In this paper, the quantification of the external noise sources in high-speed trains is discussed. A thorough understanding of the underlying causes of noise generation in high-speed trains is needed to develop effective noise control measures. However, because high-speed trains produce a complex array of sounds, it is very difficult to determine each individual source of noise. In this study, the delay-and-sum beamforming method, which uses microphone arrays, was used to separate the noise sources and analyze the sound characteristics of high-speed trains. A new microphone array with 96 microphones was designed to measure the noise produced by high-speed trains. Performance verification tests were conducted to ensure the reliability of the results obtained from the array. Then, the system was used to measure the sounds produced by Korean high-speed trains traveling at speeds between 150 and 300 km/h. Sound maps were then produced using the beamforming technique. The study determined that the majority of the noise produced by the highspeed trains originated from the front nose, bogie, pantograph and inter-coach spacing. Finally, the beampower spectra of the aerodynamic noise sources originating in the front nose, pantograph and inter-coach spacing were deduced from frequency conversion. From these results, the aerodynamic noise characteristics of the major sources of noise in highspeed trains were determined.
High-speed trains have a sustained high-noise level for long periods during operation. Although such high-noise levels are effective for acoustic energy harvesting, a practical design for an acoustic energy harvesting system from a high-speed train is lacking. In this study, the design of an energy harvesting system was implemented utilizing noise from a high-speed train during practical operation. We investigated the noise generated from a high-speed train and derived the characteristics of the main noise sources. The results confirmed that low-frequency noise of 50-200 Hz was generated in the passenger, cab, and between car sections. Results from this investigation were used to design a Helmholtz resonator for a target noise of 174 Hz based on a theoretical model. Moreover, numerical simulation was conducted using sound source speakers to investigate vibrations in the walls of the resonator. Finally, energy harvesting experiments were conducted using various types of piezoelectric elements such as rectangular and circular plates. Experimental results indicate that approximately 0.7 V was generated for an incident sound pressure level of 100 dB using a large rectangular plate. Such power level is sufficient to power a variety of low-power electric devices.
A study on the contribution analysis of interior noise and floor vibration in high-speed trains was conducted using operational transfer path analysis. Initially, noise and vibration measurement at various locations on a high-speed train was conducted with accelerometers and microphones. Measurement positions were selected based on the dominant sources of noise and vibration aboard high-speed trains when traveling at high speeds. From the measurements, the characteristics of interior noise and floor vibration were deduced at various train speeds. In addition, noise and acceleration characteristics of the source positions at various speeds were also suggested. Synthesized results regarding interior noise and floor vibration were obtained from operational transfer path analysis, and the estimation was validated by comparison with measured results. The synthesized results were obtained by combining transfer functions obtained through operational transfer path analysis and measured signals from the sources. After validation, the contribution analysis of the interior noise and floor vibration was conducted from the synthesis of the transfer functions and the measurement results. Finally, the main sources of interior noise and the floor vibration in the frequency domain were derived from the contribution analysis. From the results, wheel noise and center pivot vibration were identified as the main causes of interior noise and floor vibration in a high-speed train at a speed of 300 km/h.
In this study, noise-source identification of a high-speed train was conducted using a microphone array system. The actual sound pressure level analysis of the noise source was performed using scaling factors between the real sound pressure and the beam-power output based on the assumption that the integrated area of the main beam-power lobe is equal to half that of the actual sound pressure of the noise source. Then, the scaling factors for the 144-channel microphone array were derived from analysis of the array response function, and a verification experiment was conducted using a known noise source, an air horn, located on a high-speed train moving at 240 km/h. After the verification test, noise-source identification of the high-speed train was conducted. Based on the resulting noise map of the high-speed train moving at 390 km/h, the main noise sources were determined to be the inter-coach spacing, wheels, and pantograph. The noise generated by the pantograph was then investigated in more detail. It was concluded that the pan head of the pantograph was the main noise source at a frequency of 1000 Hz.
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