Propagation of urban transportation noise.

摘要

A simplified model based on the study of sound diffracted by a sphere above a ground surface is proposed to simulate the sound propagation confined to the hornlike geometry enveloped by the road surface and tire belt. In a parametric study, it has been shown that an increase in the thickness and porosity of a porous layer, or the use of a double layer of porous road pavement, will lead to the reduction of the horn amplification of sound. However, a decrease in the flow resistivity of a porous road pavement does little to reduce the horn amplification of sound. It has also been demonstrated that the horn effect over a porous road pavement is less dependent on the angular position of the source on the surface of tires.; Comparative studies have been conducted to investigate the applicability of oversea prediction schemes for the calculation of noise levels caused by passing trains that run on a viaduct. Calculation of Railway Noise (CRN) developed in UK, Nordic Prediction Method for Train Noise (NMT), CSTB 92 and ISO 9613 provided in the Mithra software are the schemes used for the comparisons. Among these schemes, CRN gives the best agreement with the measured results.; Four sets of noise measurements for different train operational conditions have been conducted to deduce the vertical directivity pattern for different railway systems. The vertical directivity of different railway systems shows a rather similar pattern such that it increases up to about 30° before reducing to a minimum at 90°. A multipole expansion model is proposed to account for the vertical radiation directivity of the train noise. An empirical formula is derived and compares well with the experimental data.; A new methodology for the prediction of noise levels inside the balconies is proposed. It is based on the well-known prediction scheme---the Calculation of Road Traffic Noise developed in the UK. Field measurements on four different types of balcony have been conducted to validate the scheme. It is shown that balcony of different architectural features can offer considerable screening effects in protecting dwellings against road traffic noise.