Nonlinear dynamics analysis of a bi-state nonlinear vibration isolator with symmetric permanent magnets

This paper proposes a novel bi-state nonlinear vibration isolator (BS-NVI) consisting of a linear mass–spring–damper and several permanent magnets (PMs). The working state of the BS-NVI can be monostable or bistable depending on the relative position of the PMs. The theoretical model of the BS-NVI is established. The transmissibility of the BS-NVI is derived according to the harmonic balance method. Both the simulation and experimental efforts are performed to study the nonlinear dynamics and vibration isolation performance of the BS-NVI. The results demonstrate that the monostable isolator acts like a quasi-zero-stiffness isolator and exhibits the hardening-spring-liked characteristic. With the change in the relative position of the PMs, the transmissibility and the peak frequency are decreased. However, the bistable isolator undergoes the interwell and intrawell oscillations with the change in the excitation amplitude and frequency. The motion of the bistable isolator can be periodic or chaotic. Due to the snap-through action, the transmissibility of the bistable isolator could be smaller than 1 in part of the resonance region.