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.
A pantograph in contact with a catenary for power supply is one of the major aerodynamic noise sources in high-speed trains. To reduce pantograph noise, it is essential to understand the noise generation mechanism of the pantograph. However, it is difficult to determine this mechanism through measurement. Therefore, in this study, the aerodynamic and acoustic performances of a pantograph in a high-speed train were investigated through numerical analysis using the lattice Boltzmann method. First, a real-scaled pantograph was modeled through computer-aided design. Then, the surface and volume meshes of the pantograph model were generated for simulation analysis. Numerical simulation was conducted at a speed of 300 km/h based on the lattice Boltzmann method. Based on the time derivative analysis of flow pressures, it was concluded that the panhead, joint, and base were the dominant noise sources in the pantograph. In particular, various vortexes were generated from the metalized carbon strip of the panhead. The peaks of the sound pressure level propagated from the panhead were 242, 430, and 640 Hz. The noise generation mechanism was analyzed through numerical simulation using noise characteristics.
Interior noise in high-speed trains creates passenger discomfort and fatigue. In particular, the noise generated around the gangway between carriages tends to be easily transmitted to the passenger spaces due to the large noise component in the low-frequency region. In addition, the noise from the between-cars space around the gangway exterior tends to increase significantly when the high-speed train is travelling inside a tunnel. Therefore, this study analyses the cause of the noise generated in the gangways and identifies an effective method for reducing it. First, the mechanism for noise generation around the gangways was determined by computational flow noise analysis using a simple two-dimensional cavity model. From this simulation, it was confirmed that noise is generated when air flow enters the cavity. To investigate the influence of noise reduction in the between-cars section, blocking the airflow indirectly by installing fairings or directly by using side barriers was proposed. These noise reduction methods were examined by flow noise analysis, and then applied to an actual high-speed train. The interior noise was measured, and the results show that the use of side barriers was effective in reducing interior noise by 10 dB or more. In particular, a high noise reduction effect was exhibited in the low-frequency region. Therefore, this study verifies that directly blocking the inflow into the between-cars section is an effective noise reduction method.
When a railway vehicle moves over a sharply curved section of track, intense high-frequency noises sometimes occur. These are potentially a source of annoyance to those living adjacent to railway tracks. To efficiently identify measures appropriate to reduce curve squeal, it is important to determine the dominant noise type. However, it is difficult to analyze the various noises made over curved sections of railway using general noise measurements. In this study, we analyzed squealing and flange noises using various experimental approaches. We first investigated the noise characteristics of the railway vehicle via structural analysis of the wheel. It was confirmed that a wheel has various natural frequencies and eigenmodes in the high frequency range, i.e. over 1000 Hz. A roller rig test was performed to measure and investigate the characteristics of the noise generated when an actual wheel and the curved section of the railway track come in contact with each other. In this experiment the squeal and the flange noises, in particular, were reproduced by adjustments made to the lateral angle and vertical force, respectively. Results confirmed that the squealing noise occurs in the high frequency region and the flange noise occurs in various modes. A study was also conducted to measure and analyze the noise in the actual curved section of an urban railway. By comparing the frequency analysis and the natural frequency analysis of the noise that was actually measured, the mode by which the wheel caused the squealing noise was confirmed. Furthermore, the influence of the noise generated inside and outside the curved section of the track was investigated based on velocity, and the influence of the former on the noise generated was also examined. This study provides information on the squeal and flange noises generated when a railway vehicle moves over a curved section of a railway using various experimental approaches.
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