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1、外文资料翻译A three-dimensional finite element approach for predicting the transmission loss in mufflers and silencers with no mean flowAbstractA three-dimensional finite element method has been implemented to predict the transmission loss of a packed muffler and a parallel baffe silencer for a given freq
2、uency range. Iso-parametric quadratic tetrahedral elements have been chosen due to their flexibility and accuracy in modeling geometries with curved surfaces. For accurate physical representation,perforated plates are modeled with complex acoustic impedance while absorption liningsare modeled as a b
3、ulk media with a complex speed of sound and mean density. Domain decomposition and parallel processing techniques are applied to address the high computational and memory requirements. The comparison of the computationally predicted and the experimentally measured transmission loss shows a good agre
4、ement. 2005 Elsevier Ltd. All rights reserved.IntroductionSince numerous physical phenomena include a form of wave propagation, there has always been an interest in understanding and modeling wave propagation and its interactions with other physical phenomena.In general, there are three concerns in
5、developing an appropriate model for a physical phenomenon: the complexity of the actual physical phenomenon, the minimum required accuracy and lastly, the available analytical, experimental and computational resources. Due to the fact that phenomena involving wave propagation can potentially be comp
6、lex and require high accuracy, this constraint in computational resources limits the models to address rather simple problems only. However, in recent years, swift advances in the computational capacity of microprocessors and lower prices for memory have created a new perspective for developing othe
7、r powerful models, such as finite element methods, to address complex wave propagation problems.This work focuses primarily on noise control technology. A three-dimensional finite element method is implemented and applied to solve several noise control problems. More specifically, three-dimensional
8、time-harmonic wave propagation in air and porous media is modeled whereby porous materials may be used as acoustic absorbers or as filters in mufflers and silencers. Therefore, finite element modeling can be used for predicting the transmission loss (TL) in the problem of interest at a given frequen
9、cy range.In the last decade, finite element methods have been widely used to solve Helmholtzs equation, a governing equation for time-harmonic wave propagation, mainly in two-dimensional domains. A major challenge for using finite element methods for Helmholtzs equation is that a specific resolution
10、 requirement for minimal wavelength must be respected for control of the approximation error. Dispersion analysis demonstrates that because of a pollution effect associated with a phase error, it is generally more difficult to meet the resolution requirements for higher frequencies 1. In one of the
11、most recent studies, general resolution rules that account for the pollution effect are derived by Ihlenburg 2.Several finite element methods have been developed to ease resolution requirements which are seemingly an open problem. Farhat et al. 3 briefly reviewed many suggested methods in the litera
12、ture and, consequently, offered a discontinuous Galerkin method with plane wave basis functions as the most effective approach for solving short wave Helmholtzs problems. A simpler modication of the standard Galerkin nite element method based on least-squares stabilization is provided by Harari and
13、Magoules 4 to effectively relax the resolution requirements. Since the focus of this work is on the application of the finite element method, the use of quadratic elements are deemed suffciently capable of addressing this issue.As mentioned before, due to restrictions in computational resources, mos
14、t of the early published applications of finite element methods for time-harmonic wave propagation had been limited to two-dimensional domains. This has changed in recent years, and more examples of three-dimensional applications can be found in the literature. For instance, a three-dimensional fini
15、te element model was developed by Koike et al. 5 to clarify the acoustic mechanisms of the human middle ear without direct measurements since these are difficult to conduct. Tezaur et al. 6 generated a three-dimensional finite element method with quadratic tetrahedral elements for acoustic scatterin
16、g problems in exterior domains. The acoustic absorption of multi-layer absorbers was studied by Lee and Chen 7 using a Galerkin finite element method with eight-node brick elements.While recent versions of most commercially available finite element software packages, such as FEMLAB, ABAQUS, MSC.Nast
17、ran and ANSYS, have included three-dimensional acoustic simulation, it is still advantageous to develop an open-source finite element code because many improvements to the numerical methods and the physical modeling remain. In this work, a particular parallel processing concept has been implemented
18、to address larger problems with the available resources. Furthermore specific components of mufflers and silencers, such as perforated plates and absorbing materials have been modeled.Regarding applications for mufflers and silencers, Munjal 8, in an overview of the last decade of research from the
19、Indian Institute of Science, concluded that more research is required in FEM analysis of complex geometries like perforated element mufflers in order to incorporate three-dimensional effects. In a recent study, Bwchuk and Fyfe 9 compared various numerical methods for calculating the transmission los
20、s in silencers. It was concluded that the combination of the finite element method and the three-point method is advantageous over other considered methods. A three-dimensional direct mixed-body boundary element method for packed silencers was created by Wu et al. 10, including modeling of perforate
21、d plates and two different acoustic media, i.e., air and absorbing material. This method is based on the multi-domain boundary element method which necessitates homogeneous and isotropic subdomains. To verify the formulation, several test cases were examined and the results were compared with experi
22、mental data. In this work, we examine several of those test cases using our three-dimensional finite element method.In practice, finite element simulation requires high computational and memory resources, particularly at higher frequencies. Using domain decomposition and parallel processing techniqu
23、es, one can take advantage of the simultaneous computational and memory capacity of several computers for solving one problem in parallel. Our methodology applies a domain decomposition method for division of the original system into several subproblems.Following this introduction, diverse general n
24、oise control problems, including the problems at hand, will be described in Section 2. Section 3 briey presents mathematical models of wave propagation in an ideal gas and porous media, as well as through a perforated plate. In Section 4, several common approaches to investigate noise control proble
25、ms will briey be reviewed and a finite element method is presented in more detail. Section 5 reports the finite element results and provides a comparison with experimental data. Finally, Section 6 will conclude this work and suggest future research directions.Noise control problems There are a varie
26、ty of noise sources and noise propagation problems surroundings. However, almost all noise propagation problems belong tone of the two main categories. The rst category involves noise propagation problems whereby the frequency and the amplitude of the source are known; for example, a vibrating struc
27、ture or fluid on the boundary of the domain. The second type entails noise propagation problems such that the source of the noise is coupled with the noise propagation problem. An example of this is the turbulence of fluid flow within the domain. These two main categories of noise control problems a
28、re known as, respectively, vibroacoustic and aeroacoustic problems. For the problems we examine, the major source of noise is known at the inlet pipe; hence, these problems were considered as vibroacoustic problems.Generally speaking, the goal is to reduce noise since excessive noise in our environm
29、ent is shown to have damaging effects on human beings and other living creatures. Furthermore, high amplitude noise may produce vibrations and this can consequently lead to fatigue and the eventual break down of machine parts.Passive noise control techniques, such as absorption panels, acoustic encl
30、osures, double glaze windows, muffs, silencers and earplugs, are remedies implemented for controlling the impact of noise. A more recent approach in noise control technology is known as active noise control. It is based on measuring noise or vibration and then producing a wave with almost the same a
31、mplitude but in opposite phase in order to cancel out original noise or vibration. This is a relatively expensive processsince it requires the use of microphones or accelerometers, a real-time control systemend speakers or actuators.Accurate modeling of an acoustic field is an essential part of the
32、design procedure in noise control systems. In this study, a packed muffler and a parallel baffe silencer are chosen as examples of noise control devices. Mufflers and silencers are extensively used in inlets and outlets of internal combustion engines, air compressors and fans for reducing the propag
33、ation of the noise generated in those machines. The most important acoustic property of a muffler and a silencer is its transmission loss which is defined as the difference between the output and input noise amplitude for a given frequency. The traditional method for evaluating the TL requires theso
34、lution of the acoustic field for two different boundary conditions and is called the four-pole method 11. However, described in this research work is a faster method, the three-point method 12, used for the evaluation of the TL.2.1. Three-point methodIn the three-point method, the TL can be calculat
35、ed with a single solution for each frequency. This setting is presented in Fig. 1. At the input, there is a uniform velocity (or pressure) and the output is assumed anechoic. Letting x1 and x2 represent the coordinates of two points along the muffler axis while p, generally a complex value, represen
36、ts the amplitude of the sound pressure at each point, the TL can therefore be evaluated by means of the following equation:翻 译 用于预测没有平均流动的消声器和消音器的三维有限元法摘要三维有限元法已经实施来预测一个拥挤的消声器透射-锡安损失和给定的频率范围内平行隔板消声器，异参数二次四面体元素已被选定由于其灵活性和曲面造型与几何精度。为了准确物理表示，穿孔板的建模与复杂的声阻抗，而吸收片建模为一个批量媒体的声音复杂的速度和平均密度。域分解和平行工艺加工技术已被用于解决复杂
37、的计算和记忆当中。该预测值与实验计算传输损耗测量显示了较好的对比。1. 简介因为许多物理现象包括波传播的形式，在哪儿一直是它的互动与其他物理现象的理解和建模波传播的兴趣。在一般情况下，为某一物理现象建立一个合适的模型有以下三点须注意：物理现象在现实中的复杂性，最后能达到的最佳精度要求，现有的分析使用资源的有限性。由于涉及的事实，波的传播现象有可能是复杂的，精确计算资源约束限制了相当简单的模型来解决问题的唯一.。然而，在近些年，在微处理器和内存较低的价格计算能力的迅速发展已经创造了一个发展另一强大模式的新视角，例如用于解决复杂的波的传播问题的有限元法。这项工作主要侧重于噪声控制技术。三维有限元法
38、的实施和应用已用来解决几个噪声控制问题。更具体的来说，三维空间和时间谐波是在以空气和多孔介质的电磁波传播为蓝本的，在消声器和消音器中可使用多孔或吸收材料来吸收和过滤。因此，有限元模型可以用于预测在给定的频率范围内传输损耗问题。在过去的十年里，有限元方法已被广泛用来解二维域方面，霍尔茨方程，时间谐波的传播方程。一个利用亥姆霍兹方程的有限元方法的主要难点是，一个最小的波长具体误差控制 要求。由色散分析表明，由于与相位误差相关的污染的影响，一般较难达到更高的频率分辨率的要求，在最近的一些重要研究， 一般的解决规则都是由Ihlenburg推断而来。几种有限元方法，以缓解发展决议的要求，这似乎是一个开放
39、的问题。Farhat 以及其他一些人，简要回顾了文献中的许多建议和方法，结果，提供解决短波亥姆霍兹一项伽辽金与平面波的最有效方法的基础函数法的问题，一个在标准的Galerkin有限元方法的基础上简单修改最小二乘稳定提供了哈拉里和Magoules有效决议的要求有所放宽。由于这项工作的重点放在了有限元甲基-外径的应用，对二次元素的使用被认为是足够的能力解决这一问题。正如前面提到的，由于受计算资源的限制，早期出版的有限元方法的应用时间，大部分谐波传播仅限于二维域，这些在近些年来已经有所改变，三维应用程序在学术著作上可以找到更多的例子。例如，Koike等人发展的三维有限元模型。以澄清不直接测量人体中耳
40、传音机制，因为这些都是难以进行。Tezaur 等人，产生的二次四面体单元的三维有限元外域声散射的问题的方法。Galerkin对多层吸波材料的吸声研究。虽然大多数商用有限元软件的软件包，虽然大多数商用有限元软件的软件包，如FEMLAB，ABAQUS软件，MSC.Nastran的和ANSYS，最近的版本，包括重稀土三维声学仿真，它仍然是有利的发展开放环境允许的有限元程序因为对许多改进数值方法和物理模型仍然存在。在这项工作中，特别是并行处理浓度，化学强化一级处理已经实施，以解决与现有资源的更大问题。消声器等的穿孔板消声器和吸音材料，而且具体内容是参照。关于为消声器和消音器的申请，Munjal ，概括
41、了从一个从印度科学研究所的在过去十年的探究状况，结论是，更多的研究是在FEM;有限元元素，如穿孔消声器形状复杂的分析需要，以便纳入三维效果。在最近的研究中，Bilawchuk和Fyfe为了计算消音器的传声损失对比了各种数值计算方法，有人得出结论认为，相比较其他的而言有限元法和三点法的结合是最有利的方法。为吸收式消音器设计的立体的直接混合体边界元方法是由吴等人创建的，包括建模穿孔板和两个同声媒体，即空气和吸波材料。这种方法是建立在均匀的，各项同性的子域名的多域便捷元上的，为了验证这种构想，对几个案例进行了测试并将其结果跟实验数据进行了对比。在这项研究中，我们检验了几个用我们的有限元分析法测试的案
42、例。在实践中，有限元模拟要求高的计算和内存资源，特别是在高频率中。使用域分解和并行处理技术，可以集中起来几个计算机的资源来解决某一较难的问题。我们的方法是来解决将原系统划分成若干子问题的这类问题。在此之后推出，不同于一般的噪声控制问题，包括手头上的问题，将在第二节和第三节简要介绍波在理想气体和多空介质的数学模型，以及通过多孔板。在第四节中，几种普通的用来检验噪声控制的方法将被简单的回顾，而有限元法将会被详细的阐述。第五节传达了有限元分析的结果核试验数据的对比。最后，第6节将结束这项工作，并提出今后的研究方向。2. 噪声控制问题在我们周围存着各种关于噪声传播和噪声源的问题。然而，几乎所有的噪音传
43、播问题属于这两个重要的类别之一。第一类，即涉及噪音传播的频率和振幅的来源是已知的问题；例如，振动结构或液对域的边界。第二类是产生噪音的扩展问题，即是噪声源与噪声传播耦合的问题。这方面的一个例子是域中的湍流流动问题。这两个主要的噪声控制问题，分别为振动和声学问题。对于我们研究的问题，我们知道，噪音源通常是在进气口，因此，这些问题将被作为流体振动重点考虑。一般来说，我们的目标是减少噪音过大，有研究表明，过的大噪声会对我们人类和其他生物造成严重的影响。此外，高幅度噪声可能会产生震动，这可能会使机械零件疲劳并最终导致其损坏。被动噪声控制技术，比如吸收板，双釉窗，消声器，消音器和耳塞，是对噪音影响的补救办法。最近有一种积极控制噪声的主动控制法。它是基于测量噪音或振动，然后产生一种几乎与噪音相同振幅但相位相反的波来达到消声的目的。这是一个相对昂贵的过程，因为它需要麦克风或加速度计，实时控制系统和扬声器或执行器。精确的声场建模是设计过程中的噪声控制系统的重要组成部分。在这项研究中，一个阻性消声器和一个平行板消声器被用来作噪声控制设备的例子。消声器和消音器被广泛的用在内燃机发动机的进出口处，空气压缩机和风扇上以降低这些机器产生的噪声。9