Workshop –MSC Nastran Topology Optimization …the-engineering-lab.com/pot-of-gold/ws_topex5a.pdf · The Engineering LabNastran SOL 200 questions? Email me: christian@ the‐engineering‐lab.com

The Engineering LabNastran SOL 200 questions? Email me: christian@ the‐engineering‐lab.com

Workshop – MSC Nastran Topology OptimizationManufacturing ConstraintsAN MSC NASTRAN SOL 200 TUTORIAL

2The Engineering LabNastran SOL 200 questions? Email me: christian@ the‐engineering‐lab.com 2

Goal: Use Nastran SOL 200 OptimizationBefore Optimization◦ Mass: 25.6

After Optimization◦ Mass: 7.7 (~70% mass reduction)◦ Mirror Symmetry Constraints◦ Casting


Details of the structural model


Optimization Problem StatementDesign Region/Variables

x1: PSOLID 1

Restrictions:• Mirror Symmetry Constraints

• Symmetry about the YZ plane of coordinate system 1

• Casting in Y direction of coordinate system 1, use 1 die

PSOLID 1 – Part_XDesign Objective

r0: Minimize compliance

Design Constraints

r1: Fractional mass

r1 < .3 (70% mass reduction)Plane of Symmetry

The Engineering Lab 5Nastran SOL 200 questions? Email me: christian@the‐engineering‐lab.com

Contact mechristian@ the‐engineering‐lab.com• Nastran SOL 200 training

• Nastran SOL 200 questions

• Structural optimization questions

• Access to the MSC Nastran SOL 200 Web App

6The Engineering LabNastran SOL 200 questions? Email me: christian@ the‐engineering‐lab.com

Tutorial


Special Topics Covered

Mirror Symmetry Constraints – Fit the Topology Optimization solution must be symmetric, constraints may be imposed to achieve this.

Manufacturing Constraints – The manufacturability of Topology Optimization results is important. Options exist to produce results that can be manufactured.

With Manufacturing Constraints and Symmetry

Without Manufacturing Constraints, but with Symmetry

Tutorial Overview1. Start with a .bdf or .dat file

2. Use the MSC Nastran SOL 200 Web App to:◦ Convert the .bdf file to SOL 200

◦ Design Regions/Variables◦ Design Objective◦ Design Constraints

◦ Perform optimization with Nastran SOL 200

3. Review optimization results◦ .f06◦ Topology Optimization and Structural Results


MSC Nastran SOL 200 Web App

SOL 200 BDF

SOL 1xxBDF


Before Starting1. Ensure the Downloads directory

is empty in order to prevent confusion with other files

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Go to the User’s Guide1. Click on the indicated link

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Obtain Starting Files1. Find the indicated example

2. Click Link

3. The starting file has been downloaded

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Open the Correct Page1. Click on the indicated link

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topex5a.dat

Upload BDF Files1. Click 1. Select Files and select topex5a.dat

2. Click Upload Files 1

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Create Design Region1. Click on the plus (+) icons to set PSOLID 1 as a

Design Region

2. Click + Options

3. Mark the checkboxes for the following: 1. Expand Width of Table2. Show Symmetry Constraint Columns3. Show Casting Columns

4. Set the following for the design region1. Use Symmetry Constraints: Yes2. Coordinate System ID: 13. Symmetry Planes: YZ4. Use Casting Constraints: Yes5. Draw Direction: Y6. Die Option: 1 – Single7. Is the mesh aligned to …: NO

5. Confirm the Symmetry Plane is set to YZ

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Create Design Objective1. Click on Objective

2. The objective with label r0 is automatically created. The objective is to minimize the Compliance.

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Create Design Constraints1. Click Constraints2. The constraint r1 is automatically created3. Configure the following for r1

1. Upper Allowed Limit: .3 (Retain 30% of the material / 70% mass reduction)

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Configure Optimization Settings 1. Click Settings

2. Set DESMAX to 100

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Export New BDF Files1. Click on Exporter

2. Click on Option 1 ‐ Auto Execute MSC Nastran

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Export New BDF FilesOption 1

This tutorial will use Option 1 to export a .zip file that contains all the files necessary to automatically start MSC Nastran.

Important! It is assumed MSC Nastran is installed locally and not remotely on a separate machine. If MSC Nastran is installed remotely, use Option 2.

Option 2

If you would like to only download the bdf files (model.bdf, design_model.bdf) and manually start MSC Nastran, use Option 2. A walkthrough on how to use Option 2 is available in the User’s Guide, Advanced Tutorials. The walkthrough is named Manually Starting MSC Nastran and Uploading Results.


Perform the Optimization with Nastran SOL 200A new .zip file has been downloaded

1. Right click on the file

2. Click Extract All

3. Click Extract on the following window

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Perform the Optimization with Nastran SOL 2001. Inside of the new folder, double click on

Start MSC Nastran

2. Click Open, Run or Allow Access on any subsequent windows

3. MSC Nastran will now start

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Using Linux?

Follow these instructions:1) Open Terminal2) Navigate to the nastran_working_directory

cd ./nastran_working_directory3) Use this command to start the process

./Start_MSC_Nastran.sh

In some instances, execute permission must be granted to the directory. Use this command. This command assumes you are one folder level up.

sudo chmod ‐R u+x ./nastran_working_directory


StatusWhile MSC Nastran is running, a status page will show the current state of MSC Nastran


Review Optimization ResultsAfter MSC Nastran is finished, the results will be automatically uploaded.

1. Ensure the messages shown have green checkmarks. This is indication of success. Any red icons indicate challenges.

2. The final value of objective and normalized constraints can be reviewed.

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Review Optimization Results in Patran1. Start a new Patran session

2. Right click to open a menu

3. Go to Import Model and click on MSC.Nastran Input

4. Select model.bdf (This file was used for the optimization)

5. Click Apply

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Review Optimization Results in Patran1. Click Smooth Shading

2. Go to Tools > Design Study and click on Post‐Process

3. Click Select Results File

4. Select model.des (This file was created during the optimization)

5. Click OK

6. Click Apply

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Review Optimization Results in Patran1. Change Action to Display Results

2. For Select Result Case, select the only row present (The row should be blue)

3. Set the Threshold to .4

4. Click Apply (The final result of the Topology Optimization is displayed)

5. Click on the Model Tree icon

6. Under Groups, two groups are present. Use the checkboxes to switch between groups.

1. HIGH_DENS_GRP – This group contains the topology optimization result

2. default_group ‐ This group contains the original model

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ResultsBefore Optimization◦ Mass: 25.6

After Optimization◦ Mass: 7.7 (~70% mass reduction)◦ Mirror Symmetry Constraints◦ Casting


End of Tutorial


Topology Optimization Workflows


Traditional Topology OptimizationObjective: Minimize Compliance (Maximize Stiffness)Constraint: Fractional Mass < .## (Target Mass)

Max von Misses: 150 MPaMax Displacement : 2.78 mm

1st natural Frequency: 111 Hz

FRMASS < .75Mass: 7.186 gOptimization B

Original Design

Mass: 9.737 grams

Mass: 7.739 g


Traditional Topology OptimizationObjective: Minimize Compliance (Maximize Stiffness)Constraint: Fractional Mass < .## (Target Mass)





Max von Misses: 150 MPaMax Displacement: 2.52 mm


Topology Solution Refined Design Verification

FRMASS < .9Mass: 8.756 g Optimization A

FRMASS < .75Mass: 7.186 gOptimization B

FRMASS < .6Mass: 5.718 gOptimization C

Original Design

Mass: 9.737 grams Optimization B led to a valid and light weight design

Mass: 9.094 g

Mass: 7.739 g

Mass: 6.119 g


Topology Solution

Latest Topology OptimizationObjective: Minimize Fractional Mass (Minimize Mass)Constraint: Stress Constraint

Refined Design VerificationOriginal Design


Appendix


What are the design variables in Topology Optimization?• Each element that is within a

design region is given a design variable that represents a normalized material density

• 0 ‐ Normalized density values close to 0 are not critical to the design

• 1 – Normalized density values close to 1 are critical to the design

The final values of design variables or normalized densities are plotted for each element.


What is compliance?Compliance is defined in many ways

• “Compliance is simply the product of the displacement times the applied load” (MSC Nastran Design Sensitivity and Optimization User’s Guide)

• For linear elastic solids, the work is twice the total strain energy

Total Strain Energy

Compliance


What is compliance? ContinuedThe .f06 file reports the value of compliance and strain energy. The following applies if and only if minimizing the compliance is the design objective.

1. Make sure this statement is in the Case Control Section of the .bdf file.

1. ESE(THRESH=.99)=ALL

2. Search the .f06 file for the initial design’s1. E L E M E N T S T R A I N E N E R G I E S

3. Note the value of TOTAL ENERGY OF ALL ELEMENTS IN PROBLEM

4. Search the .f06 for the 1. S U M M A R Y O F D E S I G N C Y C L E

H I S T O R Y

5. Note the value for OBJECTIVE FROM EXACT ANALYSIS for the INITIAL cycle number

6. The Compliance of 1.8222E4 is twice the TOTAL STRAIN ENERGY of 9.11E3.


What is FRMASS or Fractional Mass?• At the start of the optimization, the INITIAL

design has its material densities reduced.

• During the optimization, each normalized material density is varied in order to minimize the compliance of the entire structure (increase the stiffness)

• IMPORTANT: Always use decimal points when specifying FRMASS

1) INITIAL design• FRMASS = 1.0• Original density

2) Reduction (Start of Optimization)• FRMASS = .3• All densities are set to .3 (30%) of the

original density

1.0 1.0 1.0

1.0 1.0 1.0

.3 .3 .3

.3 .3 .3

.1 .1 1.0

.1 .1 .4

3) Optimization • FRMASS < .3• Normalized Densities are varied

Total: 6

Total: 1.8

Total: 1.8


How is it possible to increase the stiffness?• The initial design (Left) has the following

characteristics:• The optimizer will set each initial normalized material density to the FRMASS specified.

• Since each element’s density is .3 of the original density, the mass is 30% of the original

• As a result, the compliance or work done has been increased

• During the Topology Optimization, the optimizer will vary the normalized material densities while minimizing the Compliance

• The final design (Right) has the following characteristics:

• The normalized densities have been varied, but the total mass remains 30% of the original

• The compliance or work done has been minimized

For the initial design, the normalized densities start at a value of .3. The initial design satisfies the design constraint where FRMASS is

less than .3.

At the end of the optimization, each element has a different normalized density. The total mass of this design still satisfies the

design constraint, FRMASS is less than .3.


How can non‐critical elements be removed from the design?• Use the threshold to suppress non‐

critical elements

• The threshold means: ‘Keep every element that has a normalized density greater than the threshold’

• Recall from before:• 0 ‐ Normalized density values close

to 0 are not critical to the design

• 1 – Normalized density values close to 1 are critical to the design

The normalized densities are plotted for each element. Note that all the elements are present.

Documents

Workshop –MSC Nastran Topology Optimization …the-engineering-lab.com/pot-of-gold/ws_topex5a.pdf · The Engineering LabNastran SOL 200 questions? Email me: christian@ the‐engineering‐lab.com