Contributions to close-proximity method for tyre/road noise measurement in highly urbanized environment

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Contributions to close-proximity method for tyre/road noise measurement in highly urbanized environment

 

Author: Lam, Yat Ken
Title: Contributions to close-proximity method for tyre/road noise measurement in highly urbanized environment
Degree: M.Phil.
Year: 2015
Subject: Traffic noise -- Measurement.
Traffic noise -- Simulation methods.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xiii, 185 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2828709
URI: http://theses.lib.polyu.edu.hk/handle/200/8274
Abstract: Notwithstanding decades of governmental and public efforts,traffic noise problem in Hong Kong is still severe. Since the contribution by tyre/road noise is predominant, assessment to it is necessary.Close-Proximity Method is a standard tyre/road noise measurement methodology (ISO/CD 11819-2) that works by towing a trailer installed with test tyres and microphones to travel on a road section to measure the noise emitted. The reliability of its application in highly urbanized city is in doubt because of the severe disturbances to the measurement in real practice.They include the high background traffic noise,the road bumpiness, the substantial variation of temperature and the variation due to road curvature. This study aims to develop a CPX Method suitable for tyre/road noise measurement in highly urbanized city with minimal influence from these disturbances. The development of the PolyU Mark II CPX Trailer is described in this study. It is equipped with an acoustically treated enclosure for shielding the external disturbing noise with minimized internal reflection.Experiments were conducted to evaluate its acoustic performance against the certification criteria stipulated in ISO/CD 11819-2.The Mark II has passed. The vibration of the microphones installed inside the CPX trailer excited by its travel over road bumpiness induces error to the measurement results. Experimental results indicate the error can lead to a noise level overestimation as much as 3 dB(A).To alleviate such error,a correction method is proposed and illustrated. Tyre/road noise is sensitive to air temperature.ISO/CD 11819-2 suggests temperature correction to alleviate its influence. The correction is optional since temperature constants vary for different road surface types. The correction is however necessary in Hong Kong due to the relatively large temperature variation. Experiment was devised to yield the air and road surface temperature constants of two local common asphalt road surface types.Road surface temperature is found more reliable than air temperature for the correction. The choices of road sections are limited in this highly urbanized city. Sometimes it is inevitable to adopt curved road as test section.Cornering is anticipated to influence tyre/road noise radiation.Study was conducted to assess the curvature effect. Results indicate that the road curvature effect can reach up to 2 dB(A). The minimum critical radii for CPX measurement are yielded for two speeds. The radius is found to be higher for higher vehicle speed. Through evaluating the levels of influences by the disturbances above and proposals of corrective measures to the errors resulted from them, the present study contributes to the reliability of CPX Method for tyre/road noise measurement in highly urbanized city.

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