Research On The Diesel Engine Vibration And Acoustic Modeling And Simulation Techniques Considering Multifold Excitation Sources

With the development of high power density diesel engines, its work speed and performance per litre are gradually improved, the problem of vibration and noise of the engine structure has recently gained the increasing attention and it will be become an important technical index in the flow of the engine design. The analysis of engine excitation loads was base of the study of engine vibration and noise, and it is an important guarantee for the analysis results of credibility. In this paper, we analysis the excitation source in the engine working process. Combined the experiment we studied the engine whole structure vibration and noise excitation loads forming principle and numerical simulation method. By means of the built engine structure dynamic model, research the dynamic characteristics of the engine structure and the structural radiated noise was accurately prediction analysis. The acoustic optimization analysis was used to the main structure of the engine. These are described in detail in the following:According to the engine bench test results, used the modular decomposition method to establish the engine performance simulation model, the combustion performance and the inlet and exhaust system flow characteristic parameters of the engine were analyzed. Bu use of the three-dimensional fluid dynamics theory the fluctuating pressure of the engine inlet and exhaust pipe was calculated. The Lighthill acoustic analogy theory was used to analysis the engine intake, exhaust pipe dipole source pressure and frequency characteristic.By use of the dynamic substructure condensation theory analysis the nonlinear damping spring element and hydrodynamic lubrication of oil film supporting effect on the engine crankshaft system main bearing load. At the same discussed the main bearing orbit, oil film pressure, film thickness of lubricating characteristics and the crankshaft torsional vibration characteristics. The crankshaft main bearings dynamic excitation load distribution and the dynamic excitation peak load characteristics.According to the temperature field test information, using the multi-physics fields coupling theory, analysis the deformation of the structure of the engine combustion chamber component. Through the two order piston motion analysis model, analysis the piston rattling motion and discussed the influence law of the engine cooling water jacket control parameters affected the piston rattle force。By means of multi mass modal and multi body dynamic modal,studied the engine valve mechanism component motion under the multi factors. Using collision contact theory, a numerical calculation model was established for valve seating force,and the contact stiffness and mechanical index was determined. At the same time, the relation between the peak valve seating force and the valve working parameters, such as the recovery factor, valve quality, valve sitting velocity response.Base on the structural experimental test information,built the complicated engine dynamics simulation model with the correlation analysis method. Thought the calculation results, the intake and exhaust pipe structure change the whole structure of the engine modal density. modal response function peak shifted to left and the highlighting peak mode number increased. in the range of 400~600Hz, modal has high participation contribution. The high frequency vibration area is mainly concentrated on the engine intake and exhaust pipe, and the valve cover and the lower part of the body of the oil pan.By using BEM/FEM acoustic coupling analysis method,coupled with the intake and exhaust pipe gas fluctuation pressure and the dipole source, the whole engine radiation field prediction was analysis. Combined with the components of acoustic contribution, as the main noise radiation part of the engine, we optimized oil pan acoustic structure parameter, in order to reduce the whole engine sound radiation level.