WORKSHOP 4 Minimizing the Weight of a Composite Wingpages.mscsoftware.com/rs/mscsoftware/images/WS4_Composite_Wing... · Title: NAS113 Workshop 5 Author: Ken Ranger Subject: Stiffness

Composites Technology Day, February 2012

Copyright 2012 MSC.Software Corporation WS4 - 1

WORKSHOP 4

Minimizing the Weight of a Composite Wing





• Workshop Objective

– Become familiar with the steps to set up a composite optimization analysis

• Software Version

– Patran 2011

– MD Nastran 2011.1

• Required File:

– composite_wing_opt.db

• Problem Description:

– Preliminary stress analysis from workshop 1 showed the margins of safety are

high for the 8-ply carbon/epoxy quasi-isotropic layup

– Determine optimal ply thicknesses to minimize weight while maintaining a

positive strength margin of safety



b

c

a

Step 1. Open an existing Patran Database

Start Patran and open a database

containing a wing model:

a. Click File Open in the Defaults

group.

b. Select

composite_wing_opt.db as

the File name.

c. Click OK.



Step 2. Create Design Variables

Create design variables for the

thicknesses of the carbon-epoxy plies:

a.Pull down Tools > Design Study >

Pre-Process.

b.Select Design Variable for Object.

c.Select Material for Type.

d.Select Composite, Thickness, and

Local Ply for Category.

e.Click the Select Material Set(s) icon.

f.Click and hold down on bs1 and drag

down to select all 17 properties.

g.Click the Select Material Property

icon.

h.Click and hold down on 1 and drag

down to select all 4 plies.

i.Enter 0.005 for Lower bound and 0.25

for Upper bound.

j.Click Apply.

This step creates 68 ply thickness

variables.

a

f

e

d

c

b

g

i

j

h

0.0054



Step 3. Create the Design Objective

Create a Design Objective to minimize

the overall weight.

a.Select Objective for Object.

b.Select Global for Solution.

c.Select Weight for Response.

d.Enter mass for Objective Name.

e.Select minimize for MinMax.

f.Click Apply.

a

b

f

e

d

c



Step 4. Create Constraints on Composite Failure

Create constraints on composite

failure index:

a.Select Constraint for Object.

b.Select Linear Static for Solution.

c.Select Composite Failure for

Response .

d.Enter FI_Ply1 for Constraint Name.

e.Select PSET.

f.Click the Select Property Set(s)

icon.

g.Click Select All.

h.Click Apply.

i.Select Ply for Index.

j.Enter 1 for Ply Number.

k.Enter 1.0 for Upper Bound.

l.Click Apply.

Repeat steps d, j, k, l for Constraint

Names FI_Ply2 thru FI_Ply8. Enter

2 thru 8 for Ply Number, respectively.

a

b

g

f e

d

c

h

i

j

k

l



Step 5. Create Design Study Create a design study consisting of all the design

variables, responses, and constraints.

a.Select Design Study for Object.

b.Enter wing_ply_thickness for Design Study

Name.

c.Click Select Design Variables.

d.Review the design variables and click Cancel.

e.Click Select Objectives.

f.Select mass.

g.Click Select Constraints.

h.Click Select All.

i.Click Apply.

j.Click Apply.

k.Click Close.

f

g

c

b

a

e

g

h

i j k d



Step 6. Set up Optimization Analysis

Set up the optimization analysis:

a.Click the Analysis tab.

b.Set Action to Optimize.

c.Enter comp_wing_thickness_opt

for Job Name.

d.Click Design Study Select.

e.Select wing_ply_thickness.

f.Click Global Obj./Constr. Select.

g.Select mass.

h.Click OK

b

c

d

e

g

a

f

h



Step 6. Set up Optimization Analysis (Cont.)

Set up the optimization analysis (cont.):

a.Click Optimization Parameters.

b.Enter 20 for Standard Cycles

(DESMAX).

c.Click OK.

c

b

a





a.Click Subcases…

b.Select wing up bending.

c.Click Constraints/Objective...

d.Select all 8 constraints.

e.Click OK.

f.Click Apply.

g.Click Yes to the prompt to create a

new subcase.

h.Click Cancel.

c

b

a

d

e

f

g

h





a.Click Subcase Select…

b.Select wing up bending.

c.Click OK.

d.Click Apply to run the analysis.

You’ve just submitted the Nastran

optimization analysis. It will take about

a minute to run the analysis.

a

b

c

d



Step 7. Access Results

Access analysis results:

a.Select Access Results for Action.

b.Select Read Output2 for Object.

c.Click Select Results File.

d.Select

comp_wing_thickness_opt.op2

e.Click OK.

f.Click Apply.

d

c

b

e

a

f



Step 8. Plot Displacements and Failure Index

Create a deformed shape and

failure indices plot of the initial

design:

a. Click the Results tab.

b. Select the first result case to

view the results of the initial

design.

c. Under Select Fringe Result,

select Failure Indices,

Maximum Indices.

d. Under Select Deformation

Result, select Displacements,

Translational.

e. Click Apply.

a

e

b

c

d



Step 8. Plot Displacements and Failure Index

Plot failure indices for the final

design:

a. Select the last result case to

view the results of the final

design.

b. Click Apply.

a

b



Step 9. View Optimization History Plots

View Design Variable History to

review the ply thickness

optimizaton history:

a. Click Post in XY Plots group.

b. Select Design Variable History

under Post/Unpost XY

Windows.

c. Click Apply.

a

c

b



Step 9. View Optimization History Plots (cont.)

View Maximum Constraint History

to review the failure index

constraint optimization history:

a. Select

MaximumConstraintHistory


Windows.

b. Click Apply.

a

b



Step 9. View Optimization History Plots

View Objective Function History to

review the wing total weight

optimization history:

a. Select

ObjectiveFunctionHistory


Windows.

b. Click Apply.

a

b



Analysis Summary

• The total weight of the wing has been reduced substantially.

• Possible next steps:

– Add ply orientation angle variables to optimize the fiber orientations.

– A balanced layup is often desirable. Use DLINK entries to link the +45

and -45 ply thickness variables to enforce equal thickness.

– Create discrete values for ply thicknesses using the DDVAL entry to

make the final optimized thickness results possible to manufacture.

– Account for local panel buckling by adding buckling constraints



End of Workshop 4

File/Quit to exit Patran.

Documents

WORKSHOP 4 Minimizing the Weight of a Composite Wingpages.mscsoftware.com/rs/mscsoftware/images/WS4_Composite_Wing... · Title: NAS113 Workshop 5 Author: Ken Ranger Subject: Stiffness