Research On The Vibration Modeling And Simulation Of The Marine Two-stroke Diesel Engine And The Propulsion Shafting

The large low speed two-stroke diesel engine as the main power plant on ship is the key exciting source of ship vibration and noises. So, research and control on the vibration and noises are most significant. Based on the multi-body dynamics, finite element method and finite differenc method, vibration characteristics of the whole engine and propulsion shafting are studied systematically.Firstly, math model on the flexible multibody dynamics is built. Based on the Newton-Euler equations and floating frame coordinates, the degree of freedoms on componets are reduced with component mode synthesis method (dynamic condensation technology). The math models on them are set up. Numerical calculation on a single-cylinder engine is done by the Newmark, HHT and BDF method respectively. The results show that BDF method is preferred to calculate the flexible multibody dynamics of the large and complex marine diesel engine.Secondly, finite element model of the whole engine is established. According to the features of the large marine diesel engine whose components and combined structure are so big and its finite element model can not be proved, based on the finite element principle, when the natural mode of the single component doesn’t change by increasing the element number any more, the model is acted as a reference to simplify the model. In view of the cone model and the contact theory, combined structre connected by the bolts is jointed by beam elements and spring elements in the finite element formulate, which is verified by the modal test. Based on the above two steps, the finite element model of the engine block and the shafting are built and their mode are analyzed.Thirdly, the math model on the whole engine vibration of the large marine diese engine is set up and the calculation about its vibration response is done, based on the test-bench. The FEM of the large marine diesel engine is reduced with dynamic condensation technology. The components are connected by the nolinear spring-damper (NONL model). The flexible multi-body dynamics model on the whole engine is developed and its calculation is done by BDF method. It shows that3-D coupled model on the whole flexible eninge block and the flexible shafting can reveal the vibration characteristcs of the engine block more allsidely. According the inverse transformation of the condensed model, the displacement, velocity, acceleration and stress distribution of the engine block and the shafting could be got. Through comparion with the experimental results on the test frame, the possibilities of the model and the calculation method are verified.Fouthly, the elastic-hydro-dynamic mixed lubrication model is used at the main bearings and the whole engine vibration is compared under the NONL, EHD and TEHD model. The NONL model is not enough for the shafting. The elastic-hydrodynamic fixed lubrication model is introduced to the main bearings based on the Reynolds equation and Greenwood-Tripp contact model. The whole engine vibratin is done with EHD model (without temperature effect on the oil film and the bearings) and TEHD model (with) respectively by MBD, FEM and FDM method. The comparion is also made with NONL model. It is found that the order of calculation efficiency is NONL, EHD, TEHD model in trun, the order of calculation precision is TEHD, EHD, and NONL model. Therefore, the NONL model is best if only for the engine block vibration and the EHD model is best if for the whole engine vibration.Finally, the vibrations of the whole6S50MC-C marine diesel engine and propusion shafting are calculated, which are installed on the39000DWT oil tanker, based on above researches. Firstly, the vibration is developed under the in-line shafting without tuning wheel and axial vibration damper. Secondly, the shafting alignment is done with three-moment method and the bearing deflection is got. The vibration is studied considering the rational shafting alignment based on the bearing deflection. The vibration comparions of5models each other are finished. Also the effect of the double hull stiffness, transverse stiffness and bearing clearance on the vibration is done. With the TW-AVD-ALN model, the vibration properties of the whole engine are analysed under different speed. The results show that the vibrations are coupled each other among the engine block, the shafting and boundary conditons. At last, through comparion with the torsional vibration values measured on the ship, the model and calculation method are proved, which would lay foundation for optimization control on the whole engine vibration. The method has engineering value to some certain degree.