Dynamic Random: How to convert g^2/Hz to acceleration^2/Hz

[jrich]

PTC tech support says "Dynamic Random" analyses require PSD input to be in the units of acceleration^2/Hz, rather than g^2/Hz.

Does anyone know how to convert the universal, industry-wide g^2/Hz PSD input values to the PTC-freaky acceleration^2/Hz values?

For example, at 450 Hz, the PSD value is .107 g^2/Hz. What value is this number in acceleration^2/Hz?

Thanks

[RodGiles]

Mechanica like all FE systems uses a consistent units system, with no embedded conversion factors, so if you are working in metres, the PSD input will be in (m/s^2)^2/Hz, in inches it would be (in/s^2)^2/Hz.

So to convert a PSD in g^2/Hz, multiply by the value of g squared in the units system that you are working in, e.g.

metres - 9.81^2 = 96.236
inches - 386.4^2 = 149,305

I normally do this by constructing the PSD in g^2/Hz in the function definition, then putting the factor in the base excitation component and letting Mechanica do the maths.

Regards

Rod Giles
Elite Consulting Ltd.
The Mechanica Experts