1. Modal Analysis of a Simple Cantilever
Estimated time required: ~15 min
Experience level: Lower
MD Nastran / Patran

2. Topics Covered
Creating surface with XYZ method
Performing a Modal Analysis
Displaying Modal Analysis results
Obtaining results from *.f06 file

3. Problem Description y x
The beam below is cantilevered or "built in" on the left edge.
Material properties for aluminum:
Modulus of Elasticity = 70 x 109 Pa
Density = 2700 kg/m3
Poisson Ratio = 0.3
The beam has a solid rectangular cross section with thickness (z-direction) t = 0.01 meters and height (y-direction) h = 0.1 meters.
L = 1.0 m
h=0.1m x y

4. Expected Results First Mode Frequency = 8.19 Second Mode

5. Creating a New Database
Click File menu / Select New.
In the File name text field enter modal_beam
Click OK. b c

6. Database Settings for the Model
Select Tolerance radio button: Based on Model
Enter in the Approximate Maximum Model Dimension text field: 1
Select Analysis Code to be MSC.Nastran from the drop down menu
Select Analysis Type to be Thermal from the drop down menu.
Click OK. a b c d e
Remember: MSC.Patran does not handle units of measurement, so it is essential to remember to use one consistent system of measurement. In this example, SI units are used with the following measuring units:
Remember: MSC.Patran does not handle units of measurement, so it is essential to remember to use one consistent system of measurement. In this example, SI units are used with the following measuring units:
Input
Output
Length  meters
Force  Newtons
Elastic Modulus  Pa
Mass  kg
Displacement  meters
Force  Newtons
Stress  Pa

7. Creating Surface a b c d e f Click on Geometry icon
Select Create / Surface / XYZ from the drop down menus
In the Vector Coordinate List text field enter < >
Click on Auto Execute checkbox to turn Off
In the Origin Coordinate List text field enter [0 0 0]
Click on Apply b c d e f

8. Creating Mesh Seed a b c d e f g Click on Elements icon
Select Create / Mesh Seed / Uniform from the drop down menus
Click on Number of Elements radio button
In the Number text field enter 6
Click on Auto Execute checkbox to turn it off
In the Curve List text field select the bottom curve (surface1.4)
Click Apply b c d e f g

9. Creating Mesh Seed a b c e
Select Create / Mesh Seed / Uniform from the drop down menus
Click on Number of Elements radio button
In the Number text field enter 1
In the Curve List text field select the left curve (surface1.1)
Click Apply a b c e

10. Creating Mesh
Select Create / Mesh / Surface from the drop down menu
In Element Shape select Quad
In Mesher select IsoMesh
In Topology select Quad4
In the Surface List text field select the entire surface (surface 1)
Click Apply a b c d e
Note: The Global Edge Length can be ignored since the planted mesh seeds have priority over the mesh density f

11. Equivalence the Surface Mesh
Select Equivalence / All / Tolerance Cube from the drop down menus
In the Equivalence Tolerance text field enter 0.003
Click Apply
In the Command History window make sure that 0 nodes were deleted a b c
Note: No nodes have been deleted because a single surface has been meshed and no coincident nodes exist. d

12. Applying Cantilevered Boundary Condition
Click on Loads/BCs icon
Select Create / Displacement / Nodal from the drop down menus
In the New Set Name text field enter cantilever
Click on Input Data button
In the Translations text field enter <0 0 0>
In the Rotations text field enter <0 0 0>
Click Ok button
Click Select Application Region button
Under Geometry Filter, click on FEM radio button
In Select Nodes text field select the two left nodes of the surface
Click Add button
Click Apply button b i e f j k g l c d h m

13. Boundary Condition Summary
The two nodes at the left side are constrained in which are the respective XYZ for translation and rotation a

14. Creating Aluminum Material Properties
Click on Materials icon
Select Create / Isotropic / Manual Input from the drop down menu
In the Material Name text field enter aluminum
Click on Input Properties button
In Elastic Modulus text field enter 70e9
In Poisson Ratio text field enter 0.3
In Density text field enter 2700
Click Ok button
Click Apply button b e f g c h d i

15. Applying Properties a e b g f c h d i j k Click on Properties Icon
Select Create / 2D / Shell from the drop down menu
In Property Set Name text field enter plate_prop
Click on Input Properties button
Click on Select Material icon
Click on aluminum
In the Thickness text field enter 0.01
Click Ok button
In Select Members text field select the surface (surface 1)
Click Add button
Click Apply button b e g f c h d i j k

16. Analyzing Model a b d e v f Click Analysis icon
Select Analyze / Entire Model / Full Run from the drop down menus
Click on Solution Type button
Click on Normal Modes radio button
Click Ok button
Click Apply button b d e v f

17. Attaching Result Files
Select Access Results / Attach XDB / Result Entitites from the drop down menu
Click on Select Results File button
Double-click on modal_beam.xdb
Click on Apply button c b d

18. Creating Fringe Plots of Modal Analysis – First Mode
Click Results icon
Select Create / Quick Plot from the drop down menu
Under Select Result Cases click on Default, A1:Mode1: Freq = 8.19
Under Fringe Results select Eigenvectors, Translational
Under Select Deformation Result click on Eigenvectors, Translational
Click Apply button b c d e
Note: The results that you obtain might differ slightly from those shown here f

19. Creating Fringe Plots of Modal Analysis – Second Mode
Select Create / Quick Plot from the drop down menu
Under Select Result Cases click on Default, A1:Mode2: Freq =
Under Fringe Results select Eigenvectors, Translational
Under Select Deformation Result click on Eigenvectors, Translational
Click Apply button
Note: The results that you obtain might differ slightly from those shown here

20. Viewing Results in *f06 file
To obtain detailed results information about the analysis, you can create a report file with the needed information or open the *f06 file to obtain the real eigenvalues. These are the natural frequencies (in radians) or the beam.

21. Summary of Results of FEA on Given Truss Model
First Mode
Frequency = 8.19
Second Mode
Frequency =

22. Important Skills Acquired
Creating surface with XYZ method
Performing a Modal Analysis
Displaying Modal Analysis results
Obtaining results from *.f06 file

23. Further Analysis (Optional)
Study the first 5 modes shapes produced by MSC.Nastran and comment on which modes are not associated with bending about the minimum “I” direction.
Rerun the analysis using twice as many elements. Does a refinement in the mesh appear to produce more accurate results?
Change the Poisson’s ratio to 0.0. Rerun the analysis using the original global edge length (6 elements). Compare these errors with the errors found while using a Poisson’s ratio of 0.3. Propose explanation for the differences.

24. Best Practices
Keep a consistent system of units
Remember to choose the solution type adequately so that MD Nastran knows what type of solution type its solving for
Check your answer by doing hand calculations to determine if the answers obtained are within the spectrum of acceptance.