Nonlinear Rotordynamic Behaviour of Rotors on Active Magnetic Bearings

A Jeffcott rotor is used to study the rigid body rotordynamic behavior of a rotor on active magnetic suspension. The nonlinearity introduced by the electromagnetic force actuator as well as by the driving power amplifier are expected to cause a softening type behavior for the rotor and anysotropic behavior of the bearing system. A nonlinear model is used to perform numerical time domain simulations for low bias current and the presence of lateral loading. The resuts obtained show that the nonlinearities introduced into the the system are usually not very strong, at least when the airgap is not very large, but the current saturation effects increase the softening character of the response of the system.