New-type vibration isolation structure design and performance analysis

Abstract

Vibration isolation has been a hot topic in engineering for many years. Many vibration control technologies including active vibration control, passive and semi-active vibration control are being used in practice to realize good vibration isolation performance of structures and mechanisms. Passive vibration control has the advantages of simple construction, low cost, easy maintenance and the absence of a need for external power. This thesis proposes and analyzes a new, passive vibration isolator design. Two kinds of passive control techniques used in the isolation structures adopted: (i) periodic structures (phononic crystal) which possess band-gap properties and (ii) nonlinear mechanisms with nonlinear stiffness characteristics. The band-gap property is a very significant characteristic of periodic structures in view of its structural and/or material periodicities. The elastic waves that can propagate in the structure in some frequency ranges are referred to as the pass band. However, sound and vibration propagation is forbidden for certain other frequency ranges, called stop bands. This property endows periodic structures with the potential to control wave propagation, thus helping to realize passive vibration isolation control. In this study, the spectral element method (SEM) is adopted for dynamic modeling of periodic structures. The interpolation function used in SEM is based on an Eigen function of the equation of motion that can provide exact solutions in the frequency domain. If the structure has uniform geometry and material properties, it can be considered as only one spectral element, which means that the element number and the degree of freedom (DOF) can be reduced significantly. High solution accuracy in the frequency domain and assuring the minimum DOF are the two main benefits derivable from SEM during a periodic structure analysis.