Defining a PSD definition

Use the PSD definition method to define the frequency dependence of the random loading in a random response analysis step. For more information, see Defining the frequency functions.

  1. Display the Edit Amplitude dialog box as described in Selecting an amplitude type to define.

  2. Click the arrow to the right of the Specification units field, and specify the units in which you want to define the curve.

    • Select Power to define the frequency function directly in power units.

    • Select Decibel to define the frequency function in decibel units.

    • Select Gravity (base motion) if the frequency function will be used to define a base motion in g-units. If you choose these units, you must define the acceleration of gravity.

  3. If you selected Decibel units, enter a value for the Reference power.

  4. If you selected Gravity units, enter a value for the Reference gravity.

  5. In the data table, enter or import the data values for the function:

    • Real and Imaginary parts of the function, in decibels or in units2 per frequency.

    • Frequency, in cycles/time, or frequency band number (for Decibel units).

    For detailed information on how to enter data, see Entering tabular data

  6. Toggle on Specify data in an external user subroutine if you will provide the PSD function in user subroutine UPSD.

  7. Click OK to save your amplitude definition and to close the Edit Amplitude dialog box.