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 毕业论文外文翻译.doc

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 frequency 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 bulk 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 agreement. 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 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 complex 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 other 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 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 frequency 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 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 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 literature 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 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, most 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 finite 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 scattering 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.nastran 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 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 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 loss 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 perforated 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 experimental 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 techniques, 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 noise 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 problems 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 variety 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 structure 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 are 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 environment 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 enclosures, 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 amplitude 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 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 propagation 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 thesolution 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 calculated 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, represents 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