This particular model was run first and very low frequencies were captured. On the long runs of LNG header there were Line stops which were showing loads like 30 tons ( line size 40 " , LNG, loop at every 45 m ). On either side of line stop 90 m run was there. The surge load was around 100 tons at elbows. In static analysis ,the stops were showing around 55-60 tons load.
Afterwards I have run the dynamic analysis again , with frequency extracted up to 20 Hz. Necessary changes were made in parameters to ensure Sturm check was OK. Suddenly I find that the loads on stops have shot up to say around 200 tons , 150 tons etc.
Is it that there is some problem with the modeling ?
One of the senior colleague opined that water hammer can show such loads.
The load pattern is trapizoidal , 5 ms is valve time , sound velocity is 1200 m/s and fluid velocity is 5 m/s.
Please advice.