Generating random envelope 1

[FSB1]

See attachment picture

I want to place orange structure in the blue structure.

1) The orange structure was analyzed, isolated, with a specific random input. Accelerations on the structure were extracted.
2) The blue was analyzed, together with the orange, and with a similar random input of the orange alone. Then the acceleration at the orange location was extracted.

Now I want to re-analyze the orange structure with the a PSD function that envelopes the accelerations in 2)
The problem is that the accelerations in the orange structure in 2) more than 10x higher than the input in 1) and 2).

Meaning I will have to analyze and test the orange structure with 10x max acceleration than it was initially designed. Is this overconservative?

 

[rb1957]

Not sure I get the question. Are you saying that the accelerations experienced (by the orange structure when mounted in the blue) are 1/10th of the orange structure spec limits ? Do you know the PSD applied to the blue structure ?

should've looked at the pic, and thought a little more. So the accelerations of orange structure are higher than the input when it is supported by the blue structure.

So you drive the blue+orange structure with higher loads than orange alone (since it has more mass) ?

It sounds to me like the blue structure doesn't adequately support the orange, and has set up some sort of harmonic resonance.

another day in paradise, or is paradise one day closer ?

 

[IRstuff]

Meaning I will have to analyze and test the orange structure with 10x max acceleration than it was initially designed. Is this overconservative?

Yes, probably overconservative. The bigger question is how you can get 10x the acceleration from a passive structure? That would seem to violate conservation of energy. Are you referring to peak, or rms, acceleration? It's possible you have a resonance, in the range of interest, which is bad, in of itself, or you have some sort of error in your simulation.

TTFN (ta ta for now)
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[MacGyverS2000]

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