Efficient calculation of the green function for acoustic propagation above a homogeneous impedance plane

This paper is concerned with the problem of propagation from a monofrequency coherent line source above a plane of homogeneous surface impedance. The solution of this problem occurs in the kernel of certain boundary integral equation formulations of acoustic propagation above an impedance boundary, and the discussion of the paper is motivated by this application. The paper starts by deriving representations, as Laplace-type integrals, of the solution and its first partial derivatives. The evaluation of these integral representations by Gauss-Laguerre quadrature is discussed, and theoretical bounds on the truncation error are obtained. Specific approximations are proposed which are shown to be accurate except in the very near field, for all angles of incidence and a wide range of values of surface impedance. The paper finishes with derivations of partial results and analogous Laplace-type integral representations for the case of a point source

A uniformly valid far field asymptotic expansion of the green function for two-dimensional propagation above a homogeneous impedance plane

A generalized asymptotic expansion in the far field for the problem of cylindrical wave reflection at a homogeneous impedance plane is derived. The expansion is shown to be uniformly valid over all angles of incidence and values of surface impedance, including the limiting cases of zero and infinite impedance. The technique used is a rigorous application of the modified steepest descent method of O

Multiple-edge noise barriers

A numerical model using boundary element techniques is discussed which enables the insertion loss for various noise barriers of complex profile and surface cover to be calculated. The model is applied to single-foundation noise barriers to which additional side-panels are added to create fork-like profiles. Spectra of insertion loss and mean insertion loss results over a range of receiver positions for a broadband source are presented. It is concluded that ‘multiple-edged’ barriers show a significant increase in acoustic-efficiency over a simple vertical screen. Adding lightweight side-panels would be a relatively inexpensive measure, and one which could be applied to barriers already in existence. This type of barrier would also allow the height of the construction to be kept to a minimum

Influence of shape and absorbing surface: a numerical study of railway noise barriers

Results are presented of a study of a performance of various track-side railway noise barriers, determined by using a two- dimensional numerical boundary element model. The basic model uses monopole sources and has been adapted to allow the sources to exhibit dipole-type radiation characteristics. A comparison of boundary element predictions of the performance of simple barriers and vehicle shapes is made with results obtained by using the standard U.K. prediction method. The results obtained from the numerical model indicate that modifying the source to exhibit dipole characteristics becomes more significant as the height of the barrier increases, and suggest that for any particular shape, absorbent barriers provide much better screening efficiency than the rigid equivalent. The cross-section of the rolling stock significantly affects the performance of rigid barriers. If the position of the upper edge is fixed, the results suggest that simple absorptive barriers provide more effective screening than tilted barriers. The addition of multiple edges to a barrier provides additional insertion loss without any increase in barrier height

Measured and predicted acoustic performance of vertically louvred noise barriers.

NoThe paper describes model testing of the acoustic performance of vertically louvred and the corresponding predicted performance using a modified Boundary Element Method (BEM) program. The program was developed in a previous phase of the Transport Research Laboratory's research into the performance of modified barriers. Measurements on 1/20th scale model barriers were carried out in a semi-anechoic chamber designed primarily for scale model experiments to investigate outdoor sound propagation under controlled conditions. It was concluded from measurements in the scale model facility that the modified BEM code provided an adequate description of the leakage of sound through louvred barriers. The program was subsequently used to examine the performance of various designs of barrier in order to identify likely cost effective designs

Sound propagation over complex surfaces Final grant report; appendix

SIGLEAvailable from British Library Document Supply Centre- DSC:3926.78817(SERC-GR/C--03942(app.1)) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Prediction of the attenuation of road traffic noise with distance Final grant report

SIGLEAvailable from British Library Document Supply Centre- DSC:3926.78817(SERC-GR/C--03942) / BLDSC - British Library Document Supply CentreGBUnited Kingdo