Tetrahedron structure with nonlinear stiffness and inertia modulation for enhanced low frequency vibration isolation

Abstract

A novel magnetically modulated tetrahedron structure with nonlinear inertia (MMTS-NI) is proposed and systematically investigated for broadband vibration isolation. The MMTS-NI consists of the tetrahedron structure, a pair of repulsive magnets, and the attached masses. Static analysis reveals that quasi-zero stiffness (QZS) can be realized by utilizing the harden stiffness of the magnets to modulate the negative stiffness of the tetrahedron structure. And the QZS can be obtained under different loads by setting appropriate initial angles of rods and matching initial magnet spacing. Considering the achieved QZS and the inertia of the attached masses, the dynamic model of the MMTS-NI is developed to evaluate its isolation performance when subject to base excitation. By using harmonic balance method (HBM), dynamic equation is solved and the displacement transmissibility is derived. The effects of QZS and the nonlinear inertia are clarified through parametric analysis and comparative discussions. The realization of QZS is beneficial to reduce the resonance frequency and broaden the isolation band. The introduce of nonlinear inertia can considerably suppress the hardening behavior of the transmissibility curve and further reduce the starting isolation frequency. And the inertia induced anti-resonance enhances the vibration attenuation effect in the low frequency band. The experimental prototype is manufactured and thoroughly tested under sweep, periodic and random excitation. The experimental results show that the MMTS-NI can effectively isolate the frequency components above 4 Hz. And the vibration attenuation effect can be significantly enhanced in the range of 4–10 Hz by increasing the attached masses. The results provide a novel and significant methods of improving low frequency vibration isolation performance using nonlinear stiffness and inertia modulation.