摘要
发动机作为一种动力机械,在国民经济生活中应用十分广泛。振动和噪声是评价发动机产品性能好坏的一个重要参数。随着各种振动噪声标准和法规的出台,以及人们对环境保护和振动噪声舒适性(NVH)的实际需求,结构振动与噪声控制己成为现代发动机技术的一个重要研究方向。在设计阶段了解发动机振动和噪声辐射水平,基于仿真模型进行整机声学优化,对确保发动机产品满足日益严格的振动噪声要求,提高产品竞争力,具有十分重要的意义。
本课题采用有限元法(FEM)、多体动力学(MBD)和边界元法(BEM)对发动机结构辐射噪声进行了系统研究,并以F168汽油机为研究对象,进行结构噪声预测,为结构修改优化提供参考依据。主要工作如下:
(1)查阅相关文献资料和理论知识,分析发动机结构噪声预测的现状,确定本课题的工作方案和技术路线;
(2)建立发动机的实体模型和有限元模型,进行模态分析。有限元模型的建立要根据实际情况,综合考虑计算精度与速度等因素,确定单元类型及尺寸。模态分析得到影响发动机振动噪声水平的固有频率和特征值,可用来验证有限元模型,也可作为以后结构修改的依据。
(3)在Excite软件中建立发动机的动力学模型,进行动力学响应分析。发动机有限元模型的自由度数非常大,利用子结构方法,通过矩阵缩减,可将自由度数目从几十万个减少到几千个,节省计算时间和资源。Excite将有限元法和多体动力学方法相结合,考虑结构连接之间的非线性因素,较为全面地分析了发动机的动力学响应。
(4)建立发动机边界元模型,并导入动力学响应分析的结果,利用噪声预测软件Sysnoise实现结构噪声预测,得到空间场点声压、声强、声功率和辐射效率等声学结果,并结合动力学响应分析的结果,对辐射噪声较大的部位提出结构修改及优化措施。
As a kind of power machinery, the internal-combustion engine is widely applied in the national economy. Noise and vibration is the important parameter for the engine’s performance. Along with kinds of rules and standards about noise and vibration, and the practical requirements for the environment protection and good NVH performance, the structural noise prediction has been an important aspect in the field of internal-combustion engine research. Knowing the radiant level of engine noise at the stage of design and doing the optimization of whole engine structural noise control based on simulative model have great significance to insure internal-combustion engine satisfying more and more strict requirement of engine noise and to promote the product competitive capability.
Based on the F168 gasoline engine, the study of engine structural noise prediction is done systematically by using Finite Element Method (FEM),Multi-Body Dynamics (MBD) and Boundary Element Method (BEM), and the research on the structural noise prediction of F168 gasoline engine is achieved, which can be as the basis and reference for the afterwards structural modification and optimization. In detail, the main work is as follows:
(1) At first, the actuality of the research about engine structural noise prediction is reviewed after referring to some literature and relative theory, and then coming up with the main scheme and technical path of this research.
(2) Creating the 3D geometry model and the FEM model, and the modal analysis is done. According to the practical conditions, the compromise between the computation precision and speed should be taken into consideration when creating the FEM model. The natural frequencies and eigenvalues can be computed from modal analysis, which not only can validate the FEM model but also as the basis for the structural modification and optimization.
(3) Create the dynamic model in Excite software and run the dynamic response analysis. The free degree number of the FEM model is very large, using the sub-structure method, the free degree number can be deceased from millions to thousands by matrix reduction, which can save the time and computer resources. Combined with the FEM and MBD, the nonlinear factor is taken into consideration and the dynamic response analysis is carried systematically.
(4) The boundary element model of F168 gasoline engine is created, and after the import of the results of the dynamic response analysis, the structural noise prediction is carried using the professional vibro-acoustic software Sysnoise. Then we can get the acoustic results such as sound pressure, sound intensity, sound power, radiation efficiency and so on. Combined with the results of dynamic response analysis, the measure of the structural modification and optimization is received.
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