Re: Vibration

From: <Farhad>
Date: Sun Apr 08 2007 - 03:39:00 EDT

Dear Friends,

1- The effect of the sway brace is to increase the K value in MX"(t) +CX'(t)+KX(t)=F(t) which raise the natural frequencies of the modes and reduce the response of the pipe to dynamic loads & vibrations. Of course sway brace is not cheap, you may use another pipe support hardware. Snubber will resist dynamic loads whereas sway brace resist dynamic displacements (vibration). Snubber is hydraulic or mechanical device but sway brace is a variable spring device which installed horizontally with spring preload set to zero.

2- You are claiming that CII is not a right tool. So, what's the right tool?

3- I agree with Chris, you should have a good knowledge, understanding of dynamic analysis and of course CII dynamic capabilities. As a CII instructor, I believe that there are a few people who can understand and perform dynamic analysis properly.

4- In earliest response to this issue I mentiond the following steps. Please read it again. This is the same as Chris said.

i- Collect field data (displacements, RPM of pumps, pipe support configuration, etc.)
ii- Model piping system in CAESAR II.
iii- Run static analysis.
iv- perform Harmonic analysis and enter harmonic displacement at pump-pipe node.
v- Tweak some dynamic parameters to model exact problem. vi- Add some stiffness (pipe support) to your piping system, wherever possible.
vii- Run static then dynamic analysis to see changes.

5- Piping system also tends to vibrate if acoustic and mechanical natural frequencies are matched. You may use BOSFluid software from PAULIN to calculate acoustic natural frequencies and compare with mechanical natural frequencies calculated by CII or any other software.

6- No one can say which support type must be used to solve vibration problems. Each case is an individual problem. So you may find many technical articles to recommend many support types or solutions. For example, you can use X,Y or Z ROD to add more K to piping system where the amplitude is high and this solution is very cheap. Received on Sun Apr 08 03:39:00 2007

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