Loads may be input as base accelerations or applied external loads. The base excitation option in Creo Simulate assumes that the input load will excite any part of the structure that has a constraint or is attached by a spring to ground. The excitation is always defined as a linear acceleration.
PSD curves are usually defined in terms of G^2/Hz. The Creo Simulate analysis engine needs the data in Acceleration^2/Hz. A scale factor may be applied using the direction vector. The scale factor would be the magnitude of gravity in the unit system of your model.
Creo Simulate truncates numbers below 0.000001 when defining an input PSD curve in tabular form. This can sometimes be an issue. The curve may need to be scaled to larger numbers to circumvent this limitation.
Excitation may also be input in terms of an externally applied load.
