Vibration Control Of A Floating Raft Based On Flexible Hull Structure Using Synchrophasing And Active Isolation

In order to provide authentic and reliable basis for the active and passive vibration isolation design of equipments on floating raft in ships,a floating raft vibration isolation system mounted on a large flexible hull structure was built up.Experimental modal test combined with the finite element analysis was carried out in order to find out its dynamical behavior,and the acoustic transfer function was also introduced.The transfer function from any place of the floating raft to sound radiation outside the hull structure were calculated with acoustic BEM,and the mathematical model for predicting of floating raft system vibration transmission and radiation noise was developed.Based on the mathematical model,synchrophasing,optimization of sensors and active vibration isolation were deeply investigated in this dissertation,and the main work was described as follows:Based on the Propeller Signature Theory(PST),synchrophasing control technology was introduced in flexible floating raft vibration isolation system for the first time,and the solving approach of PST was improved.Relative phases between each machine were optimized in order to minimize the summation of squared acceleration responses of the hull structure by using genetic algorithm.On one hand the simulation of synchrophasing was studied in detail combined with the acoustic transfer function.On the other hand counter-rotating eccentric mass which was driven by four phase asynchronous motors were used to simulate equipments on the floating raft,and based on the servo-control theory experimental study of synchrophasing was investigated.The theoretical and experimental results show that compared with active control,no additional actuators and corresponding control system were necessary for synchrophasing control,only adjusting the relative phase between vibration equipments can achieve the purpose of vibration and sound radiation reduction,and synchrophasing control was a simple and effective method for controlling vibration transmission and sound radiation from the hull structure.Aiming at the optimization of sensors’ number and locations in active control of structural response,an existing optimization method was improved.The method can effectively reduce the number of sensors and find their relevant optimization locations.Then the extent of vibration reduction maintains almost the same as before,but the control scale of hardware can be reduced distinctly.The optimization procedure was resolved with the genetic algorithm.In order to eliminate the coupling effect between different control channels in active control system,FXLMS algorithm was applied.Four hydraulic actuators were placed between the floating raft and the hull structure,and the error signals were used as feedback signal for each actuator simultaneously,while using the improved integer coding genetic algorithm,the experimental research of active vibration isolation of multiple excitation frequencies and synchrophasing control was studied.Experimental results show that the extent of vibration reduction of 4 error signals maintains almost the same as that of 22 error signals,moreover,sound pressure of the 10 monitoring microphones were effectively suppressed,and the control effect of synchrophasing also can be improved.