SFG-GD/EB-1/17/01- 1 An Analyst’s View: STEP-Enabled CAD-CAE Integration Stephen Gordon NASA’s...

SFG-GD/EB-1/17/01- 1G E N E R A L D Y N A M IC SElectric Boat

An Analyst’s View:STEP-Enabled CAD-CAE Integration

Stephen Gordon

NASA’s STEP for Aerospace WorkshopJPL, Pasadena, CA

January 17, 2001


CAD-CAE Integration DomainsPurpose, Scope, and Scale of AnalysisCAD-Centric vs. CAE-Centric ProcessesCategories 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 ExchangeAP209 is an Enabler for CAD-CAE Integration

AP209 = CAD + CAE + FEM + FEA + PDM (Mnemonic)

Backup Slides

Outline of Topics


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.


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.

CAD and CAE Integration


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


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”.

CAD and CAE Integration


Captured CADGeometry

DerivedIdealizedGeometry

Engr. Anal.Model (FEM)

SimplifyIdealizeDe-Feature

PaveMeshDiscretize

Analysis Model Creation (e.g. FEA)

ChangeType or“Gender”

Geometry is not always the same!

A mechanical engineer, a structural engineer, and a piping engineer may each require different forms of geometry capture.


Geometry Representation

Same Object ...

Multiple/Different Forms of Geometry Capture

1D Line (Curve)

3D Solid (Volume)

2D Surface (Shell)


Exploded View - Same Geometry, Different Data Capture

1D Line (Curve)

3D Solid (Volume)

2D Surface (Shell)

“Gender Changing”


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.

Integrated CAD-CAE Process


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

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.


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.

The First “Problem” - Geometry Type


1D Lines, Curves

2D Surfaces

2D ‘Cut” Surfaces (or Sections)

3D Volumes

Beams, TrussesAxisymmetric Shells

Stiffened Plates & Shells

Plates & Shells

Plane Stress / Strain ElasticityAxisymmetric Solids(“Quasi-3D”)

3D Solid Elasticity

Creating Engineering Analysis Models

Geometry Type Analysis Model Type

Same “Gender” Geometry



IdealizedGeometry

Analysis Model Type(Eg. FEM)

1D Lines, Curves

2D Surfaces


3D Volumes



Plates & Shells

Plane Stress/ Strain ElasticityAxisymmetric Solids(“Quasi-3D”)

3D Solid Elasticity


CADStructures(1D)

CAD Solids(3D)

CAD-Centric Approaches

CAD Surfaces(2D)

Can be ‘Seamless’

‘Gender-Changing’ Required



IdealizedGeometry

Analysis Model Type(Eg. FEM)

1D Lines, Curves

2D Surfaces


3D Volumes



Plates & Shells

Plane Stress/ Strain ElasticityAxisymmetric Solids(“Quasi-3D”)

3D Solid Elasticity


3D Solid Product Model

CAD-Centric Process with a 3D Solid Product Model

Requires “Gender

Changing”


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)

JXXX

Joint Surface Index

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.

CA

D-C

entr

ic P

roce

ss

CA

E-C

entr

ic P

roce

ss


CAD Geometry = Simulation-

Specific Geometry

Engr. Anal.Model (FEM)Pave

MeshDiscretize


Simulation-Specific

Geometry


SimplifyIdealizeDe-Feature

PaveMeshDiscretize

ChangeType or“Gender”

Start

CAD-Centric Approaches

Category I

Category II


A CAE-Centric Approach

Category III

Create CADGeometry

Simulation-Specific

Geometry


AddDetails &Features

PaveMeshDiscretize

ModifyType or“Gender”

Start

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


TET Meshing HEX Paving

Automated model building options are readily available in almost all CAD and

CAE tools

3D Solids & 3D Elasticity Analysis


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

Mid-Surfaces

Trimmed and Adjusted Mid-Surfaces

1

2

Automated Mid-Surfacing

Category II (Solids-to-Shells)


COTS capabilities now exist for automatic

creation of mid-surface geometry and shell FEA

mesh.

Category II1. Thin-walled

solid part

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)


Automatically created mid-surface geometry

Solid 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)


CollaborationYou’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 ProcessesToday’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


AP209 = CAD + CAE + FEM + FEA + PDM

What is ISO STEP 10303 AP209?

Nominal CAD Geometry

Idealized CAE “Simulation-Specific”

Geometry

Finite Element Models

Finite Element Analysis Controls

& Results

Product Data Management Info

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.


STEP AP209Repository File

Archived

Design/Analysis

AP209

Snapshots

Design Analysis

STEP AP209 File

FEA ResultsFEA ControlsFE ModelsIdealized GeometryNominal Geometry

Design Model - PDM

AnalysisSTEP AP209 File

FEA Results

FEA Controls

FE Models

Idealized Geometry

Nominal Geometry

Design Model - PDM

Design

The ISO STEP 10303 Standards are not just about data

exchange!

AP209 captures and integrates design, analysis, and CM/PDM information.


Part

Part Version

Design Discipline Product Definition

Nominal Design Shape

Idealized Analysis Shape

Finite Element Analysis Shape

Analysis

Analysis Version

Analysis Design Version

Relationship

Analysis Discipline Product Definition

Assembly

Allow Analysis to Revise Independently of Design

Detailed AP209 PDM Concepts


Recommended Practices for AP209

ME007.01.00

June 25, 1999

Nominal CAD Geometry

Idealized CAE Geometry

FEA Model


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-CentricContinued role for traditional FEA pre- and post-processorsAP209 is ready to support / enable more CAD-CAE integrationAP209 is more appropriate for CAE than AP203Need more vendor support for AP209

CAD-CAE Integration Status


Back-up Slides

PDES & NAFEMS Activities

EB’s Prototype AP209


Working with larger-scale test cases for AP209

coverage

PATRAN

COMMANDS

3847 Nodes

6743 Elements


NAFEMS Benchmark LE10

Thick Plate Pressure


Z-Section Cantilever

Joint PDES & NAFEMS Activity

Recasting NAFEMS FEA Benchmarks into AP209 Format


2D Plane Stress


AP209Translator

AP209Part21

File

Electric Boat’s AP209 Translator is Interfaced

with the COMMANDS FEA System

Binary

Ascii


AP209Translator

AP209Part21

File

Ascii

COMMANDSData 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


EB’s AP209 Prototype

Geometry - Nominal & Idealized

FEA Model & Results


EB Chart 1

EB Chart 2

Common Intersection

Example = HEX20 Case -Dynamic Version of the

MacNeal-Harder Twisted Beam


EB Chart 1


EB Chart 2

SFG-GD/EB-1/17/01- 1 An Analyst’s View: STEP-Enabled CAD-CAE Integration Stephen Gordon NASA’s...

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