Improving quasi-zero-stiffness isolator performance: two hybrid isolators employing inerter elements

The pursuit of enhanced low-frequency vibration isolation motivates the development of quasi-zero-stiffness vibration isolators (QZS-VIs), yet with inherent limitations. The nonlinear hardening stiffness may distort the resonance peak rightward, narrowing the isolation bandwidth. Additionally, the high sensitivity to excitation variations can exacerbate the rightward distortion and jumping phenomenon. In this study, two types of hybrid isolators (QZS-IE isolators) are developed by integrating inerter elements (IEs) with traditional QZS-VI to enhance isolation performance. Their distinct mass block configurations yield varied enhancement behaviors. The unified dynamic equation for the two QZS-IE isolators is derived using harmonic balance and arc-length methods, validated by Runge-Kutta. Stability and periodicity analyses clarify their response characteristics. Subsequently, the study investigates the effects of geometry and excitation parameters, comparing the enhancements of the two QZS-IE isolators. The results manifest that the introduction of inerter elements improves low-frequency vibration isolation, suppressing peak transmissibility and reducing isolation beginning frequency. The type I QZS-IE isolator outperforms the type II QZs-IE and traditional QZS isolators in low-frequency isolation performance and excitation sensitivity. However, the high-frequency isolation performance of the type I isolator is hindered by the ascending transmissibility curve post anti-resonant frequency. The Type II QZS-IE rectifies resonance peak distortion while avoiding adverse effects. The different configurations of the inerter elements and the related attenuating strategies offer a guideline for diversified vibration isolation objectives.