Cirteria for Random Vibration

Hi
In a structure bearing random vibration, how can one say that it has
acceptable design or no?
What is the acceptance criteria? Stress PSD? Displ. PSD? or it is a
reliability problem?
Thanks.
Navazi
Reply to
H.M.NAVAZI
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I would recommend "Vibration Analysis for Electronic Equipment" by Steinberg. I don't work with EE stuff, but it's the best text I've found for random vibe analysis.
This is essentially what SteSince the input is random, one can assume that the resulting stresses are normally distributed. Therefore, the stress you get from your model is considered the "1-sigma" stress level. This stress would occur 68.3% of the time (assuming a normal dist). The 2-sigma stresses are 2 times your 1-sigma stress, and occur 27.1% of the time. And finally, the 3-sigma stress is obviously 3 times the 1-sigma stress, and occurs 4.3% of the time. As a first pass, you can assume that the 3-sigma stresses occur 100% of the time. If you pass with positive margins (using Goodman, for instance), then you're good. If you don't pass, then you can break your cycles down into the 1-, 2-, and 3-sigma components and sum up your damage using Miner's Rule.
Hope this helps
Reply to
Dan L.

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