ACOUSTICS

Author: Gil Alías David.
Year: 2005.
University: PONTIFICIA COMILLAS.
Place of defense: Alberto Aguilera, 25.
Place of preparation: Escuela Técnica Superior de Ingeniería.

Summary: The control of noise sources and their energy levels, especially those associated with the activities of transport, now have increasingly greater demand. Within these, due to traffic many years ago that are being explored, but the associated rail traffic has been most neglected. The progressive social pressure by environmental pollution, combined with the growing number of rail infrastructure with a bearing on the nuclei inhabited motivates the subject of interest of this thesis. The need to address real geometries, which are complicated by the location of the source for the solutions studied (noise barriers with cumbreras among others) suggest the use of a numerical method capable of resolving these difficulties. Among possible, it is preferable to the use of the method Elements Contour (MEC) for its excellent adaptation to open domains. It was an open source version of the MEC, which had to be some modifications. Once adapted proceeded to validation by comparing its results for simple geometries, algorithms based on analytical solutions approximated to the general theory of Sommerfeld. The next step was in a deep analysis of the geometry suitable to solve the problem of noise insulation rail noise by means of barriers. The results have enabled more than cover the proposed objectives consisting in the analysis and evaluation of the adequacy of the Elements Method Contour (MEC) in the resolution of calculating losses for insertion into noise barriers specific to railways and in the study of geometry more appropriate to achieve optimum protection. Regarding the former have been identified constraints MEC, putting out its big advantages in solving the problem. We have defined the convergence criteria necessary Check with the formulation used is not necessary to make a specific treatment for irregular frequencies. On the second it has been found in all the tests, the optimum configuration of the acoustic barrier is a ridge with T with absorbent material on top, but within these settings insertion losses may vary depending on location the barrier with respect to the source and the length of the ridge. The results have emerged from a comprehensive study that took into account various influences such as absorbent materials, ridge, consideration broadband noise monochrome face, and consideration of different frequencies (600 Hz to 2 kHz). From the results obtained deserves special mention those for the validation phase of MEC with the analytical procedures. Surprisingly were achieved criteria of applicability of analytical procedures, checking that they are not always valid, even in simple geometries, due to the simplification inherent in its application. This way you can narrow the margins of applicability of this type of formulations and / or to explain discrepancies between types of results (experimental / prediction). The work is highly empirical, it is believed useful remarks and the recommendations of the applicability of MEC since they are the result of countless hours of numerical simulation, which may serve as prior experience to other researchers and users of this method. The variety of results are obtained by applying the MEC are of a very high interest because it allowed characterize the sound field is not alone in the reception area, but also the sound field in the semiespacio issuer, which leads to a quantifiable image disturbance on that semiespacio due to the fact establish a barrier or bread 8 stature ac 3a5 ústica. The study allows extended without difficulty for consideration by the reverberant sound field and overpressure zones and depression in the tunnels crossing the railroad, whose problem is not completely resolved, being of great interest for high speed railways.

Author: PUIG ORTIZ JOAN.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA.
Place of defense: AULA CAPELLA DE L'ETSEIB.
Place of preparation: ETSEIB, PAVELLÓ F - SD.

Author: TORRES PICAZO MARÍA ISABEL.
Year: 2005.
University: POLITÉCNICA DE VALENCIA.
Place of defense: UNIVERSIDAD POLITÉCNICA DE VALENCIA.
Place of preparation: UNIVERSIDAD POLITÉCNICA DE VALENCIA.

Summary: This thesis focuses on the development and implementation of methods for the design and modeling of acoustic mufflers of internal combustion engines, through tools based on analytical and numerical solutions of the wave equation. The need to design quickly and efficiently provide accurate results even at high frequency has increased over time, because the noise of vehicles has become a major source of environmental pollution. The main aim of the thesis is the extension and application of the method of adjustment mode, in combination with the method of subestructuración, to model the behavior of acoustic mufflers disipativos. An important contribution is associated with obtaining modes cross silencers, which has been successfully developed a new technique for silencers disipativos including fibrous type of absorbent material. Have been studied experimentally relevant elements of silencers, and the characteristics of the behavior of absorbent materials or elements drilled, in order to obtain more precise data about them. Validating or improved models found in the literature on these experiments. They have been evaluated various methods for the characterization of absorbent material. In conclusion, it was found that no significant differences between the techniques studied. It has taken the approach of the two sources as the most desirable because the results are independent of the conditions downstream from the sample. Two materials have been characterized with this technique, getting parameters semi-empíricos model Delany and Bazley. Moreover, the method of the two sources has been used for the characterization of perforated elements, adapting the model results experimentally Sullivan. To carry out the analysis acoustic disipativos, has extended the method of adjustment mode in the case of absorbent material, combined with the method of subestructuración for calculating the transverse modes. To define the behavior of the material, it has taken a model based on two parameters, and impedance wave number. It has been the preferred method of subestructuración for its versatility and for presenting less mathematical problems in obtaining the natural frequencies and corresponding modes, compared to the direct method. Finally, various geometries silencers have been experimentally tested to validate the models developed in this thesis. Some specific configurations were analyzed to observe the influence of relevant parameters in the design of silencers including absorbent materials.