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Interpreting results in dynamic random analysis...?

Interpreting results in dynamic random analysis...?

Interpreting results in dynamic random analysis...?

(OP)
Fellow engineers,

I'm sort of a novice in vibration analysis and I now have a request to do a "Dynamic random analysis". The load case conforms to a standardized test, so the loading is well defined with specified PSD-spectra in the x-, y- and z- directions. I have no problem setting up and running the modal analysis. Also setting up and running the dynamic random analysis works fine.

But how do I interpret the results? I understand that the results, for example stress, are the RMS-values of the stress with the given load spectrum. I have found a document stating that, given that the loading is normal distributed, this result "is equal to one standard deviation".

One st. dev from what? The mean? Is the mean assumed to be zero?

I would be grateful for any feedback,

Question no2 : The model is constrained with rigid constraints. The stiffness/flexibility of the supporting structure should reduce eigenfrequencies somewhat. If the stiffness of the surrounding structure is unknown (not yet designed), is there any standard procedure as for how to estimate the stiffness of the attachement points?

/Mats

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