Example 9.1 Solved using FEMAP

1. Start up FEMAP. We will begin by making 4 nodes. From the menus select Model/Node (or type Ctrl N). The popup window will look like the one below. You are to create nodes at the following x coordinates; 0, 2, 4, 6. Thus, on the window below just click OK to make a node at x=0. In the next window, change the x coordinate to x=2 and click OK. Repeat this for x=4 and x=6. After creating 4 nodes, click the Cancel button.

2. Hold down the Ctrl button and type A. This will zoom all items in the display.

3. Next we want to create three spring elements between each of the nodes. From the menus select Model/Element (or type Ctrl E). In the popup window click the Type button. In the next popup window select the Spring/Damper radio button as shown below and click OK.

4. Back in the “Define SPRING/DAMPER Element” window, click the button. This opens the Define Property window. Key in a title, select the Axial radio button and key in a stiffness of 1.0 as shown below. Click OK.

5. Back in the “Define SPRING/DAMPER Element” window, make sure the property you just created is selected and then click in the first node box as shown below. Next select the node on the far left side and then the node just to the right of it as shown in the second figure below. Nodes 1 and 2 should appear in the node boxes. Click OK to create the element. Next, click the next two nodes to create a middle element and then repeat again to make an element on the right hand side. Now click Cancel to terminate node creation. Your display should look like the one below.

6. We will next create lumped mass elements at the nodes. From the menus select Model/Element (or type Ctrl E). In the popup window click the Type button. In the next popup window select the Mass radio button as shown below and click OK.

7. Back in the “Define MASS Element” window click the button. This opens the Define Property window. Key in a title and key in a mass of 1.0 as shown below. Click OK.

8. Back in the Define MASS element window, make sure the new property you just created is

selected and the click in the node box. Next, click the second node from the left and click OK. Next click the second node from the right. Next click Cancel to terminate creation of elements. Your display should now look like the one below.

9. We now need to apply constraints to the nodes. From the menus select Model/Constraint/Nodal. In the first popup window you can key in a title for the Constraint set (or leave it blank) and click OK. When the next popup window appears, select the end nodes with the mouse as shown below and then click OK. In the next popup window click the Fixed radio button (which constrains all three translations and all three rotations) and click OK.

10. Back in the “Entity Selection” window, pick the two interior nodes as shown below and click OK. In the next popup window, constrain translations in y and z and rotations about x, y, and z as shown below. Click OK and then Cancel. Your screen should now look like the third image below. The numbers below the nodes describe which directions are constrained (1, 2, 3 are translations in x, y, and z and 4, 5, and 6 are rotations about the x, y, and z axes).

11. We will now define the type of analysis to complete. From the menus select Model/Analysis. In the popup window click the New button. In the next popup window click the Analysis Type pull down window and select Normal/Modes/Eigenvalue as shown below. Click OK.

12. Back in the “Analysis Set Manager” window click the Analyze button. This will start the solution process. A new “Analysis Monitor” window will open on the left hand side. When the status changes to Complete as shown below, the analysis is finished. If you get an error message. There is something wrong with you model and you need to go back recheck the previous steps. You should close the “Analysis Monitor” window to make more room.

13. Select the “Post Data” icon from the ribbon bars at top of the Femap window. In the popup window use the Output Set pull down menu to select Mode 1 as shown below and click OK.

14. Next click the Select a “Deformed View” icon from the ribbon panel at the top of the

Femap window. Your display should look like the one below. This illustrates the mode shape for the first mode where both interior nodes are moving in the same direction. You may also

click the icon to see an animated display of the mode. To stop the animation just click either or the icons.

15. Thus the first mode shape is shown above. The frequency is listed as 0.159 Hz. In the solution

to Example 12.1, m

k1 . Since we set k and m equal to 1, then we get: 11 . Note this is

in radians/second. The resonant frequency in Hz. is 0.15912

111

f .

16. To view the mode shape of the second mode, you can click the icon and select Mode 2 or you can use the Model Info window as shown below. Click on the + in front of Results and All Results to see all the result sets.

17. Click on the icon. Print out the second mode using the menus File/Print and hand it in. It

does not need to be in color!

Example 9.2 Solved using FEMAP 18. Click the icon so that an undeformed mesh is displayed. We need to make the initial

conditions where u2=0, u3=2, and both velocities are zero. Only the non-zero initial conditions need to be created and Nastran assumes all unspecified values are zero. In FEMAP we apply these initial conditions as loads. From the menus select Model/Load/Nodal. In the first popup window, key in the title “Initial Conditions” and click OK. In the next popup window, select node 3 and click OK and move to the next instruction.

19. In the Create Loads on Nodes window select Displacement and key in 2 in the TX (x

displacement) and remove the check mark from the other displacement boxes. Click OK and then Cancel. Your screen should look like the one shown below.

20. From the menus select Model/Analysis. On the popup window select the New button. In the

next popup window, use the pull down menu on Analysis Type to select “3. Transient Dynamic/Time History.” DO NOT CLICK OK. Click the Next button 6 times for various popup windows. These windows all display options to set for the solution. Go to the next instruction.

21. In the “Dynamic Control Options” window, enter the data shown below. This will use Nastran to directly integrate the equations of motions. Unfortunately, Nastran does not support a Modal Transient solution with initial conditions. With a time step of 0.1 seconds and 150 time steps, the analysis will cover 15.0 seconds. The output interval of 1 requested results every time step. Click the Next button 3 more times.

22. In the “Boundary Conditions” window, make the changes shown below. Note that the Loads

input must be set to None. Click OK.

23. Back in the “Analysis Set Manager” window, click the Analyze button.

24. Analysis Monitor window will open on the left. Wait for the message “Status : Complete” as

shown below. If you get an error message, you should go back and check your model from the beginning. Next close the Analysis Monitor window to make more room on the screen.

25. The best way to display the time history results is to plot the displacement versus time. To do

this, click the Charting icon from the ribbon bar. A

new Charting window opens. Click on the Data Series Manager icon in the charting window as shown below. In the Chart Data Series Manager window, click the “New Data Series…” button.

26. In the Chart Data Series window, first select the tab at the top labeled “Vector vs. Output Set.” Next make the changes shown below. After you click the “Select Multiple” button, select the two interior nodes and click OK and then Cancel. Back in the “Chart Data Series Manager” window, click the Done button.

27. Your display should look like the one below. Compare this with the one on page 254 in your

text.

28. Click on the icons shown below and enter titles for the x and y axes.

29. Click the “Copy Chart Image to Clipboard” icon in the chart window. Now open Word or some other program and paste the figure into it. Print it out (in black and white) and hand it in too.