Acoustic problem

Hello everyone,

Now I am working on a vibration problem related to choke vale (reducing pressure from 325 bar to 80 bar) and the measurement from the site provides that after the choke valve NF is 2345 Hz and before the choke valve is 1500 Hz which is weird as there is no source for vibration before the choke valve. Do you have any idea from where this vibration (before choke valve) comes from and do you recommend any paper or reference which can help me in this problem and what is the possible solutions?

Thank you in advance

Since the piping system is a continuous system, some acoustic energy may also be transmitted to the downstream side from the upstream side.

I mean to the upstream side from the acoustic energy on the downstream side, through the wall of the pipe.

Just a wild guess.

I believe from some guidelines, that failure normally occurs on the asymmetric discontinuity (e.g. branch connection, shoe connection). Normally, it recommends full encirclement reinforcement to make the connection axisymmetric. But on the plain normally, there is no failure (not sure if there is a new development in recent studies). Another recommendation is to use a forged tee and sweepolet for new system. But since it's an existing system, another solution is to weld circumferential rings based on the outcome of a detailed AIV study (I believe using FEA).

plain pipe as a correction.

Thank you for your answer.

Also in the report, RMS is 0.7 mm/s, so I think the value is not critical. is that right?

There are charts comparing the velocity to the frequency which shows if the system is safe or unsafe. For low frequency, I am familiar with this chart, not sure about the high-frequency application.

If it helps, here's some sense of scale.

A phone vibrates at around 150 Hz.

The cell phone vibrator motor generally comes in at 10 mm x 4 mm diameter, and the spinning end can be characterized as 2 halves of a cylinder, with one side having 4mm radius, and the other having 2mm radius.

If placed on a surface, the motion of the phone would be characterized as 3*sin(x), in mm.

The RMS of the phone would be the square root of the integral from 0 to 2 pi of the frequency times the square of 3*sin(x), which equals approximately 65.12 mm/s.

https://www.wolframalpha.com/input?i=square+root+of+%28integrate%28150*%283+sin%28x%29%29%5E2%29+from+0+to+2+pi%29