Vibration-reduction Analysis Of Ocean Fishing Vessels Based On Numerical Simulation And Vibration Measurement

Ship vibration may cause not only the damage or malfunction of various equipment on board,but also the fatigue damage of some structures.Also,the noises will affect the physical and mental health of the crew on board.Therefore,the vibration of ships has attracted more and more attention.In this paper,the problem of violent vibration and intermittent roar of an ocean fishing vessel,when the main engine reaches a certain speed,is analyzed.Based on the numerical simulation and full-scale test,a ship vibration reduction scheme is proposed and verified.Firstly,the dynamic characteristics of the whole ship structure are analyzed.The threedimensional model of an ocean purse seine fishing vessel is constructed by finite element software.Considering the mass of the entrained water and the main ballast on the vessel,the modal analysis of the vessel is carried out to analyze the dynamic characteristics of the whole ship structure.Secondly,the forced vibration response of ocean fishing vessel is analyzed.First of all,the damping and boundary conditions are selected.Then the main excitation is determined as the fluctuating pressure of propeller,the bearing force and the excitation force of main engine.The representative nodes are chosen to calculate the transient response.And the characteristics of vibration acceleration are analyzed.The peak value of acceleration and vibration criterion are compared at last.Thirdly,the real ship test of ocean fishing vessel is carried out.The vibration acceleration of each point is measured at different rotation speeds of the main engine.Then the former 10 modes of acceleration amplitudes and their frequencies are obtained by FFT analysis.By analyzing the frequency characteristics of the ship at different speeds,it is found that the main reason for the excessive vibration of the ship is the propeller excitation force.Finally,the analysis and verification of vibration reduction of the ocean fishing vessel are carried out.According to the main causes of ship vibration,the corresponding vibration reduction measures are put forward,including installing a guide plate and strengthening the stern structure.The ship is tested again after the vibration reduction transformation.Compared with the results before the modification,it is found that the large amplitude vibration of the ship has been well controlled,which shows that the modification scheme is effective.In a word,the main cause of ship vibration is analyzed by numerical simulation and vibration test in this paper.By testing and verifying the test results of the ship after transformation,an important reference for vibration analysis of fishing vessels is provided.