PSD Base Excitation loads are used exclusively in random vibration analyses to provide excitation in terms of spectral value vs. frequency to your choice of the supports that were applied in the prerequisite modal analysis. The Boundary Condition setting in the Details pane includes a drop-down list where you can specify any of the following supports for excitation that are defined in the modal analysis: Fixed Support, Displacement, Remote Displacement, and Body-to-Ground Spring. If multiple fixed supports or multiple remote displacements are defined in the modal analysis, you can apply the excitation load to all fixed supports or all remote displacements or all of both loads using one of the following options:
(including Fixed, Remote Displacement, Displacement, and Grounded Springs)
Note:
Only fixed degrees of freedom of the supports are valid for excitations.
Boundary conditions defined with a local coordinate system are not supported.
You can also specify the excitation direction (X Axis, Y Axis, or Z Axis).
The user-defined PSD data table is created in the Tabular Data window. You can create a new PSD table or import one from a library that you have created, via the fly-out of the Load Data option in the Details pane.
Note: Only positive table values can be input when defining this load.
When creating PSD loads for a Random Vibration analysis in the Mechanical application, Workbench evaluates your entries by performing a "Goodness of Fit" to ensure that your results will be dependable.
Click the fly-out of the Load Data option and choose after entering data points for viewing the graph and updating the table. Interpolated points are displayed if they are available from the goodness of fit approximation. Once load entries are entered, the table provides one of the following color-code indicators per segment:
Green: Values are considered reliable and accurate.
Yellow: This is a warning indicator. Results produced are not considered to be reliable and accurate.
Red: Results produced are not considered trustworthy. If you choose to solve the analysis, the Mechanical APDL application executes the action, however the results are almost certainly incorrect. Ansys recommends that you modify your input PSD loads prior to the solution process.
Four types of base excitation are supported:
PSD Acceleration
PSD G Acceleration
PSD Velocity
PSD Displacement
The direction of the PSD base excitation is defined in the nodal coordinate of the excitation points.
Multiple PSD excitations (uncorrelated) can be applied. Typical usage is to apply three different PSDs in the X, Y, and Z directions. Correlation between PSD excitations is not supported.