MSC NASTRAN SOL 200 TUTORIAL - The Engineering Labthe-engineering-lab.com/pot-of-gold/ws_topstr2.pdf · Workshop –MSC Nastran Topology Optimization –Minimizing mass with stress

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

Workshop – MSC Nastran Topology Optimization – Minimizing mass with stress and displacement 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: 18 kg

After Optimization◦ Mass: 9.3 kg◦ Prevent excessive stress and displacements


Goal: Use Nastran SOL 200 Optimization

1) Initial Design

2) Proposed Topology Solution

3) Final Design


Details of the structural modelUnits: m, N, MPa

Material:E: 200E9 Pav: .3p: 7850 kg/m^3

Constrained

ForceTwo SUBCASEs


Optimization Problem StatementDesign Region/Variables

x1: PSOLID 1

Design Objective

r0: Minimize fractional mass (FRMASS)

Design Constraints

r1: Z displacement at node 5622 (GRID 5622)

r1 < .0008 m

x1: Maximum allowable stress, 2.0E8 Pa, on design region x1

Node 5622

PSOLID 1 ‐ Sub_Part_SectionPSOLID 2 ‐ Support_Rings

The Engineering Lab 6Nastran 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

7The Engineering LabNastran SOL 200 questions? Email me: christian@ the‐engineering‐lab.com

Tutorial


Special Topics Covered

Maximum Allowable Stress – A stress constraint cannot be created normally as is done in Size or Topometry optimization. A special option is available to specify a stress constraint for Topology Optimization.

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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topstr2.dat

Upload BDF Files1. Click 1. Select Files and select topstr2.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 checkbox for Show Stress Limit Column

4. Set the following for the design region1. Upper Allowed Limit von Mises

Stress: 2.0E8

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4Under + Options the Entry Name column may be displayed. If property or material names were created in a Pre Processor, the names will be displayed in the Entry Name column.


Create Design Objective1. Click on Objective

2. Click the x icon to delete the existing objective of compliance

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Create Design Objective1. Search for FRMASS

2. Click the plus (+) icon

3. The objective for FRMASS is added to the table, no further edit is necessary

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Create Design Constraints1. Click Constraints

2. Click the x icon to delete the existing constraint of Fractional Mass (FRMASS)

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Create Design Constraints1. Click on the plus (+) icon for Displacement

2. Configure the following for r1:1. ATTA: 3 – T3 (Z Component)

2. ATTi: 5622 (Node/GRID 5622)

3. Upper Allowed Limit: 8.0E‐4

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Assign Constraints to Load Cases (SUBCASES)1. Click Subcases

2. Click Check visible boxes

r1 or DISP constraint has been assigned to SUBCASE 1 and SUBCASE 2

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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 .3

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: 18 kg

After Optimization◦ Mass: 9.3 kg◦ Prevent yield and excessive displacement


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 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


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 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


For the initial design, the normalized densities start at a value of .9.

At the end of the optimization, each element has a different normalized density.


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


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


Exporting Topology Solution to BDF


Assumptions1. It is assumed that the results have been

displayed and a group named ‘HIGH_DENS_GRP’ has been created. See the previous slides for instructions. This group contains the all the elements that can be considered the topology optimization solution.

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Exporting a Group to a BDF FileThe following instructions are used to export a mesh contained with a group. For this example, the group named HIGH_DENS_GRP will be exported to a BDF file.

1. Right click on the group HIGH_DENS_GRP

2. Click on Set Current

3. Click the Analysis tab

4. Click on Selected Group

5. Switch the Method to Model Only

6. Rename the job name

7. Click Apply

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Exporting a Group to a BDF File1. A new BDF file has been created with the

same ‘Job Name’ from the previous slide.

This BDF file contains all the elements that were in the group named. HIGH_DENS_GRP . This group contained the topology optimization solution.

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Documents

MSC NASTRAN SOL 200 TUTORIAL - The Engineering Labthe-engineering-lab.com/pot-of-gold/ws_topstr2.pdf · Workshop –MSC Nastran Topology Optimization –Minimizing mass with stress