autodyn basics
DESCRIPTION
Autodyn BasicsTRANSCRIPT
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3-1ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.
February 27, 2009Inventory #002665
Chapter 3
AUTODYN Basics
ANSYS AUTODYN
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AUTODYN Basics
3-2ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.
February 27, 2009Inventory #002665
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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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Training ManualPart Wizard 2D Box Predef
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AUTODYN Basics
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Training ManualPart Wizard 2D Circle Predef
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AUTODYN Basics
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Training Manual
Ogive
Quads
Part Wizard 2D Predefs
Wedge
Rhombus
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AUTODYN Basics
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Training ManualPart Wizard 3D Box Predef
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AUTODYN Basics
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Training ManualPart Wizard 3D Cylinder Predef
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AUTODYN Basics
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Sphere
Bricks / FragmentsHex
Ogive
Part Wizard 3D Predefs
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AUTODYN Basics
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PlaneCylinder
Part Wizard 3D Shell Predefs
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AUTODYN Basics
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Step-by-step generation of meshes using Node
Line
Surface
Volume
Interpolation
Extrusion
Manual Zoning
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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Constant
t
Trapezoid
t
Triangular
t
ExponentPk = Pe-kt
t
User subroutineEXSTR
t
Applied to Lagrange Parts
Piecewise
t
Boundary Conditions: Stress
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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
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AUTODYN Basics
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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