Analysis For Dynamic Characteristics And Shocking Response Of A Diesel Engine Crankshaft System

The strength design of crankshafts is an important part of diesel engines design, in which the vibration of crankshafts should be taken into account, because the vibration make an impact of the strength design to a large extent. The vibration of crankshafts includes torsional vibration, bending vibration and axial vibration, which amplifies the strength of crankshafts and threatens the normal operation of diesel engines. Especially, the vibration greatly harms the reliability of crankshafts if the exciting force frequency is equal to the structural frequency. For ship diesel engines, crankshafts are long, and the engine speed corresponding to the torsional common vibration frequency is always in the area of the working speed. So the common vibration is awfully possible to happen. torsional common vibration cause large amplitude, which may affect the normal working of the camshaft and deteriorate the timing of intake and exhaust, what is more, break the crankshaft to cause accidents. Especially, diesel engine crankshafts are instantaneously loaded by shocking wave and awfully possible to break down, in the conditions of non-contact underwater explosion. Therefore, it is necessary to carry out the dynamic response analysis of crankshaft system in underwater explosion conditions.Simulation models are created, and the diesel engine shafting dynamics and crankshaft strength analysis are also carried out, in both normal conditions and underwater explosion conditions, in the paper. Specifically, the paper consists of the following content.Firstly, the three kinds of 16V240diesel engine shafting models according to different simplified degrees are created and the model analysis is carried out, and the results of the three kinds of models are contracted. The shaft & plate model and the simplified model are created, the free vibration calculation and the forced vibration calculation are carried out respectively by the Holzer Table Method and the energy law, based on the shafts& plates model. And both the results of the vibration calculation and the results of model analysis are contracted to the testing results.Secondly, shafting condensed models used for the following multi-body dynamics model are established, and the multi-body dynamics model is also created. The multi-body dynamics analysis of the diesel engine shafting, which consists of bearing force, torsional displacement of the shafting free end, orbital path of main bearings, and so on, is implemented. Furthermore, the fine single crank-beams models used for crankshaft stress calculation are also created, and the crankshaft transient stress calculation and the fatigue analysis are carried out based on the single crank-beams models.Finally, the idealistic models of non-contact underwater explosion shocking load are created, specifically, according to the typical shocking wave features, three shocking wave models as follows: half sine wave shock, saw tooth wave shock and symmetric trapezoidal wave shock are established. And load these shocks onto the dynamics model to conduct the shafting multi-body dynamics analysis, the crankshaft transient stress calculation and the yielding strength analysis. What is more, the shocking results are contracted to the results in normal conditions, and the analysis that effect degrees of non-contact underwater explosion shock, acted on the diesel engine crankshaft system, is carried out.