Use of Vibratory Power Flows to Assess the Effectiveness of a Vibration Isolation Design

Power flows from a vibratory machine to its mounting structure are of primary concern in passive or active isolation system designs. The total power flow is increasingly believed to be a more reasonable measure of the effectiveness of a vibration isolation system as compared with the traditional measure in terms of the force or displacement transmissibility. In order to calculate the power flows, one needs to know the reaction forces and the vibrations at the isolator locations on the mounting structure. In this paper, the process of determining the power flows through the vibration isolators is discussed for some commonly-used mounting structures which include platforms (reinforced plates), cylindrical shells and other complicated structures. The power flows through the rotational displacements or the bending stiffnesses of the isolators have been taken into account, which tends to become important at high frequencies. Numerical examples are given to show the modal and power flow characteristics of a composite vibration isolation system.