explicit dynamics exp dyn basics

4-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

February 27, 2009Inventory #002665

Chapter 4

Explicit Dynamics Basics

ANSYS Explicit Dynamics




Training ManualExplicit Dynamics (Mechanical) GUI

Tree Outline

Details View

Graphics Window

ToolbarsMenus

Status Bar

Message Window




Training Manual

• The menus provide much of the functionality present in Explicit Dynamics. The more commonly used menu items are covered below:

– The title bar lists analysis type, product and active ANSYS license.

– “File > Clean” to delete mesh and / or results from database.

– “Units” to change units on-the-fly.

– “Tools > Options… ” to customize settings and options.

– “Help > Mechanical Help” to access documentation.

Explicit Dynamics (Mechanical) GUI : Menus

Analysis Type Product License




Training Manual

• Toolbars provide quick access to functionality.

– Toolbars can be repositioned anywhere on the top of the Mechanical window.

– The “Context” toolbar updates depending on what branch is active in the “Outline” tree.

• Offers options similar to those available by RMB on the active branch

– Tooltips appear if the cursor is placed over a toolbar button.

Explicit Dynamics (Mechanical) GUI : Toolbars




Training Manual

• “Standard” toolbar

• “Graphics” toolbar– used for selection and graphics manipulation:

– The left mouse button can be either in “selection” mode or “graphics manipulation” mode. The above toolbar buttons are grouped as “select entities” and “graphics manipulation” control.

– The graphics selection can be done using individual selection or box-selection. This is controlled by the “Select Mode” icon.

Explicit Dynamics (Mechanical) GUI : Toolbars

Bring up Mechanical Wizard

(Not available for Explicit Dynamics)

Solve Model

Capture Snapshot

Slice Planes

Annotations Comments

Graphics ManipulationSelection ToolsSelect mode Viewports




Training ManualExplicit Dynamics (Mechanical) GUI : Outline Tree

• The Outline Tree provides an easy way of organizing the model, materials, mesh, loads, and results for the analysis.

– The “Model” branch contains the inputdata required for the analysis

– The “Explicit Dynamics” branch containsthe initial conditions, loads, supports and analysis settings required to run the analysis.

– The “Solution” branch contains resultobjects and solution information




Training ManualExplicit Dynamics (Mechanical) GUI : Outline Tree

• The Outline Tree shows icons for each branch, along with a status symbol. Examples of the status symbols are below:

– Checkmark indicates branch is fully defined / OK– Question mark indicates item has incomplete data (need input)– Lightning bolt indicates solving is required– Exclamation mark means a problem exists– “X” means item is suppressed (will not be solved)– Transparent checkmark means body or part is hidden– Green lightning bolt indicates item is currently being evaluated– Minus sign means that mapped face meshing failed– Check mark with a slash indicates a meshed part / body– Red lightning bolt indicates a failed solution

• Becoming familiar with these basic status symbols lets you debugMechanical problems quickly.




Training ManualExplicit Dynamics (Mechanical) GUI : Details View

• The Details View contains data input and output fields. The contents will change depending on the branch selected.

– White field: input data• Data in white text field is editable

– Gray (or Red) field: information• Data in gray fields cannot be modified.

– Yellow field: incomplete input data• Data in yellow fields indicates missing

information.




Training ManualExplicit Dynamics (Mechanical) GUI : Graphics Window

• The Graphics Window shows the geometry and results. It can also provide worksheet (tabular) listings, the HTML report, and a Print Preview option.

Geometry Tab

Worksheet Tab

Print Preview Tab

Report Preview Tab




Training ManualGeometry• Explicit Dynamics supports Solid,

Surface and Line bodies.

• Check that all geometric bodies have been imported

– Line bodies are not imported by default. If line bodies are not shown in the tree, select Tools > Options > Geometry Import in the Workbench project window and check the “Line Bodies” box




Training ManualGeometry• Geometry

– Solid, Surface and Line bodies

• Check that the imported material assignment for each body is correct

• By default a linear “Structural Steel” is assigned.

• Use RMB to assign a different material

– Surface bodies

• Specify the Thickness– (the Thickness mode and Offset type

fields for surface bodies are not supported for Explicit Dynamics systems)

– Line bodies

• Only symmetric cross-sections are supported




Training ManualStiffness Behavior• Stiffness Behavior

– Flexible • Can be assigned to any body type.

– Rigid • Can only be assigned to Solid and Surface bodies.• Only the density of the rigid body is used.

– Mass and inertia is derived from the density of all elements

• Rigid bodies must be discretized with a Full Mesh. – This is the default for the explicit meshing physics

preference• Kinematic rigid body motion depends on the resultant

forces and moments applied through interaction with other parts of the model

• Constraints can only be applied to an entire rigid body. – e.g. a fixed displacement cannot be applied to one

edge of a rigid body, it must be applied to the whole body




Training ManualCoordinate Systems• Co-ordinate Systems

– Local Cartesian co-ordinate systems can be assigned to bodies.

• Used to define the material directions when using the Orthotropic Elasticity property in a material definition.

• Can also used to perform mesh refinements

• Material directions 1, 2, 3 are aligned with the local x, y and z axes of the local co-ordinate system.

– Cylindrical co-ordinate systems are not supported for Explicit Dynamics systems.




Training ManualConnections - Body Interactions• The Body Interactions folder, under Connections, is

used to define global connection options for Explicit Dynamics

– Two options for Contact Detection• Trajectory (default)

• Proximity Based

– Four options for the Type of Body Interaction• Bonded (joined)

• Frictionless (sliding contact)

• Frictional (sliding contact)

• Reinforcement (for embedded beams)

• A default Frictionless interaction, using Trajectory Contact detection, is scoped to all bodies.

– Activates frictionless contact between any external node and face in the entire model that may come into contact during the simulation.

• Safe, but may be relatively inefficient




Training ManualConnections - Contact Region• By default, if two faces of

any Bodies are touching, or within a certain tolerance, a bondedContact Region will be scoped automatically to the two faces

– The tolerance can be changed in Details of “Connections”

– AutoDetection can be turned Off in Options if you wish

• By default it is On

• Always check the Objects automatically generated under Connections to make sure they are what you need

Automatically generated

bonded contact




Training ManualMesh• To generate the best meshes for

Explicit Dynamics:– Select Explicit for the Physical

preference• Sets the preferred defaults to

generate a mesh for an explicit analysis

– Open Meshing Options panel and select Automatic (Patch Conforming/Sweeping) for the default Mesh method

• Ensures that hex elements are generated automatically when a body can be “swept”

• But not the best method if a tetrahedron mesh is generated

– Override the default using the Patch Independent tetrahedron methodThese selections are default for Explicit Dynamics (ANSYS)




Training Manual

How the Physics filter affects a model

slowhighMediumCurvedDroppedExplicit

fastmediumMediumStraightKeptElectromagnetic

slowmediumFineCurvedDroppedCFD

fastlowCoarseCurvedKeptMechanical

transitionsmoothingRelevance Center Default

MidsideNodes

Solid Element Midside Nodes Default

Sets the following automatically ...Physics Preference Option

Physics Preference




Training ManualRelevance and Relevance Center• Relevance is a single setting that may be adjusted to

provide a coarser or finer mesh– The slider bar toggles the “Relevance” setting between

–100 (coarsest) and +100 (finest)– The mesh size level corresponding to the center

position of the Relevance slider bar can be set to Coarse, Medium, or Fine using the Relevance Centersetting

– Different Physics settings have different defaults for theRelevance Center setting (Explicit: Medium)

Relevance: 0Relevance Center: Coarse

Relevance: 0Relevance Center: Medium

Relevance: 0Relevance Center: Fine




Training ManualRelevance and Relevance Center


Relevance: -100Relevance Center: Medium





Training ManualSmoothing

Low HighExplicit Default




Training ManualTransition

Fast SlowExplicit Default




Training ManualDefault Mesh method for Explicit Dynamics

• Automatic (Patch Conforming/Sweeping)• Sweepable bodies are automatically meshed with Hex and Wedge

Elements

Swept Face

Produces better mesh if a size control is used on the swept face or body





• Automatic (Patch Conforming/Sweeping)• Non-sweepable bodies are automatically meshed using the Patch

Conforming tetrahedron mesher• All Faces, Edges, Vertices of the geometry are respected during mesh

generation (Delaunay Method)• Not recommended for Explicit Dynamics

Curves in Geometry are Reflected in the Mesh





• Patch Independent tetrahedron mesher• Recommended for Explicit Dynamics• Faces, Edges, Vertices are not always

respected (Octree Method)• Override the default tetrahedron mesher

(Patch Conforming)

Curves in Geometry NOT reflected in the Mesh

Max. Element Size = 2.5 mm Max. Element Size = 1.0 mm




Training ManualExplicit Dynamics • Once all the bodies used in a

simulation have been meshed and their modes of interaction defined, setup is completed in the Explicit Dynamics folder by defining:

– Initial Conditions

– Loads and Constraints

– Analysis Settings

– Solution Information




Training ManualInitial Conditions

• By default, all bodies in an Explicit Dynamics system are at rest, unconstrained and stress free.

• At least one Initial Condition, Constraint or Load must be applied to the model.

– otherwise the initial solution is the final solution and there is need to Solve.

• Two forms of velocity are available as Initial Conditions for Explicit Dynamics:

– Velocity (Translational)

– Angular Velocity (Rotational)




Training ManualInitial Conditions• Applied to single or multiple bodies in global or

local Cartesian co-ordinate systems.– If rotational and translational velocities are applied

to the same body, the initial velocity of the body will be calculated as the sum of these two conditions




Training ManualLoads and Constraints• Loads and constraints that can be

applied for Explicit Dynamics analyses:

– Acceleration– Standard Earth Gravity– Pressure– Force– Line Pressure– Fixed Support– Displacement– Velocity– Impedance Boundary




Training ManualLoads and Constraints• Acceleration

– A constant body acceleration can be applied to all bodies in the model. This results in a body acceleration vector, defined via three Cartesian components being applied to all nodes in the model prior to any constraints

• Any constraints applied to the model will over-ride an applied body acceleration

• Standard Earth Gravity– Special case of an Acceleration load

which is applied to all bodies. – Magnitude of acceleration is fixed at

standard earth gravitational acceleration – Acting direction can be applied in ± x, y, z

directions.• Any constraints applied to the model will

over-ride any applied gravity

ii

i bmF

x +=&&




Training ManualLoads and Constraints• Pressure

– Constant and tabular Pressure loads can only be applied to faces of flexible bodies.

• Pressure is applied normal to element faces of scoped bodies.

• Direction of applied pressure rotates with deformation of faces.

• Force– Constant and tabular Force loads can be applied

to flexible and rigid bodies. • Flexible bodies

– Force loads can be scoped to points, lines and faces.• Rigid bodies

– Force loads can only be scoped to bodies.• User defines total force load applied to mesh nodes of

scoped bodies. • Force applied to each node is equal to total force

divided by number of mesh nodes in the scoping. – Resulting distribution of force is mesh dependent.

• When defining tabular forces, define the analysis end time first.

• Force can be applied in global or local Cartesian co-ordinate systems.

• Line Pressure– Constant and tabular Line Pressure loads can be

applied to edges of flexible bodies.• Applied in a specified direction.• Does not rotate with the deformation of the model.




Training ManualLoads and Constraints• Fixed Support

– A Fixed Support can be scoped to flexible and rigid bodies to constrain all degrees of freedom.

• Flexible bodies: – Fixed supports can be scoped to points, lines and faces.

• Rigid bodies: – Fixed supports can only be scoped to bodies.

• Displacement– Constant and tabular Displacement constraints

can be applied to flexible and rigid bodies. • Flexible bodies:

– Displacements can be scoped to points, lines and faces.• Rigid bodies:

– Displacements can only be scoped to bodies.

– Displacements are ramped linearly over analysis time.

• For tabular displacements, the initial value at time zero should be zero.

– For rigid bodies, the rotational degrees of freedom will automatically be constrained if a displacement object is scoped to the body.

– Displacements can be applied in global or local Cartesian co-ordinate systems.




Training ManualLoads and Constraints• Velocity

– Constant and tabular Velocity constraints can be applied to flexible and rigid bodies.

• Flexible bodies: – Velocity constraints can be scoped

to points, lines and faces.• Rigid bodies:

– Velocity constraints can only be scoped to bodies.

– For rigid bodies, the rotational degrees of freedom will be automatically constrained if a displacement object is scoped to the body.

– When defining tabular velocities, define the analysis end time first.

– Velocities can be applied in global or local Cartesian co-ordinate systems.




Training ManualLoads and Constraints• Impedance Boundary

– Allows outward traveling waves to pass out of the mesh without reflection

• e.g. an expanding air blast or an underwater or underground explosion.

where uN is the normal velocity[ρc]boundary is the Material Impedancepref is the Reference Pressureuref is the Reference Velocity

(for an initially stationary structure at zero pressure, prefand uref are zero).

– Deals only with the normal component of wave velocity

• Velocity component parallel to the boundary is ignored.• Place boundaries well away from regions of interest

– If the Impedance is Program Controlled (default, recommended), the transient impedances of the elements to which the boundary is applied are used




Training ManualAnalysis Settings

• Analysis Settings are grouped in six categories

– Step Controls– Solver Controls– Damping Controls– Erosion Controls– Output Controls– Analysis Data Management

• End Time is the only required input

– All other options have defaults, e.g.

• Time step is program controlled • Results saved 20 times• Restart files saved 5 times• Time history data saved every cycle




Training ManualExplicit Dynamic Project Files

Contains cycle increment data and error / warning messagesname.loge.g. admodel.log is the log file

Log file (ASCII)

Contains a brief summary of the initial model definition and a summary of the energy and momentum distribution in the model over time.

name.prte.g. admodel.prt is the print file for the model

Print file (ASCII)

Contains complete model database. A solve can be resumed from any restart file.name_{save_cycle_no}.ade.g. admodel_500.ad is the save file for cycle 500.

Restart file (binary)

Contains base data that results files use.name_{base_cycle_no}_.adbasee.g. admodel_0.adbase is the result base file for cycle 0.

Results base file (binary)

Contains results data used for the main post-processing operations in Explicit Dynamics.

name_{base_cycle_no}_{results_cycle_no}.adrese.g. admodel_0_100.adres is the result file for cycle 100, referencing a base file

for cycle 0.

Results file (binary)

DescriptionFile type

Project files created while solving a model




Training ManualSolution

• Solver Mechanisms

– My Computer, In Process (default)

• Solution is automatically monitored in Workbench as it executes

– My Computer, Background

• Solution is obtained on the local machine in the background.

• Most current results can be retrieved while Solve is in process

– Remote Processing

– Calculation is executed on remote (networked) machines

– Set up through Tools > Solve Process Settings




Training ManualSolution Information• My Computer, In Process provides five Solution Output

options to view automatically while the calculation is running:

– Solver Output (default)• Shows the progress of the simulation.

– Cycle summaries– Warning or error messages– Estimated clock time to remaining

• A “best guess” based on time currently taken to solve a cycle and current timeincrement and the simulation time remaining.

• May be significantly over-predicted in early cycles.

– Time Increment• Shows how the time step varies with time.

– Fluctuations should be expected, but a reduction greater than a factor of 10 often indicates a problem in the model setup / progress.

– Energy Conservation• Shows how the energy is being conserved over time

– Momentum Summary• Shows how the momentum of the system varies with time

– Energy Summary• Shows how the energy components of the system vary with time

Defaults




Training ManualSolution Information• Solver Output (default)

– Shows the progress of the simulation.

• Estimated clock time remaining is a “best guess” based on

– the time currently taken to solve a cycle

– the current time step– the remaining

simulation time.

• It may be significantly over-predict in early cycles.




Training ManualSolution Information• Time Increment

– Show how the time step varies with time.

• Fluctuations in time step size should be expected.

• However, a reduction in time step greater than a factor of 10, often indicates a problem in the model setup / progress.




Training ManualSolution Information• Energy Conservation

– Shows how the total energy of the system is conserved over time




Training ManualSolution Information• Momentum Summary

– Shows how the momentum of the system varies with time




Training ManualSolution Information• Energy Summary

– Shows how the energy components of the system vary with time




Training ManualSolution Information• Adding additional solution outputs

– RMB Solution > Insert allows customized results to be specified

More details in Chapter 5: Results Processing




Training ManualWorkshop 1 – Taylor Test (Cylinder Impact)

Goal: Simulate the impact of rod into a plate (typically known as a “Taylor Test”)

Procedure:Create an Explicit Dynamics (ANSYS) Analysis System ProjectSelect the unit system and assign the material propertiesCreate the rod and plate geometry in DesignModelerMesh the two parts and set the initial velocity condition of the rodDefine the analysis settings, boundary conditions, and applied loadsInitiate the solution (AUTODYN - STR) and review the results

explicit dynamics exp dyn basics

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