• Wind and Structures
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• 제29권1호
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• pp.33-41
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• 2019

The interaction of head waves with an infinite row of identical, equally spaced, rectangular breakwaters is investigated in the presence of uneven bottom topography. Using linear water wave theory and matched eigenfunction expansion method, the boundary value problem is transformed into a system of linear algebraic equations which are numerically solved to know the velocity potentials completely. Utilizing this method, reflected and transmitted wave energy are computed for different physical parameters along with the wave field in the vicinity of breakwaters. It is observed that the wave field becomes more complicated when the incoming wavelength becomes smaller than the channel width. A critical ratio of the gap width to the channel width, corresponding to the inflection point of the transmitted energy variation, is identified for which 1/3 of the total energy is transmitted. Similarly, depending on the incident wavelength, there is a critical breakwater width for which a minimum energy is transmitted. Further, the accuracy of the computed results is verified by using the derived energy relation.

• Geomechanics and Engineering
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• 제5권6호
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• pp.595-611
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• 2013

This paper presents a three-dimensional (3D) integrated numerical model where the wave-induced pore pressures in a porous seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behaviour is considered in the seabed model. With the present model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.

• 한국항해학회지
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• 제14권4호
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• pp.41-52
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• 1990

부유식 진동수주형 파력발전기는 불규칙한 해상 상태에서의 작동으로 인하여 흡수효율의 저하를 필수적으로 수반한다. 본 논문에서는 입사파의 에너지를 적절히 흡수할 수 있는 파력발전기를 초기설계하여 모델로 이용하였으며, 이 모델의 유체력추정에는 3차원 특이점 분포법을 사용하였다. 그리고, 가변구조 시스템으로 알려진 슬라이딩 모드기법을 이용하여 파의 상태 변화에 따른 파력발전기의 자세와 위치를 제어함으로써 흡수파력의 효율을 중대시킬 수 있는 시스템을 제안하고 있다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권2호
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• pp.122-125
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• 2011

In this work, the movement pattern of a floating breakwater is numerically analyzed using Smoothed Particle Hydrodynamic (SPH) method as a Lagrangian scheme. At the seaside, the regular incident waves with varying height and period were considered as the dynamic free surface boundary conditions. The smooth and impermeable beach slope was defined as the bottom boundary condition. The effects of various boundary conditions such as incident wave characteristics, beach slope, and water depth on the movement of the floating body were studied. The numerical results are in good agreement with the available experimental data in the literature The results of the movement of the floating body were used to determine the transmitted wave height at the corresponding boundary conditions.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2004년도 춘계학술발표대회 논문집 제23권 1호
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• pp.347-348
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• 2004

Nonlinear scattering of difference frequency acoustic wave in a water-saturated sandy sediment was investigated. Difference frequency acoustic wave was observed to be scattered due to the nonlinearity of water-saturated sandy sediment when the collinear acoustic waves with two different fundamental frequencies are incident on the sediment. The pressure level of the difference frequency acoustic wave was 6 dB higher than the background noise level. It seems very useful to evaluate the nonlinear parameter of water-saturated sandy sediment without disturbing the sediment. Such nonlinear acoustic response of water-saturated sandy sediment can be used as background acoustic data for estimating the gas void fraction in marine gassy sandy sedimen.

• 한국해양공학회지
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• 제20권1호
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• pp.63-68
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• 2006

Recently, it has been widely recognized that coastal vegetations may have great value in supporting fisheries, protecting from wave attack, stabilizing the sea bed and maintaining good scenery. Hydrodynamic factors play a major role in the functions of water quality and ecosystems. However, the studies on physical and numerical process of wave propagation are few and far behind compared to those on the hydrodynamic roles of coastal vegetations. In general, Vegetation flourishing along the coastal areas attenuates the incident waves, through momentum exchange between stagnated water mass in the vegetated area and rapid mass in the un-vegetated area. This study develops a numerical model for describing the wave attenuation rate in the complex topography with the vegetation area. Based on the numerical results, the physical properties of the wave attenuation are examined under various wave, geometric and vegetation conditions. Through the comparisons of these results, the effects of the vegetation properties, wave properties and model parameters such ac the momentum exchange coefficient have been clarified.

• 한국해안해양공학회지
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• 제14권2호
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• pp.95-107
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• 2002

신뢰성설계법의 적용성을 확대하기 위하여 혼성제 직립 케이슨의 활동에 대한 신뢰성 해석이 수행되었다. 충격쇄파 효과를 고려한 결정론적 설계법에 의하여 단면의 안전성이 자세히 해석되었으며, 특히 신뢰성 해석의 결과를 직접 결정론적 설계법의 결과와 연결시키기 위한 연구가 시도되었다. 해석 결과에 의하면 현재의 결정론적 설계 법에서 적용되고 있는 안전율은 약간 안전 측에 속한다. 또한 동일한 입사조건과 안전율에 대하여 수심이 증가함에 따라 신뢰지수는 감소하는 경향을 보이고 있다. 한편 방파제가 그 기능을 수행하는데 지장이 없을 것으로 예상되는 목표 파괴확률을 설정하고 그 목표 범위내에서 가장 최적의 파괴 확률을 산정하였는데, 입사조건에 따라 약간 씩 다른 최적의 안전율이 추정되었다. 마지막으로 혼성제 케이슨의 단면 결정에 영향을 주는 변수들의 변화에 따른 민감도 분석이 수행되었다. 해석 결과에 의하면 입사각, 주기의 영향이 크게 나타났으며 하상의 경사나 마운드의 두께에 대한 영향의 정도는 상대적으로 낮게 평가되었다.

• 대한조선학회지
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• 제20권2호
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• pp.37-42
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• 1983

This paper presents a procedure within the framework of linear potential theory for predicting the lateral drifting forces on a cylinder floating on the free surface of a finite depth water. The disturbance of a regular incident wave caused by the presence of the floating body is represented by the sum of the diffracted and radiated wave potentials, which are determined by using Green's theorem. The lateral drifting forces are calculated by use of momentum theorem, and the scattered waves are expressed in their asymptotic forms. The computed lateral drifting forces on a Lewis form cylinder(b/T=1.25, $\sigma$=0.95) for water depth to draft ratio of 5.0 are compared with the Kyozuka's experimental results for a deep water, and found to be in good agreement. The water depth effects on drifting forces of the same model are also calculated.

• 한국해양공학회지
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• 제27권6호
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• pp.32-42
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• 2013

In this paper, a wave-induced swirl water chamber (SWC) for breakwater and wave power generation is introduced and its applicability to wave power generation in the coastal waters of Korea is investigated. The SWC type of wave power generation is a way to drive a turbine using the unidirectional swirl flow that is induced in the back of a curtain wall of a breakwater due to incident waves. The typical wave characteristics are obtained by analyzing the annual statistical wave data from KHOA (Korea Hydrographic and Oceanographic Administration). A numerical analysis is carried out on the variations in the SWC entrance height, wave height, and different installation conditions. For the numerical analysis, a commercial code, Fluent based on FVM, is used. As the entrance height decreases, the mass flow rate through the entrance is rarely changed, whereas the magnitude of the flow velocity of the smaller entrance height is greater than the other ones, which is better for the formation of an SWC swirl flow inside and the flow kinetic energy at the entrance. In cases of installation conditions where a wall is place behind and under SWC, it has been shown that the mass flow rate through the entrance is greater than that in the open condition, and sufficient flow kinetic energy is generated in the entrance for wave power generation. However, the swirl flow kinetic energy is relatively small. Thus, in the future, it is necessary to study the swirl flow generation, which is affected by the SWC shape.

• 한국해안해양공학회지
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• 제19권5호
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• pp.446-456
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• 2007

본 연구에서는 Lynett and Liu(2004a, b)에 의해 유도된 2층 Boussineaq방정식을 이용하여 일정수심상의 규칙파 조건에서 직립벽을 따른 연파를 해석하고, 수리모형실험결과 및 포물형근사식에 의한 해석결과와 비교하였다. 두 가지 수치모형에 의한 해석결과는 수리실험결과와 비교적 잘 일치하였으나, 입사각이 증가할수록 Boussinesq 모형이 포물형모형보다 우수한 결과를 주는 것으로 나타났다. 특히 파랑의 비선형성에 의한 고차 조화성분의 발생은 Boussinesq모형에서만 관찰되었다.