Resonant whirl

Same symptoms as bearing oil whirl, however, vibration frequency is constant even though speed IS changed. Resonant whirl Same as oil whirl except triggered by resonant component such as rotor, casing, piping, etc. 

Bearing-support excitation Loose assembly of bearing liner, bearing case, or casing and support Oil whirl Resonant whirl Clearance induced vibration... 

The frequencies of a spectrum can be divided into two parts subharmonic and harmonic (i.e., frequencies below and above the running speed). The subharmonic part of the spectrum may contain oil whirl in the journal bearings. Oil whirl is identifiable at about one-half the running speed (as are several components) due to structural resonances of the machine with the rest of the system in which it is operating and hydrodynamic instabilities in its journal bearings. Almost all subharmonic components are independent of the running speed. 

Flexible rotor balancing must be performed with the rotor whirl configuration approximating the mode in question. The operating speed(s) is in the vicinity of a major flexible mode resonance (damped critical speed). As these two speeds approach one another, a tighter... 

Another possible deflection mechanism is the occurrence of whirling. Whirling occurs when a shaft reaches a critical speed and becomes dynamically unstable with large lateral amplitudes. This phenomenon is due to the resonance frequency when the rotational speed corresponds to the natural frequencies of lateral vibration of the shaft. For uniform beams vibrating in flexure, the natural frequencies can be expressed as ... 

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