MeshingTechniques-TrainingWebinar-Abaqus612

(1)

DASSAULT SYSTÈMES SIMULIA CORP. RISING SUN MILLS 166 VALLEY STREET PROVIDENCE, RI 02909-2499 www.simulia.com

April 4, 2013

Release Authorization and Stipulations

Dassault Systemes Simulia Corp. (SIMULIA) retains the copyright to this document.

These training notes are available by special arrangement from the SIMULIA

Learning Community to the Authorized Party (company or individual) whose

details appear in the watermarked text.

Release of these training notes in PDF format is made with the following

stipulations:

1. The materials are for personal use by the Authorized Party only.

2. The Authorized Party may view and print these training files, but must not

otherwise attempt to modify their contents, or extract content from the files.

3. The training notes may not be distributed or otherwise retransmitted without

separate, express written approval from SIMULIA.

4. The training notes may not be sold.

Visit the SIMULIA Learning Community (www.simulia.com/learning) for additional

training materials, tutorials and technical commentary.

(2)

R

Meshing Techniques in Abaqus

6.12

April 2013, Abaqus 6.12

See the associated SIMULIA Learning Community post:

https://swym.3ds.com/#post:18544

More in-depth training on this topic is provided in the SIMULIA training course:

Abaqus/CAE: Geometry Import and Meshing

For more information visit

http://www.3ds.com/simulia/

w w w .3 d s.co m | © Dassa u lt S y stè m e s

About this webinar

Objectives

Getting users started with Mesh Module basics Highlight capabilities of the mesh module in Abaqus Demonstration with a simple examples

Target Audience

Simulation Analysts who have recently started using Abaqus as well as those who use Abaqus as a key meshing tool.

Prerequisites

Familiarity with Abaqus/CAE will be very useful but is not required. Basic knowledge of finite element analysis.

(3)

Agenda

General Capabilities of the Abaqus Mesh Module Mesh Generation Techniques

Orphan Meshes and Mesh Editing Tools

Demonstration 1: Importing and Editing an Orphan Mesh

Bottom-Up Meshing

Demonstration 2: Bottom Up Meshing

Verifying Mesh Quality Questions w w w .3 d s.co m | © Dassa u lt S y stè m e s

Meshing Approach

Approaches to creating a mesh

Bottom-up approach: Traditional approach is to construct mesh to create geometry

(4)

General Capabilities of the Mesh module

General capabilities of the Mesh module

Allows you to mesh an assembly using various levels of automation and controls to suit the needs of your analysis

Assign mesh attributes and set mesh controls to specify: I. Meshing technique

II. Element shape III. Element type IV. Mesh density Generate the mesh

Query and verify the mesh for: I. Number of nodes and elements II. Element type

III. Element quality IV. Mass properties

Meshing Toolbar

Global Seeds

Local Seeds

(5)

Mesh Generation Techniques (1/11)

Free meshing

Free meshing uses no pre-established mesh patterns, making it impossible to predict a free mesh pattern before creating the mesh.

Element shape options available for free meshing two-dimensional regions:

Quadrilateral, Quadrilateral-dominated, Triangular

Element shape options available for free meshing three-dimensional regions:

Tetrahederal w w w .3 d s.co m | © Dassa u lt S y stè m e s

Mesh Generation Techniques (2/11)

Swept meshing

A mesh is created on one side of the region, known as the source side.

The nodes of that mesh are copied, one element layer at a time, along the connecting

sides of the region until the final side, known

as the target side, is reached.

The source and target sides are automatically located by Abaqus.

source side

target side

nodes copied from the source side to each element layer and to the target side

Extruded mesh sweep path:

straight line

(6)

Mesh Generation Techniques (3/11)

Requirements for sweep meshable regions Topological

The source side may contain multiple faces Target side must have only one face Connecting sides may contain multiple faces

I. provided that the faces conform to a rectangular grid

connecting sides source side w w w .3 d s.co m | © Dassa u lt S y stè m e s

Mesh Generation Techniques (4/11)

Requirements (cont'd) Geometric

Adjacent faces will be combined to form the source side only if the edge dihedral angles are not too far from 180º

Not sweep meshable Sweep meshable

(7)

Mesh Generation Techniques (5/11)

Structured meshing

The structured meshing technique generates meshes using simple predefined mesh topologies.

Abaqus transforms the mesh of a regularly shaped region, such as a square or a cube, onto the geometry of the region you want to mesh.

Structured meshing generally gives the most control over the mesh.

Three-dimensional structured meshable regions

Simple mesh topology

structured tri meshes w w w .3 d s.co m | © Dassa u lt S y stè m e s

Mesh Generation Techniques (6/11)

Structured meshing (cont’d)

Limitations

The region must have no holes, isolated faces, isolated edges, or isolated vertices.

hole isolated face isolated edges isolated vertices

(8)

Mesh Generation Techniques (7/11)

You can eliminate holes (whether they pass all the way through the part instance or just part way through) by partitioning their circumference into halves, quarters, etc.

partition partitions

partitions

Limit arcs to 90or less to avoid concavities along sides and at edges. For example, the model shown at right has been partitioned so that a single region with a 180° arc becomes two regions with 90° arcs.

Mesh Generation Techniques (8/11)

All the faces of the region must have three or more sides.

For example, if the model at right is not partitioned, the semicircles at either end of the model will have only two sides each.

partition

The angles between sides should be as close to 90° as possible; partition to eliminate angles greater than 150°. The ideal region is the cube shown at right: the angles between sides are 90°.

(9)

Mesh Generation Techniques (9/11)

Cube-shaped regions can have combined

faces.

Combined faces automatically recognized; no user control available. All faces in the combined face must have same underlying geometry. Interior edges must conform to regular mesh pattern.

Meshable

Unmeshable because edges do not conform to regular mesh pattern

Mesh Generation Techniques (10/11)

Mapped meshing

Special case of structured meshing 4-sided surface regions Allows for improved mesh quality On by default for:

Swept hex/hex-dominated mesh using advancing front algorithm

Free quad/quad-dominated mesh using advancing front algorithm Free tetrahedral or triangular mesh

Mapped meshing applied

indirectly by meshing a region and allowing Abaqus/CAE to apply mapped meshing where appropriate

(10)

Mesh Generation Techniques (11/11)

Mapped mesh example

Free tet mesh Fill 4-sided patches with mapped tri meshes

Enabling Various Meshing Techniques (1/3)

“Which regions are meshable?”

Abaqus/CAE automatically determines meshability for each region based on its geometry and mesh controls.

Regions are color coded to indicate their currently assigned meshing technique:

free-meshing technique

structured-meshing technique

swept-meshing technique cannot be meshed using current mesh technique

(11)

Enabling Various Meshing Techniques (2/3)

Changing the element shape from Hex to Tet changes the technique from unmeshable to meshable.

Enabling Various Meshing Techniques (3/3)

Partitioning to make regions meshable

Most three-dimensional part instances require partitioning to permit hexahedral meshing. Complex geometries often can be partitioned into simpler, meshable regions. Partitioning can be used to:

Change and simplify the topology so that the regions can be meshed using primarily hexahedral elements with the structured or swept meshing techniques.

(12)

Mesh Compatibility (1/4)

Different regions of the same part instance can be meshed using different elements types, such as tetrahedra and hexahedra.

Tie constraints are created automatically to connect the regions.

Allows hexahedra to be used adjacent to contact surfaces or in high gradient regions where accuracy is essential, with tetrahedra in other regions.

When a region is meshed, an existing mesh on an adjacent region is unaffected.

tie constraints inserted automatically at partition w w w .3 d s.co m | © Dassa u lt S y stè m e s

Mesh Compatibility (2/4)

Currently it is not possible to obtain meshes automatically that are compatible between part instances.

If mesh compatibility is required between two or more bodies, first try to create a single part that contains all the bodies.

Multiple part instances can be merged into a single part instance in the Assembly module.

Different material regions can be separated using partitions. If the two objects must be modeled as separate parts, consider using tie constraints to “glue” two regions together.

Alternatively, merge instance meshes into a conforming orphan mesh.

Using tie constraints to glue the cylinder to the block: exploded view of assembly (top) and mesh

(13)

Mesh Compatibility (3/4)

Merging instance meshes into a conforming orphan mesh

Mesh topology and node positions must conform

Single step creates orphan mesh part and replaces instances

Works with any combination of dependent/independent/native/orphan instances

Sections are propagated from the base mesh parts to the resultant part

Mesh Compatibility (4/4)

Example

Approach 1: Tie constraints (labor intensive in this case) Approach 2: Merge meshes (relatively easy)

A part partitioned into 112 meshable cells

A 10×10 pattern of dependent part instances Part mesh

Side 1 Side 2

Side 3

(14)

Orphan Meshes (1/2)

Orphan mesh

An existing mesh can be imported from: Abaqus input (.inp) file

Abaqus output database (.odb) file

Nastran bulk data (.bdf) file

ANSYS input (.cdb) file

STL file (via plug-in)

An imported mesh is called an orphan mesh because it has no associated parent geometry.

Native mesh

A mesh generated for a geometric part in Abaqus/CAE will maintain its association with the parent geometry; this is a native mesh.

Imported mesh of a boot seal

Orphan Meshes (2/2)

By default, the imported mesh is considered a single part.

ThePart Copytool, however, can be used to separate disconnected regions of the model into individual parts.*

(15)

Mesh Editing (1/15)

Mesh editing tools are provided for both orphan and native meshes.

Orphan meshes can be modified in the Mesh

module:

Create/delete nodes or elements Move nodes (edit or drag) Merge nodes

Repair poor elements (manually or automatically)

Offset solid or shell mesh layers Flip shell element normals Convert tri shell mesh to tet mesh Remesh a planar, triangular, orphan mesh

Mesh Editing (2/15)

Native meshes can also be modified in the Mesh

module. The association with parent geometry is maintained.

Move nodes (edit or drag) Repair poor elements manually Convert elements from first-order to second-order and vice versa (via element type assignment)

Create/add orphan elements to a native mesh (“hybrid” mesh; i.e., a mesh contains

both native and orphan elements)

Offset solid or shell mesh layers (also a “hybrid” mesh)

(16)

Mesh Editing (3/15)

Creating elements

Supported in the Mesh module for both native and orphan meshes.

When an orphan element is added to a native mesh, it results in a “hybrid” mesh. A Tip button shows the node order sequence for the selected element shape.

Invalid elements are detected.

Mesh Editing (4/15)

Moving nodes (in orphan and native meshes)…method 1 The user may specify, in any coordinate system, either

the new coordinates or

the coordinate changes (offsets dx, dy, dz, dr, dq, etc.).

Sequential incremental changes can be applied without having to reselect the nodes.

(17)

Mesh Editing (5/15)

Moving nodes (in orphan and native meshes)…method 2

Can also interactively drag nodes of a mesh and obtain feedback on the mesh quality.

Elements that fail solver checks with errors are highlighted in MAGENTA.

Elements that fail solver checks with warnings are highlighted in YELLOW.

Mesh Editing (6/15)

Layers of solid meshes can be created by offsetting from a shell mesh.

The starting point is a shell orphan mesh. Shell mesh is “thickened” by offsetting nodes normal to the boundary and building

elements that propagate out in the normal direction.

Continuum shell elements can be created using this approach.

(18)

Mesh Editing (7/15)

Conversely, shell meshes can be created by offsetting from element faces.

Mesh Editing (8/15)

Repairing orphan/native meshes manually Split a quad into two triangles Combine two triangles into a quad Swap diagonal for two adjacent triangles Collapse an edge of a triangle or quad

(19)

Mesh Editing (9/15)

split element Improved mesh swap diagonal collapse edge (to vertex) collapse edge (to midpoint) move node Original mesh (orphan or native) w w w .3 d s.co m | © Dassa u lt S y stè m e s

Mesh Editing (10/15)

Merging orphan meshes

Unconnected nodes within a part can be merged. (element size 4.0) Select the nodes and specify a tolerance

(20)

Mesh Editing (11/15)

Advanced mesh editing tools

An orphan mesh part can be created from a native mesh.

The mesh is effectively disassociated from its parent geometry.

Some advanced features:

Linear triangular elements with short edges can be removed automatically. A closed shell of linear triangles can be filled with tets.

A solid mesh can be converted to a shell mesh

Mesh Editing (12/15)

Repairing orphan meshes automatically

Limitation: Only linear elements can be auto-repaired.

(21)

Mesh Editing (13/15)

Recipe for tet meshing bad geometry

1. Create a native mesh of linear triangles in one of two ways: a) Mesh the solid part with tet boundary elements b) Convert the solid part into a shell part

(Part module: Shape>Shell>From Solid), then mesh it with triangles

2. Convert the native mesh into an orphan mesh part. (Mesh module: Mesh>Create Mesh Part)

3. Automatically collapse short edges in the orphan shell mesh. 4. Manually repair any remaining bad elements or gaps. 5. Fill the closed shell of linear triangles with tets. 6. Convert to second-order tets, if needed.

Mesh Editing (14/15)

Creating a shell mesh from a solid mesh Tool allows you to convert a solid element mesh to a shell element mesh.

Typical applications:

Converting an existing tet mesh to a tri shell mesh, then improving quality of the tri elements via mesh editing and refilling with tet elements.

Converting a solid tet or hex/wedge mesh to a tri/quad mesh for a shell

analysis Hollow

(22)

Mesh Editing (15/15)

Undo/Redo for mesh editing

Multiple Undoand Redooperations are supported for all mesh editing functions

Except for merging meshes in the assembly

Intermediate mesh copies are stored in memory until the specified cache size is exceeded w w w .3 d s.co m | © Dassa u lt S y stè m e s

Demonstration 1: Importing and Editing an Orphan Mesh

This demonstration shows how to use some of the orphan mesh editing tools available in Abaqus/CAE. A mechanical component meshed with first-order tetrahedral elements will be imported and modified for the purpose of illustration.

(23)

Bottom-Up hex meshing is available for cases

where the Top-Down approach cannot complete the desired tasks

Allows a previously unmeshable cell to be filled incrementally in multiple steps

May choose to mesh some boundary faces first, before filling the cell’s interior

Bottom-Up Meshing (1/2)

Bottom-Up Meshing (2/2)

As the example below illustrates, bottom-up meshing allows more complex geometric solids to be hex meshed.

Objective is to fill regions with hex elements using an incremental, user-controlled meshing strategy.

Maintains association of the mesh with the geometry whenever possible.

unmeshable using a top-down approach sweep

region structured

(24)

Basic Features (1/4)

1. Sweep mesh

Specify source side, connecting sides, and (optionally) target side.

Specify source side, target side, number of layers.

2. Extrude mesh

Specify source side, extrusion vector, number of layers, bias ratio.

3. Revolve mesh

Specify source side, axis of revolution, angle of revolution, number of layers.

4. Offset mesh

Specify source side, total thickness, number of layers.

Target Side (Only 1 face allowed)

Source Side (1 or more faces) Connecting Sides

(1 or more faces per side)

Basic Features (2/4)

A side may comprise any of the following: geometric faces

faces of solid elements 2D elements

Examples of sweep-meshable topologies:

Source Side

Target Side

Connecting Side

(25)

Basic Features (3/4)

The bottom-up mesh is automatically associated with only the specified geometric entities (source, connecting side, target)

mesh-geometry association is often incomplete. Can manually associate bottom-up meshes with the geometry:

associate element faces with a geometric face associate element edges with a geometric edge associate a node with a vertex

Yellow mesh entities are already associated with the geometric entities. Loads, BCs, etc. will be transferred to only these mesh entities.

Basic Features (4/4)

Using bottom-up meshing with orphan meshes

All bottom-up meshing methods may be used on orphan mesh parts

Specify source side as collection of element faces on orphan mesh part or dependent part instance Extrusion examples:

Target side (colored white) is used to define the extrusion distance

Nodes are not matched or shared on target source

target

(26)

Demonstration 2: Bottom-Up Meshing

1. In this demonstration, the part shown below will be meshed using both top-down and bottom-up meshing techniques. w w w .3 d s.co m | © Dassa u lt S y stè m e s

Verifying Mesh Quality (1/3)

Shape metrics

Abaqus/CAE can generate plots that highlight elements whose aspect ratios, maximum and minimum angles, and shape factors exceed specified limits.

The following information is displayed in the message area: Total number of elements

Number of distorted elements Average distortion

(27)

Verifying Mesh Quality (2/3)

Size metrics General

Identifies short/long edges and how well native mesh conforms to parent geometry

Abaqus/Explicit analysis:

Approximates the element-by-element stable time increment

Requires material and section definitions and assignments Acoustic analysis:

Identifies elements that may not be suitable for modal or steady-state Abaqus/Standard analyses above a desired frequency w w w .3 d s.co m | © Dassa u lt S y stè m e s

Verifying Mesh Quality (3/3)

Analysis checks

Elements that will produce errors or warning in the analysis can be highlighted.

Can create:

Element sets containing highlighted elements

Geometry sets for geometric edges, faces, or cells that host the highlighted elements

In most cases it will be obvious from the element shape why the input file processor issued an error or a warning.

If necessary, you can submit a datacheck analysis from the Job module and review the messages that Abaqus writes to the data file.

Current limitation:

Analysis checks are not currently supported for beam, gasket, and cohesive elements.

(28)

Legal Notices

The Abaqus Software described in this documentation is available only under license from Dassault Systèmes or its subsidiary and may be used or reproduced only in accordance with the terms of such license.

This documentation and the software described in this documentation are subject to change without prior notice.

Dassault Systèmes and its subsidiaries shall not be responsible for the consequences of any errors or omissions that may appear in this documentation.

No part of this documentation may be reproduced or distributed in any form without prior written permission of Dassault Systèmes or its subsidiary.

Printed in the United States of America.

Abaqus, the 3DS logo, SIMULIA, and CATIA are trademarks or registered trademarks of Dassault Systèmes or its subsidiaries in the US and/or other countries.

Other company, product, and service names may be trademarks or service marks of their respective owners. For additional information concerning trademarks, copyrights, and licenses, see the Legal Notices in the Abaqus Installation and Licensing Guide.