Hello,
I want to use CAESAR II dynamic module to determine natural frequency of the piping system connected to reciprocating compressor. Material available by Intergraph/CAESAR II is detailed in how to use the module I still have a few questions on it though.
1. How far to model?
The vibrating line starts at compressor and branches off at various equipment all over the plant. The section that is vibrating is in immediate vicinity of the compressor, about first 10-15 feet. How much of modeling of piping is necessary for acceptable accuracy of natural frequency calculation? IMO, modeling up to 100-150 feet and up to two hard points/equipment would be sufficient. Is it?
2. Is modeling of small bore/tubing is necessary to include?
There is a lot of it! I know these lines will be more flexible (more vibration prone) than the main line but would this affect the frequency of the main line in a meaningful way?
3. This might be a question for Dave or Rich. What is "far removed degrees of freedom"
One of the material mentions following:"If mode shape do not show movement in the are of local vibration then not enough degrees of freedom were removed from other areas" What does that mean? Is it giving a clue on how far to take modeling effort?

I really appreciate your input in this.

Thanks very much and happy holidays!

Hello,
May be I asked a too difficult of a question?

I should mention that I'm not looking for concrete answers, just thoughts of experiences users.

I have never used the modal analysis module before and our client has asked us to provide preliminary screening/analysis. The client isn't sure of the scope either and I would like not to compromise accuracy of the software because of inexperience.

I hope to receive some direction to resource/material that I can study during holidays.

Thanks very much for your time and consideration.

Of course an anchor is your best termination.
The inter-connectivity of mass and stiffness makes stopping a model elsewhere a little more complicated.
The easiest approach for me would be to run the model to where you stop it now (e.g., a well restrained section) and again with more piping attached. If the results for the portion of interest do not change much, you probably have an adequate break point.

Thank you Dave.