Abstract
In high-Tc superconducting magnetic levitation systems, due to the strong pinning force, a levitated body can keep stable levitation without contact and control. So, there are many applications, but this system has a problem that nonlinear vibrations that derive from nonlinearity of electromagnetic force often occur. Further, structures of such a levitated body can show elastic deformation if the large electromagnetic force acts on it. Thus, nonlinear characteristics can easily appear in this elastic oscillation as follows. If the excitation frequency is the sum of two modes' natural frequencies, both of the two modes can resonate simultaneously, which is called combination resonance. If the excitation frequency is multiple of some modes' natural frequency, that mode can resonate, which is called parametric resonance. Those two resonances derive from the nonlinearity of electromagnetic force. This research investigates how parametric resonance and combination resonance affect each other. We dealt with a beam levitated above superconducting bulks which has a permanent magnet on its each end. The initial height of the beam is adjusted so that the two resonances can occur simultaneously. Numerical and experimental results show following. When excitation frequency is increasing, the above two resonances cannot occur simultaneously and transition between the two resonances rises. Furthermore, under some condition, combination resonance doesn't occur and only parametric resonance occurs. When excitation frequency is decreasing, there are states in which both resonances simultaneously occur, in which only parametric resonance occurs and in which only combination resonance occurs.
