Workbench has implemented the most common forms of PSD input. Acceleration, Velocity and Displacement are common because vibration is usually measured using an accelerometer. How did you end up with a Force PSD?
To use a Force PSD in Workbench, you have to use a Command object.
Look up the command PSDUNIT.
Use Type = FORC
https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v231/en/ans_cmd/Hlp_C_PSDUNIT.html
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