VIBRATION ISOLATION: MOMENTS AND ROTATIONS INCLUDED

Abstract

By using simplified expressions, measures of vibration isolation efficiency, for any number of isolators situated between two structures, source and receiver, including all six degrees of freedom (DOFs) of motion can be predicted. These expressions can be used to calculate, for example, transmissibilities and power input and transmission to the receiving structure. Here, two DOFs of motion are considered to simplify the study of translations contrarotations. Generally, the structures are described by their receptance (mobility or accelerance) matrices and the isolators are described as massless springs with losses in order further to simplify the analysis. Two theoretical cases are examined. The first is a parameter study for a single isolator connecting different structures. The second example consists of two beams connected via two isolators to simulate the behaviour of a resonant machine mounted on a resonant foundation. Level errors, in the vibrational power transmitted to the receiving structure, are predicted for when rotational isolator stiffness values are not considered. The effects of disregarding the power, associated with rotational DOFs, from one structure to another via isolators can lead to over- and under-estimations of the total power transmission. Finally, some results from verification measurements, for two beams connected via two isolators, with a force excitation and a combined force-moment excitation, are presented. In order to obtain good agreement with the measurements, it was found necessary to include the mass of the isolator in the theoretical calculations.