• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.1
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• pp.61-72
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• 2001

The effects of wave groups on reflection and transmission over a submerged breakwater are studied by using a hydrodynamic numerical model and five independent wave grouping parameters. Based on qualitative analyses of limited data, it is found that the reflection and transmission coefficients of submerged breakwater may be strongly correlated with the incident wave groups. The reflection and transmission coefficients tend to decrease as wave groups become relatively larger. In particular, the reflection and transmission coefficients due to wave groups are evaluated smaller than those of single incident waves. However, the reflection and transmission coefficients are not affected by the interval of higher wave groups. It is finally concluded that the mean of nul-length among wave grouping parameters can be an useful parameter for correlating the wave groups with the reflection and transmission coefficients of submerged breakwater.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.4
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• pp.206-212
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• 2004

The numerical analysis on the wave screening performance of the submerged breakwater with various crown widths is presented. The fluid motion is considered as linearized two dimensional potential flow and the finite element method is used to analyze the wave screening performance of the submerged breakwater. It is found that single-submerged breakwater with large crown width shows the most effective wave screening performance and single-submerged breakwater with small crown width also shows fairly good wave screening performance but its effectiveness is less than that of single-submerged breakwater with large crown width. However, double- or triple-submerged breakwater with small crown width shows more effective wave screening performance than that of single- or double-submerged breakwater with large crown width. It is expected that the submerged breakwater with small crown width is economical because it reduces the size of structure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.539-549
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• 2006

The performance of a pontoon-type floating breakwater (FB) is investigated numerically with the use of a second-order time domain model. The model has been developed based on potential theory, perturbation theory and boundary element method. This study is focused on the effects of weakly nonlinear wave on the hydrodynamic characteristics of the FB. Hydrodynamic forces, motion responses, surface elevation, and wave transmission coefficient around the floating breakwater are evaluated for various wave and geometric parameters. It is shown that the second-order wave component is of significant importance in calculating magnitudes of the hydrodynamic forces, mooring forces and the maximum response of a structure. The weak non-linearity of incident waves, however, can have little influence on the efficiency of the FB. From numerical simulations, the ratio of draft and depth, the relationship of wave number and width are presented for providing an effective means of reducing wave energy.

• Proceedings of the Korea Water Resources Association Conference
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• 1988.07a
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• pp.37-44
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• 1988

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3B
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• pp.323-334
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• 2008

Present study examined the functionality of the solitary wave (tsunami) control of the two-rowed porous submerged breakwater by numerical experiments, using a numerical wave tank which is based on the Navier-Stokes equation to explain fluid fields and uses a Volume of Fluid (VOF) method to capture the free water surface. Solitary wave was generated by the internal wave source installed within the computational zone in the numerical wave tank and its wave transformations by structure were compared with those in the previous study. Comparisons with the precious numerical results showed a good agreement. Based on these results, several tow-dimensional numerical modeling investigations of the water fields, including wave transformations, reflection, transmission and energy flux, by the one- and two-rowed permeable submerged breakwater under solitary waves were performed. Even if, it is a research of the limited scope, in case of two-rowed permeable submerged breakwater with $h_0/h=0.925$ ($h_0$ is height of submerged breakwater and h is water depth), the wave height damping in range of $l/L_{eff}>0.4$($L_{eff}$ is effective distance of solitary wave) can reach nearly 60% of the incident wave height. In addition, it is found that reflection coefficient increases nearly 47% and transmission coefficient decreases nearly 18% than one-rowed one. The numerical results revealed that the tow-rowed submerged breakwater can control the incident solitary wave economically and more efficiently than the one-rowed one.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.5
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• pp.439-451
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• 2008

Based on reflected and transmitted waves by a single step bottom, a new model of scatterer method is constructed which can be used to calculate wave transformation over a multi-step topography. The approximate results are tested by comparison with the more accurate results obtained from EFEM presented by Kirby and Dalrymple(1983). In the case of plane-wave approximation, solutions of the scatterer method and the EFEM are the same. Results obtained by the scatterer method with non-propagating modes are much better, in terms of phase for the calculated reflection and transmission coefficients, than those by plane-wave approximation. As the effect of non-propagating modes decreases, solutions of the scatterer method become closer to those of the EFEM.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.1
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• pp.1-9
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• 2004

In this study, several new types of floating breakwater are proposed according to the geometry of the vertical barrier and the existence of horizontal plate, and are compared to the steel floating breakwater adopted in Won-Jun fishing port and the performance of wave control is numerically investigated by using Green function method. From the numerical results, model attached the horizontal barrier under the vertical barrier is more efficient for reflection and transmission coefficient than the steel floating breakwater in Won-Jun fishing port. It is confirmed that the transmitted waves can be controlled efficiently by optimizing the length and distance of a vertical and horizontal barriers.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.29-37
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• 2007

In this study, transmission and reflection of multi-directional random waves propagating over impermeable submerged breakwaters are calculated by using eigenfunction expansion method. A series of mutiderectional random waves is generated by using the Bretschneider-Mitsuyasu frequency and Mitsuyasu type directional spectrum. Strong reflection is occurred at the Bragg reflection condition of the peak frequency. If the row of breakwaters is fixed at 3 and the relative height of breakwater is fixed at 0.6, more than 25% of incident wave energy is reflected to offshore. It is also found that the reflection of directionally spreading random waves increases as the maximum spreading parameter $s_{max}$ increases.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.4
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• pp.203-214
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• 2010

This study numerically investigates the wave control of 2-rowed Impermeable Rectangular Submerged Dike(IRSD) with an object of how to control short-period and solitary waves simultaneously based on the Bragg resonance phenomenon that elevates the wave control performance. The boundary integral method using Green formula and the 3-D one-field Model for immiscible TWO-Phase flows (TWOPM-3D) by 3-D numerical wave flume have been used for the numerical predictions for short-period and solitary waves, respectively. These numerical models were verified through the comparisons with the previously published numerical results by other researchers. Through the parametric tests of numerical experiments for short-period waves, an optimum model of 2-rowed IRSD of a lowest transmission coefficient has been found. Furthermore, the performances of 3-D wave control for solitary waves were evaluated for the various free board, crown widths and gap distance between dikes, and have been compared with those of a single-rowed IRSD. Numerical results show that a 2-rowed IRSD with a less cross sectional area than 1-rowed one improves the wave attenuation performances when it is compared to that of single-rowed IRSD. Within the test frequency ranges of the numerical simulations conducted in this study, 2-rowed IRSD with an optimum gap distance shows an outstanding improvement of the wave attenuation up to 58% compared to that of single-rowed IRSD.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.20-25
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• 2001

부유식 파랑에너지 변환시스템(Oscillating Water Column)에서 에너지 변환은 입력파와 챔버, 챔버내 공기의 상호작용으로 이루어진다. 이 논문은 파랑에너지를 기계적 운동으로 변환하는 기계적 특성을 해석한다. 단일 진동수 규칙파가 입력되었을 때에 파에 의하여 챔버의 상하운동이 선형적으로 발생하며, 이 상하운동은 챔버내의 압력 변화에 영향을 받는다. 상하운동과 챔버내로 투과한 파, 그리고 챔버내 압력에 의해 발생되는 파에 의해 챔버내의 상대운동을 정하고, 그 상대운동에 의한 공기의 압축 팽창과 온도상승을 근사적 열역학적 방정식으로 해석하여 오리피스를 통한 유량과 압력을 기준으로 에너지 변환요율을 결정하였다. 얻어진 식은 간단하면서도 관련요소의 영향을 전반적으로 표현한다. 개구율 변화에 따른 운동응답을 비교하였다.