Hi Dave,
I have to perform a Harmonic analysis of a piping system connected to a reciprocating Pump. I am trying to simulate the forced mechanical response of the system by imposing on it all the necessary shaking forces.
As mentioned in CAESAR user guide, I have calculated Harmonic shaking force using formula F=0.5*DP*A (where “DP” is the Peak-to-Peak pressure pulsation at that point and “A” is the area of the pipe section) and I am applying that harmonic shaking forces along the pipe axis (and so for each bend there are two separate loads applied with different directions and same value of amplitude and phase) at every geometric discontinuity of the system such as elbows, tees & capped ends (As described in API 688).
I have calculated phase angle (as mentioned in CAESAR user guide) between shaking forces at every bend using formula Phase angle= 360*f*(L/c), where “L” is the distance between the starting point (First elbow) and the respective concerned point, “c” is the speed of the sound of the fluid inside pipes and “f” is the frequency of the pressure pulsation.
Please confirm whether my understanding is correct or not in order to perform harmonic analysis of a piping system connected to a reciprocating pump.
I would like to let you know why I have a confusion in calculating shaking forces and phase angle with above formulas:
If you refer Caesar II manual help file there are another formulas for calculating shaking force and phase angle. Those are populated in Harmonic force and harmonic displacement tabs when we use F1 for respective fields. Those are as below:
The form of the harmonic forcing function is:
F(t) = A*cosine(wt-f)
where "F(t)" is the force as a function of time. "A" is the maximum amplitude of the dynamic force. "w" is the frequency of the excitation (in radians per second), and "f" is the phase angle (in radians).
f(degrees) = 180tw/p
where t is given in seconds and w is given in radians per second.
The phase angle is usually entered as either zero or 90. Use the phase specification when defining eccentric loads on rotating equipment.
Pl’s clarify.
If anyone has opinion on this, pl's let me know.