Time Domain vs. Frequency Domain Acoustic Analysis
Time Domain vs. Frequency Domain Acoustic Analysis
(OP)
Can anyone comment on the benefits of performing an acoustic analysis on a recriprocating nat gas compressor, via time domain method versus frequency domain.
I understand that software for performing time domain analysis has only been in use for a couple years, while frequency domain anlaysis goes back 50 or 60 years (maybe more), and has been widely successful.
However, as the end user, a couple of analysis companies are saying that doing studies in the time domain is the greatest new thing...while a couple of the analysis companies that we typically use, have not adopted this method, and still use frequency domain anaylsis.
I have a vague understanding of the fundamental difference in the two approaches, however, I'm unceratin of the differene in accuracy of the two. Does time domain actually predict actual operation more closely...and is this the way that that technology is going? Or, should we just stick to the tried and true method we've relied on for years, and let the technology grow until more people accept that method until we jump into it?
Opinions, please.
I understand that software for performing time domain analysis has only been in use for a couple years, while frequency domain anlaysis goes back 50 or 60 years (maybe more), and has been widely successful.
However, as the end user, a couple of analysis companies are saying that doing studies in the time domain is the greatest new thing...while a couple of the analysis companies that we typically use, have not adopted this method, and still use frequency domain anaylsis.
I have a vague understanding of the fundamental difference in the two approaches, however, I'm unceratin of the differene in accuracy of the two. Does time domain actually predict actual operation more closely...and is this the way that that technology is going? Or, should we just stick to the tried and true method we've relied on for years, and let the technology grow until more people accept that method until we jump into it?
Opinions, please.





RE: Time Domain vs. Frequency Domain Acoustic Analysis
Sounds like salestalk.
There are some time related analyses that are worth doing, but I'd always start in the frequency domain.
Cheers
Greg Locock
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RE: Time Domain vs. Frequency Domain Acoustic Analysis
how do you handle the dc component?
RE: Time Domain vs. Frequency Domain Acoustic Analysis
For most acoustic problems the interest is in a steady state solution due to harmonic excitations which is ideal for frequency domain analysis. There are some exceptions like simulation of explosions for example, which are more efficiently performed in the time domain. What is the issue in the simulation of reciprocating natural gas compressors that warrants time domain analysis?
Nagi Elabbasi
Veryst Engineering
RE: Time Domain vs. Frequency Domain Acoustic Analysis
http://www.novosim.com
Product Development Services (cad/cae/test)
Medical Device R&D
RE: Time Domain vs. Frequency Domain Acoustic Analysis
Jeyaselvan
RE: Time Domain vs. Frequency Domain Acoustic Analysis
To me, the end-user, basically, is that both time-domain and frequency domain both agree on the frequency response of an reciprocating gas system. However, the difference is in the amplitude prediction accuracy of the two methods...time domain accurately predicts the amplitude levels across the frequency spectrum, while a frequency domain analysis will underestimate the response and not in a consistent manner.
So if one can seperate forcing frequencies and mechanical natural frequencies by a good margin, then frequency domain is sufficient.
However, to more accurately predict shaking forces due to unblanaced acoustic forces, then time-domain analysis is the way to go.
So far, we have had good results with our tech company who solely uses frequency domain analysis. However, not a lot of testing has been done to compare pulsation amplitude levels to the original levels predicted by the model.
Hope this helps some of you in the future.
RE: Time Domain vs. Frequency Domain Acoustic Analysis
Time Domain Analysis has been around a lot longer than a few years. It just had a different name but is the same thing.
It was called the "Chart Recorder". You got amplitude versus time. Faster paper speed equals more resolution. Chart recorders were around long before swept filters which were among the first tools for frequency analysis.
RE: Time Domain vs. Frequency Domain Acoustic Analysis
Specifics can be found by viewing small sections of data in the time domain.
Many P&E engineers are spooked by anything to do with frequency domain analysis, so you have to keep reminding them that a spectrum is just another way of describing the shape of a time (or crank angle) domain signal.
- Steve
RE: Time Domain vs. Frequency Domain Acoustic Analysis
That's all well and good, but I think the OP is interested more in how you simulate time domain signals rather than display them.
I would also infer that the OP is interested in looking at pressures inside the system rather than radiated noise.
M
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Dr Michael F Platten
RE: Time Domain vs. Frequency Domain Acoustic Analysis
If one is attempting to simulate the behaviour of pressures inside the system, or noise radiated from orifices due to velocity fluctuations, then non-linear, time-domain simulation has been standard practice in the automotive engine industry for c. 15-20 years. Some die-hards still swear by their linear, frequency-domain models, but the tide has long turned.
Non-linear time-domain models can (obviously) capture non-linear effects (high SPLs, mean flow, temperature gradients). They can also simulataneously predict acoustics AND performance. It's easy to reduce radiated noise in isolation, but how will your measures afffect back pressure?
- Steve
RE: Time Domain vs. Frequency Domain Acoustic Analysis
frequency domain methods are a very good tool if properly used.
RE: Time Domain vs. Frequency Domain Acoustic Analysis
I believe we will continue to allow the use of both methods of simulation...linear, frequency domain, and non-linear time domain.
As we have installed many recip machines from 1000 to 8000 hp using frequency domain-based designs which have worked well so far.