WORKSHOP 14

BUCKLING OF A SUBMARINE PRESSURE HULL

WS14-2NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

WS14-3NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

Workshop ObjectivesCreate groups based on property sets.

Run a linear buckling analysis.

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Problem DescriptionA submarine pressure hull is modeled by plate and bar elements. Check the pressure hull for buckling at an operating depth of 1000 ft which is equivalent to an external pressure of 445 psi.

WS14-5NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

Suggested Exercise Steps1. Create a new database and name it submarine.db. 2. Import the MSC.Nastran input file pressure_hull.bdf.3. Create groups based on property sets.4. Post only the center pressure shell section.5. Apply boundary conditions.6. Post the entire pressure shell.7. Apply an external pressure of 445 psi to the pressure shell.8. Run a linear buckling analysis. Request the first 5 roots (buckled

modes).9. Read the xdb file into MSC.Patran.10. Post all the groups.11. Plot the buckled mode shapes and identify which part of the pressure

hull is buckling for each mode.

WS14-6NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

b c

d

f

g

Step 1. Create New Database

Create a new database called submarine.db

a. File / New.b. Enter submarine as the

file name.c. Click OK.d. Choose Default

Tolerance.e. Select MSC.Nastran as

the Analysis Code.f. Select Structural as the

Analysis Type. g. Click OK.

a

e

WS14-7NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

Step 2. Import File

a

b

c

Import the Nastran Filea. File: Import.b. Set the object to model and

the source to MSC.NastranInput.

c. Select pressure_hull.bdf.d. Click Apply.e. Click OK to Summary Input

File

d

WS14-8NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

Step 3. Create Groups

Create a new groupa. Group: Create. b. Select Property Set as

the method.c. Select Multiple Groups.d. Click Apply.

a

b

c

d

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Step 4. Post Entire Pressure Shell

Post two groupsa. Group: Post. b. Shift click to select

pshell.1 and pshell.2.

c. Click Apply.d. Click OK to change

the Current Group.

a

d

b

c

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Step 5. Apply Boundary Conditions

Create a boundary conditiona. Loads/BCs: Create /

Displacement / Nodal.b. Enter xyzconstraint as the

New Set Name.c. Click Input Data.d. Enter <0 0 0> for

Translations and Rotations.e. Click OK.

d

e

b

c

a

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Apply the boundary conditiona. Click Select

Application Region.b. For the Geometry

Filter select FEM.c. Select the node at the

tip of the shell as shown.

d. Click Add.e. Click OK. f. Click Apply.

e

d

b

c

Step 5. Apply Boundary Conditions

a

f

WS14-12NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

Step 7. Apply Pressure Load

Create a pressure loada. Loads/BCs: Create /

Pressure / Element Uniform.

b. Enter pressure_load as the New Set Name.

c. Set the Target Element Type to 2D.

d. Click Input Data.e. Enter 445 for the Bottom

Surface Pressure.f. Click OK.

e

f

b

a

c

d

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Apply the boundary conditiona. Click Select

Application Region.b. For the Geometry

Filter select FEM.c. Select the entire shell.d. Click Add.e. Click OK. f. Click Apply.

e

d

b

Step 7. Apply Pressure Load

c

a

f

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Step 8. Run Linear Buckling Analysis

Analyze the modela. Analysis: Analyze /

Entire Model / Full Run.

b. Enter submarineas the job name.

c. Click Solution Type.

d. Choose Buckling.e. Click Solution

Parameters.f. Verify that the Plate

Rz Stiffness Factor is 100.0

g. Click EigenvalueExtraction.

h. For the Number of Desired Roots, enter 5.

i. Click OK.j. Click OK.k. Click OK. l. Click Apply.

a

c

d

eg

h

i

j

k

l

f

b

WS14-15NAS120, Workshop 14, May 2006Copyright© 2005 MSC.Software Corporation

Step 9. Read Results into MSC.Patran

Attach the results filea. Analysis: Access Results /

Attach XDB / Result Entities.

b. Click Select Results File.c. Choose the results file

submarine.xdb.d. Click OK. e. Click Apply.

a

b

c

e

d

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Step 10. Post All Groups

Post the default groupa. Group:Post.b. Select default_group.c. Click Apply.d. Click on the Reset Graphics

Icon.

a

b

c

d

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Step 11. Plot Mode Shapes

Create a quick plota. Results: Create / Quick

Plot.b. Select a Mode.c. Select Eigenvectors,

Translational as the Deformation Result.

d. Click Apply.e. Repeat for other modes.

a

d

c

b

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Step 11. Plot Mode Shapes

Record Data in the following table:

Mode No: Buckling Load Factor: Region of Buckling:

1 _________________ ______________________________

2 _________________ ______________________________

3 _________________ ______________________________

4 _________________ ______________________________

5 _________________ ______________________________