• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.393-410
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• 2015

Two dimensional numerical models and physical models have been developed to study the highly nonlinear interactions between waves and breakwaters, but several of these models consider the effects of the structural dynamic responses and the shape of the breakwater axis on the wave pressures. In this study, a multi-material Arbitrary Lagrangian Eulerian (ALE) method is developed to simulate the nonlinear interactions between nonlinear waves and elastic seawalls on a coastal rubble mound breakwater, and is validated experimentally. In the experiment, a solitary wave is generated and used with a physical breakwater model. The wave impact is validated computationally using a breakwater - flume coupling model that replicates the physical model. The computational results, including those for the wave pressure and the water-on-deck, are in good agreement with the experimental results. A local breakwater model is used to discuss the effects of the structural dynamic response and different design parameters of the breakwater on wave loads, together with pressure distribution up the seawall. A large-scale breakwater model is used to numerically study the large-scale wave impact problem and the horizontal distribution of the wave pressures on the seawalls.

• Journal of the Korean Society for Marine Environment & Energy
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• v.5 no.2
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• pp.19-27
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• 2002

This paper deals with the experimental investigation on the hydrodynamic behavior of the submerged artificial seabed system in regular waves. This system can function as a basis of seaweed forest which will cultivate coastal fishing ground and enhance coastal productivity. The experiment was conducted with the submerged rectangular plates of different length and depth in 2-D wave flume of KRISO/KORDI. The wave exciting forces, mooring line tension and 2-D motion response are measured and analyzed to figure out the design strategy.

• Journal of Korea Water Resources Association
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• v.46 no.5
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• pp.491-504
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• 2013

In this study, wave breakings over a shelf region are investigated under irregular wave conditions through laboratory experiments in a wave flume. Numerical simulations based on the Boussinesq-type equations are also conducted. The characteristics of breaking waves such as significant wave height, crest and trough heights, the mean water level and the stable wave height are obtained by analyzing laboratory measurements in detail. Obtained results are compared with those of the Boussinesq-type equations model. A very reasonable agreements is observed. The broken waves over a horizontal bottom asymptotically approach a stable wave height($H_{stable}$). In this study, the relative stable wave height is found as $H_{stable}/h{\fallingdotseq}0.56$ for irregular wave.

• Journal of the Korean GEO-environmental Society
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• v.17 no.5
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• pp.5-16
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• 2016

A rainfall induced slope failure is a common natural hazard in mountainous areas worldwide. Sudden and rapid failures which have a high possibility of occurrence in a steep slope are always the most dangerous due to their suddenness and high velocities. Based on a series of experiments this study aimed to determine a critical angle which could be considered as an approximate threshold for a sudden failure. The experiments were performed using 0.42 mm mean grain size sand in a 200 cm long, 60 cm wide and 50 cm deep rectangular flume. A numerical model was created by integrating a 2D seepage flow model and a 2D slope stability analysis model to predict the failure surface and the time of occurrence. The results showed that, the failure mode for the entire material will be sudden for slopes greater than $67^{\circ}$; in contrast the failure mode becomes retrogressive. There is no clear link between the degree of saturation and the mode of failure. The simulation results in considering matric suction showed good matching with the results obtained from experiment. A subsequent discarding of the matric suction effect in calculating safety factors will result in a deeper predicted failure surface and an incorrect predicted time of occurrence.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.6
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• pp.593-601
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• 2020

Two-dimensional laboratory experiments were conducted in a wave flume to investigate the wave transmission phenomena of impermeable-type submerged structures armored by concrete blocks. Different experimental conditions were included by considering relative crest depth, relative freeboard, relative crest width, wave steepness, and so on. An empirical formula was proposed to predict the wave transmission coefficients over various specifications and structural designs of the impermeable submerged structure from the experimental results. The proposed formula successfully predicted the wave transmission coefficients. Therefore, in this study, the proposed empirical formula of the wave transmission over an impermeable submerged structure was improved from the existing formula.

• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.52-60
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• 2008

This study investigates the applicability of CADMAS-SURF (Super Roller Flume for Computer Aided Design of a MArtime Structure) code basal on the Navier-Stokes solver to predict bore phenomena. The time variation of ware levels and velocities due to the bore propagation were computed for the different bore strength conditions. In order to verify the numerical results by CADMAS-SURF, laboratory experiments were also performed, using the DPIV and LDV measuring system. The numerical results were compared to the experimental data and the analytical predictions by the NSC method basal on fully nonlinear shallow-water theory by the method of characteristics. It appears that the CADMAS-SURF slightly overestimated the water-surface level measured by the laboratory experiments and its discrepancy becomes prominent as the bore strength increases. The predicted propagation speed for a bore was also slaver than that by the experiment and NSC method. However, the temporal variations in velocities were in relatively good agreement with the experimental data for all cases, except for overshooting and undershooting in the front face of a bore, which may be derived from the numerical instability. Further, CADMAS-SURF successfully simulated the decrease in the water level and velocity caused by the effects of negative waves reflected from the upstream end wall.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.43 no.1
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• pp.12-27
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• 2007

This fundamental studies on for the productivity improvement and laborsaving of purse seine fishery. Given the difficulty posed from the distortion of net shape caused by the external forces, such as tide, at the time of shooting and pursing, we set the 4 steps of 0, 2, 4 and 6cm/sec in flow velocity in the flume tank for the experiment in order to examine those characteristics. We used two model seines designed on the scale of 1 to 180 based on the power block seine, which is the mackerel purse seine generally used in the near sea of Jeju Island and triplex seine, which is the mackerel purse seine of one boat system fishing expected in the future, for the experiment, and interpreted the characteristics of several motion in water, such as the shape of seine, the change in tension and area during pursing and its the analysis results are as follows. Though the experiment could be conducted up to 6cm/sec of flow velocity that was defined, the experiment could not go on because of the severe distortion in the seine at the flow velocity in excess of 6cm/sec. As for the depth of leadline and reduction rate of side area of seine when the pursing is connected, P seine turned out to be slightly higher than T seine, and the hauling speed and reduction rate of upper area of seine were found similar to each other. The correlation between the hauling time (Ht) and depth of lead line (Dhp, Dht) of P seine and T seine can be expressed by the equation, that is, Dhp=(0.99Pt-7.63)Pt+69.01, Dht=(1.03Pt-7.73)Pt+66.74. The correlation between the hauling time and hauling velocity (Hpp, Hpt) can be expressed by the equation, that is, $Hpp=-0.06Ht^2+0.88Ht+0.78,\;Hpt=-0.05Ht^2+0.81Ht+0.98$ here, Pt is pursing time. And the correlation between the pursing time and the reduction rate of side area (sArp, sArt) can be expressed by the equation, that is, $sArp=-0.48Pt^2+14.79Pt-16.74,\;sArt=-0.45Pt^2+14.56Pt-16.48$. The reduction rate of upper area of seine (tArp, tArt) can be expressed by the equation, that is, $tArp=0.34Pt^2-0.66Pt-0.74,\;tArt=0.34Pt^2-0.27Pt-1.80$. In addition, the correlation between the pursing time and tension of purse line (Tep, Tet) can be expressed by the equation, that is, $Tep=2.79Pt^2+2.26Pt-0.60,\;Tet=2.14Pt^2+8.08Pt-27.50$.

• Journal of Korea Water Resources Association
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• v.52 no.11
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• pp.917-929
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• 2019

Denitrification in streams is of great importance because it is essential for amelioration of water quality and accurate estimation of $N_2O$ budgets. Denitrification is a major biological source or sink of $N_2O$, an important greenhouse gas, which is a multi-step respiratory process that converts nitrate ($NO_3{^-}$) to gaseous forms of nitrogen ($N_2$ or $N_2O$). In aquatic ecosystems, the complex interactions of water flooding condition, substrate supply, hydrodynamic and biogeochemical properties modulate the extent of multi-step reactions required for $N_2O$ flux. Although water flow in streambed and residence time affect reaction output, effects of a complex interaction of hydrodynamic, geomorphology and biogeochemical controls on the magnitude of denitrification in streams are still illusive. In this work, we built a two-dimensional water flow channel and measured $N_2O$ flux from channel sediment with different bed geomorphology by using static closed chambers. Two independent experiments were conducted with identical flume and geomorphology but sediment with differences in dissolved organic carbon (DOC). The experiment flume was a circulation channel through which the effluent flows back, and the size of it was $37m{\times}1.2m{\times}1m$. Five days before the experiment began, urea fertilizer (46% N) was added to sediment with the rate of $0.5kg\;N/m^2$. A sand dune (1 m length and 0.15 m height) was made at the middle of channel to simulate variations in microtopography. In high- DOC experiment, $N_2O$ flux increases in the direction of flow, while the highest flux ($14.6{\pm}8.40{\mu}g\;N_2O-N/m^2\;hr$) was measured in the slope on the back side of the sand dune. followed by decreases afterward. In contrast, low DOC sediment did not show the geomorphological variations. We found that even though topographic variation influenced $N_2O$ flux and chemical properties, this effect is highly constrained by carbon availability.

• Journal of Ocean Engineering and Technology
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• v.30 no.1
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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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1887-1895
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• 2013

In this study, physical experiments were performed in a two-dimensional wave flume to investigate the hydraulic and structural performance of a SFT model. The experiments were made by generating regular waves of different heights and periods under various conditions of buoyancy to weight ratio (BWR) and water depth as well. Through the analysis of the experimental data, it was clarified that the sway and heave motions of the tunnel body linearly increased with wave height and period. In contrast, the roll motion was rather insignificant unless wave height and period were comparatively large as the design wave. Similarly proportional relationship with respect to wave height and period was obtained in case of the maximum tensile force acting on the tension legs and the wave loads on the tunnel body. Regarding the change of water depth or BWR conditions, generally decreasing trend was obtained according to increase of water depth but decrease of BWR for both of the magnitudes of structural behaviors or wave loadings on the SFT structure.