Power Flow Based Analysis of a Floating Raft Vibration Isolation System

A floating raft system (FRS) is typically used for vibration isolation of shipboard machinery. Earlier investigations have analyzed the effectiveness of this system using progressive receptance/mobility based approaches. In this paper, a vibration power flow based approach in the framework of component mode synthesis (CMS) is proposed. Both fixed-fixed and fixed-free CMS formulations are compared to understand their relative merits. The computational advantages of this method over the progressive receptance/mobility based analysis are highlighted. A simple two machine configuration on a FRS is investigated and the ratio of power transmitted to the foundation with the input power is used as performance index. From the simulations, it is demonstrated that by proper selection of upper and lower isolator spring stiffnesses, significant reduction in transmitted power can be achieved. The effect of phase difference between the excitations form the machines is also investigated.