Intermediate nodes between supports while checking the frequ

Hi all,

Recently I was reviewing a calculation carried out by my engineer on a two phase line (Steam blow down line). This was a three inch header on rack. Modal check was done to check the natural frequency of the line. Line was modelled with the supports at every 6m as available on pipe rack. We have to add guides at every support to have a frequency above the project requirement of 8Hz.
While checking I created addinational nodes at every 3M to check frequncy in between the supports assuming that CAESAR will not check the frequency for these points. And I found that the frequncy at these intermediate nodes was less than 3 Hz. Now I have a doubt if it is ok to check the freqency just at 6m span supports or we should creat intermediate nodes. I am using Lumped mass model option.
Can anybody comment on this?

Mr.558,

When ever you perform the dynamic analysis, it is good to split the node point as much as possible to get an accurate result. In you case, it is better, you even split the 6m span in to three nodes as each 2m span.

Also, can you please clarify, what is the stiffnes for friction factor used in the control parameters of Modal Dynamic Analysis?

If you use the lumped mass approach and have only nodes at support points, Caesar will lump the mass at the nodes only and thus the support points. There will then be zero dynamic (modal) response.

There are recommendations is the Caesar II documentation on node spacing for dynamics.

Thanks Sillyman & MoverZ,

I have tried friction stiffness of 500-1000 as recommended by CAESAR.
I am also of the opinion that more nodes shall be created for accurate result but not able to find this in CAESAR documentation.
Can you tell me the perticular Chapter no or any reference where I can find guidelines for this? I searched the complete documentation (technical discussion, User application etc.) in perticular the Dynamic analysis section. But could not find this information.

Try searching 'node spacing' in this forum. There are over 400 results.