The Influence of Damping on Vibrations of the summed Type under Parametric Excitation of a Rotating Shaft Driven through a Universal Joint.

This paper presents some characteristics for unstable vibrations in a rotating shaft driven by a universal or Hooke's joint. A driving shaft is assumed to be rigid and to rotate with a constant angular velocity. The driven shaft is flexible and carries a rotor at a point between the shaft ends. Discussion starts with using the results of the approximate analysis for equations of motion. The unstable vibrations occur in a certain rotating speed region, which approximately equal to one half of the sum of the natural frequencies for whirling and torsional vibrations. In this case, the whirling and torsional vibrations become unstable at the same time. A viscous damping, commonly, suppres- ses unstable vibrations, but does not always work for the present vibrations. A certain magnitude of the damping gives the minimum or maximum width of the unstable region.