geometry abstraction & section meshing

Geometry Abstraction &

Section Meshing

Geometry Abstraction &

Section Meshing

2001 Simulation Seminar

2001

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Geometric Abstraction and MeshingGeometric Abstraction and Meshing

Design Geometry Realities

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• Quickly pass through the model

construction phase- Engineering begins after the results are available

Geometry EffectsGeometry Effects

Geometry is the Geometry is the biggest inhibitor to biggest inhibitor to meshing efficiencymeshing efficiency

Geometry provides Geometry provides the most promise to the most promise to CAE impacting CAE impacting design activitiesdesign activities

“Design Engineer needs complete, high quality mesh of any automotive component in less than ½ day”.

Hiroyuki Umetanimanager, Development Dept.Information SystemsToyota Motor Corporation

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A Break-Down of the CAE ProcessA Break-Down of the CAE Process

• What is the most time consuming process?

Post Processing9% Percentage of TimePercentage of Time

Geometry Creation

42%

SDRC, 1997

Solve4%

Boundary Conditions

9%

Mesh Generation17% Prepare Geometry

for Export

6%

Repair Imported Geometry

13%

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Direction of SDRC’s CAEDirection of SDRC’s CAE

• Much Focus on Pre-Processing

• Automatic & Robust Tool for building FE Model

Tim

eT

ime

IterationIteration11

Before

Today

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Improvements during MS5 - MS7Improvements during MS5 - MS7• Some examples of the reduction time to build FE Model

0

5

10

15

20

Time (hours)

MS5 MS6 MS7

Crank Shaft

Bracket

1/101/10

1/501/50

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Powerful Geometry AbstractionPowerful Geometry Abstraction

•Part contains 300 surfaces. Abstracted to 24 meshing regions

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Customer EndorsementsCustomer Endorsements

• ZF Automotive supplier to many major OEM’s of

Driveline and chassis technology- Complex parts/assemblies (I.e. transmission cases)

• “Almost 30% development time saved by using I-DEAS

Section Meshing Technology”Dr. Kelkel

ZF, Germany

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Typical Design GeometryTypical Design Geometry

• Topology Issues- small edges

- compound edges

- sliver surfaces

- high aspect ratio

- missing surfaces

- topology too detailed

- reconstruction

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Small EdgesSmall Edges

• Force small element edges- Causes high distortions for elements larger than edge- Dictates element size

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Sliver SurfacesSliver Surfaces

• Narrow surface which causes distortions

and stretched elements

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Disconnected SurfacesDisconnected Surfaces

• Surfaces which are not “stitched” together do not

share the same edges

• Causes discontinuous mesh that do not allow forces

to transfer across the discontinuity

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Poorly Parameterized SurfacesPoorly Parameterized Surfaces• Surfaces which do not have evenly spaced iso

lines do not have evenly spaced parameter space

in 3D

• Results in skewed and stretched elements

• Especially in imported geometry

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Meshing algorithmsMeshing algorithms

• Bounded by surface shape and

boundaries- can distort elements beyond usefulness

- dictates element size

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Section MeshingSection Meshing

• Expands the boundaries of surfaces- relaxes mesh area therefore improving quality of elements

- removes boundary and shape constraints that negatively effects meshing

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• Permits edge connectors to be removed- Removes requirement of having at least one

element/edge

- Relaxes elements and therefore improves mesh quality

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Too Much DetailToo Much Detail

• Small holes usually have adverse effect

on mesh- increases number of nodes/elements in unimportant area

of model

- can distort elements because of local curvature

- but are internal boundaries which meshing algorithms must address

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Too Much DetailToo Much Detail

• Often only one single node is needed to

represent hole for boundary condition

definition

• model more efficient

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Too Much Detail

• Topology Suppression

• History Supported- requires integrated modeler

• Automatic / Manual Modes

• Loop Collapsed to Point

• Curve Collapsed to Point

• Ignores Small Edges

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Solid MeshesSolid Meshes

• Section meshing applies to solids also

• Sections can be used to map mesh

volumes for brick elements generation

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• Capture Analysis Intent- User Control- Puts the model size (degrees of freedom) within the

control of the user- Does not change the geometry (surfaces, edges, . ) of

the part- Overhead minimal because no additional geometry is

created- all nodes are on original surfaces and elements can span

surface boundaries- Integrity of part is intact

In Short Section Meshing has become the preferred In Short Section Meshing has become the preferred meshing approach to all types of partsmeshing approach to all types of parts

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Where do I start?Where do I start?

• I know I can abstract my model but with

complex models - How do I find the problem areas?

- What element size should I use?

- How much time should I spend abstracting?

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Where Do I Start?Where Do I Start?

• Real Parts- Automatically combine surfaces until user

criteria is met

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Surface and Section Quality ChecksSurface and Section Quality Checks

• The meshing job is a balance of FEM size (element

size) and how much interaction the user wants to

go through to get the element size he wants

• In the past modeling time was unpredictable

because it was impossible to anticipate how many

of these problem situations would arise

Try element size

Fail

Mesher

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Quality CheckQuality Check

• Find small edges

• Find sliver surfaces

• Find small holes

• Show me

expendable

connectors

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Quality ChecksQuality Checks

• Highlight problem

geometry

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• How many bad surfaces do I have?

• Indicates - how much work I have to do to

make useable mesh based on criteria

- if not many I know what element size this geometry will take

- if checks are made on sections, then same indications are available and user knows how much work is left

• Continue until all sections disappear

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Section Mesh LayoutSection Mesh Layout

• Auto Create• Auto Remove

Loop / Connector

• Manual Create• Single Section Create

• Display Adjacent• Display Opposite• Section Graphics Toggle

• Section Check• Show Orphan Surface• Section Graphics Toggle• Surface Patch Generator• New Meshability Check

• Replace Curve• Replace Connector

• Add Curve• Add Connector• Add Loop

• Delete Section

•Remove Curve•Remove Connector•Remove Loop

Results ResultsIsthmus Surface from IGES

Collapsed region Resulting Single Sectionmulti-looped section

Mesh on the Section

Results ResultsIsthmus Section now combined with adjacent sections using new functionality

Resulting Mesh

Results Results

Isthmus Surface

Resulting Section

Resulting Mesh

Original Surface

MS8 Replace CurveMS8 Replace Curve

Replace A portion of one curve with the other

Replace Curve Replace Curve

Eliminated the pinched area with Replace Curve

Resulting Mesh

Replace Curve Replace Curve

Replace Curve Maintains connection with other sections

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Mid-Surface Challenges for Section MeshMid-Surface Challenges for Section Mesh

Surfaces aren’t

extended to wall

Surfaces aren’t

trimmed back

and stitched

Surface extend fail

A straight Automatic

Pairing produces this

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Section Add Curve Section Add Curve

Midsurfaces not fully extended

and walls not scarred

Need to use Section Meshing

to repair

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Gap too large for auto section to closeGap too large for auto section to close

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Project surface boundary and replaceProject surface boundary and replace

User

1) Adds Curve projecting

original edge of surface

2) Replace original curve

with projected

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• All geometric problems anticipated

• Meshing reduced to one iteration in most cases

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Meshing Issues - Tet HexMeshing Issues - Tet Hex

• Tet Hex meshing allow mixing of

Parabolic Tets with Bricks

• Multipoint Constraint elements (MPCs) tie up loose mid nodes

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Meshing Issues - Manual Control Meshing Issues - Manual Control

Element Project/Element, Orient Off Geometry, Project Element Collapse

/Check Mesh, Element Collapse

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Meshing Issues - Manual ControlMeshing Issues - Manual Control

Element Extrude Normal

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Meshing IssuesMeshing Issues

• Element Collapse (under the Quality Checks icon stack)

- Collapse narrow (stretched) linear or parabolic triangular shells

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Mesh GenerationsMesh Generations

• Brick Elements from shell projection

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Mesh GenerationMesh Generation

• Project Elements to Surface

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Augmentation of GeometryAugmentation of Geometry

• Geometric information; physical representation- Additional structure.- Calculation surface to measure energy propagation.- Contact regions, FEM or geometry based.- Weld attachments, reference series of locations

• Non-geometric information; non-physical

representation- interpolated surfaces.- lumped masses, springs, or beams.- gaps, coupled dofs, or constraint equations.

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Adaptation of the FEMAdaptation of the FEM

• Associative to design definition- geometry change

- abstraction change

- boundary conditions

- loading conditions

- surface mapping

• Surface mapping/compare parts- domestic/imported

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Mesh GenerationMesh Generation

• Many new options and features for mesh

construction, including:- Automatic tetrahedral to hexahedral interface

- Create Thickness Results

- Element Extrude Normal

- Element Project

- Element Collapse

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Improve Elements’ QualityImprove Elements’ Quality

• Nodes Drag - Viewing quality values- Improve surface mesh quality

• Auto Settings during meshing- Automatic Mesh Checking & Improvement

• Tetra Fix- Move Mid Nodes + Straighten Edge

• Plump- Fix Flat tet elements

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Integrated CAE with 3D/CADIntegrated CAE with 3D/CAD

• Surfaces Mapping - Imported Geometry from other CAD

Replace Orphaned Surfaces

Update Mesh on orphaned surfaces

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Surface MappingSurface Mapping

• Can foreign CAD geometry be Associative to FE data?

• What if the model is a mixture of foreign CAD surfaces and I-DEAS generated geometry complete with history?

Foreign Foreign CADCAD

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• Section meshing used to define

meshing regions

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• New design introduced from packaging detail design work

• User can map new surfaces, edges, and surface normals into correct orientation for feature replacement

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• Associativity reintroduced to the FEM from the mapping process

• Additional features beyond mapped geometry automatically maintained

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Non-geometric RepresentationNon-geometric Representation

• Midsurface

• Weld points- usually modeled with rigid elements or couples

• Rigid bodies which I do not want to mesh- usually modeled with lumped masses and rigid element- issues about connections and associativity

• Connections to other components which transfer force but not infinitely stiff

- most conveniently modeled between two point with beams and possibly use of some rigid elements

- bolt connections

• Contacting surfaces between two bodies or portions of same part

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Non-Geometric entitiesNon-Geometric entities

• Rigid elements for U joint link

• Automated meshers need to recognize connection points between nodes on the hole and rigid element connections

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Non-Geometric entities Non-Geometric entities

• Spring elements and lumped masses need to be associative to the model which are meshed on modeled geometry

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Non-Geometric EntitiesNon-Geometric Entities

•Anchor node definition•When mesh needs to match node locations with other elements which do not share geometric associations

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Spot WeldSpot Weld

• Automatic meshing of entities without geometry

Spot weld every 40mm

3D points projected onto surface defines meshing node location creates associative element definition for rigid bar or spring

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SummarySummary

• Section meshing has become the preferred

meshing approach to all model situations where

shell and solid elements are automatically

generated

• Geometry playing a more important role in FE

efficiency- for the CAE processes to have a more positive impact on the

design- to make it a reality to evaluate as many design alternatives- automatically update the design from parameter studies and

optimization activities

geometry abstraction & section meshing

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