Fuzzy Logic Controlled Semi-Active Floating Raft Vibration Isolation System

Abstract

A warship may be detected in hostile waters because of its unique acoustic signature. A typical two-stage passive vibration isolation system used on ships and submarines to isolate onboard machinery is the floating raft isolation system. The passive isolation system, though robust, may result in substantially high transmission of forces to the foundation at certain excitation frequencies, adversely affecting the ship's stealth. This paper highlights the results of a simulation study aimed at the design of a semi-active floating raft vibration isolation system with the objective of mitigating the acoustic signature of a warship by minimising the transmission of forces, resulting from operation of onboard machinery, to the foundation. A semi-active control scheme with variable damping has been proposed for the floating raft, the variable damping being achieved by means of an electrorheological (ER) damper. A fuzzy logic controller has been designed to achieve the best isolation effect by analysing the characteristics of the frequencies in the excitation signal. The designed semi-active control system is subjected to a time-varying signal, each time-segment corresponding to a different optimal damping ratio. The MATLAB simulation results indicate that the proposed fuzzy logic control method is more effective in vibration isolation than the passive method thereby indicating the potential of the designed semi-active control system in reducing a ship's acoustic signature.