• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.3
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• pp.121-129
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• 2004

The different types of coastal souctures have been constructed for the protection of coastal region from the incident waves. Among them. the permeable submerged breakwater has been widely used as a wave dissipater and sediment transport controller because of its excellent advantages in scenery effects, construction efficiency and environment aspects. This study numerically investigated the characteristics of wave energy variations and transmission coefficient at the rear of the permeable submerged breakwater installed in the irregular wave field. To analyze it's performance numerically, a two-dimensional numerical wave flume based on VOF method was used. A frequency spectral analysis showed that the spectral peak moved to the short-period in the one-row submerged breakwater, and the wave energy was distributed evenly for the whole period in the two-row submerged breakwater in the case of breaking on the submerged breakwater. The spectral peak was shown to be converged within the significant wave period at the rear of the permeable submerged breakwater in the case of non-breaking conditions. From the result of transmission coefficients analysis. it was confirmed that a considerable quantity of wave energy was transmitted to the rear of the permeable submerged breakwater in the case of non-breaking rather than breaking.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2B
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• pp.249-259
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• 2008

The present paper studies the effect of the slope gradient of a fully permeable submerged breakwater using a newly developed numerical model that is able to consider the flow through a porous midium with inertial, laminar and turbulent resistance terms, i.e. simulate directly WAve-Structure (submerged breakwater)-Sand seabed interaction and can determine the eddy viscosity with LES turbulence model in 2-Dimensional wave field (LES-WASS-2D). The developed model was validated through the comparison with an existing experimental data, and further used for various numerical experiments in oder to investigate the complicated hydrodynamics on the varying slope gradient of permeable submerged breakwater. We found an acceptable phenomenon, as we expect intuitively, that reflection and transmission coefficients decrease simultaneously as slope gradient decrease. In addition, the breaking point, the circulation flow and mean vorticity around a submerged breakwater are throughly discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.4
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• pp.363-371
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• 2008

The aim of this study is to compare the numerical results obtained by 2-D and 3-D models which are used to examine the wave field around a permeable submerged breakwater. At first, the numerical model, which is able to consider the flow through a porous medium with inertial, laminar and turbulent resistance terms and determine the eddy viscosity with LES turbulent model, is used and validated by comparing with existing experimental data. And then, the numerical test on the wave field around a permeable submerged breakwater is performed. It is revealed from the numerical results that, at the onshore side of the submerged breakwater, the wave height by 2-D analysis is higher than that by 3-D analysis. Also, the time-averaged mean flow around a submerged breakwater is discussed in detail.

• Journal of Korea Water Resources Association
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• v.31 no.3
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• pp.223-234
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• 1998

Recently, the interests of the construction of the permeable submerged breakwaters have been increased to preserve and to improve the coastal environment, and to control the incident waves and littoral transport. It is very important to predict the wave transformation precisely over the permeable submerged breakwaters. This study discusses nonlinear wave transformation and characteristics by using BEM based on the frequency domain method of the 3rd-order Stokes waves. The Dupuit-Forchheimer formula is applied to the analysis of the fluid resistance of rubble stones, and the equation about equivalent linear frictional coefficient is newly modified based on the Lorentz's condition for the equivalent work. The numerical results are compared with the experimental ones for verification. These two results give a close agreement each other. It is confirmed that the present method of the 3rd-order Stokes waves estimates more precisely than that of the 2nd-order Stokes waves.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.335-349
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• 2017

Submerged breakwaters installed under the water surface are a representative coastal structure to prevent coastal erosion, and various types of submerged breakwaters have been proposed and discussed so far. Generally, submerged breakwaters make the complex wave fields due to abrupt change in water depth at the crown of the breakwater. In this study, wave heights and mean water level formed around a breakwater are examined numerically for three-dimensional permeable submerged breakwaters. OLAFOAM, CFD open source code, is applied in the numerical analysis, and the comparisons are made with available experimental results on the permeable upright wall and the impermeable submerged breakwater to verify its applicability to the three-dimensional numerical analysis. Based on the applicability of OLAFOAM numerical code, the wave height and mean water level distribution formed around the permeable submerged breakwaters are investigated under the formation condition of salient. The numerical results show that as the gap width between breakwaters decreases, the wave height in the center of the gap increases, while it decreases behind the gap, and the installing position of the breakwater from the shoreline has little influence on the change of the wave height. Furthermore, it is found that the decrease of the mean water level near the gap between breakwaters increases with decreasing of the gap width.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.2
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• pp.39-50
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• 2018

In this study, the nonlinear interaction of irregular waves with wave breaking and currents around permeable submerged breakwater was investigated with the aid of olaFlow model which is open source CFD software published under the GPL license. The irregular wave performance of olaFlow applied in this study was verified by comparing and evaluating the target frequency spectrum and the generated frequency spectrum for applicability to irregular waves. Based on the applicability of this numerical model to irregular wave fields, in the coexistence fields of irregular waves and currents, the characteristics of wave height, frequency spectrum, breaking waves, averaged velocity and turbulent kinetic energy around porous submerged breakwater with the respect to the beach type and current direction versus wave propagation were carefully investigated. The numerical results revealed that the shape of wave breaking on the crown of the submerged breakwater and the formation of the mean flow velocity around the structure depend greatly on the current directions and the type of the beach. In addition, it was found that the wave height fluctuation due to the current direction with respect to the wave propagation is closely related to the turbulent kinetic energy.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.399-409
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• 2017

This study numerically investigates the characteristics of the velocity field including the average flow velocity, longshore current and turbulent kinetic energy acting as the main external forces of the salient formed behind the permeable submerged breakwaters. Shoreline response is also predicted by the longshore-induced flux. In this paper, a three-dimensional numerical wave tank based on the OLAFOAM, CFD open source code, is utilized to simulate the velocity field around permeable submerged breakwaters under the formation condition of salient. The characteristics of the velocity field around permeable submerged breakwaters with respect to the gap width between breakwaters and the installing position away from the shoreline under a range of regular waves for different wave height are evaluated. The numerical results revealed that as the gap width between breakwaters increases, the longshore currents become stronger. Furthermore, as the gap width becomes narrower, the point where flow converges moves from the center of the breakwater to the head part. As a result, it is possible to understand the formation of the salient formed behind the submerged breakwaters. In addition, it was found that the longshore currents caused by the gap width between breakwaters and the installation position away from the shoreline are closely related to the turbulent kinetic energy.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.4
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• pp.153-165
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• 2018

In this study, the performance of irregular wave field generation of olaFlow is first verified by comparing the frequency spectrum of the generated waves by the wave-source using olaFlow and the target wave. Based on the wave performance of irregular waves of olaFlow, the characteristics of the velocity field including the average flow velocity, longshore current and turbulent kinetic energy around the three-dimensional permeable submerged breakwaters, which act as the main external forces of the salient formation, are numerically investigated. The numerical results show that as the gap width between breakwaters decreases, the wave height in the center of the gap increases and as the gap width between breakwaters increases, the longshore currents become stronger. As a result, it is possible to understand the formation of the salient formed behind the submerged breakwaters.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.107-113
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• 2001

This study is focused on the wave control by economical multi-rowed impermeable submerged breakwaters which need less materials than a one-rowed submerged breakwater. A boundary element method and eigenfunction expansion method based on the Green\`s theorem are appled to analyze the characteristics of wave transformation. Submerged breakwaters are consisted of one and two-row with rectangular section. Wave transformation characteristics are investigated by the various combinations of placement distance and crown water depth.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.4
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• pp.166-179
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• 2018

This study aims at numerically investigating the water-surface characteristics such as wave height distribution depending on the current direction around the three-dimensional permeable submerged breakwaters in wave-current coexisting field which has not been considered in detail so far. In addition, the characteristics of the velocity field including the average flow velocity, longshore current and turbulent kinetic energy, which act as the main external forces of formation of salient, are also examined. For numerical analysis, olaFlow which is open source code of CFD was used and the numerical tests included different types of target waves, both regular waves and irregular waves. Numerical results indicated that wave height variation with wave following or opposing a current behind the submerged breakwater is closely related to turbulent kinetic energy. Furthermore, it was found that weaker longshore currents are formed under wave-current coexisting field compared to the non-current conditions, and transport flow is attenuated. As a result, it was possible to understand the influence of current existence and direction (following and opposing) on the formation of the salient formed behind the submerged breakwaters.