Study On Fluid-Structure Interaction And Longitudinal Vibration Characteristics Of Ship Flexible Propeller-Shaft

With the development of large-scale ships and the improvement of the requirements of vibration and noise reduction,large-sided propellers and composite propellers are widely used,resulting in more and more obvious elastic effects of propellers,and the non-linear coupling between propellers and fluids is more complex.The elastic effect of propeller not only affects the hydrodynamic characteristics and structural performance,but also strengthens the coupling vibration characteristics between propeller and shaft,and affects the transmission characteristics of longitudinal excitation force.Based on the key project of the National Natural Science Foundation of China,this paper takes the propulsion shaft and propeller of a multi-purpose cargo ship on the Xijiang River as the research object,establishes an elastic propeller-shaft model,considers the elastic effect of the propeller,and studies the influence of the elastic effect of the propeller blade on hydrodynamic characteristics,propeller-shaft coupling vibration characteristics and transmission characteristics of excitation force by means of numerical simulation analysis method.The main contents and conclusions are as follows:(1)Fluid-structure interaction analysis of elastic propeller-shaft.A three-dimensional model of propeller and shaft is established.The two-way fluid-solid interaction calculation of propeller-shaft is carried out in uniform flow field and simulated wake field.The effects of blade elasticity on hydrodynamic characteristics,structural performance and axial excitation force of flow field are studied.The results show that the elastic effect of the blade increases the instability of the flow field,resulting in a larger fluctuation range of fluctuating pressure and longitudinal excitation force;the elastic effect of the blade has different effects on the open water performance under different advance coefficient;with the increase of the elasticity of the blade,the shape variable and strain of the elastic propeller increase,and the stress decreases.(2)Coupled longitudinal vibration analysis of elastic propeller-shaft structure.Three models of elastic propeller,mass point propeller-shaft and elastic propeller-shaft are established respectively.The longitudinal coupling vibration mechanism between blade and shafting is analyzed by modal analysis.On this basis,the effects of additional mass of fluid and flow field load on the natural vibration characteristics of propeller-shaft are analyzed.The results show that the longitudinal modal distribution of the elastic propeller-shaft includes the longitudinal modal modes of the elastic propeller and the mass point propeller-shaft respectively;the attached-water reduces the natural frequency of the structure,and the elastic effect of the blade weakens the influence of the attached-water;the flow field load as the prestressing force slightly increases the natural vibration frequency of the propeller-shaft,and the elastic effect of the blade weakens the influence of the prestressing force.(3)Analysis of longitudinal excitation force transfer characteristics of elastic propeller-shaft structure.The harmonic response analysis method is used to study the effect of blade elasticity on the longitudinal excitation force transmission path and vibration response,and the frequency matching design of the propeller-shaft structure is carried out.The results show that the umbrella mode of the elastic blade is reflected in the transmission path of the longitudinal excitation force,and the elastic effect of the blade enlarges or attenuates the longitudinal excitation force.The vibration of the propulsion shaft system can be effectively controlled by adjusting the umbrella mode frequency through the frequency matching design of the elastic propeller-shaft.