Multi-body Dynamics Analysis Of Internal Engine Crankshaft System In Marine Vessels At Swing Conditions

The crankshaft system,as an integral component of marine power systems,plays a vital role in the performance of the entire engine under oscillating conditions.In this thesis,focusing on the crankshaft system of marine engines,the lubrication characteristics of supporting bearings,modal characteristics of the crankshaft,and dynamic analysis of the multi-flexible body crankshaft system bases on ADAMS are investigated.The main research work and content are summarized as follows:(1)After analyzing the geometric structure and operating conditions of the radial sliding bearing,a nonlinear oil film force model is established.The finite difference method is employed to calculate and analyze the oil film thickness and pressure of the bearing under different eccentricities and swing angles.The nonlinear variation of the oil film force with swing angle and eccentricity under oscillating conditions is obtained.(2)Corresponding motion differential equations are established based on the oscillating conditions of the dynamic system.The Newmark integration method is utilized to compute the dynamic response of the system under oscillating conditions.The results indicate that with increasing rotational speed,the system exhibits nonlinear response characteristics such as periodic and quasi-periodic motion.(3)Based on the modal analysis theory,free modal analyses are conducted on the parameterize one-dimensional crankshaft and three-dimensional solid crankshaft using APDL.The effective dominant modes and corresponding frequencies up to the 6th order are obtained.The variation patterns of the modes between the one-dimensional and three-dimensional crankshafts are generally similar.However,due to the differences in geometric configuration,material properties,boundary conditions,mass distribution,and equivalent cross-sections between the one-dimensional beam element crankshaft and the three-dimensional solid crankshaft,there exist certain discrepancies in the analysis results.(4)A multi-rigid body model of the three-dimensional crankshaft system is established using ADAMS,and the crankshaft is made flexible.Based on the actual operating conditions of the engine crankshaft system,constraints and loads are set in the ADAMS system model for the analysis of torsional,radial,and axial vibrations of the crankshaft.The results demonstrate that the torsional vibration of the crankshaft,radial vibration of the main journal and crankpin exhibit similar variation patterns of "sub-harmonic resonance" with increasing swing angle.Additionally,the axial vibration of the crankshaft will experience "multiple harmonic resonance" with increasing swing angle.