An Analyst’s View: STEP-Enabled CAD-CAE Integration Stephen Gordon NASA’s STEP for Aerospace Workshop JPL, Pasadena, CA January 17, 2001. Outline of Topics. CAD-CAE Integration Domains Purpose, Scope, and Scale of Analysis CAD-Centric vs. CAE-Centric Processes
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An Analyst’s View:
STEP-Enabled CAD-CAE Integration
Stephen Gordon
NASA’s STEP for Aerospace Workshop
JPL, Pasadena, CA
January 17, 2001
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
CAE Functionality
Computer-Aided Engineering (CAE) is made up of many varied and diverse functions, depending upon one’s organization and it’s 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.
CAD and CAEIntegration
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.
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!
Large-Scale Simulation, Full Vehicle Models
Part of the CAE Domain
Such analyses and simulations likely include multi-physics and media-structure interaction
CAD and CAEIntegration
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 today’s world!)
The more abstract, idealized geometry used for analysis is also referred to as “Simulation-Specific” or “FEA-Specific Geometry”.
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.
Geometry Representation
1D Line (Curve)
Same Object ...
2D Surface (Shell)
Multiple/Different Forms of Geometry Capture
3D Solid (Volume)
Exploded View - Same Geometry, Different Data Capture
1D Line (Curve)
2D Surface (Shell)
3D Solid (Volume)
“Gender Changing”
Integrated CAD-CAEProcess
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.
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 Int’l. Conf., Newport, RI, April 1999
“Don’t 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
“Don’t 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 geometry”or “FEA-specific geometry”
CAD-CAE Integration
Today’s bottleneck in CAD-CAE integration is not automated mesh (grid) generation, it lies with efficient creation of appropriate simulation-specific geometry.
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.
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
CAD-Centric Approaches
Creating Engineering Analysis Models
Captured CAD
Geometry
Idealized
Geometry
Analysis Model Type
(Eg. FEM)
CAD
Structures
(1D)
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
Surfaces
(2D)
CAD
Solids
(3D)
Can be ‘Seamless’
‘Gender-Changing’ Required
CAD-Centric Process with a 3D Solid Product Model
Creating Engineering Analysis Models
Captured CAD
Geometry
Idealized
Geometry
Analysis Model Type
(Eg. FEM)
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
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.
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.
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
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
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
Category I
Solids Examples
Mechanical parts and components
Automated model building options are readily available in almost all CAD and CAE tools
3D Solids & 3D Elasticity Analysis
TET Meshing
HEX Paving
Categories II & III
Thin-Walled Structures
(Where the product model is solids)
EB Example -Automated Mid-Surfacing
CAD-Centric Category II (Solids-to-Shells)
Welded Plate Tank Structure - Multiple Brep Manifold Solids
Solids
1
2
Mid-Surfaces
Automated Mid-Surfacing
Category II (Solids-to-Shells)
Trimmed and Adjusted Mid-Surfaces
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
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)
Solid geometry
Automatically created mid-surface geometry
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)
Collaboration
You’ve heard a lot at this workshop about inter-company collaboration, multi-tiered supply chains, even world-wide collaboration.
Large 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.
The ISO STEP 10303 Standards are Enablers for Improved Design-Analysis-Construction Processes
Today’s 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
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.
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
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
Nominal CAD Geometry
Idealized CAE Geometry
Recommended Practices for AP209
ME007.01.00
June 25, 1999
FEA Model
CAD-CAE IntegrationStatus
COTS Vendor Report Card
Category I A Mature, MCAD for solids good
Category IIB-,C+Improving, recent mid-surfacing attention
Category IIID,FVery 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
Back-up Slides
PDES & NAFEMS Activities
EB’s Prototype AP209
Working with larger-scale test cases for AP209 coverage
3847 Nodes
6743 Elements
PATRAN
COMMANDS
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
AP209
Part21
File
Ascii
AP209
Translator
Binary
Electric Boat’s AP209 Translator is Interfaced with the COMMANDS FEA System
AP209
Translator
AP209
Part21
File
Ascii
COMMANDS
Data Base
(CDB)
Binary
EB’s currently implemented prototype AP209 Translator is closely interfaced with EB’s 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.
Initial Checkout of AP209 Import to COMMANDS
Initial Checkout of AP209 Import to COMMANDS
EB’s AP209 Prototype
FEA Model & Results
Geometry - Nominal & Idealized
EB Chart 1
Common Intersection
Example = HEX20 Case -Dynamic Version of the MacNeal-Harder Twisted Beam
EB Chart 2
EB Chart 1
EB Chart 2