Hormonic Piping Vibration
Hormonic Piping Vibration
(OP)
Hi everybody,
I am using Caesar II to solve a piping vibration problem in one of our petrochemical plant. The problem consists of a piping system for chiller water is vibrating due to an external harmonic frequency at 11, 22 and 33 Hz. The max displacement occurs at 11 Hz.
The main problem for me that how can I calculate the exciting harmonic force to excite the model before we can make modifications. The piping system includes reducer from 8” and 6” to 4” and 4” equal tee.
Also, how we can calculate the dynamic force, which is coming from the reducers and branches due to fluid direction change.
Looking for your appreciated help.
Regards,
I am using Caesar II to solve a piping vibration problem in one of our petrochemical plant. The problem consists of a piping system for chiller water is vibrating due to an external harmonic frequency at 11, 22 and 33 Hz. The max displacement occurs at 11 Hz.
The main problem for me that how can I calculate the exciting harmonic force to excite the model before we can make modifications. The piping system includes reducer from 8” and 6” to 4” and 4” equal tee.
Also, how we can calculate the dynamic force, which is coming from the reducers and branches due to fluid direction change.
Looking for your appreciated help.
Regards,





RE: Hormonic Piping Vibration
OK What I would do in this situation would be to look for likely candidates that are exciting the pipe. These may be wind, machines (most likely) or fluid. Determine the exciting frequency, amplitude etc by test or investigation and try and replicate that in your model of the system. It may sound a bit long winded but at least you will understand whats happening.
If you want a quicker answer hire a consultant. Preferably one at COADE then at least you will learn from how they do it. An outside consultant may not want to show you how to do it so next time you have to pay again.
RE: Hormonic Piping Vibration
On the force due to the flow directional changes at the tee, you'll need a flow velocity at the tee to compute the reaction force with an equation I know exists but haven't yet found.
RE: Hormonic Piping Vibration
F=(pA+Q*V*rho/g)*(2-2cosAlpha)^0.5 [From Design News 10/30/63] where p=Pressure differential across the bend
A= Pipe area at entry to bend
Q= Pipe flowrate
V= Flow velocity at entry to bend
rho= Fluid density
g= Gravitational constant (for Engl units)
alpha = Bend angle
For a compressible fluid the equation becomes;
F=pA(1+gamma*M^2)*(2-2cosalpha)^0.5 where
gamma = gas parameter
M=Flow Mach number at entry to bend
The gas equation is based on choked flow at an open exit downstream of the bend.
RE: Hormonic Piping Vibration
Regards,