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Approche modale de la propagation acoustique dans les guides d'ondes ouverts et application à l'acoustique urbaine

Abstract : In urban areas, noise has become the main form of ''pollution'' recognized by the population. To address this major issue for society, much research has helped to describe the acoustic propagation in urban areas. However, as consequence of the high geometrical and physical complexity of urban areas, the energetic models implemented in usual predictive software limit the physical description of sound fields. It appears that fundamental work on acoustic propagation in complex environments must be pursued upstream from applications directly related to urban acoustics. In this context of upstream research, the essential idea of this work is to consider the street as an open waveguide. Indeed, the typical elongated shape promotes guided waves along the axis of the street. In contrast, the opening of this guide on an infinite domain - the sky - results in wave radiation leading to energy losses. The study of these competitive effects between guided waves and radiated waves is the key point of this work. To solve the wave equation in such an open three-dimensional guide, the principle of modal decomposition is used. In this approach, the wave field is a combination of a set of modes (called modal basis) whose contributions notably depend on end conditions at the guide extremities. The extension of the modal approach to the case of open waveguides need to introduce the concept of leaky modes. Through a preliminary study about two-dimensional closed guides with variable cross-section, the possibilities of the modal approach are apprehended in simple cases in order to be extended to the more complex case of three-dimensional open guides. Subsequently, a first work about leaky modes is done in the academic case of an open cylindrical guide with rectangular cross-section. In this work, the behavior and properties of leaky modes are studied in details when they are used in a modal approach. It is notably shown that only a small number of modes is necessary to accurately describe the field. Based on the findings of this first research, a coupled Modal-Finite Elements method, more suitable to the ''urban waveguide'' specificities is proposed. This work shows how, using PML (Perfectly Matched Layers), a new problem of propagation in closed guide may be substituted for the original problem of propagation in open guide. In this approach, several characteristics of the geometrical and physical complexity of urban areas can be taken into account. Illustrations based on the numerical implementation of the method reveal physical phenomena related to irregularities and absorption of facades, or the consideration of meteorological effects, and open both academic and applied research prospects.
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Submitted on : Monday, January 4, 2010 - 1:45:04 PM
Last modification on : Tuesday, May 26, 2020 - 2:44:07 PM
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  • HAL Id : tel-00439840, version 2


Adrien Pelat. Approche modale de la propagation acoustique dans les guides d'ondes ouverts et application à l'acoustique urbaine. Acoustique [physics.class-ph]. Université du Maine, 2009. Français. ⟨tel-00439840v2⟩



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