Study On The Bending-Axial-Torsional Coupling Vibration Of The Diesel Engine Crankshaft System

The diesel engine is the main source of ship vibration and noise.The vibration of diesel engine directly affects the smooth operation of the ship.With the development of the marine industry,marine diesel engines have the characteristics of complex structure and worse operating environment and frequently changing operating conditions,which put forward higher requirements on the index of shaft vibration.In the actual operation of a diesel engine,the crankshaft will generate three forms of vibration: bending,axial and torsion.These three forms of vibration are coupled with each other.Therefore,the bending-axial-torsional coupling vibration problems of the diesel crankshaft system is studied in this paper.This paper conducts the tasks including the establishment of three-dimensional coupled vibration dynamic equation of diesel engine crankshaft system,the verification of double crank test bench and the simulation calculation of three-dimensional coupled vibration characteristics of crankshaft system.Firstly,the single crank is simplified as a five segment straight beam structure.Based on the continuum vibration theory,the three-dimensional space field transfer matrix of the straight beam is derived.The point transfer matrices of coordinate transformation,lumped mass and elastic support is established by the conditions of displacement continuity and force equilibrium.The three-dimensional coupled vibration dynamic equation of the crankshaft system is constructed by using the multiplication of the transfer matrices.In this paper,the calculation methods of free vibration and forced vibration of the system are given.Based on the analysis of the exciting force,the load chart under the actual operation condition is given.The correctness of the theoretical method is verified by two simple examples.Secondly,according to the coupled vibration characteristics of the crankshaft,the physical model of the double crank was designed.The modal and response tests were performed on the double crank experimental bench.The modal test and the response test of the double crank experimental bench was tested.Through the comparison of theoretical calculation and experimental result,the correctness and feasibility of the theoretical method are proved.Finally,the finite element model of the crankshaft system was built by HYPERMESH.The free vibration and forced vibration of the diesel engine crankshaft system are calculated by ANSYS.The coupling vibration characteristics of the crankshaft system under the normal working condition are analyzed.The coupling vibration characteristics of diesel engine under the abnormal conditions of uneven ignition,single cylinder flameout and reverse ignition are studied.The results provide theoretical support for the design and vibration control of diesel engine crankshaft system.