Dynamics of a Flexible Rotor With Circumferentially Non-Uniform Magnetization Supported by a Superconducting Magnetic Bearing

A superconducting magnetic bearing has many opportunities in which it is driven higher than their critical speeds. Under those circumstances, the rotor can easily show elastic deformation and complicated phenomena by nonlinearity of electromagnetic force. Therefore, evaluation of its dynamics taking nonlinearity and elasticity into consideration in the vicinity of its critical speeds is demanded. This research examines the effects of magnetic nonuniformity of a rotor in its circumferential direction on dynamics. First, an essential model of a rotor with an elastic shaft supported by a superconducting magnetic bearing was introduced. By taking account of magnetic non-uniformity, our numerical result showed its three effects: anisotropy of the rigidity, characteristics equivalent to those of an asymmetrical cross section of the axis, and nonlinearity of electromagnetic force. These effects cause difference of critical speeds in thex,ydirections, a frequency band showing instability of the rotor's motion, and change of eigenfrequencies depending on the amplitude, respectively. These effects may emerge simultaneously when the rotor has magnetic nonuniformity in its circumferential direction.