• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.63-69
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• 2000

Korea Institute of Geology Mining and Materials(KIGAM) cooperating with Southern Methodist University(SMU) has been operating seismo-acoustic array in Chul-Won area to discriminate man-made explosions from natural earthquakes since at the end of July 1999. In order to characterize propagation parameters of detected seismo-acoustic signal and to associate these signals as a blast event accompanying seismic and acoustic signals simultaneously it is necessary to understand infrasound wave propagation in the atmosphere. Two comparable Effective Sound Velocity Structures(ESVS) in atmosphere were constructed by using empirical model (MSISE90 and HWM93) and by aerological observation data of Korea Meteorological Administration (KMA) at O-San area. Infrasound propagation path computed by empirical model resulted in rare arival of refracted waves on ground less than 200km from source region. On the other hand Propagation paths by KMA more realistic data had various arrivals at near source region and well agreement with analyzed seismo-acoustic signals from Chul-Won data. And infrasound propagation in specific direction was very influenced by horizontal wind component in that direction. Linear travel time curve drawn up by 9 days data of the KMA in autumn season showed 335.6m/s apparent sound velocity in near source region. The propagation characteristics will be used to associate seismo-acoustic signals and to calculate propagation parameters of infrasound wave front.

• 한국통신학회논문지
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• 제35권1C호
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• pp.130-137
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• 2010

본 논문에서는 상향 실내음향측위를 위한 자체발성음으로서 휘파람소리, 손가락딱소리, 박수소리의 시간 및 주파수영역, 상관 및 전력스펙트럼밀도, 최대지연시간, 최대주파수, 대역폭 분석을 통해 여러 자체발성음의 측위음원으로서의 적합성을 판단한다. 그리고 자체발성음의 도달지연시간차에 기반을 둔 실내측위시스템을 설계하고 그 성능을 평가한다. 자체발성음 분석과 측위성능평가를 위해 여성과 남성 각 50명씩, 총 100명의 자체발성음 데이터베이스를 구축해 활용하였다.

• 대한조선학회논문집
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• 제61권1호
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• pp.1-7
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• 2024

Underwater sound speed is an important analysis parameter on an estimation of the underwater radiated noise (URN) emitted from vessels. This paper aims to present an underwater sound speed measurement procedure using a cross-correlation of time-domain acoustic signals and validate the procedure through an experiment in a reverberant water tank. For the purpose, time-domain acoustic signals transmitted by a Gaussian pulse excitation from an acoustic projector have been measured at 20 hydrophone positions in the reverberant water tank. Then, the sound speed in water has been calculated by a linear regression using 190 cross-correlation cases of distances and time lags between the received signals and the result has been compared with those estimated by the existing empirical formulae. From the result, it is regarded that the presented experimental procedure to measure an underwater sound speed is reliably applicable if the time resolution is sufficiently high in the measurement.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 하계종합학술대회논문집
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• pp.623-626
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• 1998

NLMS algorithm is degraded by the ambient noises and the near-end speech signals. In this paper, a robust acoustic echo cancellation algorithm is proposed. To enhance the echo cancellation performance, the step size of the proposed algorithm is normalized by the sum o fthe power of the reference signals and the primary signals. as results of comparing the excess mean square errors, it is shown that the proosed algorithm can enhance the performance of cancelling the echo signals. Some experiments, which is used multimedia personal computer, are carried out. As results of experiments, the proposed algorithm shows better performance than conventional ones.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.678-682
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• 1996

Acoustic emission(AE) is monitored during end milling with a sensor attached to the cutting fluid discharge nozzle. Cutting forces are also measured and compared with the AE signals to examine the reliability of the AE signals. It is demonstrated that the AE signals provide reliable informations about the cutting processes and tool states. Moreover, edge chipping and fracture of tools can be successfully detected using both the AE signals and cutting forces.

• Journal of information and communication convergence engineering
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• 제8권2호
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• pp.163-167
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• 2010

In underwater acoustic communication, acoustic signals from transducers or hydrophones are used. And the underwater acoustic communication channels are very complicated, because of vertical distribution of acoustic velocity according depths, and reflections from boundaries like as surface or bottom. For the implementation of the underwater acoustic communication channel, the image method or ray tracing method have been used. In this paper, we introduce a new approach for implementation of underwater acoustic communication channel using the simulation of the Transmission Line Matrix Modeling and cross-correlations from the input and output signals.

• 한국정보통신학회논문지
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• 제16권11호
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• pp.2388-2396
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• 2012

본 논문에서는 스테레오 음향반향제거기의 수렴특성을 향상시키기 위한 간략화된 직교투사법을 제안한다. 간단하고 안정되어 널리 사용되고 있는 기존의 NLMS 알고리즘과 비교하여, 이 기술은 음성신호와 같이 상호상관도가 높은 신호에 대해 수렴성능이 향상되고 연산량이 감소한다. 본 연구에서 제안한 SOP 알고리즘의 성능을 검증하기 위하여 모의실험용 프로그램을 작성하고 시뮬레이션을 수행하였다. 입력신호의 종류와 적응 알고리즘에 따라서 반향제거기의 수렴특성을 관찰한 결과, 제안한 알고리즘을 적용한 스테레오 반향제거기는 백색 잡음을 입력으로 사용하는 경우 약 3dB 정도, 유색 음성신호를 입력으로 사용하는 경우 약 5dB 이상의 ERLE 성능이 개선되는 것을 보여 주었다.

• 대한토목학회논문집
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• 제33권2호
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• pp.433-442
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• 2013

이 논문에는 길이가 50m인 프리스트레스트 콘크리트 박스거더를 이용한 1차원, 2차원 음원위치 산정을 위한 실험연구 내용을 수록하였다. 슈미트 햄머를 이용하여 콘크리트 표면에 타격하여 충격음파를 발생시켰으며 PSC박스거더 복부판에 평균 9.34m 간격으로 부착한 AE센서를 통해 충격 음파를 감지하였다. 공용중인 PSC박스거더 교량에 발생할 수 있는 잡음을 고려하여 음파의 도달시간을 음파의 세기가 0Volt, 0.5Volt, 그리고 1.0Volt일 때를 기준으로 산정하였다. 음파의 도달시간들에 대한 측정결과를 토대로 충격음파의 음원위치를 최소제곱법을 이용해 산정하였다. 실험결과를 토대로 2차원 음원위치 산정시 오차를 최소화하기 위해 필요한 음향센서 간격과 음향센서의 네트워크에 대해 고찰하였다.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제4권1호
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• pp.51-55
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• 2001

The characteristics of elastic waves emanating from crack initiation in 2024 and 5052 aluminum alloys subject to static and fatigue loading are investigated through laboratory experiments. The objective of the study is to determine difference in the properties of the signals generated from static and fatigue tests and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission (AE) waveforms. The signals are recoded using non-resonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Three distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the material and the type of fracture associated with the signals. Analysis of the waveforms indicated that some signals could be attributed to plastic deformation associated with static tests. The potential application of the approach in health monitoring of aging aircraft structures using a network of surface mounted broadband sensors is discussed.

• 한국음향학회지
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• 제28권4호
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• pp.328-335
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• 2009

음향수신신호의 위상은 매질에 대한 정보를 포함하고 있기 때문에 위상 변동을 연구하는 것은 매질에 대한 연구와 동반 되어야 한다. 또한 SAS (Synthetic Aperture Sonar)나 수중통신 등의 신호처리 시 수신신호의 위상변동 보정이 필요하다. 본 연구에서는 미세구조 난류에 의한 수신신호의 위상분산을 고찰하였다. 국지적으로 등방성이고 균질한 난류 환경 하에서 난류세기인자를 구하였고 음파 전달경로에 따라 난류세기가 미치는 영향을 고려하여 위상분산을 계산하였다. 난류세기 계산에 필요한 CTD자료와 ADCP자료는 묵호항 근처에 설치된 부표에서 획득하였으며 음파 전달경로는 Bellhop알고리즘을 이용한 음선 모델을 사용하였다. 결과적으로 난류세기인자는 주로 수온과 유속의 변화에 의해 결정되었으며 수신신호의 위상분산에 영향을 주었다. 이러한 위상분산은 소나 운용에 고려되어야 할 사항으로 여겨진다.