An Analyst

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An Analysts View STEP-Enabled CAD-CAE
Integration Stephen Gordon NASAs STEP for
Aerospace Workshop JPL, Pasadena, CA January 17,
2001
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Outline of Topics
CAD-CAE Integration Domains Purpose, Scope, and
Scale of Analysis CAD-Centric vs. CAE-Centric
Processes Categories of Integration (What is
truly Seamless?) De-Featuring Geometry
(Content, Amount of Detail) Geometry Gender
Changing Needs and Tools Simulation-Specific
Geometry vs. CAD Geometry Collaboration (Inter-
and Intra-Company) ISO STEP 10303 is not just
about Data Exchange AP209 is an Enabler for
CAD-CAE Integration AP209 CAD CAE FEM
FEA PDM (Mnemonic) Backup Slides
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CAE Functionality
Computer-Aided Engineering (CAE) is made up of
many varied and diverse functions, depending upon
ones organization and its structure. My focus
will be on the exchange and sharing of design and
engineering data (largely geometry and material
information) for use in computational analysis
tools, specifically finite element method
codes. My purpose today is to define where I
see, as an analyst, the potential and growing use
for ISO STEP AP209. There is no attempt to
slight many other important (non-analytical)
engineering functions in the CAD-CAE domain
related to the overall design, approval, and
life-cycle of the products we create.
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CAD and CAE Integration
The key to understanding CAD-CAE Integration, is
related to the scale, scope and purpose of the
required engineering analysis - e.g. Finite
Element Analysis (FEA). It is not simply related
to the existence of captured CAD geometry, a
perception unwittingly left during product model
walk-throughs. The closer the scale, scope and
purpose of an engineering analysis is to the type
and detail of the existing CAD product model
geometry, the greater the likelihood that a
closely-coupled, automated, or even seamless
integrated CAD-CAE process can be implemented.
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Scope, Purpose, and Scale
Small-scale, single part optimization Widgets
Gadgets
Large-scale simulation, e.g. vehicle
crash-worthiness
These may both employ the same software, but with
significantly different models!
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Large-Scale Simulation, Full Vehicle Models Part
of the CAE Domain
Such analyses and simulations likely include
multi-physics and media-structure interaction
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CAD and CAE Integration
When the scale, scope and purpose of an
engineering analysis are not consistent with the
type and detail of the existing CAD product model
geometry, a computer-assisted man-in-the-loop
or semi-automated process may be more feasible
and appropriate than a fully-automated process.
(Still a place for engineering judgement.) We
have found that the time and cost to change,
re-work, and de-feature CAD geometry can
sometimes be greater than that for creating
analysis models from readily-generated
idealized geometry. (Not a popular view in
todays world!) The more abstract, idealized
geometry used for analysis is also referred to as
Simulation-Specific or FEA-Specific Geometry.
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Analysis Model Creation (e.g. FEA)
Geometry is not always the same!
Change Type or Gender
Derived Idealized Geometry
Engr. Anal. Model (FEM)
Captured CAD Geometry
Simplify Idealize De-Feature
Pave Mesh Discretize
A mechanical engineer, a structural engineer, and
a piping engineer may each require different
forms of geometry capture.
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Geometry Representation
1D Line (Curve)
Same Object ...
2D Surface (Shell)
Multiple/Different Forms of Geometry Capture
3D Solid (Volume)
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Exploded View - Same Geometry, Different Data
Capture
1D Line (Curve)
2D Surface (Shell)
3D Solid (Volume)
Gender Changing
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Integrated CAD-CAE Process
The value of engineering analysis and
optimization early (up front) in the design
process is now readily accepted and is generally
unassailable. Unfortunately, there is often the
perception (sometimes from MCAD vendor hype) that
engineering analysis is a totally seamless
process within CAD. This view can be a
disservice to many sectors of business, where
solid product models have become the CAD approach
of choice, but the wrong geometry for
analysis. Fortunately, articles in the
literature have recently begun to reflect some of
these different views on delivering analysis.
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Recent Articles Show Enlightened Views
Three-Dimensional CAD Design and Analyzing with
Shell Elements - A Soluble Contradiction?, by M.
W. Zehn, H. M. Baumgarten, P. Wehner, NAFEMS
7th Intl. Conf., Newport, RI, April 1999 Dont
Change the Model Till the Simulation Finishes,
by Paul Kurowski, Machine Design, August 19,
1999 Rookie Mistakes - Over Reliance on CAD
Geometry, by Vince Adams, NAFEMS Benchmark,
October 1999 Common Misconceptions About FEA,
by Vince Adams, ANSYS Solutions, Fall 2000 Eight
Tips for Improving Integration Between CAD and
CFD, by Scott Gilmore, Desktop Engineering, May
2000
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Dont Change the Model Till the Simulation
Finishes by Paul Kurowski Machine Design August
19, 1999 When analysis geometry is not the same
as design geometry! Simulation-specific
geometryor FEA-specific geometry
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CAD-CAE Integration

• Whether CAD-CAE applications can be
  closely-integrated and automated depends upon
• The scale, scope, and purpose of the CAE
  analysis.
• The nature and type (order, or gender) of the
  captured CAD geometry.
• The amount of detail required for the CAE
  application.

Todays bottleneck in CAD-CAE integration is not
automated mesh (grid) generation, it lies with
efficient creation of appropriate
simulation-specific geometry.
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The First Problem - Geometry Type
In general, the most automated CAD-to-CAE
processes are for MCAE same gender geometry
classes, eg. widgets and gadgets, or 3D volumes
filled with 3D elasticity tet or hex solid
elements or piping analysis employing 1D
geometry. In the structures discipline, our ship
product lines most often involve large scale,
simplified geometry and analysis models, e.g.
large assemblages of stiffened 2D plate/shell
surfaces and framework structures. However,
enterprise CAD product model geometry capture is
fundamentally 3D solid modeling supplemented with
1D structures entities. Thin-walled structure
is more accurately and efficiently analyzed as
plates and shells.
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Same Gender Geometry
Creating Engineering Analysis Models
Geometry Type
Analysis Model Type
1D Lines, Curves 2D Surfaces 2D Cut
Surfaces (or Sections) 3D Volumes
Beams, Trusses Axisymmetric Shells Stiffened
Plates Shells Plates Shells Plane Stress
/ Strain Elasticity Axisymmetric
Solids (Quasi-3D) 3D Solid Elasticity
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CAD-Centric Approaches
Creating Engineering Analysis Models
Idealized Geometry
Analysis Model Type (Eg. FEM)
Captured CAD Geometry
1D Lines, Curves 2D Surfaces 2D Cut
Surfaces (or Sections) 3D Volumes
Beams, Trusses Axisymmetric Shells Stiffened
Plates Shells Plates Shells Plane Stress/
Strain Elasticity Axisymmetric Solids (Quasi-3D)
3D Solid Elasticity
CAD Structures (1D)
CAD Surfaces (2D)
CAD Solids (3D)
Can be Seamless Gender-Changing Required
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CAD-Centric Process with a 3D Solid Product Model
Creating Engineering Analysis Models
Idealized Geometry
Analysis Model Type (Eg. FEM)
Captured CAD Geometry
1D Lines, Curves 2D Surfaces 2D Cut
Surfaces (or Sections) 3D Volumes
Beams, Trusses Axisymmetric Shells Stiffened
Plates Shells Plates Shells Plane Stress/
Strain Elasticity Axisymmetric Solids (Quasi-3D)
3D Solid Elasticity
Requires Gender Changing
3D Solid Product Model
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The Second Problem - Model Content and Amount
of Detail
In general, the captured CAD geometry contains a
great deal of detail, necessary for creating
drawings and for manufacturing support, but too
much detail for most idealized FEA
models. Therefore, the idealization portion of
FEA requires simplifying the geometry, removing
unwanted details which are not commensurate with
the scale of the idealized FEA model. Examples
include removing small holes, adding or removing
fillets, even eliminating whole portions which
may be idealized as a rigid mass, or may not be
in the analysis at all! This process of
simplification is sometimes referred to as
suppressing the details or de-featuring the
geometry. For welded structure adding features
(weld fillets) to the CAD product model may be
required for detailed stress analysis.
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Welded Thin-Walled Structure with a 3D Solid
Product Model
Portion of foundation for resilient mounts and
shock snubbers Weld material is annotated
(e.g.weld symbols), but not explicitly captured
as fillets in the product model (as it would be
for a machined part)
Joint Surface Index
JXXX
Typical de-featuring might include eliminating
the small holes but keeping the larger
ones. Whereas, a featuring change could be
adding weld fillets to avoid stress
concentrations or singularities at sharp corners.
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Categories of CAD-CAE Integration
Category I - The CAD Geometry and the
Simulation-Specific Geometry are the same
(identical). This is the truly seamless case
there is no change in detail, no de-featuring,
and no geometry gender changing required.
Analysts and designers use the same (or duplicate
copies of the same) geometry. Category II -
Existing (available) CAD geometry has the wrong
content it is too detailed and/or of the wrong
type to support the scale, scope, and purpose of
the required or most appropriate type of
analysis. Changes are required to add features or
remove unnecessary detail from, and/or modify the
gender of, the CAD geometry to create
Simulation-Specific Geometry amenable to
analysis. Automated and semi-automated procedures
are required. Category III - Engineering analyses
are performed first to define and refine a design
concept using idealized geometry prior to
establishment of the enterprise (CAD) product
model. Simulation-Specific Geometry employed for
analysis models will require modification and the
addition of details and features to support
drawings and manufacturing. Automated and
semi-automated procedures are desirable.
CAD-Centric Process
CAE-Centric Process
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CAD-Centric Approaches
CAD Geometry Simulation-Specific Geometry
Category I
Engr. Anal. Model (FEM)
Pave Mesh Discretize
Start
Category II
Change Type or Gender
Simulation- Specific Geometry
Engr. Anal. Model (FEM)
Captured CAD Geometry
Simplify Idealize De-Feature
Pave Mesh Discretize
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A CAE-Centric Approach
Category III
Start
Modify Type or Gender
Simulation- Specific Geometry
Engr. Anal. Model (FEM)
Create CAD Geometry
Add Details Features
Pave Mesh Discretize
More mature or optimized concept prior to CAD
geometry capture designers add detail later for
drawing creation, design disclosure, and
manufacturing
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Category I Solids Examples
Mechanical parts and components
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Automated model building options are readily
available in almost all CAD and CAE tools
3D Solids 3D Elasticity Analysis
TET Meshing
HEX Paving
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Categories II III Thin-Walled
Structures (Where the product model is solids)
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EB Example -Automated Mid-Surfacing CAD-Centric
Category II (Solids-to-Shells)
Welded Plate Tank Structure - Multiple Brep
Manifold Solids
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Solids
1
2
Mid-Surfaces
Automated Mid-Surfacing Category II
(Solids-to-Shells)
Trimmed and Adjusted Mid-Surfaces
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Category II
1. Thin-walled solid part
COTS capabilities now exist for automatic
creation of mid-surface geometry and shell FEA
mesh.
2. Mid-surface geometry
3. Meshed FEA shell model
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Section of Stiffened Deck Plate
DECK_ASSY Assembly with deck plate and
replicated (dittoed) tee stiffeners
(Example used in Nov. 98 PDES demo using PATRAN
and COMMANDS)
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Solid geometry
Automatically created mid-surface geometry
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FEA Idealization 1 Explicitly Modeled
Stiffeners (8-noded shell elements shown)
FEA Idealization 2 Eccentric Beam
Stiffeners (4-noded shell elements with 2-noded
eccentric beam elements)
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Collaboration Youve heard a lot at this workshop
about inter-company collaboration, multi-tiered
supply chains, even world-wide collaboration. Larg
e companies, such as those many of us work for,
often have separate groups and departments which
requires intra-company cooperation and
collaboration. Integration with standards (such
as ISO STEP) is a logical way to build an
intra-company architecture of sharing between
separate design and analysis organizations. Such
an in-house, multi-department business process
built on standards is easily transitioned into an
external collaborative teaming endeavor, when and
if that would be prudent.
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The ISO STEP 10303 Standards are Enablers for
Improved Design-Analysis-Construction
Processes Todays business enterprises must have
access to enterprise-wide PDM information which
integrates design, analysis, construction and
life-cycle support. AP209 provides a means to
more closely integrate design and analysis, by
including nominal (CAD) geometry, various
idealized CAE geometries, and associated FEM
analysis models and results, along with PDM and
separate version control. Mnemonic AP209 CAD
CAE FEM FEA PDM
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What is ISO STEP 10303 AP209?
Idealized CAE Simulation-Specific Geometry
Nominal CAD Geometry
Product Data Management Info
AP209 CAD CAE FEM FEA PDM
Finite Element Models
Finite Element Analysis Controls Results
Mnemonic (Engineers like equations!) One can use
AP209 with any one or more of these pieces, but
the real power lies with the assemblage of all
these parts.
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The ISO STEP 10303 Standards are not just about
data exchange! AP209 captures and integrates
design, analysis, and CM/PDM information.
Design
Analysis
STEP AP209
Repository File
Design
Archived
Design/Analysis
AP209
Snapshots
STEP AP209 File
Analysis
FEA Results
FEA Controls
FE Models
Idealized Geometry
STEP AP209 File
Nominal Geometry
Design Model - PDM
FEA Results
FEA Controls
FE Models
Idealized Geometry
Nominal Geometry
Design Model - PDM
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Detailed AP209 PDM Concepts
Allow Analysis to Revise Independently of Design
Part
Analysis
Analysis Design Version Relationship
Part Version
Analysis Version
Assembly
Analysis Discipline Product Definition
Design Discipline Product Definition
Nominal Design Shape
Idealized Analysis Shape
Finite Element Analysis Shape
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Nominal CAD Geometry
Idealized CAE Geometry
Recommended Practices for AP209 ME007.01.00 June
25, 1999
FEA Model
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CAD-CAE Integration Status
COTS Vendor Report Card Category I A Mature,
MCAD for solids good Category II B-,C Improving,
recent mid-surfacing attention Category
III D,F Very little for CAE-centric leading
design, need shell thickening tools, or
solids-on-demand Overall Still too
CAD-Centric Continued role for traditional FEA
pre- and post-processors AP209 is ready to
support / enable more CAD-CAE integration AP209
is more appropriate for CAE than AP203 Need more
vendor support for AP209
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Back-up Slides PDES NAFEMS
Activities EBs Prototype AP209
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Working with larger-scale test cases for AP209
coverage
3847 Nodes 6743 Elements
PATRAN COMMANDS
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Joint PDES NAFEMS Activity
Recasting NAFEMS FEA Benchmarks into AP209 Format
NAFEMS Benchmark LE5 Z-Section Cantilever
NAFEMS Benchmark LE1 2D Plane Stress
NAFEMS Benchmark LE10 Thick Plate Pressure
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AP209 Part21 File
Ascii
AP209 Translator
Binary
Electric Boats AP209 Translator is Interfaced
with the COMMANDS FEA System
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AP209 Translator
AP209 Part21 File
Ascii
COMMANDS Data Base (CDB)
Binary
EBs currently implemented prototype AP209
Translator is closely interfaced with EBs
COMMANDS Data Base using binary reads and writes.
It was kept separate to enable appending multiple
analysis models and results onto a single
repository (Part21 file), or selecting and
extracting one model with results. Other features
(next two slides) were implemented to aid
developers as we learned about STEP and Express
representation.
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Initial Checkout of AP209 Import to COMMANDS
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Initial Checkout of AP209 Import to COMMANDS
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EBs AP209 Prototype
FEA Model Results
Geometry - Nominal Idealized
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EB Chart 1
Common Intersection
Example HEX20 Case -Dynamic Version of the
MacNeal-Harder Twisted Beam
EB Chart 2
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EB Chart 1
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EB Chart 2