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#39754 - 12/26/10 03:45 AM Natural Frequency_ harmonic Analysis
prakash_26jan Offline
Member

Registered: 05/09/09
Posts: 19
Loc: oman
can some body tell me

"why higher natural frequencies usually cause less trouble than low natural frequency"?

Regards
prakash kumar

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#39763 - 12/27/10 03:07 AM Re: Natural Frequency_ harmonic Analysis [Re: prakash_26jan]
Rajinder Singh Offline
Member

Registered: 07/25/06
Posts: 55
Loc: New Delhi
Make use of the search option on top right corner of the forum page.
Read posts on Natural Frequency, especially written by Anindya ji.
_________________________
Rajinder

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#39765 - 12/27/10 05:57 AM Re: Natural Frequency_ harmonic Analysis [Re: Rajinder Singh]
Rajinder Singh Offline
Member

Registered: 07/25/06
Posts: 55
Loc: New Delhi
Let me put in this way: NF=sqrt(k/m)radian/sec, where k=stiffness and m=mass. This equation relates NF with stiffness and mass. A piping system that is not adequately supported will have less stiffness and hence low NF. However, a well supported system has higher stiffness and thus higher NF.
A loosely supported piping system usually has NF less than 1Hz. 5-6Hz is NF for fairly stiff system. There is no written document/literature confirming (as far as I know) that system with 5Hz or 6Hz NF is well supported. This is a general practice to have NF more than 5-6Hz. Adding supports will increase NF of system (in other words response of system) and will prevent it from resonance. On the contrary, low NF will increase the system response and is more prone to resonance.
Also, pipe NF should never match equipment NF. If for example equipment NF is 5Hz then shifting NF of piping well above 5Hz will prevent the resonance completely. Care should be taken to calculate or know the NF of the equipment and modeling of piping system in CAESAR.

At the end (sorry for reiterating) make use of the search option on top right corner of the forum page. Read posts on Natural Frequency, especially written by Anindya ji.
_________________________
Rajinder

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#39774 - 12/28/10 06:17 AM Re: Natural Frequency_ harmonic Analysis [Re: Rajinder Singh]
Rajinder Singh Offline
Member

Registered: 07/25/06
Posts: 55
Loc: New Delhi
A small correction......
Adding supports will increase NF of system (in other words decrease system response) and will prevent it from resonance.
_________________________
Rajinder

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