• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.144-151
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• 2006

Sound generated from a moving vehicle often carries information on the condition of vehicle, for example, whether it has faults or not, where the fault exists. The latter is possible especially by MFAH(moving frame acoustic holography) and beamforming method. MFAH is applicable to the sound source of pure tone or narrow band noise. For the beamforming method, we have to know what kind of wave the sound source radiates, for example, plane wave or spherical wave. That is, whether the above methods are applicable depends on the characteristics of sound source. To apply these methods to the fault detection, we have to know the characteristics of wave from faults. In this research, a machine diagnosis technique based on the above holographic approaches is introduced to find the position of faults. The signal due to faults is modeled based on the fact that the faults radiate impulsive noise, and analyzed in time and frequency domain. The way how MFAH and beamforming method can be used is introduced to find the position of source.

• 한국군사과학기술학회지
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• 제24권2호
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• pp.228-236
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• 2021

In order to understand the underwater noise source factor of the linear pump type forced ejection system, a reduced-model compressed water experiment device was developed. The reduced-model compressed water experiment device consists of a reverberation tank, a linear pump type forced ejection device, and an underwater vehicle. The underwater noise source was selected from the hydraulic ram moving speed, the hydraulic ram/piston pipe spacing, the ejection pipe inlet/water ram area ratio, and the number of water ram inlets. The underwater vehicle was ejected into the reverberation tank by the device. The source level was derived from the measured sound pressure. The source level tends to increase as the hydraulic ram/piston tube spacing and the hydraulic ram moving speed increase. The source level tended to increase as the area ratio was increased, but the level was weak. The number of water ram inlet did not affect the source level.

• 한국소음진동공학회논문집
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• 제26권5호
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• pp.501-510
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• 2016

Capabilities of several beamforming techniques are compared for estimating the position of a moving source. Beamforming has enabled to widen our perspective of aeroacoustics in wind tunnel experiments and has provided useful approach in array measurements. Meanwhile beamforming techniques have been developed in a way to improve estimation accuracy and to save ing effort at the same time. In order to achieve reasonable outcome from aeroacoustic measurement, it is important to identify the spectral characteristics of source and to select an appropriate beamformer. Though aeroacoustic sources normally generates broadband noises, many array signal processing have been focused on narrowband processing which makes calculation numerically efficient. However, calculation in frequency-domain requires selection of single frequency of interest which affects spatial resolution and sidelobe level as a consequence. To be able to localize broadband noise source, it is proposed to use broadband beamforming. The formulas implements the deletion of diagonal term from cross spectral matrix. In this study, trajectory of flying source emitting broadband noise was simulated and several beamformers are applied.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 추계학술대회 논문집
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• pp.225-228
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• 2009

The simulated indoor pass-by noise measurement system is the tool to measure and evaluate the pass-by noise at the test laboratory, without doing measurement at the field. This measurement system can realize the precision measurement under the specific condition and overcome the limitations of the field measurement, i.e. weather conditions, repeatability, .. This measurement system is done in time domain process using the array techniques, which synchronizes the time signals. The reliability of the obtained result depends on the array shapes, which can generate the moving source effect. In this paper, the validations are checked focusing the time domain synchronization of the signals with the optimum microphone array shape.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.147-152
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• 2012

An instantaneous environmental noise simulation method emitted by a moving high-speed train by quasi-stationary analysis is proposed in this study. In the method, the propagation attenuations from stationary point sources on segmented railways to a receiver are calculated using a general purpose environmental noise prediction program ENPro based on the ISO 9613-2 method. Then, the instantaneous environmental noise at a receiver due to a moving high-speed train considering convection effect is evaluated with the information on the propagation attenuations from the instantaneous train location to the receiver and the sound power levels and directivity of stationary point sources evaluated by German Schall 03 (2006). To demonstrate the validity of proposed method, simulated and measured time history of instantaneous noise for KTX-I and KTX-II on running are compared and the results show that the method can be utilized for the train noise source identification as well as the simulation of instantaneous environmental noise emitted by a high-speed train.

• 한국음향학회지
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• 제35권4호
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• pp.310-318
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• 2016

본 연구는 해상 운항체에서 발생하는 소음원의 위치를 3차원적으로 추정하는 방법에 대해 다루었다. 해상 운항체인 선박이나 잠수함의 내부에 존재하는 소음원과 같이 근접이 어려운 경우라도 상대적으로 이동한다면 외부의 수중청음기에 수신된 신호는 도플러 효과가 발생한다. 본 연구에서는 이동 물체에 의한 도플러 효과를 바탕으로 소음원의 3차원 위치 추정 알고리즘을 제안하였다. 해상 운항체의 알고 있는 위치에 추가의 음원을 설치하여 예상되는 도플러 중심의 범위와 최단 접근점의 범위를 점차 줄여가며 최소자승법을 통하여 내부 소음원의 위치를 추정하였다. 알고리즘을 통해 계산한 값과 이론값을 비교하여 효용성을 입증하였으며, 수치시험을 통해 고정된 두 개의 외부 수중청음기와 음원 역할을 하는 수중체에 고정시킨 한 개의 신호발생기로 도플러 효과를 기반으로한 소음원의 3차원 위치 추정이 가능함을 증명하였다.

• 한국소음진동공학회논문집
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• 제17권6호
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• pp.477-483
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• 2007

Major noise source in high speed rotating optical disk drives (CD and DVD-ROM) arises due to the high-speed airflow produced from the upper and lower surfaces on the rotating disk. The present paper deals with the experimental approach how to identify the noise source based on the fundamental principles of aeroacoustics and to propose a reduction method of the noise source. The CD-ROM device is composed of disk, window tray, motors at the bottom place and electronic circuit plate also located below the window plate. The window is cut in the tray to read the disk information using the optical device located below the tray and moving linearly from the center of the disk through the end of the disk. All components are possible noise generators. Experimental studies were carried out in the anechoic room with various design modifications, such as tray geometry, window size and hole location on tray, to identify the major aerodynamic noise source and significant reductions of the aerodynamic noise were obtained.

• 설비공학논문집
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• 제13권7호
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• pp.621-626
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• 2001

The flow induced noise of the cross-flow fan with uniform/random pitch blades is predicted by computational methods. With the time dependent surface pressure data obtained by solving the incompressible Navier-Stokes equations in moving coordinates, the acoustic pressure is predicted by the Ffowcs Williams-Hawkings equation. The positions of the blade noise source are identified through an investigation of the acoustic pressure history induced by one blade, and it is confirmed that the dominant noise source is near the stabilizer. Since the acoustic pressure of the random pitch fan fluctuates according to the blade passin, the dominant BPF noise of the uniform pitch fan is modulated into some reduced discrete noises which have multiples of a 50Hz difference from BPF.

• 한국음향학회지
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• 제21권5호
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• pp.446-454
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• 2002

본 연구는 이동 표적체에서 주파수가 서로 다른 신호가 서로 다른 위치에서 발생할 때 도플러 주파수 편이량을 추정하여 이들의 상대적인 신호 발생 위치를 추적하는 도플러 스캐닝 기법에 관한 연구이다. 예를 들어 선박의 발전기와 프로펠러 등과 같은 탑재 기계장치들의 진동에 의해 야기되는 기계적 소음의 각 특징 주파수들의 도플러 주파수 편이는 최단근접거리 (CPA: Closest Point of Approach)에 따라 유일한 시간 정보를 갖고 각 소음원들의 위치에 관련되는 함수이다. 따라서 도플러 스캐닝 기법을 적용하면 이동 선박의 각 기계적 소음원들간의 공간적인 상대 위치 추정이 가능하다. 그러나 일반적으로 기계류 소음의 주파수는 저주파수대역이므로 도플러 주파수 편이량을 추정하기 위해서는 주파수 분해능이 높아야 하고 아울러 탑재장치의 공간분해능을 높이기 위해서는 동시에 시간 분해능이 높아야 한다. 따라서 상호 역비례 관계에 있는 이들 분해능을 동시에 높이기 위해 확장 칼만 필터 알고리즘을 적용하여 특징 신호들의 도플러 주파수 편이량을 추정하여 기계류의 상대적인 탑재 위치를 규명할 수 있음을 보인다. 먼저 수치모의 실험으로 그 가능성을 검증하고 자동차에 탑재된 스피커 음원을 사용한 실험 결과를 통해 그 성능을 확인하도록 한다.

• 한국소음진동공학회논문집
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• 제14권3호
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• pp.224-229
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• 2004

In order to control the railway noise, the radiation characteristic of the noise when the train passes by should be analyzed. Generally, the major noise sources of the Korea Train Express are the rolling noise and power unit noise up to 300km/h. In this paper, a train model that is considered to be a row of point sourcesis introduced to analyze the radiation characteristic. The analysis results are compared with the measurement ones. It is shown that the propagation characteristic of the rolling noise is a dipole type and the noise generated by the power unit is radiated as a cosine type. With increasing of the train speed, the noise level at a receiving point is increased in the direction of motion and reduced in the direction opposite to the motion. The analysis results including the moving effect of the noise source at 300km/h show good agreement with the measurement results.