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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 PowerPoint PPT Presentation


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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

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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

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An analyst s view step enabled cad cae integration stephen gordon nasa s step for aerospace workshop jpl pasade

An Analyst’s View:

STEP-Enabled CAD-CAE Integration

Stephen Gordon

NASA’s STEP for Aerospace Workshop

JPL, Pasadena, CA

January 17, 2001


An analyst s view step enabled cad cae integration stephen gordon nasa s step for aerospace workshop jpl pasade

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 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.


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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.


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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


An analyst s view step enabled cad cae integration stephen gordon nasa s step for aerospace workshop jpl pasade

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”.


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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-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.


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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 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


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“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”


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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.

Today’s 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.


An analyst s view step enabled cad cae integration stephen gordon nasa s step for aerospace workshop jpl pasade

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

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


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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


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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

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.


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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


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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 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


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Back-up Slides

PDES & NAFEMS Activities

EB’s Prototype AP209


An analyst s view step enabled cad cae integration stephen gordon nasa s step for aerospace workshop jpl pasade

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 Boat’s AP209 Translator is Interfaced with the COMMANDS FEA System


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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.


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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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EB’s 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


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