Workshop MSC Nastran Topology Optimization Manufacturing Constraints

Transcription

1 Workshop MSC Nastran Topology Optimization Manufacturing Constraints AN MSC NASTRAN SOL 200 TUTORIAL The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com

2 Goal: Use Nastran SOL 200 Optimization Before Optimization Mass: 25.6 After Optimization Mass: 7.7 (~70% mass reduction) Mirror Symmetry Constraints Casting The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 2

3 Details of the structural model The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 3

4 Optimization Problem Statement Design 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 Plane of Symmetry PSOLID 1 Part_X Design Objective r0: Minimize compliance Design Constraints r1: Fractional mass r1 <.3 (70% mass reduction) The Nastran Engineering SOL 200 questions? Lab me: christian@ the engineering lab.com 4

5 Contact me Nastran SOL 200 training Nastran SOL 200 questions the engineering lab.com Structural optimization questions Access to the MSC Nastran SOL 200 Web App 5

6 Tutorial The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 6

7 Tutorial Overview 1. 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 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. Without Manufacturing Constraints, but with Symmetry With Manufacturing Constraints and Symmetry 3. Review optimization results.f06 Topology Optimization and Structural Results The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 7

8 MSC Nastran SOL 200 Web App SOL 1xx BDF SOL 200 BDF The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 8

9 Before Starting 1. Ensure the Downloads directory is empty in order to prevent confusion with other files 1 9

10 Go to the User s Guide 1. Click on the indicated link 1 10

11 1 Obtain Starting Files 2 1. Find the indicated example 2. Click Link 3. The starting file has been downloaded 3 11

12 Open the Correct Page 1. Click on the indicated link 1 12

13 Upload BDF Files 1. Click 1. Select Files and select topex5a.dat 2. Click Upload Files 1 2 topex5a.dat 13

14 Create Design Region 1. Click on the plus (+) icons to set PSOLID 1 as a Design Region 1 2. Click + Options 3. Mark the checkboxes for the following: 1. Expand Width of Table 2. Show Symmetry Constraint Columns 3. Show Casting Columns 4. Set the following for the design region 1. Use Symmetry Constraints: Yes 2. Coordinate System ID: 1 3. Symmetry Planes: YZ 4. Use Casting Constraints: Yes 5. Draw Direction: Y 6. Die Option: 1 Single 7. Is the mesh aligned to : NO Confirm the Symmetry Plane is set to YZ 14

15 1 Create Design Objective 1. Click on Objective 2. The objective with label r0 is automatically created. The objective is to minimize the Compliance. 2 15

16 1 Create Design Constraints 1. Click Constraints 2. The constraint r1 is automatically created 3. Configure the following for r1 1. Upper Allowed Limit:.3 (Retain 30% of the material / 70% mass reduction)

17 Configure Optimization Settings 1 1. Click Settings 2. Set DESMAX to

18 Export New BDF Files 1. Click on Exporter 1 2. Click on Option 1 Auto Execute MSC Nastran 2 18

19 Export New BDF Files Option 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. 19

20 1 Perform the Optimization with Nastran SOL 200 A new.zip file has been downloaded 2 1. Right click on the file 2. Click Extract All 3. Click Extract on the following window 3 20

21 Perform the Optimization with Nastran SOL 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 1 2 Using Linux? Follow these instructions: 1) Open Terminal 2) Navigate to the nastran_working_directory cd./nastran_working_directory 3) Use this command to start the process./start_msc_nastran.sh 3 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 21

22 Status While MSC Nastran is running, a status page will show the current state of MSC Nastran 22

23 Review Optimization Results After 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 The final value of objective and normalized constraints can be reviewed. 23

24 Review Optimization Results in Patran 1. 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) Click Apply

25 Review Optimization Results in Patran Click Smooth Shading 2. Go to Tools > Design Study and click on Post Process Click Select Results File 4. Select model.des (This file was created during the optimization) 5. Click OK 6. Click Apply 25

26 Review Optimization Results in Patran Change Action to Display Results 2. For Select Result Case, select the only row present (The row should be blue) 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 4 26

27 Results Before Optimization Mass: 25.6 After Optimization Mass: 7.7 (~70% mass reduction) Mirror Symmetry Constraints Casting The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 27

28 End of Tutorial The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 28

29 Topology Optimization Workflows The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 29

30 Traditional Topology Optimization Objective: Minimize Compliance (Maximize Stiffness) Constraint: Fractional Mass <.## (Target Mass) Original Design Max von Misses: 150 MPa Max Displacement : 2.78 mm 1 st natural Frequency: 111 Hz Mass: grams FRMASS <.75 Mass: g Optimization B Mass: g The Nastran Engineering SOL 200 questions? Lab me: christian@ the engineering lab.com 30

31 Traditional Topology Optimization Objective: Minimize Compliance (Maximize Stiffness) Constraint: Fractional Mass <.## (Target Mass) Topology Solution Refined Design Verification Original Design Max von Misses: 150 MPa Max Displacement: 2.52 mm 1 st natural Frequency: 114 Hz FRMASS <.9 Mass: g Optimization A Mass: g Max von Misses: 150 MPa Max Displacement : 2.78 mm 1 st natural Frequency: 111 Hz Mass: grams FRMASS <.75 Mass: g Optimization B Mass: g Optimization B led to a valid and light weight design Max von Misses: 250 MPa Max Displacement : 3.57 mm 1 st natural Frequency: 109 Hz FRMASS <.6 Mass: g Optimization C Mass: g The Nastran Engineering SOL 200 questions? Lab me: christian@ the engineering lab.com 31

32 Latest Topology Optimization Objective: Minimize Fractional Mass (Minimize Mass) Constraint: Stress Constraint Original Design Topology Solution Refined Design Verification The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 32

33 Appendix The Nastran Engineering SOL 200 questions? Lab me: the engineering lab.com 33

34 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. 34

35 What is compliance? Compliance is defined in many ways Total Strain Energy 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 Compliance 35

36 What is compliance? Continued The.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 s 1. 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 E4 is twice the TOTAL STRAIN ENERGY of 9.11E3. 36

37 Total: 6 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) Total: ) 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 IMPORTANT: Always use decimal points when specifying FRMASS Total: ) Optimization FRMASS <.3 Normalized Densities are varied

38 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. 38

39 How can noncritical elements be removed from the design? Use the threshold to suppress noncritical elements The threshold means: Keep every element that has a normalized density greater than the threshold The normalized densities are plotted for each element. Note that all the elements are present. 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 39