• 한국수산과학회지
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• 제20권5호
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• pp.457-462
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• 1987

Stochastic stability criterias for ocean wave analysis add simulation are studied using the data simulated by the linear superposition method. To clarify the criterias, the effects of the simulation parameters on the variance of stochastic properties of ocean waves are investigated, and the stable conditions of the parameters are estimated through the comparative study on the stochastic properties of simulated waves and well-known ocean waves. The simulation parameters considered are high frequency cut-off, data length, and number and phase angle of component waves. Statistical characteristics analysed are wave height, period and steepness, and the formation of groups of higher waves, resonance periods, steeper higher waves and extreme run-length of the run.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권1호
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• pp.13-21
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• 2016

Parametric pitch instability of a Deep Draft Semi-submersible platform (DDS) is investigated in irregular waves. Parametric pitch is a form of parametric instability, which occurs when parameters of a system vary with time and the variation satisfies a certain condition. In previous studies, analyzing of parametric instability is mainly limited to regular waves, whereas the realistic sea conditions are irregular waves. Besides, parametric instability also occurs in irregular waves in some experiments. This study predicts parametric pitch of a Deep Draft Semi-submersible platform in irregular waves. Heave motion of DDS is simulated by wave spectrum and response amplitude operator (RAO). Then Hill equation for DDS pitch motion in irregular waves is derived based on linear-wave theory. By using Bubnov-Galerkin approach to solve Hill equation, the corresponding stability chart is obtained. The differences between regular-waves stability chart and irregular-waves stability chart are compared. Then the sensitivity of wave parameters on DDS parametric pitch in irregular waves is discussed. Based on the discussion, some suggestions for the DDS design are proposed to avoid parametric pitch by choosing appropriate parameters. The results indicate that it's important and necessary to predict DDS parametric pitch in irregular waves during design process.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.105-112
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• 2006

Freak waves in the ocean are recently drawing much attention as a natural disaster to ocean structures and navigating ships as well. Several observation data, among them the Draupner New Year Wave, show the very impressive feature of Freak waves whose wave height is up to three times as high as the significant wave height of surrounding waves, In addition, Freak wave appears as an isolated very high crest in somewhat stationary random waves of same order in their wavelengths. Bearing such characteristics in mind, one notices its extraordinary steepness. This strongly suggests that Freak wave is not long lived but transient nature on the whole. A great number of studies to explain these natures were published from both theoretical and numerical point of view. However it is not sure if they are applicable to actual ocean environment. In this paper, we deal with the results concerning abnormal and/or Freak waves from in-situ ocean wave data and point out several remarks to the problems lain behind the contributions in this context. A physical experiment is described to reinforce the subject discussed from the observation data.

• 한국해양공학회지
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• 제22권5호
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• pp.1-6
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• 2008

A kinematics model of a ship wake in the presence of surface waves generated by wind is presented. It was found that a stationary wave structure behind a ship covered a wedge region with the angle at the top of the wake and that only divergent waves were present in a ship wake instead of both the longitudinal and cross-waves, which are known as the Kelvin model. Ship motion at some angle to wind waves can cause an essential asymmetry of the wake, compressing its windward half.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.263-267
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• 2004

This paper presents a comparative study on numerical and wave-maker generated waves. The wave-makers employed to carry out the experiments have mathematical forms. The linear and quadratic models were tested. When it comes numerical analysis, the authors used the FLUENT which is widely used commercial code. Only two dimensional cases were considered. The experiments were done in a small wave flume. The waves were generated for various frequencies to examine the characteristics of the water waves. The comparison of the numerical and wave-maker generated waves were made.

• 해양환경안전학회지
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• 제21권2호
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• pp.215-222
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• 2015

본 기술보고에서는 선박운항 시뮬레이터를 위한 해양파 가시화의 개선을 목적으로 여러 해양파 가시화 요소 및 그에 대한 전체적인 재현 방안에 대해 고찰하였다. 이를 위해 우선 해양파 가시화 요소를 해양파 표면, 해양파 부서짐, 상호작용, 광원, 수중 등으로 구분하고, 각 구성 요소별 가시화가 필요한 세부 가시화 요소들을 정리 하였다. 또한 이를 재현하는 과정에서 설계에 반영해야 할 내용들을 사실적 해양파 가시화 및 실시간 해양파 가시화, 선박 운동특성 재현, 시뮬레이터의 활용 관점에서 분석하였다. 분석을 통해, 사실적 해양파 가시화가 몰입감 형성 및 보다 정확한 선박 운동특성 재현, 다양하고 제어 가능한 시뮬레이션 시나리오 생성 등에 중요한 역할을 수행함을 확인하였다. 또한 선박운항 시뮬레이터를 위한 해양파 가시화는 고려해야 할 요소 및 그에 대한 구현 방안, 관련 제약 사항이 많은 만큼 구현 전 종합적이고 체계적인 접근이 필요함을 확인하였다.

• 한국해양공학회지
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• 제33권3호
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• pp.236-244
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• 2019

Internal waves occur at the interface between two layers caused by a seawater density difference. The internal waves generated by a body moving in a two-layer fluid are also related to the generation of surface waves because of their interaction. In these complex flow phenomena, the experimental measurements and experimental set-up for the wave patterns of the internal waves and surface waves are very difficult to perform in a laboratory. Therefore, studies have mainly been carried out using numerical analysis. However, model tests are needed to evaluate the accuracy of numerical models. In this study, the various experimental conditions were evaluated using CFD simulations before experiments to measure the wave patterns of the internal waves and surface waves in a stratified two-layer fluid. The numerical simulation conditions included variations in the densities of the fluids, depth of the two-layer fluid, and moving speed of the underwater body.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.143-153
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• 2019

In this study, numerical simulations for the prediction of added resistance for KVLCC2 with varying wave steepness are performed using a Computational Fluid Dynamics (CFD) method and a 3-D linear potential method, and then the non-linearities of added resistance and ship motions are investigated in regular short and long waves. Firstly, grid convergence tests in short and long waves are carried out to establish an optimal mesh system for CFD simulations. Secondly, numerical simulations are performed to predict ship added resistance and vertical motion responses in short and long waves and the results are verified using the available experimental data. Finally, the non-linearities of added resistance and ship motions with unsteady wave patterns in the time domain are investigated with the increase in wave steepness in both short and long waves. The present systematic study demonstrates that the numerical results have a reasonable agreement with the experimental data and emphasizes the non-linearity in the prediction of the added resistance and the ship motions with the increasing wave steepness in short and long waves.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 추계학술대회 논문집
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• pp.220-226
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• 2001

It is important to estimate exactly wave forces acting on various types of offshore structures under the severe environmental conditions in the ocean site. This paper presents an easy experimental method which deals with transient waves. The proposed scheme made it possible to generate breaking waves at any position in the wave tank by changing the maximum slope of the component waves. The theoretical and experimental methods were investigated by generating concentrated waves which acted on a single and multiple cylinders. The waves forces increased rapidly when the models encountered breaking waves. The theoretical results underestimates the forces due to breaking waves. Therefore, the effects due to breaking waves should be considered carefully in the design process of a structure under the influence of breaking waves.

• 한국해양공학회지
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• 제15권4호
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• pp.8-13
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• 2001

It is important to estimate exactly wave forces acting on various types of offshore structures under the severe environmental conditions in the ocean site. This paper presents an easy experimental method which deals with transient waves. The proposed scheme made it possible to generate breaking waves at any position in the wave tank by changing the maximum slope of the component waves. The theoretical and experimental methods were investigated by generating concentrated waves which acted on a single and multiple cylinders. The waves forces increased rapidly when the models encountered breaking waves. The theoretical results underestimates the forces due to breaking waves. Therefore, the effects due to breaking waves should be considered carefully in the design process of a structure under the influence of breaking waves.