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Random vibration (PSD)

Random vibration (PSD)

Random vibration (PSD)

(OP)
Hi all,

I am struggling with the concept of applying different PSD curves in multiple directions (x, y and z) to the supports of a structure. Assuming that there is no correlation between the different PSD curves, how is determined the response of the structure in one particular direction?

To test this concept, I built a simple model with a mass and three springs (with equal stiffness) placed along the axes of the coordinate system. Each spring was then excited with a PSD curve (white noise) in the direction of its axis.

Surprisingly, the response of the mass in the each direction (x, y and z) is not the same...
Furthermore, it seems that it also depends on the order at which the PSD curves are applied to the model.

The input file is attached.

Does someone have an idea of what is happening?

Thanks and best regards.   

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