Selecting Eigenmodes for Mode-Based Procedures

You can select a subset of eigenmodes computed from the preceding frequency step to use for a mode-based procedure, which can reduce the computational expense of your simulation. Selecting a subset of eigenmodes might affect the accuracy of your simulation.

The methods available for selecting the eigenmodes depend on the type of mode-based procedure. All of the mode-based procedures except substructure generation support selecting all eigenmodes, and all support selecting eigenmodes by specifying frequency ranges. These are the preferred methods for eigenmode selection.

This task shows you how to:

Before you begin: Define at least one mode-based procedure.
See Also
Defining Complex Frequency Steps
Defining Harmonic Response Steps
Defining Modal Dynamic Steps
Defining Random Vibration Steps

Select All Eigenmodes

  1. From the Procedures section of the action bar, click Complex Frequency Step , Harmonic Response Step , Modal Dynamic Step , or Random Vibration Step .
  2. Expand the Eigenmodes section, and select All modes from the Retained eigenmodes options.

The step you created uses all eigenmodes computed in the preceding frequency step, including residual modes if activated.

Select Eigenmodes by Specifying Frequency Ranges

  1. From the Procedures section of the action bar, click Complex Frequency Step , Harmonic Response Step , Modal Dynamic Step , Random Vibration Step , or Substructure Generation Step .
  2. Expand the Eigenmodes section, and select Frequency range from the Retained eigenmodes options.
  3. In the table, enter values for Low Frequency and High Frequency, which are the lower and upper boundaries of the frequency range (in cycles/time).

    You can define mulitple frequency ranges in the table.

The step you created uses only the eigenmodes from the frequency ranges you specified, including boundaries.

Select Eigenmodes by Specifying Mode Ranges

  1. From the Procedures section of the action bar, click Random Vibration Step or Substructure Generation Step .
  2. Expand the Eigenmodes section, and select Mode range from the Retained eigenmodes options.
  3. In the table, enter values for the following:
    OptionDescription
    First Mode Mode number of the lowest mode in a range of modes.
    Last Mode Mode number of the highest mode in a range of modes.
    Increment Number by which to increment from the First Mode to the Last Mode, including boundaries. For example, if you set the first mode equal to 10, the last mode equal to 40, and increment by 5, you select modes 10, 15, 20, 25, 30, 35, and 40.

    You can define multiple mode ranges in the table.

The step you created uses only the eigenmodes from the ranges you specified, including boundaries.

Select Eigenmodes by Specifying Mode Numbers

  1. From the Procedures section of the action bar, click Random Vibration Step or Substructure Generation Step .
  2. Expand the Eigenmodes section, and select Mode list from the Retained eigenmodes options.
  3. List the specific Modes to include in the random vibration step.

    Enter only integers, commas, or hyphens. For example, 1, 3-5, 10-20.

The step you created uses only the eigenmodes from the list of numbers you specified, including boundaries.