• Ocean Systems Engineering
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• 제6권1호
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• pp.23-60
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• 2016

The major objective of this study was to develop further understanding of 3D nearshore hydrodynamics under a variety of wave and tidal forcing conditions. The main tool used was a comprehensive 3D numerical model - combining the flow module of Delft3D with the WAVE solver of XBeach - of nearshore hydro- and morphodynamics that can simulate flow, sediment transport, and morphological evolution. Surf-swash zone hydrodynamics were modeled using the 3D Navier-Stokes equations, combined with various turbulence models (${\kappa}-{\varepsilon}$, ${\kappa}-L$, ATM and H-LES). Sediment transport and resulting foreshore profile changes were approximated using different sediment transport relations that consider both bed- and suspended-load transport of non-cohesive sediments. The numerical set-up was tested against field data, with good agreement found. Different numerical experiments under a range of bed characteristics and incident wave and tidal conditions were run to test the model's capability to reproduce 3D flow, wave propagation, sediment transport and morphodynamics in the nearshore at the field scale. The results were interpreted according to existing understanding of surf and swash zone processes. Our numerical experiments confirm that the angle between the crest line of the approaching wave and the shoreline defines the direction and strength of the longshore current, while the longshore current velocity varies across the nearshore zone. The model simulates the undertow, hydraulic cell and rip-current patterns generated by radiation stresses and longshore variability in wave heights. Numerical results show that a non-uniform seabed is crucial for generation of rip currents in the nearshore (when bed slope is uniform, rips are not generated). Increasing the wave height increases the peaks of eddy viscosity and TKE (turbulent kinetic energy), while increasing the tidal amplitude reduces these peaks. Wave and tide interaction has most striking effects on the foreshore profile with the formation of the intertidal bar. High values of eddy viscosity, TKE and wave set-up are spread offshore for coarser grain sizes. Beach profile steepness modifies the nearshore circulation pattern, significantly enhancing the vertical component of the flow. The local recirculation within the longshore current in the inshore region causes a transient offshore shift and strengthening of the longshore current. Overall, the analysis shows that, with reasonable hypotheses, it is possible to simulate the nearshore hydrodynamics subjected to oceanic forcing, consistent with existing understanding of this area. Part II of this work presents 3D nearshore morphodynamics induced by the tides and waves.

• 한국해양공학회지
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• 제30권1호
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• pp.44-50
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• 2016

An experimental study was performed to investigate the behavior of green water on a structure with a rectangular cross section under wave conditions, along with the flow characteristics in bubbly water flow. An experiment was conducted in a two-dimensional wave flume using an acrylic model (1/125) of FPSO BW Pioneer operating in the Gulf of Mexico under its design wave condition. The occurrence of green water, including its development, in front of the model was captured using a high-speed Charge Coupled Device (CCD) camera with the shadowgraph technique. Using consecutive images, the generation procedure for green water on the model was divided into five phases: flip through, air entrapment, wave run-up, wave overturning, and water shipping. In addition, the distinct water elevations of the green water were defined as the height of flip through, height of splashing jet, and height of freeboard exceedance, and showed a linear relationship with the incoming wave height.

• 한국해안·해양공학회논문집
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• 제21권1호
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• pp.30-38
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• 2009

최근에 해안구조물의 시공에 있어 친수성 및 방재 기능을 동시에 갖는 구조물이 검토되는 사례가 증가하고 있다. 본 연구의 목적은 비교적 급한 1:5 사면을 가진 해안구조물 위로 전파하는 파랑변형 및 파의 처오름을 예측하는 것이다. 사면 위의 파랑변형 및 처오름을 해석하기 위하여 비선형 천수방정식을 사용하였으며, 투수층 내의 유체운동에는 확장형 Forchheimer의 저항법칙에 근거한 비선형, 비정상 Darcy법칙을 적용하여 규칙파 및 불규칙파를 대상으로 수행되었고, 계산결과는 PBREAK 수치모델의 적용성 및 한계성을 검토하기 위하여 수리모형실험 결과와 비교검토 되었다. PBREAK 수치모델은 사면 위의 파형의 변화를 잘 예측하였으나 질량 및 운동량의 교환이 많이 발생하는 쇄파대 내에서 수리모형실험 결과와 약간의 차이를 보여주었다. 또한 수심평균된 수립자 유속은 파봉 부근을 제외하고 파곡 아래에서 계측한 실험치와 잘 일치하였다.

• 한국해양공학회지
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• 제24권2호
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• pp.18-24
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• 2010

Submerged rubble structures include artificial reef and the mound part of the rubble mound breakwater. Artificial reef is a type of the submerged wave absorbing structure installed in a coastal zone to prevent beach erosion and designed to initially reduce the energy of incoming waves so that its run-up height and overtopping quantity can be decreased. In order to ascertain the stability of such submerged rubble structures, minimum weight of the rubble has to be calculated first from the incoming wave height using Hudson's formula or Brebner-Donnelly formula. Based on the calculated minimum weight, a model is built for use in a hydraulic model test carried out to check its stability. The foregoing two formulas used to calculate the minimum weight are empirically derived formulas based on the result of the tests on the rubble mound breakwater and it is, therefore, difficult for us to apply them directly in the calculation of the minimum weight of the submerged structures. Accordingly, this study comes up with a numerical simulation method capable of deformation analysis for rubble structures. This study also tries to identify the deformation mechanism of the submerged rubble structures using the numerical simulation. The method researched through this study will be sufficient for use for usual preparations of the design guidelines for submerged rubble structures.

• 대한환경공학회지
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• 제27권10호
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• pp.1030-1034
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• 2005

본 연구에서는 파도에너지가 비교적 작은 폐쇄성수역의 사질 조간대를 대상으로 하여 입자상 물질의 토양 침투거동을 파악하고, 유출된 기름의 조간대 사면표착이 입자상 물질의 토양침투 차단 여부를 규명하는 것을 목적으로 하여 모의 조간대 실험장치를 이용하여 실험을 하였다. 폐쇄성 수역과 같은 파도에너지가 작은 조간대에서는 쇄파대에서 붕괴된 파도에 의해서 입자상물질이 orbital 운동을 하면서 반원형태의 침투거동 (semi-circular penetration behavior)을 보였다. 또한 사면의 구배와 쇄파파고의 증가에 따라서 입자상물질의 침투속도도 증가하였다. 조석에 의해서는 토양중 해수의 이동방향과 동일한 방향으로 $45^{\circ}$ 각도를 이루며 토양중으로 침투하였다. 유출된 기름이 토양사면에 표착됨으로 인해 형성된 점착성의 유막은 입자상 물질의 토양침투를 차단하였으며, 이로인해 해수중의 식물성 플랑크톤, 세균, 유기쇄설물과 같은 입자상물질의 침투를 방해하여 조간대에 서식하는 저서생물의 먹이 공급을 감소시켜 연안 생태계에 악영향을 미칠것으로 판단된다.

• 대한조선학회논문집
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• 제30권2호
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• pp.98-111
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• 1993

2차원 비정상 비선형 자유표면파를 해석하고 자유표면파에서의 점성효과를 관찰하였다. 유동장내의 Navier-Stokes 방정식과 연속방정식을 풀기 위해 유한해석법을 적용하였고, 자유표면의 처리를 위해 MAC 기법을 적용하였다. 그리고, 자유표면에서는 표면장력을 고려한 경계조건을 적용하였으며, 층류에 대한 점성효과만을 고려하였다. 계산모델은 천수역에서의 점성영향, 자유표면 근처에서의 보오텍스 쌍(vortex-pair)의 거동 및 전진하는 부유체 앞에서의 자유표면파문제 등이다. 천수역문제에서는 바닥과의 마찰에 기인한 자유표면파의 변화를 고찰하였으며, 특히 고립파에 대한 적용으로서 파고의 감소정도, 수직벽면에서의 파상승(wave run-up) 및 수심의 변화로 인한 유장변화 등을 살펴보았다. 보오텍스 문제에서는 보오텍스의 이동에 따른 자유표면주위의 유동변화를 관찰하였으며, 사각부유체 주위의 유동문제에서는 전진속도의 차이에 따른 자유표면파의 차이 및 물체주위의 유동특성을 관찰하였다.

• 대한조선학회논문집
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• 제53권1호
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• pp.1-9
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• 2016

It is important to research and understand the physical phenomenon around a semi-submersible offshore structure on waves and currents because the wave run-up and load occurs owing to the waves and currents. In this study, the numerical simulations are performed about flow around a fixed semi-submersible offshore structure. The Modified Marker-density method is adopted in the present computation procedure, this method is one of the various methods to define the free-surface. The present computation results are compared with existing experimental and numerical simulation(VOF method) results. And, the computation results are relatively coincident with the existing results of model test and numerical simulation by VOF method.

• 대한조선학회논문집
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• 제39권4호
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• pp.32-41
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• 2002

본 논문에서는 고차경계요소법을 사용하여 폰툰형 초대형 구조물의 유탄성 응답을 해석하였다. 폰툰형 구조물의 설치가 예상되는 천수심 해역에서 유탄성 응답 해석에서 흘수의 영향을 고찰하였다. 초대형 구조물인 경우 실제 해상파의 파장 범위인 단파장 구간일 때 흘수의 영향을 무시한 해석은 구조물의 유탄성 응답과 상대파고를 과소평가 하는 것으로 나타나 폰툰형 구조물에서도 흘수 영향을 고려한 해석이 중요함을 보였다.

• 한국해양공학회지
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• 제31권2호
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• pp.81-90
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• 2017

The 1MW OTEC (Ocean Thermal Energy Conversion) platform was designed for application in equatorial seas. In this study, the OTEC platform was investigated using numerical and experimental methods. An octagon-shaped OTEC platform was investigated using the Ocean Engineering Basin of KRISO. These experiments included various tests of regular waves, irregular waves and irregular waves with current (wave+current). The responses of the platform in regular waves showed good agreement between the numerical and experimental results, including the motion RAO, wave run up, and mean drift force. The peak period of heave and pitch motions were observed around 0.5 rad/s, and the effect of the total reflection was found under short wave conditions. The standard deviation (STD) of the platform motion was checked in irregular waves of equatorial and Hawaiian seas. The STD of the pitch was less than $4^{\circ}$ different from the operability requirement under equatorial conditions and the surge STD of the wave frequency showed good agreement between the numerical and experimental results. The STD values of the surge and pitch were increased 66.6% and 92.8% by the current effects in irregular waves, but the pitch STD was less than $4^{\circ}$ under equatorial conditions. This study showed that the STD of the surge was affected by spring effects. Thus, the watch circle of the platform and tension of the mooring lines must be evaluated for a specific design in the future.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.168-171
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• 2007

The stability of a typical rubble mound breakwater defenced by a submerged structure is investigated using hydraulic experiments. Incident irregular waves are obtained from the Bretschneider-Mistuyasu spectrum. Experiments are carried out for different spacings between two breakwaters (X/d=2-3) and for different relative widths (B/h=0.7-3.0) of the submerged structure. It is observed that a submerged structure of (B/h) of 0.7-3.0 constructed at a seaward distance (X/d) of 2-3 breaks all the incident waves and dissipates energy and breakwater.