【作者】 梁兴雨；

【导师】 舒歌群；

【作者基本信息】 天津大学 ， 动力机械及工程， 2006， 博士

【摘要】 “能源与环境”是汽车和发动机工业在21世纪发展所面临的两大课题,解决发动机的排放和噪声污染控制已经成为发动机工业发展的最具有挑战性的问题,因此开展降低发动机噪声的研究具有十分重要的意义。本文通过理论、实验以及虚拟设计等多种手段对发动机噪声控制技术及声辐射预测进行了深入细致的研究,全文共分为上、下两篇。上篇是围绕发动机噪声控制技术展开的,主要论述的是噪声源识别及低噪声内燃机改进所进行的研究工作。在噪声源识别方面,为解决采用表面振动法最关键的声辐射效率问题,采用理论与实验相结合,进行了离散计算法内燃机表面振动声辐射效率研究。研究结果表明,离散计算法具有很高的精度,可以对受各种因素影响的内燃机零部件声辐射问题进行研究,同时这一研究成果也是噪声辐射预测的基础。通过采用单缸熄火法、表面振动速度法以及近场声压扫描法系统地对内燃机功能性噪声和表面辐射噪声识别后,将层次识别理论引入内燃机复杂噪声源识别中,采用基于相干功率谱分析的层次识别,建立了功能性噪声和表面辐射噪声之间的关系,对于功能性噪声的控制按照识别后的对应频率关系就可以找到对应的控制策略。在内燃机低噪声改进方面,通过对曲轴激励与机体表面振动间传递关系的研究,发现机体群部表面振动是由轴系三维振动激励导致的,控制轴系振动可以降低群部表面振动,同时改变曲轴到机体表面的振动传递特性也可能降低群部表面振动。而长期以来人们对车辆发动机更加关注曲轴的扭转振动,对曲轴的耦合振动还研究不多。本文根据瑞利法建立了扭纵耦合强迫振动模型,为探索内燃机轴系扭纵耦合强迫振动的计算方法提供了一种有益的尝试,采用谐次分析法对模型求解后,通过与实际测量所得到的结果进行比较发现,扭振和纵振与实际测量的结果在各主要谐次都保持相当的一致,表明所建立的模型能够被用来进行扭振减振器优化设计,通过对扭振系统进行参数灵敏度分析以及减振器设计参数的优化求解,得到了扭振系统的最优减振器参数,实测结果证明了设计的正确性。对内燃机薄壁件的降噪研究是从两方面进行的,一是进行了阻尼因子的减振机理研究,揭示了复合阻尼材料具有这一优点的原因,同时考察了频率、温度以及润滑油等因素对阻尼因子的影响;二是进行了结构刚度对减振降噪作用的研究,通过灵敏度分析找到了控制整体刚度的主要因素,并在发动机上进行了验证。最后通过对多台内燃机系统降噪研究工作的分析和总结,根据内燃机的激励源以及传递途径的规律,提出了低噪声设计工作的频率分布理论,为内燃机进行设计时指出具体的工作方向。下篇主要论述的是内燃机声辐射预测的研究内容,包括多体动力学主轴承载荷的计算,基于组合体的动力响应分析以及边界元声辐射预测等。在分析和合理简化的基础上,建立包括曲轴柔性体部件模型、活塞连杆组在内的刚性部件模型,并将它们综合建立了刚柔混合多体动力学分析模型。在ADAMS中仿真计算得出在发动机运转情况下考虑刚、柔两种曲轴得到的轴承载荷,结果发现柔体曲轴的自身变形及相邻气缸做功的叠加增加了曲轴的载荷,使工作状况更加复杂。在组合体模态分析的基础上,确定了组合体的边界条件及计算初始条件,通过对某柴油机进行有限元动力响应分析,得到了时域和频域的响应结果,并与实测数据的动态特性进行了对比,说明了所采取的建模技术及分析手段的正确性。噪声预测模型是基于边界元技术建立的,通过振动边界条件以及声辐射效率的导入后,采用直接边界元算法,计算得到了声辐射的声功率、近场及远场辐射声压和辐射效率等结果,为在设计阶段进行噪声预测评价提供了基础。更多还原

【Abstract】 Energy shortage and environment pollution are the two serious problems which faced by both the automobile and the engine industries. Together with the reduction of the pollution exhaustion, noise reduction is one of the highest challenging targets for ICE development. Aiming at the key problems of engine noise, this thesis presents a deep study of noise control and sound radiation prediction which integrate multiple methods, such as theory, experiment and virtual design. This paper is divided into two parts according to the main content.Aimed at the noise control technique, the former part of this paper mainly studied noise identification and low-noise engine design. In the aspect of the noise identification, sound radiation efficiency, the key issue of using the surface vibration technique, was investigated by the Discrete Calculation Method (DCM). Some conclusions can be drawn that the DCM which is in high precision can be used in any parts of ICE. These results are also the basis of noise radiation prediction which will be shown in the latter part. Some methods such as partial cylinder misfire, surface vibration technique and near field scan technique were adopted to identify the functional noise and the surface radiated noise of the engine. After that, Analytical Hierarchy Process (AHP) was applied to identify the complex diesel engine noise source. Based on coherent power spectrum analysis, a relationship between the functional noise and the surface radiated noise was established. The functional noise can be controlled by corresponding strategy which is related to surface radiated noise.In the aspect of low-noise engine design, the relationship between three- dimensional vibration of the crankshaft and surface vibration of the crankcase was studied. The result shows that surface vibration of the crankcase is induced by 3—D vibration of the crankshaft and the surface vibration of the crankcase can be depressed by controlling the vibration of the crankshaft and changing the transfer function. But for a long time, people have paid a little attention to the coupled vibration of crankshaft. This paper presents a model of coupled torsional-axial vibration based on Rayleigh differential method. Applied with a vector matrix, a single order or a whole system vibration can be analyzed. Compared with the experiment results, the calculated results are to be in agreement in main order. This is to say, the model can be used to design torsional vibration absorber. Through sensitivity analysis andparameter optimization design, an absorber was designed and an experiment verified its validity.The noise reduction research on the thin-wall part is carried out in two aspects: the first aspect is aiming at the reducing vibration mechanism of composite vibration-damping steel plates. The impact of frequency, temperature and lubricating oil on the damp factor are also introduced. The second aspect is the research on the mechanism of structure stiffness. Through sensitivity analysis, the dominating factor of mode stiffness was founded and the result was verified by test. According to the analysis and the summarization of the noise reduction tasks, the author puts forward a new design method based on principle of stimulation source and transfer path.The latter part of this paper is mainly on the prediction of sound radiation, the content includes load calculation of main bearing based on multiply dynamics, dynamics response of combined structure and prediction of sound radiation based on boundary element method (BEM).Used the multi-body dynamic analysis and considered the flexibility of crankshaft, the piston-crankshaft system can be simulated as a dynamic system consisting of both the flexible bodies and the rigid bodies. A numerical method is contributed to simulate the influence of the crankshaft on the main bear dynamic behavior. The result shows that the working condition of crankshaft becomes more complex if considering the flexibility of crankshaft which is the result of the deformation of flexible crankshaft.Based on joint parameter method, mode analysis is carried out to combined structure of a diesel engine. Applied with the exciting forces and boundary condition on the model, the time-history and frequency domain results can be obtained by performing transient dynamic FEM analysis using MSC/NASTRAN. The vibration experiment and mode experiment results verified the validity of the model.A prediction model of noise radiation is set up based on BEM and the sound radiation is calculated by direct BEM. The results of sound pressure level, sound intensity vectors and the contributing factors of main radiating surfaces could be obtained and this method provided a basis on noise evaluation during design period.更多还原