Bertrand Lihoreau

Outdoor sound propagation modeling in realistic environments: Application of coupled parabolic and atmospheric models

Predicting long-range sound propagation over a nonurban site with complex propagation media requires the knowledge of micrometeorological fields in the lower part of the atmospheric boundary layer, and more precisely its characteristics varying in both space and time with respect to local (“small-scale”) and average (“long-term”) conditions, respectively. Thus in this study, a mean-wind wide-angle parabolic equation (MW-WAPE) code is coupled with a dedicated micrometeorological code (SUBMESO) which simulates wind and temperature fields over moderately complex terrain with high resolution. Its output data are used as input data for the MW-WAPE code, which can also deal with different boundary conditions, such as the introduction of impedance jumps, thin screens or complex topography. Both codes are presented in the present paper. Comparisons between numerical predictions, and experimental data are also presented and discussed. Finally, we present an example of such a coupling method (MW-WAPE/SUBMESO) for t...

Three-dimensional parabolic equation model for low frequency sound propagation in irregular urban canyons

A three-dimensional wide-angle parabolic equation (3DPE) is used to model low frequency sound propagation in irregular urban canyons at low computational cost. This one-way wave equation is solved using the Alternating Direction Implicit method. A finite difference scheme adapted to the geometry of the urban environment is then developed. Abrupt variations of the street width are treated as a single scattering problem using the Kirchhoff approximation. Numerical results are compared with experimental data obtained on a scale model of a street. Comparisons show the ability of the 3DPE model to provide reliable transmitted fields even for large irregularities.

Coarse-grid computation of the one-way propagation of coupled modes in a varying cross-section waveguide.

A one-way approximation is investigated for the computation of wave propagation in varying cross-section waveguides. The proposed method derives as a basic approximation of the extensively studied multimodal admittance method. When integrated with a Magnus scheme, this matrix one-way equation exhibits an unexpected behavior, as the deviation from the exact solution is minimum when only two discretization points per wavelength are taken. This peculiar property makes this method efficient to compute the wave propagation for a large variety of geometries, beyond the initially stated framework of weakly non-uniform waveguides.

Acoustical waves propagation in rough walls street

We present a method for the numerical calculation of a sound wave propagating in a two dimensional rough‐sided street. Is this situation, the wave is subject to multiple scattering at the two boundaries. The propagation is governed by a parabolic equation. We show that the amplitude of a pulse may be expressed as the fractional Fourier transform of the incident pulse, and that the order of the transformation is related to the distance between the source and the point of observation. Numerical simulations are proposed as illustration of this model and are compared to experimental results.