what is critical speed?

Answer Posted / natig

In solid mechanics, in the field of rotordynamics, the
critical speed is the theoretical angular velocity which
excites the natural frequency of a rotating object, such as
a shaft, propeller or gear. As the speed of rotation
approaches the objects's natural frequency, the object
begins to resonate which dramatically increases systemic
vibration. The resulting resonance occurs regardless of
orientation.
When the rotational speed is equal to the numerical value
of the natural vibration then that speed is called critical
speed.
For a rotating shaft there is a speed at which, for any
small initial deflection, the centripetral force is equal
to the elastic restoring force. At this point the
deflection increases greatly and the shaft is said
to "whirl". Below and above this speed this effect is very
much reduced. This critical (whirling speed) is dependent
on the shaft dimensions, the shaft material and the shaft
loads. The critical speed is the same as the frequency of
traverse vibrations.

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