## What can we get from modal analysis beside natural frequencies and corresponding shapes ?

## What can we get from modal analysis beside natural frequencies and corresponding shapes ?

(OP)

My question is : Can we get a hint about overall structural behaviour of a system from modal analysis ? Such as: even under a static case the system will try to deform like its mode shapes. Is this statement true ? I am trying to understand what can I get from modal analysis so I can use these informations in the early design phase of a system. (Where to add more parts/structural elements etc.)

## RE: What can we get from modal analysis beside natural frequencies and corresponding shapes ?

## RE: What can we get from modal analysis beside natural frequencies and corresponding shapes ?

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

## RE: What can we get from modal analysis beside natural frequencies and corresponding shapes ?

- determine the lowest natural frequency

- calculate the corresponding time period (t) from that frequency

- estimate the deflection in the direction of impact (d)

- calculate impact velocity: v=d/t

- make sure that v is less than 1% of the wave speed of particular material

## RE: What can we get from modal analysis beside natural frequencies and corresponding shapes ?

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## RE: What can we get from modal analysis beside natural frequencies and corresponding shapes ?

Not generally true, no. The response at 0 Hz is governed by the low frequency residuals of the modes, is the closest I'd get to that. Often the lowest frequency mode dominates, but that is very dependent on the point of application of the load and its direction.

Once you have a correlated set of modes then you can be fairly sure your model isn't fundamentally wrong, and you can go ahead and use it for other linear range simulations.

Cheers

Greg Locock

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## RE: What can we get from modal analysis beside natural frequencies and corresponding shapes ?

## RE: What can we get from modal analysis beside natural frequencies and corresponding shapes ?

"even under a static case the system will try to deform like its mode shapes. Is this statement true ? "

Still no, but if you just hit a system, much of the response will usually be at the first mode shape.

Cheers

Greg Locock

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