Explicit Dynamics Chapter 4 Exp Dyn Basics

7/15/2019 Explicit Dynamics Chapter 4 Exp Dyn Basics

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1-1ANSYS, Inc. Proprietary

2009 ANSYS, Inc. All rights reserved.February 27, 2009

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Chapter 4

Explicit Dynamics Basics

ANSYS Explicit Dynamics


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Expl ic i t Dynam ics Basics



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Training ManualExplicit Dynamics (Mechanical) GUI

Tree Outline

Details View

Graphics Window

Toolbars

Menus

Status Bar

Message Window


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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


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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


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Training Manual

Standard toolbar

Graphics toolbar used for selection and graphics manipulation:

The left mouse button can be either in selection mode or graphicsmanipulation mode. The above toolbar buttons are grouped as selectentities 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


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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 input

data required for the analysis

The Explicit Dynamics branch contains

the initial conditions, loads, supports and

analysis settings required to run the

analysis.

The Solution branch contains result

objects and solution information


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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 debug

Mechanical problems quickly.


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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.


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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


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Training ManualGeometry

Explicit Dynamics supports Solid,Surface and Line bodies.

Check that all geometric bodieshave been imported

Line bodies are not imported bydefault. If line bodies are notshown in the tree, select Tools >Options > Geometry Import in theWorkbench project window andcheck the Line Bodies box


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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


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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 physicspreference.

Kinematic rigid body motion depends on the resultantforces and moments applied through interaction withother 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 ofa rigid body, it must be applied to the whole body.

Bonded connections can be applied to connectflexible and rigid bodies

They cannot be combined in Multi-body Parts.


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Training ManualCoordinate Systems

Co-ordinate Systems

Local Cartesian co-ordinate systems can beassigned to bodies.

Used to define the material directions when usingthe Orthotropic Elasticity property in a materialdefinition.

Can also used to perform mesh refinements

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

Cylindrical co-ordinate systems are not supportedfor Explicit Dynamics systems.


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Training ManualBody Interactions (Connections)

The Body Interactions folder, underConnections, isused 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 externalnode and face in the entire model that may come intocontact during the simulation.

Safe, but may be relatively inefficient


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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 paneland selectAutomatic (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

method

These selections are default for Explicit Dynamics (ANSYS)


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How the Physics filter affects a model

Physics Preference

Option

Sets the following automatically ...

Solid Element

Midside Nodes

Default

Midside

Nodes

Relevance

Center

Default

smoothing transition

Mechanical Kept Curved Coarse low fast

CFD Dropped Curved Fine medium slow

Electromagnetic Kept Straight Medium medium fast

Explicit Dropped Curved Medium high slow

Physics Preference


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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 Center

setting

Different Physics settings have different defaults for the

Relevance Center setting (Explicit: Medium)

Relevance: 0

Relevance Center: Coarse

Relevance: 0

Relevance Center: MediumRelevance: 0

Relevance Center: Fine


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Training ManualRelevance and Relevance Center

Relevance: 0

Relevance Center: Medium

Relevance: -100Relevance Center: Medium

Relevance: 100

Relevance Center: Medium


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Training ManualSmoothing

Low High

Explicit Default


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Training ManualTransition

Fast Slow

Explicit Default


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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


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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


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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

E li i D i B i


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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

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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 finalsolution and there is need to Solve.

Two forms of velocity are available as

Initial Conditions for Explicit Dynamics:

Velocity(Translational)

Angular Velocity(Rotational)

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Training ManualInitial Conditions

Applied to single or multiple bodies in global orlocal Cartesian co-ordinate systems.

If rotational and translational velocities are appliedto the same body, the initial velocity of the bodywill be calculated as the sum of these twoconditions

E li i t D i B i


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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

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Acceleration

A constant body acceleration can be

applied to all bodies in the model. Thisresults in a body acceleration vector,defined via three Cartesian componentsbeing applied to all nodes in the modelprior to any constraints

Any constraints applied to the model willover-ride an applied body acceleration

Standard Earth Gravity

Special case of an Acceleration loadwhich is applied to all bodies.

Magnitude of acceleration is fixed atstandard earth gravitational acceleration

Acting direction can be applied in x, y, zdirections.

Any constraints applied to the model willover-ride any applied gravity

i

i

ib

m

Fx



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Pressure Constant and tabular Pressure loads can only be

applied to faces of flexible bodies.

Pressure is applied normal to element faces of scopedbodies.

Direction of applied pressure rotates with deformationof 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 ofscoped bodies.

Force applied to each node is equal to total forcedivided by number of mesh nodes in the scoping.

Resulting distribution of force is mesh dependent.

When defining tabular forces, define the analysis endtime 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.



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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 constraintscan 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 timezero should be zero.

For rigid bodies, the rotational degrees of freedomwill automatically be constrained if a displacementobject is scoped to the body.

Displacements can be applied in global or local

Cartesian co-ordinate systems.



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Velocity

Constant and tabular Velocityconstraints 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 bescoped 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.



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Impedance Boundary

Sometimes advantageous (more efficient) to limit the mesh

size by applying a boundary condition which allows outwardtraveling waves to pass out of the mesh without reflection. e.g. an expanding air blast or an underwater or underground

explosion.

Impedance Boundary provides a reasonable approximation.

where uN is the normal velocity

[c]boundary is the Material Impedance

pref is the Reference Pressure

uref is the Reference Velocity

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

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), it is taken to be the transient impedances ofthe elements to which the boundary is applied.



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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



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Training ManualExplicit Dynamic Project Files

File type Description

Results file (binary) Contains results data used for the main post-processing operations in Explicit

Dynamics.

name_{base_cycle_no}_{results_cycle_no}.adres

e.g. admodel_0_100.adres is the result file for cycle 100, referencing a base file

for cycle 0.

Results base file (binary) Contains b ase data that results fi les use.name_{base_cycle_no}_.adbase

e.g. admodel_0.adbase is the result base file for cycle 0.

Restart file (binary) Contains complete model database. A solve can be resumed from any restart file.

name_{save_cycle_no}.ad

e.g. admodel_500.ad is the save file for cycle 500.

Print 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

Log file (ASCII) Contains cycle increment data and error / warning messages

name.log

e.g. admodel.log is the log file

Project files created while solving a model



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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 localmachine 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



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Training ManualSolution Information

My Computer, In Process provides five Solution Outputoptions 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 time

increment 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 10often 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



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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.



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Time Increment

Show how the time step varies with time.

Fluctuations in time

step size should beexpected.

However, a reduction

in time step greater

than a factor of 10,

often indicates a

problem in the model

setup / progress.



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Energy Conservation

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



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Momentum Summary

Shows how the momentum of the system varies with time



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Energy Summary

Shows how the energy components of the system vary with time



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p y


Adding additional solution outputs

RMB Solution > Insert allows customized results to be specified

More details in Chapter 5: Results Processing

Explicit Dynamics Chapter 4 Exp Dyn Basics

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Transcript of Explicit Dynamics Chapter 4 Exp Dyn Basics