A STUDY ON DAMPED VIBRATION ISOLATION SYSTEM

Abstract

In engineering works and factories, usually engines, compressors and other such vibration generating machines are installed. The unbalanced forces generated by rotating and reciprocating parts of these machines are quite severe. Effective, vibration isolation is required for proper functioning of machines and their foundations. Conventionally the isolators are designed considering infinite rigidity of the supporting ground. Since the soil possesses finite rigidity, a two degree mathematical model has been proposed, for a realistic study. In this model both the stiffness and damping in soil has been considered. Parametric studies have been carried out on both two degree undamped and damped mathematical models. In undamped model effect, of stiffness of isolator, stiffness of soil and mass of machine has been studied. In damped model the study incorporates the effect of increase in damping along with the effect of above parameters. It has been found that usually the isolators are designed on the basis of the assumption that if the natural frequency of the system is appreciably lower than the operating frequency of the machine, the isolation system will be effective. Present study indicates that a system designed on this basis may prove useless if the response of supporting ground is neglected. Moreover, in case of an undamped system the machine has to sustain very large forces, though only for a short duration, during its starting. If the machine is vary sensitive, additional damping is necessary. The present study indicates that damped systems transfer more force than undamped system. Therefore neglecting the damping naturally present in the system will lead to erroneous design of foundations. Hence in the present work apart from parametric studies, comparative study of damped and undamped systems has also been emphasized.