Paper Title:
Noise Source Localization Investigation in High Speed Train Based on Microphone Array
  Abstract

The method to use planar array to identify the noise sources in high speed train is described. Through investigating the noise sources in high speed train, it is shown that the important noise sources are situated at windshield, door, air outlet, joints between headwall and sidewall. The spectra characteristics and sound pressure contour of these noise sources are obtained. The sound energies of these noise sources are concentrated in the frequency range of 0~1000 Hz mainly. Some effective countermeasures against interior noise of high speed train are suggested.Interior train noise decreases the comfort for the passengers inside the vehicle. As speeds increase, noise inevitably also increases. It has been known that rolling noise levels increase at a rate of 30log10v (with v the speed). The noise from aerodynamic sources increases more rapidly with speed, increasing at typically around 60log10v, and above 300 km/h aerodynamic noise becomes significant [1-2]. In order to carry out effective countermeasures against high speed noise, a detailed knowledge of the distribution and the properties of the sound sources is necessary. One of the methods to identify the different train sources is to carry out noise measurements with devices such as antennae. An acoustic antenna is a series of microphones, whose outputs are processed in order to focus on acoustic sources and to enable an acoustic map to be drawn. Accurate measurements on high-speed train usually require the development of specific tools [4-6]. The main sources identified from different studies on various high-speed trains are the pantograph, the recess of the pantograph, the inter-coach spacing, the bogie, the nose of the power car, the surfaces, the rear power car, louvres, ventilators[7-11]. However, it has not been reported how to locate interior train noise sources, which is critical for interior noise abatement and reduction design. In this paper, a planar microphone array is introduced and used to study the noise sources and spectra characteristics in high speed train. Measurement principle of planar microphone arrayAccording to the distance between the sound source and microphone array, the propagation model of sound signal can be divided as near-field and far-field model. Near-field model is suitable for source location and measurement of interior train noise. At near field, the sound wave near microphone array can be taken as spherical wave. According to spherical wave propagation theory, sound waves from source q at tf will reach the i-th microphone in the microphone array at the moment of tf +tiq. Where, tiq is the time for sound waves to get to the microphone position (xi, yi, zi) from sound source q at (xf, yf, zf). The microphone will take t to receive sound emitted from sound source, where (1)For homogeneous medium with the sound speed c, propagation time can be obtained as (2)Where,riq is the distance between sound source and i-th microphone: (3)According to delay-sum beamforming principle, the sound radiated from sound source focused by planar microphone array is decided by the microphone array’s output pq(tf) : (4)Where, Where, pi(tf+ti) is the signal recorded by the i-th microphone at tf +ti , T is transpose operation, rref is reference distance of sound radiation, wi is the window function of array, which can reduce the sidelobe level after beamforming.After focusing, the output power spectrum of the sound source is: (5)Based on sound field information obtained by microphone array, sound source can be effectively identified after acoustic signal processing by beamforming or power spectrum estimation theory.Sound power spectrum analysis of measured areasAccording to the main noise sources and the weak parts of train structure, 8 measurement areas are arranged as Table 1. In test, high speed train runs at 300km/h. 8×8 planar microphone array and self-developed acquisition and analysis system of train noise are used. A-weighted sound pressure level (SPL) of measured areas are shown in Table 1.Table 1 A-weighted SPL of the measured areasAs seen from Table 1, the SPL are higher at windshield, door, air outlet, joints between headwall and side walls. To reduce interior noise of high speed train, these areas should be treated heavily.The sound power spectrum of the measured area are shown in Fig. 1-Fig. 9. As seen from the figures, the noise energy is concentrated in the frequency range of 0~1000 Hz. To reduce the interior noise of high-speed train, noise reduction strategies must be adopted at low frequency parts.Fig. 1 Sound power spectrum of measured areaFig. 2 Sound power spectrum of measured area 2Fig.3 Sound power spectrum of measured area 3Fig. 4 Sound power spectrum of measured area 4Fig. 5 Sound power spectrum of measured area 5Fig. 6 Sound power spectrum of measured area 6Fig. 7 Sound power spectrum of measured area 7Fig. 8 Sound power spectrum of measured area 8Fig. 9 Sound power spectrum of measured area 9Noise distribution of the measured areasNoise distribution at the door. Fig.10 and Fig.11 are the sound pressure contours at the measured area 1 and 2 respectively. It can be shown that the SPL are higher at the upper right corner and at the bottom of the door. So it can be sure that the junction between the door and train wall is not sealed well, which results in acoustic leak. The sound pressure at lower right corner is significantly greater than that of upper right corner. The maximum sound pressure at lower right corner is 93.8 dB. Lower right corner is near to the compartment floor, so compartment floor vibration is one of the major noise sources.It is beneficial for reducing noise at the door to improve the seal, to reduce the floor vibration and to use good soundproof deck.Fig. 10 Sound pressure contours of measured area 1Fig. 11 Sound pressure contours of measured area 2Noise distribution at air outlet. Figures 12 and 13 are the sound pressure at air supply outlet and air return outlet respectively. It can be shown that the SPL are higher at these two measured places, and they will become the main sources of interior noise. So noise elimination measures should be adopted at air duct to reduce the compartment noise. Fig. 12 Sound pressure contours of measured area 3     Fig. 13 Sound pressure contours of measured area 4Noise distribution at center in carriage and floor above the bogie. Fig. 14 and Fig. 15 are the sound pressure contours at center in carriage and floor above the bogie respectively. It is shown that the SPL at the center in carriage are 5.21dB(A) greater than that of floor above the bogie, so the vibration from bogie is greater. By optimizing the bogie structure to reduce the panels vibration, interior train noise can be reduced greatly.Fig. 14 Sound pressure contours of measured area 5Fig. 15 Sound pressure contours of measured area 6Noise distribution at joints of the sidewall and window. Fig. 16 is the sound pressure contours at joints of sidewall and window. It is shown that the noise level is higher at the left joints, so the seals is not tight at the left joints, measures should be taken to improve the seals at left joints.Fig. 16 sound pressure contours of measured area 7Noise distribution at joints of the sidewall and headwall. Fig. 17 is the sound pressure contours at joints of the sidewall and headwall. It is shown that the noise level is higher at the right joints between sidewall and headwall. So the seals is not tight at the right joints, and there are acoustic leak. It is beneficial for reducing interior noise to optimize the coupled type between sidewall and headwall, which will improve the seal effect.Fig. 17 sound pressure contours of measured area 8Noise distribution at windshield. Fig. 18 is the sound pressure contours at windshield. It is shown that the SPL level at the windshield is 1-3dB(A) higher than that of other areas. It is helpful for reducing noise at the windshield to use tight lock windshield with good flexibility, which will enhance connection strength and connection tightness between coaches. Fig. 18 Sound pressure contours of measured area 9ConclusionsA good understanding of the sources and their characterizations are necessary to find a good solution. In order to locate noise sources in high speed train, a technique is introduced based on a spectrum analysis of those noise sources by using the data measured with a microphone array. Through a series of experiments and analysis, the conclusions can be obtained as follows:The SPL are higher at low frequency range of 0~1000 Hz and at the areas of windshield, door, windshield, the joints between sidewall and headwall. To reduce noise in high speed train, the low frequency noise at these areas should be treated seriously. Some effective countermeasures against interior noise of high speed train are suggested. AcknowledgementsThe authors wish to thank China Natural Science Foundation(50975289), China Postdoctoral Science Foundation(20100471229) for funding this work.REFERENCES[1] Talotte C. Aerodynamic noise: a critical survey. Journal of Sound and Vibration. 2000, 231(3):549-562[2] Mellet C, Letourneaux F, Poisson F, Talotte C. High speed train noise emission: Latest investigation of the aerodynamic/rolling noise contribution. Journal of Sound and Vibration. 2006, 293(3): 535-546[3] Kitagawa T, Nagakura K. Aerodynamic noise generated by shinkansen cars. Journal of Sound and Vibration 2000, 231(5):913-924.[4] BARSIKOW B. Experiences with Various Configurations of Microphone Arrays Used to Locate Sound Sources on Railway Trains Operated by the DB AG [J], Journal of Sound and Vibration, 1996, 193 (1): 283-293[5] BARSIKOW B, KING W F and PFIZENMAIER E. Wheel/rail noise generated by a high speed train investigated with a line array of microphones Journal of Sound and Vibration 1987,118(1):99~112.[6] Nagakura K. Localization of aerodynamic noise sources of Shinkansen trains. Journal of Sound and Vibration, 2006, 293(3):547-556[7] Iwamoto K, Higashi A. Some consideration toward reducing aerodynamic noise on pantograph. Japanese Railway Engineering, 1993, 122 (2):1-4[8] Ikeda M, Morikawa T, Manabe K. Development of low aerodynamic noise pantograph for high speed train. Proc 1994 Int Congr Noise Control Eng, 1994, 1, 169-178[9] Ikeda M, Suzuki M, Yoshida K. Study on optimization of panhead shape possessing low noise and stable aerodynamic characteristics. Quarterly Report of Railway Technical Research Institute, 2006, 47(2):72-77[10] Fremion N, Vincent N, Jacob M. Skirts and barriers for reduction of wayside noise from railway vehicles—an experimental investigation with application to the BR185 locomotive. Journal of Sound and Vibration. 2003, 267(3):709-719 [11] Frid A. Aerodynamic noise radiated by the intercoach spacing and the bogie of a high-speed train. Journal of Sound and Vibration. 2000, 231(3):577-593

  Info
Periodical
Edited by
Qiancheng Zhao
Pages
285-291
DOI
10.4028/www.scientific.net/AMM.103.285
Citation
X. F. Zhang, Y. G. Xiao, H. L. Deng, "Noise Source Localization Investigation in High Speed Train Based on Microphone Array", Applied Mechanics and Materials, Vol. 103, pp. 285-291, 2012
Online since
September 2011
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