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Apr 25, 2006
12:22 PM

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Apr 25, 2006
12:22 PM

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

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

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

1 REPLY 1

Apr 26, 2006
12:55 PM

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Apr 26, 2006
12:55 PM

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

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