Multi-body Dynamics Modeling And Simulation Analysis Of Marine Diesel Engine

With the development of diesel engine in the direction of heavy load,high speed,supercharging and so on,the technical means generated by the new direction of development lead to the increase of load and vibration problem of diesel engine parts and components.Excessive vibration will cause parts damage of diesel engine and fatigue damage of hull structure in high stress zone.The noise caused by vibration will also worsen the working environment of crew.Therefore,the construction of virtual prototype of diesel engine,static performance simulation and dynamic response prediction of engine body become more and more important,and have important engineering application value.In this paper,taking 4L20 marine diesel engine as the research object,the rigid-flexible mixed multi-body dynamic model of crank and connecting rod mechanism under four working conditions is established,and the dynamic characteristics of crank and connecting rod mechanism are obtained by analyzing and comparing the simulation data under four working conditions.The excitation curve of the connecting rod and the engine body is output,and the diesel engine is simulated and analyzed from the static and dynamic aspect in order to predict its static and dynamic performance.In the static aspect,the static strength analysis of the connecting rod and the engine body is carried out,and the dynamic analysis of the modal and time domain dynamic response of the body is carried out,and the vibration characteristics of the main concerned points on the engine body are selected to analyze the vibration characteristics.The main research contents of this paper are as follows:(1)According to the two-dimensional drawing of diesel engine and the prototype which has been produced,the three-dimensional model of diesel engine is established by using the modeling software Pro/E according to the reasonable modeling principle.(2)The finite element model of diesel engine is established in Hyperworks,and the modal analysis of crankshaft and engine body is carried out,and the main modal modes and frequencies are obtained.The MNF file is output from the modal analysis results of the crankshaft,which prepares for the establishment of the rigid-flexible mixed model,and provides modal parameters for the dynamic response analysis through the modal analysis results of the engine body.(3)The rigid-flexible mixed model is established by using MNF file in ADAMS,and the excitation curve is output,which provides incentive data for static and dynamic response analysis.Compared with the excitation curves under four working conditions,the known bearing force is most affected by the burst time.With the increase of the working condition,the maximum lateral thrust position moves to the early stage of the work stroke.(4)Through the dynamic parameters outputted by the multi-body dynamic model,the static strength of the engine body and the connecting rod is analyzed under the main working conditions.It is concluded that the stress at the connection between the small head of the connecting rod and the rod body is easy to concentrate,and the stress at the connection between the partition and the body is large.The strength check is carried out to obtain the safety factor,which provides a reference for structural optimization.(5)Through the multi-body dynamic model to output the time domain curve of gas force,piston side thrust and main bearing excitation,based on these three kinds of excitation,the dynamic response analysis of the engine body is carried out,and the vibration velocity vector cloud diagram of the engine body is obtained.The analysis shows that the oil pan is the main source of vibration and noise radiation.The main concerned characteristic points on the body are selected,and the vibration law of the main concerned part is analyzed by vibration curve.