Harmonic Analisys

Existing a problem with the centrifugal pump, this equipment has vibration, the fluid is gas-oil, could i use the caesar´s harmonic analisys for solve this problem and what is the right way, if this is not possible, how could i use the caesar´s software for solve it.

Yes, you can use CAESAR II to evaluate this problem. However, since you don't really know the load applied to the system, you have to simulate it. The steps are as follows:

• Measure the response of the system in the field. Elbow "a" moves up and down "x" inches, elbow "b" moves side to side "y" inches, all at a frequency of "w".
• Model the system as usual.
• Start a harmonic analysis, where the driving frequency is the observed frequency of the system response.
• Pick a unit load (1000 or 10000 lbs) and apply it axially in a straight run near the pump.
• Run the analysis. Observe the CAESAR II animation and determine if it matches (in shape) the vibration of the system in the field. If it doesn't move the force to a different straight run of pipe, and try again.
• After matching the shape of the vibration (between the animation and the actual system), scale the applied load (up or down) until the magnitude of the displacements match.
• Now you have simulated the load. Do not change the location or magnitude of the force.
• Evaluate the system stresses/loads and determine if you have a problem. If you do, change the system so that it does not respond to the applied load. Usually this involves finding a natural frequency with a mode shape similar to the observed field vibration, and adding a restraint sufficient to eliminate this mode.

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Regards,
Richard Ay (COADE, Inc.)

Hello Richard,

"The driving frequency is the observed frequency of the system response" meaning that the frequency of "w"?

Is the "w" frequency need to be measured at the elbows?

Please advice.

Thank you.

I'd suggest measuring the frequency at the pump nozzle.