necessary constraint is the BEAD_HEIGHT which is not allowed in BEAD_SENSITIVTITY. Static analysis
Gravity / Inertia
Frequency response
DISP_ABS
CENTER_GRAVITY_X
FS_ACCEL_X
DISP_X
CENTER_GRAVITY_Y
FS_ACCEL_Y
DISP_X_ABS
CENTER_GRAVITY_Z
FS_ACCEL_Z
DISP_Y
INERTIA_XX
FS_DISP_ABS
DISP_Y_ABS
INERTIA_XY
FS_DISP_X_ABS
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SIMULIA Tosca Structure Bead Optimization
DISP_Z
INERTIA_XZ
FS_DISP_Y_ABS
DISP_Z_ABS
INERTIA_YY
FS_DISP_Z_ABS
ROT_X
INERTIA_YZ
FS_VELOCITY_X
ROT_Y
INERTIA_ZZ
FS_VELOCITY_Y
ROT_Z
FS_VELOCITY_Z
STRAIN_ENERGY
Independent of analysis type: BEAD_HEIGHT* Table 29
Modal analysis DYN_FREQ
Possible design responses for constraints for Tosca Structure.bead. * BEAD_HEIGHT is only allowed in BEAD_CONTROLLER but not in BEAD_SENSITIVITY. For sensitivity algorithm same functionality is achieved using DVCON_BEAD instead.
Remark: 1. The Gravity / Inertia design response types are only usable if at least one design response of the other types is used in the objective function or constraints.
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7.8
Settings Each OPT_PARAMcommand has a unique name (ID_NAME parameter) and references a previously defined optimization job (OPTIMIZE parameter). The specified parameters only relate to the given optimization task. A typical OPT_PARAM command appears as follows: OPT_PARAM ID_NAME OPTIMIZE ...
= param_for_bead_optimization = bead_optimization
END_
The following parameters may be set in bead optimization: BEAD_CONTROLLER: • Direction of the optimization displacement
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• Update of normal vectors (optimization displacement vector) • Influence on bead width • Number of iterations • Minimum stress for a optimized area • Maximum membrane stress for a optimized area • Mesh enhancing parameters BEAD_SENSITIVITY • Filtering of sensitivities • Move limit • MMA asymptote update • Sensitivity calculation • Optimization parameters for mode tracking • Optimization parameters for frequency response - damping parameters - Q-factor Remarks 1. IMPORTANT: The parameters for controller are ignored for the sensitivity based algorithm and vice versa.
3. Please note that BEAD_WIDTH and BEAD_ITER has no effect in sensitivity based optimization. Therefore always define a STOP-command; ITER_MAX = 20 is recommended. Realization in Tosca ANSA environment BEAD_CONTROLLER Example of setting the SCALE parameter for controller based bead optimization:
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2. The OPT_PARAM command is also used in shape and topology optimization. However, the optimization parameters that can be set, depend upon the given type of optimization. The only parameters that can be set here are those allowable for bead optimization. Topology and shape optimization parameters cannot be set.
SIMULIA Tosca Structure Bead Optimization
Tosca Structure Task | PRE-PROCESSING BEAD_OPTIMIZATION_ | [New] | [SETTINGS]
|
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BEAD_SENSITIVITY Example of setting the FILTER_RADIUS parameter for sensitivity based bead optimization: Tosca Structure Task | PRE-PROCESSING | BEAD_OPTIMIZATION_ | [New] | [SETTINGS]
Realization in Tosca Structure.gui BEAD_CONTROLLER
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SIMULIA Tosca Structure Settings
Example of setting the SCALE parameter for controller based bead optimization:
7.8.1
Parameters for controller based bead optimization The controller based bead optimization has be given numerous default settings (OPT_PARAM) that produce satisfactory results for various optimization models. Usually, these default settings do not need to be changed by the user. However, by specifically configuring the controller for a given optimization task, the controller response and consequently the optimization procedure can be improved. The user can set several optimization parameters using the OPT_PARAM command and thereby influence the controller response.
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BEAD_SENSITIVITY Example of setting the FILTER_RADIUS parameter for sensitivity based bead optimization:
SIMULIA Tosca Structure Bead Optimization
7.8.1.1 Scaling of displacements (SCALE) BEAD_CONTROLLER By default, the positive normal vector of the elements in the design domain is used as an optimization displacement direction. This direction depends on the orientation of the finite elements in the design domain. To invert the displacement direction, a negative SCALE parameter can be defined. Correspondingly, the absolute value of the optimization displacement is then applied in the negative direction. The value of the scaling parameter is not needed by Tosca Structure. Only the sign is needed in order to determine direction. OPT_PARAM ... SCALE ...
= -1
END_
7.8.1.2 Update of optimization displacement vectors (VECTOR) BEAD_CONTROLLER As explained in vol.2 chapter 7.3, an optimization displacement vector is determined by the optimization algorithm for every design node. This vector graphically corresponds to the outer surface unit normal of the nodes and indicates the optimization displacement direction. Restrictions influencing the direction (DVCON_BEAD with CHECK_DOF and CHECK_BC) are included when calculating the optimization displacement vectors. The VECTOR parameter enables the user to specify the design cycle which determines the optimization displacement vectors: OPT_PARAM
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... VECTOR ...
= FIRST
END_
The optimization displacement direction of the start model is used in bead optimization. As bead designed sheet metal structures are manufactured by a deep drawing process generated undercuts would lead to a non-manufacturable design. This may be avoided by updating the optimization displacement direction with each iteration (VECTOR = EVER).
7.8.1.3
Bead width (BEAD_WIDTH) BEAD_CONTROLLER A geometric parameter for the stiffeners is the bead width. The optimization system automatically determines a bead width based on the element edge length and the thickness of the shell structure. Default
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SIMULIA Tosca Structure Settings
BEAD_WIDTH=2*max(2*height_of_bead, 3.2*mean_edge_length) of the elements attached to design nodes. The user can define own values for the bead width by the OPT_PARAM command. Remarks 1. The value for the bead width is used for internal filtering. The generated beads will not have the exact width specified by the user. 2. Because bead optimization is a very ill-posed optimization problem (many "optimal" solutions), it is recommended that a couple of optimizations is done with different BEAD_WIDTH’s.
7.8.1.4 Number of iterations (BEAD_ITER) BEAD_CONTROLLER The number of iterations modifies the stepsize of the optimization. The number of recommended iterations is 2.
7.8.1.5 Penalty conditions (BEAD_MIN_STRESS and BEAD_MAX_MEMBRANE) BEAD_CONTROLLER Two penalty functions are available in Tosca Structure.bead: BEAD_MIN_STRESS = BEAD_MAX_MEMBRANE =
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The functions make sure that the areas that either have very low stresses or a low bending/membrane stress ratio are disregarded by the optimization.
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The BEAD_MIN_STRESS penalty value is the relative to the maximal Von Mises stress in the design area. If a element has a lower Von Mises stress than this value, the element is left out of the optimization.
Load
Load
Fig. 251 The penalized elements are dark blue. Left is the BEAD_MIN_STRESS criteria used, and right is the BEAD_MAX_MEMBRANE used.
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The BEAD_MAX_MEMBRANE is based on the ratio between the highest principal of the two tensors, Differential Stress Tensor and Membrane Stress Tensor, respectively. The Differential Stress Tensor is a mesure for the bending of a plate whereas the Membrane Stress Tensor is a mesure for inplane stress.
Load Load Fig. 252 Left with no penalization criteria used and right with both.
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Remarks 1. The default settings are: BEAD_MIN_STRESS = 0.001 BEAD_MAX_MEMBRANE = 1.0
This means that if an element has less than 0.1% of the Von Mises stress or the membrane stress is higher than the bending stress, it will not be optimized. 2. Both penalty conditions can be shut of by setting the parameters to zero: BEAD_MIN_STRESS = 0.0 BEAD_MAX_MEMBRANE = 0.0
3. After optimization or after a run of the type TEST2 (vol.2 chapter 12.2.8), the penalized areas can be visualized by generating a bead_ctrl vtfx-file (vol.2 chapter 10.2). The penalized areas for BEAD_MAX_MEMBRANE and BEAD_MIN_STRESS have the "Bead-values" -3 and -4, respectively in the resulting bead_ctrl-plot.
7.8.1.6 Mesh enhancing parameters (CURV_SMOOTH and BEAD_NODE_SMOOTH)
a)
b)
c)
Fig. 253 CURV_SMOOTH for values 1.0 (a), 5.0 (b) and 10.0 (c). The node smoothing (BEAD_NODE_SMOOTH) ensures that the optimization displacement of neighbouring nodes does not become too great. This is especially an issue near boundaries or active design variable constraints.
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These two parameters control the filter radius of two mesh enhancing features in Tosca Structure.bead. It is recommended not to change these parameters. Curvature smoothing (CURV_SMOOTH) filters the optimization direction, so that normals in areas with high curvature do not cross, which results in poor or useless mesh. Default is 5.0, which means the filter size is 5 times the middle element edge length. In case of mesh problems try setting this value higher, eg. CURV_SMOOTH = 10.0.
SIMULIA Tosca Structure Bead Optimization
Default is 0.25*BEAD_WIDTH. Values between 0.0*BEAD_WIDTH and 0.5*BEAD_WIDTH (entered as absolute values in mm) are allowed.
a)
b)
c)
Fig. 254 BEAD_NODE_SMOOTH for values 0.0*BEAD_WIDTH (a), 0.25*BEAD_WIDTH (b) and 0.49*BEAD_WIDTH (c).
7.8.2
Optimization parameters (sensitivity based bead optimization) BEAD_SENSITIVITY The following is a description of different optimization parameters (OPT_PARAM). It should not be necessary to change any for basic use.
7.8.2.1 Filtering (FILTER_RADIUS) BEAD_SENSITIVITY To avoid known problems of fluctuations in sensitivity values one should define a filter radius:
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OPT_PARAM ... FILTER_RADIUS = , END_
Default value is 4.0, REL. First item is the filter radius. Second option is whether the radius is relative to the medium edge length of elements in the design area (REL). Radius may also be set to an absolute value (ABS), fx. : FILTER_RADIUS = 5.0, ABS
7.8.2.2 MMA parameters The mathematical optimizer MMA is used to determine the new nodal positions. Following parameters may be set:
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Move limit (NODAL_MOVE) BEAD_SENSITIVITY A move limit adjusts the change in the nodal coordinates per iteration. The relative move limit of the nodal optimization displacement for each iteration is set by the optimization parameter. NODAL_MOVE =
Default value is NODAL_MOVE = 0.1. The value must be between 0.0 and 1.0. The absolute move limit is the maximum possible optimization displacement times NODAL_MOVE. MMA asymptote update (NODAL_UPDATE) BEAD_SENSITIVITY The optimization parameter NODAL_UPDATE can be used to control the update of asymptotes in MMA. The value of nodal update may be conservative (NODAL_UPDATE =CONS) which is default or normal (NODAL_UPDATE =NORM). Only advanced users should change this parameter. Sensitivity calculation (ONLY_DES_NODES) BEAD_SENSITIVITY Tosca Structure.bead calculates sensitivities only for design nodes: ONLY_DES_NODES = YES
In the opposite case (ONLY_DES_NODES = NO) Tosca Structure is forced to calculate sensitivities for ALL_NODES which is not recommended. Only advanced users should change this parameter.
7.8.2.3 Optimization parameters for mode tracking
MODETRACKING=, MODENUMBERS =
Mode tracking is activated by setting the optimization parameter MODETRACKING= ON. The second item on MODETRACKING can be used to with a (small) node group which is used for the mode tracking which can improve performance. Default by Tosca Structures mode tracking is to take 5 modes into account, but this can be changed by the item MODENUMBERS = . This should not be set too high because of computational effort.
7.8.2.4 Optimization parameters for frequency response BEAD_SENSITIVITY
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BEAD_SENSITIVITY Mode tracking is controlled by two optimization parameters
SIMULIA Tosca Structure Bead Optimization
Following optimization parameters are only active by frequency response models. DAMP_STRUCTURAL_MASS =
! Structural mass ! damping α
DAMP_STRUCTURAL_STIFF = ! Structural stiffness ! damping β DAMP_VISCOUS_MASS =
! Viscous mass ! damping α Ω
DAMP_VISCOUS_STIFF =
! Viscous stiffness ! damping β Ω
SUM_Q_FACTOR =
! Exponent to emphasize ! high values Q
All damping factors are zero and SUM_Q_FACTOR = 6 by default.
7.9
Check run (TEST_BEAD) The test run in bead optimization is controlled by the TEST_BEAD command. A test run is always based on a previously defined optimization job that is referenced in the OPTIMIZE command. The format information for postprocessing is specified with the parameter FORMAT. The name of the file, which the postprocessing data is written into, is specified with the parameter FILE_NAME. The test displacement in a specified direction (DIRECTION) is applied in a number of increments (INCREMENT parameter) defined by the user until reaching a specified maximum displacement (DISPLACEMENT parameter). A typical TEST_BEAD command appears as follows:
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TEST_BEAD OPTIMIZE FORMAT FILE_NAME DIRECTION DISPLACEMENT INCREMENT
= = = = = =
ONF GROW
END_
Remarks 1. If all information entered by the user is correct, the TEST_BEAD command is executed immediately after it is entered. The command does not have its own name with which it can be referenced, i.e. all command data is only temporarily active during the execution of the command.
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2. Referencing a previously defined optimization task (OPTIMIZE command) is mandatory. The test displacements are applied to the design nodes of the optimization job. 3. Specification of a format (FORMAT parameter) is mandatory. This can either be FORMAT=ONF for the Tosca Structure specific optimization neutral format to generate a vtfx sequence or FORMAT=VRML for vrml 2.0 output. 4. Specification of a file name (FILE_NAME parameter) is optional. By default the file name TEST_BEAD is used. An increment number is always attached to the file names (for example, 000, 001, 002 etc.) to enable identification of the results from the various increments. 5. Specification of a displacement direction (DIRECTION parameter) is optional. The default setting is GROW. Two possibilities can be selected to specify the displacement direction: uniform growth of all design nodes in the optimization group outwards (DIRECTION=GROW) or non-uniform ‘randomly controlled’ displacement of the design nodes in the optimization group (DIRECTION=RANDOM). For sensitivity based algorithm DIRECTION=SHRINK does also make sense. 6. Specification of the maximum absolute displacement (DISPLACEMENT parameter) is optional. If no maximum absolute displacement is specified by the user then a maximum absolute displacement depending upon the FE mesh will automatically be determined.
8. If DIRECTION=RANDOM is selected, it is possible that the design node with the maximum displacement will have a smaller absolute displacement than specified in the DISPLACEMENT parameter. Here, the maximum specified displacement only represents an upper limit that does not need to be achieved due to the ‘randomly controlled’ distribution of the displacements. Example: The optimization task named bead_optimization should be subjected to a test run. Patran neutral file format is the selected output format. The file names have the name test_grow. In the growth direction five displacement increments should be applied with a maximum displacement of 1.5 length units, i.e. the displacements are applied in increments of 0.0, 0.3, 0.6, 0.9, 1.2 and 1.5. TEST_BEAD
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7. Specification of a number of increments (INCREMENT parameter) is optional. The default value is INCREMENT=1. If the user specifies 5 increments, for example, 6 results files are generated, whereby the first result file has the file extension ‘000’ and represents the initial state.
SIMULIA Tosca Structure Bead Optimization
OPTIMIZE FORMAT FILE_NAME DIRECTION DISPLACEMENT INCREMENT
= = = = = =
bead_optimization MSC/PATRAN test_grow GROW 1.5 5
END_
Realization in Tosca ANSA environment Example TEST_BEAD with 5 steps to show the maximal displacement of 5.0: [New] |
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1.Tosca Structure Task | CHECK_INPUTS | [TEST_BEAD_CHECK]
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SIMULIA Tosca Structure Check run (TEST_BEAD)
3. To view results directly afterwards use Tosca Structure Task | CHECK_INPUTS | [New] | [VTF_VISUALIZATION]
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2.Tosca Structure Task | CHECK_INPUTS | TEST_BEAD_CHECK | [New] | [TEST_BEAD]
SIMULIA Tosca Structure Bead Optimization
Realization in Tosca Structure.gui Change module to Start Tosca Structure. Choose Type test1 as run type and Start Tosca Structure.
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7.10 Stop Condition For most tasks it is not necessary to change the stop condition for bead optimization - especially not for BEAD_CONTROLLER because the main change is done in the first iteration (although this is difficult to see for the user). The default of 3 iterations for controller based algorithm should normally not be changed. For BEAD_SENSITIVITY the default NODAL_MOVE in OPT_PARAM is 10% (0.10) of the maximal allowed nodal optimization displacement. This implies that in most cases the maximum bead height should be reached in the 10th iteration. Nevertheless, the sensitivity based algorithm usually improves the design remarkably until the 20th iteration. Therefore, this value is the default setting. For some difficult optimization problems where the convergence is bad, a lower NODAL_MOVE can be chosen and it is necessary to use more than 20 iterations. Command syntax Changing the maximum number of optimization steps to 30. STOP ID_NAME ITER_MAX
= MY_STOP = 30
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Realization within Tosca ANSA environment Tosca Structure Task | GLOBAL_STOP_CONDITION | [Edit]
PRE-PROCESSING
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7.11 Special Remarks Using Sensitivity Based Algorithm BEAD_SENSITIVITY The sensitivity based algorithm uses semi-analytical sensitivities based on a finite difference of the stiffness and mass element matrices:
∂-----Kjk ≈ ΔK∗ = ΔK + α ∂x
where
K0 + p – K0 ΔK = -------------------------Δx
Where K is the stiffness matrix, K 0 is the original matrix and K 0 + p is the perturbed matrix when one of the nodes is moved. The first term in the above
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SIMULIA Tosca Structure Bead Optimization
equation is necessary to calculate the sensitivity for most of the design responses that are available in Tosca Structure.bead. To get this term we utilize a "matrix-step" (see Fig. 255).
Fig. 255 Matrix step work flow This matrix step's only purpose is to perturb all design nodes to get these pertubed matrices - the original matrix is obtained in the last perturbation (PERTURBATION = 0) where also the results of the FE-problem is wanted. To avoid too long optimization run times it is important to understand this workflow. It has two potential pitfalls which may slow the optimization tremendously: 1. Too long calculation during matrix steps
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2. Too many pseudo loads 1. The first case is discussed in more detail in the chapters concerning the specific solvers, chapter 11 Solver Specific Features. But in short, the problem is that some solvers have no possibility of only writing the element matrices without solving the whole system. The number of matrix steps usually varies between 4-8 which in worst case leads to 9 full solvers runs every iteration. 2. The second case is a mutual problem with almost every sensitivity based optimization algorithm; using the adjoint method to calculate sensitivities one has to solve the adjoint problems. The adjoint problems are added as "pseudo loads" or extra load cases which are added to the original input deck. The number of these pseudo loads depends on the types of design responses and how they are defined. It would demand a lengthy discussion to explain in detail exactly when and why which loads are added but some rules of thumb is given here:
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• Compliance and eigenvalue optimization do not add pseudo loads (self adjoint problems) and are therefore preferable optimization quantities. • Avoid the DRESPs without any direction (DISP_ABS, FS_DISP_ABS etc.). These design responses lead to three pseudo loads (in all 3 dimensions) whereas the single directional (DISP_X, DISP_X_ABS, FS_DISP_X_ABS, etc.) only lead to one pseudo load. • Define the load case of interest directly in the DRESP definition using LC_SET. If only one load case is referenced Tosca Structure will only add one pseudo load. If LC_SET = ALL,ALL,ALL (which is default!) Tosca Structure will add a pseudo load for each load case found in the original input deck.
7.12 References Barthelemy, B. and Haftka, R.T. (1988). Accuracy analysis of the semi-analytical method for shape sensitivity analysis. AIAA Paper 88-2284: Proc. AIAA/ASME/-ASCE/ASC 29th Structures, Structural Dynamics and Materials Conference. 1: 562-581. Also Mechanics of Structures and Machines.18:407-432 (1990). Bletzinger, K.-U., Firl, M. and Daoud, F. (2006). Approximation of derivatives in semi-analytical structural optimization. III ECCM Lisbon, Portugal. June 5-8.
Clausen, P. and Pedersen, C.B.W. (2006): Non-parametric large scale structural optimization for industrial applications. III ECCM Lisbon, Portugal. June 5-8. Emmrich, D. (2004): Entwicklung einer FEM-basierten Methode zur Gesaltung von Sicken für biegebeanspruchte Leitstützstrukturen im Konstruktionsprozess. Forschungsberichte des Instituts für Produktentwicklung. 13. Karlsruhe Svanberg, K. (1987). The Method of Moving Asymptotes -A New Method For Structural Optimization. International Journal for Numerical Methods in Engineering.24:359-373.
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Bletzinger, K.-U., Daoud, F. and Firl, M. (2006). Filter techniques in shape optimization with cad-free parametrization. III ECCM Lisbon, Portugal. June 5-8.
SIMULIA Tosca Structure Sizing Optimization
8
Sizing Optimization At the beginning of the conventional design process, the design engineer often defines new components using the experience and the results gained from existing designs. This results in an evolution process that might require several manual design iterations and a long process development time. Optimization tools provide the engineer with an automatic procedure to develop fundamentally new designs and shorten the development process. For sheet metal structures ideal sheet thicknesses according to the existing load and boundary conditions have to be derived. With Tosca Structure, it is possible to carry out sizing optimization in the existing CAE environment. Within this process shell thicknesses are calculated automatically to obtain optimal sheet metal structures.
Fig. 256 Sizing for chassis components
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8.1
General Information Sizing is a tool to optimize sheet metal components through modification of sheet thicknesses. It is mostly applied at a later stage of the development process when the general layout of a component (i.e. the topology) is more or less fixed. Starting with the design area (which represents the sheet structures to be modified) and with the boundary conditions, such as loads, fixtures and manufacturing conditions, the optimization system will determine a new thickness distribution by modification of the shell thicknesses in the design area. This design proposal should fulfill all mechanical requirements and often represents a weight-optimal design proposal. Sizing with Tosca Structure allows changes for each single shell element in the model as well as clustering of thicknesses, i.e. simultaneous modification of shell thicknesses for specific areas.
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For the optimization, the following constraints and objectives can be applied: • stiffness (compliance and displacements); • eigenfrequencies; • internal and reaction forces; • weight, volume; • center of gravity; • moment of inertia. Different constraints can be defined, like member size constraints, freezing of parts, symmetry and different coupling constraints. As result, the optimization creates a design proposal with new shell thicknesses. This design proposal can then be transferred back to your CAD system.
8.2
The Optimization Task In Tosca Structure a sensitivity based approach is used for solving sizing problems. This algorithm uses the sensitivities of the design variables with regard to the objective function and the constraints. Tosca Structure uses an algorithm based on the Method of Moving Asymptotes from Krister Svanberg (Sweden). In one optimization run approximately 10 to 15 iterations are required - much fewer compared to the sensitivity based approach for topology optimization. The number of iterations as well as the CPU-time is independent of he number of shell element thicknesses chosen as design variables.
Tosca Structure.sizing supports the responses of linear static (non-conservative forces) and linear eigenfrequency (not allowed to be prestressed) finite element analysis. Temperature loading is allowed for Abaqus and ANSYS. Non-linearities Tosca Structure.sizing supports contact for Abaqus and ANSYS.Furthermore, prescribed displacements are allowed in the CAE model for static sizing optimization. However, prescribed displacements are not allowed for modal and frequency response analysis. Model Tosca Structure.sizing supports only single layered shells (admitted for sensitivity based opimization). For specific aspects regarding supported element types please refer to chapter 11 Solver Specific Features. Contact for Abaqus and ANSYS is supported in and outside the design area.
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Analysis types
SIMULIA Tosca Structure Sizing Optimization
Outside the design area all sorts of constitutive non-linear modeling is allowed, e.g. a non-linear spring. In the design area constitutive non-linear material is not supported. Geometrical non-linearities are not supported. Further, “constant” temperature loading is supported. Allowed objective functions and constraints For sizing a variety of combinations of objective functions and constraints can be selected • Static load cases: Stiffness (= compliance) Displacements Forces • Modal eigenfrequency load cases: Eigenfrequencies • Frequency response Also vibroacoustic • Mass Several constraints and several terms for the objective function for an arbitrary number of load cases can be specified.
8.2.1
How to create the optimization model
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The following describes the general procedure for defining an optimization task. These procedures are supported by the command tree in Tosca Structure.pre screen of Tosca Structure.gui (GUI), but they are not supported by Tosca ANSA environment yet. For more information about Tosca Structure.gui see vol.1 chapter 2.1.2. The CAE analysis model must previously be completely defined. Analysis Model 1. Question: Which file(s) contains the FE- model for the optimization? Procedure: Link file(s) to optimization task. GUI: Choose your model file in FEM_INPUT. Design Area 2. Question: Which part of the FE model should be selected as the design space? Procedure: Assign an element group to the design area. GUI: Choose or define the element group for the selected design area (GROUP_DEF) and define the design variables (DV_SIZING).
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3. Question: Are there elements in the design space which have to have certain restrictions (e.g. symmetry and manufacturing restrictions)? How can these restrictions be described? Procedure: Define design variable constraints for element group. GUI: Choose or define element groups with restrictions (GROUP_DEF). Define the restrictions using DVCON_SIZING command. 4. Question: Are there certain symmetry conditions that should be fulfilled? Procedure: Create a symmetry coupling condition. GUI: Create a LINK_SIZING condition and reference it in the restriction command (LINK_SIZING). Objective Function 5. Question: Which terms describe the values to be optimized? Should these values be minimized or maximized or otherwise combined using the minmax formulation? Are any special weighting factors or target values required? Procedure: Choose the terms for optimization (design responses) and the target type. GUI: Define the design response (DRESP) and assign it to the objective function (OBJ_FUNC). Constraint
Optimization Task 7. Question: Are all of the command definitions listed above complete and ready for the optimization job? Procedure: If necessary, make the additional definitions and prepare the optimization job. GUI: Reference all definitions above in OPTIMIZE. Stop Condition 8. Question: Should the stop condition be modified? Procedure: Modify stop condition GUI: STOP.
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6. Question: Which terms describe the constraint? What value should the constraint have? Procedure: Choose the term for the constraint and set the target value or upper/lower boundary. GUI: Define the design response (volume 3: DRESP) and assign it to the constraint (CONSTRAINT).
SIMULIA Tosca Structure Sizing Optimization
Completion 9. Question: Is all required data specified? Procedure: If yes, finish the definition of the optimization problem and save your definition. GUI: Save as .par The essential commands required for the optimization model for sizing are described in the following. The definitions for the optimization job are assembled in a parameter file. The exact syntax of the commands can be looked up in vol.3 Commands Manual. Fig. 257 gives an overview of a standard optimization task and the relation between the several commands. Only commands which are referenced in the OPTIMIZE command will be included in the optimization.
Fig. 257 Block structure of sizing commands
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8.3
Design Area During an optimization, only part of the model may be changed. This part is defined as design area.
8.3.1
Design variables For each optimization problem, the design variables represent the values to be changed during the optimization. The elemental thicknesses of shell elemenents are the design variables for the sizing optimization in Tosca Structure.
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The thicknesses change during the optimization in order to fulfill the optimization goals.
Fig. 258 Design variables for sizing
Valid design elements are the most typical shell elements. The list of valid element types for sizing is given in vol.2 chapter 11, Solver Specific Features for the different FE solvers. Design variable definition in Tosca ANSA environment
Fig. 259 DV_SIZING definition in the Tosca ANSA environment
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In order to choose the design element group, the command Edit should be applied on the item DESIGN_AREA. Then, pressing "?" key in GROUP_DEF field (after the field EL_GROUP is set to GROUP_DEF) opens the window SET HELP where all existing groups are listed; if needed, a new element group can be created by using New command of this window.
SIMULIA Tosca Structure Sizing Optimization
Design variable definition in Tosca Structure.gui The DV_SIZING command is used to assign a previously defined element group to be the design element group for the sizing optimization. The element group has to be a group of elements which are allowed as design elements for the sizing optimization.
Fig. 260 DV_SIZING definition in Tosca Structure.gui The resulting command is the DV_SIZING command. For further details please refer to DV_SIZING in the command manual. DV_SIZING ID_NAME EL_GROUP
= dv_design_elem = design_elem
END_
8.3.2
Manufacturing conditions and geometrical restrictions For sizing with Tosca Structure, it is possible to define constraints (DVCON_SIZING) that have a direct influence on the individual design variables(DV_SIZING). This allows the manufacturing restrictions or geometrical design aspects to be taken into consideration in the sizing optimization. The different restrictions are listed below:
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• Frozen area • Element fixing by exclusion from the optimization group. • Element fixing by freezing elements (CHECK_TYPE = FROZEN). • Shell thickness control • Upper and lower bounds for shell thicknesses (CHECK_TYPE = THICKNESS_BOUNDS). • Clustering of element areas with the same shell thickness (CHECK_TYPE = CLUSTER) • Symmetry control • Area linking (LINK_SIZING) • Symmetry restriction(LINK_SIZING)
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• Member size control • minimum cluster width control (CHECK_TYPE = MIN_CLUSTER_WIDTH)
8.3.2.1 Frozen areas Sometimes it is required to maintain material in certain parts of the design area, such that they remain unchanged in the optimized model. Element groups describing these parts can be defined as frozen area. This option is used to exclude the so-called frozen elements from being modified during the optimization, even though these elements are included in the design space. This is the case, e.g., when the elements are used in order to fix the component and therefore should be preserved independently of their internal loads. The inclusion into the design space may be necessary, e.g., to control the target volume (see constraints “absolute volume” or “relative volume”, Bd.1, Chapter 5.5.1). Defining a frozen area in Tosca ANSA environment
Fig. 261 Workflow for the definition of FROZEN_AREA Defining a frozen area in Tosca Structure.gui The DVCON_SIZING command has to be selected in Tosca Structure.pre screen when defining the design variable constraints. The name of the element group that is to be frozen follows after the obligatory ID_NAME field. If the element group is not already defined, it is necessary to define it in advance using GROUP_DEF command.
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Manufacturing constraints are defined using DV_CONSTRAINTS item. Each of these restrictions relates to an element group that is either the design area or a subset of it. For the definition of the frozen area, only an element group is necessary. No further properties have to be set.
SIMULIA Tosca Structure Sizing Optimization
Choose Type = Frozen.
Fig. 262 Definition of a FROZEN design variable constraint for an existing element group The resulting command looks like: DVCON_SIZING ID_NAME EL_GROUP CHECK_TYPE
= frozen_area = frozen_grp = FROZEN
END_
This constraint for the design variables is activated when it is referenced in the OPTIMIZE command.
Shell thicknesses can be controlled to vary between a lower or upper bound (CHECK_TYPE = THICKNESS_BOUNDS). For the definition of the thickness bounds, either an absolute or relative value for the upper and lower bound can be defined. In case of relative bounds a real number is specified for each bound which is multiplied with the initial value for the shell thickness to get the absolute upper and lower bounds. The parameter MAGNITUDE defines if the lower and upper bound are defined as absolute or relative values.
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8.3.2.2 Shell thickness bounds
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Defining a thickness bound in Tosca ANSA environment Thickness bounds are defined using DV_CONSTRAINTS item. The restriction relates to an element group that is either the design area or a subset of it.
Fig. 263 Workflow for the definition of THICKNESS_BOUNDS Defining thickness bounds in Tosca Structure.gui
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The DVCON_SIZING command has to be selected in Tosca Structure.pre screen when defining the design variable constraints. Choose your element group for the thickness bounds below the obligatory ID_NAME field. If the element group is not already defined, it is necessary to define it in advance using GROUP_DEF command.
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Choose Type = Thickness_bounds and define a relative (REL) or absolute (ABS) upper and lower value..
Fig. 264 Definition of thickness bounds for an existing element group The resulting command looks like: DVCON_SIZING ID_NAME EL_GROUP CHECK_TYPE MAGNITUDE LOWER_BOUND UPPER_BOUND
= = = = = =
dvcon_thickness_bounds
my_group THICKNESS_BOUNDS REL/ABS … …
END_
8.3.2.3 Cluster groups Shell thicknesses can be clustered to remain the same in certain areas during the optimization (CHECK_TYPE = CLUSTER_GROUPS). Clustering reduces the number of design variables (without influence on calculation time). Defining cluster groups in Tosca ANSA environment Cluster groups are defined using DV_CONSTRAINTS item. Each of these restrictions relates to an element group that is either the design area or a sub-
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This constraint for the design variables is activated when it is referenced in the OPTIMIZE command.
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set of it. For the definition of the frozen area, only an element group is necessary. No further properties have to be set.
Fig. 265 Workflow for the definition of Cluster groups Defining cluster groups in Tosca Structure.gui
Fig. 266 Definition of a design variable constraint to "cluster" shell thicknesses of an existing element group The resulting command looks like: DVCON_SIZING ID_NAME EL_GROUP EL_GROUP EL_GROUP
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= = = =
cluster_area
cluster_grp_1 cluster_grp_2 cluster_grp_3
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The DVCON_SIZING command has to be selected in Tosca Structure.pre screen when defining the design variable constraints. Choose your cluster groups below the obligatory ID_NAME field. If the element group is not already defined, it is necessary to define it in advance using GROUP_DEF command. Choose Type = Cluster Groups.
SIMULIA Tosca Structure Sizing Optimization
... CHECK_TYPE
= CLUSTER_GROUPS
END_
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This constraint for the design variables is activated when it is referenced in the OPTIMIZE command. In general clustering areas correspond to areas made from one sheet metal. Nevertheless performing the optimization without clustering may give you ideas where to construct borders between (i.e. where to combine or cut) your single sheets.
Fig. 267 Example with free sizing optimization and clustering (below) for certain (approx. 200) areas.
8.3.2.4 Width control (minimum cluster width) Small sheet parts in the resulting structure are often undesirable. Defining a minimum sheet width (minimum cluster width) avoids the creation of small substructures in the final result. The minimum cluster width is often applied
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for avoiding high oscillations in the thickness distribution and that the structure has subcomponents with a minimum width. Additionally, the minimum cluster width for the width control can partly circumvent the two following problems: 1. First, checkerboards might appear if one is applying a minimal value of the lower bound of the thickness and applying lower order shell elements as 3 node triangular shell elements. When using higher order shell elements or the lower bound of the thickness is not minimal then checkerboards are not frequent. 2. Secondly, a minimum cluster width ensures uniqueness of the optimization solution independent upon the mesh size and discretization. A coarse mesh and a fine mesh lead to the same optimized structure if the minimum cluster widths for both cases are set to the same absolute size. Please note that the size in both cases should be larger than the average element edge length.
Fig. 268 minimum cluster width for sheet structures Remark 1. Note, thin sheet thickness is controlled by lower and upper bound settings and not by the filter which controls the width. Defining a minimum cluster width in Tosca ANSA environment
Fig. 269 Minimum cluster width restriction
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For the definition of the minimum cluster width, the element group and the desired minimum width should be entered in CLUSTER_WIDTH dialog.
SIMULIA Tosca Structure Sizing Optimization
Defining a minimum cluster width in Tosca Structure.gui
Fig. 270 Minimum cluster width definition The minimum cluster width is defined using the DVCON_SIZING command: DVCON_SIZING ID_NAME EL_GROUP CHECK_TYPE WIDTH thickness>
= = = =
MIN_CLUSTER_WIDTH ,
