Quasi-zero-stiffness Nonlinear Vibration Isolation,Vibration Energy Harvesting And Their Synergistic Design

Most of the engineering vibrations are harmful,which may cause structural failure or damage,poor working accuracy and other problems,so vibration isolation or attenuation measures are necessary for reducing or eliminating the unfavorable effects of vibration.The stiffness characteristics of traditional linear vibration isolators make the contradiction between isolation frequency band and static load bearing capacity,and cannot be applied for low frequency vibration isolation.The quasi-zero-stiffness(QZS)vibration isolation technology breaks the linear stiffness limitation and can significantly reduce the dynamic stiffness while maintaining high static stiffness,thereby extending the isolation band to low frequency region.However,the existing QZS isolators still have problems such as rightward bending of resonance region,inability to optimize high and low frequency performances simultaneously,and poor adaptability to complex excitation conditions,etc.Therefore,it is necessary to conduct the improvement design and structural optimization for QZS isolators to further enhance the vibration isolation performance and environmental adaptability.From the perspective of energy flow,the essence of vibration isolation is to inhibit the transfer of mechanical energy to the vibration isolation object.Therefore part of the vibration energy can be converted into other forms via energy transduction element in the vibration transmission path to reduce the amount of vibration energy flowing to the isolation object.In doing so,both the purposes of vibration isolation and energy harvesting can be achieved,and the emphasis is placed on how to integrate the two objectives and synergistically benefit each other.In this dissertation,we propose and investigate various ways of refining QZS isolation systems,based on deeper nonlinear dynamic analysis on an archetypal QZS isolator,to further enhance the isolation performance and environmental adaptability;We propose and investigate compact large-stroke multi-stable vibration energy harvesters based on the nonlinear vibration theory of multi-stable systems,to broaden the energy harvesting frequency band;We integrate vibration isolation and energy harvesting for the design of QZS dual-objective synergistic systems.The main research contents of this dissertation are as follows:(1)The test results on the experimental prototype of an archetypal QZS isolator indicate that there exists specific gap between experimental results and the theoretical results obtained by traditional dynamic model.In view of this discrepancy,a more accurate dynamic model is established with consideration of some practical factors,and the effects of these practical factors on the dynamic behaviors are analyzed.Based on the modified dynamic model,numerical simulations are employed to study various bifurcation patterns(including PH,SB,PD,SN bifurcations,etc.)and various response types(including symmetric and asymmetric period-1,multi-period and chaotic responses),with focusing on the superharmonic resonance and the effect of superharmonic resonance on the isolation performance.(2)A variety of extended QZS(or HSLDS)vibration isolation systems are designed and studied.The viscoelastic damping is introduced into the QZS isolator and turns it to a thirdorder dynamical system,which increases the roll-off rate of high frequency transmissibility while significantly reducing the transmissibility in resonance region and the peak transmissibility,realizing the simultaneous optimizations in high-frequency region and resonance region.By attaching a small mass at the key position of the QZS isolation structure,the whole system attains nonlinear inertia characteristics;by elastically connecting a small suspending mass to the HSLDS isolator,the stiffness hardening effect is weakened;both methods effectively solve the problem of rightward bending of the transmissibility curve in resonance region,so as to maintain a low isolation beginning frequency and a low peak transmissibility even under large excitation and small damping.A magnetic in-plane QZS isolator is proposed using two radially magnetized rings and several pretensioned cables to extend the QZS isolation technique from single direction to horizontal arbitrary direction.A HSLDS strut is proposed and utilized for constructing a HSLDS vibration isolation platform with the well-designed orthogonal configuration which decouples the linear part of the dynamic equations,achieving good low-frequency vibration isolation performance in six directions.(3)Two kinds of multi-stable vibration energy harvesters with simple structures are proposed and studied to broaden the energy harvesting frequency band.An inverted pendulum is placed at the top of an inverted piezoelectric cantilever beam via an elastic hinge;by designing the stiffness of the elastic hinge,a compact 2DOF bi-stable piezoelectric energy harvester is obtained.Based on the geometric nonlinearity and electromagnetic induction,a large-stroke tri-stable electromagnetic energy harvester is constructed by utilizing precompressed springs,slider,permanent magnet and coil,to achieve broadband low-frequency vibration energy harvesting,and the power density is increased to almost ten times that of the magnetically coupled piezoelectric cantilever beam tri-stable energy harvesters.(4)Based on the synergistic integration of vibration isolation and energy harvesting and the implementation principle of vibration energy targeted transfer,two kinds of dualobjective synergistic systems are proposed and studied.A single-stage dual-objective synergistic system is designed by utilizing piezoelectric buckled beams and transverse groove spring;the structural layout of the piezoelectric buckled beams can not only produce negative stiffness in the vibration direction but also ensure that the piezoelectric layers always have large stress/strain which is conducive to higher output power;the structural parameters are designed properly to make the whole system possess QZS characteristic,so as to extend both vibration isolation and energy harvesting to low frequency region,which is then validated by theory and experiment.Several radially distributed piezoelectric cantilever beams with tip masses are integrated with a QZS support formed by the cam-roller-spring mechanism,to construct a MDOF dual-stage dual-objective synergistic system;the QZS characteristic makes the isolation region start from a low frequency,and the two-stage configuration makes the energy harvesting region lie within the isolation region;by tuning some key structural and electrical parameters,the location of energy harvesting region,the energy harvesting bandwidth and the peak power can be regulated without degrading the vibration isolation performance.