ANSYS System Coupling Users Guide

System Coupling User's Guide

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Table of Contents About This Manual ...................................................................................................................................... vii Document Conventions ........................................................................................................................ vii Technical Support ................................................................................................................................ viii System Coupling Overview ........................................................................................................................ 1 Supported System Couplings .................................................................................................................. 3 Product Licensing Considerations when using System Coupling .............................................................. 4 System Coupling Workspace ...................................................................................................................... 7 Setting Up a Simulation that Uses System Coupling ................................................................................. 7 Components of the System Coupling Workspace ..................................................................................... 7 Outline View ..................................................................................................................................... 8 Properties View ................................................................................................................................ 8 System Coupling Chart View ............................................................................................................. 9 Solution Information View ................................................................................................................ 9 Settings for Completing a System Coupling Setup ................................................................................... 9 Analysis Settings .............................................................................................................................. 9 Analysis Type .............................................................................................................................. 9 Initialization Controls ................................................................................................................ 10 Coupling Initialization ......................................................................................................... 10 Duration Controls ..................................................................................................................... 10 Duration Defined By ........................................................................................................... 10 Step Controls ............................................................................................................................ 11 Analysis Settings Best Practices ................................................................................................. 12 General Analysis Type ......................................................................................................... 12 Transient Analysis Type ....................................................................................................... 13 Participants .................................................................................................................................... 13 Data Transfers ................................................................................................................................. 14 Working with Data Transfers ..................................................................................................... 16 Data Transfer Rules ......................................................................................................................... 18 Execution Control ........................................................................................................................... 19 Co-Simulation Participant Sequencing ...................................................................................... 20 Sequential Solutions ........................................................................................................... 20 Simultaneous Solutions ...................................................................................................... 20 Debug Output Control .............................................................................................................. 20 Intermediate Restart Data Output ............................................................................................. 22 Validation and State of the System Coupling Setup Cell ................................................................... 23 System Coupling Setup Cell Context Menus .................................................................................... 23 Expert Settings ............................................................................................................................... 24 Settings for Running a System Coupling Solution .................................................................................. 28 Solution Information ...................................................................................................................... 28 System Coupling Chart ................................................................................................................... 29 Chart Properties ....................................................................................................................... 29 Chart Variable ........................................................................................................................... 30 Chart Variable Properties .......................................................................................................... 30 Working with System Coupling Charts ...................................................................................... 30 Using the System Coupling Chart View ...................................................................................... 31 Validation and State of the System Coupling Solution Cell ............................................................... 32 System Coupling Solution Cell Context Menus ................................................................................ 32 Workflows for System Coupling ............................................................................................................... 33 Executing System Couplings Using the Command Line .......................................................................... 33 System Coupling Command Line Options ....................................................................................... 34 Release 16.0 - © SAS IP, Inc. 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System Coupling User's Guide Restarting a System Coupling Analysis .................................................................................................. 35 Generating Restart Files .................................................................................................................. 35 Executing the Restart Run ............................................................................................................... 36 Recovering from a Workbench Crash ............................................................................................... 37 Stopping the Coupled Analysis Run ....................................................................................................... 38 Understanding the System Coupling Service ........................................................................................... 41 Coupling Management ......................................................................................................................... 41 Inter-Process Communication ......................................................................................................... 41 Process Synchronization and Analysis Evolution .............................................................................. 41 Convergence Management ............................................................................................................. 43 Evaluating Convergence of Data Transfers ....................................................................................... 43 Data Transfers ....................................................................................................................................... 44 Data Pre-Processing Algorithms ...................................................................................................... 45 Creating Nodal Data from Face/Element Centroid Data .............................................................. 45 Creating Face/Element Data from Node Data ............................................................................. 46 Mapping Algorithms ....................................................................................................................... 46 Data Transfer Algorithms .......................................................................................................... 46 Profile Preserving ................................................................................................................ 47 Conservative Profile Preserving ........................................................................................... 47 Bucket Surface .......................................................................................................................... 48 General Grid Interface (GGI) ...................................................................................................... 51 Interpolation Algorithms ................................................................................................................ 52 Interpolated Data Post-Processing Algorithms ................................................................................. 53 Ramping Algorithm .................................................................................................................. 53 Under-Relaxation Algorithm ..................................................................................................... 54 Initial Values used in Ramping and Under-Relaxation Algorithms ............................................... 54 Clipping Algorithm ................................................................................................................... 55 Files Used by the Coupling Service ........................................................................................................ 55 System Coupling Service Input File (scInput.sci) ...................................................................... 55 System Coupling Service Shutdown File (scStop.stop) ............................................................... 55 Files Generated by Coupling Service ..................................................................................................... 56 System Coupling Server File (scServer.scs) ............................................................................... 56 System Coupling Service Log File (scLog.scl_, scLog_##.scl) ............................................ 57 System Coupling Results File (scResults_##_######.scr) ..................................................... 57 Understanding the System Coupling Input File ...................................................................................... 58 Understanding the System Coupling Log File ........................................................................................ 64 Best Practice Guidelines for Using System Coupling ............................................................................... 73 Building up a Coupled Analysis from Decoupled Systems ...................................................................... 73 Troubleshooting Two-Way Coupled Analyses Problems ......................................................................... 73 Using Text-Based Monitor Output to Debug Coupled Analyses ........................................................ 74 Using Graphical Monitor Output to Debug Coupled Analyses .......................................................... 75 Using Supplemental Output to Debug Coupled Analyses ................................................................ 75 Supplemental Output for Diagnosing Mapping Problems ................................................................ 75 Improving Coupled Analysis Stability .................................................................................................... 76 Data Transfer Ramping .................................................................................................................... 76 Participant Solution Stabilization .................................................................................................... 76 Co-Simulation Participants Sequencing .......................................................................................... 76 Controlling Participant Sequencing ........................................................................................... 77 Using Sequencing to Reduce Coupled Solution Execution Time ................................................. 77 Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction ...................................................... 79 Overview of the Problem to Solve ......................................................................................................... 80 Creating the Project .............................................................................................................................. 81

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System Coupling User's Guide Optional: Preparing for a Command-line Run ......................................................................................... 82 Adding Analysis Systems to the Project ................................................................................................. 82 Adding a New Material for the Project ................................................................................................... 84 Adding Geometry to the Project ........................................................................................................... 85 Defining the Physics in the Mechanical Application ............................................................................... 86 Generating the Mesh for the Structural System ................................................................................ 86 Assigning the Material to the Geometry .......................................................................................... 87 Setting the Basic Analysis Values ..................................................................................................... 88 Inserting Loads ............................................................................................................................... 88 Defining the Fixed Support ....................................................................................................... 88 Defining the Fluid-Solid Interface .............................................................................................. 89 Defining the Pressure Load ....................................................................................................... 89 Preparing for a Command-Line Run of the Structural System ........................................................... 90 Completing the Setup for the Structural System .............................................................................. 91 Setting up your Fluid Analysis ............................................................................................................... 91 Generating the Mesh for the Fluid System ....................................................................................... 91 Defining the Physics in the ANSYS Fluent Application ...................................................................... 94 Adding the Solution Setup Settings .......................................................................................... 94 Defining the Dynamic Mesh ...................................................................................................... 94 Adding the Solution Settings .................................................................................................... 96 Preparing for a Command-Line Run of the Fluent System .......................................................... 97 Defining and Running the Coupling in the System Coupling Application ............................................... 97 Setting the Basic Analysis Values ..................................................................................................... 98 Creating the Data Transfers ............................................................................................................. 98 Preparing System Coupling for Restarts ........................................................................................... 99 Solving and Restarting the Coupled Analysis ................................................................................... 99 Preparing for a Command-Line Run of the System Coupling System .............................................. 100 Viewing Results in CFD-Post ................................................................................................................ 101 Creating an Animation .................................................................................................................. 101 Plotting Results on the Solid ......................................................................................................... 103 Post-Processing in Mechanical ...................................................................................................... 104 Setting Up and Executing a Coupled Analysis Restart from Workbench ................................................ 104 Executing the Coupled Analysis from the Command Line .................................................................... 105 Preparing the Required Input Files ................................................................................................ 106 Running the Analysis .................................................................................................................... 106 Restart Analysis Execution ............................................................................................................. 108 Preparing the Required Input Files .......................................................................................... 108 Run the Analysis ..................................................................................................................... 108 Loading the Results into CFD-Post ........................................................................................... 109 Tutorial: Heat Transfer from a Heating Coil ............................................................................................ 111 Overview of the Problem to Solve ....................................................................................................... 111 Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis .................. 112 Creating the Project ...................................................................................................................... 112 Setting the Units in ANSYS Workbench .................................................................................... 113 Adding Analysis and Component Systems ..................................................................................... 113 Adding New Materials for the Project ............................................................................................ 114 Adding Geometry to the Project .................................................................................................... 115 Preparing the Steady-State Thermal Source Data ........................................................................... 115 Assigning the Material to the Geometry .................................................................................. 115 Generating the Mesh .............................................................................................................. 115 Defining the Physics for the Structural Analysis ........................................................................ 116 Defining the Steady-State Thermal Analysis ....................................................................... 116 Release 16.0 - © SAS IP, Inc. 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System Coupling User's Guide Executing the Structural Analysis ............................................................................................ 117 Post-Processing the Structural Analysis Results ........................................................................ 117 Using External Data to Access the Steady-State Thermal Source Data ............................................. 119 Preparing the Fluid Flow Analysis .................................................................................................. 120 Importing the Mesh for the Fluid Flow Analysis ........................................................................ 120 Defining the Physics for the Fluid Flow Analysis ....................................................................... 120 Preparing and Executing the Coupled Thermal Analysis ................................................................. 122 Reviewing Results in CFD-Post ...................................................................................................... 123 Part 2: Transferring Data from the Fluid Flow Analysis to the Steady-State Thermal Analysis .................. 126 Exporting the Data ....................................................................................................................... 126 Adding Additional Analysis and Component Systems .................................................................... 127 Using External Data to Access the Fluid Flow Source Data ............................................................. 128 Preparing the Steady-State Thermal Analysis ................................................................................. 128 Preparing and Executing the Coupled Thermal Analysis ................................................................. 128 Reviewing Results in the Mechanical Application ........................................................................... 129 Index ........................................................................................................................................................ 133

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About This Manual This manual describes how to use the System Coupling component to control otherwise independent physics solvers or external data sources so that they work together in a coupled analysis such as FluidStructure Interaction (FSI). This manual contains the following chapters: • System Coupling Overview (p. 1) describes how System Coupling works and the types of simulations you can perform. • System Coupling Workspace (p. 7) describes how to use the System Coupling views in ANSYS Workbench to control the analysis. • Workflows for System Coupling (p. 33) describes common workflow topics such as using the command line, and restarting coupled analyses • Understanding the System Coupling Service (p. 41) describes files used by the Coupling Service, the communication technology, the run time environment, and the mapping technologies. • Best Practice Guidelines for Using System Coupling (p. 73) describes best practices for using System Coupling. • Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction (p. 79) guides you through performing an example of a coupled analysis. • Tutorial: Heat Transfer from a Heating Coil (p. 111) demonstrates how to execute a sequence of one-way thermal transfers in a heat exchanger using System Coupling.

Document Conventions This section describes the conventions used in this document to distinguish between text, file names, system messages, and input that you need to type. File and Directory Names File names and directory names appear in this font: /usr/lib. User Input Input you must type exactly is shown like this: cd /usr Input Substitution Input that you must supply in a command is shown like this: fluent 3d -schost="HostName" That is, you should actually type fluent 3d -schost=" " and substitute a computer's name for HostName. Optional Arguments Optional arguments are shown using square brackets: export -cgns [-verbose] file

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About This Manual Here the argument -verbose is optional, but you must specify a suitable file name.

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Technical Support UK: 0800 048 0462 Republic of Ireland: 1800 065 6642 Outside UK: +44 1235 420130 Email: [email protected] Support for University customers is provided only through the ANSYS Customer Portal. JAPAN Mechanical Products Telephone: +81-3-5324-8333 Email: Mechanical: [email protected] Fluids Products Telephone: +81-3-5324-7305 Email: Fluent: [email protected]; CFX: [email protected]; Polyflow: [email protected]; Icepak Telephone: +81-3-5324-7444 Email: [email protected] Licensing and Installation Email: [email protected] INDIA All ANSYS Products Web: Go to the ANSYS Customer Portal (http://support.ansys.com) and select the appropriate option. Telephone: +91 1 800 209 3475 (toll free) or +91 20 6654 3000 (toll) (Please have your Customer or Contact ID ready.) Support for University customers is provided only through the ANSYS Customer Portal. FRANCE All ANSYS Products Web: Go to the ANSYS Customer Portal (http://support.ansys.com) and select the appropriate option. Toll-Free Telephone: +33 (0) 800 919 225 Toll Number: +33 (0) 170 489 087 (Please have your Customer or Contact ID ready.) Email: [email protected] BELGIUM All ANSYS Products Web: Go to the ANSYS Customer Portal (http://support.ansys.com) and select the appropriate option. Telephone: +32 (0) 10 45 28 61 Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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About This Manual Email: [email protected] Support for University customers is provided only through the ANSYS Customer Portal. SWEDEN All ANSYS Products Web: Go to the ANSYS Customer Portal (http://support.ansys.com) and select the appropriate option. Telephone: +46 (0) 10 516 49 00 Email: [email protected] SPAIN and PORTUGAL All ANSYS Products Web: Go to the ANSYS Customer Portal (http://support.ansys.com) and select the appropriate option. Telephone: +34 900 933 407 (Spain), +351 800 880 513 (Portugal) Email: [email protected], [email protected] Support for University customers is provided only through the ANSYS Customer Portal. ITALY All ANSYS Products Web: Go to the ANSYS Customer Portal (http://support.ansys.com) and select the appropriate option. Telephone: +39 02 89013378 Email: [email protected] Support for University customers is provided only through the ANSYS Customer Portal.

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System Coupling Overview The ANSYS suite of analysis software facilitates creation of a spectrum of single- and multidisciplinary simulations. Multidisciplinary simulations are offered within the context of a single piece of software (for example, within one solver) and using various dedicated mechanisms to couple a single piece of software with others. Examples of the latter include mechanisms to import external data from static sources, and the Multi-Field External (MFX) solver used for co-simulation between ANSYS Mechanical MAPDL and ANSYS CFX. These coupling mechanisms provide optimal solutions for the analyses that follow the single, specific workflow that they were built to solve. The System Coupling infrastructure discussed in this manual should be considered for generic workflows involving any number of analysis types, static data source and co-simulation participants, and data transfer quantities and directions. The Workbench System Coupling component system is an easy-touse, all-purpose infrastructure that facilitates comprehensive multidisciplinary simulations between coupling participants. Coupling participants are systems that will provide and/or consume data in a coupled analysis. Example systems in Workbench include: • Analysis Systems – Steady-State Thermal, Transient Thermal, Static Structural, Transient Structural, Fluid Flow (Fluent) • Component Systems – Fluent, External Data The execution of analyses involving couplings between any of these participants is managed by the System Coupling Service, which is the runtime component of the System Coupling system. During execution, a variety of one- and two-way data transfers are performed between coupling participants. For example, when multiple participants are executing their parts of a coupled analysis together, which is often referred to as co-simulation, they may engage in both one- and two-way data transfers as either a source or target. Similarly, when participants are providing access to existing results or data, which shall be referred to as a static data source, they may engage in only one-way data transfers as a source. This documentation provides a detailed description of capabilities supported by the System Coupling component system. All of these capabilities may, however, not yet be supported in conjunction with other Workbench systems. For information about systems that may act as participants in system couplings, see the summary of Supported System Couplings (p. 3). For information regarding product licensing details and interactions with System Couplings, see Product Licensing Considerations when using System Coupling (p. 4). To set up and execute a system coupling simulation, perform the following steps: 1.

Create the project.

2.

Add the individual, participant systems to the project.

3.

Add the System Coupling system to the project.

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System Coupling Overview 4.

Set up each individual, participating system (generally from top-to-bottom, until you have completed all the required steps for your analysis).

5.

Connect the systems together as shown in Figure 1: Example of Connecting a System Coupling Component System with Various Types of Systems (p. 2). For co-simulation participants and the External Data static data participant, connections are drawn from the participants’ Setup cells.

6.

Set up the System Coupling system (see System Coupling Workspace (p. 7)).

Figure 1: Example of Connecting a System Coupling Component System with Various Types of Systems

It is important to note that updates of co-simulation participant (for example, a solver) Solution cells are disabled for Workbench systems connected to the System Coupling system; these updates (and execution of the respective solvers) are automatically initiated when the System Coupling Solution cell

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Supported System Couplings is updated. Note, however, that these updates respect all settings (for example parallel, precision, and so on) already made for them.

Important Using System Coupling in conjunction with the Remote Solver Manager (RSM) is not supported. In the isolated case of Mechanical, the use of RSM for runs on a single local host is, however, permitted. After you have updated the System Coupling Solution cell, you can: • Pause the analysis by interrupting its progress. • Restart the analysis as described in the Initialization Controls (p. 10). • Debug your system coupling simulation by using the system coupling command line arguments (see System Coupling Command Line Options (p. 34)). You can also perform additional debugging of the connected systems as described in Troubleshooting Two-Way Coupled Analyses Problems (p. 73). • Use CFD-Post to simultaneously analyze the results of the simulation by: – Connecting other participant systems’ Solution cells to the Results cell of the Fluid Flow system, or – Connecting all participant systems’ Solution cells to a Results component system that you introduce in the schematic.

Supported System Couplings The following is the list of supported coupling participants: • Fluent • Static Structural • Transient Structural • Steady-State Thermal • Transient Thermal • External Data Fluent can be connected with any of the other supported participants. In addition, the Steady-State Thermal system can be connected with external data. Note that Steady-State and Static systems cannot be coupled with Transient systems.

Note Only two coupling participants can be connected to the System Coupling system at one time. However, more than one System Coupling system may be introduced within the same project schematic.

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System Coupling Overview For information about using System Coupling with the ANSYS Fluent system in Workbench, see Performing System Coupling Simulations Using Fluent in Workbench in the Fluent in Workbench User's Guide. For information about restarting a coupled analysis with Fluent, see Restarting Fluent Analyses as Part of System Couplings. For information about using System Coupling with the ANSYS Mechanical system in Workbench, see System Coupling in the ANSYS Mechanical User's Guide. For information about restarting a coupled analysis with Mechanical, see Restarting Structural Mechanical Analyses as Part of System Coupling. For information about using System Coupling with the External Data system in Workbench, see External Data.

Product Licensing Considerations when using System Coupling The licenses needed for System Coupling analyses are listed in Table 1: Licenses Required for Participating Systems in System Coupling (p. 4). No additional licenses are required for the System Coupling infrastructure. The simultaneous execution of coupling participants currently precludes the use of the license sharing feature that exists for some product licenses. The following specific requirements consequently exist: • Distinct licenses are required for each coupling participant. • Licensing preferences should be set to ‘Use a separate license for each application’ rather than ‘Share a single license between applications when possible.’ The requirements listed above are particularly relevant for ANSYS Academic products. Table 1: Licenses Required for Participating Systems in System Coupling System

Commercial License Required

Academic License Required

Fluent

• ANSYS CFD,

• ANSYS Academic Associate,

• ANSYS Fluent, or

• ANSYS Academic Associate CFD,

• ANSYS Fluent Solver

• ANSYS Academic Research, • ANSYS Academic Research CFD, • ANSYS Academic Teaching Advanced, • ANSYS Academic Teaching Introductory, or • ANSYS Academic Teaching CFD

Static Structural or Transient Structural

• ANSYS Structural,

• ANSYS Academic Associate,

• ANSYS Mechanical,

• ANSYS Academic Research,

• ANSYS Mechanical CFD-Flo,

• ANSYS Academic Research Mechanical,

• ANSYS Mechanical Emag, 4

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Product Licensing Considerations when using System Coupling System

Commercial License Required

Academic License Required

• ANSYS Multiphysics,

• ANSYS Academic Teaching Advanced,

• ANSYS Structural Solver, • ANSYS Mechanical Solver, or

Steady-State Thermal or Transient Thermal

• ANSYS Academic Teaching Introductory, or

• ANSYS Multiphysics Solver

• ANSYS Academic Teaching Mechanical

• ANSYS Mechanical,

• ANSYS Academic Associate,

• ANSYS Mechanical CFD-Flo,

• ANSYS Academic Research,

• ANSYS Mechanical Emag,

• ANSYS Academic Research Mechanical,

• ANSYS Multiphysics,

External Data

• ANSYS Structural Solver,

• ANSYS Academic Teaching Advanced,

• ANSYS Mechanical Solver, or

• ANSYS Academic Teaching Introductory, or

• ANSYS Multiphysics Solver

• ANSYS Academic Teaching Mechanical

No license is needed to run External Data.

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System Coupling Workspace This chapter discusses the following topics: Setting Up a Simulation that Uses System Coupling Components of the System Coupling Workspace Settings for Completing a System Coupling Setup Settings for Running a System Coupling Solution

Setting Up a Simulation that Uses System Coupling The general workflow for setting up a System Coupling simulation is presented in System Coupling Overview (p. 1). Most participant systems with connections originating from their Setup cells will participate in the analysis in a co-simulation mode (visually indicated in the Project Schematic with connections between the Setup cells, and different icons and colors for the Solution cells). The exception to this is the External Data participant system, since a connection originates from its Setup cell, but it acts as a static data participant. The Update option is disabled from within the right-click menu of the co-simulation participant systems' Solution cells because the update (and solution execution) is now controlled by the System Coupling Solution cell. Note that using System Coupling in conjunction with the Remote Solver Manager (RSM) is not supported for runs on multiple host machines. In the isolated case of Mechanical, the use of RSM for runs on a single local host is, however, permitted. The System Coupling system in the Project Schematic has two cells: • Setup: Use this cell to see participant, region, and variable information, and to define analysis settings and data transfer between participants. Double-click the Setup cell, or right-click and choose Edit from the context menu to display the System Coupling workspace. • Solution: Use this cell to solve a coupled analysis and to see solution information and charts monitors. Double-click the Solution cell, or right-click and choose Edit from the context menu to display the System Coupling workspace.

Components of the System Coupling Workspace When you edit the Setup or Solution cells of the System Coupling component system, the same System Coupling workspace is displayed in a tab within your workbench project. The Outline view, Properties view, System Coupling Chart view, and Solution Information view are displayed by default. For more information about the tabbed views in Workbench, see Workbench Tabs and Views in the Workbench User's Guide.

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System Coupling Workspace Figure 2: The System Coupling Workspace

See the following sections for additional information: Outline View Properties View System Coupling Chart View Solution Information View

Outline View The Outline view (in the upper left corner of Figure 2: The System Coupling Workspace (p. 8)) presents various fields related to the coupling participants and to the setup and solution of the coupled systems. The deepest fields can be edited in the Properties view. For additional information, see Settings for Completing a System Coupling Setup (p. 9) and Settings for Running a System Coupling Solution (p. 28).

Properties View The Properties view (in the lower left corner of Figure 2: The System Coupling Workspace (p. 8)) presents the properties of an editable item selected in the Outline view. For additional information,

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Settings for Completing a System Coupling Setup see Settings for Completing a System Coupling Setup (p. 9) and Settings for Running a System Coupling Solution (p. 28).

System Coupling Chart View The System Coupling Chart view (in the upper right corner of Figure 2: The System Coupling Workspace (p. 8)) presents chart monitors in the System Coupling workspace during the solution process. For additional information, see System Coupling Chart (p. 29) and Using the System Coupling Chart View (p. 31).

Solution Information View The Solution Information view (in the lower right corner of Figure 2: The System Coupling Workspace (p. 8)) presents a text-based solution log of information output during the execution of the coupled analysis. For additional information, see Solution Information (p. 28).

Settings for Completing a System Coupling Setup This section describes: • All the settings that appear in the Outline and Properties views under the “Setup” branch. • Context menus (that is, the menus that appear with a right-click) for the Setup cell. See the following sections for additional information: Analysis Settings Participants Data Transfers Data Transfer Rules Execution Control Validation and State of the System Coupling Setup Cell System Coupling Setup Cell Context Menus Expert Settings

Analysis Settings The Analysis Settings field has the following properties: • Analysis Type • Initialization Controls • Duration Controls • Step Controls Suggested best practices for analysis settings are discussed in Analysis Settings Best Practices (p. 12).

Analysis Type This option is used to define the overall coupling type for the analysis. The available options are:

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System Coupling Workspace • General – This is the only available option when one or more of the coupling participants is executing steady or static analyses. Note that mixed steady/static and transient analyses are not currently possible. • Transient – This is the only available option when all of the coupling participants are executing transient analyses.

Initialization Controls This option is used to define the initialization controls available for all coupling types.

Coupling Initialization The available options are: • Program Controlled – For initial runs (that is, not restart runs), the initial time and step are each set to 0. – For restart runs, the initial time and step are set to the values obtained from the latest valid restart point. • Restart Points (indicated by Step and Time) – The system coupling simulation can have multiple restart points when Intermediate Restart Data Output (p. 22) is selected for either all coupling steps or for a set of coupling step intervals. The next coupled analysis will be started based on the restart point that you have selected. For more information regarding restarts, see Restarting a System Coupling Analysis (p. 35).

Important Program controlled or explicitly specified restart points only affect the coupling step and/or time used to restart the coupling service. Appropriate restart points must also be specified for the co-simulation participants that are part of the coupled analysis. For more information about coupling participants, see Restarting a System Coupling Analysis.

Duration Controls This option is used to define the duration for the analysis.

Duration Defined By The options available to define the duration of a coupled analysis are: • End Time – Available only when the Analysis Type is Transient – When the End Time option is used, the coupling service will execute coupling steps until the specified end time is reached. In a transient analysis, each coupling step is a time step (with the time interval specified by the step size). Note that the final coupling step size is reduced automatically, if needed, so that the specified end time is respected.

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Settings for Completing a System Coupling Setup – Some of the participant systems, such as ANSYS Mechanical, require the end time specified in their setup to be respected. When a coupled analysis involves one or more participants that require their setup’s end time be respected, then the maximum allowable end time for the coupled analysis is the minimum of the end times reported by such participants. In this case, a validation error will be reported if the coupled analysis’ specified end time is greater than the minimum identified. Other participant systems, such as Fluent, can run past the end time specified. These participant systems have no effect on the allowable end time of the coupled analysis. • Number of Steps – Available only when the Analysis Type is General. – When this option is used, the coupling service will execute coupling steps until the specified number of steps is reached.

Step Controls The duration of the coupled analysis is broken into a sequence of coupling steps. Data transfers between the coupled solvers occur at the beginning of each coupling iteration within a coupling step. Coupling steps are always indexed. During the analysis, each new coupling step is started when: • The coupling analysis duration has not been reached, and • Either the maximum number of coupling iterations has been reached or the coupling step is converged. The available options are: • Step Size – If the coupling is defined in terms of time (a transient analysis), then a coupling step is associated with a time interval. The Step Size option specifies the time interval associated with each coupling step (in seconds). The final coupling step size is reduced automatically, if needed, so that the specified end time is respected. This reduction does not occur if the analysis duration is set by the Number of Steps. – The coupling step size is fixed for the duration of the System Coupling analysis, but it can be changed when restarting the analysis. • Minimum Iterations – This option allows specification of the fewest number of coupling iterations (at least 1) that could be executed per coupling step. – The specified minimum number of coupling iterations will be executed even if all measures of convergence are realized in fewer iterations. • Maximum Iterations – This option allows specification of the greatest number of coupling iterations that could possibly be executed per coupling step. – The specified maximum number of coupling iterations may not be executed if the analysis converges prior to the maximum iteration step being reached.

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System Coupling Workspace

Analysis Settings Best Practices This section provides information about best practices for the following analysis settings: General Analysis Type Transient Analysis Type

General Analysis Type With a General analysis type, accurate coupled solutions can be achieved using different combinations of coupling step and coupling iteration specifications. The two cases described below are: when an analysis is solved using one coupling step, and when an analysis is solved using many coupling steps. Your choice of the combination of coupling steps and coupling iterations will: • determine when result and/or restart data is able to be written, as the restart points can only be written at the end of a coupling step, • allow you to balance the required file storage space and your need for analysis restarts, • determine how you can use system coupling’s under relaxation factor (see Under-Relaxation Algorithm (p. 54)) and ramping (see Ramping Algorithm (p. 53)), as these only apply to coupling iterations and cannot be applied over coupling steps. For more information about restarting your coupled analysis, see Restarting a System Coupling Analysis (p. 35).

Coupled Analysis solved using only one Coupling Step A coupled analysis can be solved using only one coupling step. In this case, the coupling step is made up of many coupling iterations, and the solution is complete at the end of this one step. The analysis will continue executing until either the solution converges, or the specified maximum number of coupling iterations is completed. Only the end of a coupling step can be used as a restart point. When only one coupling step is used, results and restart data is generated only at the end of the solution. The analysis can be terminated as usual, but because intermediate restart data is not generated, the coupled analysis cannot be restarted if it terminates abnormally (due to an error, power interruption, etc.) or if you terminate it before the coupling step is completed. Using only one coupling step within a coupled analysis minimizes file storage space at the expense of the ability to restart the analysis. Interrupting the analysis will not affect the analysis, because System Coupling will complete the current coupling step (and so complete the solution) before stopping the analysis. Ramping and under-relaxation can be applied across coupling iterations within the single coupling step.

Coupled Analysis solved using many Coupling Steps A coupled analysis can be solved using many coupling steps. In this case, the coupling steps are made up of one or more coupling iterations. The analysis will continue executing until the specified number of coupling steps is completed. The transition from one coupling step to the next will occur when either the solution converges or the specified maximum number of coupling iterations is completed. Only the end of a coupling step can be used as a restart point (you are able to specify which steps are used). Results and restart data is generated at the specified restart points. If the analysis should terminate abnormally within a coupling step, you can restart the analysis from the previous restart point. By using more coupling steps with fewer coupling iterations per step, as opposed to one coupling step with many coupling iterations, more points at which restarts can be done are created. For difficult or complex analyses, which might experience abnormal terminations, more restart points allow restarts of the analysis (saving time and computational effort) at the expense of file storage space. System Coupling’s ramping and under-relaxation can be used across coupling iterations, but cannot be used across 12

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Settings for Completing a System Coupling Setup coupling steps, so System Coupling always transfers the full data transfer value at the end of each coupling step. Participant solvers may ramp data received from System Coupling at the coupling steps.

Transient Analysis Type In a transient analysis, a coupling step is associated with a time interval by specifying the coupling step size (in seconds). With a time specified, a coupling step is the same as a time step within the transient analysis. The coupling step size used should reflect the time scales of the physics being studied. Note that unless sub-stepping is supported by the co-simulation participants being coupled, the coupling step size will typically be limited by the finest/smallest time scale of the co-simulation participants. If the analysis duration is specified using an End Time, then care should be taken to ensure that an integral number of coupling steps can be executed between the (re)start time and the specified end time. If this is not done, then the final coupling step size will be reduced to respect the specified end time, and this may introduce temporal discretization error into the coupled analysis. The minimum number of coupling iterations may be set to a value larger than one (one is the default). If the data transfers have been under relaxed, you want to ensure a minimum number of coupling iterations is performed so that you iterate out the effect of the under-relaxation. Note that the data transfer convergence criteria would usually make this unnecessary. The maximum number of coupling iterations should be set to allow complete convergence within each coupling step. Failure to fully converge within a given coupling step will modify the transient behavior from that step onward.

Participants You can connect a participant system's Setup cell to the System Coupling Setup cell in the project schematic. The system coupling workspace displays a read-only summary of the participant data after a refresh of the System Coupling Setup cell. The participant summary includes: System name The name of the participant as presented in the schematic. Regions The collection of regions from and to which data can be transferred. A region is most often a point, line, surface or volume that is part (or all) of the geometry or topology of a coupling participant. Note, however, that equations or probe (monitored) values may also be considered as point regions.

Note System Coupling requires participants to use 3D meshes, with data transfer regions consisting of element faces from a 3D mesh. System Coupling data transfers cannot exist in 2D meshes.

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System Coupling Workspace Variables The collection of input and output variables available for data transfer for each region. A variable is a physical quantity such as force, length, or temperature that can be transferred between regions of participant systems. Variables are defined as input or output variables for the specific region.

Note For structural applications, data transfers are limited to force and displacement; for thermal heat transfer applications data transfers are limited to temperature, heat flow, heat transfer coefficient (also known as “convection coefficient”), and near wall temperature (also know as “bulk temperature” or “ambient temperature”).

Data Transfers A data transfer is defined by one source and one target region, and is able to transfer one variable type in one direction between two participants. Each data transfer is defined by a variety of properties such as Source, Target, and Data Transfer Control. A one-way coupled analysis has data transfer(s) in only one direction between the coupled participants. In this type of analysis, the source region(s) are defined on only the participant sending data, and the target regions(s) are defined on only the participant whose solver is receiving the data. A two-way coupled analysis has data transfers in both directions between the coupled participants. In this type of analysis, source and target regions are defined on both participants. For example, consider a coupled two-way fluid-structure interaction analysis where a Fluent system and a Static Structural system are the two participants. The Fluent system would have a region which is the source region for the transfer of force, and the target region for the transfer of incremental displacement. The Static Structural system would have a region that is the source region for the transfer of incremental displacement, and the target region for the transfer of force. Source/Target Both Source and Target are each defined by a coupling participant along with a region and a variable defined within the context of that participant. For a two-way data transfer on one region, you define two individual data transfers. When you set up your data transfers, a top-down approach should be followed when selecting Source and Target. Select in this order: 1. Source Participant 2. Source Region 3. Source Variable 4. Target Participant 5. Target Region 6. Target Variable Data Transfer Control Additional properties can be defined to control the way in which the specified data transfers are executed. For each data transfer you can specify controls that determine: • When the transfer is to occur.

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Settings for Completing a System Coupling Setup • The under relaxation factor applied to the transfer. • The convergence target. • If ramping is used when applying data from the source-side to the target-side of the data transfer. Transfer At The Transfer At property is used to control when the data transfer is executed by the solver. The only available option is: Start of Iteration Transfer data at the start of every coupling iteration within a coupling step. Under Relaxation Factor The factor multiplying the current data transfer values when under-relaxing them against the previous values. This is overridden with unity in the first coupling iteration of every coupling step only when the Analysis Type is Transient.

Note When under-relaxation is used, there is no guarantee that the full value from the source side of the data transfer is applied to the target by the end of the coupling step. RMS Convergence Target The target value used when evaluating convergence of the data transfer within a coupling iteration. The default value is 1e-2. The convergence target is RMS-based. For information regarding how this target is applied, see Evaluating Convergence of Data Transfers (p. 43). Ramping The available options for ramping controlled by System Coupling are as follows: None The full data transfer value is applied to the target side of the interface for all coupling iterations. No ramping is the default option. Linear to Minimum Iterations Within each coupling step, the ramping factor is used to linearly increase the change in the data transfer value applied to the target side of the interface. The data transfer value is increased during each coupling iteration until the specified minimum number of coupling iterations, , is reached. The ramping factor is applied to the change in the data transfer value from the previous coupling step. If there is no change in this value from the last coupling step, the full data transfer value is applied to the target side of the interface for all coupling iterations of that coupling step. During the coupling iteration (for ), the ramping factor equals . The full data transfer value is applied for all coupling iterations that are equal to or greater than the minimum number of coupling iterations. As is always reached, the full data transfer value is always applied by the end of each coupling step. This ramping behavior is demonstrated in Figure 3: Schematic of the Linear to Minimum Iterations Ramping Concept (p. 16) for the case where the minimum number of iterations specified is 5. When ramping using Linear to Minimum Iterations, if the minimum number of iterations is the same as the maximum number of iterations, then it is unlikely that the data transfer will Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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System Coupling Workspace converge. It is a best practice for your maximum iterations to be larger than your minimum iterations. Figure 3: Schematic of the Linear to Minimum Iterations Ramping Concept

Ramping and under-relaxation are independent operations. Ramping is applied before under-relaxation.

Note System Coupling’s ramping will interact with ramping behaviors within the participant systems. To understand the full ramping behavior, verify ramping settings to see if your participant system is ramping loads received from System Coupling. For ramping behavior in Mechanical, see System Coupling Related Settings in Mechanical in the ANSYS Mechanical User's Guide. See Working with Data Transfers (p. 16) for details about how to create, modify data transfers and do other common operations.

Working with Data Transfers After you connect a participant system's Setup cell to the System Coupling Setup cell in the project schematic, the System Coupling workspace displays the regions and variables available to create data transfers after a Refresh of the Setup cell: Create Data Transfer There are different ways to create single and multiple data transfers using the Create Data Transfer context menu option. Create uninitialized data transfer Select the "Data Transfers" tree node in Outline view, then select Create Data Transfer from the context menu. This creates a new data transfer without any source or target properties defined. You can later modify the data transfer definition in Properties view.

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Settings for Completing a System Coupling Setup Create data transfers for two regions from different participants Select two regions from different participants in the Outline view, then select Create Data Transfer from the context menu. This creates multiple data transfers that vary based on the following criteria: • Whether the two regions have the same topology • Whether the input variable from one region has the same properties (such as the physical type) as the output variable from the other region Create data transfers for single region Select a region from a participant in the Outline view, then select Create Data Transfer from the context menu. This creates data transfers for each variable associated with the region. If the variable is an output variable, then the source participant, source region, and source variable are defined for the new data transfer. If the variable is an input variable, then the target participant, target region, and target variable are defined for the new data transfer. Create a data transfer for single variable Select a region from a participant in Outline view, select a variable in the Properties view, then select Create Data Transfer from the context menu. This creates a new data transfer. If the selected variable is an output variable, then the source participant, source region, and source variable are defined for the new data transfer. If the selected variable is an input variable, then the target participant, target region, and target variable is defined for the new data transfer. Modify Data Transfer Select a data transfer in the Outline view. The Properties view displays all the properties for the data transfer. You can modify all the properties for the data transfers in the same view. Rename Data Transfer Select a data transfer in the Outline view. Double-click to rename the data transfer. Duplicate Data Transfer Select one or more data transfers in the Outline view. Right-click and select Duplicate. This operation creates new data transfers with the same Source, Target, and Data Transfer Control properties. Note that you can change these properties as needed for these new data transfers. Suppress Data Transfer Select one or more data transfers in the Outline view. Right-click and select Suppress to prevent the data transfer. Delete Data Transfer Select one or more data transfers in the Outline view. Right-click and select Delete to remove them.

Note If the data transfer definition is not valid or the data is invalidated for any reason, the state of the node will show as a ? and the incorrect properties will need to be changed.

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System Coupling Workspace

Data Transfer Rules When you create data transfers in System Coupling, certain rules must be observed in order to correctly define the analysis.

Note Participant data transfer regions must consist of triangular or quadrilateral faces. Polyhedral faces as well as faces with hanging nodes (cut-cells) are not supported in System Coupling. Currently, the following three types of transfers are supported. Details of these three types of transfers are given in Table 2: Data Transfers available in System Coupling (p. 18). • Force transfers • Motion transfers • Thermal transfers Force and motion transfers are typical for fluid-structure interaction problems, where a load to the structure is transferred from a fluid solver, and the deformations to the fluid are transferred from the structural solver. There can only be one force transfer and one motion transfer for each data transfer region. Thermal transfers can be transferred between ANSYS Fluent and ANSYS Mechanical directly through System Coupling, or through the coupling of the External Data system. Three thermal transfers are available, each transferring different thermal variables. The three thermal transfers are described in the table below. For one-way thermal transfers, only one of the three options below for thermal transfers can be defined for a given pair of source and target regions. For two-way thermal transfers, two data transfers are set up on the same data transfer region. In a twoway transfer: • the two variables, heat transfer coefficient and near wall temperature, cannot be transferred on the same data transfer region as heat flow, and • a participant’s data transfer region cannot provide and receive the same thermal variable(s); for example, Fluent cannot send and receive temperature data on the same data transfer region. Table 2: Data Transfers available in System Coupling Transfer Type

Variable(s) Transferred

Data Transfer Direction

Force transfer

• Force (VectorXYZ*)

• from a fluid solver to a structural solver

Motion transfer**

• Incremental displacement (VectorXYZ*)

• from a structural solver to a fluid solver

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Settings for Completing a System Coupling Setup Transfer Type Thermal Data Transfers

1. Temperature transfer

Variable(s) Transferred

Data Transfer Direction

• Temperature (Scalar)

• from a structural solver to a fluid solver, or • from a fluid solver to a structural solver

2. Heat flow transfer

• Heat flow (also known as heat rate) (Scalar)

• from a structural solver to a fluid solver, or • from a fluid solver to a structural solver

3. A pair of variables***

• Heat transfer coefficient (also known as convection coefficient)** (Scalar)

• from a fluid solver to a structural solver

• Near wall temperature (also known as bulk temperature, or ambient temperature)** (Scalar)

* Represents the force vector respectively.

( ,

,

) and the incremental displacements vector

(

,

,

)

**In a general coupled analysis, when the solver receiving the motion (such as Fluent) solves before or simultaneously to the solver sending the motion (such as Mechanical), then the incremental displacement transferred during the first coupling iteration of each coupling step is identically zero. This behavior can be changed by using GeneralAnalysis_IncrDisp_InitIterationValue_Zero in the Expert Settings (p. 24). ***You must correctly define both variables in the data transfer in order for this thermal transfer to be valid.

Note For a given target region, there can only be one source region. However, a given source region can send data to multiple target regions. In other words, 1-to-M data transfers are supported, where M is an integer and is greater than or equal to 1. Note that M-to-1 data transfers are not supported.

Execution Control Execution Control has the following capabilities: Co-Simulation Participant Sequencing Debug Output Control Intermediate Restart Data Output Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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System Coupling Workspace

Co-Simulation Participant Sequencing The System Coupling system offers comprehensive control over the sequencing of co-simulation participants, and specifically over the data transfers that are required to obtain a solution. This is controlled through the settings in the Co-Sim Sequence. The participants are sequenced by assigning a sequence value, which is an integer value between 1 and the number of participants in the analysis, to each participant. Each participant executes its solutions (that is, all required data transfers, followed by obtaining the equation solution) in the order of its sequence value, where the participants with the lower sequence values execute first. The coupled analysis will use sequential solutions or simultaneous solutions, depending on the assigned sequence values. This is described in more detail below.

Note To improve solution stability, sequential solutions are used by default. Note as well that, to facilitate synchronization of interface geometry, participants that consume geometrical or mesh deformations (for example, the Fluids solver in a Fluid Structure Interaction analysis) are automatically assigned larger sequence values by default. Additional information can also be found in Best Practice Guidelines for Using System Coupling (p. 73).

Sequential Solutions A sequential solution is done when all co-simulation participants are assigned different solution sequence values. In particular, participants perform their solutions (that is, all required data transfers, followed by obtaining the equation solution) in the order of the sequence values specified in the user interface. Sequential solutions are optimal for analyses that involve strong physical couplings, because the most recent information from one participant is always used by subsequent participants. This typically translates into requiring the fewest coupling iteration per coupling step to reach a converged solution. However, it may not yield the shortest (wall-clock) solution time if the participants are run on different CPUs.

Simultaneous Solutions A simultaneous solution is done when one or more co-simulation participants are assigned identical solution sequence values. In particular, when the same sequence value is applied to multiple participants, then all those participants perform their respective data transfers, after which those same participants perform their equation solutions simultaneously. Simultaneous solutions are optimal for analyses that involve weak physical couplings because the most recent information from one co-simulation participant is not required by other simultaneously executed participants in order to reach a converged solution. Additionally, the overall (wall-clock) solution time may be reduced if the simultaneously executed participants are run on different CPUs. However, if used with co-simulation participants that exhibit strong physical couplings, simultaneous solutions may adversely affect the rate of convergence, and possibly lead to divergence.

Debug Output Control The Debug Output entity under Execution Control in the outline model controls the level of debug information written in the System Coupling Log (*.scl) file during the execution of the solution. The basic level of detail included is controlled using one of the following levels: • None

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Settings for Completing a System Coupling Setup • Level 1 • Level 2 • Level 3 • Level 4 • All Levels By default, the value set for the Global Level is applied to all stages of solution execution listed below. To use a different value for one or more of the specific stages of solution execution, change the value from Use Global Level to the desired output level. Note that stages of solution execution that are associated with Data Transfers are grouped together, and have their own default Data Transfers Level value. To use a different value for one or more of these stages of solution execution, change the value from Use Data Transfers Level to the desired output level. The following properties control the debug level for different sections of the log: Startup Controls the level of output from the start of the coupling service until creation of the "Summary of SC Setup" banner in the SCL file. Participant Connection Controls the level of output from the end of the setup validation until the Initial Synchronization synchronization point (that is, between the Setup Validation and System Coupling Summary banners). Analysis Initialization Controls the level of output from the end of the setup validation until the Analysis Initialization synchronization point (that is, between the System Coupling Summary and Solution banners). Solution Initialization Controls the level of output during the setup of coupling steps and coupling iterations. This output does not include information related to the data transfers. Data Transfers Specifies the debug output generated for data transfers. Note that header information for mapping is generated whenever the mesh coordinate or mesh topology output is requested. Similarly, header information for the data transfers is generated whenever the transfer data output is requested. Data Transfers Level Provides the default level for the different debug output controls in the Data Transfers group. If the debug level of any property in the Data Transfers group is set to Default, then the debug level of that entry is governed by the level set here. If the Data Transfers Level itself is set to Use Global Level, then it derives its value from the default level defined for all debug output controls. Source Mesh Coordinates Controls the level of output for mesh coordinates of the source region in all data transfers. Source Mesh Topology Controls the level of output for mesh topology (elements and nodes) of the source region in all data transfers.

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System Coupling Workspace Source Data Controls the level of output for the source data in all data transfers. Target Mesh Coordinates Controls the level of output for mesh coordinates of the source region in all data transfers. Target Mesh Topology Controls the level of output for mesh topology (elements and nodes) of the source region in all data transfers. Target Data Controls the level of output for the target data in all data transfers. Convergence Checks Controls the level of output from the Check Convergence synchronization point until the next synchronization point, which may be either Shutdown or Solution. Shutdown Controls the level of output after the Shutdown synchronization point. For information about synchronization points, see Process Synchronization and Analysis Evolution (p. 41).

Note The debug level for all the properties, except Default, can be set at any level. For the Default property, the available levels are from None to All Levels. Increasing levels always generate more detailed output. Note, as well, that the output level settings for each of the mesh coordinates, topology, and transfer data, control the number of lines of output generated. Specifically, 10L lines of data will be written for an output level setting of L (for example, 100 lines will be written for an output level of 2, or Level 2).

Intermediate Restart Data Output The Intermediate Restart Data Output entity under Execution Control in the outline model allows the selection of time points at which restart data should be generated during the execution of the solution. Depending on the participant, the restart data may or may not be the same as the results data. Writing of results data for post-processing should be set from within the participant setup cell.

Important During execution of the coupled analysis, co-simulation participants will automatically be requested to generate intermediate restart data at the same frequency as the System Coupling service. Note that this feature only affects the frequency at which data is generated; the content of data is determined by the participant. To see if this feature is supported, see Supported System Couplings (p. 3). Choose one of the following options to control when restart data is produced. None No intermediate restart output files are generated using this option. This option is enabled by default.

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Settings for Completing a System Coupling Setup All steps Restart output files are generated at the end of each coupling step. At Step Interval Restart output files are generated at the end of the coupling steps corresponding to the interval specified in the Step Interval box below.

Note If you specify a Step Interval that is above or below the allowed limit, an error is displayed; change the Step Interval as required.

Validation and State of the System Coupling Setup Cell Validation of the Setup cell depends upon the validation of the individual nodes in the Tree View (for example, Analysis Settings and Data Transfer). If any of these nodes is invalid, it would be marked by a ? (Attention Required) in front of the Setup cell. Details regarding why validation failed are presented when the mouse pointer is hovered over the ? symbol.

System Coupling Setup Cell Context Menus The System Coupling Setup cell has several context menus: • Start/Stop highlighting linked nodes: From the Setup cell, this option controls whether cells that are related to the selected cell are highlighted in the Outline view. • Create Data Transfer: From Data Transfers you can create one or more data transfers using this context menu. See Working with Data Transfers (p. 16) for details. • Auto Show/Hide • Toolbar Option • Rename: From Data Transfers you can rename the selected data transfers using this context menu. See Working with Data Transfers (p. 16) for details. • Duplicate: From Data Transfers you can duplicate the selected data transfers using this context menu. See Working with Data Transfers (p. 16) for details. • Display Validation Failure: Select this to display error messages when System Coupling setup settings are found to be incorrect due to validation problems. • Add Property: From Execution Control>Expert Settings, you can add specific expert settings. See Expert Settings (p. 24) for details about these settings. • Remove Property: From Execution Control>Expert Settings, you can remove specific expert settings. See Expert Settings (p. 24) for details about these settings. • Read restart points: From Properties of Analysis Settings>Initialization Controls>Coupling Initialization, you can use this command to populate the list of restart points. This command is useful for abnormal situations such as a workbench crash. In such situations, the restart point list may be empty even though the intermediate restart files exist on your disk. Read restart points is used to repopulate your list of restart points, so that you can restart from a previously saved restart point.

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System Coupling Workspace See Understanding Cell States in the Workbench User’s Guide for detailed information on typical cell states.

Expert Settings This subsection is used to specify the expert settings that are available. Expert settings provide you with additional advanced controls for many of the settings available in the Outline and Properties views under the Setup branch. • General Expert Settings – DumpInterfaceMeshes (string) The only valid value for this setting is CFDPost. When this expert setting is used, files named source.csv or target.csv are generated during the mapping process. These files report values of 0 and 1 for unmapped and mapped nodes, respectively. These files are appropriate for import into CFD-Post as user defined surfaces for the visualization of mapping data. – MeshSyncOption (integer) Value is 0, 1, 2, or 3 (default: 0). This setting is only relevant for coupled analyses with a participant that consumes geometric data (for example, the Fluids solver in a Fluid Structure Interaction analysis, which receives displacement data). This setting can be used when the solution of the participant consuming geometrical data is either sequenced identically as, or sequenced before, the solution of the participant that provides the geometric data. Available options are: → 0 (default): If the maximum number of coupling iterations per coupling step is 1, then the solution sequence is changed so that the participant that consumes geometrical data is solved last. If the maximum number of coupling iterations per coupling step is greater than 1, then one additional coupling iteration is performed at the end of the coupling step and only the participant that consumes geometrical data is re-solved. → 1: Regardless of the maximum number of coupling iterations per coupling step, the solution sequence is changed so that within each coupling iteration, the participant that consumes geometrical data is solved last. → 2: Regardless of the maximum number of coupling iterations per coupling step, one additional coupling iteration is performed at the end of the coupling step and only the participant that consumes geometrical data is re-solved. → 3: No setup modifications are applied, and the solution proceeds with the specified participant sequencing. – GeneralAnalysis_IncrDisp_InitIterationValue_Zero (integer) Value is 0 or 1 (default: 1). This setting is only relevant in a general coupled analysis, when displacement is transferred, and when the solver receiving the displacement (such as Fluent) solves before or simultaneously to the solver sending the displacement data (such as Mechanical). → 1: During the first coupling iteration of each coupling step the displacement transferred to the target is 0 [m] (irrespective of the value provided by the source). This override of the transfer value is to avoid possible double displacement, which could create folding of the mesh.

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Settings for Completing a System Coupling Setup → 0: The value for displacement provided by the source is transferred with no interference by this expert setting (this value transferred may be modified by other settings such as ramping). • Participant Variable Initial Value Settings The following expert settings are useful for overriding the default initial values of variables of a given type for all participants. These initial values are currently used in the ramping as well as the underrelaxation of data transfers. Note that for the ramping algorithm, the reference target-side value for displacement is always 0.0 [m]. The expert settings below will have no effect on the value used in this case. – Participant_Variable_InitValue_IncrDisp_X (real) Participant_Variable_InitValue_IncrDisp_Y (real) Participant_Variable_InitValue_IncrDisp_Z (real) Replace initial value for Cartesian components of all variables of type "Incremental Displacement" for all coupling participants. Default is 0.0 [m]. – Participant_Variable_InitValue_Force_X (real) Participant_Variable_InitValue_Force_Y (real) Participant_Variable_InitValue_Force_Z (real) Replace initial value for Cartesian components of all variables of type "Force" for all coupling participants. Default is 0.0 [N]. – Participant_Variable_InitValue_Temperature (real) Replace initial value for all variables of type "Temperature" for all coupling participants (variables include temperature and near wall temperature). Default is 295.15 [K]. – Participant_Variable_InitValue_HeatRate (real) Replace initial value for all variables of type "Heat Rate" for all coupling participants. Default is 0.0 [W]. – Participant_Variable_InitValue_HeatTransferCoef (real) Replace initial value for all variables of type "Heat Transfer Coefficient" for all coupling participants. Default is 0.0 [W m^-2 K^-1]. • Data Transfer Control Settings The following expert settings are useful for controlling the behavior of data transfers. – DataTransfer_ScaleFactor_Force (double) Scale, by the factor specified, source values for all data transfers of Force variables. Default value is 1.0. – DataTransfer_ScaleFactor_HeatRate (double)

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System Coupling Workspace Scale, by the factor specified, source values for all data transfers of Heat Rate variables. Default value is 1.0. – DataTransfer_ScaleFactor_HeatTransferCoef (double) Scale, by the factor specified, source values for all data transfers of Heat Transfer Coefficient variables. Default value is 1.0. – DataTransfer_ScaleFactor_IncrDisp (double) Scale, by the factor specified, source values for all data transfers of Incremental Displacement variables. Default value is 1.0. – DataTransfer_ScaleFactor_Temperature (double) Scale, by the factor specified, source values for all data transfers of Temperature variables. Default value is 1.0. • SC Log Output Control Settings The following expert settings are useful for controlling the output of various supplemental diagnostics to the SC log file: – DTDiagShowRMSChange (string) Activates reporting of RMS change in data transfers if set to true. Default is ‘False’. When RMS change is the type of data checked against the convergence target (this is the default), this expert setting does nothing. – DTDiagShowMaxChange (string) Activates reporting of Max change in data transfers if set to true. Default is ‘False’. If Max change is the type of data checked against the convergence target, this expert setting does nothing. Note that the type of data checked (RMS change or Max change) can only be changed through the System Coupling Input File. – DTDiagShowMinValue (string) Activates reporting of minimum nodal value in data transfers if set to true. Default is ‘False’. – DTDiagShowMaxValue (string) Activates reporting of maximum nodal value in data transfers if set to true. Default is ‘False’. – DTDiagShowAvgValue (string) Activates reporting of average nodal value in data transfers if set to true. Default is ‘False’. – DTDiagShowSum (string) Activates reporting of sum of nodal values in data transfers if set to true. Default is ‘False’. – DTDiagShowAll (string)

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Settings for Completing a System Coupling Setup Activates reporting of all diagnostics of nodal values in data transfers if set to true. Default is ‘False’. • Expert Settings Related to Mapping The coupling service uses a Profile Preserving mapping (ProfMap) for non-conservative quantities (for example, displacement) data transfers, and a Conservative mapping (ConsMap) for conservative quantities (for example, forces). – ProfMapBucketScale (integer) Value (ranging from 0 to 100, default: 50) that represents the number of discrete search ‘buckets’, as a percentage of the number of nodes, to use during mapping. The objective is to generate ‘buckets’ that will contain roughly equal numbers of nodes. This setting will affect the speed of the mapping, but it should not affect the outcome. – ProfMapBucketTol (double) Value (ranging from 0 to 1, default: 1e-4) that is used to create a bounding region around each target node. The bounding region is used to increase the number of buckets that will be included in the Bucket Surface Algorithm's search, which in some cases will improve the number of mapped nodes. – ProfMapEdgeTol (double) Value (ranging from 0 to 1, default: 0.05 in natural coordinate space) that specifies the tolerance within which a target node may be found in a source element. See the discussion on Bucket Surface (p. 48) mapping algorithm in the section Mapping Algorithms (p. 46) for more information regarding this tolerance setting. – ProfMapTolOption (integer) Value is either 0 or 1 (default: 0), where 0 indicates that the specified tolerance is relative to the maximum Cartesian extent of the region being mapped, and 1 indicates that the specified tolerance is absolute (using the same units as the mesh coordinates). – ProfMapTol (double) Value (ranging from 0 to 1, default: 1e-6) that specifies the tolerance for the 'gap' distance between a target node and the source element that it is mapped to. – ProfMapEnforceTol (integer) Value is either 0 or 1 (default: 0), where 0 indicates that the distance between a target node and the source element that it is mapped to (also known as the ‘gap’ distance) is not checked against the tolerance specified with the expert setting ProfMapTol. Target nodes with final ‘gap’ distances larger than the specified tolerance will be reported as mapped in the SCL file. These nodes are mapped to the source nodes like all of the other mapped nodes and given a value accordingly. A setting of 1 (which means on) indicates that such a check is performed. Target nodes with final ‘gap’ distances larger than the specified tolerance will be reported as unmapped in the SCL file. These nodes are mapped to the source nodes like all of the other mapped nodes and given a value accordingly. – ConsMapPixelRes (integer)

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System Coupling Workspace Value, (ranging from 10 to 256, default: 100), that indicates the number of pixels to use when forming the surfaces of intersection for each pair of source and target mesh element faces on the interface. Larger values are needed if interface mesh lines are very nearly coincident. Any value entered that is less than 10 or greater than 256 will be reset to 100 automatically. – ConsMapTol (double) Value, (ranging from 0.1 and 1, default: 0.1), that specifies the tolerance, in the element-face-normal direction, to use when determining whether the source and target meshes map to one another. This tolerance is normalized by the local element size. Any value entered that is less than 0.1 or greater than 1 will be reset to 0.1 automatically.

Settings for Running a System Coupling Solution This section describes: • All the settings that appear in the Outline and Properties views under the “Solution” branch. • Context menus (that is, the menus that appear with a right-click) for the Solution cell. See the following sections for additional information: Solution Information System Coupling Chart Validation and State of the System Coupling Solution Cell System Coupling Solution Cell Context Menus

Solution Information Solution information is automatically generated for output of the system coupling service and the coupling participants. Figure 4: An Example of the Solution Information Branch (p. 29) displays an example of the “Solution Information” branch from the Outline view. Select an entry from the listed solution information sources to display its output in the Solution Information view.

Note The default behavior of the Solution Information view is to always show the latest information in the log file. Each time new information is added, the file will automatically scroll to the end. However, if you move the vertical scroll bar away from the bottom, the view will not scroll to the end when new information is added until you move the scroll bar back to the end. There are also some keyboard short-cuts that are available when operating in this view: • Page Up scrolls up one page. • Page Down scrolls down one page. • Ctrl+Home jumps to the top of the log. • Ctrl+End jumps to the bottom of the log.

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Settings for Running a System Coupling Solution Figure 4: An Example of the Solution Information Branch

For additional details about the solution information displayed for the coupling service, see System Coupling Service Log File (scLog.scl_, scLog_##.scl) (p. 57). For additional details about solution information displayed for coupling participants, see Supported System Couplings (p. 3).

System Coupling Chart System Coupling's chart monitor allows you plot data produced during the coupled solution process. You can use this data to monitor convergence. The chart monitors can plot data from the system coupling execution and from the coupling participants, such as Fluent. Convergence data is available for plotting once the solution is running or has been completed. You can create multiple charts (p. 30), and select the variables (p. 30) that you want to plot. In the chart monitor, data is available for plotting against different levels (X axis data). The higher (coarser) levels at which the data is present are referred to as parent levels, whereas the lower (finer) levels at which the data is present are referred to as child levels. Any data present in a child level are also available at the parent level for plotting. For example: In the graphic that follows, the flow chart shows different variables and levels for a sample run. "Coupling Step" is the parent level for "Coupling Iteration", whereas "Solver 1 Step", "Solver 1 Iteration", "Solver 2 Step", and "Solver 2 Iteration" are child levels of "Coupling Iteration". There are two variables, "Variable 1" and "Variable 2", present. "Variable 1" is present at "Solver 1 Iteration" and hence is available for plotting at "Solver 1 Iteration" or any of its parents, that is, "Solver 1 Step", "Coupling Iteration" or "Coupling Step". Similarly, "Variable 2" is available for plotting at "Solver 2 Iteration", "Solver 2 Step", "Coupling Iteration", and "Coupling Step".

Chart Properties Axis X Property: • Quantity: The level at which the X data for the variables is plotted. This can be any level at which the data is available. For example: For a variable "Data Transfer:Change:RMS", the available levels can be

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System Coupling Workspace "Coupling Step" and "Coupling Iteration". The X axis level can be defined by selecting an option in the drop-down options list in the Properties view of a chart. Axis Y Property: • Title: The title of the axis Properties Supported for Both Axes: • Scale: The scale of the axis. Scale can be defined as Linear, Common Log (Log base 10) or Natural Log. • Automatic Range: The property to define whether or not automatic scaling should be applied to the axis, or whether the RangeMin and RangeMax should be used. • Range Minimum: The minimum range of the values in this axis. • Range Maximum: The maximum range of the values in this axis.

Chart Variable The System Coupling Chart Monitor plots data produced during the coupled solution process. These variables that you can plot are organized according to coupling participants and include: • measures of convergence obtained from co-simulation participants (for example, solver residuals from Fluent) • the change (RMS or maximum) in data transfer values • diagnostic values (for example, minimum, maximum, average, and sum) taken from the nodal data associated with data transfers The variables that are obtained from co-simulation participants are only plotted at the intervals that they are available. Intermediate data points are not artificially created.

Chart Variable Properties Refinement Level The data plotted at the level defined by the X axis can be further refined to any of the child levels of the X axis. For example: For X axis level defined at the "Coupling Step", the X data values for a variable can be refined to the "Coupling Iteration" level. In this case the intermediate values available at "Coupling Iteration" level between consecutive "Coupling Steps" are distributed equally between the coupling steps; that is, if "Coupling Step" 2 has three "Coupling Iterations", then the data points are plotted at 1.33, 1.66, and 2. The refinement level can be defined by selecting an option in the drop down options list in the Properties view of a chart. Style • Color: The line color of the chart variable in a plot • Line Width: The width of the line drawn for this chart variable in pixels • Symbol Size: The size of a symbol in pixels when a symbol is drawn for this variable

Working with System Coupling Charts The following context menu options are available:

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Settings for Running a System Coupling Solution Create Chart You can create convergence charts by using the Create Chart context menu option. In the Outline view, right-click Chart Monitors, then select Create Chart from the context menu. This creates a new system coupling chart without any variables defined. The default X axis level is "Coupling Iteration". Add Variable Once the solution is running or completed, variables to be plotted can be added to a system coupling chart. Select an existing chart in the Outline view, and then select Add Variable from the context menu. From this context menu, select data of interest to add it to the chart. The default refinement level for the added variable is set to the X axis level. If the data for the new variable is not available at the level defined by the X axis, the X axis level and the refinement level for the new variable are set to "Coupling Iteration". Remove Variable Select a variable under the Remove Variable context menu option to remove that variable from the chart. Delete Variable A variable included in the chart can be removed using the Delete context menu option. Delete Select Delete in the chart’s context menu to delete the chart. Editing Chart and Chart Variable Properties Chart and Chart Variable properties are displayed and can be edited in Properties view based on selection in Outline view.

Note When the solution is started, a default chart is added if one is not already present. The default variables added correspond to the RMS Change in data on the target side of all data transfers. For example if "Data Transfer" and "Data Transfer 2" are defined with target participants equal to "Transient Structural" and "Fluid Flow", respectively, then the chart variables "Transient Structural: Data Transfer: Change: RMS" and "Fluid Flow: Data Transfer 2: Change: RMS" are added to the default chart. If you add/delete variables to the default chart, then new variables are not added by default on consecutive runs.

Using the System Coupling Chart View Chart Zoom, Pan, and Fit You can manipulate the display of a chart using the zoom, pan, and fit features. • Zoom by using the mouse wheel or Shift+middle mouse button • Box zoom by using the right mouse button • Pan by using Ctrl+middle mouse button • Fit by using the F key. Saving a Chart You can save the chart that you are viewing as a graphic. To do so, right-click the background of the chart and select Save Image As. In the dialog box that appears, you will see a small image of the chart, and can select the Size (resolution) that will be used when saving the chart. Click the button and navigate to the folder where you want to save the file. Enter a file name. You can select either .png or .bmp as the Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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System Coupling Workspace graphic file type. Click Save to select that file path as your save location. Click OK to save the file to the location that you selected, with the resolution that you have selected.

Validation and State of the System Coupling Solution Cell The state of the Solution cell is coupled to the states of the Solution cells for all co-simulation participants. In particular, all coupled Solution cells will have the same state, which will reflect the least complete state of all coupled cells.

System Coupling Solution Cell Context Menus The System Coupling Solution cell has several context menus: • From the Solution cell, right-click and you can: – Update the solution, – Continue Calculation if the solution was interrupted, – Refresh the solution, – Clear Generated Data, – Reset the solution. These commands are the same as those available on the System Coupling’s Solution cell in the Project Schematic. • From the Solution > Chart Monitor cell, right-click and select Create Chart to create a system coupling chart. • From the Solution > Chart Monitor > Chart cell, right-click and select Add/Remove Variable to add or remove variables from the selected chart. For details, see Working with System Coupling Charts (p. 30). • Display Validation Failure: Select this to display error messages when System Coupling solution items (for example, charts) are found to be incorrect due to validation problems.

Note If a coupled analysis is interrupted before reaching the specified coupling duration, then the Solution cells will remain in an ‘Update Required’ state once execution stops, because the calculation needs to be continued to complete the analysis. Downstream Results cells may be refreshed and/or updated to review the results generated up to the point at which the analysis was interrupted. See Understanding Cell States in the Workbench User’s Guide for detailed information on typical cell states.

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Workflows for System Coupling This chapter describes general issues common to working with System Coupling systems. Executing System Couplings Using the Command Line Restarting a System Coupling Analysis Stopping the Coupled Analysis Run

Executing System Couplings Using the Command Line You can set up system coupling simulations by using the command line, rather than by using the Workbench user interface. To perform a system coupling simulation from the command line, you need to ensure paths to all required scripts and executables are added to the PATH environment variable so that these applications can be launched from command line.

Tip Search your installation to help resolve any missing dynamic libraries. To run an analysis from the command line, execute the steps below. If you would like an example of this process, the tutorial Oscillating Plate with Two-Way Fluid-Structure Interaction provides detailed steps on how to use the Command Line in the section Executing the Coupled Analysis from the Command Line. 1.

Generate the System Coupling Input file and place this file in the desired working directory for the Coupling Service. To do this, enter (double click) the System Coupling Setup cell in the Workbench schematic, and select the Export SCI File option from the File menu. Note that this option is only available when the state of the Setup cell is up-to-date.

2.

Generate all input files required for the co-simulation participants (that is, input files required for the solvers involved in the coupling) and place these files in the respective desired working directories.

3.

The command to start the Coupling Service differs between Linux and Windows: • Linux: .workbench -cmd ansys.services.systemcoupling.exe -inputFile oscillating_plate.sci

where .workbench is a script located in /ansys_inc/v160/aisol on Linux. The typical location of the executable on Linux 64-bit Workbench installations is: /ansys_inc/v160/aisol/CommonFiles/linx64

• Windows: ansys.services.systemcoupling.exe -inputFile oscillating_plate.sci

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Workflows for System Coupling The typical location of the executable on Windows 64-bit Workbench installations is: C:~\ANSYS Inc\v160\aisol\bin\winx64

These commands launch the Coupling Service and create a System Coupling Server file (scServer.scs) in the working directory. As described in System Coupling Server File (scServer.scs) (p. 56), this file contains information needed to start each of the co-simulation participants, specifically port and host information for the coupling service and identifiers for the participants. Additional information needed to run from the command line is accessible below for each of the co-simulation participants that support system couplings. For more information about command line execution and options for supported co-simulation participants, see Supported System Couplings (p. 3). Co-simulation participants will tend to use a common set of system coupling related command line options (such as -schost, -scport, and -scname). You are strongly encouraged, however, to develop some expertise in running each of the participants without system couplings before attempting to execute coupled analyses from the command line. Additional system coupling command line information can also be found in the following section: System Coupling Command Line Options

System Coupling Command Line Options The following command-line options are available in the command line: -debugLevel [ 0 | 1 | 2 | 3 | 4 | 5 ] Generates debug output to the System Coupling Log (.scl) file. The level of debug output increases with each level, with the default (0) providing no debug output and level 5 providing the most complete debug output. -extractInputFile input_file_name Extracts the content of an identified System Coupling Input (scInput.sci) file that is contained in the specified System Coupling Results (scResults_##_######.scr) file (via -resultFile). Valid names are the ones returned by the -listInputFiles command line option. -help Displays the option summary. -inputFile path_to_sci_file Inputs to the coupled analysis are extracted from the specified System Coupling Input file, where path_to_sci_file is the location of the input file. -listInputFiles Lists all of the input files stored in the specified System Coupling Results file (via -resultFile). Output is written to the System Coupling Log file for the run. -logFile path_to_scl_file Generates the System Coupling Log file with a specific name in a specific directory, where path_to_scl_file is the location of the generated log file. The default log file name is scLog.scl and will be generated in the same directory from which the coupling services executable is run.

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Restarting a System Coupling Analysis -resultFile path_to_scr_file Continue the analysis from the specified System Coupling Results file, where path_to_scr_file is the location of the results file. Note that if the -inputFile option is also used, then inputs to the coupled analysis are extracted from that file. For more information about command line execution and options for supported co-simulation participants, see Supported System Couplings (p. 3).

Restarting a System Coupling Analysis The sections below walks you through the steps needed to restart a coupled analysis using System Coupling, but you will also need restart information specific to the participants connected to your System Coupling system. See Supported System Couplings for a list of supported systems and references to their corresponding documentation regarding restarts. Restarting a coupled analysis is further described in the following sections: Generating Restart Files Executing the Restart Run Recovering from a Workbench Crash

Note • The System Coupling Results file generated by the coupling service contains all the information and data that are required to restart the coupling service only. Information and data that are required to restart the coupling participants, as well as the act of restarting those participants, are managed by the participants themselves. • The convergence history for a restarted run is generally not identical to that observed in a continuous run. There are two factors contributing to changes in convergence: interfaces are remapped upon restart, thereby changing the interpolation weights; and restart- and continuousrun convergence histories are not always identical (for example, the HHT transient discretization used by ANSYS Mechanical will not yield identical convergence histories while the Newmark discretization will). • Changes in convergence history across restarts will yield changes in solution values if solutions are not fully converged within coupling steps.

Generating Restart Files Restarts of a system coupling analysis requires corresponding restart points to exist in the coupling service and in each of the solvers participating in the analysis. During a coupled analysis, restart points that contain information for restarts need to be created by all of the systems involved in your coupled analysis. System Coupling’s restart file is the System Coupling Results (scr) file. Creation of restart points is controlled in System Coupling to ensure participant solvers are writing data at synchronized coupling steps. To generate restart files for a coupled analysis, follow the steps below: 1.

Before starting the analysis’ initial run, ensure that all coupling participants are set up to save (or retain) the corresponding restart points during the run. For information on how to do this, see Supported System

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Workflows for System Coupling Couplings for a list of supported systems and references to their corresponding documentation regarding restarts. 2.

Set up the System Coupling system to control the creation of restart points at certain intervals during the coupled analysis run. a.

From the Project Schematic, double-click System Coupling's Setup cell to open the System Coupling tab.

b.

In System Coupling's Outline view on the left, select System Coupling > Setup > Execution Control > Intermediate Restart Data Output.

c.

In the Properties view, under Output Frequency, select the appropriate setting. See Intermediate Restart Data Output for more information.

Executing the Restart Run Once the coupled analysis run is finished or interrupted, or if the solution fails, you can restart this run from any of the saved restart points. You need to select the same restart point in all coupling participants, as well as in the System Coupling system. To execute the restart run: 1.

Specify a restart point in each participant connected to System Coupling. Make sure that these restart points correspond to the restart point you will choose in System Coupling. For information on how to do this for participant systems in your coupled analysis, see Supported System Couplings for a list of supported systems and references to their corresponding restart documentation.

2.

If setup changes in the participant systems are needed before restarting, make these required changes. For information on how to do this for participant systems in your coupled analysis, see Supported System Couplings for a list of supported systems and references to their corresponding restart documentation.

3.

In some cases, setup changes are desired or are required to avoid failure of the coupled analysis. To make these changes: a.

Double-click the System Coupling Setup cell or Solution cell to open the System Coupling tab.

b.

Modify the required settings in System Coupling. Setup changes commonly include changes to a combination of the following: • Coupling analysis type • Coupling initialization and duration settings • Coupling step size • Minimum and maximum number of coupling iterations per coupling step • Data transfer convergence targets and under-relaxation factors

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Restarting a System Coupling Analysis If running your analysis from the command line, note that each of the –inputFile and –resultFile command line options are required for this type of restart. If no modifications were made, only the –resultFile command line option is required for the restart. 4.

5.

Select the restart point for the System Coupling system. To do this: a.

If the System Coupling tab is not already open, double-click the System Coupling Setup cell or Solution cell to open the System Coupling tab.

b.

In the System Coupling tab, select Analysis Settings, then in Properties of Analysis Settings > Coupling Initialization, pick a restart point that corresponds to the restart point you selected in the participant systems.

Start your restart run. To do this, in the System Coupling tab, right-click Solution and select Update. Your restarted coupled analysis will now begin to solve.

Recovering from a Workbench Crash Workbench or one of the components may crash such that restart files are available but they are not recognized or populated in the Workbench project. If this is the case, you will be able to recover your project and restart your analysis using the steps below. The usual project directory (ProjectName_files) contains the latest System Coupling results and restart points (these solvers use the live project instead of running in a temporary directory). Note that the .backup directory contains the original version of any files which have been modified since the last save. These files are useful to recover the last saved state, but they are not useful for restarting your analysis. To recover the project to be able to restart from a restart point: 1.

Launch Workbench and open the project. Since the project was not closed down cleanly, a lock file will exist. Select Unlock in the dialog box that appears.

2.

The next dialog box that appears asks if you want to recover the last saved state before opening. Select No here despite the warnings. Your Project Schematic now shows a state as if the solution had not started, but examination of the project files shows that backup files are available. Your Workbench project will not know about these files.

3.

Populate the restart data from the participant systems connected to System Coupling. Make sure that these restart points correspond to the restart point chosen in System Coupling. For information on how to do this for participant systems in your coupled analysis, see Supported System Couplings for a list of supported systems and references to their corresponding restart documentation.

4.

Recover the System Coupling restart points: a.

On the Project Schematic, right-click System Coupling's Setup cell, and select Update.

b.

Double-click the System Coupling Setup cell to open the System Coupling tab.

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Workflows for System Coupling c.

Select Analysis Settings, then in Properties of Analysis Settings, right-click Coupling Initialization and select Read Restart Points. The restart points will now be available in System Coupling as usual.

d.

5.

In Properties of Analysis Settings > Coupling Initialization, pick a restart point that corresponds to the restart point you selected in the participant systems.

You can now start your restart run. To do this, in the System Coupling tab, right-click Solution and select Update. Your restarted coupled analysis will now begin to solve.

Stopping the Coupled Analysis Run During the analysis run, you may wish to interrupt or abort the analysis before it is completed. The interrupted analysis can be thought of as a clean stop, where the run continues until the current coupling step is finished, and the restart data are generated. Such a run can be restarted later from end of the coupling step in which it was stopped, as described in Restarting a System Coupling Analysis (p. 35). The aborted analysis, on the other hand, terminates the run immediately. This run cannot be restarted from the coupling step in which it was stopped. The workflow for stopping the coupled analysis run in Workbench is as follows: 1. Start the analysis by selecting Update from the context menu of the Solution cell of the System Coupling component. 2. In the Progress view of Workbench, click the Stop button

.

3. A popup window, shown in Figure 5: Interrupt Prompt from Workbench (p. 38), will appear asking how the run should be stopped. Figure 5: Interrupt Prompt from Workbench

You can choose from the following options: • Select Interrupt to perform a clean shutdown. The analysis will stop once the current coupling step is completed. • Select Abort to stop the analysis run immediately. All available generated data will be discarded. • Select Cancel to continue with the current run. 4. See Restarting a System Coupling Analysis (p. 35) for information on how to restart the coupled analysis run.

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Stopping the Coupled Analysis Run If you are running your analysis from the command line, to stop a run an scStop.stop file must be created in the working directory for the System Coupling service. See System Coupling Service Shutdown File (scStop.stop) (p. 55) for more information.

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Understanding the System Coupling Service This chapter provides information about the System Coupling Service used in the execution of coupled analyses. The two main roles of the coupling service are: coupling management, and the mapping of data transfers. This chapter also describes the various files used by and generated by the coupling service. Coupling Management Data Transfers Files Used by the Coupling Service Files Generated by Coupling Service Understanding the System Coupling Input File Understanding the System Coupling Log File

Coupling Management The primary role of the System Coupling Service is to manage the coupled analysis. There are three aspects to this: • Inter-Process Communication • Process Synchronization and Analysis Evolution • Convergence Management For more information, see the following sections. Inter-Process Communication Process Synchronization and Analysis Evolution Convergence Management Evaluating Convergence of Data Transfers

Inter-Process Communication The coupling service and participants, which are often highly optimized physics solvers, are executed as independent computational processes, and this introduces the need for Inter-Process Communication (IPC). This communication is realized using a proprietary, light-weight, TCP/IP based client-server infrastructure that does not interact with other communication mechanisms like the Message Passing Interface (MPI). All high level communication needed for process synchronization, brokering data transfers and managing convergence between the coupling service and participants are defined in terms of Application Programming Interfaces (APIs) that use the low level IPC infrastructure.

Process Synchronization and Analysis Evolution The coupling service and participants advance synchronously through a coupled analysis. High-level synchronization is managed with the use of synchronization points, and low-level synchronization, between synchronization points, is managed using a token-based protocol.

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Understanding the System Coupling Service The five primary synchronization points used to manage advancement through the coupled analysis are shown in Figure 6: Execution Sequence Diagram for the Coupling Service and Co-Simulation Participants (p. 42). This figure also features notes regarding the processing that occurs between these points, as well as the coupling step and iteration loop structure. Each of these synchronization points, shown in dark gray, represents a gateway beyond which a given process may not advance until all other processes (or a subset thereof, as controlled by the coupling service) arrive. Note, as well, that while a process may serve data both between and at synchronization points, it may only request data between synchronization points. Figure 6: Execution Sequence Diagram for the Coupling Service and Co-Simulation Participants

Details regarding processing between the Solution and Check Convergence synchronization points are shown in Figure 7: Processing Details for the Coupling Service and Co-Simulation Participants (p. 43). During this stage of the analysis, the coupling service controls the advancement of co-simulation participants, or solvers, through two secondary synchronization points: Data Transfer and Solve, both shown in light gray. The sequencing of solvers is controlled by manipulating the relative order in which the solvers advance beyond these secondary synchronization points. For example, solvers with identical sequence indices all advance through the Data Transfer synchronization point together, and then do the same for the Solve synchronization point.

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Coupling Management Figure 7: Processing Details for the Coupling Service and Co-Simulation Participants

These figures highlight that all participants traverse the duration of the entire coupling step during each coupling iteration. They have complete freedom, however, to traverse the coupling step duration in one or more ‘solver’ steps, each of which may include one or more solver iterations. If multiple ‘solver’ steps are used within one coupling step, then this is referred to as sub-stepping (or sub-cycling). Review the participant systems’ documentation to see if sub-stepping occurs and is supported with System Coupling.

Convergence Management By default, the system coupling log file reports Root Mean Square (RMS) convergence for data transfers for both the source and target side of the transfer. Convergence of the coupling step is evaluated at the end of each coupling iteration. Coupling step convergence requires that: • the target side RMS values have reached the convergence criteria that you specified in the input to the system coupling setup, and • that the minimum number of coupling iterations that you specified are met. If the coupling step is not yet converged, then a new coupling iteration is started. If the coupling step is converged, then a new coupling step is started if the coupling duration has not yet been reached.

Evaluating Convergence of Data Transfers To evaluate convergence of data transfers, each iteration is measured against the previous iteration. The change in all of the data transfer values between these two successive iterations is reduced to a normalized value. When two successive iterations produce a normalized value that is under the convergence target (you can change this convergence target, the default value is 1e-2), the data transferred is converged. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service Two global (that is, over all locations) measures of convergence are evaluated and reported during execution of the coupled analysis. These include the maximum and Root Mean Square (RMS) of the normalized change in data transfer values. The RMS is the default measure used to determine convergence. The measure can be changed to the maximum of the normalized value through the System Coupling Input file. The RMS value is evaluated as: (1) where is the normalized change in the data transfer value between successive iterations within/across a given coupling step, and is measured as: (2) where

is the data transfer value, and l is the location of the data transfer on the coupling interface.

In Equation 2 (p. 44), the denominator, or normalization factor, is evaluated differently in the transient and general coupling analyses. In the transient coupling case, the normalization factor equals the average of the range and mean of the magnitude of data transfer values over all locations for the current iteration. In the general coupling case, it equals the average of the range and mean of the magnitude of data transfer values over all locations for all iterations in the entire analysis. This normalization factor is a representative scale for the data transfer values and ensures that division by zero (due either to zero range or zero mean) is avoided. In Equation 2 (p. 44), the numerator, and is expressed as:

, is the un-normalized change between successive iterations, (3)

where

and

correspond to the current and the previous iterations respectively, and

is the

under-relaxation factor applied in forming the final value applied during the current iteration. In the first coupling iteration of every coupling step, is assumed to be unity. When there is no change in data transfer values, the default for RMS/MAX is 1.0e-014.

Note The global data transfer convergence measures are set to unity in the first coupling iteration of the first coupling step during an initial run. After a restart, if a data transfer involving a new variable is defined or if the region is remeshed, these measures are set to unity in the first coupling iteration of the first coupling step. Although monotonic convergence to the specified target values is ideal, oscillatory convergence and/or divergence (that is, constant or increasing convergence measures) may also occur.

Data Transfers Data transfers in System Coupling use one of two data transfer algorithms:

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Data Transfers • Profile Preserving data transfer algorithm is used when transferring non-conserved quantities like displacements and temperatures. • Conservative Profile Preserving data transfer is used when transferring conserved quantities like mass, momentum, and energy flows (for example, forces). These two data transfer algorithms are discussed in the section Data Transfer Algorithms (p. 46). Both data transfer algorithms incorporate the following components: • Data Pre-Processing: This is the first component used in the data transfer process and could involve creation of supplemental data on mesh locations that are needed by the mapping and interpolation algorithms. • Mapping: This is the second component used in the data transfer process and involves the matching/pairing of a source and a target location to generate weights. For example, in a fluid-solid interaction problem, a fluid node must be mapped to a solid element to receive displacements. Similarly, either a solid node or a Gauss point in a solid element must be mapped to a fluid element to receive stress. • Interpolation: This is the third component used in the data transfer process and involves the (re)use of the generated weights to project source data onto target locations. • Interpolated Data Post-Processing: This is the final component of the data transfer process and could involve explicit under-relaxation, ramping, and/or clipping of the target data, as well as the creation of supplemental data on mesh locations needed by the consumers of interpolated, target data. Note that participant data transfer regions must consist of triangular or quadrilateral faces. Polyhedral faces as well as faces with hanging nodes (cut-cells) are not supported by System Coupling. A variety of algorithms exist in the literature to address these components. In the discussions below, only those that are used in System Coupling are presented. • Data Pre-Processing Algorithms (p. 45) • Mapping Algorithms (p. 46) • Interpolation Algorithms (p. 52) • Interpolated Data Post-Processing Algorithms (p. 53)

Important Unit conversions are automatically applied for all data transfer algorithms during each of the mapping and interpolation phases.

Data Pre-Processing Algorithms Data pre-processing algorithms are used to create supplemental data on mesh locations that are needed for mapping and interpolation. These pre-processing algorithms may also be used during post-processing of interpolated data to provide data on the mesh locations required by co-simulation participants.

Creating Nodal Data from Face/Element Centroid Data Conservative data (for example, heat flows and forces) may be available on element (face) centroids. If these data are required on nodes, the following steps are executed: Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service • an element-node value is calculated by dividing the total value by the number of nodes that define the element, and • the element-node values are scattered to, and accumulated at, each node.

Creating Face/Element Data from Node Data Conservative data (for example, heat flows and forces) may be available on nodes. If these data are required on elements/faces, the following steps are executed: • the area for each face/element that shares a common node is calculated for all nodes, • the nodal area is calculated as the sum of all areas for each face/element that shares a common node, • the area fraction is calculated as the area divided by nodal area for each face/element that shares a common node, and • the face/element value is calculated for each element-node as the nodal value times the respective area fraction. The face/element values corresponding to each element-node are summed if a total face/element value is required.

Mapping Algorithms Several mapping algorithms are used when executing data transfers during system couplings. To assist in evaluating the quality of the mapping, a mapping summary is included in the System Coupling service log file (see System Coupling Service Log File (scLog.scl_, scLog_##.scl) (p. 57)). Note that summary data depends upon on the availability and relevance of specific information (for example, the number of nodes or area on the surface and/or target meshes) for each mapping algorithm. Mapping is performed only at the start of the System Coupling simulation. Because of this, the mesh topology on the data transfer regions cannot change (that is, cannot be dynamically remeshed) during the simulation. The two mapping algorithms used in System Coupling (discussed below) are Bucket Surface and General Grid Interface (GGI).

Data Transfer Algorithms Data transfer algorithms are combinations of mapping/interpolation algorithms (discussed in the sections above) that are used in the System Coupling service. Note that the fidelity of the data transferred to the target side of the interface is limited by the leastresolved side of the interface. For example, if the target side of the interface is significantly coarser than the source side, then only the large scale features of the source data will be captured in the data

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Data Transfers transfer. Similarly, if the target side of the interface is significantly finer than the source side, then the resulting target data will be a linearly interpolated representation of the data on the source side.

Note A number of advanced controls for the data transfer algorithms are exposed via expert settings. For more information, see Expert Settings Related to Mapping in Expert Settings (p. 24).

Profile Preserving The Profile Preserving data transfer algorithm is the default algorithm used by System Coupling when transferring non-conserved quantities like displacements and temperatures. For this data transfer algorithm, the Bucket Surface mapping algorithm is used to generate mapping weights. In this algorithm, the mesh nodes on the target side of the data transfer interface are mapped onto mesh elements on the source side as illustrated in Figure 8: Mapping target node to source element for Profile Preserving Data Transfer (p. 47). Standard, weight-based interpolation (resulting in the values shown) and subsequent under-relaxation are used to evaluate the final data applied on the target side of the interface. Figure 8: Mapping target node to source element for Profile Preserving Data Transfer

Profile Preserving data transfer algorithm is the default algorithm used when transferring non-conservative quantities because of the profile-preserving nature of the mapping weights generated by the Bucket Surface algorithm.

Conservative Profile Preserving The Conservative Profile Preserving data transfer algorithm is the default algorithm used by System Coupling when transferring conserved quantities like mass, momentum, and energy flows (for example, forces). For this data transfer algorithm, the General Grid Interface (GGI) mapping algorithm is used to generate mapping weights. Standard, weight-based interpolation and subsequent under-relaxation are used to evaluate the final data applied on the target side of the interface. Conservative Profile Preserving data transfer algorithm is the default algorithm used when transferring conserved quantities because of the conservative nature of the mapping weights generated by the GGI algorithm. Resulting target values are locally (in the vicinity of each source and target element) conservative. If the source side of the interface is completely mapped to the target side of the interface, then the resulting target values are also globally conservative. If any portions of the source side of the interface are not mapped onto the target side, then the data transfer is not globally conservative. Note that any portions of the target side of the interface that are unmapped (that is, weights equal to zero) are automatically assigned a value of zero, which differs from the handling of unmapped nodes using the Profile Preserving data transfer algorithm.

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Understanding the System Coupling Service

Bucket Surface The underlying ideas for this algorithm are presented in the book Computational Nonlinear Mechanics in Aerospace Engineering, American Institute of Aeronautics and Astronautics, edited by S. Atluri, ISBN 1563470446, Chapter 5, Fast Projection Algorithm for Unstructured Meshes by K. Jansen, F. Shakib, and T. Hughes, 1992. Specifically, the implementation of the Smart Bucket Algorithm as described in the chapter stated above is used in system coupling. This algorithm generates weights that are ideal for transferring the profiles of non-conserved quantities like stresses, displacement, temperature, and heat transfer coefficient from a source mesh to a target mesh. Since a complete description of the algorithm is available in the reference quoted above, only a brief overview of it is presented below. The first step in the process of computing the mapping weights using the Smart Bucket Algorithm is to divide the mapping source mesh into an imaginary structured grid, with each grid section called a “bucket.” A 2D bucket is used to demonstrate this concept in Figure 9: Example of a Bucket Grid on a 2D Source Mesh (p. 48). Similarly, a 3D bucket grid is generated for a 3D mesh, and this is what is used in System Coupling. Next, each node on the data transfer regions of the target mesh is initially associated with a bucket. In System Coupling, data transfer regions consist of element faces from the 3D mesh. Two cases arise: buckets associated with the target node are either empty (without even one source element in it) or non-empty. For example, bucket A shown in Figure 9: Example of a Bucket Grid on a 2D Source Mesh (p. 48) is empty. Each case (empty and non-empty buckets) is discussed separately in the sections below. Figure 9: Example of a Bucket Grid on a 2D Source Mesh

Case 1: The bucket associated with a target node is non-empty If the bucket associated to a given target node is non-empty, the mapping algorithm attempts to match each of the target nodes to one source element in the bucket.

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Data Transfers First, each target node is checked to see if it is in the domain of any of the source elements. This is done by looping through all the source elements in that bucket and checking to see if the target node is within their domain. For each source element in the bucket, the vector element–local (or natural) coordinates (corresponding to the vector of global coordinates of the target node, ) is found by solving the set of nonlinear equations given by the isoparametric mapping below: (4) where is the matrix of linear shape functions associated with the source element and is the vector of global coordinates of element–local node . It is then checked to see if lies within the domain of the source element based on certain criteria discussed next. For a four-noded quadrilateral source element, if the natural coordinates corresponding to a target node satisfy the conditions in Equation 5 (p. 49) below, the target node is said to be exactly within the domain of the element. (5)

where and are the components of the vector of natural coordinates . However, if the natural coordinates do not satisfy the conditions in Equation 5 (p. 49) but do satisfy the ones in Equation 6 (p. 49) below, then the target node is in the domain of the source element but only within the specified tolerance (also known as element edge tolerance). The value of tolerance is exposed in the System Coupling UI as one of the expert settings. See the description of ProfMapEdgeTol in the section Expert Settings Related to Mapping in Expert Settings (p. 24). (6) This concept is explained with the help of Figure 10: A Quadrilateral Source Element in the Natural Coordinate Space (p. 50) wherein a quadrilateral source element is shown along with two different target nodes, one of which satisfies Equation 5 (p. 49), and other that satisfies Equation 6 (p. 49).

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Understanding the System Coupling Service Figure 10: A Quadrilateral Source Element in the Natural Coordinate Space

Similarly, for a three-noded triangle element, the conditions listed in Equation 7 (p. 50) below, are used to check if a target node is exactly within the domain of the element: (7)

And the conditions in Equation 8 (p. 50) below will determine if the target node is within the domain but up to a tolerance . (8)

Now that target nodes are determined to be in the domain of specific source elements, each node must be paired with only one source element. In both of the cases above (four-noded quadrilateral and threenoded triangle), it is possible that a target node occurs (either exactly or within a tolerance) in more than one source element’s domain. The finite element interpolation of the nodal solution requires each target node to be paired with only one source element. To satisfy this requirement, the target node is consequently paired with that source element for which the gap is minimized. The gap is defined as the Euclidean distance between the target node and its projection onto/into a source element. In some cases, such as when candidate source elements are coplanar, the gap values may be identical and an alternate approach is required to pair the target node with one source element. Under these conditions, only the source elements with identical (and minimized) gaps are considered. The target node may be exactly in the domain of any of these source element, or

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Data Transfers it will be in their domain within a tolerance. Preference is given to the last source element for which the target node is exactly in its domain. If the target node is only in the different domains within a tolerance, then the last candidate source element is used. Once the target node is paired with a source element, mapping weights are computed by evaluating the finite element shape functions associated with the paired source element at the target node. If no target node-to-source element match is found in a non-empty bucket, then the target node is reported as being unmapped. It is important to note, however, that mapping weights are still evaluated for such nodes using the Bucket Surface Algorithm. Specifically, all unmapped target nodes are simply mapped to the nearest source node in the bucket and the target node is assigned the solution value corresponding to that source node.

Note Significant ‘gap’ distances between successfully-mapped target nodes and source elements may occur. For information about how to have mapped nodes with ‘gap’ distances larger than a specified tolerance be reported as unmapped, see Expert Settings Related to Mapping in Expert Settings (p. 24). Case 2: The bucket associated with a target node is empty If the bucket initially found for the target node is empty, then the closest non-empty bucket is found and the same procedure as highlighted in Case 1 is followed so that each target node is mapped to one source element and mapping weights are calculated. Unmapped Nodes With the Bucket Surface algorithm, there are two types of target nodes that can be reported as unmapped: nodes that do not fall within a bucket (these are “unmatched nodes”), and nodes that do fall within a bucket, but that do not meet the gap tolerance (these are "gap nodes”). Unmatched nodes are mapped to the nearest source node in the bucket and the target node is simply assigned the solution value corresponding to that source node. Unmatched nodes are always reported as unmapped in the SCL file. Gap nodes are within a bucket, and so are mapped to the source nodes like all of the other mapped nodes and given a value accordingly. Gap nodes are reported as mapped in the SCI file. The gap tolerance and the reporting of gap nodes in the SCI file can be modified using Expert Settings (p. 24).

General Grid Interface (GGI) The underlying ideas for this algorithm are presented in the article on Three- Dimensional Navier Stokes Predictions of Steady-State Rotor/Stator Interaction with Pitch Change, 3rd Annual Conference of the CFD, Society of Canada, Banff, Alberta, Canada, Advanced Scientific Computing Ltd, by P.F. Galpin, R.B. Broberg and B.R. Hutchinson, June 25-27, 1995. This algorithm generates weights that are ideal for transferring conserved quantities such as mass, momentum and energy flows. In this algorithm, each element face on both the source and the target sides is first divided into n integration point (IP) (sub-) faces, where n is the number of nodes on the face. The three-dimensional IP faces are then converted into a two-dimensional quadrilaterals made up of rows and columns of pixels. Pixels from the converted quadrilaterals on the source and target sides are intersected, creating a number of overlapped areas called ‘control surfaces.’ Mapping weight contributions are evaluated for each control surface based upon the associated source and target element face areas and the pixel intersections. Final mapping weights for each of the target (or source) nodes are evaluated by accumulating these control surface contributions. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service If no control surfaces are created (for example, when no polygon intersection between mapping source and target exists), then mapping weights are identically zero and nodes and elements on the target (or source) side of the interface are reported as being unmapped. As an example, consider the schematic shown in Figure 11: General Grid Interface Mapping (p. 52) that corresponds to a typical interface between the source (sending) and target (receiving) sides. In the schematic, the control surfaces resulting from the intersection of all IP faces on the interface (labeled with an ‘X’), are shown. For example, the IP faces S1 and S2 on the source side intersect with the IP faces R1 and R2 on the target side creating areas A1, A2, and A3 on the control surface. In this case, the mapping weight contributions for the target IP face R1 (and associated target node) that are associated with the source IP faces S1 and S2 (and nodes) are respectively given by: (9) and (10) Figure 11: General Grid Interface Mapping

Interpolation Algorithms The interpolation algorithm is responsible for providing target node values using the source data and mapping weights that were generated by the mapping algorithm(s) (see Mapping Algorithms (p. 46)). The mapping weights are applied in Equation 11 (p. 53) to evaluate , which is the target node, or iteration point (IP) face value.

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Data Transfers

(11)

where is the value at the source node, and is the associated weight. For weights obtained with the bucket surface mapping algorithm, is the number of nodes in the source element. For weights obtained via the GGI mapping algorithm, is the number of areas (associated with a target IP face) obtained due to the intersection of the sender and receiver faces on the control surface.

Interpolated Data Post-Processing Algorithms Interpolated data post-processing algorithms are the last step in the data transfer process. In many situations (such as an implicit coupling where the number of coupling iterations within a coupling step is more than one), the interpolated target data needs to be post-processed before it is exposed to the target participant of the data transfer. Two optional post-processing algorithms may be applied to the target data generated during interpolation: ramping and under-relaxation. Each of these algorithms is used to improve convergence of the overall analysis. Other post-processing algorithms that are automatically applied involve: • clipping unphysical data values (p. 55), and • creation of supplemental data on mesh. For information on the creation of supplemental data, see Data Pre-Processing Algorithms (p. 45). Unless otherwise noted, post-processing algorithms are applied to each: • data transfer location (node), and • component of vector data transfers

Ramping Algorithm The ramping controlled by the System Coupling service works by slowing the application of the sourceside value on the target-side of the data transfer. For each data transfer location (node) where is true, the following formula is applied: (12) where is the ramped, target-side value. is the reference target-side value, which for the first coupling step is the initial value for the data transfer variable (see Table 3: Initial Values used for the Reference Target-Side Value (p. 54)). Thereafter, the reference target-side value is the final value from the previous coupling step. The one exception is displacement, where for every coupling step, is always 0.0 [m]. is the raw, target-side value obtained from interpolation. is the current coupling iteration number within the coupling step. is the minimum number of coupling iterations per coupling step.

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Under-Relaxation Algorithm Under-relaxation works by limiting a potentially large variation of the target-side data between two successive coupling iterations. For each data transfer location (node), the following formula is applied: (13) where is the relaxed, target-side value. is the reference target-side value. For coupling iterations within a coupling step, the reference target-side value is the final value from the last coupling iteration. For the first coupling iteration of the first coupling step, the reference target-side value is the initial value for the data transfer variable (see Table 3: Initial Values used for the Reference Target-Side Value (p. 54)). For the first coupling iteration of all subsequent steps, the reference target-side value is the final value from the last coupling step. is the raw, target-side value obtained from interpolation or from ramping (if applied). Note that if you have applied both ramping and under-relaxation, the data is first ramped and then under-relaxed. In this case, for the under-relaxation’s raw target-side value. ω is the under-relaxation factor (URF). In a transient analysis, in the first coupling iteration of every coupling step, the URF is overridden and set to 1, and so data transferred at this coupling iteration is not under-relaxed.

Initial Values used in Ramping and Under-Relaxation Algorithms The default for the initial value used as the reference target-side value (

) in Equation 12 (p. 53)

and Equation 13 (p. 54) is based on the physical type of the variable. The default values are listed in Table 3: Initial Values used for the Reference Target-Side Value (p. 54). Table 3: Initial Values used for the Reference Target-Side Value Variable Type

Initial Value used for the Reference Target-Side Value ( )

Notes

Incremental displacement

0.0 [m]

For the ramping algorithm, the reference target-side value for incremental displacement is always 0.0 [m] for every coupling step.

Force

0.0 [N]

Temperature

295.15 [K]

Heat Rate

0.0 [W]

Heat Transfer Coefficient

0.0 [Wm-2K-1]

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Variables of this type include temperature and near wall temperature.

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Files Used by the Coupling Service These defaults for the initial values above can be overridden using the methods discussed in the section Expert Settings (p. 24). Note that for the ramping algorithm, the reference target-side value for displacement cannot be modified using expert settings.

Clipping Algorithm Although uncommon, it is possible that unphysical values, such as negative heat transfer coefficients, are provided by the data transfer source or are generated during mapping. To ensure unphysical values are not applied to the data transfer target, these unphysical values are clipped to be within a valid range. For example, any negative heat transfer coefficient values are changed to 0 [Wm-2K-1] before being transferred to the target participant. The variable(s) that are clipped and their valid range are listed in the table below. Note that at the end of any coupling step where clipping is used, the System Coupling Log file will have a message about the clipping. Variable Type

Minimum Value

Maximum Value

Heat Transfer Coefficient

0 [Wm-2K-1]

unlimited

Files Used by the Coupling Service This section outlines the files used by the coupling service during its execution. System Coupling Service Input File (scInput.sci) System Coupling Service Shutdown File (scStop.stop)

System Coupling Service Input File (scInput.sci) The scInput.sci file, which is an XML file generated by the System Coupling system in Workbench, provides analysis-related inputs to the coupling service. The input XML file is composed of several different sections: participants, analysis, transfers, and execution control. You can modify this file, with an appropriate XML editor, although this is not encouraged. When the System Coupling system's Setup cell is up-to-date and the System Coupling user interface is active (by editing either the System Coupling Setup or Solution cell), you will be able to export, and save, the input file using the Export SCI File option available from the Workbench File menu. For more detailed information about the input file contents, see Understanding the System Coupling Input File (p. 58).

System Coupling Service Shutdown File (scStop.stop) If a text file named scStop.stop is found in the coupling service’s run directory, then the service will shut down as soon as possible. The shutdown file should contain two (or more) lines as shown below: 0 The reason for terminating the analysis

The first line contains an integer flag that indicates whether or not the termination should be interpreted as an ‘interrupt’ or as a ‘stop’.

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Understanding the System Coupling Service • With an integer value of 0, the analysis will be interrupted; the coupling service will complete the current coupling step and signal the co-simulation participants that the execution has ended. This will cause the coupling service and participants to shutdown cleanly. • With an integer value of 1, the analysis will be stopped; the coupling service will signal the co-simulation participants to abort the run as quickly as possible. This will not produce a clean shutdown. The second and subsequent lines in the file are reported in the coupling service’s log file when summarizing the reason for shutting down the coupled analysis.

Files Generated by Coupling Service This section outlines the files generated by the coupling service during its execution. System Coupling Server File (scServer.scs) System Coupling Service Log File (scLog.scl_, scLog_##.scl) System Coupling Results File (scResults_##_######.scr)

System Coupling Server File (scServer.scs) The scServer.scs file, which is written to the service’s run directory, contains information that is used to connect the participants to the coupling service. This file is generated shortly after the coupling service is started, and indicates that the coupling service is ready to receive connections from the cosimulation coupling participants. This text file contains the following lines of data: • The server’s port and host, separated by an ‘@’ character. • A block containing the number of co-simulation participants connected to the System Coupling system in the Workbench schematic, and their unique and display names. In the Workbench environment: – the unique names are automatically generated and are reported as the ComponentID in the Properties view of the co-simulation participant’s Solution cell, – the display names correspond to the names (which you are able to specify) below the participant’s system Example 1: An Example scServer.scs File [email protected] 2 Solution 1 Fluid Model Solution 2 Solid Model

Note When the participants are started and instructed to connect to the running SC Service, they must connect to the service using the unique names (for example Solution 1 and Solution 2 in the example above).

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Files Generated by Coupling Service

System Coupling Service Log File (scLog.scl_, scLog_##.scl) The scLog.scl file provides key runtime information related to a coupled analysis between various participants, including: • The command line used to start the system coupling service • System coupling header and build information • A summary of system coupling setup information, including: – Analysis information – Coupling participant information (number of participants, and summary information pertaining to each participant) – Data transfer information (number of data transfers, and summary information pertaining to each data transfer) – Execution control information (co-simulation sequence, debug output) – Setup validation (summary of system coupling input file validation) – System coupling co-simulation summary (summary of system coupling participants) • Solution information, including: – Mapping summary (including percentages of mapped source and target nodes and the percentages of mapped source and target areas, depending upon the mapping algorithm that was used) – Convergence information at each coupling step and iteration The information here includes the coupling step index, the current analysis time for transient couplings, the coupling iteration index, the participant name and data transfer name, the participant convergence status (for example, “Not Yet Converged...”, “Converged”, and so on), and the data transfer convergence (for example, the RMS/Maximum normalized change). • Shutdown information, including: – Run completion status During the execution of a run, the service log file, named scLog.scl_, is generated, evolving with the analysis, and is finally renamed at the end of the run. The final log file is named with the convention: scLog_##.scl, where the suffix _## denotes the run index. For example, scLog_13.scl corresponds to the 13th run (that is, the 12th restart) executed for the analysis. For more detailed information about the log file contents, see Understanding the System Coupling Log File (p. 64).

System Coupling Results File (scResults_##_######.scr) The system coupling results file contains important data generated and used by the system coupling service during the analysis. This data enable you to: • Restart the analysis or continue from a previous analysis Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service • Post-process the heavy weight interface data • Monitor the analysis’ convergence • Reconstruct the analysis The specific data contained in the file are summarized as: • A history of the input (SCI) files used to drive the coupling service’s execution • Convergence data corresponding to the data transfers and solvers’ field equations • Heavyweight data corresponding to the source and target regions and variables for defined data transfers A system coupling results file is always created at the end of the analysis. The default file naming convention is of the form scResults_##_######.scr, where the run index is recorded in the “_##” suffix and the coupling step index is recorded in the “_######” suffix (for example, scResult_13_000101.scr corresponds to the 101st coupling step within the 13th run of the analysis). Intermediate results files, with the same naming convention, can also be created at various coupling step intervals (defined by you) during the analysis.

Important All data stored in the System Coupling Result file(s) are written in the SI unit system.

Understanding the System Coupling Input File The input XML file is composed of several different sections: participants, analysis, transfers, and execution control. The participant section contains information obtained through the coupling data interface (CDI) and the connections to upstream solver systems. It is intended to be read-only. In the participants section, you can view the Count (an integer representing the number of connected participants). For each connected participant, you can view the following: Note that depending upon the type of participant (co-simulation or static data), some of the options may or may not be applicable. • Type (integer attribute) The type of coupling participant (0 – co-simulation, 1 – static data) • Name (string) The name of the participant. This is the name with which the participant identifies itself to the system coupling. This corresponds to the “Component ID” which is unique to a specific system’s Solution cell in the Workbench user interface. • DisplayName (wide string) The display name of the participant provided by you in the in Workbench user interface. • FilePath (string) The full path to the primary file used to access source data from a static data participant.

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Understanding the System Coupling Input File • SupportsCouplingIterations (boolean) Whether or not the co-simulation participant supports the execution of multiple coupling iterations per coupling step. • UnitSystem • Regions (options below are applicable to an individual region) – Name (string) The name of the region (intrinsic to the participant). – DisplayName (wide string) The display name of the region given by you in the Workbench user interface. – TopologicalDimensionality (integer) The geometry type of the region (0 – undefined, 1 – point, 2 – curve, 3 – surface, 4 – volume). • Variables (options below are applicable to an individual variable) – Name (string) The name of the variable (intrinsic to the participant). – DisplayName (wide string) The display name of the variable given by you in the Workbench user interface. – PhysicalType (string) The physical type of the variable (options include: Length / Force). • BaseUnits (strings denoting base units for all data of noted physical type) – Length (string) – Time (string) – Mass (string) – Luminance (string) – Angle (string) – SolidAngle (string) – Temperature (string) – ChemicalAmount (string) – Current (string) The analysis section contains details used to define the coupled analysis. In the analysis section, you can set the following: Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service • AnalysisType (integer) This setting defines the nature of the sequential steps used in coupling co-simulation participants. Available option is 0 (general), and 1 (transient). • Initialization This setting defines the initial time for the coupled analysis – Option (integer) Available options are 0 (Program Controlled) and 1 (Start Time). The former is the default option for coupling initialization. When this option is used, the coupling service will make the most appropriate choice of an initial time value. When the latter option is used, the coupling service will override the initial/start time for the analysis with the value specified as part of Time (see below). – Time (double) If option 1 is chosen above, then this is the initial time for the coupling analysis. • Duration This setting defines the duration of the coupled analysis. – Option (integer) Available options are 0 (NumberOfSteps) and 1 (EndTime). – NumberOfSteps (integer) This option is available only if no end-time requirements exist for co-simulation participants. – Time (double) Final time of coupling analysis. • Step – MaximumIterations (integer) The maximum number of coupling iterations allowed per coupling step. – MinimumIterations (integer) The minimum number of coupling iterations allowed per coupling step. – Size (double) The size of the coupling step when it is associated with a time (this is done for transient analyses, size is measured in seconds). – Option (integer) Available option is 1 (coupling step size, used for transient analyses) and 0 (non dimensional step size, used for general analyses).

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Understanding the System Coupling Input File • UnitSystem (string) The transfers section contains details used to define the data transfers between any static and co-simulation coupling participants. In the transfers section, you can set the Count (an integer representing the total number of data transfers) as an attribute. For each coupling transfer, you can set the following: • Name (string) The name of the transfer (which you provided) in the Workbench user interface. • ExecuteCouplingAt (integer) This setting defines “when” the current data transfer is executed during the coupled analysis. The only available option is 2 (Start of Iteration). • Source The information related to the source participant involved in the data transfer. – Participant (string) The name of the source participant. – Region (string) The name of the source region (defined for a given participant) participating in the data transfer. – Variable (string) The name of the source variable, the data corresponding to which is exchanged during the data transfer (also defined for a given participant). • Target The information related to the target participant involved in the data transfer – Participant (string) The name of the target participant – Region (string) The name of the target region participating in the data transfer – Variable (string) The name of the target variable, the data corresponding to which is exchanged during the data transfer • ConvergenceOption (integer) Specifies the type of data transfer convergence check in an implicit coupling (that is, if more than one coupling iteration per coupling step is specified; a value of 0 indicates the RMS normalized change). • ConvergenceTarget (double) Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service The target value that determines the convergence of the data transfer • UnderRelaxationFactor (double) The under-relaxation factor (URF) applied to the data increments between any two successive coupling iterations. The URF has a range of . Note that when transferring incremental displacement, the URF must equal 1. In this case, a value less than 1 can lead to an accumulation of errors, and the following warning will be displayed in your SCL file: The under relaxation factor for the data transfer named '' is smaller than one. Under relaxation factor less than one for incremental displacement might lead to errors.

• Ramping (integer) This setting defines if and how ramping is used when applying data from the source-side to the targetside of the data transfer. Valid options are: 0 – none (that is, stepped), and 1 – linearly ramped up to the minimum number of coupling iterations. The default is none, which implies the target side of the data transfer experiences the full value from the source side during the first coupling iteration. The execution control section contains details used to define the solution sequence between the coupling participants, the system coupling debug output, intermediate result files output, and expert settings. For each participant, you can set the following: • CoSimulationSequence This subsection is used to specify the sequencing of co-simulation coupling participants (most often solvers) during a coupling iteration. In the CoSimulationSequence subsection, the 'Count' attribute specifies the number of participants for which sequencing information will be provided. – Participant A Participant subsection is required for each co-simulation participant. → Name (string) The name of the participant. → SolutionSequence (integer) The sequence number of the participant in the coupled solution. Within a coupling iteration, a participant with a larger sequence number will solve later than another with a lower sequence number. • DebugOutput This subsection is used to specify the section(s) of debug output to write to the system coupling log (SCL) file. As presented below, the level of detail is specified for each section or all sections (the default). – DefaultOutputLevel (integer) This setting provides the default level for the different sections of debug output. If this entry is set and another specific entry (for example, Startup) also exists, then the output level for the specific entry will override the level set here. – Startup (integer)

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Understanding the System Coupling Input File This setting controls the level of output from the start of the coupling service until creation of the “Summary of SC Setup” banner in the SCL file. – ParticipantConnection (integer) This setting controls the level of output from the end of the setup validation until the “Initial Synchronization” synchronization point. – AnalysisInitialization (integer) This setting controls the level of output from the “Analysis Initialization” until the “Solution” synchronization point. – SolutionInitialization (integer) This setting controls the level of output during the setup of coupling steps and iterations. This output does not include information related to the data transfers. – ConvergenceChecks (integer) This setting controls the level of output from the “Check Convergence” synchronization point until the next synchronization point, which may be either “Shutdown” or “Solution.” – Shutdown (integer) This setting controls the level of output after the “Shutdown” synchronization point. – Transfers This section is used to specify the debug output generated for data transfers. Note that header information for mapping is generated whenever the mesh coordinate or mesh topology output is requested. Similarly, header information for the data transfers is generated whenever the transfer data output is requested. → DefaultOutputLevel (integer) This setting provides the default level for the different kinds of debug output. If this entry is set and another specific entry (for example, SourceMeshCoords) also exists, then the output level for the specific entry will override the level set here. → SourceMeshCoords (integer) This setting controls the level of output for mesh coordinates of the source region in all data transfers. → SourceMeshTopol (integer) This setting controls the level of output for mesh topology (elements and nodes) of the source region in all data transfers. → SourceData (integer) This setting controls the level of output for the source data in all data transfers. → TargetMeshCoords (integer) Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service This setting controls the level of output for mesh coordinates of the source region in all data transfers. → TargetMeshTopol (integer) This setting controls the level of output for mesh topology (elements and nodes) of the source region in all data transfers. → TargetData (integer) This setting controls the level of output for the target data in all data transfers. The level of detail to include in debug output is controlled using one of the following integer values for either the default or specific sections of output: – 0: None – 1: Level 1 – 2: Level 2 – 3: Level 3 – 4: Level 4 – 5: All Levels Increasing values always generate more detailed output. Note, as well, that the output level settings for each of the mesh coordinates and topology, and transfer data control the number of lines of output generated. Specifically, 10L lines of data will be written for an output level setting of L (for example, 100 lines will be written for an output level of 2, or “Level 2”). • IntermediateResultsFileOutput This subsection is used to specify the frequency at which intermediate result files, which can be used for restarts, are written by the System Coupling service. – FrequencyOption (integer) Available options are 0 (every coupling step) and 1 (coupling step interval) – StepInterval (integer) The coupling step interval at which intermediate result files should be generated (Note that this is valid only when FrequencyOption is set to Step Interval). For example, using a step interval of 3, results will be generated at steps 3, 6, 9, ... The following entry may be reported in the SCI file, but is not used by the System Coupling service: • MappingSettings

Understanding the System Coupling Log File The System Coupling Service log file (scLog.scl) provides key run time information and is divided into four blocks:

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Understanding the System Coupling Log File • start-up and executable information, • coupled analysis setup information, • solution details, • and shut-down information. The start time and date, command line information and executable details for the run appear as follows: Run start time and date:

10:15:41, Sep 19 2014

Command line used to start this service: C:\Program Files\ANSYS Inc\v160\aisol\bin\winx64\Ansys.Services.SystemCoupling.exe -inputFile scInput.sci ====================================================================== ====================================================================== ====================================================================== | | | ANSYS System Coupling Service | | Version 16.0, Copyright 2014 | | (Build Info. - 10:09:03, Sep 19 2014) | | | ====================================================================== ====================================================================== ======================================================================

The command used to start the System Coupling service is given next as shown below: Command line used to start this service: C:\Program Files\ANSYS Inc (Dev)\v160\aisol\bin\winx64\Ansys.Services.SystemCoupling.exe

An echo of the SC service input file is provided next in the log file below the following header: ====================================================================== ====================================================================== | | | Summary of System Coupling Setup | | | ====================================================================== ======================================================================

The information generally found in this section includes unit system data (for example, MKS, and so on), as well as information relating to coupling (time versus coupling step), initialization (options such as time value or initial coupling step), duration (for example, end time), and step size and the maximum/minimum number of iterations.

Note When the coupling is defined by coupling step (and not by time), then time-related information (initial time, end time, or step size) is not displayed in this section of the log file, and only step-related information is available (for example, initial step, number of steps, maximum and minimum iterations). Summary of System Coupling Setup Under this section of the log file, there are sub-blocks (for example, “Analysis Information”, “Coupling Participant Information”, “Data Transfer Information”, “Execution Control Information”, “Setup Validation“ and “System Coupling Co-Simulation Summary”). A brief description of these sub-blocks is provided below. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service The Analysis Information section includes basic information about the coupling definition, the unit system, as well as time and step information. ====================================================================== | Analysis Information | ====================================================================== General : Analysis Type Unit System

= Transient = MKS

Initialization : Option

= Automatic

Step : Option Size Minimum Iterations Minimum Iterations

= = = =

Duration : Option Time

= End Time = 0.05

Step Size 0.05 5 5

The Coupling Participant Information section includes information about each of the solvers connected to the system coupling simulations (for example, internal name, type (either Co-Simulation or Static Data), units, and so on). Additional information for coupled regions and variables that appear in data transfers is also displayed in this section of the log file. This additional information includes: the coupled name and type (for regions); and the variable name and physical type (for variables). This information is not displayed for regions and/or variables that do not participate in data transfers. If such regions or variables exist, a message is written to indicate that the related information has been omitted from this section of the log file. ====================================================================== | Coupling Participant Information (2) | ====================================================================== +--------------------------------------------------------------------+ | Participant: Fluent | +--------------------------------------------------------------------+ General : Unit System Type Name

= MKS_STANDARD = CoSimulation = Fluent

Summary of Coupling Regions (1) Region : plate Internal Name = plate Type = Surface Summary of Variable : Internal Physical Variable : Internal Physical

Coupling Variables (2) Displacement Display Name Name = INCD Type = Length Force Display Name Name = FORC Type = Force

Summary of Base Units (9) Angle = radian ChemicalAmount = mol Current = A Length = m Luminance = cd Mass = kg SolidAngle = sr Temperature = C Time = s

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Understanding the System Coupling Log File +--------------------------------------------------------------------+ | Participant: External Data | +--------------------------------------------------------------------+ General : Unit System Type Name File Path

= = = =

SI Static Data Setup 2 external_load_data.xml

Summary of Coupling Regions (1) Region : File1 Internal Name = ExtDataReg_Setup 2_0 Type = Surface Summary of Variable : Internal Physical

Coupling Variables (1) Temperature1 Name = ExtDataVar_Setup 2_0_1 Type = Temperature

Summary above omits variables not used in data transfers. Summary of Base Units (9) Angle = radian ChemicalAmount = mol Current = A Length = m Luminance = cd Mass = kg SolidAngle = sr Temperature = K Time = s

The Data Transfer Information section includes: • Region and variable information for the source and target of each data transfer • Data transfer options, such as the convergence criteria and target • The under-relaxation factor • Ramping option ====================================================================== | Data Transfer Information (2) | ====================================================================== +--------------------------------------------------------------------+ | Data Transfer: Mechanical Displacement to Fluent | +--------------------------------------------------------------------+ Source : Mechanical Region Variable

= Mechanical Wall Display Name = DISP Display Name

Target : Fluent Region Variable

= plate = Displacement Display Name

General Information : Name Execute Transfer At Convergence Option Target Value Under Relax. Factor Ramping

= = = = = =

Mechanical Displacement to Fluent Start Of Iteration RMS Change In Data 0.01 0.25 None

+--------------------------------------------------------------------+ | Data Transfer: Fluent Force to Mechanical | +--------------------------------------------------------------------+ Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Understanding the System Coupling Service

Source : Fluent Region Variable

= plate = Force Display Name

Target : Mechanical Region Variable

= Mechanical Wall Display Name = FORC Display Name

General Information : Name Execute Transfer At Convergence Option Target Value Under Relax. Factor Ramping

= = = = = =

Fluent Force to Mechanical Start Of Iteration RMS Change In Data 0.01 0.25 Linear to Min. Iterations

The Execution Control Information section includes a summary of the sequencing of co-simulation participants, and requests for debug and intermediate result file output. Note that the debug and intermediate result output summaries are generated only if such output is requested. For example: ====================================================================== | Execution Control Information | ====================================================================== +--------------------------------------------------------------------+ | Co-Simulation Sequence | +--------------------------------------------------------------------+ Sequence Index : Fluent Solver

1

Sequence Index : 2 Mechanical Solver +--------------------------------------------------------------------+ | Debug Output | +--------------------------------------------------------------------+ General Output : Default Startup Participant Conn. Analysis Init. Solution Init. Convergence Checks Shutdown

= = = = = = =

Level 1 None None None None None None

Data Transfer Output : Default Source Coords. Source Topology Source Data Target Coords. Target Topology Target Data

= = = = = = =

Level 1 None None None None None None

+--------------------------------------------------------------------+ | Intermediate Restart Data Output | +--------------------------------------------------------------------+ Output Frequency : Option Interval

= Step Interval = 3

The Setup Validation section includes any warning or error messages that may have been generated. For example:

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Understanding the System Coupling Log File ====================================================================== | Setup Validation | ====================================================================== +--------------------------------------------------------------------+ | Warnings ( 1) | +--------------------------------------------------------------------+ 1 ) Auto-Correction: The specified maximum iterations per step is less than the specified minimum iterations. The maximum iterations will be set to the minimum iterations.

+--------------------------------------------------------------------+ | Errors ( 1) | +--------------------------------------------------------------------+ 1 ) The solution sequence specified for the participant named 'Fluent' is not greater than zero. Adjust this (and other) sequence values appropriately.

The System Coupling CoSimulation Summary section includes a brief summary of the participants in the co-simulation. ====================================================================== | System Coupling CoSimulation Summary | ====================================================================== Participant : Mechanical APDL Version/Build Info = Mechanical APDL Release 16.0 UP20130905 DISTRIBUTED WINDOWS x64 Version Participant : Fluent Version/Build Info = ANSYS Fluent 16.0.0

Solution Next is the “Solution” block. Under it, the following information is provided. ====================================================================== ====================================================================== | | | Solution | | | ====================================================================== ======================================================================

The Solution block contains a Mapping Summary section: +--------------------------------------------------------------------+ | MAPPING SUMMARY | +--------------------------------------------------------------------+ | Data Transfer | | | Diagnostic | Source Side | Target Side | +----------------------------------+----------------+----------------+ | Mechanical Displacement to Fluent| | | | Percent Nodes Mapped | N/A | 100 | | Fluent Force to Mechanical | | | | Percent Nodes Mapped | 100 | 100 | | Percent Area Mapped | 100 | 100 | +----------------------------------+----------------+----------------+

The current coupling step number and the current simulation time are reported as shown below. This information will be a part of a box that is repeated in the log file at the beginning of every coupling step. It looks similar to the following: +====================================================================+ | COUPLING STEP = 1 SIMULATION TIME = 0.001 | |--------------------------------------------------------------------| | Solver | Solution Status |

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Understanding the System Coupling Service | Data Transfer | | | Diagnostics | Source Side Target Side | +====================================================================+

Note that if the simulation is defined only by steps (and not by time), then the log file output will only present step-related information. Next is another box that repeats every coupling iteration of every coupling step. It looks like: +--------------------------------------------------------------------+ | COUPLING ITERATION = 1 | +--------------------------------------------------------------------+ | Fluent | Not yet converged... | |- - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - | | Mechanical Displacement to Fluent| Not yet converged... | | Change:RMS | 1.00000e+000 1.00000e+000 | |--------------------------------------------------------------------| | Mechanical | Not yet converged... | |- - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - | | Fluent Force to Mechanical | Not yet converged... | | Change:RMS | 1.00000e+000 1.00000e+000 | +--------------------------------------------------------------------+ | COUPLING ITERATION = 2 | +--------------------------------------------------------------------+ | Fluent | Converged | |- - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - | | Mechanical Displacement to Fluent| Converged | | Change:RMS | 2.82982e-005 1.42982e-004 | |--------------------------------------------------------------------| | Mechanical | Converged | |- - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - | | Fluent Force to Mechanical | Converged | | Change:RMS | 1.30000e-004 2.08200e-000 | +--------------------------------------------------------------------+

As indicated above, after every coupling iteration, the convergence status is given for each participant. Common participant status values are Converged and Not yet converged..., however, Divergence detected... and Status Unavailable could also be reported. Below the solver status is a list of the data transfers for which the participant is the target, plus diagnostics used to evaluate convergence of the data transfer. Any supplemental diagnostics (as described in the SC Log Output Control Settings section in Understanding the System Coupling Input File (p. 58)) that have been requested are also included here. Notes specific to the execution of a given coupling step will be reported under the final coupling iteration of the step. For example: +====================================================================+ | NOTES | | * During this coupling step, the target variable, Convection | | Coefficient, was clipped for the data transfer: Upper HTC. | | * Intermediate result file written: scResult_01_000475.scr | +====================================================================+

Shutdown Next is the “Shut Down” block under which the following information is included: ====================================================================== ====================================================================== | | | Shut Down | | | ====================================================================== ====================================================================== System Coupling Service shut down...

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Understanding the System Coupling Log File

Run completed successfully.

The preceding output is generated under normal shutdown conditions. If a co-simulation participant (or the coupling service itself ) fails during the analysis, the normal shutdown output will be replaced by messages similar to the following: +====================================================================+ | NOTICE | | An exception has occurred and has been transmitted to the coupling | | participants. These participants have been disconnected from the | | coupling service. | +====================================================================+

+====================================================================+ | System Coupling Exception | +====================================================================+ | Origin : Fluids Problem (Solution 1) | | Error Code : 2 | | Error Description : | | Fluent encountered fatal error after sync point Solve | +====================================================================+

System coupling run completed with errors.

The first block indicates that all co-simulation participants have been notified of the problem. The second block indicates the origin (that is, the coupling participant) of the failure, and an error code and description. For additional information, see Troubleshooting Two-Way Coupled Analyses Problems (p. 73).

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Best Practice Guidelines for Using System Coupling This chapter presents ideas to facilitate the successful setup and execution of a coupled analysis via the System Coupling infrastructure: Building up a Coupled Analysis from Decoupled Systems Troubleshooting Two-Way Coupled Analyses Problems Improving Coupled Analysis Stability

Building up a Coupled Analysis from Decoupled Systems Coupling otherwise independent analysis systems often introduces additional non-linearity to the solution and solution process. For this reason, it is strongly recommended that you verify that all of your constitutive analyses run independently before you systematically build up your one- and twoway coupled analyses. The independent analyses executed prior to coupled analysis should attempt to replicate the effects of the coupled problem as closely as possible. For fluid-structure interaction problems, for example, the fluid-only analysis could include user-specified motion that approximately models the expected motion (or range thereof ) from the structural analysis. Similarly, the structure-only analysis could include a userspecified load that approximately models the expected load (magnitude and distribution) from the fluid analysis. Prior to executing two-way coupled analyses, it is also strongly recommended that you execute a set of one-way coupled analyses. The benefits of building up coupled analyses this way include: • Augmenting the fully decoupled analyses proposed above with a more accurate approximation of the inputs expected from the independent analysis • Verifying the need for a two-way coupled analysis by assessing the sensitivity of the dependent analysis to inputs expected from the independent analysis For fluid-structure interaction problems, for example, loads exported from the fluid-only analysis could be applied in the structure-only analysis. If, under these conditions, a significant deformation due to the applied loads is observed, then a two-way coupled analysis may be appropriate. Note, however, that two-way coupled analyses are significantly more computationally expensive (by approximately an order of magnitude) than one-way coupled analyses. Execution of a two-way coupled analysis follows once fully decoupled and one-way coupled analyses are verified to run as expected and the need to execute a two-way coupled analysis is confirmed. Even at this point, however, difficulties may be encountered during the execution of the two-way coupled analysis due to the increased complexity of this problem. The following information will aid in debugging such analyses.

Troubleshooting Two-Way Coupled Analyses Problems Once any solution difficulties associated with executing fully decoupled and one-way coupled analyses have been addressed, a two-way coupled analysis may be attempted. The information presented in this

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Best Practice Guidelines for Using System Coupling section provides a summary of tools and strategies available to facilitate debugging two-way coupled analyses. These focus on text based and graphical monitor output, and supplemental output for visualization in ANSYS CFD-Post. For more information, see the following sections: Using Text-Based Monitor Output to Debug Coupled Analyses Using Graphical Monitor Output to Debug Coupled Analyses Using Supplemental Output to Debug Coupled Analyses Supplemental Output for Diagnosing Mapping Problems

Using Text-Based Monitor Output to Debug Coupled Analyses Text-based monitor output is contained in the System Coupling Log (SCL) file that is created in the run directory. Sections of the SCL file that are most relevant to the debugging process are identified below. If problems are encountered, you should carefully review all of these sections. • Setup Validation: This section facilitates review and verification of the input settings made for the system coupling service. These inputs are validated by the coupling service, and both warnings and errors generated during validation are reported here. Any automatic corrections applied to the inputs are listed with validation warnings. • Mapping Summary: This section summarizes the extent to which the source and target regions associated with each data transfer are correctly mapped onto one-another. Under normal conditions, diagnostics should report a nearly perfect mapping. Less than perfect mappings should be critically considered for their validity. • Coupled Solution Convergence History: This section summarizes the convergence of both the coupling participants and the data transfers that target each of the participants. It is strongly recommended that sufficient coupling iterations be executed, per step, to ensure that the field equations solved by all coupling participants and the data transfers defined for the coupled analysis converge fully. Note, however, that the coupling service will advance to the next coupling step, regardless of convergence, once the maximum number of coupling iterations per step has been executed. You are advised to identify and understand all reasons for poor convergence of coupling participants or data transfers. • Error Messages: Fatal errors are reported, as they occur, in the log output. These errors may have originated either within the coupling service itself or within any of the coupling participants. When such an error occurs, output from the service and all participants should be critically reviewed. • Shutdown Reporting: Under normal conditions, the end of the log output generated by the coupling service reports whether or not the coupled analysis completed successfully. When the analysis does not complete successfully, additional information is provided as to what may have caused the problem. For more information on the content of the SCL file see System Coupling Service Log File (scLog.scl_, scLog_##.scl) (p. 57). Note, as well, that supplemental debug output can also be written to the SCL file to facilitate debugging. This output is generated by adding debug output specifications to the system coupling setup. Similar output files often exist (either by default or by user request) for the coupling participants. For example, the ANSYS Fluent solver can generate a text based transcript file and the ANSYS Mechanical APDL solver can generate a text based output file. Please refer to Supported System Couplings (p. 3) for more information regarding the text based monitor output that they can generate.

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Troubleshooting Two-Way Coupled Analyses Problems

Using Graphical Monitor Output to Debug Coupled Analyses Graphical monitor output is provided in the form of charts within the System Coupling user interface. This output is most useful to quickly identify convergence problems. Once such problems are identified, a review of text monitor output is usually appropriate. Data that can be displayed in the system coupling chart includes: • Data transfer convergence and diagnostics, corresponding to the numerical data written to the system coupling log file. • Co-simulation participant convergence, most often corresponding to the (normalized) field equation convergence values from the solvers. Each co-simulation participant provides whatever convergence data it can. Different amounts of data may be available for charting from each co-simulation participant. Convergence data is collected from a co-simulation participant at the end of that participant’s solution during a given coupling iteration. In particular, the set of solver substep and solver iteration convergence data corresponding to the coupling iteration are updated all at once. If rapid divergence and failure of a solver occurs during a given coupling iteration, this information will not be included in the charted output for that iteration.

Using Supplemental Output to Debug Coupled Analyses At your request, the system coupling service will generate output that supplements the text-based and graphical monitor output. As discussed below, the supplemental output facilitates the diagnosis of mapping problems. Note that visualization of multi-dimensional features (for example, mesh interface regions) of a problem currently requires the use of an external viewer such as the Results component system (that is, CFDPost) in the ANSYS Workbench environment.

Supplemental Output for Diagnosing Mapping Problems Supplemental output, which is specifically aimed at diagnosing mapping problems, includes: • Data transfer source and target interface meshes. • A scalar field indicating (un)mapped nodes. To enable this output, create and set the expert setting DumpInterfaceMeshes to the value CFDPost. When this setting is made, one user surface definition file (in a comma separated value, CSV, format) will be generated by the coupling service during the mapping process for each source and target for each data transfer. This data is used in the CFD-Post application either using the "Import Surface or Line Data" functionality or by creating a user surface location directly from the definition file(s). Once the user surfaces associated with the source and target interface meshes are created in CFD-Post, they may be visually examined for consistency (for example, if the source and target surfaces or nodes are coincident). The surface may be colored by the ‘Unmapped’ variable, which will report values of 0 and 1 for unmapped and mapped nodes, respectively. This corresponds to blue and red, respectively, using the default color map.

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Best Practice Guidelines for Using System Coupling Unmapped nodes may also be visualized by inserting a point location with the Method set to Variable Minimum for the ‘Unmapped’ variable on the surface of interest. Attributes of the plotted points, such as the symbol shape and size, may be edited to facilitate visualization.

Improving Coupled Analysis Stability There are several ways to improve the stability of a coupled analysis: Data Transfer Ramping Participant Solution Stabilization Co-Simulation Participants Sequencing

Data Transfer Ramping In some cases, applying the full magnitude of data on the target side of data transfer interface will initiate oscillatory convergence or even divergence within and between the coupled co-simulation participants. For this reason, the target side data may be ramped from the final value observed in the previous coupling step (or zero during the first coupling step) to the full magnitude during the initial coupling iterations within the current step. For more information about ramping behavior and controls, see Data Transfers (p. 14). For more information about the algorithm used for System Coupling’s ramping, see Ramping Algorithm (p. 53).

Participant Solution Stabilization Solution instabilities that manifest as a very rapid divergence of the coupled analysis may arise if a given coupling participant is particularly sensitive to data obtained from another participant. In these cases, it may be advantageous to use various solution stabilization algorithms that have been implemented in the target participant. For an example of participant solution stabilization, refer to the dynamic mesh system coupling solution options used in ANSYS Fluent, described in System Coupling Motion in the Fluent User's Guide.

Co-Simulation Participants Sequencing In general, the driver of the physical problem should be processed first (that is, given a lower sequence index). If, in a fluid-structure interaction (FSI) simulation, the fluid flow (such as air flow around a wing) causes the structure (that is, the wing) to deform, then the fluid analysis should be first in the processing sequence. The System Coupling infrastructure allows the co-simulation of multiple coupling participants. In many cases, the execution (for example, solve) sequence of the co-simulation participants is inconsequential. In some cases, however, the sequence may affect solution stability and/or the time required to execute the complete coupled analysis.

Note To improve solution stability, sequential solutions are used by default. To facilitate synchronization of interface geometry, participants that consume geometrical or mesh deformations (e.g., the Fluids solver in a Fluid Structure Interaction analysis) are executed last.

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Improving Coupled Analysis Stability

Controlling Participant Sequencing Participant sequencing controls the order in which co-simulation participants collect data (as prescribed by defined data transfers) and execute their part of the coupled analysis. Ordering is specifically controlled by assigning a sequence index to each of the co-simulation participants. Participants with the smallest sequence index are processed first. If two (or more) participants are assigned the same sequence index, they are processed simultaneously (that is, required data is first collected from other participants, and then the participants all execute (for example, solve) simultaneously. Care is taken to ensure that the geometry and mesh are properly synchronized at the end of each coupling step for all co-simulation participants. This is required to ensure consistency during post-processing and during restarts. An extra ‘partial’ coupling iteration reprocesses all participants that are targets of deformation or motion-related data transfers. An extra partial iteration is executed once after all convergence targets are met or the maximum number of coupling iterations for the step is realized. A warning that extra partial iterations will be performed is provided in the validation output that follows the setup summary in the System Coupling Service Log File (scLog.scl_, scLog_##.scl) (p. 57). When an extra 'partial' coupling iteration is used to properly synchronize the interface geometry and mesh, there will be no noticeable change in the geometry and mesh during the first coupling iteration of the subsequent step. In this case, the system coupling chart output will have near-zero values for the change in motion for the related data transfer values.

Using Sequencing to Reduce Coupled Solution Execution Time As noted above, all co-simulation participants that share the same sequence index will collect data and execute their respective parts of the coupled analysis at the same time. This is a way of parallelizing the coupled solution process and potentially reducing the overall execution time of the coupled analysis. However, convergence difficulties (for example, more coupling iterations per step) and possible divergence may occur when multiple participants run simultaneously. This is because each participant in the group that is solved simultaneously collects and uses less up-to-date information from other participants. The stronger the physical coupling between each participant is, the more likely convergence difficulties will be encountered if the participants are processed simultaneously.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction In this tutorial you will learn how to solve a Fluid-Structure Interaction (FSI) case. You will model structural deformation in a fluid using System Coupling to coordinate the ANSYS Mechanical and ANSYS Fluent solvers. Component

Feature

Details

ANSYS Workbench

Analysis Systems

Transient Structural Fluid Flow (Fluent)

Component Systems Engineering Data

Defining new materials

DesignModeler

Geometry

Mechanical

Meshing

System Coupling Import

Defining the physics Named Selections Coupled analysis restart Coupled analysis batch execution from command line Meshing

Meshing

ANSYS Fluent

Defining the physics Coupled analysis restart Coupled analysis batch execution from command line

System Coupling

Defining the coupling Coupled analysis restart Coupled analysis batch execution from command line

CFD-Post

Plots

Vector

Animation This tutorial includes: Overview of the Problem to Solve Creating the Project Optional: Preparing for a Command-line Run Adding Analysis Systems to the Project Adding a New Material for the Project Adding Geometry to the Project Defining the Physics in the Mechanical Application Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction Setting up your Fluid Analysis Defining and Running the Coupling in the System Coupling Application Viewing Results in CFD-Post Setting Up and Executing a Coupled Analysis Restart from Workbench Executing the Coupled Analysis from the Command Line

Note In the main flow of the tutorial, you use the user interface to completely solve the simulation. However, at a series of points during the tutorial you have optional instructions that produce files that will enable you to solve the simulation from the command line. The steps related to this are: 1. 2. 3. 4. 5.

Optional: Preparing for a Command-line Run (p. 82) Preparing for a Command-Line Run of the Structural System (p. 90) Preparing for a Command-Line Run of the Fluent System (p. 97) Preparing for a Command-Line Run of the System Coupling System (p. 100) Executing the Coupled Analysis from the Command Line (p. 105)

If you do not want to solve the simulation from the command line, you may ignore those steps.

Overview of the Problem to Solve This tutorial uses an example of an oscillating plate within a fluid-filled cavity to demonstrate how to set up and run a simulation involving a two-way coupled analysis in ANSYS Workbench. A thin plate is anchored to the bottom of a closed cavity filled with fluid (air), shown in Figure 12: Dimensions of the oscillating plate case (p. 80). There is no friction between the plate and the side of the cavity. An initial pressure of 100 Pa is applied to one side of the thin plate for 0.5 s to distort it. Once this pressure is released, the plate oscillates back and forth to regain its equilibrium, and the surrounding air damps this oscillation. You will simulate the plate and surrounding air for a few oscillations to be able to observe the motion of the plate as it is damped. Figure 12: Dimensions of the oscillating plate case

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Creating the Project To simulate this case, you will set up a two-way Fluid-Structure Interaction (FSI) analysis. You will model the motion of the oscillating plate using the Mechanical application’s Transient Structural analysis system. You will model the motion of the fluid in the closed cavity using the Fluent application’s Fluid Flow (Fluent) analysis system. The two analyses are solved at the same time with the System Coupling system coordinating the solution process as well as the data transfers between the two analysis systems. The two-way coupling involves two data transfers: • Force data from the motion of the air is received by the Transient Structural analysis system as it solves the structural behavior over time. • Displacement data from the motion of the plate is received by the Fluid Flow (Fluent) analysis system as it solves the fluid behavior over time. The oscillation of the plate is dependent on time, and so you need to choose appropriate time values for the coupled transient analysis: • Time duration is the total time observed in the analysis. In this analysis, you will set the time duration to be 10 s, which is enough time to observe the plate oscillating a few times. With this time duration, you will not model the full damping back to the plate’s equilibrium. When setting up a transient analysis, make sure that you choose a time duration that will allow you to observe the behavior of interest in your system. • Time step is the size of the time increments that you are solving within your transient analysis. In this analysis, you will set the time step to be 0.1 s, which is fine enough to observe the oscillations to a reasonable degree. When setting up a transient analysis, make sure you choose a time step that works for the physics you are solving. Too large a time step will miss behavior of the system, and too small a time step will be computationally expensive.

Creating the Project Create the project by setting up Workbench and importing the project files: 1.

Start ANSYS Workbench: • To launch ANSYS Workbench on Windows, click the Start menu, then select All Programs > ANSYS 16.0 > Workbench 16.0. • To launch ANSYS Workbench on Linux, open a command line interface and enter the path to runwb2. For example: ~/ansys_inc/v160/Framework/bin/Linux64/runwb2 The Project Schematic appears with an Unsaved Project. By default, ANSYS Workbench is configured to show the Getting Started dialog box that describes basic operations in ANSYS Workbench. Click the [X] icon to close this dialog box.

2.

Create a directory where you will store your project (this is your working directory). For example, under My Documents, create a directory named SystemCouplingOscillatingPlate.

3.

Select File > Save or click Save

4.

Select the path to your working directory to store files created during this tutorial.

.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction 5.

Under File name, type SystemCouplingOscillatingPlate and click Save. The project files and their associated folder locations appear under the Files view. To make the Files view visible, select View > Files from the main menu of ANSYS Workbench.

6.

This tutorial uses the geometry file, oscillating_plate.agdb, for setting up the project. To access tutorials and their input files on the ANSYS Customer Portal, go to http://support.ansys.com/training. Copy the supplied geometry file, oscillating_plate.agdb, to the user_files directory that is in the SystemCouplingOscillatingPlate_files directory. By working with a copy of the geometry file in your working directory, you prevent accidental changes to the original geometry file.

Optional: Preparing for a Command-line Run This tutorial runs from within Workbench. However, you also have the option of taking files created from applications running in Workbench and performing a second system coupling run from a command line. If you want to try this alternative, follow the instructions below to prepare the locations where this second system coupling run will be performed. As you work through the tutorial in Workbench, you will be prompted to add source files from the applications running in Workbench to the directories you create here. To prepare a directory structure for executing the analysis from a command line: 1.

Create a high-level directory named SystemCouplingOscillatingPlate_CmdLine. This directory should be a sibling to SystemCouplingOscillatingPlate.

2.

In the SystemCouplingOscillatingPlate_CmdLine directory, create subdirectories within which the Mechanical APDL, Fluent, and System Coupling service executables will be run. Name these subdirectories: Structural_CmdLine, FluidFlow_CmdLine, and Coupling_CmdLine.

Adding Analysis Systems to the Project You are doing a two-way FSI analysis by coupling two analysis systems: a Transient Structural system and a Fluid Flow (Fluent) system. You will use the System Coupling system to couple the other two systems and to coordinate the solution execution. To add these three systems to your Workbench project: 1.

From the Analysis Systems toolbox located on the left side of the ANSYS Workbench window, select the Transient Structural template. Double-click the template, or drag it onto the Project Schematic to create a standalone system. A Transient Structural system is added to the Project Schematic, with its name selected and ready for renaming.

2.

Type in the new name, Structural, to replace the selected text. In this tutorial,“Structural system” will be used to refer to the Transient Structural system. If you missed seeing the selected text, right-click the first cell in the system and select Rename from the context menu. You will then be able to edit the name.

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Adding Analysis Systems to the Project 3.

Drag a Fluid Flow (Fluent) analysis system on top of the Structural system’s Geometry cell (A3) and drop it there. A Fluid Flow (Fluent) system, coupled to the Structural system, is added to the Project Schematic. This Fluid Flow (Fluent) system is connected to the Structural system through the Geometry cell (A3 to B2), and so both of these systems will share the same geometry.

4.

Change the name of this system to Fluid. In this tutorial,“Fluid system” will be used to refer to the Fluid Flow (Fluent) system.

5.

Expand the Component Systems toolbox, drag a System Coupling system and drop it to the right of the Fluid Flow (Fluent) system.

6.

Drag the Structural system's Setup cell (A5) and drop it on the System Coupling system’s Setup cell (C2).

7.

Drag the Fluid system's Setup cell (B4) and drop it on System Coupling system’s Setup cell (C2). Now all three systems are connected for a two-way FSI analysis.

8.

Save the project.

The Project Schematic should appear as shown in Figure 13: System Coupling of Transient Structural and Fluid Flow (Fluent) Systems (p. 83). Figure 13: System Coupling of Transient Structural and Fluid Flow (Fluent) Systems

The Structural and Fluid systems have various cells. The icons on the right side of each cell provides visual indications of a cell's state at any given time. In your current Project Schematic in Workbench (shown in Figure 13: System Coupling of Transient Structural and Fluid Flow (Fluent) Systems (p. 83)), most cells appear with a blue question mark ( ), indicating that cells need to be set up before continuing the analysis. As these cells are set up, the data transfer occurs from top to bottom. See Understanding Cell States for a description of various cell states. Now that your project systems are in place, you can start working through your analysis. Your current project systems enables you to perform your analysis by: • adding a new material, • sharing the geometry, • setting up the physics in the Structural system, Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction • setting up the physics in the Fluid system, • defining and running the coupling in the System Coupling system, and • viewing the results in CFD-Post.

Adding a New Material for the Project In the Project Schematic, the Structural system’s Engineering Data cell (A2) appears in an up-to-date state because default material is already available for the project. You will use material for the oscillating plate that is not in the default material available, and so you need to update this cell by adding this new material to the Engineering Data. The case requires a new material with properties that allow it to oscillate when pressure is applied. You will create a new material named Plate, define its properties to be suitable for oscillation, and set it as the default material for the analysis. 1.

On the Project Schematic, double-click the Engineering Data cell (A2) in the Structural system. Engineering Data opens in a new tab in Workbench. The Outline and Properties views are among the views that appear.

2.

In the Outline of Schematic A2: Engineering Data view, click the empty row at the bottom of the table to add a new material for the project. Type in the name Plate. When you click away from that cell, Plate is created and appears with a blue question mark, indicating that its properties need to be defined.

3.

From the Toolbox on the left, expand Physical Properties. Select Density and drag it onto the cell containing Plate (A4) in the Outline of Schematic A2: Engineering Data view. If the toolbox is not visible by default, select View > Toolbox to make it visible. Density is added as a plate property in the Properties of Outline Row 4: Plate view, as shown in the following figure.

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Adding Geometry to the Project

4.

In the Properties of Outline Row 4: Plate view, set the Value of Density (B2) to 2550 kg m^-3. Do not type in units.

5.

In the toolbox under Linear Elastic, drag Isotropic Elasticity onto Plate (A4) in the Outline of Schematic A2: Engineering Data view. Isotropic Elasticity is added as the plate property in the Properties of Outline Row 4: Plate view.

6.

In the Properties of Outline Row 4: Plate view, expand Isotropic Elasticity by clicking the plus sign. Now set Young’s Modulus to 2.5e06 [Pa] and Poisson’s Ratio to 0.35. Do not type in units.

The desired plate data is created and is available to the remaining cells in the Structural system. The next step is to set Plate as the default material for the analysis as outlined below: 1.

In the Outline of Schematic A2: Engineering Data view, under Material, right-click Plate (A4) and select Default Solid Material For Model.

2.

From the main menu, select File > Save to save material settings to the project.

3.

Close the Engineering Data tab to return to the Project Schematic.

Adding Geometry to the Project You will add geometry to your project by importing an existing DesignModeler file. Once you add the geometry, it will be shared between the Structural and Fluid systems because you have connected their geometry cells in the Project Schematic. All of the geometry parts have to be unsuppressed at this point in your project so that they are available for use later in the Structural and Fluid systems. 1.

On the Project Schematic, right-click the Structural system’s Geometry cell (A3) and select Import Geometry > Browse.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction 2.

In the Open dialog box, browse to your working directory, select SystemCouplingOscillatingPlate_files > user_files > oscillating_plate.agdb from your working directory, and click Open.

3.

In the Structural system, double-click the Geometry cell (A3) to edit the geometry using DesignModeler. The DesignModeler application opens in a separate window.

4.

In DesignModeler’s Tree Outline on the left, expand the branch 2 Parts, 6 Bodies to see all of the bodies that compose the geometry. The one solid body is listed, and under Part are the five fluid bodies. Ensure that all of these bodies are already unsuppressed (they should all have small green check marks).

5.

The geometry is set up for the project. Save any changes by selecting File > Save Project from the main menu in DesignModeler, and then select File > Close DesignModeler to return to the Project Schematic. The updated geometry is now available for both the Structural and Fluid systems.

Later in the tutorial, when you generate the structural mesh, the fluid bodies will first be suppressed. Similarly, when you generate the fluid mesh, the solid body will be suppressed. You will suppress these bodies from within the Mechanical and Meshing applications, so no further changes are needed in DesignModeler.

Note Because the Structural system’s Geometry cell (A3) shares its content directly with the Fluid system’s Geometry cell (B2), you can edit the geometry only through the Structural system’s Geometry cell (A3).

Defining the Physics in the Mechanical Application In the Mechanical application, you are setting up the structural analysis and defining the coupling interface. You will not solve the structural analysis from the Mechanical application because you will use the System Coupling system to solve both structural and fluid systems at the same time. When setting up your own two-way coupled analysis, it is a best practice to set up and solve the structural analysis within the Mechanical application before continuing with your coupled analysis. If issues occur within your structural system, the isolated analysis is easier to troubleshoot than the more complex coupled analysis. The structural Geometry cell (A3) is up-to-date, and so you start your setup by generating the structural mesh. This section describes the step-by-step definition of the structural physics: Generating the Mesh for the Structural System Assigning the Material to the Geometry Setting the Basic Analysis Values Inserting Loads Preparing for a Command-Line Run of the Structural System Completing the Setup for the Structural System

Generating the Mesh for the Structural System Generate the mesh for the Structural system directly in the Mechanical application:

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Defining the Physics in the Mechanical Application 1.

On the Project Schematic, double-click the Structural system’s Model cell (A4) to open the Mechanical application. The Mechanical application opens in a separate window.

2.

In Mechanical’s Outline on the left, expand Geometry to see the two geometries, solid and Part.

3.

For the structural analysis, you need to generate the mesh for only the solid body. To do this, you need to first suppress the Fluid bodies. Right-click the Part geometry (which contains all of the fluid bodies), and select Suppress Body. The fluid bodies are now suppressed and their status changes to an x mark. You now will see only the solid body in the Graphics view. Click Zoom to Fit view.

4.

5.

6.

to view the entire model in the Graphics

You will define the mesh by marking divisions on the edges of the solid. These divisions will be used as guides for the mesh creation: a.

Click Edge

.

b.

Click an edge that lies parallel to the X axis.

c.

In the Outline, right-click Mesh and select Insert > Sizing.

d.

Beside Type, select Number of Divisions from the drop-down menu.

e.

Beside Number of Divisions, select 1.

Repeat steps a to d to create 10 divisions on an edge that is parallel to the Y axis and 4 divisions on an edge that is parallel to the Z axis. To summarize: Edge Direction

Number of Divisions

X axis

1

Y axis

10

Z axis

4

In the Outline, right-click Mesh and select Generate Mesh from the shortcut menu. A hex mesh is generated on your solid body.

Assigning the Material to the Geometry When you defined the Plate material, you set it to be the default for your solid body. In the Mechanical application, you can see that this material is set correctly. 1.

In the Mechanical’s Outline on the left, select Project > Model > Geometry > solid.

2.

In the Details of “solid”, ensure that Material > Assignment is set to Plate. Otherwise, click the material name and use the arrow that appears to make the appropriate change.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction

Setting the Basic Analysis Values You now need to set up information about the transient analysis’ time steps, which are the basic analysis values needed for the transient structural analysis. The time duration (10 s) is chosen so that the plate oscillates a few times during the analysis. A single substep is used per coupling iteration. The coupling step size of 0.1s (which is also the size of the iterations) will be defined later in System Coupling. These time settings are dependent on the physics that you are observing, including the material properties of the plate. When setting your own transient analysis, make sure that you choose time settings appropriate to the physics you are solving. 1.

In the Mechanical application’s Outline view, select Project > Model > Transient > Analysis Settings. The details of Analysis Settings appear in the Details of “Analysis Settings” below the Outline view.

2.

In the Details of “Analysis Settings”, specify the following settings under Step Controls (do not type units next to the time values): 1.

Set Step End Time to 10.

2.

Set Auto Time Stepping to Off.

3.

Set Define by to Substeps.

4.

Set the Number of Substeps to 1.

Inserting Loads The loads applied for the structural analysis are equivalent to the boundary conditions in a fluid analysis. In this section, you will set the following loads and interface: • a fixed support on the bottom of the plate • a fluid-solid interface where the plate interacts with the fluid • a pressure load on one side of the plate, to start the oscillation On the surfaces of the plate that lie coincident with the symmetry planes, you will not set a load. With no load set, the default of an unconstrained condition will be applied on these two surfaces. For this particular case, this unconstrained condition is a reasonable approximation of the frictionless support that would otherwise be applied.

Defining the Fixed Support The fixed support is needed to hold the bottom of the thin plate in place. Set up the fixed support: 1.

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Right-click Transient in the Outline view, and select Insert > Fixed Support from the shortcut menu.

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Defining the Physics in the Mechanical Application

2.

Rotate the geometry using the Rotate then select Face

button so that the bottom (low-y) face of the solid is visible,

and click the low-y face.

That face is highlighted to indicate the selection. 3.

In the Details of “Fixed Support” view, click Apply beside Geometry to set the fixed support. If the Apply button is not visible, select Fixed Support in the Outline view and, in the Details view, click the text next to the Geometry setting to make the Apply button reappear. The text next to the Geometry setting changes to 1 Face.

Defining the Fluid-Solid Interface The fluid-solid interface defines the interface between the fluid in the Fluid system and the solid in the Structural system. Data will be exchanged across this interface during the execution of the simulation. When setting up your structural system for a coupled analysis, you need to define this interface on regions in the structural model that will receive force data from the Fluid system. 1.

In the Outline view, right-click Transient and select Insert > Fluid Solid Interface from the shortcut menu.

2.

Using the same face-selection procedure described earlier in Defining the Fixed Support (p. 88), select the three faces of the geometry that form the interface between the structural model and the fluid model (low-x, high-y and high-x faces). Hold down Ctrl to be able to select multiple faces.

3.

In the Details of “Fluid Solid Interface”, beside Geometry, click Apply. The text next to the Geometry setting changes to 3 Faces. Note that this load (fluid-solid interface) is automatically given an Interface Number of 1.

Defining the Pressure Load The pressure load on one side of the plate provides the initial pressure of 100 Pa for the first 0.5 s of the simulation. This pressure to the plate starts the oscillation. It is defined using tabular data. 1.

In the Outline view, right-click Transient in the tree view and select Insert > Pressure from the shortcut menu.

2.

In the Viewer, select the low-x face. In the Details of “Pressure” view beside Geometry, click Apply. The text next to the Geometry setting changes to 1 Face.

3.

In the Details of “Pressure” view, click the cell next to Magnitude, and using the arrow that appears, select Tabular. The Tabular Data view appears on the bottom right of the Mechanical application window. The times of 0 s and 10 s are the beginning and end of your analysis, based on the time duration (10 s) that you specified earlier.

4.

In Tabular Data, set a pressure of 100 Pa in the table row corresponding to a time of 0. Do not type in units. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction 5.

You now need to add two new rows to the table. Do this by typing the new time and pressure data into the empty row at the bottom of the table. Notice that the rows are automatically re-ordered based on the time value. Add the data from Table 4: Tabular Data for Step Pressure Load (p. 90). Table 4: Tabular Data for Step Pressure Load Time (s)

Pressure (Pa)

0

100

0.5

100

0.51

0

10

0

You now have tabular data similar to a step function for your pressure, with 100 Pa applied for 0.5 s. The step function is displayed in the graph to the left of the table. 6.

The settings for the structural physics are now complete. Save these settings by selecting File > Save Project from Mechanical’s main menu.

7.

If you do not intend to execute a command line run using the set up from the Mechanical system, proceed to Completing the Setup for the Structural System (p. 91). If you do intend to execute a command line run, continue with the next section.

Preparing for a Command-Line Run of the Structural System If you intend to execute a command-line run using the set up from the structural system: 1.

From the Mechanical application, select Tools > Write Input File.

2.

Specify the path and APDL Input File (SystemCouplingOscillatingPlate_CmdLine\structural.dat) that you will use later.

Tip The Write Input File option is available only if you have Transient (A5) selected in the Outline tree.

Note Though out of the scope of this tutorial, below is information about augmenting your structural setup, and transferring the structural setup from the Mechanical application to the Mechanical APDL application. • In some cases, you may need to augment your structural setup in the Mechanical APDL application. If this is the case, then open that application and select File > Read Input From to choose the .dat file created by Mechanical. Once the .dat file has been read, make your setup modifications and write a Mechanical APDL Database file using File>Save As Jobname.db or File >Save As. Starting the Mechanical APDL solver from the created database file is explained later in the tutorial.

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Setting up your Fluid Analysis • Transferring the structural setup from the Mechanical application to the Mechanical APDL application is facilitated in ANSYS Workbench. To do this, right-click the Mechanical system's Setup cell (A5), and select Transfer to New > Mechanical APDL. Once the new Mechanical APDL system is introduced, update the upstream Mechanical system's Setup cell (A5). The setup will be read into the Mechanical APDL user interface by right-clicking that system's Analysis cell and selecting Edit in Mechanical APDL.

Completing the Setup for the Structural System On the Project Schematic, the Structural system’s Setup cell (A5) appears in an update-required state. To complete the setup in the Structural system, you need to ensure that all the data is in the right state in the Project Schematic. 1.

In the Structural system, right-click the Setup cell (A5) and select Update from the shortcut menu. The status of the Setup cell changes to up-to-date. All cells in the Structural system down to the Setup cell should now appear in an up-to-date state.

2.

From the main menu, select File > Save to save the project.

The set up for the Structural system is complete. Remember that you will not solve the structural analysis from the Mechanical application because you are using the System Coupling system to solve both Structural and Fluid systems at the same time. In the next section, you will set up the Fluid system.

Setting up your Fluid Analysis You will use the Fluent application to set up your Fluid system, but first you need to generate the mesh using the Meshing application. The fluid Geometry cell (B2) is up-to-date because it shares the geometry with the structural analysis, and so you start your Fluid system’s setup with creating a mesh.

Generating the Mesh for the Fluid System You will generate a mesh for the Fluid system using the Meshing application. For this geometry, you will use a swept mesh across the x-y plane, creating a hex mesh with a depth of one element. 1.

In the Project Schematic, double-click the Fluid system’s Mesh cell (B3) to open the Meshing application. The Meshing application appears in a separate window.

2.

In the Meshing application’s Outline view on the left, expand Geometry to see the two geometries, solid and Part.

3.

For the fluid analysis, you need to generate the mesh for only the fluid bodies. To do this, you need to first suppress the structural body. Right-click solid and select Suppress Body The solid body is now suppressed and its status changes to an x mark. You now will only see the fluid bodies in the Graphics view.

4.

In the Outline on the left, click Mesh. In the Details of “Mesh” below, under Defaults, notice that the Physics Preference is set to CFD and Solver Preference is set to Fluent. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Now you need to define sweep as the meshing method, and set up all of the information that the sweep method needs: a.

In the Outline, right-click Mesh and select Insert > Method. Automatic Method will appear under Mesh

b.

Click Body , and then select all five fluid bodies in the Graphics view. Use the Ctrl key to select multiple bodies. Note that the fifth fluid body is very thin, and is above the plate.

c.

With all five bodies selected, in the Details of “Automatic Method” – Method, beside Geometry click No Selection. Click the Apply button that appears. The text next to Geometry changes to 5 Bodies.

d.

Under Definition, set Method to Sweep. Notice that in the Outline above, under Mesh, the method is now renamed to Sweep Method.

e.

In the Details of “Sweep Method” – Method, next to Src/Trg Selection, click Automatic. Using the arrow that appears, select Manual Source. Manual Source enables you to dictate which surfaces are used as the source for the sweep meshing. Source is highlighted, indicating that information about which surfaces to use is needed.

f.

Select Face , then Ctrl-select all five fluid faces on one of the walls in the x-y-plane (either side of the wall will work).

g.

In the Details view, beside Source, click No Selection. Click the Apply button that appears. The text next to Source changes to 5 Faces.

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Setting up your Fluid Analysis

6.

h.

Set Free Face Mesh Type to All Quad so that all of the mesh elements are quadrilateral.

i.

Next to Sweep Num Divs, set the value to 1.

j.

In the Outline above, click Mesh. In the Details of “Mesh”, expand Sizing and set Min Size to 0.06 and Max Face Size to 0.2. These settings control the size of the mesh elements that will be generated.

Now that all of the settings for your swept mesh are complete, you need to generate the mesh. In the Outline, right-click Mesh and select Update. The swept mesh that you have defined is now generated for your fluid bodies.

7.

Select File > Save Project, and then File > Close Meshing to close the Meshing application.

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Defining the Physics in the ANSYS Fluent Application In the Fluent application, you are setting up the fluid analysis, and defining the coupling interface. You will not solve the fluid analysis from the Fluent application because you are using the System Coupling system to solve both structural and fluid systems at the same time. When setting up your own two-way coupled analysis, it is a best practice to set up and solve the fluid analysis before continuing with your coupled analysis. If issues occur within your fluid system, the isolated analysis is easier to troubleshoot than the more complex coupled analysis. This section describes the step-by-step definition of the fluid physics: Adding the Solution Setup Settings Defining the Dynamic Mesh Adding the Solution Settings Preparing for a Command-Line Run of the Fluent System

Adding the Solution Setup Settings You now need to open your analysis in the Fluent application, set the Fluid analysis to be transient, and add material to the fluid geometry. 1.

In the Project Schematic, double-click the Fluid system’s Setup cell (B4) to open the Fluent application.

2.

The Fluent Launcher opens in a new window. Under Options, select Double Precision.

3.

Use the remaining default options (3D and serial), and click OK to close the Fluent Launcher. The Fluent application opens in a new window, and the mesh file is automatically loaded.

4.

On the left, select Setup > General. Under Time, click the Transient option.

5.

On the left, select Setup > Materials > Air to assign material to your geometry. Click the Create/Edit button, and in the dialog box that appears, for Density (kg/m3) type 1 and Viscosity (kg/m-s) type 0.2. Do not type units. Click Change/Create to save these changes, and then click Close.

6.

Under Setup > Models, note that by default, the viscous model is laminar and the energy model is turned off. No changes are needed to these settings.

Defining the Dynamic Mesh A dynamic mesh is needed for any coupled analysis where a system receives displacements. In this tutorial, the plate is oscillating back and forth, and the dynamic meshing settings determine how the mesh of the fluid bodies react to this deformation of the moving structural body. The mesh on the fluid-structural interface is static, so as the fluid mesh is modified to accommodate the deformation in the transient system, the mapping on this coupling interface stays consistent. Set up the dynamic mesh: 1.

On the left, select Setup > Dynamic Mesh.

2.

Check the Dynamic Mesh option in the panel. The settings for Dynamic Mesh are now available.

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Setting up your Fluid Analysis 3.

Under Mesh Methods, Smoothing is checked by default. Click the Settings button to specify the settings for the smoothing used. The Mesh Method Settings dialog box appears.

4.

a.

On the Smoothing tab, set Method to Diffusion.

b.

For the Diffusion Parameter, type 2. Click OK to close the dialog box.

Under Dynamic Mesh Zones, click Create/Edit to specify which zones in your geometry will have dynamic meshing. The Dynamic Mesh Zones dialog box appears.

5.

Define the dynamic mesh settings needed for the surface “symmetry1”, which is the wall in the x-y plane that goes through the origin. This surface will be affected by the solid body’s displacement, and its mesh needs to be able to deform. a.

In the Dynamic Mesh Zones dialog box, under the Zone Names drop down list, select the zone “symmetry1”.

b.

Set its Type as Deforming.

c.

Select the Geometry Definition tab.

d.

Specify the Definition as “plane”.

e.

Specify Point on Plane as 0,0,0

f.

Specify Plane Normal as 0,0,1

g.

Click Create at bottom of dialog box to create this dynamic mesh zone. The list of Dynamic Mesh Zones on the right side of the dialog box now includes the “symmetry1”.

6.

Define the dynamic mesh settings needed for the surface “symmetry2”, which is the second wall in the x-y plane. This surface will be affected by the solid body’s displacement, and its mesh needs to be able to deform. a.

Under the Zone Names drop down list, select the zone “symmetry2”.

b.

Set its Type as Deforming.

c.

Select the Geometry Definition tab.

d.

Specify the Definition as “plane”.

e.

Specify Point on Plane as 0,0,0.4

f.

Specify Plane Normal as 0,0,1

g.

Click Create at bottom of dialog box to create this dynamic mesh zone. The list of Dynamic Mesh Zones now includes the “symmetry2”. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Define the dynamic mesh settings needed for the surface “wall_bottom”, which is the two surfaces on the bottom of the fluid zones (the two surfaces are interrupted by the solid body in the middle of the geometry). This surface is not affected by the solid body’s displacement, and so its mesh should remain stationary. a.

Under the Zone Names drop down list, select the zone “wall_bottom”.

b.

Set its Type as Stationary, then click Create at bottom of dialog box to create this dynamic mesh zone. The list of Dynamic Mesh Zones now includes the “wall_bottom”.

8.

Repeat the previous step's instructions to create stationary dynamic mesh zones for the three surfaces below. These three surface complete the enclosed cavity, and they are not affected by the solid body’s displacement. Their mesh should remain stationary. • “wall_top” • “wall_side1” • “wall_side2”

9.

Define the dynamic mesh settings needed for the surfaces in the zone “wall_deforming”, which are the surfaces surrounding the solid body. These surface will deform throughout the simulation. a.

Under the Zone Names drop down list, select the zone “wall_deforming”.

b.

Set its Type as System Coupling, then click Create at bottom of dialog box to create this dynamic mesh zone. The list of Dynamic Mesh Zones now includes the “wall_deforming”.

10. You now have seven dynamic mesh zones defined and listed on the right of the dialog box. Click Close.

Adding the Solution Settings Set the solutions settings in the Fluent application so that your fluid system is ready to be solved: 1.

On the left side of the Fluent application, select Solution > Solution Methods. a.

Under Pressure-Velocity Coupling > Scheme, select Coupled.

b.

Under Spatial Discretization > Momentum, ensure Second Order Upwind is selected.

2.

On the left side of the Fluent application, select Solution > Calculation Activities, then specify Autosave Every (Time Steps) to be 2.

3.

On the left side of the Fluent application, select Solution > Run Calculation, then: a.

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Specify Number of Time Steps to be 10. Note that the system coupling’s number of time steps will override this value.

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Defining and Running the Coupling in the System Coupling Application b.

Specify the Max Iterations/Time Step to be 5. This value is the maximum amount of times that Fluent can iterate within a coupling iteration.

c.

Leave the default Time Step Size (s) as 1, but note that the system coupling’s time step size will override this value.

4.

On the left side of the Fluent application, select Solution > Solution Initialization. Under Initialization Methods, ensure the Standard Initialization option is selected.

5.

In Solution > Solution Initialization, click Initialize.

6.

Save the project.

7.

If you intend to execute a command line run using the setup from the Fluent system, go to Preparing for a Command-Line Run of the Fluent System (p. 97).

8.

If you do not intend to execute a command line run using the setup from the Fluent system, Select File > Close Fluent to close Fluent and to return to the Project Schematic. The setup for the Fluid system is complete. Remember that you will not solve the fluid analysis from the Fluent application because you are using the System Coupling system to solve both structural and fluid systems at the same time. In the next section, you will set up the System Coupling system. Proceed to the section Defining and Running the Coupling in the System Coupling Application (p. 97).

Preparing for a Command-Line Run of the Fluent System If you intend to execute a command line run using the set up from the Fluent system, select File > Export > Case from the main menu in the Fluent user interface, and specify the path and Case File (SystemCouplingOscillatingPlate_CmdLine\fluidFlow.cas) that you will use later.

Important You should perform this step before updating the coupled solution within the Workbench environment for the following reasons: • Editing the Fluent system’s Setup cell after a solution is executed will clear all existing solution files. • Editing the Fluent system’s Solution cell after a solution is executed will load the most recent (rather than the original) case and data files.

You may now close Fluent.

Defining and Running the Coupling in the System Coupling Application In the System Coupling system, you are setting up the coupling between your Structural and Fluid analyses. You will use the System Coupling system to solve both of these analyses at the same time. Notice that in the Structural and Fluid systems, all of the cells up to Setup are marked as up-to-date. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Setting the Basic Analysis Values To set up the transient analysis settings for your coupled analysis: 1.

In the Project Schematic, double-click the System Coupling system’s Setup cell (C2). In the dialog box, click Yes to allow upstream data to be read. The System Coupling system is obtaining data from the Structural and Fluid systems’ Setup cells (A5 and B4). The System Coupling application opens in a new tab in your Workbench project.

2.

In Outline of Schematic C1: System Coupling, select System Coupling > Setup > Analysis Settings.

3.

In Properties of Analysis Settings (on the bottom left): a.

Set Duration Controls > End Time to 10. The end time is the same as the Structural system’s time duration. The choice of 10 s gives enough time to observe the plate oscillating a few times. System Coupling’s end time value always overrides the number of time steps specified in the Fluent application.

b.

Set Step Controls > Step Size to 0.1. The coupling iteration size is same as the transient analysis’ time step, and the choice of 0.1 s is small enough for use to observe the plate’s oscillations to a reasonable degree. System Coupling’s step size value always overrides the time steps size specified in the Fluent application.

c.

Ensure the Maximum Iterations is set to 5. For this system to converge, 5 coupling iterations within each coupling step is sufficient. If your own system has trouble converging within the coupling step, you may want to increase the number of maximum iterations or reduce the time step size.

Creating the Data Transfers For your two-way coupled analysis, data from the Structural and Fluid solutions need to be shared throughout the solution process. System Coupling coordinates the transfer of data between these two systems using the Data Transfers that you create. 1.

In Outline of Schematic C1: System Coupling, expand System Coupling > Setup > Participants until all region components are visible.

2.

Ctrl-select the "wall_deforming" (from the Fluid system) and "Fluid Solid Interface" regions (from the Structural system). With both selected, right-click on one of those regions and select Create Data Transfer. Under System Coupling > Setup > Data Transfers, Data Transfer and Data Transfer 2 are created:

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a.

Data Transfer:here, the surface of the Structural system around the plate transfers displacement to the surface of the Fluid system around the plate.

b.

Data Transfer 2: here, the surface of the Fluid system around the plate transfers force to the surface of the Structural system around the plate. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

Defining and Running the Coupling in the System Coupling Application Click on System Coupling > Setup>Data Transfers > Data Transfer. In the Properties of DataTransfer on the bottom left, notice that the source, target and variable transferred are already defined for each of these data transfers. These settings are also already defined for Data Transfer 2.

Preparing System Coupling for Restarts You should ensure that System Coupling is producing restart data, in the event that the System Coupling analysis needs to be restarted. 1.

Under System Coupling > Setup > Execution Control, select Intermediate Restart Data Output. The restart output frequency for the system coupling analysis is defined and controlled by these settings.

2.

In Properties of Intermediate Restart Data Output: • Set Output Frequency to At Step Interval. • Set Step Interval to 5.

3.

Select File > Save to save your settings before solving.

Note Recall that earlier, the Fluent auto-save frequency was set to 2 so that Fluent will output result files (case and data files) every two time steps (that is, 2, 4, 6, 8, 10, etc.). Fluent will also output additional result files at 5, 10, 15, 20 etc. based on the Step Interval frequency specified for the Intermediate Restart Data Output. In CFD-Post, both sets of files will be available for post-processing.

Solving and Restarting the Coupled Analysis During the solution process, the System Coupling system coordinates the solving of your Structural and Fluid systems as well as the data transfers between these two systems. The Fluid system solves using the Structural solution’s displacement data, and the Structural system solves using the Fluid solution’s force data. 1.

To start solving the coupled analysis, in Outline of Schematic C1: System Coupling, right-click Solution and select Update. The solution progress begins, and progress is summarized in the System Coupling Chart and Solution Information views, as well as the Workbench schematic progress view. This solution will run for 100 coupling steps because you specified an end time of 10 s in System Coupling (“time duration” in Mechanical), and each coupling step represents 0.1 s (“step size” in System Coupling, and “time step” in Mechanical). Note that you can alternatively start solving the coupled analysis from Workbench’s Project Schematic: a.

To return to the Project Schematic, click on the Project tab in Workbench. To start the solution process from the Project Schematic view, right-click the System Coupling system’s Solution cell (C3) and choose Update.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction Notice that the Structural and Fluid systems’ Solution cells’ (A6 and B5) update operations are disabled because the coupled solution process must be run through the System Coupling system. b.

Click on the System Coupling tab to return to the System Coupling system and observe the coupled solution progress. If you closed the System Coupling application and so there is no System Coupling tab, you can re-open the System Coupling user interface by double-clicking on its Solution cell (C3).

2.

On the bottom right of the screen, click on Show Progress to see the progress of your solution.

3.

As your analysis is solved, in the Solution Information view, information from the System Coupling Log file is displayed. Useful information includes: a.

Each coupling step and coupling iteration is recorded with information about convergence of the data transfer.

b.

At the beginning of the file (scroll up in your Solution Information view), there is an overview of the participants (the Fluid and Structural system), the data transfers, the System Coupling settings, and a mapping summary.

c.

The Mapping Summary has information about the percentage of nodes on your fluid-structure interface that are mapped. This information is used to determine the quality of the mapping in your system.

4.

Restart data will be output during the solution process. An additional note will be seen in the System Coupling log output under Solution Information indicating the name and frequency of the system coupling result file. For example, the intermediate result file is written: scResult_01_000005.scr. The restart data for Fluent will also be output at the same frequency during the coupled solution. When the coupled solution completes, Mechanical restart files (that is, file.r001, file.r002 etc.) will be visible in the Workbench project files (that is, they are automatically transferred from the solver temporary/scratch folder). The file naming convention is such that file.r001 refers to a Mechanical restart file at step 5, file.r002 refers to a Mechanical restart file at step 10, and so on.

5.

The System Coupling solution is complete when the System Information view reads “System coupling run completed successfully.”

6.

Select File > Save to save the project, and then click on the Project tab to return to the Project Schematic.

Preparing for a Command-Line Run of the System Coupling System If you intend to execute a command-line run using the setup from the System Coupling system, you need to export the System Coupling Input (SCI) file. To do this: 1.

In your Project Schematic, make sure that the System Coupling Setup cell (C2) is in an up-to-date state.

2.

If your System Coupling tab is not open, double-click System Coupling’s Setup cell (C2).

3.

From the System Coupling tab, in the main menu, select File > Export SCI File.

4.

Specify the path and SCI file (SystemCouplingOscillatingPlate_CmdLine\coupling.sci) that you will use later.

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Viewing Results in CFD-Post 5.

Select File > Save to save the project, and then click on the Project tab to return to the Project Schematic.

Viewing Results in CFD-Post You will use CFD-Post to view the results of your coupled analysis. You have simulated the plate oscillating in a closed cavity filled with air. The results you have obtained show the plate and surrounding air for a few oscillations, and you will be able to use CFD-Post to see the motion of the plate as it is damped. In Workbench, you need to set up the Project Schematic so that CFD-Post can read the solution of your Structural and Fluid systems. To view the results in CFD-Post: 1.

In the Project Schematic, drag the Structural Solution cell (A6) to the Fluid Results cell (B6).

2.

Double-click the Fluent Results cell (B6) in the Fluid system to launch CFD-Post. CFD-Post opens in a new window. Both sets of results are loaded into the CFD-Post session, and are ready for you to view.

Creating an Animation An animation is a good way to view results in a transient analysis. In this animation, you will show: • The pressure and velocity of the fluid on the symmetry plane • The deformation of the plate geometry, with stress visible Set up your animation: 1.

From the task bar at the top of the CFD-Post application, select Tools > Timestep Selector to open the Timestep Selector dialog box. The Timestep Selector dialog box shows the results time history for both Fluent and MAPDL system coupling.

2.

In the Timestep Selector dialog box, on the Fluid tab, select a Time of 0.2 s for the Fluid case, then click Apply. Close the Timestep Selector dialog box.

3.

Under Cases > Fluid at 0.2s > Part Fluid, check the “symmetry1” zone under the Fluid case to display that zone, then double-click to edit it. a.

In Details of symmetry1, on the Color tab set the Mode to Variable and set Variable to Pressure.

b.

On the Render tab, clear the Lighting check box and check Show Mesh Lines.

c.

Click Apply to save your changes. The pressure at 0.2 s is now visible on the one side of the fluid geometry.

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5.

Under Cases > Structural at 0.2s > Default Domain, check the Default Boundary zone, then doubleclick to edit it. a.

In the Details of Default Boundary, on the Color tab, set the Mode to Variable and set Variable to Von Mises Stress.

b.

On the Render tab enable Show Mesh Lines.

c.

Click Apply. Stress is now visible on the structural body.

From the task bar at the top of the CFD-Post application, select Insert > Vector to create a vector plot. Accept the default name and click OK. a.

In the Details view on the Geometry tab, set the Locations to symmetry1, set Sampling to Face Center, and ensure that Variable is set to Velocity.

b.

On the Symbol tab, set Symbol to Arrowhead3D.

c.

Click Apply. A vector plot of the velocity is now visible on the one side of the fluid geometry.

6.

In the Outline under User Locations and Plots, clear the Default Legend View 1 check box.

7.

From the task bar at the top of the CFD-Post application, select Insert > Text and click OK to accept the default name. a.

In the Details of Text 1 view, for Text String, type Time = . Check the Embed Auto Annotation, and from the Expression drop-down list select Time.

b.

On the Location tab, set X Justification and Y Justification to None, and set the Position text as 0.1 in the first field, and 0.2 in the second field.

c.

Click Apply.

The corresponding transient results are loaded into the Animation in CFD-Post, and when you run the animation, you can see the mesh move in both the Fluent and Mechanical regions. 1.

Zoom in so that you can see the oscillating plate clearly.

2.

At the top of the CFD-Post application, click Animation

.

The Animation dialog box appears. 3.

Select Keyframe Animation.

4.

In the Animation dialog box:

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a.

Click New

to create KeyframeNo1.

b.

Highlight KeyframeNo1, then change # of Frames to 48.

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Viewing Results in CFD-Post c.

Load the last timestep (100) using the Timestep Selector face).

d.

Back in the Animation dialog box, click New

(found at the top of the CFD-Post Inter-

to create KeyframeNo2.

The # of Frames parameter has no effect for the last keyframe, so leave it at the default value. e.

Click the More Animation Options button

f.

Click Browse

, then check the Save Movie check box.

next to Save Movie to set a path and file name for the movie file.

If the file path is not given, the file will be saved in the directory from which CFD-Post was launched. g.

Click Save. The movie file name (including path) will be set, but the movie will not be created yet.

h.

If frame 1 is not loaded (shown in the F: text box in the middle of the Animation dialog box), click To Beginning

to load it.

Wait for CFD-Post to finish loading the objects for this frame before proceeding. i.

Click Play the animation

.

The movie will be created as the animation proceeds. This process will be slow, since a timestep must be loaded and objects must be created for each frame. j.

Save the results by selecting File > Save Project from the main menu.

k.

Close the animation dialog box. Your animation is now saved in the file path you specified. You can play the video in any media player.

Plotting Results on the Solid You will use a chart to display the deformation of the solid body. One point at the top of the plate is used to track the displacement in the chart. This chart is a useful way to view the damping that occurs in the plate’s motion due to the interaction with the fluid. 1.

Create a point in the solid domain by using node number 77. This point is at the top corner of the solid body, and will be used to track the deformation of the plate. a.

From the task bar at the top of the CFD-Post application, select Insert > Location > Point. Click OK to accept the default name.

b.

In the Details view, on the Geometry tab, set Domains to Default Domain, set Method to Node Number, and set Node Number to 77.

c.

Click Apply. On your model, cross hairs appear on node number 77, so you can see where this point is on your solid body.

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3.

To view the deformation using the point you just created, insert an XY Transient Chart for the data at this node (“Point 1”). In the chart you create, the x-axis is time, and the y-axis is the total mesh displacement. a.

From the task bar at the top of the CFD-Post application, select Insert > Chart; click OK to accept the default name.

b.

In the Details view, on the General tab, set Type to XY - Transient or Sequence

c.

On the Data Series tab, for Name type System Coupling, and set Location to Point 1.

d.

On the X Axis tab, ensure that the Expression is Time.

e.

On the Y Axis tab, set the Variable to Total Mesh Displacement X.

Click Apply to generate the chart of mesh displacement over time. After the chart is generated, note the damping that is visible in the plate’s motion. The plate does not return to equilibrium in this chart because of the length of time we chose for the simulation of this case. To see the full damping of the system, you would need to simulate the case for a longer time duration.

4.

Save the project and then select File > Close CFD-Post.

Post-Processing in Mechanical You can also see the structural results of your FSI analysis in the Mechanical application. Note that the Mechanical system does not have any information about results on the fluid bodies. 1.

From the Project Schematic, double-click the Results cell (A7) to relaunch ANSYS Mechanical. The Mechanical application opens in a new window.

2.

In the Outline view, right-click Solution A6 and select Insert > Stress > Equivalent (von Mises) results.

3.

Right-click Solution A6 again and select Insert > Deformation > Directional results.

4.

Right-click Solution A6 again and select Evaluate All Results. The equivalent stress and directional deformation of the place are now visible on your model.

5.

Under Solution A6 click Equivalent Stress to view the stress on the structural body.

6.

Under Solution A6 click Directional Deformation to view the deformation of the structural body.

7.

From your Project Schematic, save the project.

All systems are now complete and the Project Schematic is up-to-date.

Setting Up and Executing a Coupled Analysis Restart from Workbench 1. In the Mechanical application, a. Under Project > Model > Transient, select Analysis Settings. b. In Analysis Settings Details, set Restart Type to Manual. 104

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Executing the Coupled Analysis from the Command Line c. In Analysis Settings Details, set Current Restart Point to Load Step 50, Substep 1 (that is, 5s). d. Close ANSYS Mechanical. 2. From the Project Schematic, double-click the Fluid Solution cell (B5): a. From the File menu, select Solution Files.... b. In the Solutions Files dialog box that appears, click on 100 time steps, 10s - Current to deselect it, and then click on 50 time steps, 5s to select this time step. c. Select the Read button. Fluent will read in the case/data file associated with 5s. d. Close Fluent. 3. From the Project Schematic, double-click the System Coupling Setup cell (C2): a. From the outline, select Setup > Analysis Settings. b. In Properties of Analysis Settings, under Initialization Controls, from the Coupling Initialization drop-down list, select Step 50, Time 5[s]. c. Optional: Under Execution Control > Intermediate Restart Data Output, set Output Frequency to None. If this is not done, there will be a second set of restart files output under the Workbench project. 4. To start solving the coupled analysis restart, right-click the Solution branch in Outline of Schematic C1: System Coupling, and select Update. A summary of the solution progress in the System Coupling Chart (starting from 5s) and Solution Information views (also starting from 5s), as well as the Workbench Schematic Progress view. 5. Once your solution is complete, select File > Save to save your project. 6. You have now used the Workbench, Fluent, Mechanical, and System Coupling interfaces to complete this tutorial’s simulation. If you would like to complete the optional steps to run this tutorial using the command line, continue with Executing the Coupled Analysis from the Command Line (p. 105). Otherwise, you are now finished Oscillating Plate with Two-Way Fluid-Structure Interaction tutorial. When you are finished viewing your results, and select File > Save from the main menu, and then File > Exit to close your Workbench project.

Executing the Coupled Analysis from the Command Line This section describes how to execute the analysis for this tutorial from the command line. In this example, all executables are run in batch mode (there are no user interfaces or launchers) from a standard installation on a single Windows 64-bit machine.

Note In order to be able to execute runs from the command line, all executables and dynamic library dependencies must be properly resolved. For more information, see Executing System Couplings Using the Command Line.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction

Preparing the Required Input Files Runs executed from the command line require input files for each of the executables used in the coupled analysis. 1.

If you have not been creating the input files for the command-line analysis as you worked through the tutorial, then follow the instructions in Optional: Preparing for a Command-line Run (p. 82) to create the file structure for the command-line run.

2.

If you have not been creating the input files for the command-line analysis as you worked through the tutorial, then follow directions in the sections referenced below and create the listed input files in the SystemCouplingOscillatingPlate_CmdLine directory:

3.

a.

Create the file structural.dat according to Preparing for a Command-Line Run of the Structural System (p. 90).

b.

Create the file fluidFlow.cas according to Preparing for a Command-Line Run of the Fluent System (p. 97).

c.

Create the file coupling.sci according to Preparing for a Command-Line Run of the System Coupling System (p. 100).

An additional input file is required to execute the Fluent solver in batch mode. In the SystemCouplingOscillatingPlate_CmdLine directory, create a journal file named fluidFlow.jou that contains the following: file/start-transcript "Solution 1.trn" file set-batch-options , yes , file/read-case/fluidFlow.cas s i i (sc-solve) wcd FLUENTRestart.cas.gz exit ok

Running the Analysis To run the analysis: 1.

Open a command window, and from the SystemCouplingOscillatingPlate_CmdLine\Coupling_CmdLine subdirectory, run System Coupling service using the following command: "C:\Program Files\ANSYS Inc\v160\aisol\bin\winx64\Ansys.Services.SystemCoupling.exe" –inputFile ..\coupling.sci

Tip You may prefer to add the previous command to a batch file. Now when you run the System Coupling service command, the coupling service starts and creates the System Coupling Server File (SystemCouplingOscillatingPlate_CmdLine\Coupling_CmdLine\scServer.scs). For details, see Files Generated by Coupling Service (p. 56). 2.

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Open scServer.scs and review its contents, which will be similar to the following:

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Executing the Coupled Analysis from the Command Line 12345@yourmachine 2 Solution Structural Solution 1 Fluid

where: • 12345 is the server port • yourmachine is the host's name • 2 indicates that two participant connections are expected • The unique names to be used when starting the structural and fluid flow solvers are, respectively: "Solution" and "Solution 1". The unique names from the solver(s) are encoded in the coupling service input file and are reported here along with the names of the systems in the Workbench schematic. Note this correlation, since the unique names are needed when starting the respective solvers. Note, as well, that the unique names are determined by Workbench and can vary depending upon the order in which systems were introduced into the schematic. 3.

Copy the fluidFlow.cas file into the FluidFlow_CmdLine subdirectory. This step ensures that Fluent treats that subdirectory as the run directory, and generates all subsequent case and data files there. By keeping the basic input files separate from the run directories, you can easily clear or delete the run directories for retries.

4.

From a new command window, change to the FluidFlow_CmdLine subdirectory, then run the Fluent solver by entering the following command: "C:\Program Files\ANSYS Inc\v160\fluent\ntbin\win64\fluent.exe" 3ddp -hidden -driver null -scport=12345 -schost=yourmachine -scname="Solution 1" -i ..\fluidFlow.jou>FLUENT.out

5.

From a new command window, change to the Structural_CmdLine subdirectory, then run the Mechanical APDL solver by entering the following command: "C:\Program Files\ANSYS Inc\v160\ansys\bin\winx64\ANSYS160.exe" -b -scport 12345 -schost yourmachine -scname "Solution" -i ..\structural.dat -o ANSYS.out

Note • In steps 4 and 5 above, you may need to adjust the coupling service port and host (12345 and yourmachine, respectively) and solvers' unique names ("Solution" and "Solution 1" for the Mechanical APDL and Fluent solvers, respectively) based upon information extracted from the system coupling server file. • The input file name, structural.dat, will need to be replaced with the name of the manually-created input file (e.g. mapdl.dat) if such a file was created to enable a resume from a Mechanical APDL database file.

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Tutorial: Oscillating Plate with Two-Way Fluid-Structure Interaction

Restart Analysis Execution For the sake of simplicity, the restart analysis uses the same solver and coupling service directories in which the initial analysis was performed.

Preparing the Required Input Files In the SystemCouplingOscillatingPlate_CmdLine directory, create the following: 1.

Create a restart journal file for the Fluent solver. Name this file fluidFlowRestart.jou, and have it contain the following: file/start-transcript "Solution 2.trn" file set-batch-options , yes , rcd/fluidFlow-1-00050.cas (sc-solve) exit ok

Note The "-1-" in the file name fluidFlow-1-00050.cas represents the run number and may be different in your system, depending upon how many runs were completed before writing the .cas file.

2.

Create a restart input file for the Mechanical APDL solver. Name this file structuralRestart.dat, and have it contain the following: /batch /solu /gst,on,on antype,4,rest,50,1,continue solve save finish /exit

Run the Analysis Much as when you ran the initial analysis: 1.

Open a command window, change to the Coupling_CmdLine subdirectory, and run the System Coupling service using the following command: "C:\Program Files\ANSYS Inc\v160\aisol\bin\winx64\Ansys.Services.SystemCoupling.exe" –inputFile ..\coupling.sci –resultFile scResult_01_000050.scr

2.

Open the system coupling server file (scServer.scs) and note the coupling server’s port and host. Note that the solvers’ unique names have not changed because they are encoded in the coupling service’s input file.

3.

Change to the FluidFlow_CmdLine subdirectory, and run the Fluent solver by entering the following command: "C:\Program Files\ANSYS Inc\v160\fluent\ntbin\win64\fluent.exe" 3ddp -hidden -driver null -scport=12345 -schost=yourmachine -scname="Solution 1" -i ..\fluidFlowRestart.jou>FLUENTRestart.out

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Executing the Coupled Analysis from the Command Line 4.

Change to the Structural_CmdLine subdirectory, and run the Mechanical APDL solver by entering the following command: "C:\Program Files\ANSYS Inc\v160\ansys\bin\winx64\ANSYS160.exe" -b -scport 12345 -schost yourmachine -scname "Solution" -i ..\structuralRestart.dat -o ANSYSRestart.out

Note In steps 3 and 4 listed above, you may need to adjust the coupling service port and host (12345 and yourmachine, respectively) and solvers' unique names ("Solution" and "Solution 1" for the Mechanical APDL and Fluent solvers, respectively) based upon information extracted from the system coupling server file.

Loading the Results into CFD-Post To load the Results files into CFD-Post: 1.

To start CFD-Post, from the Start menu, go to Start > All Programs > ANSYS 16.0 > Fluid Dynamics > CFD-Post 16.0.

2.

From CFD-Post, select File > Load Results.

3.

Open the final CAS file, which will have a name similar to FluidFlow_CmdLine\fluidFlow-100100.cas.

4.

Again select File > Load Results.

5.

In the dialog box that appears, select Keep current cases loaded, and clear Open in new view.

6.

Open the file Structural_CmdLine\file.rst. When post-processing results, your structural results are named after the name of the file they are loaded from. From this command line run, your structural results will appear under the name “file” (because of file.rst).

7.

Proceed to Viewing Results in CFD-Post (p. 101) for instructions on how to post-process the results. When following these instructions, remember that your command line structural results will appear under the name ”file”, and not “Structural”.

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Tutorial: Heat Transfer from a Heating Coil In this tutorial you will learn about executing a sequence of one-way thermal transfers in a heat exchanger using the System Coupling infrastructure. Component ANSYS Workbench

Feature Analysis Systems

Details Steady State Thermal Fluid Flow (Fluent)

Component Systems

System Coupling External Data

DesignModeler

Geometry and Named Selections

Steady State Thermal

Defining the physics

ANSYS Fluent

Defining the physics

System Coupling

Defining the coupling

CFD-Post

Case Comparison

Import

Compare film coefficients Examine temperatures and temperature distributions

This tutorial includes: Overview of the Problem to Solve Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis Part 2: Transferring Data from the Fluid Flow Analysis to the Steady-State Thermal Analysis

Overview of the Problem to Solve In this tutorial, a variety of ANSYS Workbench systems are used to analyze conjugate heat transfer in a simple heat exchanger. The heat exchanger involves the coupling of solid and fluid models. The solid model consists of a copper alloy heating coil and the fluid model consists of an annular region with flowing water that envelops the coil. A constant heat generation source of 8.72 e+6 W/m3 is specified for the coil and the heat generated is made to convect away from its surface by water flowing at a nominal speed of 0.4m/s.

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Tutorial: Heat Transfer from a Heating Coil

The tutorial is divided into two parts. In the first part, the convective heat transfer experienced by the heating coil is estimated and the steady-state thermal analysis is executed for the solid model. The resulting temperature from the coil surface is then used to execute the fluid analysis. In the second part of the tutorial, the thermal analysis for the solid model is also executed, however the convective heat transfer obtained from the fluid analysis is used instead of the original estimate. In a case such as the one described here, there are advantages to using one-way data transfer instead of conjugate heat transfer or two-way analysis. One-way data transfer works well when separate groups are performing the computational fluid dynamics analysis and the thermal finite element analysis. The individual solutions are simpler with a one-way analysis than they would be with a two-way coupled analysis. Another advantage of one-way data transfer is that it provides a more flexible workflow; any thermal variable of interest can be transferred. Coordinate transformations can also be applied when using one-way data transfer.

Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis This part of the analysis has the following steps: Creating the Project Adding Analysis and Component Systems Adding New Materials for the Project Adding Geometry to the Project Preparing the Steady-State Thermal Source Data Using External Data to Access the Steady-State Thermal Source Data Preparing the Fluid Flow Analysis Preparing and Executing the Coupled Thermal Analysis Reviewing Results in CFD-Post

Creating the Project 1.

Start ANSYS Workbench: • To launch ANSYS Workbench on Windows, click the Start menu, then select Start > All Programs > ANSYS 16.0 > Workbench 16.0.

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Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis • To launch ANSYS Workbench on Linux, open a command line interface and enter the path to runwb2. For example: ~/ansys_inc/v160/Framework/bin/Linux64/runwb2 The Project Schematic appears with an Unsaved Project. By default, ANSYS Workbench is configured to show the Getting Started dialog box that describes basic operations in ANSYS Workbench. To control the display of this dialog box, select Tools>Options from the main menu and go to Project Management>Startup and select or clear the Show Getting Started Dialog check box. 2.

Create a directory where you will store your project (this is your working directory). For example, under My Documents, create a directory named SystemCouplingHeatingCoilTutorial.

3.

Select File>Save. A Save As dialog box appears.

4.

Select the path to your working directory to store files created during this tutorial.

5.

Under File name, type SystemCouplingHeatingCoil and click Save. The project files and their associated directory locations appear under the Files view. To make the Files view visible, select View>Files from the main menu of ANSYS Workbench.

6.

This tutorial uses the geometry file, HeatingCoil.agdb, and a Fluent mesh file, HeatingCoilFLUENTMesh.msh, for setting up the project. To access tutorials and their input files on the ANSYS Customer Portal, go to http://support.ansys.com/training. Copy the supplied geometry file, HeatingCoil.agdb, and the mesh file, HeatingCoilFLUENTMesh.msh, to the user_files directory that is in the SystemCouplingHeatingCoil_files directory. By working with copies of the geometry and mesh files in your working directory, you prevent accidental changes to the original files.

Setting the Units in ANSYS Workbench To ensure that the units for this project are set correctly, select Units from the top menu bar and confirm that Metric (kg,m,s,°C,A,N,V) is checked.

Adding Analysis and Component Systems In ANSYS Workbench, set up an analysis system in order to transfer data from a Steady-State Thermal system to a Fluid Flow system, as outlined in this section. 1.

Drag a Steady-State Thermal system from the Analysis Systems toolbox and drop it onto the Project Schematic.

2.

From the Analysis Systems toolbox, drag a Fluid Flow (Fluent) system onto the Project Schematic and drop it to the right of the Steady-State Thermal system.

3.

You will use the System Coupling infrastructure to obtain data from the Steady-State Thermal system for use in the Fluid Flow (Fluent) system. From the Component Systems toolbox, drag a System Coupling system and drop it to the right of the Fluid Flow (Fluent) system.

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Tutorial: Heat Transfer from a Heating Coil 4.

Drag the Setup cell from the Fluid Flow (Fluent) system (B4) and drop it onto the Setup cell in the System Coupling system (C2). That establishes the relationship between the fluid flow and the external data that is coming in through system coupling.

5.

From the Component Systems toolbox, drag an External Data system onto the Project Schematic and drop it between the Steady-State Thermal system and the Fluid Flow (Fluent) system. Note that this changes the lettering of the Fluid Flow (Fluent) system from (B) to (C) and the System Coupling system from (C) to (D).

6.

Drag the Setup cell from the External Data system (B2) and drop it onto the Setup cell in the System Coupling system (D2).

7.

Save the project: click Save

.

The Project Schematic should appear as shown in Figure 14: Project Schematic of a Fluid Solid Interface, System Coupling Problem (p. 114). Figure 14: Project Schematic of a Fluid Solid Interface, System Coupling Problem

The Structural and Fluid systems contain various cells. ANSYS Workbench provides visual indications of the state of a cell at any given time via icons on the right side of each cell. In Figure 14: Project Schematic of a Fluid Solid Interface, System Coupling Problem (p. 114), most cells appear with a blue question mark , indicating that cells need to be set up before continuing the analysis. As these cells are set up, the data transfer occurs from top to bottom. See Understanding Cell States for a description of various cell states. Now the project is ready for further processing. A project schematic such as this with interconnected systems enables you to perform a multiphysics analysis by adding a new geometry, setting up the physics of the individual systems (Steady-State Thermal, and Fluid Flow systems in this example), and also viewing the results.

Adding New Materials for the Project 1.

On the Project Schematic, double-click the Engineering Data cell in the Steady-State Thermal system (A2). In the tab that appears, you will set the Material Properties for the coil.

2.

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In the Outline of Schematic A2: Engineering Data window, note that Structural Steel is the first entry in the Material section. Right-click the empty row at the bottom of the Material section, just below the Structural Steel entry to add a new material for the project. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

3.

Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis Select Engineering Data Sources.

4.

In the Data Source column of the Engineering Data Sources tab, select General Materials.

5.

In the Outline of General Materials section, click the plus sign beside the Copper Alloy option to add copper alloy material to the project.

6.

You now have all the material properties that you need for the project. At the top of your Workbench window, close the Engineering Data tab to return to the Project Schematic.

7.

From the main menu, select File>Save to save material settings to the project.

Adding Geometry to the Project Add the geometry by importing an existing DesignModeler file. 1.

On the Project Schematic, right-click the Geometry cell in the Steady-State Thermal system (A3) and select Import Geometry>Browse.

2.

In the Open dialog box, browse to your working directory, select SystemCouplingHeatingCoil_files>user_files>HeatingCoil.agdb, and click Open.

Preparing the Steady-State Thermal Source Data You will now define the physics for the steady-state thermal analysis.

Assigning the Material to the Geometry To assign the material to the geometry: 1.

On the Project Schematic, double-click the Model cell in the Steady-State Thermal system (A4). This will open the Mechanical application.

2.

In the Mechanical application, right-click Project>Model (A4)>Geometry>Part>Container and select Suppress Body.

3.

Click Project>Model (B4)>Geometry>Part>Coil.

4.

In the Details of “Coil” view, use the Material>Assignment drop-down box to select Copper Alloy.

Generating the Mesh Define and generate a mesh for the structural model of the heating coil. 1.

In the Mechanical application Outline view, right-click Project>Model (A4)>Mesh and select Insert>Method.

2.

In the viewer window, select the whole coil geometry in the viewer window by clicking on it.

3.

In the Details of “Automatic Method” - Method view, click Scope>Geometry>Apply.

4.

In the Details of “Automatic Method” - Method view, select Definition>Method>Sweep.

5.

Click the box to the right of Definition>Free Face Mesh Type. Select All Tri.

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Tutorial: Heat Transfer from a Heating Coil This creates triangular elements on the source face. These triangular elements then get swept through the coil body during the Sweep. Quad elements are not used for this case because the coarse mesh that is used would result in a poor quality mesh on the source face. 6.

Click Project>Model (A4)>Mesh to open the Details of “Mesh” view.

7.

In the Details of “Mesh” view, select Sizing>Element Size and enter 0.05.

8.

Right-click Project>Model (A4)>Mesh and select Generate Mesh.

Defining the Physics for the Structural Analysis Define the physics for the steady-state thermal portion of the problem.

Defining the Steady-State Thermal Analysis 1.

2.

Define the initial temperature: 1.

In the Mechanical application Outline view, click Project>Model (A4)>Steady-State Thermal (A5)>Initial Temperature.

2.

In the Details of “Initial Temperature” view, change Definition>Initial Temperature Value to 250°C.

Define the internal heat generation: 1.

Right-click Project>Model (A4)>Steady-State Thermal (A5) and select Insert>Internal Heat Generation.

2.

Select the coil body in the viewer window.

3.

In the Details of “Internal Heat Generation” view, click Geometry>Apply.

4.

In the Details of “Internal Heat Generation” view, change Definition>Magnitude to 8.72e6 W/m3. This is the source for the steady-state thermal calculation.

3.

Define the convection boundary condition to allow the heat to escape from the area around the coil: 1.

In the Mechanical application Outline view, right-click Project>Model (A4)>Steady-State Thermal (A5) and select Insert>Convection. Convection values will reflect the heat removal from the coil surface.

2.

In the Details of “Convection” view, change Scope>Scoping Method to Named Selection.

3.

In the Named Selection drop-down box, select CoilSurface.

4.

Change Definition>Film Coefficient to 1000 W/m2·°C.

5.

Change Definition>Ambient Temperature to 30°C. The convection boundary condition is applied to the outer coil surface, not to the ends. The heat that was introduced in the previous step will be dissipated due to convection.

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Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis The heat transfer (film) coefficient value should be approximately 1000 W/m2·°C. This will be the estimate that you use for this part of the tutorial. In a later part of this tutorial, you will run the CFD analysis and compare the estimated number to the calculated number for the heat transfer coefficient value. At that time, you will replace the estimated heat transfer coefficient value with the full set of heat transfer coefficient values that are calculated from the fluid dynamics side. 4.

Define the fluid-solid interface: 1.

In the Mechanical application Outline view, right-click Project>Model (A4)>Steady-State Thermal (A5) and select Insert>Fluid Solid Interface.

2.

In the Details of “Fluid Solid Interface” view, change Scope>Scoping Method to Named Selection.

3.

In the Named Selection drop-down box, select CoilSurface.

4.

In the Export Results drop-down box, select Yes. This setting will make Mechanical export the static results to an ANSYS External Data file (the .axdt file). The .axdt files are generated from the results on defined fluid solid interfaces. These files will be used to transfer thermal data from ANSYS Mechanical to ANSYS Fluent when you are using External Data and System Coupling (this is the method used in this tutorial).

5.

6.

Add the temperature and total heat flux results to review: 1.

In the Mechanical application Outline view, right-click Project>Model (A4)>Steady-State Thermal (A5)>Solution (A6) and select Insert>Thermal>Temperature.

2.

In the Mechanical application Outline view, right-click Project>Model (A4)>Steady-State Thermal (A5)>Solution (A6) and select Insert>Thermal>Total Heat Flux.

Click File>Save Project.

Executing the Structural Analysis To create the temperature and heat flux distribution solutions, click the Solve button main toolbar at the top of the Mechanical application.

from the

Post-Processing the Structural Analysis Results When the solution is complete, review the temperature and total heat flux distribution results. 1.

To look at the temperature distribution, in the Mechanical application Outline view, click Project>Model (A4)>Steady-State Thermal (A5)>Solution (A6)>Temperature.

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Tutorial: Heat Transfer from a Heating Coil Figure 15: Temperature of the Coil

2.

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To look at the total heat flux distribution, in the Mechanical application Outline view, click Project>Model (A4)>Steady-State Thermal (A5)>Solution (A6)>Total Heat Flux.

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Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis Figure 16: Total Heat Flux Distribution on the Coil

In the Messages view, just under the viewer window, there will be an Info message that states, "The thermal results at the Fluid Solid Interface(s) have been written to the solver files directory." This tells you that the .axdt file has been created. You now have an ANSYS External Data file (.axdt file) that can be brought into External Data. This file contains the Temperature and Heat Flow values exported from the Fluid Solid Interface region that you defined. You will import this file into External Data to provide thermal boundary conditions for Fluent via the System Coupling component. 3.

Click File>Save Project and File>Close Mechanical.

Using External Data to Access the Steady-State Thermal Source Data You can access the ANSYS External Data file (.axdt file) as follows: 1.

In the Files window, scroll down to find the .axdt file, and note that it’s named fsin_1.axdt.

2.

On the Project Schematic, double-click the Setup cell in the External Data system (B2).

3.

Under Location in the Outline of Schematic section, click the the fsin_1.axdt file.

4.

Select the fsin_1.axdt file and click Open.

button and select Browse. Browse to

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Tutorial: Heat Transfer from a Heating Coil All the information about the external data for this project has been automatically entered into the appropriate data sections. In the Properties of File section, the format type is AXDT. The Table of File section summarizes the x, y and z coordinate data that appear in the Preview of File section. There are also temperature values in Celsius and heat rate in Watts that have been imported from the fsin_1.axdt file. You can scan this data to ensure that it seems reasonable for this project. 5.

Close the External Data tab to return to the Project Schematic.

6.

On the Project Schematic, right-click the Setup cell in the External Data system (B2) and select Update.

Preparing the Fluid Flow Analysis To prepare the fluid flow analysis, import the fluid mesh, and set up the physics in Fluent.

Importing the Mesh for the Fluid Flow Analysis Import an existing Fluent mesh file into the fluid analysis. 1.

In the ANSYS Workbench Project Schematic, right-click the Mesh cell in the Fluid Flow (Fluent) system (C3) and click Import Mesh File>Browse.

2.

Browse to your working directory, select SystemCouplingHeatingCoil_files>user_files>HeatingCoil FLUENTMesh.msh, and click Open. In the Fluid Flow (Fluent) system, notice that the Geometry cell is automatically deleted and the Mesh cell is renamed to Imported Mesh.

Defining the Physics for the Fluid Flow Analysis Define the physics for the fluid analysis. 1.

In the Fluid Flow (Fluent) system (C3), double-click the Setup cell to start Fluent.

2.

In the Fluent Launcher, select Double Precision. Click OK. The mesh file is automatically loaded into the Fluent session.

3.

Right-click Setup>Models>Energy (Off) and select Edit. Check the Energy Equation check box and click OK.

4.

Right-click Setup>Models>Viscous (Laminar) and select Edit. For the Model, select k-epsilon (2 eqn). For the Near-Wall Treatment, select Scalable Wall Functions. Click OK.

5.

Change the fluid material to water:

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1.

Right-click Setup>Materials>Fluid and select New....

2.

Click the Fluent Database button.

3.

In the Fluent Fluid Materials section, select water-liquid (h2o).

4.

Click the Copy button to add water as the material and click Close.

5.

In the Create/Edit Materials panel, click Change/Create and Close.

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6.

6.

Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis Select Setup>Cell Zone Conditions, then select Edit.

7.

In the Fluid dialog box, change Material Name to water-liquid. Click OK.

Set the boundary conditions, starting with the fluid-solid interface on the coil’s surface: 1.

Select Setup>Boundary Conditions.

2.

Before you select a zone, select the Highlight Zone check box in order to display only the selected zone in the viewer.

3.

Under Zone, select coilsurface, and then select the Edit button.

4.

In the Wall dialog box, one the Thermal tab, set the Thermal Conditions to via System Coupling. Click OK. This boundary is now marked as one that will participate in couplings. It will be able to accept either temperature or heat flow data.

7.

8.

9.

Set the inflow boundary: 1.

Under Zone, select inflow.

2.

Change the Type to velocity-inlet and click Yes to accept this change.

3.

In the Velocity Inlet dialog box, set the Velocity Magnitude to 0.4 and click OK.

Set the outflow boundary: 1.

Under Zone, select outflow.

2.

Change the Type to pressure-outlet and click Yes to accept this change.

3.

In the Pressure Outlet panel, verify that the Gauge Pressure is 0. Click OK.

Set up the solution controls: 1.

Select Solution>Solution Methods and set the Scheme to Coupled.

2.

Select Solution>Monitors>Residual, and right-click to select Edit.

3.

In the Residuals Monitors panel, under Equations, change Absolute Criteria for energy residual from 1e-06 to 1e-05.

4.

Click OK. In this problem, energy residuals level off around 8e-06. This step ensures that Fluent terminates once this level of convergence is reached during the coupled analysis.

5.

Select Solution>Run Calculation and set the Number of Iterations to 200.

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Tutorial: Heat Transfer from a Heating Coil 11. Now that the physics is defined, close Fluent. The next step is to set up the coupled thermal analysis.

Preparing and Executing the Coupled Thermal Analysis 1.

Set up the data transfer in the system coupling system: 1.

In the ANSYS Workbench Project Schematic, double-click the Setup cell in the System Coupling system (D2).

2.

Click Yes in the pop-up window to read the upstream data.

3.

In Outline of Schematic D1: System Coupling, select System Coupling>Setup>Participants >External Data>Regions>File1. This file is the .axdt file that was copied into External Data in the Using External Data to Access the Steady-State Thermal Source Data (p. 119) section.

4.

In Properties of Region: File1, right-click Topology>Output>File1:Temperature1 and select Create Data Transfer.

5.

In Outline of Schematic D1: System Coupling section, select System Coupling>Setup>Data Transfers>Data Transfer.

6.

In Properties of Data Transfer : Data Transfer section, in Target>Participant, select Fluid Flow (Fluent).

7.

In Target>Region, select coilsurface.

8.

In Target>Variable, select temperature.

9.

Select File>Save.

Note For one-way steady thermal coupled analyses, it is good practice to use one coupling iteration per run. This can be done by selecting Analysis Settings in the tree view and changing Maximum Iterations to 1 in the details view. However, in this tutorial, default settings will be used.

2.

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Add Fluent’s solution monitor: 1.

Click on the Project tab in Workbench to return to the Project Schematic, keeping the System Coupling tab open.

2.

From the Project Schematic, right-click the Fluid Flow (Fluent) system’s Solution cell (C4) and select Properties. In the Properties view that appears in Workbench, ensure that Solution Monitoring is checked. This setting will allow you to monitor Fluent’s solution from Workbench.

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3.

3.

Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis Right-click the Fluid Flow (Fluent) system’s Solution cell (C4) and select Show Solution Monitoring. A new tab opens with the solution monitor. When you solve your analysis using System Coupling, use this tab to watch Fluent solve the fluid part of this analysis.

Solve the coupled analysis and add a new chart to monitor the solution: 1.

Click on the System Coupling tab in Workbench to return to the system coupling interface.

2.

In Outline of Schematic D1: System Coupling, right-click System Coupling>Solution and select Update. This starts the coupled analysis. Fluent connects up to the coupling service and will run endto-end. Fluent will accept external data and will run through its full convergence. A summary of the solution progress is in the System Coupling Chart and Solution Information views.

3.

In Outline of Schematic D1: System Coupling, right-click System Coupling>Solution>Chart Monitors and select Create Chart to create a new system coupling chart.

4.

Right-click the new Chart 2 that appears and select Add Variable>External Data>Data Transfer>Value>Average.

5.

Right-click the Chart 2 again and select Add Variable>Fluid Flow (Fluent)>Data Transfer>Value>Average. This new chart shows the difference between the average nodal temperature values in Kelvin, transferred from the source region to the target region. Notice that the source and target values differ by approximately 11 degrees. This difference is due to mismatching of the nodes on the source and target sides.

4.

Close the System Coupling tab to return to the Project Schematic.

Reviewing Results in CFD-Post Review the graphical results of the project in CFD-Post. 1.

In the ANSYS Workbench Project Schematic, double-click the Results cell in the Fluid Flow (Fluent) system (C5) to start CFD-Post.

2.

View the temperature along the ZX plane: 1.

From the CFD-Post toolbar, click

and select Plane.

2.

Click OK to accept the default name of Plane 1.

3.

In the Details of Plane 1 section, in the Geometry tab, set the Method to ZX Plane.

4.

In the Color tab, set the Mode to Variable and the Variable to Temperature.

5.

Set the Range to User Specified, the Min to 300 K, and the Max to 305 K. The full temperature range is much larger due to temperature extremes on a small fraction of the surface. By neglecting those extreme temperatures, more colors are used over the range of interest. Release 16.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

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Tutorial: Heat Transfer from a Heating Coil 6.

Click Apply.

7.

For a better view, click the y axis on the Viewer triad. Figure 17: Advection of Heated Water Out of the Heat Exchanger (p. 124) shows the thermal boundary layer around the coil surface and illustrates how the warmed-up fluid is being advected out of the heat exchanger. Figure 17: Advection of Heated Water Out of the Heat Exchanger

3.

View the heat transfer coefficient on the coil’s surface: 1.

Disable the plane view by deselecting the Outline>User Locations and Plots>Plane1 check box.

2.

Select the Outline>Cases>FFF>part container>coilsurface check box.

3.

Right-click the coil surface in the Viewer and select Color>Wall Heat Transfer Coefficient. Earlier in the tutorial, the heat transfer (film) coefficient value was estimated at approximately 1000 W/m2·°C. This estimate is slightly lower than with the average calculated value on the coil surface in Figure 18: Wall Heat Transfer Coefficient on the Coil Surface (p. 125). Note that there is variability in the distribution of the heat transfer coefficient on the coil surface. In the second part of this tutorial where you will replace the estimated heat transfer coefficient

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Part 1: Transferring Data from the Steady-State Thermal Analysis to the Fluid Flow Analysis value with the full set of heat transfer coefficient values that are calculated from the fluid dynamics side. The data calculated here will be exported from CFD-Post and brought into a system coupling analysis of a steady state thermal system. Figure 18: Wall Heat Transfer Coefficient on the Coil Surface

4.

View the wall adjacent temperature on the coil’s surface: •

Right-click the coil surface in the Viewer and select Color>Wall Adjacent Temperature. In the Defining the Steady-State Thermal Analysis (p. 116) section, we estimated that the ambient temperature of the coil surface would be approximately 30°C. Figure 19: Wall Adjacent Temperature on the Coil Surface (p. 126) shows that the calculated wall adjacent temperature is close to this value with some variation. In the second part of this tutorial, you will replace the estimated ambient temperature with the full set of adjacent temperature values that are calculated from the fluid dynamics side. The data calculated here will be exported from CFD-Post and brought into a system coupling analysis of a steady state thermal system.

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Tutorial: Heat Transfer from a Heating Coil Figure 19: Wall Adjacent Temperature on the Coil Surface

Part 2:Transferring Data from the Fluid Flow Analysis to the Steady-State Thermal Analysis This part of the analysis has the following steps: Exporting the Data Adding Additional Analysis and Component Systems Using External Data to Access the Fluid Flow Source Data Preparing the Steady-State Thermal Analysis Preparing and Executing the Coupled Thermal Analysis Reviewing Results in the Mechanical Application

Exporting the Data Export results from the first part of the tutorial. 1.

If you are not already in CFD-Post, in the ANSYS Workbench Project Schematic, double-click the Results cell in the Fluid Flow (Fluent) system (C5) to start CFD-Post.

2.

Click File>Export>Export External Data File.

3.

In the Export External Data File panel, confirm that the File path is pointing to user_files/ex port.axdt.

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4.

Part 2: Transferring Data from the Fluid Flow Analysis to the Steady-State Thermal Analysis For the Location, select coilsurface.

5.

In the Select Recommended Variables box, select HTC and Wall Adjacent Temperature.

6.

Click Save and close CFD-Post.

Adding Additional Analysis and Component Systems The physics for this steady-state thermal system is identical to the physics in the first part of this tutorial, except that the data for the convection boundary condition will be obtained from the output from the first part of this tutorial through system coupling. 1.

In order to create a copy of the first system, right-click the Setup cell (A5) in the Steady-State Thermal system and select Duplicate. The setup for this duplicate system (E) is identical to the setup of the A Steady-State Thermal system. Duplicating from the Setup cell in this way produces a new system with shared Engineering Data, Geometry and Model. The existing Setup cell state is copied to the new system.

2.

From the Component Systems toolbox, drag a System Coupling system and drop it to the right of the Copy of Steady-State Thermal system.

3.

Drag the Setup cell from the Copy of Steady-State Thermal system (E5) and drop it onto the Setup cell in the System Coupling system (F2).

4.

From the Component Systems toolbox, drag an External Data system onto the Project Schematic and drop it to the left of the Copy of Steady-State Thermal system. This External Data system will provide data to the Steady-State Thermal system through the System Coupling system. Note that adding this system changes the lettering of the Copy of Steady-State Thermal system from (E) to (F) and the System Coupling system from (F) to (G).

5.

Drag the Setup cell from the External Data system (E2) and drop it onto the Setup cell in the System Coupling system (G2). Figure 20: Project Schematic of a Fluid Solid Interface, System Coupling Problem Part 2

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Tutorial: Heat Transfer from a Heating Coil

Using External Data to Access the Fluid Flow Source Data The fluid flow source data was generated in the fluid analysis in the first part of this tutorial. Provide the path to this data so that it can be used in the analysis. 1.

In the Project Schematic, double-click the Setup cell in the second External Data system (E2).

2.

In the Outline of Schematic section, under the Location column, click the ellipsis button and select Browse. Browse to the file named export.axdt that was exported from CFD-Post. Click Open.

3.

Close the External Data tab to return to the Project Schematic.

4.

In the Project Schematic, right-click the Setup cell in the External Data system (E2) and select Update.

Preparing the Steady-State Thermal Analysis Remove the estimated convection value from the thermal analysis. 1.

Double-click the Setup cell in the Copy of Steady-State Thermal system (F5).

2.

In the Outline view of the Mechanical application, under Project>Model (A4, F4)>Steady-State Thermal 2 (F5), the estimate for the Convection condition is present. Remove this estimate by right-clicking Convection and selecting Delete.

3.

The Fluid Solid Interface condition does not need to be modified. In the first part of this tutorial, the fluid solid interface was used so that an .axdt file was created and temperature values and heat rates from that fluid solid interface region were output. In the second part of this tutorial, the Fluid Solid Interface will be used to receive data from system coupling as well as to create an .axdt file.

4.

Close the Mechanical application.

5.

Right-click the Setup cell in the Copy of Steady-State Thermal system (F5) and select Update.

Preparing and Executing the Coupled Thermal Analysis Set up the data transfer and solve the coupled analysis. 1.

Double-click the Setup cell in the System Coupling system (G2). Click Yes to read the upstream data.

2.

In the Outline of Schematic G1: System Coupling window, Ctrl-select Fluid Solid Interface and File 1. Right-click File 1 and select Create Data Transfer to automatically create a pair of data transfers. Data Transfer created transfers the heat transfer coefficient, and Data Transfer 2 created transfers the reference temperature.

3.

Save the project.

4.

Right-click the Solution section and select Update. As the system solves, system coupling draws the data from the external data system and provides it to the Mechanical application.

5.

After the solution has finished, close the System Coupling tab to return to the Project Schematic.

6.

Right-click the Results cell in the Copy of Steady-State Thermal system (F7) and select Update.

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Part 2: Transferring Data from the Fluid Flow Analysis to the Steady-State Thermal Analysis

Reviewing Results in the Mechanical Application 1.

Double-click the Results cell in the Copy of Steady-State Thermal system (F7) to open the Mechanical application.

2.

To compare the results from the first part of the tutorial with those from the second part, split the viewer window into two parts. Click the Viewport icon in the top menu bar and select Vertical Viewports.

3.

Click in the left viewport and then in the Outline view, click Steady-State Thermal (A5)>Solution (A6)>Temperature.

4.

Click in the right viewport and then in the Outline view, click Steady-State Thermal 2 (F5)>Solution (F6)>Temperature. The left view now shows the original, uncoupled case and the right view is the coupled result.

5.

To synchronize the two views, click the Manage Views icon in the top menu bar.

6.

The Manage Views window appears in the lower left part of the Mechanical application window. Click in the left viewport and click the Create a View icon,

.

7.

Click in the right viewport, select View 1 and click the Apply a View icon,

.

8.

To allow a better comparison of the two sets of results, both the scales should be changed to the same values. Double-click the second-lowest value in the colored legend and change it to 200 and change the second-highest value in the colored legend to 1600. Do this in both the left and right viewports.

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Tutorial: Heat Transfer from a Heating Coil Figure 21: Comparison of Coil Temperature Contours from the First and Second Parts of the Tutorial

As noted at the end of the first part of the tutorial, the constant heat transfer coefficient value applied in the thermal analysis of the coil under-predicts the spatially-varying values generated by the fluid analysis. Qualitative and quantitative differences are consequently observed between thermal analyses of the coil in the first and second parts of the tutorial. When the larger, spatially-varying heat transfer coefficient values are applied, the resulting temperature values decrease appropriately and temperature variations occur over the coil surface. For example, the lowest temperatures are observed on the lower, side portions of the coil cross-section due to increased convective cooling in those regions. Convective cooling decreases on the lower and upper portions due to flow stagnation and recirculation, respectively. The effect of the larger, spatially-varying heat transfer coefficient values on the heat flux solution values from the thermal analyses corroborate these observations. 1.

To compare the total heat flux, select the left viewport and click Steady-State Thermal (A5)>Solution (A6)>Total Heat Flux.

2.

Select the right viewport and select Steady-State Thermal 2 (F5)>Solution (F6)>Total Heat Flux.

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Part 2: Transferring Data from the Fluid Flow Analysis to the Steady-State Thermal Analysis Figure 22: Comparison of Coil Total Heat Flux Contours from the First and Second Parts of the Tutorial

3.

When you are finished viewing your results, select File>Save Project from the main menu, and then File>Close Mechanical. Select File>Exit to close your Workbench project.

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using graphical monitor output, 75 using text based monitor output, 74 duration controls, 10 Duration Defined By property, 10

Index A analysis settings, 9 best practices, 12 Analysis Settings field, 9 Analysis Type property, 9

B best practices, 73

C chart monitors, 29 CHT (Conjugate Heat Transfer) example, 111 co-simulation participant controlled by the system coupling service, 1 co-simulation participant sequencing, 76 co-simulation participant stability, 76 ramping, 76 solution stabilization, 76 command line options, 34 command line usage, 33 conjugate heat transfer example, 111 coupled analyses debugging using graphical monitor output, 75 debugging using text based monitor output, 74 restarting, 35 coupled solution execution time using sequencing to reduce, 77 coupling initialization, 10 coupling service files used by, 55

D Data Transfers creating, 14 data transfers, 16, 44 algorithms, 46 profile preserving, 47 conservative profile preserving, 47 interpolation algorithms, 52 mapping algorithms, 46 bucket surface, 48 General Grid Interface (GGI), 51 postprocessing interpolated data, 53 ramping, 53 under-relaxation, 54 pre-processing algorithms, 45 Debug Output control, 20 debugging two-way coupled analyses, 73

E End Time, 10 examples CHT, 111 conjugate heat transfer, 111 heat exchanger, 111 solid region, 111 steady state simulation, 111 transient mechanical analysis, 88

F fluid-solid interactions, 79

G general analysis type, 12

H heat exchanger example, 111

I initialization controls, 10 input file, 58

L log file, 20 scLog.scl, 64

M maximum iteration, 11 minimum iteration, 11

O Outline view, 8 output intermediate, 22 output frequency all steps, 23 at step interval, 23 none, 22

P participant exchanges data in a coupled analysis, 1 summary, 13 performance improving in system coupling, 77

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Index Properties view, 8

system coupling states Setup cell, 23 Solution cell, 32

R ramping, 53 region part of the topology of a coupling participant, 13 restart data intermediate, 22 restart points, 10 results file scResults_##_######.scr, 57

T transient analysis type, 13 transient mechanical analysis example, 88

U under-relaxation, 54

S

V

Scene view, 9 sequencing of solution steps, 20 sequential solutions, 20 server file scServer.scs, 56 service input file scInput.sci, 55 service log file scLog.scl_, 57 service overview, 41 service shutdown file scStop.stop, 55 simulation example steady state, 111 simultaneous solutions, 20 solid region example, 111 Solution Information view, 9 solvers coupling two-model interactions, 80 steady state simulation example, 111 Step Controls property, 11 step size, 11 structural deformations modeling, 79 structural properties assigning the material to geometry, 87 system coupling analyze decoupled systems first, 73 context menus Setup cell, 23 Solution cell, 32 overview, 1 workspace, 7 system coupling management, 41 convergence management, 43 evaluating convergence, 43 inter-process communication, 41 process synchronization, 41

view convergence plots, 9 outline, 8 properties, 8 scene, 9 solution information, 9

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