A Study of the Effects of Rotational Terms in the Power Transmission through Vibration Isolation Systems on Beam-like Structures

Abstract

The performance of a multi-dimensional vibration isolation system can be evaluated in several ways, one of which is to employ the concept of vibration power to define the isolation efficiency. It is especially useful in the high frequency range where the radiation of noise from the receiver structure is concerned. The idea is basically simple to understand but rather complicated to formulate and apply in practice. For an accurate estimation of power flow especially over a high frequency range, it is well known that, in principle, rotational motions should be taken into consideration together with translational motions at the isolator locations. In reality, however, power transmissions related to rotational terms are often neglected mainly due to difficulties in the instrumentation. In this paper, the effects of neglect of rotational terms in the power estimation are investigated for several different approximation methods; the mobility approach, impedance approach, and force and velocity approach. Since it is not possible to derive formulas analytically of the vibration power for structures of finite dimension, numerical simulations for a beam-like structure are presented to investigate the characteristics of the distortions in the power estimation induced by neglect of the rotational terms for each approximation approach.