Vibration Isolation

Abstract

The ability to isolate a structure or machine from the undesirable effects of applied motion (especially vibration) has wide application. Suspension systems are incorporated into large buildings to protect them from earthquake excitation, mountain bikes and vehicles in general are designed to minimize the transfer of unwanted accelerations from the terrain to the occupants, and sensitive equipment often needs to be isolated from ambient vibrations in the surrounding environment. This chapter explores the ways in which specifically nonlinear components can be utilized to advantage in vibration isolation in the context of steady excitation (Platus (1991); Rivin (2006); Virgin and Davis (2003); Virgin et al. (2008)). There have been other attempts to take advantage of nonlinearity in a vibration isolation context. A zero-spring-rate suspension system (Woodard and Housner (1991)) was developed in which a clever arrangement of (linear) springs acted together such that, under preload, they behaved in a nonlinear geometric sense. The system is essentially the same as a negative-stiffness mechanism described by Platus (1991) and developed commercially. In most design situations there is a trade-off between constraints, and in the case of vibration isolation, the springs need to sufficiently soft for dynamic transmissibility requirements but sufficiently stiff that they can provide static support. Other approaches have been studied by Virgin and Davis (2003); Winterflood et al. (2002); Zhang et al. (2004); and Carrella et al. (2006).