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jrich10-Marble
10-Marble
Apr 25, 2006 4:22 PM UTC
Question

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

    1 reply

    RodGiles1-Visitor
    1-Visitor
    Apr 26, 2006 4:55 PM UTC
    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


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