Guidelines for low-transmissibility semi-active vibration isolation

Abstract

The vibration transmissibility of passive vibration isolation systems is designed to be lowin the expected frequency range of the disturbances but is significantly higherat lower frequencies. The goal of semi-active damping systems is to reduce theisolation system transmissibility in the low-frequency range, without sacrificingperformance at high frequencies, by controlling the stiffness and damping propertiesof the isolation system via feedback measurements. In this study, experimentalimplementation of a semi-active damping system in a very small scale lightlydamped structure combines electrorheological (ER) fluids with a nonlinear analogfeedback circuit. Detailed modeling of the experiments enables the estimation ofunmeasurable internal forces in the ER damping wall, which, in turn, providesinsight into desirable stiffness and damping characteristics of semi-active dampingsystems. The guidance provided by these experiments is applied to the analysis anddesign of semi-active visco-elastic vibration isolation systems. The benefits of thecontrollable damping and controllable stiffness effects are compared in the frequencydomain through transfer function estimates computed from simulated response towide-band disturbances. Frequency response analysis of these numerical modelsfor different levels of isolation level stiffness, device stiffness, maximum devicedamping, and minimum device damping are presented to provide guidelines forthe design of low-transmissibility semi-active damping systems. The coupling ofcontrol experiments with numerical modeling illustrates that controllable dampingoffers more effective vibration isolation of base-excited structural systems andminimum device damping is the most dominant factor that controls the accelerationtransmissibility.