Random Vibration Of Propeller-shaft System Induced By Inflow Turbulence

With the development of shipbuilding industry in china,as the main propulsion device of the conventional submarine,the excitation force of the propeller increases sharply with the increase of propulsion power.The vibration caused by the propeller is one of the factors hindering the development of the submarine.It is of great significance to describe the unsteady thrust of the propeller in the turbulence field.Based on the theory of unsteady force spectrum and random vibration theory,the unsteady thrust of the submarine propeller shaft system in homogeneous turbulent flow field is calculated,which provides an insight to the vibration and noise reduction of the skewed propeller in the submarine.The main work and conclusions of the research includes:(1)The calculation process of this paper is as follows: Firstly,the propeller is divided into many strips along the radial direction.The unsteady force spectrum of the homogeneous turbulence acting on the propeller surface is calculated by the correlation analysis method,and the spatial distribution of the pressure spectrum is obtained.And the pressure spectrum is mapped to the point of each strip as the input of the system.Then the model is divided into finite element in ABAQUS and the vibration modes are extracted.Finally,the elastic vibration response including the unsteady thrust is obtained based on modal dynamics.The advantage of this method is that resonance effect at low frequencies due to the input of the system and the vibration mode of the system could be calculated precisely.(2)The influencing factors of the input force spectrum includes: integral length scale,tunnel velocity,turbulence level and rotation speed.The larger the integral length scale is,the more sharply the force spectrum decreases.The smaller the tunnel velocity is,the more pronounced the unsteady thrust is.The higher the turbulence level is,the higher the amplitude of the unsteady thrust is.Increasing the rotation speed of the propeller could increase the unsteady thrust and there could be more resonance peaks.(3)Taking the Sevik propeller as an example,the influence of elasticity and damping on the random vibration response of the system is analyzed by changing the system dynamics parameters.It is showed that the greater the elastic modulus of the shaft system,the greater the vibration response of the system;the greater the elasticity of the propeller,the smaller the response of the system.Increasing the damping of shaft and propeller,and the vibration amplitude caused by the corresponding resonant frequency could be reduced.However it has little effect on the vibration response at non-resonant frequencies.(4)The response of the skewed propeller is calculated in the same method.It is found that the response characteristics are similar to Sevik propeller.The difference is that the unsteady thrust of the Sevik propeller is higher than that of the skewed propeller,and the peak of the Sevik propeller is more pronounced.According to the vibration response characteristics of the propeller shaft system,it is useful to vibration reduction by decreasing the elastic modulus of the shaft material,increasing the elastic modulus of the propeller material and increasing damping of the system.