Study About Vibration Characters Of Marine Low-speed Engine And Valid Methods Of Vibration Reduction In Shop Trial

Before delivered to customer,it must be carried out a series of rigorous official shop trial in which vibration intensity is an important parameter,to make sure the main engine in a good condition.Comparing the condition in workshop with on board the base of workshop is softer and no top bracing is equipped with,so the connection stiffness on test bed is so low that the resonance happens in the range of main engine rotate speed,and sometimes excessive vibration result in official shop trial failure.This thesis focus on the vibration character of test bed system and analyzes the coupling loads,modes and dynamic behaviors by the means of multi-body dynamics(MBD)and Finite Element Method(FEM)and comparing the analysis result with the actual vibration measurements demonstrates if the analysis result is reliable.Further the resonance frequency of the test bed system and the effective vibration control method are attained.The research is carried out on the specified marine low speed diesel engine MAN 5S60ME.First,the multi-body and rigidity-flexible model of main engine is established including pistons,connecting rods,cross heads,crankshaft etc.,and meanwhile crankshaft is regarded as flexible component.Every guide force and main bearing load is calculated by inputting cylinder pressure to MBD,and they are simplified to the middle of two guide plates and two main bearing supports respectively.And then they are gotten as input parameters for vibration.Second,the FEM model is established for harmonic analysis and dynamic analysis,by which the system nature frequency is gotten,and this result shown that resonance happens in the 2nd mode.The vibration response at 25%,50%,75%,90%and 100%condition is attained by multi-body dynamic analysis.Based on the above outcomes,the scheme of adding tilting support on the basements is determined from several changes,and the resonant speed of the rig test system is 13 r/min higher than the current state.The result has achieved the desired goal of vibration control.