September 25, 2002

Probabilistic Design

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September 25, 2002

September 25, 2002

Probabilistic Design System by Rod Scholl, PADT

Overview At some point, most ANSYS users have had to vary some parameter in their model to investigate impact on results. Perhaps you�ve done this through the GUI and multiple runs � or maybe you�ve written a macro that Do Loops through a few input values. ANSYS Probabilistic Design System (PDS) automates the process. Using simple menu picks (or commands) you can specify many input variables and their variation in statistical terms (Gaussian, Weibul, etc.) and then ANSYS manages the many runs that sample the �terrain�. You can choose the sampling method (Random, Monte Carlo, etc,). Finally ANSYS builds an .html report (via the Automatic Report Generator) that graphs the specified output variables. It will even evaluate correlations between inputs and outputs! This is the best application of the Report Generator that I�ve encountered. An Ideal-World Case Study: Your materials person gives you Gaussian distributions for your properties. Your dimensions are specified with tolerances as well as distributions based on SPC generated data at the vendor. (This is why this is titled �Ideal-World� case�). You also receive boundary conditions that are in terms of means and standard deviations assuming a Gaussian distribution.

Mat. Props

σy

Tolerance Distributions

Load / Temp Distributions

Baseline Model

ANSYS PDS

Report

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You set up the model as usual with a single case, but then specify inputs statistically in the PDS module. ANSYS runs the model 1,000 times (I�ve seen people do as much as 40,000) and summarizes the results in a report. You can then provide a distribution of peak stress for your lifing person. Unless you�re the lifing person, and then you can specify a probability of life rather than a discrete number of cycles! A Real World Case Study: You are given the model of a flange with fixed dimensions and material properties. However, the deflections are unknown at the inner and outer radii. Non unusually, you must know characterize the stress before the deflections are finalized.

The Procedure:

1. Build a database that solves for a single case and verify results. 2. Change the database to have the BC�s applied using variables. 3. Specify statistical distributions of the input variables using PDS. 4. Specify desired output variables using PDS. 5. Instruct PDS to solve the model multiple times. 6. Review the report generated by PDS.

1. Build a database that solves for a single case. (You should cut and paste this text to a file then name it FLANGE.INP) You can then read in the file into a clean database using Utility Menu > File > Read Input From�

/PREP7 /title,Axisymmetric Flange (PDS by PADT) UIMP,1,EX, , ,11.13948e6, !Sets Material Properties UIMP,1,NUXY, , ,.3326, K,1,6,2 !Draws Outline k,2,6,0 k,3,4.5,0

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k,4,4.5,.1 k,5,5.95,.1 k,6,5.95,2, LSTR, 2, 3 !Makes Lines LSTR, 2, 1 LSTR, 1, 6 LSTR, 5, 6 LSTR, 5, 4 LSTR, 4, 3 LFILLT,1,2,.05, , LFILLT,5,4,0.1, , al,5,8,4,3,2,7,1,6 !Makes Areas et,1,82 !Meshes keyopt,1,3,1 esize,.0175 amesh,all

/solu dl,6,,ux,.05 !Apply Deflection Loads d,346,,.025,,,,ux d,2,,0,,,,uy solve /post1 PLNSOL,s,eqv lsel,s,,,6 !Store Output Variables nsll,s,1 nsort,s,eqv *get,INNRSTRS,sort,0,max lsel,s,,,8 nsll,s,1 nsort,s,eqv *get,CORNSTRS,sort,0,max allsel 1. Cont’d – Verify Results – They should look as follows:

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2. Change the database to have the deflections applied as variables.

Original

Modified /solu dl,6,,ux,.05 !Apply Deflection Loads d,346,,.025,,,,ux d,2,,0,,,,uy solve

/solu INNERDF=.05 OUTERDF=.025 dl,6,,ux,INNERDF !Apply Deflection Loads d,346,,OUTERDF,,,,ux d,2,,0,,,,uy solve

You should be able to rerun your macro and get the same results!!! 3. Specify Statistical Distribution of the Input variables using PDS. 3.1) Open the Probabilistic Design Module

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3.2) Specify Random Input Variables

Choose OUTERDF

(Notice ANSYS �found� your Variables.)

Accept the default Gaussian distribution

Use These Values

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Use These Values

3.2 Cont’d) Do the same for the variable INNERDF. Rather than Guassian, choose Gamma:

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4) Specify Desired Output Variables. Note that we had to define these FIRST using *GET�s at the end of our original macro -- PDS will not do this for you!

Add INNRSTRS also.

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5) Instruct PDS to solve the model multiple times. PDS is designed to distribute these runs over multiple computers in your company. It will compile all the results back on your own PC. This distributed computing is not too difficult to set up � but for this example we will run them all on our own machine. Use the Method Wizard�

There are several other dials to turn, but these defaults will work in our case. The other bells and whistles are fairly self-explanatory; just browse around someday when you are bored�

• Skip past the first screen with the clock hitting NEXT • Accept default of No by hitting NEXT • Select the 1st three boxes as shown below then hit NEXT

• Skip past the last screen by hitting FINISH

September 25, 2002

5) Setting up the PDS runs Cont’d… You must �Assign� to ANSYS PDS what macro file to execute. This is the input file we named FLANGE.INP and then modified to have variables control the deflection.

DON’T FORGET THIS NEXT STEP!!!! You must comment out(using the !)the variable definitions in your macro. Or else, PDS will run the same version 100 times!

Original Modified /solu INNERDF=.05

OUTERDF=.025

/solu ! INNERDF=.05 ! OUTERDF=.025

(or you could have just deleted the lines of code…) (don’t forget to save the file!) Another Note – if you used any /CLEAR’s in a macro – you must get rid of them Yet Another Note – if you used any RESUME’s in a Macro you must preface it with PARSAV and PARRES to help ANSYS track the PDS variables.

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5) Now you are ready to go… Just a few more clicks…

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6) Generate Report

Use whatever settings you like, I chose these just for kicks…

September 25, 2002

Below are a few samples from the automatically generated report. You can view the entire report online. Also, there are other files stored such as parameter history for each run, etc., which are not addressed here. See the ANSYS documentation for details. EXAMPLE REPORT:

Axisymmetric Flange (PDS by PADT)

By Date: September 18, 2002; Time: 15 : 44 : 38

An ANSYS Probabilistic Analysis Report

Generated by the ANSYS Probabilistic Design System

Introduction Deterministic Model Information Probabilistic Model Information Probabilistic Analysis Summary Regression Analysis Summary Probabilistic Analysis Results

I. Introduction

The ANSYS Probabilistic Design System (PDS) analyzes a component or a system involving uncertain input parameters. These input parameters (geometry, material proerties, boundary conditions, etc.) are defined in the ANSYS model. The variation of these input parameters are �

II. Deterministic Model Information The analysis file containing the deterministic model is stored in FLANGE.INP . ANSYS executes or "loops through" multiple times during the probabilistic analysis.

September 25, 2002

Table 2 . Material Properties

Modulus of Elasticity 1.1139E+07

Poisson's Ratio 0.3326

III. Probabilistic Model Information

Random Input Variables The deterministic model has 2 parameters that are regarded as random input variables. A list of these random input variables, the distribution they are subjected to, and their distribution parameters are provided in Table 3 . The probability density functions and cumulative distribution functions are shown in Figures 2 to 3 . Table 3 . Random Input Variable Specifications

No. Name Type Par1 Par2 Par3 Par4

1 OUTERDF GAUS 3.50000E-02 2.50000E-02

2 INNERDF GAMA 2.0000 75.000

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Figure 2. PDF & CDF of Input Random Variable OUTERDF

VI.1 Statistics of the Probabilistic Results

Result Set FLANGE-BY-PADT Table 5 . Result Set FLANGE-BY-PADT - Statistics of the Random Input Variables

Name Mean Standard Deviation

Skewness Kurtosis Minimum Maximum

OUTERDF 3.4971E-02 2.4709E-02 -7.5428E-

03 -0.2193

-2.5259E-02

9.3599E-02

INNERDF 2.6657E-

02 1.8893E-02 1.354 2.388 1.7564E-03 0.1037

Table 6 . Result Set FLANGE-BY-PADT - Statistics of the Random Output Parameters

Name Mean Standard Deviation

Skewness Kurtosis Minimum Maximum

CORNSTRS 4.7380E+04 3.3403E+04 1.358 2.396 3756. 1.8358E+05

INNRSTRS 7.7384E+04 5.4640E+04 1.352 2.382 5338. 2.9996E+05

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Figure 11. Result Set FLANGE-BY-PADT - Histogram of Input Variable INNERDF

Figure 13. Result Set FLANGE-BY-PADT - Histogram of Output Parameter INNRSTRS

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Result Set FLANGE-BY-PADT Table 7 . Result Set FLANGE-BY-PADT - Linear Correlation Coefficients Between Input And Output Variables

Out\Inp OUTERDF INNERDF

CORNSTRS -0.060 1.000

INNRSTRS -0.061 1.000

Table 8 . Result Set FLANGE-BY-PADT - Spearman Rank Order Correlation Coefficients Between Input And Output Variables

Out\Inp OUTERDF INNERDF

CORNSTRS 0.013 1.000

INNRSTRS 0.012 1.000

Acknowledgement: Thanks to Stefan Reh, from whom’s presentation I swiped some graphics! Please contact Rod Scholl with questions Back to Table of Contents

September 25, 2002

Extra! Extra! What's New . . .

� Enhanced Technical Support � Heal Method

� ANSYS Offers Probabilistic Design Seminars

� Advanced Analysis Applications: Impact, Metal Forming, HF EMAG, and MEMS

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September 25, 2002

Enhanced Technical Support by Rod Scholl, PADT

A part of my day I most enjoy is supporting “Enhanced Technical Support” agreements. We provide this service to a host of customers under other names like “Mentoring”, “Customization”, etc. I suppose I enjoy it, because I usually get to help people in a minor jam. I hear Tow Truck drivers have similar experiences. Are you are ever working on ANSYS and think, �It would save me a lot of effort if only someone would stop by my office and ____ __ help me get this thing to converge� __ help me get results by 3 PM today� __ help me modify this macro� __ write a generic macro�then I can pick it up and tweak it from there� __ teach me how to use this new feature, X� __ help me check for errors� __ put another set of eyes on this, just to be sure�?� Many of us have resources like that in our own companies (and maybe you�re one of them) � of course, these folks are usually quite popular and often it is hard to get their time. I feel lucky working at an ANSYS reseller, because I always have an expert nearby to help with my own ANSYS analyses:

Daniel Larusso (Karate Kid): Yeah, but you knew karate. Mr. Miyagi: hmph . . . someone always know more.

Some customers have enough users that we make regular visits, drop by offices and sit with people. Other customers purchase a chunk of time like 10 hrs, and we use it over several visits, or phone calls as the demand arises. The best benefit of all this, is that “Enhanced Technical Support” not only helps you achieve your goal, it prioritizes your learning. We want to make you the expert.

Combining your understanding of your analysis goals, process and skills, with PADT’s knowledge of ANSYS, analysis methods and automation, allows us to realize huge time-savings. Often a 15-minute

discussion, explanation, script debugging, macro-writing, etc. will save someone an afternoon of irritation. Set this service up before you run into trouble – then we’re only a phone call away! Back to List of Articles

September 25, 2002

~Heal Method by Rod Scholl, PADT

There have been some changes in the relationship between ANSYS, Inc. and Cadfix (Transcendata). Some results of these changed are:

• �Cadfix For ANSYS� is no more. • Automatic Geometry Healer (AGM) is a

new product sold by ANSYS, Inc. • CADFix is sold by Transcendata • �Cadfix for ANSYS� customers will

receive licensing for both CADFix and the Automatic Geometry Healer (AGM) through the end of their TECS agreement. (Contact your ANSYS ASD for details).

The Automatic Geometry Healer (AGM) is invoked by a single command ~HEAL. There is no menu selection (but should be in ANSYS 7.0). When ~HEAL is issued, ANSYS will import the file and attempt to repair using the AGM. The AGM is based on �CADFix for ANSYS� technology, but it is all run in batch mode. There is no user interaction. ~HEAL, Name, Extension, Path, Method

The key to the ~HEAL command is in the Method option. You have the choice of either Method=ANSYS or Method=Cadfix. If you�re geometry is being imported via a connection product (Pro/E, Catia, UG, Para, Sat, Ideas, etc.) then you will use Method=ANSYS. If you�re file is an .IGES file, you will use Method=Cadfix.

Method=ANSYS Upon issuing the ~HEAL command with the Method set to ANSYS, the file will be imported using your connection product for which you need a license. Then the resulting .anf file is processed by the Automatic Geometry Healer (AGM), for which you need a license. NOTE: You must have CADFix 5.0 installed locally, even though you don’t need a license for it.

Method=Cadfix Upon issuing the ~HEAL command with the Method set to Cadfix, the file will be repaired using the Automatic Geometry Healer (AGM), for which you need a license. NOTE: You must have CADFix 5.0 installed locally, for which you need a license!

I have tested the Method=ANSYS on a Pro/E model. The AGM was unable to remove slivers, sew surfaces, repair poor Cad-tolerancing problems, etc; albeit was a fairly poor model. Perhaps it would also not have been repairable with Cadfix for ANSYS. The nice part was that without any options to set, it only takes one try with the AGM to fail! The bad part was that it

September 25, 2002

took several hours for the repair and several more hours to read in the geometry; albeit it was a somewhat complex 3D model. I have not tested the Method=Cadfix option.

Recommendations If you use a connection product (Pro/E, Catia, UG, Para, Sat, Ideas, etc.), we recommend that you test out your class of CAD generated geometry using the AGM (~HEAL). If you do not have success, you may want to evaluate a seat of CADFix from Transcendata. If you do not use a connection product, and simply use .IGES, hopefully your geometry comes in clean. If it does not (big surprise), then you will need a CADFix license to repair geometry, regardless of whether you use AGM. If you can take advantage of the automation provided by AGM, compared to the learning curve to operate CADFix alone, you may want to purchase a seat of AGM as well. Back to List of Articles

September 25, 2002

Whether it�s one of our regularly-scheduled classes in our training room or a customized class tailored to your specifications and location, you can be assured that the training you receive will have immediate, positive results on your capabilities in design, analysis, and product and process improvement.

See the upcoming schedule below. Or, learn more about how training at PADT can save you time and money. (Or drop an e-mail to Ted Harris!)

Month Start End Course Description Location

Oct '02 3-Oct 3-Oct 103 DesignSpace 6.0 Irvine, CA

7-Oct 9-Oct 101 Introduction to ANSYS, Part I Tempe, AZ

10-Oct 11-Oct 301 Heat Transfer Tempe, AZ

15-Oct 17-Oct 201 Basic Nonlinearities, Advanced Contact, and Bolt Pretension

Tempe, AZ

21-Oct 23-Oct 101 Introduction to ANSYS, Part I Los Angeles, CA

24-Oct 25-Oct 801 Introduction to ANSYS Customization

Tempe, AZ

28-Oct 29-Oct 701 Design Optimization and Probabilistic Design

Tempe, AZ

30-Oct 1-Nov 601 Introduction to FLOTRAN Irvine, CA

Nov '02 4-Nov 6-Nov 101 Introduction to ANSYS, Part I Tempe, AZ

7-Nov 8-Nov 301 Heat Transfer Irvine, CA

11-Nov 13-Nov 201 Basic Nonlinearities, Advanced Contact, and Bolt Pretension

Los Angeles, CA

14-Nov 15-Nov 501 ANSYS/LS-DYNA Tempe, AZ

18-Nov 20-Nov 101 Introduction to ANSYS, Part I Irvine, CA

21-Nov 22-Nov 203 Dynamics Tempe, AZ

25-Nov 26-Nov 602 FLOTRAN II Los Angeles, CA

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September 25, 2002

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September 25, 2002

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September 25, 2002

The Nitty-Gritty

PHOENIX ANALYSIS AND DESIGN TECHNOLOGIES (PADT) MAKES NO REPRESENTATIONS ABOUT THE SUITABILITY OF THE INFORMATION CONTAINED IN THESE DOCUMENTS AND RELATED GRAPHICS FOR ANY PURPOSE. ALL SUCH DOCUMENTS AND RELATED GRAPHICS ARE PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND AND ARE SUBJECT TO CHANGE WITHOUT NOTICE. THE ENTIRE RISK ARISING OUT OF THEIR USE REMAINS WITH THE RECIPIENT. IN NO EVENT, INCLUDING INACCURATE INFORMATION, SHALL PADT BE LIABLE FOR ANY DIRECT, CONSEQUENTIAL, INCIDENTAL, SPECIAL, PUNITIVE OR OTHER DAMAGES WHATSOEVER (INCLUDING WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS PROFITS, BUSINESS INTERRUPTION, OR LOSS OF BUSINESS INFORMATION), EVEN IF PADT HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

THE VIEWS EXPRESSED IN THE ANSYS FOCUS ARE SOLEY PHOENIX ANALYSIS AND DESIGN TECHNOLOGIES AND NOT THOSE OF ANSYS, INC. Designed by: Rod Scholl Prepared by: Julie Canepa

ANSYS Focus is a periodical publication provided by Phoenix Analysis & Design Technologies (PADT).

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