On Analytical And Experimental Assessment Of Quai-Zero-Stiffness Isolator

On the basis of practical engineering and design theory of the nonlinear vibrationisolation system, a quasi-zero-stiffness (QZS) isolator is put forward as a solution forthe low-frequency vibration isolation. By the positive and negative stiffness parallelcombination, this new type isolator has the characteristic of high-static-low-dynamicstiffness near the equilibrium, which makes the system possess high load capacity andlow natural frequency and thus good vibration isolation performance. Specifically, themain content of this paper is as follows:1. Firstly, the mathematical model is provided for examining the characteristic ofthe QZS system. A unique relationship between the geometry configuration and thestiffness of the spring elements is obtained in order to design the property ofhigh-static-low-dynamic stiffness. The relationship between force and displacement issimplified to facilitate subsequent dynamic analysis and the error is also quantified.The static load quality making the system work in the equilibrium is calculated andthe influence of the system parameters on it is also discussed.2. The dynamic characteristics of the nonlinear QZS system are analyzed withharmonic excitation. The dynamic model is established to obtain the governingequation of the system. Analytical solutions of the equation are derived with theharmonic balance method for the characteristic analysis of jumping phenomena,bifurcation and the force and displacement transmission. Compared with the linearsystem, it is found that under appropriate excitation conditions QZS system can havea lower resonance frequency and larger vibration frequency interval and also has asmaller force and displacement transmissibility, which makes it more suitable for lowfrequency vibration isolation.3. The force transmissibility of the QZS and the linear isolator is tested on thevibration table. By comparing the experimental results, it can be found that the QZSisolator can reduce the natural frequency of the system, thus expanding the range ofvibration isolation and obtaining the destination of the low frequency or ultra-lowfrequency vibration isolation. In addition, the performance of the QZS system is alsodependent on the amplitude of vibrations observed from experiments, namely that theQZS system can only exhibit its excellent isolation capability in the condition whererelatively large oscillations are involved. It may limit its applications in real engineering practice. Nevertheless, the QZS system is still an outstanding performerin low-frequency vibration isolation, particularly for the applications where largeoscillations occur.