WS15 Submarine Buckling

WORKSHOP 15

BUCKLING OF A SUBMARINE PRESSURE HULL

NAS120, Workshop 15, January 2003 WS15-1

WS15-2NAS120, Workshop 15, January 2003


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.


Workshop ObjectivesCreate groups based on property sets.Run a linear buckling analysis.


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.


Step 1. Create New Database

a

b c

d

f

g

e

a

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.


Step 2. Import File

b

c

d

a

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

and the source to MSC.Nastran Input.

c. Select pressure_hull.bdf.

d. Click Apply.


Step 3. Create Groups

bc

d

a

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

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


Step 4. Post Entire Pressure Shell

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

pshell.1 and pshell.2.c. Click Apply.


Step 5. Apply Boundary Conditions

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c

d

e

a

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.


Step 5. Apply Boundary Conditions

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.

ae

f

d

b

c


Step 7. Apply Pressure Load

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d

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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.


Step 7. Apply Pressure Load

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.

ae

f

d

b

c


Step 8. Run Linear Buckling Analysis

Analyze the modela. Analysis: Analyze /

Entire Model / Full Run.

b. Click Solution Type.

c. Choose Buckling.d. Click Solution

Parameters.e. Enter 100 for the

Plate Rz Stiffness Factor.

f. Click Eigenvaule Extraction.

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

h. Click OK.i. Click OK.j. Click OK. k. Click Apply.

a

b

c

df

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h

i

j

k

e


Step 9. Read Results into MSC.Patran

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b

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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.


Step 10. Post All Groups

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b

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

Icon.


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


Step 11. Plot Mode Shapes

Record Data in the following table:

Mode: Factor: Region of Buckling:

1 ______ _____________________________________

2 ______ _____________________________________

3 ______ _____________________________________

4 ______ _____________________________________

5 ______ _____________________________________

WS15 Submarine Buckling

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