Modal analysis with Caesar II

[T5580]

Hello Everyone,
Has anyone done the Modal analysis with Caesar II? I have a steam piping system experiencing of vibration problem and attemp to run modal analysis with Caesar II, but don't know where to start. I appreciate if someone can help how to set up the control parameter and determine if the system need additional restraint to control the vibration.
Regards

 

[xhpipe]

Some points to consider can be found at ....

http://www.coade.com/newsletters/jul03.pdf

http://www.coade.com/newsletters/feb02.pdf

And then read thru the online help available in the program itself.

An important consideration is the krate of the supports, and the steel members the restraints are attached to. People usually ignore this but that will lead to answers that are grossly in error.

Regards,
XHPIPE

 

[DSB123]

T5580,
Remember to "model2 the rotary inertias of any of the in-line equipment. If it's a steam line then presumably there are parallel slide valves which have different rotational inertias when closed or open. (worst being when the valve is open). Some of the software about ignores rotational effects.

 

[T5580]

xhpipe,
Thank you for the info. I have read it, but still don't have a clue. Could you post more detail how to run and evaluate the piping system with Ceasar II if you have done it.
Thanks in advance.

 

[SPLIT]

I propose to measure the piping vibration as a first step. that is amplitude in function of frecuency, and use it as a forced frecuency.After that to perform an harmonic analysis and a modal as well.Then you can obtain the acelerations of the pipe for the actual conditions.
Try to add some supports in the points of max. aceleration and check the stresses and acelerations.Repeat the operation until you have reduced the acelerations and comply with the Code allowable stresses.

Regards,

SPLIT

 

[VBHMBG]

TS 5580,

The Caesar II manual is containing the explanations of the several settings to be made. Also, hitting the F1 buttton while the cursor placed in the relevant fields will pop up some help text.

But before this step a basic understanding is required to interprete the computed eigen frequencies and eigen shapes.

Also the piping model needs sufficient nodes between restraints, elbows etc. to compute all eigen values up to the cutoff frequency. On the Coade website a little tool is available to calculate the maximum node distances (

http://www.coade.com/dwnld/CAESARII/MASSSPACE.ZIP).

All the best,
VBHMBG

http://www.pipestressanalysis.com