Assessment of Acoustic Iterative Inverse Method for Bubble Sizing to Experimental Data

최복경,김봉채,윤석왕,김병남 한국해양과학기술원 2006 Ocean science journal Vol.41 No.4

Comparative study was carried out for an acoustic iterative inverse method to estimate bubble size distributions in water. Conventional bubble sizing methods consider only sound attenuation for sizing. Choi and Yoon [IEEE, 26(1), 125-130 (2001)] reported an acoustic iterative inverse method, which extracts the sound speed component from the measured sound attenuation. It can more accurately estimate the bubble size distributions in water than do the conventional methods. The estimation results of acoustic iterative inverse method were compared with other experimental data. The experimental data show good agreement with the estimation from the acoustic iterative inverse method. This iterative technique can be utilized for bubble sizing in the ocean.

수중 공기방울의 선형 배열에 의한 음향 방출

최복경,윤석왕,Choi, Bok-Kyeoung,Yoon, Suk-Wang 한국음향학회 1994 韓國音響學會誌 Vol.13 No.3

수중에서 공기방울들의 선형 배열에 의해 방출된 음향의 주파수 특성을 이론 및 실험적으로 살펴보았다. 공기방울들의 상호 작용을 고전적 조화진동자의 결합으로 다루었으며, 이론적으로 공기방울들의 선형 배열을 인접한 공기방울들간의 효과만을 고려한 유효 결합 조화진동자 모델로서 제안하였다. 공기방울 중심 사이의 거리가 공기방울 직경의 두 배가 넘는 약한 결합의 경우에 대해, 제안된 유효 결합 조화진동자 모델은 실험 결과들과 잘 일치함을 보여주었다. The frequency characteristics of sound radiated by a line array of bubbles in water was investigated theoretically and experimentally. In the theory we proposed an effective coupled harmonic oscillator model for a line array of bubbles treating the interaction of only adjacent bubbles as the coupling of classical harmonic oscillators. For weak coupling of bubbles that the distance between adjacent bubbles is larger than the diameter of a bubble, the pressented theoretical model shows very good agreement with the experimental results.

음속의 수직분포에 따른 해수중 주위잡음의 의존성

최복경,김봉채 한국음향학회 1998 韓國音響學會誌 Vol.17 No.3

해수중 주위잡음에 미치는 음속구조의 영향을 조사하기 위하여 다양한 수직 음속분 포를 가지는 경우에 대한 음파전달 모델의 결과를 논의하였다. 그리고 해수중 주위잡음의 실측자료를 이러한 모델결과와 비교하여 고찰하였다. 특히 표층 도파관(surface waveguide) 이 형성되는 조건에 대하여 조사하였다. 주위잡음의 실측자료와 모델결과를 비교한 결과, 표 층 도파관은 수심의 증가에 따라 음속이 증가하는 양의 음속 기울기를 가질 때 뿐만 아니라 음속이 어느 수심에서 급격히 감소하여 상하 두 층의 음속 균일층이 존재하는 환경에서도 잘 형성되고 있었다. 특히, 표층 도파관내의 주위잡음 레벨은 도파관 이심의 주위잡음 레벨 보다 높게 나타나고 있음을 실험적으로 확인할 수 있었다. 그리고 이러한 결과는 음파전달 모델에 의한 수치계산 결과로부터도 입증할 수 있었다.

한반도 주변해역 수중배경소음의 풍속과 선박분포에 따른 의존성 분석

최복경,김봉채,김철수,김병남 한국음향학회 2003 韓國音響學會誌 Vol.22 No.3

한반도의 연근해에서 9년간 ('90∼'98)에 걸쳐 200m이내의 수심을 보이는 13개 정점에서 배경소음을 측정한 자료를 환경별로 통계 처리하여 소음준위를 분석하였다. 주파수 스펙트럼은 1/3옥타브 밴드의 중심주파수 25㎐부터 20㎑까지 분석하였다. 분석결과, 대양의 배경소음스펙트럼으로 알려진 Wenz의 결과와는 다소간의 차이를 보여주었다. 연근해에서 측정된 결과는 다양한 선박활동 및 연안소음, 파도의 영향 등으로 인해 같은 조건에서의 대양의 결과 보다 높은 배경소음준위를 보이고 있었으며, 통계분석에 근거하여 천해 소음 추정식을 산출하였다. It is statistically analyzed the underwater ambient noise measured at 13 sites less than 200 m deep in the shallow water surrounding the Korean Peninsula for 9 yews from 1990 to 1998 in various environmental conditions. Frequency spectra were obtained with the 1/3-octave band center frequencies from 25㎐ to 20 ㎑. The analyzed shallow water noise spectra were some different from the deep water blown as the Wenz spectra. We could know that the ambient noise level shows higher than it in same condition by effect of various ship activity and the coastal noise, surface waves, and so on. As a result, we produced the coastal ambient noise spectra curve based on these results in shore of the Korea Peninsula.

시계열 신호의 혼돈분석 기법 소개: 해양 수중소음 신호를 중심으로

최복경,김봉채,신창웅 한국해양과학기술원 2006 Ocean and Polar Research Vol.28 No.4

Ambient noise as a background noise in the ocean has been well known for its the various and irregular signal characteristics. Generally, these signals are treated as noise and they are analyzed through stochastical level if they don't include definite sinusoidal signals. This study is to see how ocean ambient noise can be analyzed by the chaotic analysis technique. The chaotic analysis is carried out with underwater ambient noise obtained in areas near the Korean Peninsula. The calculated physical parameters of time series signal are as follows: histogram, self-correlation coefficient, delay time, frequency spectrum, sonogram, return map, embedding dimension, correlation dimension, Lyapunov exponent, etc. We investigate the chaotic pattern of noises from these parameters. From the embedding dimensions of underwater noises, the assesment of underwater noise by chaotic analysis shows similar results if they don't include a definite sinusoidal signal. However, the values of Lyapunov exponent (divergence exponent) are smaller than that of random noise signal. As a result, we confirm the possibility of classification of underwater noise using Lyapunov analysis.

이어도 해역에 대한 해양물리환경 특성 분석

김성현,최복경,김병남,김동선 해양환경안전학회 2014 해양환경안전학회 학술발표대회 논문집 Vol.2014 No.11

Propagation of Ultrasonic Guided Waves in an Acrylic Plate as a Cortical-bone-mimicking Phantom

이강일,최복경 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.11

The present study aims to investigate the propagation of ultrasonic guided waves in an acrylicplate as a cortical-bone-mimicking phantom. The velocities of the guided waves in a 5-mm-thickacrylic plate were measured by using the axial transmission technique. A pure A0 Lamb mode couldbe successfully launched in the 5-mm-thick acrylic plate through a time reversal process of Lambwaves, consistent with the fact that the time reversal process can automatically compensate for thedispersive nature of Lamb waves. The experimental velocities of the slow guided wave (SGW) andthe time-reversed Lamb wave were found to be in reasonable agreement with the theoretical groupvelocity of the A0 Lamb mode, suggesting that both the SGW and the time-reversed Lamb waveexcited in the 5-mm-thick acrylic plate correspond to the A0 Lamb mode. These results suggestthat the time reversal process of Lamb waves can be usefully applied to noninvasive characterizationof long cortical bones.

동해에서 저주파 음파전파에 미치는 난수성 소용돌이의 영향

김봉채,최복경,김병남 한국해양과학기술원 2012 Ocean and Polar Research Vol.34 No.3

It is well known that sound waves in the sea propagates under the influence of sea surface andbottom roughness, the sound speed profile, the water depth, and the density of sea floor sediment. Inparticular, an abrupt change of sound speed with depth can greatly affect sound propagation through aneddy. Eddies are frequently generated in the East Sea near the Korean Peninsula. A warm eddy withdiameter of about 150 km is often observed, and the sound speed profile is greatly changed within about400 m of water depth at the center by the eddy around the Ulleung Basin in the East Sea. The characteristicsof low-frequency sound propagation across a warm eddy are investigated by a sound propagation model inorder to understand the influence of warm eddies. The acoustic rays and propagation losses are calculatedby a range-dependent acoustic model in conditions where the eddy is both present and absent. We foundthat low-frequency sound propagation is affected by the warm eddy, and that the phenomena dominate theupper ocean within 800 m of water depth. The propagation losses of a 100 Hz frequency are variable within±15 dB with depth and range by the warm eddy. Such variations are more pronounced at the deep sourcenear the sound channel axis than the shallow source. Furthermore, low-frequency sound propagation fromthe eddy center to the eddy edge is more affected by the warm eddy than sound propagation from the eddyedge to the eddy center.

Variation of Underwater Ambient Noise observed at IORS Station as a Pilot Study

김봉채,최복경 한국해양과학기술원 2006 Ocean science journal Vol.41 No.3

The Ieodo Ocean Research Station(IORS) is an integrated meteorological and oceanographic observation base which was constructed on the Ieodo underwater rock located at a distance of about 150 km to the south-west of the Mara-do, the southernmost island in Korea. The underwater ambient noise level observed at the IORS was similar to the results of the shallow water surrounding the Korean Peninsula (Choi et al. 2003) and was higher than that of deep ocean (Wenz 1962). The wind dependence of ambient noise was dominant at frequencies of a few kHz. The surface current dependence of ambient noise showed good correlation with the ambient noise in the frequency of 10kHz. Especially, the shrimp sound was estimated through investigations of waveform and spectrum and its main acoustic energy was about 40dB larger than ambient noise level at 5 kHz.

동중국해 북부해역의 하 추계 수온역전현상 연구

김성현,최복경,김병남,김동선,서호산 해양환경안전학회 2015 해양환경안전학회 학술발표대회 논문집 Vol.2015 No.04