Create and solve a random base excitation

This example shows how to create and solve a random base excitation event in the Response Dynamics solution process from a Simcenter Nastran SOL 103 Response Dynamics solution. The following steps are necessary:

1. Set up and solve the solution.

2. Create a Response Dynamics solution process.

3. Create and solve the random base excitation event.

Set up and solve the solution

Make sure that a Simcenter Nastran SOL 103 Response Dynamics solution is the active solution. The solution must contain a translational enforced motion constraint on a single node, which must have a fixed constraint. You can enforce any combination of DOF1, DOF2, and DOF3 if the CSYS corresponds to BASIC. Otherwise, enforce all three DOFs.

1. In the Simulation Navigator, right-click the active solution node and choose Edit.

2. In the Solution dialog box, on the General page, under Purpose, select Random Base Excitation Event .This check box enables the computation of homogeneous and laminate element failure metrics, and the validation of the solution setup for solving the random base excitation event.

3. Click OK.

4. Solve the Simcenter Nastran SOL 103 Response Dynamics solution.

Create a Response Dynamics solution process

1. Choose Response Dynamics tab→Response Dynamics group→Response Dynamics .

2. In the Solution group, select the solved solution.

3. Click OK.

4. In the Simulation Navigator, select the Normal Modes (#) node.The number in parenthesis represent the number of normal modes in the Response Dynamics solution process.

5. In the Response Dynamics Details View subpanel, select all modes, right-click and choose Edit Damping Factor.

6. Set a viscous damping ratio and click OK.

Create and solve the random base excitation event

1. Choose Response Dynamics tab→Response Dynamics group→Random Base Excitation .

2. (Optional) In the Random Output Requests group, click Edit .On the Acceleration page, otice that peak acceleration contours are requested for all nodes. You can modify the selection and request more output results. For example, to request margin of safety results for homogeneous and laminate elements, do the following:On the Failure Metrics page, select Failure Metrics .Clear Failure Index .In the Safety Factor box, set 2.5 as the safety factor for the margin of safety calculation.The random base excitation solver computes Von Mises stresses for all homogeneous elements and compares them to the associated yield or ultimate strength, which are exported to the Nastran input file when you selected Random Base Excitation Event in the step 2 of Set up and solve the solution.On the Failure Metrics - Laminates page, select Failure Metrics - Laminates .Clear Failure Index and Strength Ratio .In the Safety Factor box, set 2.0 as the safety factor for the margin of safety calculation.The random base excitation solver computes ply margins of safety using the failure theories that are defined in the FEM and exported to the Nastran input file when you selected Random Base Excitation Event in the step 2 of Set up and solve the solution. The stress limits are retrieved from the materials.Click OK.

3. (Optional) In the Analysis Parameters group, in the Confidence Level % box, modify the value.The confidence level of 99.73% is the equivalent of 3-sigma (3 times the standard deviation) level typically used in industry for this type of events. The random base excitation solver computes and displays peak results that correspond to the specified confidence level.

4. Click OK.

5. In the Simulation Navigator, under the Random Base Excitation 1 node, right-click Excitations and choose New Excitation→Translational Nodal.Notice that, in the New Translational Nodal Excitation dialog box:In the Excitation Location group, the node at which you defined the enforced location is pre-selected.In the Excitation Functions group, only the DOFs that were enforced are selectable.

6. Select the active direction check box and use the button to assign a base excitation power spectral density function in that direction.

7. (Optional) In the Scale Factors group, modify the scale factor for the corresponding direction.

8. (Optional) To specify the response dynamics mode frequency range, in the Frequency Range group, clear Inherit from Function and set the upper and lower frequency bounds.You must include the specified response dynamics mode frequency range within the bounds of the PSD function that you selected in step 6.

9. Click OK.

10. In the Simulation Navigator, right-click the Random Base Excitation 1 node and choose Solve→Solve Event.

Learn more

Random Base Excitation

Solving a random base excitation event

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Right-click commands for Random Base Excitation nodes

Random base excitation results

Random base excitation output files

Running a random base excitation event from a command line

Random Base Excitation dialog box

Random Output Requests dialog box

Random Output Requests Manager dialog box

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Create and solve a random base excitation, Simcenter 3D 2021.1 Series

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