Geometry Abstraction

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Geometry Abstraction Section Meshing
2001 Simulation Seminar
2001
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Geometric Abstraction and Meshing

• Design Geometry Realities

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Geometry Effects

• Quickly pass through the model construction phase
• Engineering begins after the results are available

Geometry provides the most promise to CAE
impacting design activities
Geometry is the biggest inhibitor to meshing
efficiency
Design Engineer needs complete, high quality
mesh of any automotive component in less than ½
day. Hiroyuki Umetani manager,
Development Dept. Information
Systems Toyota Motor Corporation
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A Break-Down of the CAE Process

• What is the most time consuming process?

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Direction of SDRCs CAE

• Much Focus on Pre-Processing
• Automatic Robust Tool for building FE Model

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Improvements during MS5 - MS7

• Some examples of the reduction time to build FE
  Model

1/10
1/50
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Powerful Geometry Abstraction

• Part contains 300 surfaces. Abstracted to 24
  meshing regions

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Customer Endorsements

• ZF Automotive supplier to many major OEMs 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 Geometry

• Topology Issues
• small edges
• compound edges
• sliver surfaces
• high aspect ratio
• missing surfaces
• topology too detailed
• reconstruction

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Small Edges

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

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Sliver Surfaces

• Narrow surface which causes distortions and
  stretched elements

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Disconnected 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 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 algorithms

• Bounded by surface shape and boundaries
• can distort elements beyond usefulness
• dictates element size

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Section 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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Section Meshing

• 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 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 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 Meshes

• Section meshing applies to solids also
• Sections can be used to map mesh volumes for
  brick elements generation

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Section Meshing

• 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
meshing approach to all types of parts
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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?

• Real Parts
• Automatically combine surfaces until user
  criteria is met

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Surface 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
Mesher
Fail
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Quality Check

• Find small edges
• Find sliver surfaces
• Find small holes
• Show me expendable connectors

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Quality Checks

• Highlight problem geometry

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Quality Checks

• 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 Layout

• Remove Curve
• Remove Connector
• Remove Loop

• Add Curve
• Add Connector
• Add Loop

• Auto Create
• Auto Remove Loop / Connector

• Replace Curve
• Replace Connector

• Manual Create
• Single Section Create

• Delete Section

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

• Display Adjacent
• Display Opposite
• Section Graphics Toggle

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Approach

• Natural operation - editing the wireframe -
  interactive
• Add / Remove / Replace
• Loops
• Curves
• Connectors
• Build sections on all surfaces
• Addressed isthmus, sliver topology
• UI consistency
• Additional Functionality
• Robust auto create
• Extended loop modification commands

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I-DEAS 8 - Procedure

• New Auto create
• Intelligent methods deployed to generate desired
  sections
• User controlled
• Conservative section generation
• 95 of generated section are meshable
• Wireframe edits
• Easy modification of the sections once all are
  defined
• Consistent UI (Add / Remove / Replace)
• Sections will rebuild after modifications without
  being deleted
• Full Process supported
• Other commands that enable the overall process
• Meshability check (Enhancement of existing check)
• New Manual element tools to correct resulting
  mesh
• Surface Patch Generation

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Performance

• Increased performance of sections generate on
  large models
• Wireframe edits are interactive regardless of
  model size
• New Auto create yields a base set of sections
  that are usable
• User now in a modify mode
• Highlights the strength and performance of the
  edit commands
• Extendable for better section generation
• For multi-surfaced sections use Meshability Check
  to verify limitations are not violated
• Feedback indicates where problem may be if check
  fails

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Workflow

• Workflow
• Auto Generate Sections
• Perform meshability check
• Perform section check
• Perform section free curve check
• Evaluate abstraction
• Wireframe Edits
• Target areas that need additional abstraction or
  modification for meshability
• Interactive commands allow user to quickly
  complete the abstraction
• Perform meshability checks as the user edits the
  sections
• Mesh sections
• Apply geometry based boundary conditions AFTER
  section meshing

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Results
Isthmus Surface from IGES Collapsed region
Resulting Single Section multi-looped section
Mesh on the Section
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Results
Isthmus Section now combined with adjacent
sections using new functionality
Resulting Mesh
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Results
Isthmus Surface
Resulting Section
Resulting Mesh
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MS8 Replace Curve
Original Surface
Replace A portion of one curve with the other
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Replace Curve
Eliminated the pinched area with Replace Curve
Resulting Mesh
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Replace Curve
Replace Curve Maintains connection with other
sections
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Mid-Surface Challenges for Section Mesh
A straight Automatic Pairing produces this
Surface extend fail
Surfaces arent trimmed back and stitched
Surfaces arent extended to wall
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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 close
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Project surface boundary and replace
User 1) Adds Curve projecting original edge
of surface 2) Replace original curve with
projected
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Quality Checks

• All geometric problems anticipated
• Meshing reduced to one iteration in most cases

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Meshing 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
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Meshing Issues - Manual Control
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Meshing Issues

• Element Collapse (under the Quality Checks icon
  stack)
• Collapse narrow (stretched) linear or parabolic
  triangular shells

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Mesh Generations

• Brick Elements from shell projection

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Mesh Generation

• Project Elements to Surface

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Augmentation 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 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 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 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/CAD

• Surfaces Mapping
• Imported Geometry from other CAD

Update Mesh on orphaned surfaces
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Surface 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?

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Surface Mapping

• Section meshing used to define meshing regions

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Surface Mapping

• 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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Surface Mapping

• Associativity reintroduced to the FEM from the
  mapping process
• Additional features beyond mapped geometry
  automatically maintained

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Non-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 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

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

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Non-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 Weld
Spot weld every 40mm
3D points projected onto surface defines
meshing node location creates associative
element definition for rigid bar or
spring

• Automatic meshing of entities without geometry

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Non-Geometric entities

• Lumped mass for CG of connecting body
• Rigid element network for force distribution to
  center of mass

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Summary

• 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

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Future Development

• Further abstraction of outer boundary of section
  to remove narrow sliver areas without having to
  expand to neighboring surface
• Abstraction via feature recognition
• make a beam abstraction from 3D geometry
  (stiffeners)
• select surfaces
• software automatically creates cross section
  properties
• define connection information to rest of model
• Automatic multi-surface section definition based
  on element size selection
• Expand the element support to entire element
  library

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