• Proceedings of the Acoustical Society of Korea Conference
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• 1996.06a
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• pp.64-68
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• 1996

수중음파전달 모델은 benchmark 시험을 통해 정확도, 적용범위, 계산시간 등의 성능을 평가받는다. 본 논문에서는 analytic 모델, 정상 모드 모델(normal mode model), 포물선 방정식 모델(parabolic equation model), 가우시안 빔 모델(Gaussian beam model), 스펙트럼 모델(spectral model) 등 거리의존 모델에 대해 benchmark 시험을 수행하였으며, benchmark 시험은 다음과 같은 세 가지 거리의존 해양환경으로 나누어 실시했다 : 1) 해수면과 해저면이 Dirichlet 경계조건인 이상 쐐기 문제(ideal wedge problem), 2) 해수면은 앞서 말한 Dirichlet 경계조건이나 해저면은 전달 손실이 있는 손실 통과 해저면 쐐기 문제(penetrable lossy bottom wedge problem), 3) 해수면은 앞서 말한 Dirichlet 경계조건이고 해저면은 Neumann 경계조건으로 서로 평행이면 음파전달 속도가 거리방향 의존인 경우, 경우 1은 anaytic 모델을 사용하고 경우 2는 정상 모드 모델, 포물선 방정식 모델, 스펙트럼 모델을 사용하였으며, 경우 3에 대해서는 가우시안 빔 모델과 포물선 방정식 모델을 사용하였다.

• The Journal of the Acoustical Society of Korea
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• v.25 no.6
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• pp.298-304
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• 2006

This paper proposes a ray-based forward modeling scheme which is suitable for the shallow water acoustic wave propagation simulations. The proposed model comprises of ray tracings for the layered media of which sound speed profiles are interpolated linearly. considerations of plane and spherical wave reflection coefficients. and calculations of the phases and the amplitudes of eigen rays. The main characteristic of the scheme is fast simulation time due to direct calculation of the broad-band time signals in the time-domain, i.e. without transformation of the frequency-domain solutions to the time si 밍 131s. Finally, we applied the model to 4-types of test environments and compared the resulting signals with those of ORCA and Ram in order to validate the proposed model.

• Proceedings of the Acoustical Society of Korea Conference
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• 1992.06a
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• pp.112-120
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• 1992

수심 100m 이하 천해에서 저주파 대역 음파의 전달손실 양상을 규명하기 위해 한국 동해 남부해역 3개 정점에서 특정 주파수 모의신호 발생을 통한 전달손실을 측정하였다. 10개의 특정 주파수에 대해서 연속파(Continuous Wave)를 방생시킬 수 있는 저주파 음원기를 5 kts의 속도로 예인하고, 다시 육상으로 무선전송하여 각 센서에서의 수진준위를 정확하게 보정하였다. 음원으로부터 DIFAR 센서까지의 전달손실은 거리에 대한 Log 함수로 표시할 수 있었으며, 주파수별 전달손실을 비교, 분석한 결과 동해 남부해역에서의 최적 주파수는 800Hz 내외에서 존재하는 것으로 추정된다.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.2
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• pp.201-211
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• 2015

Acoustic propagation in shallow water with changing environments is a major concern of navy. Temporal and spatial variability of acoustic propagation in the northern East China Sea (ECS) is studied, using the 11 years hydrographic data and the Bellhop acoustic model. Acoustic propagation in the northern ECS is highly variable due to extensive interaction of various ocean currents and boundaries. Seasonal variations of transmission loss (TL) with various source depths are highly affected by sharp gradient of sound speed and bottoms interaction. Especially, various bottom sediment types lead to severely degrading a waterborne propagation with bottom loss. In particular, the highly increased TL near the ocean front depends on the source position, and the direction of sound propagation.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.286-291
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• 1997

이상 유동에서의 음파 전달 현상을 비평형, 비균질 이상 유동 방정식에 의하여 이론적으로 유도하였다 개발된 방법은 이상 계면에서의 압력 불연속성을 표면 장력 방정식에 의하여 해결하였으며, 이로 인하여 이상 유동 지배 방정식의 불량 설정된 초기치 문제(Ⅰ11-posed initial value problem)가 완전한 쌍곡형 편 미분 방정식군(Complete hyperbolic partial differential equation system)으로 만들어졌다. 새로이 개발된 방정식의 고유값인 음파의 속도는 실험 결과와 정확히 일치한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.5
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• pp.421-427
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• 2010

In order to visualize the transfer of sound waves, we performed real-time processing with the fast operating system of GPU, the Graphics Processing Unit. Simulation by using the method of the discrete Huygens' model was also implemented. The sound waves were visualized by varying the real-time processing, the reflecting surfaces within the two-dimensional virtual sound field, and the states of the sound source. Experimental results have shown that reflection and diffraction patterns for the sound waves were identified at the reflecting objects.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.4
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• pp.249-258
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• 2001

Compressional wave velocity and electrical resistivity of muddy sediments in the southeastern inner shelf of Korea were studied using nine piston core samples. The acoustic and physical properties were measured with 10 cm depth interval. Sediment structures were examined by x-radiographs of the cored sediments. Subbottom profiles were obtained by a high-resolution acoustic subbottom profiler. Acoustic turbid layers are clearly seen on the profiles, and x-radiographs of the sediments showed degassying structures formed by gas escaping. On the basis of x-radiographic images, velocities, electrical resistivities and physical properties, the sediments are divided into gassy and non-gassy sediments. The presence of gas and degassying structures result in a marked variation in velocity and electrical resistivity. It can be concluded that velocity and electrical resistivity arep arameter to recognize gassy sediment. The velocity is important parameter to indicate gassy sediment.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.187-197
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• 2009

The bubbles are created by waves, raindrops, water collision, vessels sailing at sea, life activities of various marine organisms in the ocean and other sources. The bubbles affect the intensity and sound speed of acoustic waves in the ocean. We indirectly observed bubbles in order to understand the creation of and the effects of bubbles on sound waves, using an Acoustic Bubble Spectrometer (ABS) and CTD, from 04:00 to 17:00, 19 September, 2007. We also analyzed the correlation of wind speed and the generation of bubbles, the amount of bubbles, and the sound speed variation at 50, 60, and 70 kHz. Finally, We simulated the way how bubbles affect sound transmission based on the analysis results.

• The Journal of the Acoustical Society of Korea
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• v.19 no.3
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• pp.77-85
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• 2000

Laboratory determinations of acoustic and physical properties in Korea Strait sediment were carried out. Sediment sound velocimeter(SSV) was employed to measure the sound velocity of sandy sediment. Distribution patterns of the acoustic and physical properties are controlled by sediment texture. The study area is divided into three provinces(mid-shelf, shelf margin and enough) based on the acoustic and physical properties. This classification matches well with the previous result[14] based on the systems tracks and depositional systems. We suggest a geoacoustic model of the Korea Strait that replacing the old model of Briggs and Fisher[5].

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.601-609
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• 2022

In August 2007, coastal upwelling occurred off the east coast of Korea, and vertical water temperature and salinity data were obtained from a real-time surface ocean buoy. Based on the time series observation data, a vertical sound velocity structure was calculated before, during, and after the occurrence of the coastal upwelling, and how the coastal upwelling affects the sound propagation and detection environment through acoustic modeling considering the horizontal scale and actual seabed topography. As a result of comparing and analyzing the low-frequency (500 Hz) sound transmission loss and the target detection range by depth using the parabolic equation model, it was analyzed that if coastal upwelling occurs, a detection gain of up to about 10 dB can be expected. In addition, through this study, it was confirmed that the characteristics of sound propagation can be greatly changed even in a short period of about 2 to 3 days before and after coastal upwelling.