Research On Multi-dimensional Coupled Vibration Characteristics Of Ship Propulsion Shafting Under Propeller Excitation

In general,the most common power propulsion systems used in all types of boats include the engine-propulsion shafting-propeller.As the ship progresses,the system is subject to a variety of complex loads and produces vibration and noise radiation.Complex vibrations negatively affect the navigation performance and the stability of the shipborne equipment,more recently,noise radiation is a key factor affecting the stealth performance of submarines.By studying the structural vibration of propeller shafting and hull,the transfer characteristics of propeller vibration energy in propulsion shafting can be understood,which is of great value for controlling vibration noise and improving the mechanical navigation performance and stealth safety performance of a ship.Based on the general structure of ship propulsion shafting and the research status of coupling vibration of shafting and ship body at home and abroad,this paper combines the analysis of propeller excitation characteristics with vibration energy transfer analysis to study the multi-dimensional coupling vibration characteristics of propulsion shafting from torsion to longitudinal to bending.Then the transfer mechanism of vibration energy in multi-dimensional coupling vibration of shafting is discussed based on simulated working conditions,which provides theoretical basis for improving the design method of coupling vibration reduction between shafting and hull and optimizing the control strategy of vibration and noise.Specific work includes:Firstly,calculate the exciting force of the propeller bearing.The lift line method and the CFD method were selected to theoretically calculate the bearing force of the target propeller.The program of the lift line method was calculated using MATLAB software and the Fluent fluid simulation was applied to solve the open water performance of the propeller.After comparing the advantages and shortcomings,CFD method is adopted to select the sliding mesh model to simulate the periodic change of bearing excitation force under open water condition.The change of bearing excitation force in the frequency domain is obtained through fast Fourier transform,which is used as the excitation source of the input coupled vibration system.Then,the simplified kinematics model of the coupled oar-shaft-boat vibration system is established.Three kinds of vibration forms were distinguished to discuss the dynamic transmission relationship between the substructures of the propulsion shafting:longitudinal,bending and torsion.A set of interrelated differential equations of motion were constructed and solved by the wave method and the admittance method.The MATLAB calculation program was edited according to the derived equation.Based on the results of the above stages,The unit excitation and the calculated propeller excitation are respectively input into the computational analysis model of the coupling system in three directions.According to the output images,the characteristics of power flow transfer and energy transfer dissipation under three vibration modes are discussed emphatically.The power flow and energy of multi-dimensional vibration were added and 'distinguished into multiple frequency bands,and the influence of three kinds of vibration on the coupling vibration of the system is analyzed from the perspective of energy.