82215765 autodyn basics

3-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

February 27, 2009Inventory #002665

Chapter 3

AUTODYN Basics

ANSYS AUTODYN

AUTODYN Basics



Training ManualStructured and Unstructured Parts (Meshes)• An AUTODYN Part can use a

Structured mesh or an Unstructuredmesh

– 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

AUTODYN Basics



Training Manual

i

j i = 1 i = 11

j = 1

j = 6

Structured Parts - Index Space

• 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

AUTODYN Basics



Training Manual

x

yi = 1 i = 11

j = 1

j = 6

Structured Parts - Physical Space

• 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

AUTODYN Basics



Training Manual

Index Space Physical Space

Unused

Elements

• 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

Structured Parts – Unused Elements

AUTODYN Basics



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

– Shells• Plate, Cylinder

• Manually build quality structured meshes – Nodes

– Lines

– Surfaces

– Volumes

• Import Structured Meshes– ICEM-CFD

– TrueGrid

Part Wizard

Creating Structured Parts

AUTODYN Basics



Training ManualPart Wizard

Geometry Zoning Fill

• Part Wizard generates a Part in three steps

– Define a Predef geometry

– Define the zoning

– Fill the whole Part

AUTODYN Basics



Training ManualPart Wizard – 2D Box Predef

AUTODYN Basics



Training ManualPart Wizard – 2D Circle Predef

AUTODYN Basics



Training Manual

Ogive

Quads

Part Wizard – 2D Predefs

Wedge

Rhombus

AUTODYN Basics



Training ManualPart Wizard – 3D Box Predef

AUTODYN Basics



Training ManualPart Wizard – 3D Cylinder Predef

AUTODYN Basics



Training Manual

Sphere

Bricks / FragmentsHex

Ogive

Part Wizard – 3D Predefs

AUTODYN Basics



Training Manual

PlaneCylinder

Part Wizard – 3D Shell Predefs

AUTODYN Basics



Training Manual

• Step-by-step generation of meshes using

– Node

– Line

– Surface

– Volume

• Interpolation

• Extrusion

Manual Zoning

AUTODYN Basics



Training Manual

• ANSYS, ICEM-CFD

– Powerful 3D hex mesh generator

– Direct links to CAD

• CATIA, Pro/Engineer, SDRC I-DEAS, 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

Importing 3D Structured Parts

AUTODYN Basics



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.

DefineApply

Apply (Part Wizard)

Materials and Initial Conditions

AUTODYN Basics



Training ManualFilling Parts with Materials and Initial Conditions

Additional Block Fills

• 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)

Additional Geometry FillWizard Fill

AUTODYN Basics



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

Boundary Conditions

Define

Apply

AUTODYN Basics



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

Boundary Conditions

AUTODYN Basics



Training Manual

Constant

t

Trapezoid

t

Triangular

t

ExponentPk = Pe-kt

t

User subroutineEXSTR

t

• Applied to Lagrange Parts

Piecewise

t

Boundary Conditions: Stress

AUTODYN Basics



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

Boundary Conditions: Velocity

AUTODYN Basics



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

Boundary Conditions: Force

AUTODYN Basics



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

• 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

cI ρ=

Boundary Conditions: Transmit

AUTODYN Basics



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

Boundary Conditions: Flow

AUTODYN Basics



Training ManualLagrange Interactions• 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

AUTODYN Basics



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 mm– Mass mg– Time ms– Velocity m/s– Force mN– Stress kPa– Density g/cm3

– Energy mJ

• Workbench Units will be converted to the chosen AUTODYN units when linked

Units

AUTODYN Basics



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

Solution Controls

AUTODYN Basics



Training ManualConservation Equations• 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

• Conservation of energy and momentum can be monitored using history plotting features. Good model set-ups and analyses will tend to have low errors

Problem

Good energy conservation

AUTODYN Basics



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

Output Controls

AUTODYN Basics



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

Output Controls

AUTODYN Basics



Training ManualWorkshop 1: 2D Fragment Impact

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

82215765 autodyn basics

Documents

structured parts index

structured euler

structured mesh

index space unstructured

defined index space

ale parts

physical space elements

d box predefautodyn