Harmonic Forces and Displacements

Hello all,

I'm working in a Centrifugal Pumps revision by vibration,

I have the vibration reports and show the (A) Amplitud and the Frecuency.

I want to review my model by Harmonic Forces, but when I checked the Formula for the forces F(t) = A*cosine( ωt-φ), is the same by displacement D(t)=(A)*cosine(ωt-φ) according to the Technical Reference Manual,

Could anyone tell me if my appreciation is correct, or maybe am I in wrong direction?

Best Regards all,

I tis important to model the true loading in the pipe. You are modeling the load as it enters your system. Do not impose some observed response as your cyclic load.

If the cyclic response is caused by a pressure pulsation or by flow-induced vibration, model as a force (where and how big is a different question). If the response is caused by mechanical vibration, model as a displacement on that boundary condition.

Thank you very much for your answer Dave,

Yes, the responce in the pump is by Mechanical Vibration then I need to include the displacements according to the Graph,

I get one more question, the units of the amplitude in my graphs appear as in/s 0pk, I know the amplitude it's a lenght magnitud, then Why appear like velocity units?

Regards

Since harmonic response is tied to frequency, you can say:
x=A sin(wt)
v=wA cos(wt)
a=-w^2A sin(wt)
So amplitude in displacement (x) equals velocity amplitude/frequency (v/w).
Frequency (w) is in radians per second.

Dave I really appreciate all your help,

Success always

Regards

Dave and AGA 76,

I am new to pipe stress analysis.

AGA 76 said that the response in the pump is by mechanical vibration and then the displacement need to be included. Is that the displacement of the pipe? The displacement is measured and included in the Harmonic Analysis?

And, how one to identify flow-induced vibration and mechanical vibration?

I am working on preheater pipe by vibration and I do not know what causes the pipe to vibrate excessively.

Please advice.

Thank you.