Example of Using Adams Linear to Verify Flexible Bodies
Overview
The following example uses a model of a slender, 2-meter long beam that was modeled in an FEA product with attachment points at the two ends and exported to Adams View. A separate finite element analysis for this beam, with one end fixed and the other end pinned, yielded the following natural frequencies for the first 3 bending modes in the XY plane:
1. 0.938486 Hz
2. 3.028538 Hz
3. 6.278326 Hz
Figure 8 shows a simplified view of the beam.
Figure 8 Beam with Fixed-Pinned Boundary Conditions
In this example, you’ll import the beam into Adams View. You’ll then fix the beam at one end and pin it to the other and verify the flexible body to ensure that its results in Adams Linear match the three bending modes listed above.
The sections of the tutorial are:
Starting Adams View and Importing the MNF
You’ll start the tutorial by running Adams View and creating a new model. You’ll then integrate the MNF file into the new model.
To start Adams View and create a database for the flexible body:
1. Copy the file full_beam.mnf to your local directory. This file is located in install_dir/flex/examples/mnf, where install_dir is the directory where the Adams software is installed.
2. Start Adams View and create a new model that has no gravity. Use the default units.
3. Import full_beam.mnf into your model using a damping ratio of 0.
Familiarizing Yourself with the Beam
In this section, you’ll look at each of the modes in the beam to familiarize yourself with the modal content of the flexible beam.
To familiarize yourself with the beam modes:
1. Double-click the flexible body in Adams View to display the Flexible Body Modify dialog box.
2. From the Flexible Body Modify dialog box, select the Next Mode tool 
to view the next mode.
to view the next mode. 3. Continue selecting the Next Mode tool 
until you’ve viewed most of the modes.
until you’ve viewed most of the modes. 4. Close the Flexible Body Modify dialog box by selecting Cancel.
Fixing the Beam
Now you’ll fix one end of the beam to ground using a fixed joint and pin the beam on the other end using a revolute joint.
To fix the ends of the beam:
1. Click the Connectors tab. Select Joints container and select the Fixed Joint tool.
2. In the settings container of the Main toolbox, select the construction method 1 Location.
3. Place the cursor at the left end of the beam near the origin. Node numbers flash on the screen as you move the cursor. Select node 1000 for the location of the fixed joint by clicking the left mouse button when the cursor is over node 1000.
4. Click the Connectors tab. Select Joints container and select the Revolute tool 
5. In the settings container of the Main toolbox, select the construction method 1 Location.
6. Place the cursor at the right end of the beam. Select node 1001 for the location of the revolute joint by clicking the left mouse button when the cursor is over node 1001.
Running a Simulation
After fixing the beam, you can run a static simulation of the beam to establish an operating point for the linearization.
To run a simulation:
1. Click the Simulation tab. From the Simulate container, select Simulate tool 
.
. 2. Click the Simulation Settings from the bottom of the Simulation Control dbox. Check the More box.
3. The Solver Settings dialog box appears.
In the Simulation Control dialog box, select the Static Equilibrium tool
to perform a single static simulation at time zero. An alert box appears informing you that the equilibrium operation was successful.
to perform a single static simulation at time zero. An alert box appears informing you that the equilibrium operation was successful. Running Adams Linear
Now that you’ve found the static equilibrium of the beam, you can use Adams Linear to view the linear mode frequencies that Adams Linear has computed.
To run Adams Linear:
1. Click the Simulation tab. From the Simulate container, select Simulate tool .
. 2. Select the Linear tool.
A message appears, informing you that the linear modes are done and asking you if you want to review the results now.
3. Click Animate.
The Linear Modes Controls dialog box appears.
4. Using the Linear Modes Controls tool, display mode 1.
5. In the Max Translation text box, enter a value to scale the mode.
Note that Adams Linear has accurately computed a natural frequency of 0.9385. Note also that the corresponding mode shape is unlike any of the component mode shapes for this flexible body. Adams Linear has synthesized this system mode using a combination of component modes.
6. Verify that the other modes in the XY plane, modes 3 and 5, have acceptable results.
7. Close the Linear Modes Controls dialog box and display the Flexible Body Modify dialog box.
8. Modify the flexible body by disabling mode 9.
9. Recompute the static equilibrium and the linear solution and note how the system mode solution deteriorated when this important mode shape was disabled.
If either the attachment points or units were incorrectly specified when generating the MNF, your Adams Flex body would fail this simple validation test. For more on specifying attachment points and units, see FE Model Requirements in the Adams Flex online help (under the Translate tab).