Acoustic Induced Vibration 1

[4Pipes]

The Carruci & Mueller paper on acoustic induced vibration as shown in the CONCAWE, MTD, Exxon vibration guide etc gives an equation for the acoustic power generated by a gas pressure drop through a fitting.
There is no indication of range of pressure drop for which the equation is valid. The equation appears to give the same acoustic power as IEC 534 Regime 1. i.e. Subsonic pressure drop. Is the Carruci equation valid for all pressure drops - I suspect not? (Taking the "acoustic energy as calculated from Carruci with high pressure drops and back calculating the acoustic efficiency produces what appear to be unrealistically high values).
Thanks

 

[GregLocock]

Are you sure that the pressure drop you are using is achievable without getting Mach choked flow?


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[4Pipes]

Greg, Thanks for the reply.
I am interested in pressure drops well in excess of that needed for choked flow. Hence, why would Carucci use what appears to give the same numerical result as IEC 534 Regime I?

 

[GregLocock]

Sorry, I've got no experience with that paper.

Once you have choked flow you have a variety of sound creating mechanisms that are (say) 10-20 dB louder than you'd otherwise expect. In fact you could say that choking is a way of turning kinetic energy into heat and pressure fields, the latter of which are sound, when all is said and done.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[fwcatr]

4Pipes,

I have read through that paper a few times and I have some colleagues who have analyzed the results of that paper and expanded upon it and that subject matter. They wrote a paper on dynamic stress predictions of acoustic induced pipe vibration failures. The paper was presented in 2005 at the 24th international conference on offshore mechanics and arctic engineering (OMAE 2005). The paper number is OMAE2005-67515, the author is Karczub, et al.

Here are some other references if you can access them, they all deal with piping fatigue.

[1] Norton, M.P., "Acoustically Induced Structural Vibration and Fatigue - A Review", Third International Congress on Air- and Structure-borne Sound and Vibration, Montreal, Canada, 1994.
[2] Eisinger, F., 1997, "Designing Piping Systems against Acoustically Induced Structural Fatigue", Journal of Pressure Vessel Technology, Vol 119.
[3] Cowling, J., and Lin D., 1999, "Acoustically Induced Vibration and Fatigue in Piping Systems – A Review", Inter-Noise 99, Fort Lauderdale.
[4] Norton, M.P., and Karczub, D.G., 2003, Fundamentals of Noise and Vibration Analysis for Engineers, Second Edition, Cambridge University Press.

For your awareness, the IEC standard is being revisited and there is a possiblity of removing the regimes. I am not sure when the new standard is coming out, but there are some really good enhancements to the noise predictions.

I am not sure why there are the similarities you point out.

Hope this helps.

Regards,
Fred

 

[4Pipes]

Fred,
Thanks for the info.