Explicit Dynamics Explicit Meshing

8/12/2019 Explicit Dynamics Explicit Meshing

1/51

6-1ANSYS, Inc. Proprietary

2009 ANSYS, Inc. All rights reserved.February 27, 2009Inventory #002665

Chapter 6

Explicit Dynamics:Meshing

ANSYS Explicit Dynamics


2/51

Explicit Dynamics: Meshing


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

Inventory #002665

Training ManualWhat is required of Meshes for Explicit Applications?

Uniform element size (in finest zoned regions)

Smallest element size controls the time step used to advance thesolution in time

Explici t analyses compute dynamic stress waves that propagate

throughout the entire mesh

Element size controlled by the user throughout the mesh

Not automatically dependent on geometry

Implic it analyses usually have static region of stress concentration wheremesh is refined (strongly dependent on geometry)

In explici t analyses, the location of regions of high stress constantly changeas stress waves propagate through the mesh

Mesh refinement is usually used to improve efficiency

Mesh transitions should be smooth for maximum accuracy

Hex-dominant meshing preferred

More efficient

Sometimes more accurate for slower t ransients


3/51




Inventory #002665

Training ManualMesh

Right-click Mesh in the Outl ine Tree to:

Insert

Method

Sizing

Contact Sizing Refinement

Mapped Face Meshing

Match Control

Pinch Inflation

Update

Generate Mesh

Preview Surface Mesh

Show Sweepable Bodies

Preview Inflation

Clean

Rename

Important for Explic it


4/51




Inventory #002665

Training ManualMeshing Methods

Solid Bodies Automatic

Tetrahedron

Hex Dominant

Sweep

Multizone

CFX-Mesh

Surface Bodies (Shells) Quadrilateral Dominant

Triangles

Uniform Quad / Tri Uniform Quad

Line Bodies (Beams)

Automatic


5/51




Inventory #002665

Training Manual

Tetrahedrons

Advantages

An arbitrary volume can always be filled

with tetrahedra

Can be generated quickly, automatically,

and for complicated geometry

Disadvantages

Element and node counts are higher than

for a hex mesh with a similar mesh density

Generally not possible to align the cells

with a flow direction

Not well suited for thin solids or annuli due

to non-isotropy of geometry and nature ofelement

Meshing Methods Solid Bodies


6/51




Inventory #002665

Training ManualMeshing Methods Solid Bodies

Tetrahedrons - Patch Conforming

Default Tetrahedron Mesher

All Faces, Edges, Vertices of the

geometry are respected during meshgeneration

Delaunay Method

Not good for Explicit Dynamics

Curves in Geometry are Reflected in the Mesh


7/51




Inventory #002665


Tetrahedrons - Patch Independent

Recommended Tet mesher for Explicit

Faces, Edges, Vertices not always respected

Octree Method

Element size Defined By

Maximum Element Size

Approx. number of Elements

Curves in Geometry NOT reflected in the Mesh

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


8/51




Inventory #002665

Training Manual

Hex Dominant Useful for meshing bodies that cannot be swept

Recommended for meshing bodies with large interior

volumes

The hex-dominant meshing algorithm creates a quad-

dominant surface mesh first, then pyramid and

tetrahedral elements are filled in as needed

Always check interior of mesh for good element structure

Control Messages will appear to warn you if volume may

not be suitable for hex-dominant meshing

Solid Model with Hex dominant mesh :

Tetrahedrons 443 (9%)

Hexahedron 2801(62%)

Wedge 124 (2%)

Pyramid 1107 (24%)

Meshing Solid Bodies


9/51




Inventory #002665


Hex Dominant Sometimes produces a better (more uniform) mesh if a size control is

placed on one or more edges / surfaces of a body


10/51




Inventory #002665

Training ManualMesh Methods - Sweeping

Sweep

Sweeping from a single source face to a single target face

Thin Sweep Good at handling multiple sources and targets for thin parts

Multizone

Uses a free decomposition approach

Attempts to automatically slice geometry into

sweepable regions

Supports multi-source and multi-target

Sweep methods for generating pure hex meshes


11/51




Inventory #002665

Training ManualMeshing Methods Sweeping

Multizone Direct decomposition of complex geometries at the time of meshing to

create a hex mesh

Select source andtarget surfaces forthe Multizone sweepmesher


12/51




Inventory #002665

Training ManualSweep vs. Thin Sweep

Use Sweep When: The side faces are not thin

You only have 1 source and 1target

The sweep direction changesalong the path

Use Thin Sweep When: The side faces are thin

In general, thin means that theside faces are small in relation to

the source faces (aspect ratio ofsides/sources is ~ 1/5th)

You only have multiple sourcesand targets

Path is linear

Sweep

Thin Sweep


13/51




Inventory #002665

Training ManualSweep vs. MultiZone

Use Sweep when you have a multibody part where some bodies should bemeshed with Sweep, and some with Patch Conforming Tet

Preview Sweepable Bodies shows all bodies that are sweepable

Use MultiZone when

you are meshing single body parts that are too complicated for Sweep

you have multiple sources and targets you need to respect

Example:

Using Sweep, the single body part (left) must be manually sliced into a Multibody part

containing five bodies (center) to obtain a pure hex mesh (right) With Multizone, it is meshed automatically!


14/51




Inventory #002665

Training ManualThin Sweep vs. MultiZone

Use Thin Sweep when you have a thin solid part where the source and target facesdont exactly match, and you dont care about the features on the target side

Multiple source Multiple target

Multiple sources captured Multiple targets ignored


15/51




Inventory #002665

Training ManualThin Sweep vs. MultiZone

Use MultiZone when you have a thin solid part where the source and target faces dontexactly match, and you care about the features on both sides

Multiple source Multiple target

Multiple sources captured Multiple targets captured


16/51




Inventory #002665

Training ManualMeshing Methods - Solid Bodies

This is the default Method for Explicit Ensures that preferred Hex meshes are generated whenever bodies can be

swept

If any bodies are not swept, the tetrahedron meshes generated for these bodies

should be remeshed by inserting a method that generates a Patch IndependentTet. mesh for those bodies

Automatic (Patch Conforming/Sweeping) Sweepable bodies are automatically swept

If a solid body cannot be swept it will be meshed using the Patch

Conforming Tetrahedron mesher

E li i D i M hi


17/51




Inventory #002665

Training ManualMeshing Methods Surface Bodies (Shells)

Quad Dominant Triangles Uniform Quad / Tri(not recommended for explicit)

Use sizing controls to obtain uniform element size

E li it D i M hi


18/51




Inventory #002665

Training ManualMeshing Line Bodies (Beams)

Method is Automatic

Cross-section is

assigned

Can be visualized as

line segments or

showing cross-section

Use sizing controls to

obtain uniform

element size

E li it D i M hi


19/51




Inventory #002665

Training ManualMesh Sizing

Sizing can be applied to Body

Face

Edge

Vertex

Three options

Element Size (Body, Face, Edge)

Number of Divisions (Edge)

Sphere of Influence (Body, Face, Edge, Vertex)



20/51




Inventory #002665

Training Manual

Element Size Element Size specifies average element edge length for bodies,

faces or edges

Often will also improves mesh quality

Mesh Sizing



21/51




Inventory #002665

Training Manual

Number of Divisions Specifies number of elements on

edge(s) of bodies or faces

Bias Type

Edge is discretized to include a bias

towards one end, both ends, or the

center

Bias Factoris ratio of largest element

size to smallest element size

Effect of the Bias Factor is displayed

Mesh Sizing



22/51




Inventory #002665

Training Manual

Number of Divisions Behavior

Soft (default)

Size control and Number of Divisions used is controlled by the

meshing algorithmAffected by proximity, curvature and local re-meshing

during the meshing process

Hard

Specified Number of Divisions is fixed and cannot be changed

by the meshing algorithm

Increases likelihood of mesh generation failure

Can have positive or negative effects on mesh quality

Soft HardNo Edge

Sizing

Mesh Sizing



23/51




Inventory #002665

Training Manual

Sphere of Influence Elements associated with the scoped entities, that are within the

Sphere Radius have the specified Element Size

Vertex Sizing

Body Sizing

For any entity other than a

vertex, the definition of a

Sphere of Influence

requires that a Coordinate

System be defined to set

the center of the Sphere

Vertex is the center of

the sphere

Vertex sizing is appliedto all entities

Mesh Sizing



24/51




Inventory #002665

Training Manual

Sphere of Influence Elements associated with the scoped entities, that are within the

Sphere Radius have the specified Element Size

Surface meshing

identical

Interior meshing

different

Scoped to 1 Face Scoped to 2 Faces

Scoped to 3 Faces Scoped to 1 Body

Mesh Sizing



25/51




Inventory #002665

Training ManualDefeaturing

Defeaturing reduces the influence that geometric

features have on the meshing process

Avoids generating small elements that may force explicitcalculations to run with a small time step

Two Meshing options are available for Defeaturing

Virtual topology

Defeaturing tolerance Can only be used with for Patch Independent Tetrahedral

meshes



26/51

p c t y a cs es g



Inventory #002665


Virtual TopologyDefault Mesh

Small feature controls smallest

element size and mesh type

Create a virtual face

from small feature

and larger bodyMesh is now uniform Hex

Feature is simply meshed over

Element size significantly improved



27/51

p y g



Inventory #002665


Virtual Cell

Virtual Topology & CAD



28/51

p y g



Inventory #002665


Defeaturing Tolerance

Only for Patch Independent Tetrahedrons

Without Defeaturing Tolerance

With Defeaturing Tolerance

mesh ignores small feature

Much better element size



29/51



Inventory #002665

Training ManualDM (DesignModeler) and Meshing

Bodies and Parts

Design-Modeler contains three different body types:

Solid body: Body has surface area and volume

Surface body: Body has surface area but no

volume

Line body: Body consists entirely of edges, no

area, no volume

By default, DM places each body into one part by itself

Individual parts will always be meshed separately

If bodies in separate parts share faces, the meshes

on those shared faces will not be matched

Multiple bodies in a single part will have matched

meshes on shared faces



30/51



Inventory #002665

Training Manual

Example:

In DM: 1 part, 1 body consisting of

1 solid

During Meshing: 1 solid ,1body

Entire solid meshed as one entity

No internal surfaces

DM

Mesh

DM and Meshing Bodies and Parts



31/51



Inventory #002665

Training Manual

Example:

In DM: 3 parts, 3 bodies consisting of 3

solids

During Meshing: 3 solids, 3 bodies

Each solid meshed independently

Nodes are not shared

Nodes do not line-up

DM

Mesh




32/51



Inventory #002665

Training Manual

Example:

In DM: 1 multi-body part, 3 bodies / solids

During Meshing:1 multi-body part, 3 bodies /

solids

Each solid meshed independently but node

connectivity among solids is preserved

DM

Mesh




33/51



Inventory #002665

Training ManualDM and Meshing - Slice

Slice geometry in Design Modeler to generate a Swept Hex Mesh

Original Geometry

Sliced Geometry

Default Mesh

Default Mesh



34/51



Inventory #002665

Training ManualDM and Meshing Slice

Combine Sliced Bodies into single Part to get Mesh to Match acrossbody boundaries

Single Body

Parts

Multi-body

Part



35/51



Inventory #002665

Training ManualDM and Meshing Shared Topology & Match Mesh

Overlapping Meshes and

Contact

Explicit Dynamic Analyses

require that there are no initialpenetrations at contact surfaces

For arbitrarily shaped bodies,

this requires that nodes on

surfaces that are initially incontact must match

Shared Topology and Match

Mesh Where Possible options

allow you to do this



36/51



Inventory #002665

Training ManualDM and Meshing - Shared Topology and Match Mesh

Specified for each Part (in DM) Applied at common boundaries of al l Bodies in the

Part

Options

Automatic (default)

Nodes are merged (bodies are bonded)

None

Bodies are meshed independently

Imprint

Meshes are across interfaces of bodiescontained in Multi-Body Parts

When used with Match Mesh Where

Possible option for Patch Independent

Tetrahdron meshing, can prevent unwantedinit ial contact penetration

New feature in 12.0. Currently only

implemented for tetrahedra


DM d M hi Sh d T l d M t h M h


37/51



Inventory #002665

Training ManualDM and Meshing - Shared Topology and Match Mesh

Automat ic None Imprint

No Match Mesh

Only Automatic has

matching meshes


DM d M hi Sh d T l d M h M t hi


38/51



Inventory #002665

Training ManualDM and Meshing - Shared Topology and Mesh Matching

Automatic None Imprint

Mesh matching

where possible

All cases have

matching meshes


DM d M hi S t W ld


39/51



Inventory #002665

Training ManualDM and Meshing - Spot Welds

Define points on source geometry

at location of the spot welds

Corresponding points on target

geometry are generated

Source geometry and target

geometry can be in contact or

separated

Meshing ensures that nodes are

generated at the spot weld points

Explicit Dynamics uses nodes todefine solid or breakable joints


DM and Meshing Mid Surface Creation


40/51



Inventory #002665

Training ManualDM and Meshing - Mid-Surface Creation

Mid-SurfaceReduces 3D geometry of constant thickness to a simplified

shell representation

Automatically places surface body at mid point between 3D

face pairs

Allows shell element type meshing in Explicit Dynamics

3D Model Mid-Surface representation


DM and Meshing Surface Extension


41/51



Inventory #002665

Training ManualDM and Meshing Surface Extension

Surface Extension

Creates a surface extension based on edgeselection

Often required after Mid-Surface operation

A th in solid modelThe model is converted

to a mid plane surface

model. The result is a

gap at the intersection

of the 2 parts

Extending the circular

edge closes the gap


DM and Meshing Named Selections


42/51



Inventory #002665

Training ManualDM and Meshing Named Selections

Create Named Selections in DM orMeshing

Can be used to apply constraintsand boundary conditions inExplicit Dynamics


DM and Meshing Cleanup and Repair of CAD


43/51



Inventory #002665

Training Manual

Edge and Face Merge for Model Simplification

Merge edges and faces based on angle criteria to simplify

the model

DM and Meshing - Cleanup and Repair of CAD




44/51



Inventory #002665

Training Manual

Repair





45/51



Inventory #002665

Training Manual

Face Delete

Selected faces for delete

Patch healing

Natural healing



FEModeler


46/51



Inventory #002665

Training ManualFEModeler

Import a finite element (FE) model from a NASTRAN bulk data file

orABAQUS Input file.

Import FE information from Workbench Meshing or Advanced

Meshing Import archived ANSYS data created using the CDWRITE

command.

Navigate and visualize the data contained in the model. Generate a geometry from an FE Model using the Geometry

Synthesis feature.

Create named components based on element selections.

Generate an ANSYS, NASTRAN, or ABAQUS input deck for

downstream analysis.


FEModeler


47/51



Inventory #002665

Training Manual

Import ANSYS model fi le into Workbench

Open the imported model in FEModeler

FEModeler


T i i M lFEModeler


48/51



Inventory #002665

Training Manual

Display Element Statistics in FEModeler

FEModeler


T i i M lFEModeler


49/51



Inventory #002665

Training Manual

Convert to Geometry (Geometry Synthesis / Skin Detection)

FEModeler


Training ManualFEModeler


50/51



Inventory #002665

Training Manual

Pass Geometry to Meshing

FEModeler


Training ManualWorkshop 3 Can Crush


51/51



Inventory #002665

Training Manual

Goal:Crush an aluminum beverage can and allow it to springback

Procedure:

Create an Expl ici t Dynamics (ANSYS) Analysis System Project

Select the units system and define the material propertiesImport, modify, and mesh the soda can geometry

Define analysis settings, boundary conditions, and external loads

Initiate the solution (AUTODYN - STR) and review the results

Explicit Dynamics Explicit Meshing

Documents

Transcript of Explicit Dynamics Explicit Meshing