Study On Coupling Between Dynamic Bearing Load And Vibration Of Shipping Propulsion Shafting

The marine propulsion shaft is the power transfer device that connecting the main engine and the propeller.With the trend of ship's growing large,the shaft and propeller diameter are increased in order to meet the demand of larger torque transmission,the rigidity of the shaft is increased relative to the hull,which makes the deformation of the shaft axis increase,resulting in more intense changes of the bearing load and reduced reliability of the shaft.It is almost impossible to measure the actual load of the bearing in the ship,but the shafting vibration detection is relatively simple,and the bearing load variation directly affects the shafting vibration and bearing vibration.Therefore,it is necessary to study the coupling relationship between the bearing load variation and the shafting and bearing vibration,and to explore the possibility of identifying bearing load variation by vibration detection.The coupling relationship between the radial position variation of bearing and the bearing load variation is analyzed.Firstly,the shafting test bed was discretized using mass centralized method.Secondly,establish the transfer matrix of shaft stress and deformation by transfer matrix method,and calculate the load influence coefficient matrix combining with the free boundary conditions of both shaft ends.The source of the propulsion shaft bearing vibration is analyzed and summarized.Based on the hydrodynamic lubrication theory,the oil film dynamic parameters under different loads are calculated to analyze the influence of bearing load variation on oil film stiffness and damping.A mathematical model of rotor-oil film – bearing system is established,numerical simulation of step load and sine load is carried out respectively and solved by the Runge-Kutta method to analyze the effects of different types of load variation on the rotor and the bearing vibration,the step load corresponds to the static displacement of the bearing,and the sine load corresponds to the dynamic displacement of the bearing.The finite element model of the shafting test bed is established in the ANSYS software,change the radial position of the bearing according to the bearing load variation,considering the change of oil film stiffness at the same time,that is,changing the stiffness of the corresponding spring element,this finite element model is used to study the influence of the bearing load variation on the natural frequency of the lateral vibration of the shaft system.The data acquisition system is set up on the shafting test bed to extract the time domain characteristic parameters of the shaft lateral vibration and the bearing vibration,which are used to verify the results of the numerical simulation,and the effects of load changes on these time domain parameters are further analyzed.The power spectrum analysis of the bearing vibration signal and the order analysis of the lateral vibration signal are carried out to further study the influence of the load variation on the frequency distribution of the two vibration signals.The shaft centerline orbit is synthesized using the lateral vibration signal and purified,some parameters are proposed to characterize the shape of the shaft centerline orbit,and the effect of load vibration on these characteristic parameters are analyzed;the time domain analysis and order analysis of torsional vibration are carried out to study the effect of load variation on torsional vibration.