• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.50-55
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• 1995

진동하는 경계면의 진동장 및 음장을 재구성하기 위하여 음장측정치 및 경계요소법을 이용한 음향 홀로그래피 방법을 연구하였다. 특히, 측정잡음 및 전달행렬의 특이성에 의해 발생하는 재구성 오차에 대하여 고찰하였다. 재구성의 정확도를 나타내기 위하여 전달행렬의 특이인자를 도입하였다. 예제로 한면이 진동하는 직육면체 상자를 고려하였다. 결과로부터 매우 작은 측정잡음에 대해서도 전달행렬의 특이성 재구성 오차가 크게 발생하며, 측정위치에 따라 전달행렬의 특이성이 크게 영향 받음을 확인하였다. EfI방법을 이용하여 최적의 측정점을 선택한 결과 전달행렬의 특이성을 크게 줄일 수 있었으며 이때 측정점의 위치는 가진주파수에 관계없이 큰 음장이 형성되는 소음원의 근접장에 위치함을 알 수 있다. 또한 저주파 가진에 비해 고주파 가진이 작은 특이인자값을 나타내며, 따라서 재구성 오차가 작음을 알 수 있었다. 재구성장의 정밀도를 향상시키기 위하여, 부가적으로 진동장의 norm을 제한하는 적절화방법을 도입하였다. 모델의 최소자승오차를 최소화 하는 최적의 적절화변수를 추정하여 이로부터 재구성 오차를 줄일 수 있었다.

• Journal of the KSME
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• v.24 no.6
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• pp.446-451
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• 1984

최근 기계구조물로부터 발생되는 소음. 진동의 수준을 평가하고 그 대책을 수립하는데 스펙트 럼분석(spectral analysis)과 상관기술(correlation technique)의 이용도가 점증하고 있다. 전자계 산기에 의한 데이터처리기술의 진보에 따라 불규칙한 입력을 받는 기계구조물의 고유진동수추정 및 진동모우드해석, 많은 소음. 진동원을 갖는 플랜트. 선박. 차량기기등의 발생원검출 및 기여 량파악, 그리고 acoustic emission 및 bispectrum에 의한 기기이상진단기술에 적용함으로써 공 학분야에서 한층 중요한 위치를 점하고 있다. 따라서 본 강좌에서는 먼저 상관해석에 의한 스 펙트럼의 정의에 대해서 기술하고 샘플링이론에 만족하는 시간간격으로 샘플링함으로써 얻어지는 시계열데이타를 Fourier 변환하여 주파수영역에서 계의 특성을 해석하는 원리 및 기여함수에 대해 설명하고자 한다. 그리고 입력원간에 상관이 존재하는 경우에 있어서 소음. 진동원을 검 출하고 기여량을 추정할 수 있는 방법으로서의 다차원스펙트럼해석법에 대해 간단하게 기술하 고자 한다.

• Journal of the Korean Society for Railway
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• v.15 no.1
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• pp.23-28
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• 2012

In this paper, noise of Korean high-speed trains (KTX) running at different speed from 150 to 300km/h was measured by a microphone array system. From the measurement, relation between maximum sound pressure levels and train moving speeds of KTX was drawn and a regression coefficient from the relation was also derived. Moreover, increases of SPL with speeds of KTX were analyzed in the frequency domain. From the analysis, sound characteristics of passing-by noise of KTX were provided. Then, dominant noise source areas were obtained from the measurements and propagation patterns of KTX in vertical direction were also investigated. Finally, noise sources of KTX were identified from inspection of noise maps.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.253-256
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• 2004

일반적으로 빔형성 방법은 다수의 독립된 소음원들을 찾아 내기 위한 매우 효과적인 방법으로 각 어레이 마이크로폰들간의 간격에 따른 위상의 차이를 이용한다. 그러나 이러한 위상차는 파장의 길이와 밀접한 관계를 가지므로 어레이의 형상 및 마이크로폰들의 위치는 주파수에 의해 제한 받으며 빔조정 벡터 또한 주파수의 함수로 여러 주파수가 섞여 있는 경우 한계가 있을 수 밖에 없다. 본 논문에서는 크기가 임의적인 음원들에 대하여 주파수와 무관한 빔조정 벡터를 구성함으로써 위상에 대한 제한 없이 소음원을 찾을 수 있는 방법을 제안하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.324-329
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• 2003

An air-conditioner has various noise sources such as cooling fan noise, pumping noise, flow noise and impact noise. Among these, impact noise is the most unpleasant source. This is because the noise is produced in indoor unit of air-conditioner. To control the noise source effectively, first we must identify the noise sources. When we identify impact noise source, the measurement have to be carried out simultaneously. So we use beamforming method that requires less measurement points than intensity method and acoustic holography. The objective of this paper is to estimate the location of impact source. This objective can be achieved by using minimum variance cepstrum that is able to detect impulse embedded in noise. In this study, modified beamforming method based on cepstrum domain is proposed. Then this method applied to air-conditioner noise sources which produce impact noise.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.23-28
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• 2019

A track type underwater construction robot(URI-R) which can trench on seabed is being developed by Korea Institute of Ocean Science & Technology. During the underwater trenching work, the robot is exposed high intensive noise and vibration so the underwater localization signal may not be obtained properly by the acoustic tracking system. Therefore it is necessary to research about continuous localization even though the measured position signal comes in intermittently. In this paper, the experiments were carried out on land to simulated the underwater operating environment characteristics. To estimate its position, inertial navigation system and global navigation satellite system are used. The effects of the period variation while localizing is investigated by the experiments, and the application for URI-R is proposed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.543-543
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• 2010

The objective of this research is estimating the location of interested sound source by using the similarity between a beamformer output in time domain and the candidate signal. The waveform of beamformer output at the location of sound source is similar with the waveform emitted by that source. To estimate the location of sound source by using this feature, we define quantified similarity between candidate signal and beamformer output. The candidate signal describes the signal which is generated by interested source. In this paper, similarity is defined by four methods. The two methods use time vector comparison, and the other two methods use time-frequency map or linear prediction coefficients. To figure out the results and performance of localization by using similarities, we demonstrate two conditions. The one is when two pure tone sources exist and the other condition is when several bird sounds exist. As a consequence, inner product with two time-vectors and structural similarity with spectrograms can estimate the locations of interest sound source.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.822-825
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• 2005

In the case of aeroacoustic test in windtunnel, measurement accuracy is reduced by not only Doppler effects but also by the microphone self noise due to airflow and high turbulence in the wall boundary layer. Microphone array measurements can be easily utilized for the solutions of these problems. In this paper, geometrical optics approach and diagonal term elimination of cross spectral matrix was introduced to the de-dopplerization and self noise reduction methods for the microphone array measurement. For the validation, beamforming tests for sinusoidal point source were performed in the closed type test section of windtunnel, and their performances of beam width and sidelobe rejection were significantly improved.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.69-74
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• 2016

A technique for improving estimation accuracy is introduced in order to locate the impact position of artillery shell during the weapon scoring test. Study on localization of impacts using acoustic measurement has been conducted and the usability of sensor array is verified with experiments. When the blast occurs above the ground in the firing range, the acoustic sensor above the ground can measure the directly propagated sound with the ground-reflected one. In this study, a method for reducing estimation error by using the reflection signal measurements based on the time difference of arrival method. Considering the reflection sound works as same as placing a virtual sensor symmetrically through the ground. This idea enables a virtual three-dimensional array configuration with a two-dimensional plane array above the ground as such. The time difference between the direct and the reflected propagations can be estimated using cepstrum analysis. Performance test has been made in the simulation experiment in the football size area.

• The Journal of the Acoustical Society of Korea
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• v.27 no.1
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• pp.40-46
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• 2008

Weak target detection and localization in the presence of loud surface ship noise is a critical problem for matched field processing (MFP) in shallow water. For stationary sources, each signal component of received signal can be separated and interference can be suppressed using eigen space analysis schemes. However, source motion, in realistic cases, causes spreading of signal energies in their subspace. In this case, eigenvalues of target and interfere signal components are mixed and hard to be separated with usual phone space eigenvector decomposition (EVD) approaches. Our technique is based on mode space and utilizes the difference in their physical characteristics of surface and submerged sources. Performing EVD for modal cross spectral density matrix, interference components in the mode amplitude subspace can be classified and eliminated. This technique is demonstrated with synthetic data, and results are discussed.