Numerical models of noise barrier designs

Abstract

Barriers are commonly used as a control measure to reduce outdoor sound propagation from road traffic noise affecting nearby residential areas. This thesis explores novel numerical techniques and designs of barriers for tailored low frequency noise reduction. Analytical and numerical models of a straight noise barrier are initially presented. The effect of single and multiple sources and their location on barrier insertion loss is described. Elevated sources representing realistic locations of light and heavy vehicle engine and exhaust noise sources are considered. Diffraction over the top edge of the barrier and reflections from the ground on both the source and receiver sides of the barrier are taken into account.

Numerical models of three-dimensional barriers are developed using a quasi-periodic boundary element method (BEM), whereby the barrier is represented by a finite number of periodic sections along its length. Using the quasi-periodic BEM technique, the size of the numerical domain and the computational cost associated with large-scale exterior acoustic models are significantly reduced. The quasi-periodic boundary element method is then implemented to design a three-dimensional barrier with embedded Helmholtz resonators tuned to single or multiple frequencies.

Numerical models of sonic crystal barriers developed using both the finite element method and quasi-periodic boundary element method are presented. The acoustic performance of a sonic crystal barrier comprising of locally resonant scatterers is investigated using perforated and C-shaped cylindrical shell scatterers. The effects of the number, size and orientation of the holes in the perforated cylindrical shells, as well as the size of the opening of the C-shaped scatterers and their orientation with respect to the incident plane wave, on the barrier insertion loss are described in detail.