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Propagation acoustique en milieu extérieur complexe: problèmes spécifiques au ferroviaire dans le contexte des trains à grande vitesse

Abstract : Outdoor sound propagation involves complex physical phenomena, mainly associated with temperature and wind variations in the atmospheric boundary layer and with boundary conditions (influence of the ground impedance, terrain effects, ...). Furthermore, in the context of high speed trains (TGV), noise sources are in motion at a relatively high speed, cannot be considered as compact, and are of different types (rolling noise, aerodynamic noise, ...). This work aims at modeling TGV noise propagation outdoors and at understanding the physical phenomena associated with this type of propagation. In a first part, acoustic scattering by turbulent fluctuations of temperature and wind is considered in the presence of a refractive shadow zone. The scattering effect of a given turbulence scale depends on acoustic frequency and propagation geometry. This coupling between turbulent structures, acoustic frequency and geometry is studied using tools from the theory of wave propagation in random media and parabolic equation simulations, in order to estimate the smallest and largest turbulence scales to be taken into account in a given configuration. In a second part, a solver of the linearized Euler equations is described which uses finite-difference time-domain methods. The use of optimized numerical schemes enables to apply this propagation model to long range sound propagation configurations. One of the main difficulties encountered with time domain propagation models is to take into account the reflection of acoustic waves by an impedance ground. Time-domain impedance boundary conditions that are efficient from a numerical point of view are proposed for impedance models commonly used in outdoor sound propagation studies. To obtain these boundary conditions, the impedance is approximated by well chosen template functions, which enables the use of the recursive convolution method. They are validated in two- and three-dimensional propagation geometries, considering a homogeneous atmosphere and then a stratified atmosphere. Finally, specific applications to TGV noise are presented in a third part. First, a TGV noise propagation model is described where the train is represented by a set of equivalent point sources. Model results are compared to measurements performed at different distances from the track assuming homogeneous propagation conditions. The equivalent sources model is also coupled to a parabolic equation code in order to take into account the influence of a vertical profile of temperature or wind. Second, the characteristics of a "rumbling" noise that can be heard tens of second before or after some TGV pass-bys are analyzed. In some circumstances, it is indeed possible to hear a relatively low-frequency noise perceived as an aircraft pass-by, which is referred to as "rumbling" noise. The analysis is mainly based on experimental results and enables to determine the characteristics of this "rumbling" noise and the circumstances in which it occurs. Parabolic equation simulations are also performed to show the importance of the wind in the appearance of this phenomenon.
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Submitted on : Monday, January 16, 2012 - 6:19:44 PM
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  • HAL Id : tel-00660494, version 1

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Benjamin Cotté. Propagation acoustique en milieu extérieur complexe: problèmes spécifiques au ferroviaire dans le contexte des trains à grande vitesse. Acoustique [physics.class-ph]. Ecole Centrale de Lyon, 2008. Français. ⟨tel-00660494⟩

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