Hi,
We are currently using Caesar II s/w for Dynamic analysis of Piping Systems. We have a problem on a GAS Compressor which needs Harmonic Analysis. Kindly let us know the source for the following input data :
1. Starting & Ending Frequencies. Is the Starting Frequency the one that causes the max. displacement as measured in the field? What is the Ending Frequency then? & also what is the Frequency Increment.
2. What is the source for the Harmonic force and how is it measured. Is this calculated similar to the unbalanced forces for the Hammer Analysis based on the Differential Pressure and sonic velocity.Please clarify the criteria for compressible fluids(Gas).
3. Please also tell us how to determine Load Cycles & Harmonic Displacements

1) In a "harmonic problem", you can often measure the frequency at which the "problem" occurs. If this is the case, then you specify this frequency as the "starting frequency" and leave the "ending frequency" and "increment" blank. If on the other hand, you only knew the frequency approximately, then you could specify the "starting frequency" as 90% of your approximate value, the "ending frequency" as 110% of your approximate value, and the "increment" as 1% of your approximate value. Then review the results to see which frequency generates the results closest to what you experience in the field. Go back and change the frequency values to further narrow things down until you find the exact frequency you need.

2) Typically you can't measure a harmonic force. Usually the "harmonic force specification" is used to "simulate" (or guess) at the load causing a problem. Once the specified force correctly "simulates" the problem in the field, you can then adjust the model so that it doesn't respond to this load.

3) The "Load Cycles" specification is used only for fatique analysis. It is the anticipated number of applications of this load (or displacement) on the system. "Harmonic Displacements" are a measured value.