Research On Alignment Of A Propulsion Shafting System And Offset Control Via An Active Stern Support

Propulsion shafting system is an important part of the power system of vessels.Installation state of the shaft,deformation of the hull,wearing of the bearings and other factors may change the position of the bearings,resulting in the deterioration of the working condition of the stern bearing and the shaft,and may leading to the abnormal vibration of the shafting system.At the same time,the stress of the aft bearing can be reduced and evenly distributed through the reasonable change of the bearing offset,so that the working performance and life of the propulsion shafting system can be improved.Aiming at the above problems,the model of the propulsion shafting system,the influence of the misalignment of the aft bearing on the shafting system characteristics and the offset control of the active stern support were mainly focused in this paper.The main contents of this paper are as follows:?1?Research on the equivalent stiffness of the stern bearing of the propulsion shafting system.The shaft-bearing nonlinear contact model of the propulsion shafting system was established using the finite element method.According to the results of the gravity solution of the model,an equivalent method of static stiffness of the rubber stern bearing was proposed.Compared with the single-support equivalent method and the multi-supports equivalent method,this method can be more accurate to calculate the deformation of the propulsion shafting system.Based on the static stiffness equivalent method,the equivalent method of dynamic stiffness of the rubber stern bearing was proposed.The dynamic stiffness is about 1.5² times of the static stiffness of each support,which is in agreement with the dynamic coefficient of NBR.?2?Semi-analytical model of the propulsion shafting system was built.Based on the Timoshenko beam theory,the propulsion shafting system was regarded as a multi-span beam with multiple concentrated mass and elastic support.The semi-analytical solution of the natural frequencies and mode shapes of the lateral vibration and longitudinal vibration of the shafting were derived using the modal shape coefficient conversion matrix method.The orthogonality of the mode shapes of multi-span Timoshenko beams with multiple concentrated and elastic supports was derived.Based on the orthogonality of the vibration mode,the mode superposition method was used to solve the lateral and longitudinal steady-state forced response of the propulsion shafting system.The comparison between the semi-analytical model and the finite element model shows that the semi-analytical model is effective and accurate.?3?Research on the effect of the aft bearing misalignment on the characteristics of the propulsion shafting system.Based on the semi-analytical model and the finite element model of the propulsion shafting system,the changes of the static behavior and the dynamic characteristics of the shafting system were studied under the conditions that the aft bearing was raised 0.6mm,the aft bearing was lowered 0.6mm and the aft bearing was tilted 1×10^-3 rad.The results show that compared to the condition that the aft bearing was lowered,when the aft bearing was appropriately raised or tilted,the rotation angle of the aft shaft can be smaller,the bearing deformation and stress distribution can be more uniform,the maximum stress of the bearing can be reduced,and the vibration of the hull transmitted from the bearing can also be suppressed.?4?Kinematic analysis,dynamic analysis and experimental study of the active stern support of the aft bearing.The kinematics analysis of the active stern support was carried out,and the Jacobi matrix of the active stern support structure was solved,which provides a theoretical basis for the stern bearing offset control.The dynamic model of the coupling system of the active stern bearing and the propulsion shafting system was established using the frequency response synthesis method,and the influence of the active stern support on the dynamic characteristics of the whole system was studied.The experimental system of the active stern support was built,and the experimental study on the active stern support were carried out.The result shows that the vibration on the surface of the shell can be reduced obviously when the active stern support is used to control the offset of aft bearing.