Modelado y análisis de la influencia del gradiente de temperatura en silenciadores de escape disipativos mediante elementos finitos
[EN] This Master Thesis is focused on the development and implementation of a numerical methodology, based on the finite element method, which allows the characterization and simulation of the acoustic behaviour of dissipative exhaust silencers that include absorbent materials in the presence of hig...
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| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2016 |
| País: | España |
| Institución: | Universitat Politècnica de València (UPV) |
| Repositorio: | RiuNet. Repositorio Institucional de la Universitat Politécnica de Valéncia |
| Idioma: | español |
| OAI Identifier: | oai:riunet.upv.es:10251/76172 |
| Acceso en línea: | https://riunet.upv.es/handle/10251/76172 |
| Access Level: | acceso abierto |
| Palabra clave: | Elements perforats Elements finits Equació d&apos ones Resistivity Absorbent material Thermal gradient Silencers Transmission loss Chamber length Perforated elements Finite elements Wave equation Acoustics Resistividad Material absorbente Gradiente de temperatura Comsol multiphysics Sysnoise Silenciadores Atenuación acústica Longitud de cámara Elementos perforados Elementos finitos Ecuación de ondas Acústica INGENIERIA MECANICA Máster Universitario en Ingeniería Mecánica y Materiales-Màster Universitari en Enginyeria Mecànica i Materials |
| Sumario: | [EN] This Master Thesis is focused on the development and implementation of a numerical methodology, based on the finite element method, which allows the characterization and simulation of the acoustic behaviour of dissipative exhaust silencers that include absorbent materials in the presence of high temperature and thermal gradients. In addition, the influence of several parameters on the acoustic attenuation is assessed, such as the variation of the chamber length and the relevant properties of perforated surfaces. The work is organized as follows. First the acoustic fundamentals are presented with the basic concepts used in this study. For this reason, the acoustic theory is reviewed, as well as the silencer definition from an acoustical point of view. Also, details are given about the silencer typologies and the traditional methods for their acoustic analysis, such as plane wave models. Furthermore, a bibliography review related to the characterization of absorbent materials and perforated surfaces is made. The importance as noise attenuators is highlighted and their most important properties and features are defined. Next, the formulation of the acoustic problem is developed presenting the governing equations describing the acoustic sound propagation and its application to the silencer. Thereupon, the fundamentals of the finite element method are described for solving the wave equation inside silencers with absorbent material and the numerical technique is applied to different geometries of silencers. Finally, the importance of the following parameters on the acoustic attenuation is analysed: chamber length, perforated surface parameters (e.g. pososity), average temperature and thermal gradient. In the silencers analysed in the current investigation, it is considered that the flow resistivity of the absorbent material changes due to the presence of axial temperature gradients. These changes in resistivity, in turn, cause modifications in the equivalent acoustic properties of the absorbent material (sound propagation speed and air density).To perform these simulations, some commercial packages are used such as Ansys, Sysnoise, Comsol Multiphysics and also in-house codes developed in the department using Matlab. The in-house codes are used to simulate the effect of temperature using a continuous model. Some auxiliary codes developed in collaboration with the research group are also considered. Through the developed tools, the finite element method is applied to different silencer geometries, making a detailed study about the influence of the temperature on the silencer acoustic attenuation. A study is also carried out to assess the influence of the chamber length and the perforated tube on the acoustic attenuation of different geometries. Moreover, the validity of the segmented model for the acoustic computation is studied. The research group has a wide experience in the modelling and experimental characterization of the acoustic behaviour of the exhaust system in internal combustion engines. Over the past decades, an exhaustive work has been done related to the development, implementation and validation of computational tools based on the finite element method to consider more complex cases, as for instance: the presence of high temperatures, temperature gradients and mean flow. Besides, Sysnoise software has been used for validation tasks. This programme did not work autonomously, but it required the external definition of geometry and mesh, previously done in another programme (e.g. Ansys). It also required external data, file transfer and format conversion, making the associated work toilsome. For this reason, the research group has recently acquired the commercial software Comsol Multiphysics as acoustic modelling and simulation tool (in addition, Sysnoise has become obsolete). This Master Thesis makes a comparison of the two programmes in order to validate the Comsol Multiphysics efficiency as an alternative to Sysnoise. |
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