A novel QZS isolator with rotational mass inertia for low-frequency vibration isolation

This paper presents a novel quasi-zero-stiffness (QZS) vibration isolator that integrates a rotational mass inertia (RMI) into a nonlinear negative-stiffness structure, aiming to address hardening response commonly observed in traditional QZS isolators under low damping and large amplitude of excitations. The proposed QZS-RMI system employs an L-shaped configuration with tip-mounted masses that simultaneously generate negative stiffness, nonlinear damping, inertia amplification, and inertia-induced damping through coupled motion. A nonlinear mathematical model is developed using Lagrange's principle and Taylor expansion to capture the coupling between displacement-dependent stiffness, inertia amplification, inertia-induced damping, and horizontal damping. The steady-state response under low damping and relatively large excitation amplitudes is analyzed using the harmonic balance method (HBM) and further verified through numerical techniques, multibody dynamics simulations in MSC Adams, and finite element analyses in ANSYS. The findings show that the RMI mechanism suppresses the hardening-type nonlinearity typically present in conventional QZS systems and introduces beneficial inertia-induced damping, resulting in reduced resonance peaks and a wider effective isolation bandwidth. Comparative studies with a tunable nonlinear inerter QZS system and a lever-type QZS isolator confirm that the QZS-RMI system provides lower transmissibility, smoother response, and broader low-frequency isolation under equivalent design conditions.