Internal resonance of a flexible rotor supported by a magnetic bearing

Magnetic bearings can support rotating rotors without any contacts. So it is possible to rotate a rotor at extremely high rotational speed. On the other hand, they can easily show elastic deformation with nonlinear oscillation, which is complicated and difficult to deal with. This study investigates nonlinear coupling of oscillation modes appearing in such a flexible rotor system with a magnetic bearing, by considering both the nonlinearity of the electromagnetic force and the continuousness of the rotor. First, an essential model of a rotor with an elastic shaft supported by a magnetic bearing was introduced. The numerical results indicate occurrence of internal resonance caused by the nonlinear coupling of the modes, if the ratio of their natural frequencies is 1 to 3 Experiments were also carried out and obtained results showed qualitative accordance to the numerical results.