Adams Advanced Package > Adams Flex > Setting Up Flexible Bodies for Testing > Testing Setup

Testing Setup

Once you've built your flexible body into Adams View, you can set it up for testing or simulation. For example, you can change its modal content to improve the efficiency of the simulation.

Accessing the Flexible Body Modify Dialog Box

To modify a flexible body for simulation, you use the Flexible Body Modify dialog box. Follow the instructions below to learn how to display the Flexible Body Modify dialog box.

To display the modify dialog box for a flexible body on the screen:

1. Right-click the flexible body whose properties you want to modify. You may want to zoom in on the flexible body on the screen to more easily place the cursor over just that body. Learn about View Options.

2. From the shortcut menu that appears, point to the flexible body that you want to modify, and then select Modify.

The Flexible Body Modify dialog box appears.

Tip:	Double-click the flexible body to display the modify dialog box.

To use the Database Navigator to display the Flexible Body Modify dialog box:

1. Double-click the background of the Adams View main window to clear any selections.

2. From the Edit menu, select Modify.

The Database Navigator appears.

3. Select the current model and the flexible body whose properties you want to modify.

4. Select OK.

The Flexible Body Modify dialog box appears.

Changing Flexible Body and Modal Initial Conditions

You can set the initial velocity and position for a flexible body before the Simulation starts just as you can for any part in Adams View. You can set how you want Adams View to calculate these properties as well as define these properties yourself. You can also set modal initial conditions.

To set the flexible body initial velocity and position:

1. In the Flexible Body Modify dialog box, select either of the following:

■Position ICs

■Velocity ICs

2. Set the velocity and position values in the dialog boxes that appear. Learn about:

■Position ICs with Modify Body - Position Initial Conditions dialog box help.

■Velocity ICs with Modify Body - Velocity Initial Conditions dialog box help.

To set the modal initial velocity and displacement:

1. In the Flexible Body Modify dialog box, select Modal ICs:

The Modify Modal ICs dialog box appears.

2. Highlight the mode whose initial velocity or displacement you want to set.

3. Enter the velocity or displacement in the text box:

■Enter the velocity in the text box above the button Apply Velocity IC.

■Enter the displacement in the text box above the button Apply Displacement IC.

4. Select either Apply Velocity IC or Apply Displacement IC.

5. To make Adams Flex enforce the displacement initial conditions exactly, select Set Exact.

6. Select OK.

Modifying the Modal Formulation

Adams Flex computes the time varying mass matrix of the flexible body using nine inertia invariants. (For details, see Theory of Flexible Bodies.) Four combinations of invariants have special significance and they are provided with Adams Flex. If, the modal basis in the MNF is an orthogonal set including six rigid body modes, theoretically, invariant 3 and 4 are zero in this situation even though you may see some small nonzero entries due to numerical errors. Invariants 3 and 4 are disabled in all the four combinations by default. If the rigid body modes are less than six, invariants 3 and 4 are no longer zero values and you must enable them. You can choose to customize the invariant formulation based on your requirements. The available formulations are:

■Rigid body - In this formulation, Adams Flex disables invariant 6, the modal mass, and the flexible body is considered rigid. Adams View ignores all modes, even those you enable, during the simulation. The results of the flexible body simulation closely resemble those for an Adams rigid part although formulation differences can cause subtle result variations.

■Constant - In this formulation, Adams Flex disables invariants 3, 4, 5, 8 and 9. The flexible body's inertial properties are unaffected by deformation (that is, deformation and rigid body motion are uncoupled).

The Constant option may only have academic value because computational savings will be modest while potentially having a dramatic effect on results. When you select Constant, Adams View does not account for changes in the moment of inertia due to deformation.

■Partial coupling - In this formulation, which is the default, Adams Flex disables invariants 3, 4, 5 and 9. Invariants 5 and 9 provide a second-order correction to the flexible body inertia tensor. These invariants impose the greatest computational overhead on the evaluation of the flexible body equations of motion. Disabling these invariants can reduce CPU time significantly while having minor impact on results in most cases.

■Full coupling - In this formulation, Adams Flex enables all of the invariants except for invariants 3 and 4. Use this method to achieve full accuracy.

■Custom coupling - In this formulation, Adams Flex can enable or disable invariants 3, 4, 5, 6, 8 and 9. Use this method to enable invariants 3 and 4 when needed.

When Adams Flex creates a flexible body, it uses the Partial Coupling formulation by default because Partial Coupling has significant computational efficiency over the more accurate Full Coupling formulation. You should verify, however, that your model does not require Full Coupling.

You should always be careful when using the Constant formulation even when you expect deformations to be small. Use it only after careful experimentation.

The Rigid Body formulation removes all flexibility effects, and you should only use it as a debugging tool.

To set a modal formulation:

1. In the Inertia modeling area of the Flexible Body Modify dialog box, select a formulation option or select Custom.

When you select Custom, Adams Flex displays a Custom Inertial Modeling dialog box that lets you set up the invariants that you want selected.

2. Use the dialog box to select the inertia invariants, and then select OK.

You can also use this dialog box to view the effects of the different options. For example, select Partial Coupling to view the invariants that option disables and enables.

Controlling Errors During Simulations

You can customize the error control for flexible body numerical results using the Solver Settings - Dynamics dialog box. This is the same dialog box you use in Adams View to control the amount of error control during a Dynamic simulation. You use the Scale text box to control the flexible body numerical results.

The Scale text box takes three values: r1, r2, and r3. These values are used to rescale the sum of the relative and absolute error tolerances. If T is the sum of the relative and absolute error tolerances applied to the state vector, then:

■A tolerance of r1 x T is applied to the translational coordinates.

■A tolerance of r2 x T is applied to the rotational coordinates.

■A tolerance of r3 x T is applied to the modal coordinates.

The scaling applies to only the WSTIFF, DSTIFF, and ABAM integrators. It does not apply to GSTIFF and Constant BDF. See Comparison of Integrators.

The default value of r3 is 1E-3, but if the flexible body deformations are so subtle that the modal coordinates are of the order 1E-7, then the integrator will probably have insufficient accuracy. In this case, you should decrease the scale factor, for example, to 1E-7.

To set the error control:

1. On the Settings menu, point to Solver, and then select Dynamics.

The Solver Settings - Dynamics dialog box appears.

2. If necessary, at the bottom of the dialog box, select More.

3. In the Scale text box, enter the three values representing the error control.