• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.121-126
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• 2006

Modern Ocean wave forecasting systems predict the mean sea state, as characterized by the wave spectrum, in a box of size ${\Delta}x{\Delta}y$ surrounding a grid point at location x. It is shown that this approach also allows the determination of deviations from the mean sea state, i.e. the probability distribution function of the surface elevation. Hence, ocean wave forecasting may provide valuable information on extreme sea states.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.127-134
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• 2006

Based on a weakly non-Gaussian theory the occurrence probability of freak waves is formulated in terms of the number of waves in a time series and the surface elevation kurtosis. Finite kurtosis gives rise to a significant enhancement of freak wave generation in comparison with the linear narrow banded wave theory. For fixed number of waves, the estimated amplification ratio of freak wave occurrence due to the deviation from the Gaussian theory is 50% - 300%. The results of the theory are compared with laboratory and field data.

• 한국항만학회지
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• 제12권1호
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• pp.87-93
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• 1998

항만공학 분야의 해양파 문제에서 비선형이 강한 자유수면 문제를 수치적으로 해석하였다. 자유수면 격자를 유한차분법의 이산화 과정을 통해 재연한 것으로 자유표면 경계조건에 3차 미분항을 추가시켜 수치실험을 수행하였다. MAC 방법에 새로운 수치 기법을 도입하여 수면깊이 및 받음각에 따른 수치결과를 기존의 방법과 상호 비교하였다. 본 수치연구는, 점성유동장 계산에서 3차 풍상미분항이 자유표면파 생성에 효과가 크게 나타남을 보여 주었다.

• 한국해양공학회지
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• 제24권2호
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• pp.1-9
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• 2010

Oscillating Water Column is one of the most widely used converting systems all over the world. The operating performance is influenced by the efficiencies of the two converting stages in the OWC chamber-turbine integrated system. In order to study the effects of the pressure drop induced by the air turbine, the experiments using the impulse turbine and the orifice device are carried out in the wave simulator test rig. The numerical simulation utilizing the orifice and porous media modules is calculated and validated by the corresponding experimental data. The numerical wave tank based on the two-phase VOF model embedded with the above modules is employed to investigate the wave elevation, pressure variation inside the chamber and the air flow velocity in the duct. The effects of the air turbine on the integrated system and interaction among the wave elevation, pressure and air flow velocities variations are investigated, which demonstrates that the present numerical model are more accurate to be employed.

• 한국해안·해양공학회논문집
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• 제34권6호
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• pp.266-274
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• 2022

본 연구에서는 한반도 서해안에 위치한 해상기상관측타워에서 관측된 수면변동자료를 이용하여 첨두주기 산정의 정확도 향상을 위한 평활화 기법을 적용하였다. 평활화 기법 적용에 대한 검증은 파형의 분산값과 관측 자료의 에너지 총량을 통해 수행하였으며, 이후 평활화 적용에 대한 영향을 분석하였다. 분석결과, 파형의 분산값과 관측 자료의 에너지 총량의 상관계수는 0.9994로 나타났으며, 해당 기법 적용에 문제가 없음을 확인하였다. 이후, 평활화 영향 검토를 수행한 결과, 기존 추정 스펙트럼의 신뢰구간에 비해 최대 26% 감소하는 것으로 나타남으로서, 추정되는 첨두주기의 정확도가 향상됨을 확인하였다. 평활화 적용으로 인하여 4~6초 사이에서 확률밀도는 통계적으로 유의미한 차이가 발생하는 것으로 나타났다. 또한, 최적 평활화를 위해 통계적 기법을 이용하여 유의파고 범위에 따른 적정 평활화 개수를 산정하였으며, 평활화 개수는 유의파고가 작아짐에 따라 불안정한 스펙트럼 형상에 의해 증가하는 것으로 나타났다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.61-64
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• 2007

Subsurface Internal Waves (IWs) can be detected in satellite images as periodic alternating brighter/darker stripes. It is known that there are two types of IWs - depression type and elevation type - depending on the water depth in stratified oceans. In this study, we have quantitatively verified the process of converting polarity from depression waves to elevation waves using ERS-2 SAR images acquired over the northern South China Sea. We simulated the evolution of IWs near a turning point with a numerical model for internal wave propagation. The simulation results near the turning point clearly showed us not only a conversion process of IWs from depression to elevation waves, but also a similar wave pattern with the observed SAR image. We also simulated SAR intensity variation near the turning point. The upper layer currents were computed at regular intervals using the numerical model, as the IWs were passing through the turning point. Then, an integrated hydrodynamic-electromagnetic model was used for simulating SAR intensity profiles from the upper layer currents at each position. The simulated SAR intensity profiles at each position were compared with the observed SAR intensities.

• 대한원격탐사학회지
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• 제23권5호
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• pp.385-391
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• 2007

Subsurface Internal Waves(IWs) can be detected in satellite images as periodic alternating brighter/darker stripes. It is known that there are two types of IWs-depression type and elevation type-depending on the water depth in stratified oceans. In this study, we have quantitatively verified the process of converting polarity from depression waves to elevation waves using ERS-2 SAR image acquired over the northern South China Sea. We simulated the evolution of IWs near a turning point with a numerical model for internal wave propagation. The simulation results near the turning point clearly showed us not only a conversion process of IWs from depression to elevation waves, but also a similar wave pattern with the observed SAR image. We also simulated SAR intensity variation near the turning point. The upper layer currents were computed at regular intervals using the numerical model, as the IWs were passing through the turning point. Then, an integrated hydrodynamic-electromagnetic model was used for simulating SAR intensity profiles from the upper layer currents. The simulated SAR intensity profiles were compared with the observed SAR intensities.

• Journal of information and communication convergence engineering
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• 제6권2호
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• pp.146-149
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• 2008

Simulation and signal conditioning on the time domain surface elevation records are conducted to verify the proposed Welch's method in non-directional ocean wave spectrum analysis. These spectrum data are further conditioned to provide wave characteristic that better describe the sea states. Comparison of significant wave height and zero crossing period between the proposed method and a reference toolkit are presented.

• 대한토목학회논문집
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• 제35권4호
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• pp.845-852
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• 2015

파랑의 처오름높이는 항만 및 호안구조물의 마루높이 산정에 있어 주요한 설계요소이다. 본 연구에서는 TTP로 피복된 경사식구조물을 대상으로 2차원 수리실험을 수행하였으며, 실험에 적용된 실험파는 불규칙파로서 구조물 toe 위치에서 비쇄파, 쇄파 및 쇄파된 파의 조건을 포함한다. 본 실험결과를 이용하여 사면경사 1:1.5인 경사식구조물의 처오름높이를 산정할 수 있는 경험식을 쇄파 유사성 매개변수를 이용하여 제안하였다. 그리고 본 실험결과는 기존 연구결과인 van der Meer and Stam(1992)의 결과와 비교하였다.

• 한국해양공학회지
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• 제17권6호
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• pp.1-6
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• 2003

Wave energy dissipation and energy transfer between wave components, during the directional wave breakings, are investigated. Directional incipient and plunging breakers were generated by focusing the multi-frequency and multi-directional wave components at a designed location, based on a constant wave amplitude and a constant wave steepness frequency spectrum. The time series of surface wave elevation was measured at 9 different locations around the wave focusing point, using a wave gauge array. In order to examine the variation of the directional spreading function, the horizontal velocity of fluid motion was also measured. By comparing energy spectrums, before and after the breaking, the characteristics of energy dissipation and energy transfer, caused by wave breaking, are investigated. Their dependencies on directionality, as well as frequency, are analyzed. The breakings significantly dissipate wave energy, through energy transfer, in the upper region of the peak-frequency band, while enhancing wave energy in the low-frequency band.