• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.5-16
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• 2002

A hydrogeomechanical numerical model is presented to evaluate rainfall impacts on groundwater flow in slopes and slope stability. This numerical model is developed based on the fully coupled poroelastic governing equations for groundwater flow in deforming variably saturated geologic media and the Galerkin finite element method. A series of numerical experiments using the model developed are then applied to an unsaturated slope under various rainfall rates. The numerical simulation results show that the overall hydromechanical slope stability deteriorates, and the potential failure nay initiate from the slope toe and propagate toward the slope crest as the rainfall rate increases. From the viewpoint of hydrogeology, the pressure head and hence the total hydraulic head increase as the rainfall rate increases. As a result, the groundwater table rises, the unsaturated zone reduces, the seepage face expands from the slope toe toward the slope crest, and the groundwater flow velocity increases along the seepage face. From the viewpoint of geomechanics, the horizontal displacement increases, and the vertical displacement decreases toward the slope toe as the rainfall rate increases. This may result from the buoyancy effect associated with the groundwater table rise as the rainfall rate increases. As a result, the overall deformation intensifies toward the slope toe, and the unstable zone, in which the factor of safety against shear failure is less than 1, becomes thicker near the slope toe and propagates from the slope toe toward the slope crest. The numerical simulation results also suggest that the potential tension failure is likely to occur within the slope between the potential shear failure surface and the ground surface.

• Journal of Navigation and Port Research
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• v.36 no.5
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• pp.339-347
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• 2012

After towing rope connecting a barge to a tug was subdivided into multiple finite elements, then those dynamic models was established using Newton's second law and considering the external force and moment such as tension, drag, Coriolis force, gravity, buoyancy, and impact due to free surface acting on each element. While the previous research on the model of towing rope considered only translation, five-degree-of-freedom equations of motion except roll based on the body-fixed frame were established in this paper. All elements are connected by a spring and a damper, and the stiffness of the spring was set as the equivalent value of the real rope. In order to confirm the established multiple finite element model, various scenarios such as freely falling of towing rope in the air and above the free surface, accelerating of a tug which tows a barge connected by towing rope, and sinusoidal moving of a tug were set up and simulated. As the results, the trajectories of the tug, the barge, and the towing rope showed good tendencies to the ones of real expected situations.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.2
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• pp.94-101
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• 2015

To mitigate the greenhouse gas emission, many carbon capture and storage projects are underway all over the world. In Korea, many studies focus on the storage of $CO_2$ in the offshore sediment. Assurance of safety is one of the most important issues in the geological storage of $CO_2$. Especially, the assessment of possibility of leakage and amount of leaked $CO_2$ is very crucial to analyze the safety of marine geological storage of $CO_2$. In this study, the leakage of injected $CO_2$ through fault was numerically studied. TOUGH2-MP ECO2N was used to simulate the subsurface behavior of injected $CO_2$. The storage site was 150 m thick saline aquifer located 825 m under the continental shelf. It was assumed that $CO_2$ leak was happened through the fault located 1,000 m away from the injection well. The injected $CO_2$ could migrate through the aquifer by both pressure difference driven by injection and buoyancy force. The enough pressure differences made it possible the $CO_2$ to migrate to the bottom of the fault. The $CO_2$ could be leaked to seabed through the fault due to the buoyancy force. Prior to leakage of the injected $CO_2$, the formation water leaked to seabed. When $CO_2$ reached the seabed, leakage of formation water stopped but the same amount of sea water starts to flow into the underground as the amount of leaked $CO_2$. To analyze the effect of injection rate on the leakage behavior, the injection rate of $CO_2$ was varied as 0.5, 0.75, and $1MtCO_2/year$. The starting times of leakage at 1, 0.75 and $0.5MtCO_2/year$ injection rates are 11.3, 15.6 and 23.2 years after the injection, respectively. The leakage of $CO_2$ to the seabed continued for a period time after the end of $CO_2$ injection. The ratios of total leaked $CO_2$ to total injected $CO_2$ at 1, 0.75 and $0.5MtCO_2/year$ injection rates are 19.5%, 11.5% and 2.8%, respectively.

• Journal of Korea Water Resources Association
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• v.50 no.1
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• pp.55-64
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• 2017

This study presents a numerical model for simulating turbidity currents using the ULTIMATE scheme. For this, the layer-averaged model is used. The model is applied to laboratory experiments, where the flume is composed of sloping and flat parts, and the characteristics of propagating turbidity currents are investigated. Due to the universal limiter of the ULTIMATE scheme, the frontal part of the turbidity currents at a sharp gradient without numerical oscillations is computed. Simulated turbidity currents propagate super-critically to the end of the flume, and internal hydraulic jumps occur at the break-in-slope after being affected by the downstream boundary. It is found that the hydraulic jumps are computed without numerical oscillations if Courant number is less than 1. In addition, factors that affect propagation velocity of turbidity currents is studied. The particle size less than $9{\mu}m$ does not affect propagation velocity but the buoyancy flux affects clearly. Finally, it is found that the numerical model computes the bed elevation change due to turbidity currents properly. Specifically, a discontinuity in the bed elevation, arisen from the hydraulic jumps and resulting difference in sediment entrainment, is observed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.189-196
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• 2012

The heavy moderator acts as the ultimate heat-sink in an operating CANDU reactor. HUKINS has been developed to investigate moderator flow patterns. HUKINS consists of a 38.4-mm-thick cylindrical shell with a 0.95 m inner diameter and 88 sus-tubes that produce a total heat of 10 kW. A chemical visualization method was selected to estimate the occurrence of typical moderator flow patterns. Momentum-dominated flow, mixed flow, and buoyancy-dominated flow are detected under conditions of a heat load of 7.7 kW and input mass flow rates of 4, 7, and 11 L/min. The experimental results are similar to the results of a CFD simulation that consisted of approximately 1.9 million grids and was conducted using the k-${\varepsilon}$ turbulence model. Therefore, both the present experiments and simulations using HUKINS, a 1/8-scale model, represent all three important flow patterns expected in the real CANDU6 reference reactor. Thus, it has been demonstrated that HUKINS could be useful in the study of CANDU6 moderator circulation.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.155-168
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• 2011

Coastal boundary current flows along the eastern boundary of the Yellow Sea and its speed was about 0.l m/s during the summer 2007. In order to find major factors that affect the coastal boundary current in the eastern Yellow Sea, three-dimensional numerical model experiments were performed. The model simulation results were validated against hydrographic and current meter data in the eastern Yellow Sea. The eastern boundary current flows along the bottom front over the upper part of slopping bottom. Strength and position of the current were affected by tides, winds, local river discharge, and solar radiation. Tidal stirring and surface wind mixing were major factors that control the summertime boundary currents along the bottom front. Tidal stirring was essential to generate the bottom temperature front and boundary current. Wind mixing made the boundary current wider and augmented its north-ward transport. Buoyancy forcing from the freshwater input and solar radiation also affected the boundary current but their contributions were minor. Strong (weak) tidal mixing during spring (neap) tides made the northward transport larger (smaller) in the numerical simulations. But offshore position of the eastern boundary current's major axis was not apparently changed by the spring-neap cycle in the mid-eastern Yellow Sea due to strong summer stratification. The mean position of coastal boundary current varied due to variations in the level of wind mixing.

• Korean Journal of Remote Sensing
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• v.22 no.6
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• pp.469-483
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• 2006

An algorithm was developed to estimate stability indices (SI) over the Korean peninsula using Terra Moderate Resolution Imaging Spectroradiometer (MODIS) infrared brightness temperatures (TBs). The SI is defined as the stability of the atmosphere in the hydrostatic equilibrium with respect to the vertical displacements and is used as an index for the potential severe storm development. Using atmosphere temperature and moisture profiles from Regional Data Assimilation and Prediction System (RDAPS) as initial guess data for a nonlinear physical relaxation method, K index (KI), KO Index (KO), lifted index (LI), and maximum buoyancy (MB) were estimated. A fast radiative transfer model, RTTOV-7, is utilized for reducing the computational burden related to the physical relaxation method. The estimated TBs from the radiative transfer simulation are in good agreement with observed MODIS TBs. To test usefulness for the short-term forecast of severe storms, the algorithm is applied to the rapidly developed convective storms. Compared with the SIs from the RDAPS forecasts and NASA products, the MODIS SI obtained in this research predicts the instability better over the pre-convection areas. Thus, it is expected that the nowcasting and short-term forecast can be improved by utilizing the algorithms developed in this study.

• Journal of Navigation and Port Research
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• v.42 no.6
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• pp.427-436
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• 2018

In this study, experimental and numerical analysis were performed on the survivability of a long pipe-type buoy structure in waves. The buoy structure is an articulated tower consisting of an upper structure, buoyancy module, and gravity anchor with long pipes forming the base frame. A series of experiment were performed in the ocean engineering basin of KRISO with the scaled model of 1/ 22 to evaluate the survivability of the buoy structure at West Sea in South Korea. Survival condition was considered as the wave of 50 year return period. Additional experiments were performed to investigate the effects of current and wave period. The factors considered for the evaluation of the buoy's survival were the pitch angle of the structure, anchor reaction force, and the number of submergence of the upper structure. Numerical simulations were carried out with the OrcaFlex, the commercial program for the mooring analysis, with the aim of performing mutual validation with the experimental results. Based on the evaluation, the behavior characteristics of the buoy structure were first examined according to the tidal conditions. The changes were investigated for the pitch angle and anchor reaction force at HAT and LAT conditions, and the results directly compared with those obtained from numerical simulation. Secondly, the response characteristics of the buoy structure were studied depending on the wave period and the presence of current velocity. Third, the number of submergence through video analysis was compared with the simulation results in relation to the submergence of the upper structure. Finally, the simulation results for structural responses which were not directly measured in the experiment were presented, and the structural safety discussed in the survival waves. Through a series of survivability evaluation studies, the behavior characteristics of the buoy structure were examined in survival waves. The vulnerability and utility of the buoy structure were investigated through the sensitivity studies of waves, current, and tides.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.1
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• pp.21-30
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• 1985

The tension leg platform (TLP) is a kind of compliant structures, and is also a type of moored stable platform with a buoyancy exceeding the weight because of having tensioned vertical anchor cables. In this paper, among the various kinds of tension leg structures, Deep Oil Technology (DOT) TLP was analyzed because it has large-displacement portions of the immersed surface such as vertical corner pontoons and small-diameter elongated members such as cross-bracing. It also has results of hydraulic model tests, comparable with theorectical analysis. Because of the vertical axes of symmetry in the three vertical buoyant legs and because there are no larger horizontal buoyant members between these three vertical members, it was decided to develop a numerical algorithm which would predict the dynamic response of the DOT TLP using the previously developed numerical algorithm Floating Vessel Response Simulation (FVRS) for vertically axisymmetric bodies of revolution. In addition, a linearized hydroelastic Morison equation subroutine would be developed to account for the hydrodynamic pressure forces on the small member cross bracing. Interaction between the large buoyant members or small member cross bracings is considered to be negligible and is not included in the analysis. The dynamic response of the DOT TLP in the surge mode is compared with the results of the TLP algorithm for various combinations of diffraction and Morison forces and moments. The results which include the Morison equation are better than the results for diffraction only. This is because the vertically axisymmetric buoyant members are only marginally large enough to consider diffractions effects. The prototype TLP results are expected to be more inertially dominated.