Random Vibration - Advanced

The Advanced dialog box sets the advanced options for the random vibration study.

Method

Sets the method of integration.

Standard

It takes more time but generates more accurate results (recommended).

Approximate

Gauss integration order Gauss integration order to be used in integration of response power spectral densities. The options are two-point and three-point Gaussian integration.
Biasing parameter Sets the value of biasing parameter, which controls the selection of frequency points for integration. The power spectral density (psd) of the response is evaluated at these frequency points.
See topics Methods of Integration and Selection of Frequency Points for more information.
Cross-mode cut-off ratio

Sets the cut-off ratio of any two natural frequencies above which the cross-mode effects are neglected.

For example, if you set this ratio to 5, cross correlation effects are neglected between modes i and j (i>j), if wj / wi is larger than 5.

Include extra frequencies for response

Select this option to include extra frequencies of interest for the calculation of the response parameters to random vibration loads.

In addition to the natural frequencies, which are included in the random vibration analysis by default, you can select up to 20 extra frequency points of interest. Enter the extra frequency points in ascending order (positive values).

The number of solution frequency points at which the solver calculates the response (that is, the clustered frequency solution points between two consecutive frequencies) is identical to the number of frequency points used for the natural frequencies (see No. of points for each frequency).

Edit Select this option to enter up to 20 frequencies in ascending order (positive values).
Tolerance to merge extra frequency points
Sets a tolerance limit (%) that defines how close an extra frequency point is to a natural frequency or to its consecutive extra frequency point so that the solver can merge the two consecutive frequencies into one frequency. The default tolerance limit is 1%.
The solver does not apply the tolerance criterion to natural frequency points (that is, natural frequencies are not merged).


represents natural frequencies calculated by the solver (all natural frequencies are included in the calculation of RMS output).

represents user-defined extra frequency points to include in the calculation of RMS output.

represents tolerance (%).

For example, the solver merges an extra frequency point to its closest natural frequency, based on the following criteria: