Development of linear and nonlinear isolation techniques for passive and semi-active applications

Vibration isolators play a pivotal role in a range of industries from construction to transportation. During the past century the design and optimization of the performance of vibration isolators has attracted enough attention that several criteria have been defined to quantify the performance of the isolators. In general, the performance of an isolator depends on the shape and characteristics of the component materials. Conventional methods of isolation, based on passive linear systems, are insufficient in many cases. Although nonlinear passive elements have improved the performance of isolators, the nonlinearity in such systems has adverse effects such as instability and chaos, which should be carefully examined. Semi-active systems significantly improve the performance of the isolator over that of passive systems. However, these systems require a well designed control algorithm for optimizing the resistive force depending on the system excitation.; In this research we have defined a Root Mean Square (RMS) cost function, based on the frequency response of the isolator. With this standard of measurement, the optimized parameters of linear system are obtained. These parameters are also optimized for shock and transient inputs that have been usually ignored in traditional approaches. The design of nonlinear systems is derived from that of an optimal system for the study of performance improvement. The RMS optimization method is adopted to study the performance of piecewise linear and cubic nonlinear systems in detail. Moreover the transient response of each type of nonlinearity is compared to that of the optimal linear system.; Finally, the behavior of a linear MR damper is investigated in detail and several analytical models are offered. The research of this thesis is concluded by measuring the performance of the linear MR damper to that of the linear isolator system.