Re: dynamic stress analysis .

Dear Friend,
I have a little information abt these problem.

Modal analysis needed since we have to know the dynamics char. of the system (natural freq., mode shapes, and damping ratio).

Natural freq. information can indicate the tendency of a piping system to respond to dynamics load. A system's modal natural freq. should not be too close to equipment operating frequencies and, as general rules, higher natural freq. usually cause less trouble than low natural freq.

With the modal freq. response we can know how much overall stress (dynamics + sustained/statics loads) that happen in one condition (that is the percentage of the difference is depend on the condition or the harmonic excitation happen in the system).

The time history analysis usually used at the transient load, such as relief valve load, water hammer, etc. These loads actually preserve as impact force that is much much bigger than statics and/or stationary condition. Impact force is a force that contain many frequencies, so theres a high probability that some of the frequencies are close enough or even coincident with the major natural freq.

Regards,

Firman Tuakia
Mechanical Engineering Dept., ITB

On Tue, 28 Dec 2004, gautam wayse wrote:

>
>
> dear friend
> if some one working on dynamic analysis and having
> expertise in same .please solve my fallowing problems
> .
> why it is essential to perform modal frequency
> response and time histry analysis .
> how much differece (in per cent )one can expect in
> calculated stress
> value at static condition and dynamic cases.
>
> gautam wayse
>
>
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Received on Wed Dec 29 01:23:00 2004