Mechanical APDL Basic Analysis Guide

8.8.1. Random Vibration (PSD) Results Postprocessing

8.8.2. Generating a Response Spectrum

8.8.3. Data Smoothing

8.8.1. Random Vibration (PSD) Results Postprocessing

Covariance and response PSD are of interest when postprocessing random vibration analysis results.
The calculations use Jobname.rst and Jobname.psd files from a random vibration analysis.

8.8.1.1. Interactive

To choose whether to compute the covariance or the response PSD when reviewing the results of a
random vibration analysis, follow these steps:

1. Launch the variable viewer by selecting Main Menu> TimeHist Postpro. If the variable viewer is
   already open, click the Clear Time-History Data button, located in the toolbar. The Spectrum Usage
   dialog box appears. (See Figure 8.3: Spectrum Usage Dialog Box (p. 216).)


2. Select “Find the covariance of quantities” or “Create response power spectral density (PSD).”

Note

You can improve the “smoothness” of the response PSD curves by specifying the

number of points on either side of a natural frequency point (STORE,PSD) with the

slider, shown in Figure 8.3: Spectrum Usage Dialog Box (p. 216).

3. Click OK.

Figure 8.3: Spectrum Usage Dialog Box

8.8.1.1.1. Covariance

Follow these steps to calculate covariance using the variable viewer:

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.

Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information

The Time-History Postprocessor (POST26)