Research On Vibro-acoustic Characteristics And Active Control Simulation Of Floating Raft Vibration Isolation System Based On Plate-shell Coupled Structure

Floating raft vibration isolation technology,which has been paid more attention,is currently a key technology for vibration and noise control in marine application.However,comprehensive researches on the floating raft vibration isolation system coupled with the sound radiation of hull structures for the purpose of sound radiation control are lack at the moment.In this paper,a floating raft vibration isolation system based on a plate shell coupled structure is investigated.A coupled mathematical model for the floating raft vibration isolation system and the structure acoustic radiation with arbitrary boundary conditions is established.The internal relationship between the transmitting law of vibration power flow and vibration characteristics of the elastic plate shell coupled structure is deeply studied.Then the influences of the physical parameters of the system structure,the number and relative phase relationship of vibration sources on power flow transmission is discussed.On the basis of that,the active vibration control simulation of the floating raft vibration isolation system for acoustic radiation control is carried out.The effect of different positions and actuating styles of actuators on the performances of the active floating raft vibration isolation system and the external acoustic radiation control is studied,which may be a reference for the active floating raft vibration isolation system design.An analysis model of the floating raft vibration isolation system based on a coupled plate shell structure with arbitrary boundaries is established by using the dynamic stiffness matrix method.Four types of coupling springs are adopted to simulate the coupled relationship between the elements and the general elastic boundary.Combined with the improved Fourier series-spectral geometry method,a unified function description of the displacements of each elastic structure component is realized.Then the natural vibration characteristics and modal analysis of the system are carried out.The feasibility and accuracy of the modeling method in this paper are verified by comparing with the numerical results of finite element method and the experimental results.The forced vibration responses and power flow transfer characteristics of the system are analyzed based on the established analysis model of the floating raft vibration isolation system installed on an elastic plate shell coupled structure with arbitrary boundaries.The corresponding relationship between the modes of the floating raft vibration isolation system with the total input power flow,the power flow transmitted to the elastic plate,the power flow transmitted to the shell is studied.From the point view of practical application,the effects of key system parameters such as the stiffness and damping coefficients of vibration isolators,structural damping coefficients,masses of the upper equipment and intermediated raft on the vibration transmission characteristics of the system is analyzed by combining the natural vibration characteristics of the system.In addition,the influence of the number of vibration sources,the relative phase relationship between the excitations on the power flow transmission is investigated.The relationship between the optimal phases and the number,exciting frequency and amplitude of the vibration sources is obtained,in which the power flow transfer is minimizedBased on the coupling relationship between acoustic radiation modes of the shell in the system and the external acoustic radiation,the corresponding relationships between the external radiated sound power of the shell and the input power flow of vibration sources,power flow transferred to the basic elastic plate,power flow transferred to the shell are studied.The internal relationship between vibration transmission mechanism and sound radiation,power flow transmission and external radiated sound power is clarified.By combining with the influence of the physical parameters on the sound power radiated of the system,the influence mechanism between vibration transmission of the floating raft vibration isolation system and the sound energy radiated into the far field is revealed.An active vibration control model of a floating raft vibration isolation system based on a plate shell coupled structure is established.Three control strategies,including the minimum total input power flow of the floating raft vibration isolation system,the minimum square of the vibration velocity of the elastic structure,and the minimum shell radiated sound power,are adopted and active control simulation researches aimed at controlling external acoustic radiation are carried out.The influences of actuators installation positions and actuating styles on acoustic radiation control under different control strategies are discussed,which will provide a reliable theoretical foundation and scheme references for the active floating raft vibration isolation system design.