|Title:||Advancement of close-proximity (CPX) measurement methodology for tyre/road noise|
|Advisors:||Leung, Chi Kin Randolph (ME)|
|Subject:||Tires -- Noise|
Automobiles -- Tires -- Noise
Traffic noise -- Measurement
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Mechanical Engineering|
|Pages:||xliv, 369 pages : color illustrations|
|Abstract:||Tyre/road interaction is the main source of noise emission caused by road traffic when cruising at high speeds. Various measurement methods were presented in the literature to assess the rolling noise emission. The Close-Proximity (CPX) Method is a standard methodology (11819-2 2017) for the tyre/road noise measurement, which allows evaluating tyre/road noise level with at least two microphones operating in the near field of the tyre. Several kinds of facility layouts were developed including one trailer with an enclosure running test tyres for measurement. The anechoic enclosure is equipped for shielding the external disturbing noise. The PolyU Mark II Twin-wheeled CPX trailer was developed for conducting the tyre/road noise measurement in Hong Kong. Good knowledge of the acoustic quality of the anechoic enclosure is very important for accurate tyre/road noise measurement. Generally, the enclosed acoustic quality of such trailer enclosure is not well presented even though the ISO certification tests are passed. The measurement at ISO prescribed microphone positions may be contaminated by any potential room resonance of the enclosure. It is necessary to obtain more information to better describe the acoustic performance in the overall enclosed space. Thus, numerical methodology based on the finite element method (FEM) was proposed to analyze sound waves propagations and sound energy distributions within the CPX trailer enclosure. Highly favorable consistency between numerical and experimental results was obtained at specific microphone locations within the PolyU Mark II CPX trailer enclosure. The accuracy and reliability of using numerical simulation on the CPX measurement method were thus validated.|
Further, extensive numerical simulations on enclosures of various dimensions occupying consistent absorption parameters were also conducted, the acoustic quality of the CPX enclosure design was then investigated for enhancement of the noise measurement quality. Through analyzing sound pressure level (S P L) distributions along specific lines and planes for cases with and without enclosure, the effects of enclosure dimensions on the acoustic behaviors in the enclosed space could be compared. The appropriate design of the enhanced PolyU Mark III CPX trailer enclosure can then be determined based on models presenting lower sound reflections and less room resonance. The absorption materials for application in the PolyU Mark III CPX trailer enclosure were investigated and taken into comparison with those applied in the Mark II enclosure. Thicker advanced foam together with micro-perforated honeycomb panels would possibly provide higher absorption performance. The measured and numerical results of S P L on microphone locations and specific lines show a great consistency within the PolyU Mark III CPX trailer enclosure, which gives sound evidence of the feasibility of using the numerical method on the CPX measurement method.
Based on modifications of the PolyU Mark III CPX trailer enclosure, a comparison method was introduced for measuring the sound power level (SW L) of the noise generated from the tyre/road contact patch. The reverberant chamber was built up with several diffuser panels installed within the sub-enclosure covering the foam. The design of the reverberant chamber could be determined with the numerical simulations, as long as the standard deviation (S D) of S P L within the final design of the chamber is lower compared with the others for all frequencies of interest. Several microphone locations were fixed up based on the recommended distance away sound source and the walls, as well as the numerically resulted S P L contours and S D on specific planes. Provided with the measured S P L distributions in the reverberant field generated by a reference sound source of known sound power, the other series of SP L values can also be obtained for the tyre/road noise at the same microphone locations inside the reverberant chamber when the trailer is running on a road at a specific speed. Therefore, the SW L of the tyre/road noise can be calculated with the comparison method specified in BS EN ISO 3741 (2010).
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