Environmental noise prediction for urban planning: Outdoor sound propagation using the nodal discontinuous Galerkin finite element method

Environmental noise pollution in cities is a public health concern affecting a large portion of the urban population. In the European Union, mandatory strategic noise mapping has been introduced to evaluate the extent of the issue in large European cities but the conventional methods used are not adapted to predict the noise distribution at the scale of a street or a building. At this local urban level, various numerical methods can solve the governing equation of sound propagation to predict environmental noise.

This PhD thesis aims to establish a methodology to simulate noise propagation and analyze the impact of urban sound sources. For this purpose, the nodal discontinuous Galerkin finite element method (DG-FEM) has been employed and developed as it has multiple advantages. This numerical method can easily conform to complex geometries which is often the case for urban setups, it can reach high-order accuracy with limited computational resources and the computation of the simulations can be accelerated because calculations can be done in parallel for the acoustic wave equation. For these reasons, DG-FEM schemes are seeing growing adoption in modern computational tools that target realistic engineering applications.

To simulate outdoor sound propagation using a DG-FEM framework, the computational domain must be truncated in order to lower the computational resource requirements. However, this boundary should be placed at a reasonable distance from the source, receiver(s) and eventual obstacles along the sound propagation path to maintain the accuracy of the calculations. This PhD thesis proposes:

1. a novel and stable 3D perfectly matched layer (PML) at this truncation that was conceptualized, implemented and tested using the DG-FEM,

2. two urban noise scenarios were simulated in DG-FEM with this PML formulation and experimentally validated using scale models,

3. the inclusion of the atmospheric refraction of the sound path from the wind in the DG-FEM solver and the PML formulation, since this meteorological effect can be significant.

This PhD dissertation first presents the highlights of the reasons why DG-FEM is adapted for the prediction of environmental noise for urban planning. It then introduces the contributions of this PhD project to the current state-of-the-art and finally, those contributions are elaborated in the associated collection of publications.