CAD-CAE Integration
Yogesh Kulkarni
Software Development Manager, Autodesk, Pune, India
Speaker’s Bio-data
• Currently, Software Development Manager at
Autodesk, Pune, India
• Before Autodesk, worked in companies like
PTC, SDRC, UGS, with total CAD software
development experience of about 14-15 years.
• Bachelors and Master’s degree in Mechanical
Engineering.
Agenda
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Introduction
CAD-CAE interop
Idealization/Model Simplification
Can features help?
Feature info export and issues
References/Videos
Introduction
• CAD: Computer Aided Design
• CAE: Computer Aided Engineering
(FEA : Finite Element Analysis)
• CAD->CAE happens “over the wall”.
– Once CAD design is done, designer passes
model “over the wall” to CAE analyst.
– After reviewing results, Analyst may suggest
design changes.
– Model is sent back again “over the wall”.
– This process may happen multiple times
(iterative)
Typical Workflow
Model Pre-Processing
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Healing
Tweaking Geometry
Removing Geometric Features
Regularizing Geometry
Finding Surface Overlap
Validating Geometry
Dimension Reduction
CAD-CAE Interop – Its different !!
• CAD-CAD interop between system aims at
preserving Geometry-Topology-Intent as
intact as possible.
• Whereas, CAD to CAE interop:
– Can Involve change in dimension of entities
– Will Usually Employ Differing Amounts of Detail
– Most Often Requires Idealization (using Engineer’s
Judgment)
The difference – Idealization!!
• CAD models are detailed mainly for manufacturing
requirement
• Whereas CAE typically does not like minute details
• Apart from removing small details, it may take help of
symmetry of part and even dimension reduction to reduce
complexity so as to have quicker, well-formed analysis
results
CAD centric or CAE centric
• In the CAD-centric process, the design is done in
CAD system and then in an iterative design
process, where design changes and analysis is
repeatedly performed, is used to improve or
refine the design.
• In the CAE-centric process, engineering analyses
are performed initially to define and refine a
design concept using idealized analysis models
before establishing the CAD product model.
• Model Simplification discussed in this
presentation is of CAD-Centric approach.
Idealization in CAD model
• To safeguard proprietary knowledge many CAD
modelers do not expose feature information.
• Also, data capture methods like laser scanning,
neutral data translators give CAD models which
do not have feature information.
• Idealization on such ‘dumb’ CAD models is
classified into two types:
– Tessellated : faceted geometry, typically triangles,
generated from point cloud data
– Exact: either Boundary Representation [B-rep] or
Constructive Solid Geometry [CSG]
CAD model idealization approaches
• Surfaces : low pass filtering, face cluster based
simplification and size based entity
decimation.
• Volumes : voxel based and effective volume
based techniques. It is advantageous for
multi-resolution modeling and capable of LOD
(Level of Details) simplification of features
• Dimension Reduction: Medial axis, Midsurface generation, Skeletal shape
Surfaces : Low Pass Filtering
• Electrical signals often carry noises which are
equivalent to the small features we wish to
remove.
• Noises are smoothed out by discarding the extra
frequency terms after representing the signal by
sinusoidal functions
• Challenge is to define Shape as function which is
combination of Sinusoidal Functions.
• Each vertex location is changed to the weighted
average of neighboring vertex locations.
Averaging has the effect of low-pass filtering
Face Clusters
• Clusters(groups) are regions of interest
• Faces are grouped based on certain geometric
properties, say, distance or angles.
• Based on Error criterion, Face groups are
further grouped by collapsing edges in
between.
Size based
• Works typically on cellular topology. Shapes
have explicit volumetric representation called
cells.
• Edges in cells are ranked by geometric error
introduced if they are removed. Edges are
then contracted starting with lowest cost.
• Volumes below certain threshold are
suppressed.
Voxel based
• Octree is generated.
• Shape is divided into cubes which are further
classified into Inside (Black),Outside (White),
Border (Grey). Greys are further divided up to
a set level.
• Surface is passed through Grey nodes.
Dimension Reduction
• Reducing the dimensions of CAD models is also
beneficial in some application areas.
• For example, if long slender round bar is modeled as a
1D beam , there is negligible effect on the accuracy of
the analysis but the computational time will reduce
dramatically.
• Techniques are:
– volume-based, where the input is iteratively thinned until
a final skeleton is derived.
– Boundary based, boundaries are extracted and skeletons
are generated directly from the boundary data.
Creating Engineering Analysis Models
Idealized Type
Element Type
1D Lines, Curves
Beams, Trusses
Axisymmetric Shells
2D Surfaces
Plates & Shells
3D Volumes
3D Solid Elasticity
Medial Axis Transform (MAT)
• Can be used to obtain the skeleton of a shape,
and provides radius value which represents
the distance from a medial axis point to its
nearest boundary points, or equivalently, to
where the medial axis ball touches the
boundary.
Mid-surface Abstraction
• Candidate surface pairs
are identified on the
solid model which
represent thin walls on
the part. A medialsurface is then
constructed between
each surface pair, and
the resulting surfaces
are trimmed and
extended to form a
consistent model.
Feature based
• Ready access to features helps in defeaturing
• Process:
– If there are no ready features do feature
recognition first
– Identify features to remove
– Once faces are removed, heal so as to fill the
volume removed
What is feature?
• “Features are defined as geometric and
topological patterns of interest in a part model
and which represent high level entities useful in
part analysis.” – Henderson, 1990
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functional feature: for example, a pivot,
design feature: Extrude, revolve
manufacturing feature: a turned cylinder, a milled slot
application specific feature: these could be any
combination of topological, geometric, metric, color
and texture attributes or non-visual features
Feature based reordering
• Decomposition : Easy to
de-feature
• Reordering of Features
Summary of Simplification techniques
Problems in adopting feature based
approach
• Most of CAD-CAE integrations are without
design intent i.e. features.
• Features are typically not fully exported by
CAD software to protect intellectual property
captured in design intent.
• But, there ARE ways in which feature
information can be transferred…
Need ready feature info
• Designer intent is captured in CAD data model
mainly in form of features. Better integration with
downstream applications is possible if this intent
gets translated as much as possible, but that's not
the typical case.
• To correct the loss of feature data, wherever
available, Feature Recognition (FR) is carried out.
• FR is a difficult problem and even with heuristic
algorithms, its far from being useful on complex
models.
Direct Modelers
• Off-late some Direct Modelers
like Space-claim, Autodesk Fusion
do provide edit-ability to model
even though feature tree did not
get exchanged.
• These, typically, do not do true
feature-editing-update
operations but just minor
modifications/tweaking , giving a
feel of feature editing.
Feature Export
• Neutral File formats supporting features : say,
STEP. Need to mold your feature info into
neutral format which may not be possible.
• API : Using programming. Limited by what has
been exposed by APIs.
• Macros: Log files sometimes do reveal feature
recipes but again to a level they have been
allowed to expose.
STEP
• International Organization for Standardization
(ISO) Technical Committee 184 has been working
to cover parameterization of models, geometrical
constraints commonly used into product shape
modeling.
• This can transfer parametric information and
constraints in 2D sketches only.
• Construction history of the shape configurations
generated by extruding or revolving 2D sketches
can only be transferred.
Application Programming Interfaces
(APIs)
• Some modelers
provide APIs to
customize their
application as well
as building 3rd
party sofwtare on
top.
• These APIs can be
used as neutralcommand-map
Macro Parametric approach
• A macro file that
records modeling
command sequence
is exchanged.
• Even if some CAD
modelers do log
operations, they
may not be revealing
enough to
reconstruct model
exactly.
Dual Model approach
• The primary model defines the construction
history. It has an associated secondary model
of the B-rep type.
• The secondary model can be used in the
receiving system to check the validity of model
transfer.
• The model is reconstructed in receiving
system by transferring primary model.
Neutral Commands, XML approach
• To transfer parametric information including
design history, a set of standard commands is
defined and used as a neutral format.
• Neutral format can be extensible mark up
language (XML) technology to express a set of
standard modeling commands extracted from a
CAD model.
• This approach transfers model history, however it
can transfer design history based only on limited
set of modeling commands.
Problems : Persistent naming
• In Feature based modeling system, feature is defined
referring to entities (faces, edges, vertices) in the
explicit (B-rep) geometry. Each feature, however,
introduces a modification in the model which is
regenerated when a feature is added to the tree.
• In many cases the entities that have been used to dene
a feature may be split-ed or deleted by the feature
itself or by subsequent features. For this reason
references to entities used during the design process
can be re-evaluated in an erroneous way, resulting in
unexpected results.
What are others doing?
• Ansys supports bidirectional connections with the CAD environments like
CATIA V5, Siemens NX etc. The associative capabilities of these geometry
interfaces allow users to change a model’s geometry without having to
reapply loads. Not sure if full or localized re-meshing happens as well as
about Model Simplification.
• Automatic associative import allows to transfer models from a Catia V5
session to an Abaqus/CAE session. Any features you create in Abaqus, such
as partitions, loads, boundary conditions, sets and surfaces, are regenerated
each time you import the modified Catia model into Abaqus.
• Autodesk Project Centaur: Uses Inventor parameter table driven
optimization in cloud to come up with best solution. Not sure if it does
optimized re-meshing and model simplification.
References:
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“Closing the CAD/CAE gap” – Scientific Computing
“Software offers full associativity with Design changes”
An Analyst’s View : STEP-Enabled CAD-CAE Integration
"A Survey of CAD Model Simplification Techniques for Physics-based
Simulation Applications", Atul Thakur, Ashis Gopal Banerjee, and
Satyandra K. Gupta
An approach to B-rep model simplification based on region
suppression
“Geometry Simplification”, Carlos Andujar
"Medial Object Extraction - A State of the Art"; Yogesh Kulkarni, Dr.
Shailesh Deshpande
“Bridging the Gap Between CAD and CAE”; David A. Selliman, James
Ackron,
“Feature-based Techniques for Handling Geometric Models”, Dinesh
Shikhare
Exchange of CAD Part Models Based on the Macro-Parametric
Approach, Choi et al.
Q&A
Yogesh.Kulkarni@autodesk.com