Propagation of urban transportation noise

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Propagation of urban transportation noise


Author: Lui, Wai-keung
Title: Propagation of urban transportation noise
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Traffic noise
City noise
Noise control
Department: Dept. of Mechanical Engineering
Pages: xiv, 220 leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: In the present study, the particular condition of sound propagation confined to the hornlike geometry enveloped by the road surface and tire belt is investigated in details. A simplified model based on the study of sound diffracted by a sphere above a ground surface is proposed to simulate this so-called horn effect. 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. In the present context of booming railway networks, there is a great concern about noise due to moving trains. 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. The results from an outdoor field measurement are compared with the calculated results of the prediction schemes. 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, although it does not provide a term for correcting the vertical directivity characteristic of a passing train. In order to study the source characteristics of a passing train, four sets of noise measurements for different train operational conditions have been conducted at three different sites, including ballast tracks at grade and railway on a concrete viaduct. The measured sound exposure levels are used to deduce the vertical directivity pattern for different railway systems. It is found that the vertical directivity of different railway systems shows a rather similar pattern. The vertical directivity of train noise is shown to increase up to about 30o before reducing to a minimum at 90o. 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. The empirical model is found to be applicable to different train/rail systems at train speeds ranging up to 120 km/h in this study. 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. An effective noise-shielding effect is achieved when the incident angle of traffic noise is large and without ceiling reflection. The noise screening effects decrease with an increase of height above the balcony floor. Furthermore, it is found that the effectiveness of a parapet or side wall against road traffic noise depends on their orientations with the affecting roads.

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