Damping of rotor conical whirl by asymmetric dry friction suspension

A new technique for the rotor whirl damping in rotating machinery, based on the elastic suspension of the journal boxes and the use of dry friction surfaces normal to the shaft axis between their supports and the frame, is here analysed theoretically for several cases of rotor systems characterized by mass and constraint asymmetry, where gyroscopic effects are to be expected and conical whirl motions may grow up. The critical flexural speeds can be easily cut off by an adhesive state of the supports and the whirl amplitude can be minimized as well throughout the remaining sliding range. Confining the operative angular speed of the rotor in the range of adhesive contact between the dry friction surfaces, no significant increase of power dissipation or heat production has to be ascribed as a whole to this type of suspension system, whose task is just to suppress the resonant peaks when passing the critical speeds. On the other hand, the rubbing surface wear can be easily compensated in the long run by use of suitable spring devices to close the friction contact. The uniqueness and the stability of the steady motion are proved, both in the absence and in the presence of possible additional viscous sources of dissipation. It is also shown how the destabilizing influence of the shaft material hysteresis can be counterbalanced by the other external dissipative forces.