Mechanical APDL Basic Analysis Guide - Ansys

Chapter 8:The Time-History Postprocessor (POST26)
1. Select “Find the covariance of quantities” from the Spectrum Usage dialog box and click OK.
Note
If you have performed RPSD calculations, click the Clear Time-History Data button to load
the Spectrum Usage dialog box.
2. Using the Variable Viewer, define the variables between which covariance is to be calculated.
3. Specify a variable in the variable name input area of the variable viewer. The name must be unique
or you will be asked to overwrite the existing variable.
4. Click the CVAR button in the calculator area of the variable viewer. The following dialog box appears.
5. Select the variables to operate on from one or both of the pull down lists (corresponds to the IA,IB
argument for the CVAR command).
6. Select the type of response to be calculated (corresponds to the ITYPE argument for the CVAR
command).
7. Choose whether to calculate the covariance with respect to the absolute value or relative to the base
(corresponds to the DATUM argument for the CVAR command).
8. Click OK to save your preferences and close the dialog box. The function cvar(IA,IB,ITYPE,DATUM) will
be displayed in the expression area of the calculator.
9. Click Enter in the calculator portion of the variable viewer to start the evaluation.
When the evaluation is finished, the covariance value is stored; the variable name is displayed in the variable
list area for further postprocessing.
8.8.1.1.2. Response PSD
Follow these steps to calculate the Response PSD using the variable viewer.
1. Select “Create response power spectral density (PSD)” from the Spectrum Usage dialog box and click
OK.
2. Using the Variable Viewer, define the variables for which the Response PSD is to be calculated.
3. Specify a variable in the variable name input area of the variable viewer. The name must be unique
or you will be asked to overwrite the existing variable.
4. Click the RPSD button in the calculator area of the variable viewer. The following dialog box appears.
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