Mechanical Vibration is created by rotating equipment that is not balanced. A rotor imbalance in a motor is very typical. A mechanical analysis will include dynamic driving forces (from this imbalance) as well as natural frequency studies.
Another source of vibratory forces is Acoustical Vibration. Acoustical Vibration is created by pressure waves reflecting off of surfaces in piping. Typically these waves are created by reciprocating compressors. The frequency of this vibration needs to be compared to the natural frequency of the overall system.
I'd say that the difference between the two types of analysis is mainly the frequency range observed in your system.
Let's say that beyond the 50th mode you should go to a propagative analysis.
But that's not a law, just an advice. There are sonic sources that can excite the low frequencies of mechanical structures, for example.
But I'm sure that someone will give you a more precise answer.
Acoustical analysis of equipment and structures is usually done when audiblity health, personnel annoyance or warship-related detectability are the issues of concern. Mechanical vibration analysis of equipment is usually done when damage, mechanical failure, endurance and/or structural reliability are the issues of concern. Acoustics generally involves airborne, waterborne or fluidborne noise sources and transmission paths, whereas mechanical vibration sources are more generally stuctureborne in nature and propagation is not an issue.
The principle is the same, the freqeuncy range and the expected problems make the difference. Unbalance may be the most important aspect in E-motors, once diesels, large pumps, or reciprocating compressor or other types of such equipment are to be considered, the range of relevant freqeuncies increase dramatically, and so the possible problems. The most important item to consider is ususally resonance behaviour, when one or more of the generated frequencies coincide with a natural frequency of (a part of) the system. This can lead to vibration hinder, discomfort, noise and most of all fatigue damage or at least decreased servide life.
look at our website for some examples (cases section)
If it is not periodic, there is little use in trying to control it. If the problem is not caused by a periodic source, it is most likely to be impulse related (a blow, collision, or such) causing local resonances of related components. Then applying suitable damping is the most simple thing you can do. It will be fighting the symptons than..
Well of course you're "fighting the symptoms" in controlling non-periodic noise or vibration. This certainly doesn't mean that non-periodic noise/vibration isn't important. Stone impacts on an inner fender are no less annoying for being non-periodic.
Not all noise or vibration control is control of the source; in fact, probably little of it is.
In many if not most cases, you find yourself treating the path or applying damper or absorber to "fight the symptom."
Sorta like having a cold - you try to reduce the fever or the headache, not having any effective way to defeat the virus.
