82215765 Autodyn Basics

Chapter 3 AUTODYN Basics

ANSYS AUTODYN

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Structured and Unstructured Parts (Meshes)

Training Manual

• An AUTODYN Part can use a Structured mesh or an Unstructured mesh – Structured meshes can be generated in AUTODYN • Use (I,J,K) index space

– Unstructured meshes must be imported (e.g. from Workbench)

• Lagrange Parts (Solid, Shell, Beam) – Can be Structured or Unstructured – Unstructured Parts are solved more efficiently (speed and memory) • A Structured Part can be converted to an Unstructured Part prior to solving

– Lagrange Parts (structured or unstructured) can be used to “fill” regions of Euler and SPH Parts

• Euler and ALE Parts – Always Structured – Euler meshes are usually rectilinear ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Structured Parts - Index Space

Training Manual

• Each Structured Part in AUTODYN has a defined index space (i,j) in 2D or (i,j,k) in 3D, where i, j and k are integer values ranging from 1 to Ni, Nj, Nk – This index space is always rectangular

j=6

j

i=1

i = 11

i j=1 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Structured Parts - Physical Space

Training Manual

• Each Structured Part is also defined in a physical xyz-space, where x, y and z are real values – The mesh can have a general shape in physical space

j=6

i = 11

i=1 y

j=1

x

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February 27, 2009 Inventory #002665

AUTODYN Basics

Structured Parts – Unused Elements

Training Manual

• Not all elements defined in the index space need to be defined in physical space – Elements not assigned a material are Unused – Allows complicated geometries to be meshed

Unused Elements

Physical Space

Index Space

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February 27, 2009 Inventory #002665

AUTODYN Basics

Creating Structured Parts

Training Manual

• Part Wizard allows automatic generation of quality structured Parts for predefined (Predef) geometries – 2D Volume • Box, Quad, Circle, Ogive, Rhombus, Triangle, Wedge

– 3D Volume • Box, Hex, Cylinder, Sphere, Ogive, Fragments/Bricks Part Wizard

– Shells • Plate, Cylinder

• Manually build quality structured meshes – Nodes – Lines – Surfaces – Volumes

• Import Structured Meshes – ICEM-CFD – TrueGrid ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Part Wizard

Training Manual

• Part Wizard generates a Part in three steps – Define a Predef geometry – Define the zoning – Fill the whole Part

Geometry ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

Zoning 3-7

Fill February 27, 2009 Inventory #002665

AUTODYN Basics

Part Wizard – 2D Box Predef

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

Training Manual

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AUTODYN Basics

Part Wizard – 2D Circle Predef

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

Training Manual

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AUTODYN Basics

Part Wizard – 2D Predefs

Training Manual

Ogive

Rhombus

Quads Wedge ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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AUTODYN Basics

Part Wizard – 3D Box Predef

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

Training Manual

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AUTODYN Basics

Part Wizard – 3D Cylinder Predef

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Training Manual

February 27, 2009 Inventory #002665

AUTODYN Basics

Part Wizard – 3D Predefs

Training Manual

Sphere Ogive

Hex

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Bricks / Fragments

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AUTODYN Basics

Part Wizard – 3D Shell Predefs

Training Manual

Plane Cylinder

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February 27, 2009 Inventory #002665

AUTODYN Basics

Manual Zoning

Training Manual

• Step-by-step generation of meshes using – Node – Line – Surface – Volume

• Interpolation • Extrusion

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Importing 3D Structured Parts

Training Manual

• ANSYS, ICEM-CFD – Powerful 3D hex mesh generator – Direct links to CAD • CATIA, Pro/Engineer, SDRC IDEAS, SolidWorks, Unigraphics, ….

– An interface to ICEM-CFD is provided to allow import of structured (mapped) meshes into AUTODYN • ICEM multiblock meshes (.geo file) • Same import procedure as for TrueGrid

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Materials and Initial Conditions

Training Manual

• Materials and Initial Conditions are defined from the Materials and Init. Cond. Dialog Panels respectively • Once defined, they can be applied to Parts using the Part Wizard and / or the Fill options in the Parts dialog panel.

Apply (Part Wizard)

Apply Define

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Filling Parts with Materials and Initial Conditions

Training Manual

• The Wizard fills each Part with one material • Additional fills can be performed after the Wizard completes – Each fill replaces materials / initial conditions of previous fills

• Lagrange elements are filled if their center lies inside the fill region (no multi-material cells are permitted)

Wizard Fill Additional Geometry Fill

Additional Block Fills ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Boundary Conditions

Training Manual

• Boundary Conditions are defined from the Boundaries Dialog Panel • Once defined, Boundary Conditions can be applied to structured Parts using index space from the Boundary option in the Parts dialog panel

Apply

Define

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February 27, 2009 Inventory #002665

AUTODYN Basics

Boundary Conditions

Training Manual

• Boundary Conditions can be applied the outside faces of a mesh and the outside faces of Unused regions of the mesh • The default boundary condition is: – Lagrange: Free boundary (pressure = 0.0) – Euler

: Rigid wall (no flow, velocity = 0.0)

Unused elements Filled elements Boundary Conditions can be applied here

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Boundary Conditions: Stress

Training Manual

• Applied to Lagrange Parts Trapezoid

Constant

t

t

Triangular

Exponent Pk = Pe-kt

t

User subroutine EXSTR

Piecewise

t ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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t

t February 27, 2009 Inventory #002665

AUTODYN Basics

Boundary Conditions: Velocity

Training Manual

• Applied to Lagrange, ALE, Shell, Beam and SPH Parts – X, Y, Z Velocity Constraints • Constant – Fixed at a constant value

• Limit – Limit position between max and min coordinates – Displacement constraint in Explicit Dynamics

• Piecewise – Piecewise linear segments

– General Velocity Constraints • Fixed constant velocities in X, Y, Z (3D) and fixed rotational velocities about coordinate axes

– User subroutine EXVEL • User Time-Dependant X, Y, Z velocity

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February 27, 2009 Inventory #002665

AUTODYN Basics

Boundary Conditions: Force

Training Manual

• Applied to Beam Parts – Nodal force boundary conditions • Constant, Piecewise, User Subroutine EXFOR • x, y, z and general directions – Element force/unit length boundary conditions • Constant, Piecewise, User Subroutine EXFOR • x, y, z and general directions

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Boundary Conditions: Transmit

Training Manual

• Applied to Lagrange, ALE and Euler Parts – Transmits waves through cell faces – Only the perpendicular component is transmitted – The impedance of the boundary can be specified

I = ρc

• If impedance is set to zero the impedance of the adjacent cell is used

– The Transmit boundary condition is only approximate and should be placed as far as possible from regions of interest – For air blast in Euler, Outflow boundary with p = 0.0 is recommended ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Boundary Conditions: Flow

Training Manual

• Applied to Euler Parts – Inflow • Specify the full state of the material flowing into the grid (density, internal energy and velocity)

– Outflow (P = ρ = e = 0) • Only the preferred material needs to be set • Reverse flow can be specified. If conditions of reverse flow are reached, an external reservoir with prescribed conditions controls inflow – You must specify the full state of the material flowing into the grid (density, internal energy and velocity)

• The Outflow boundary condition is only approximate and should be placed as far as possible from regions of interest

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Lagrange Interactions

Training Manual

• Options are the same as those used in Explicit Dynamics (ANSYS) – Details given in the Body Interactions section of the Explicit Dynamics training course

• Contact type – Trajectory (default) • Method (Formulation) – Penalty – Decomposion Response • Shell Thickness Factor – External Gap (Proximity Based) • Gap Size = Pinball Factor • Parts must be initially separated by the Gap Size

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Units

Training Manual

• AUTODYN uses single precision to make optimum use of solver power and memory, so the choice of units is important, particularly for Euler problems – Avoid pressures below 10-6 of a unit – Avoid cell masses less than 10-6 of a unit • The default set of units work well for virtually all problems – – – – – – – –

Length Mass Time Velocity Force Stress Density Energy

mm mg ms m/s mN kPa g/cm3 mJ

• Workbench Units will be converted to the chosen AUTODYN units when linked ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Solution Controls

Training Manual

• Wrapup Criteria – Must specify Cycle limit and Time limit – AUTODYN will stop and give warning if energy error exceeds Energy fraction (default 5%)

• Timestep Options – Defaults are usually OK – If Initial timestep is left zero, it is computed as half the stability timestep – If Minimum timestep is left zero, it is computed as 1/10th of the Initial time step – Safety factor can be safely increased to 0.9 for most Lagrange calculations ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Conservation Equations

Training Manual

• Mass and Momentum are conserved exactly • Energy is not conserved exactly •

– Practical numerical methods which are fully conservative have problems of stability and can be noisy Good energy conservation

• Conservation of energy and momentum can be monitored using history plotting features. Good model set-ups and analyses will tend to have low errors ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Problem

February 27, 2009 Inventory #002665

AUTODYN Basics

Output Controls

Training Manual

• Save Files / Results Files – Frequency specified by • Cycle increment • Time increment – Calculation can be re-started from Save files (not Results files) – Results files are significantly smaller than Save files – Plots can be created from any Save file or Results file – Animations can be created from a sequence of Save / Results files • More flexible than Capture image

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

AUTODYN Basics

Output Controls

Training Manual

• Results Files (3D only) – Used to create plots • Allows post-processing of large models on computers with limited resources

– Files are stored in a sub folder, ident_adres • Base files ident_bcyc.ad_base – Stores model data required by Results files – Must be present to load Results file data

• Results files ident_bcyc_ncyc.adres – bcyc - the cycle number for the Base file – ncyc - the cycle number for the Results file

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February 27, 2009 Inventory #002665

AUTODYN Basics

Workshop 1: 2D Fragment Impact

Training Manual

Goal: Model a multi-material cylindrical fragment impacting a plate

Procedure: Start AUTODYN standalone Set up the problem in using 2D Axial Symmetry Solve the problem View the results Create animations of the results

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