Abstract
Recently flywheel energy storage systems using superconducting magnetic bearings have reached its validation phase. And varied combinations of magnetic bearings have been used in this system. However, increasing in amplitude has become a problem because of its low damping. Also nonlinear phenomena can occur in such low-damping systems using an electromagnetic force. This study investigates vibration reduction of a rotor system with an electromagnet. The nonlinearity of magnetic force is taken into consideration in the case. First of all, we developed an essential model of a rotor supported by a superconducting bulk, a permanent magnet and an electromagnet. Equations were derived by taking into account the nonlinearity of the electromagnetic force. Nonlinear analyses were conducted about these equations of motion of the rotor. These equations were then calculated by using the Runge-Kutta method. Numerical results show vibration reduction of a rotor by changing electromagnetic force at appropriate rotating speed. Good agreements were obtained between experimental results and numerical results. As summary, changing of not only linear stiffness but also nonlinear stiffness affects vibration reduction of a rotor supported by superconducting bulk, a permanent magnet and an electromagnet.
