Vibration analysis of Structure attached to Rotating Machinery

[struclearner]

Dears,
How the speed in rpm of a rotating machinery like an engine or motor can be used to compare the natural frequency of an attached structure. For example, what could be the excitation of a bracket with natural frequency in the range of say, 10 Hz to 50 Hz, attached to the engine, which is operating, say at 1000 rpm (16.6 cycles/second) under idle conditions (purely excitation coming from engine side, no input due to road travelling).
The engine or any rotating machinery operating speed is in angular velocity with the units of rpm or cycles per second, but the attached structure, one of the mode shapes having the natural frequency close to rotating machinery operating rotational speed, could be bending, so how these engine speed could be related to as the external excitation to an attached structure range of natural frequencies.
Any input, explanation, referring to article/technical literature or to a book dealing with the subject is appreciated.

Thanks & Regards!

 

[GregLocock]

A rotating machine generates frequencies at multiples of (and occasionally half) the rpm of the shaft. So an IC engine at 1000 rpm might generate 8, 16, 32, maybe a bit at 24, and 48 Hz, in your frequency range.

A book on engine noise and vibration would be most instructive, sadly i've forgotten which i used to use. Mostly we used to work off SAE papers.



Cheers

Greg Locock


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