Recent advances in nonlinear passive vibration isolators

To reduce the severity of high-magnitude vibrations and shock, end-stop buffers was used for the most suspension cabs or seats of work vehicles. This paper employs a pair of symmetric linear viscoelastic end-stops to improve the performance of a single-degree-of-freedom nonlinear suspension system under primary resonance conditions, which has cubic nonlinearity. Firstly, a piecewise symmetry tri-nonlinear model is introduced. The frequency response of relative displacement corresponding to the steady-state motion is obtained by applying the multiple-scale method, which is found to be the same with the averaging method solution. And it is further verified by numerical simulation. Its stability is then studied. Subsequently, a design criterion is proposed for jump avoidance, which is caused by the saddle-node bifurcation. Also, parametric studies are carried out to illustrate effects of design parameters for the end-stop on the isolation performance at primary resonance, including responses of the relative displacement and the absolute acceleration. The results show that with dynamic parameters properly designed by using viscoelastic end-stops, the relative displacement response can be effectively suppressed and the jump can be eliminated for both hardening and softening primary isolators. Besides, the end-stop can effectively attenuate the absolute acceleration response for a hardening primary isolator, while more damping is needed to attenuate that for a softening primary isolator, although the degree of the softening nonlinearity is mitigated. It is suggested that a moderate stiffness compared to that of the primary isolator and also a high damping of the end-stop be beneficial to both vibration isolation and jump avoidance under primary resonance conditions.

Primary resonance analysis and vibration suppression for the harmonically excited nonlinear suspension system using a pair of symmetric viscoelastic buffers

In this paper, the transmissibility of a viscoelastic beam supported by vertical springs is defined by proposing a new vertical elastic support boundary. By contrasting with the viscoelastic beam with rigid vertical supports and the rigid rod with vertical elastic support ends, the necessity of the transmissibility of an elastic structure with vertical elastic supports is proved. In order to approximately solve the steady-state responses of the nonlinear transverse vibration of the viscoelastic beam under periodic excitation, the harmonic balance method in conjunction with the pseudo arc-length method is adopted. The numerical results are calculated to confirm the approximate analytic results. The comparison between the rigid rod and the elastic beam shows that neglecting the bending vibration of the structures will underestimate the frequency range in which the elastic support produces an effective vibration isolation. On the other hand, the comparison between the rigid support and the spring support demonstrates that ignoring the elasticity of the support ends will create a false understanding of the force transmission of elastic structures. In general, this paper presents the necessity of studying the force transmission of elastic structures with elastic supports. Moreover, this paper will become the beginning of the study of the vibration isolation of the elastic structure.

Nonlinear vibration isolation of a viscoelastic beam

Study on vibration isolation properties of solid and liquid mixture

Influence of uncertainty and excitation amplitude on the vibration characteristics of rubber isolators

The purpose of this study is to explore the advantages and characteristics of nonlinear butyl rubber (type IIR) isolators in vibratory shear by comparison with linear isolators. It is known that the mechanical properties of viscoelastic materials exhibit significant frequency and temperature dependence, and in some cases, nonlinear dynamic behavior as well. Nonlinear characteristics in shear deformation are reflected in mechanical properties such as stiffness and damping. Furthermore, even when the excitation amplitude is small the response amplitude may often be large enough that nonlinearities cannot be ignored. The treatment involves developing phenomenological models of the effective storage modulus and effective loss factor of a rubber isolator material as a function of excitation amplitude. The transmissibility of a nonlinear viscoelastic isolator is compared with that of a linear isolator using an equivalent linear damping coefficient. Forced resonance vibration and impedance tests are used to characterize nonlinear parameters and to measure the normalized transmissibility. It is found that as the excitation amplitude of the nonlinear viscoelastic isolator increases, the response amplitude decreases and the transmissibility is improved over that of the linear isolator for excitation frequency that exceeds a particular value governed by the temperature and excitation amplitude. The method of multiple scales and numerical simulations are used to predict the response characteristics of the isolator based on the phenomenological modeling under different values of system parameters.

R. F. Gibson

Papers

Influence of excitation amplitude on the characteristics of nonlinear butyl rubber isolators