Explicit Dynamics Exp Dyn Basics

Chapter 4 Explicit Dynamics Basics

ANSYS Explicit Dynamics

ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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February 27, 2009 Inventory #002665

Explicit Dynamics Basics

Explicit Dynamics (Mechanical) GUI

Training Manual

Menus Toolbars

Graphics Window

Tree Outline

Message Window

Details View

Status Bar ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Explicit Dynamics (Mechanical) GUI : Menus

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. Analysis Type


Product

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License



Explicit Dynamics (Mechanical) GUI : Toolbars

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.


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Explicit Dynamics (Mechanical) GUI : Toolbars

Training Manual

• “Standard” toolbar Bring up Mechanical Wizard (Not available for Explicit Dynamics)

Annotations

Comments

Capture Snapshot Solve Model

Slice Planes

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

Select mode

Selection Tools

Graphics Manipulation

Viewports

– 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. ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Explicit Dynamics (Mechanical) GUI : Outline Tree

Training Manual

• 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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Explicit Dynamics (Mechanical) GUI : Outline Tree

Training Manual

• 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. ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Explicit Dynamics (Mechanical) GUI : Details View

Training Manual

• 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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Explicit Dynamics (Mechanical) GUI : Graphics Window

Training Manual

• 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

Print Preview Tab

Report Preview Tab

Worksheet Tab ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Geometry •

Explicit Dynamics supports Solid, Surface and Line bodies.

•

Check that all geometric bodies have been imported –

Training Manual

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


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Geometry

Training Manual

• 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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Stiffness Behavior •

Training Manual

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


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Coordinate Systems

Training Manual

• 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.


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Connections - Body Interactions

Training Manual

• 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


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Connections - Contact Region • By default, if two faces of any Bodies are touching, or within a certain tolerance, a bonded Contact Region will be scoped automatically to the two faces

Training Manual

Automatically generated bonded contact

– 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 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Mesh

Training Manual

• 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 method

These selections are default for Explicit Dynamics (ANSYS) ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Physics Preference

Training Manual

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


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Relevance and Relevance Center

Training Manual

• 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: Medium

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Relevance: 0 Relevance Center: Fine



Relevance and Relevance Center

Training Manual

Relevance: -100 Relevance Center: Medium




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Smoothing

Training Manual

High

Low

Explicit Default ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Transition

Training Manual

Fast

Slow Explicit Default


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Default Mesh method for Explicit Dynamics

Training Manual

• Automatic (Patch Conforming/Sweeping) • Sweepable bodies are automatically meshed with Hex and Wedge Elements Produces better mesh if a size control is used on the swept face or body

Swept Face ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Training Manual

• 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 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Training Manual

• Patch Independent tetrahedron mesher • Recommended for Explicit Dynamics • Faces, Edges, Vertices are not always respected (Octree Method) • Override the default tetrahedron mesher (Patch Conforming) Max. Element Size = 2.5 mm

Max. Element Size = 1.0 mm

Curves in Geometry NOT reflected in the Mesh ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Explicit Dynamics

Training Manual

• 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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Initial Conditions

Training Manual

• 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)


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Initial Conditions

Training Manual

• 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


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Loads and Constraints

Training Manual

• 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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Training Manual

• 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

&x& i =

Fi +bi m

• 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 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Training Manual

• 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 coordinate 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. ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Training Manual

• 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. ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Training Manual

• 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.


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Training Manual

• 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 Impedance pref is the Reference Pressure uref is the Reference Velocity

(for an initially stationary structure at zero pressure, pref and 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 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Analysis Settings

Training Manual

• 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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Explicit Dynamic Project Files

Training Manual

Project files created while solving a model 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 base data that results files 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.prt e.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


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Solution

Training Manual

• 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 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Solution Information

Training Manual

• My Computer, In Process provides five Solution Output options to view automatically while the calculation is running:

Defaults

– 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 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 ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Training Manual

• 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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Training Manual

• 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.


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Training Manual

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


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Training Manual

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


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Training Manual

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


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Training Manual

• Adding additional solution outputs – RMB Solution > Insert allows customized results to be specified

More details in Chapter 5: Results Processing ANSYS, Inc. Proprietary © 2009 ANSYS, Inc. All rights reserved.

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Workshop 1 – Taylor Test (Cylinder Impact)

Training Manual

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

Procedure: Create an Explicit Dynamics (ANSYS) Analysis System Project Select the unit system and assign the material properties Create the rod and plate geometry in DesignModeler Mesh the two parts and set the initial velocity condition of the rod Define the analysis settings, boundary conditions, and applied loads Initiate the solution (AUTODYN - STR) and review the results


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Explicit Dynamics Exp Dyn Basics

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