## Vibration vs. Wave Propagation Analysis

## Vibration vs. Wave Propagation Analysis

(OP)

The other day I was having lunch with a engineer I know. A subject we talked about began with me expressing frustration with displacement/modal based dynamic analysis (in programs like STAAD) that sometimes didn't predict vibrations (that occurred in real life) at other levels /locations of buildings. He suggested to me a wave propagation model could possibly solve those issues. I personally have never used such a model (I'm not even aware of any software that does). So I thought I'd ask here: has anyone here used such a technique? If so, were you satisfied with the results? Does it indeed "spread out" the vibration "better"?

## RE: Vibration vs. Wave Propagation Analysis

## RE: Vibration vs. Wave Propagation Analysis

Yes (in fact, I was asked to look at it to see what went wrong). It basically was a compressor on bolted down to a steel frame (up on the 4th floor of a building). It caused some noticeable vibrations at other levels that the model failed to predict. Looking at it, I think the main culprit was likely the estimate for the foundation stiffness at the column bases. Modifying that, I got a bit closer to what was observed in the field.

But that comes back to my original question: does a "wave propagation" model transfer these vibrations better? I would assume that it has similar boundary constraint issues (i.e. to a normal displacement/modal based dynamic analysis).......but, in the situation i describe above (i.e. the original model), I would assume (famous last words) that if it is propagating waves, it would have propagated them to the other levels (at least to some degree) regardless of the foundation stiffness assumption.

## RE: Vibration vs. Wave Propagation Analysis

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

## RE: Vibration vs. Wave Propagation Analysis

## RE: Vibration vs. Wave Propagation Analysis

## RE: Vibration vs. Wave Propagation Analysis

Is this directed at me or Greg?

## RE: Vibration vs. Wave Propagation Analysis

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

## RE: Vibration vs. Wave Propagation Analysis

## RE: Vibration vs. Wave Propagation Analysis

you have to look at the accoustic velocity in the individual components to assess whether wave propagation is significant relative to the natural frequencies of your structure. This establishes the cut-off frequency of the accoustic propagation.

many times you can rely on the quasi-static analysis for frequencies below cut-off.