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 =

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 = = 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

autodyn basics

Documents