Dynamic Stability of Rotor Equipped with Physical Pendulums.

A rotor containing movable masses, solids or liquids, often undergoes asynchronous whirling motions under certain conditions. In such a rotor the motions of the contained masses due to the vibration of the rotor can produce an unbalanced force which rotates backward relative to the rotor and induces unstable motions of the system. This paper presents a theoretical and experimental study on the dynamic stability of rotating shaft attached with several physical pendulums which can rotate in a plane containing the shaft. It has been found that the system is substantially stable when the shaft is whirling in the parallel mode, while in the conical mode it becomes unstable at a certain range of rotating speed. The self-excited vibration can be induced in the region where the rotor speed is nearly equal to the sum of the forward-precession natural frequency of the rotor and that of the pendulums.