• Journal of Radiation Protection and Research
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• v.27 no.1
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• pp.67-75
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• 2002

The groundwater flow and contaminant transport numerical models have been established for understanding the movement of pollutants in surface soil environment. The numerical solutions were compared with the analytic solutions for the verification and the application of the models. The numerical solutions from the groundwater and transport models agreed welt with analytic solutions. Especially, the results of groundwater flow model were validated in one- and two-dimensional heterogeneous media. Therefore, it will represent well the characteristics of the heterogeneous media in the field applications. Also, the phenomena of the pollutant dispersion represented quite well by the advection and the hydrodynamic dispersion in the results of the transport model. The important input factor is the choice of complicated boundary conditions in operating the numerical models. The numerical results are influenced by the choice of the proper boundary conditions.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.4
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• pp.569-579
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• 2013

A steel-type breakwater that uses a submerged dual horizontal porous plate was originally proposed by Kweon et al. (2005), and its hydrodynamic characteristics and design methodology were investigated in a series of subsequent researches. In particular, Kweon et al. (2011) proposed a method of estimating the vertical uplift force that acts on the horizontal plate, applicable to the design of the pile uplift drag force. However, the difference between the method proposed by Kweon et al. (2011), and the wave force measured at a different time without a phase difference, have not yet been clearly analyzed. In this study, such difference according to the method of estimating the wave force was analyzed, by measuring the wave pressure acting on a breakwater model. The hydraulic model test was conducted in a two-dimensional wave flume of 60.0 m length, 1.5 m height and 1.0 m width. The steepness range of the selected waves is 0.01~0.03, with regular and random signals. 20 pressure gauges were used for the measurement. The analysis results showed that the wave force estimate in the method of Kweon et al. (2011) was smaller than the wave force calculated from the maximum pressure at individual points, under a random wave action. Meanwhile, the method of Goda (1974) that was applied to the horizontal plate produced a smaller wave force, than the method of Kweon et al. (2011). The method of Kweon (2011) was already verified in the real sea test of Kweon et al. (2012), where the safety factor of the pile uplift force was found to be greater than 2.0. Based on these results, it was concluded that the method of estimating the wave force by Kweon et al. (2011) can be satisfactorily used for estimating the uplift force of a pile.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.5
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• pp.333-343
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• 2010

In Mokpo coastal zone, the characteristics showing ebb-dominant tidal flow was confirmed by analysis of observed tide and tidal currents, Physical factors occurring ebb-dominant flow were reviewed. Influence of critical depth for drying, bottom shear stress, coastal reclamation, tidal amplitude, nonlinear tide, and eddy viscosity on the change of ebb-dominant flow was investigated by applying a two-dimensional circulation model. The simulation results for a variety of conditions showed that eddy viscosity and critical depth for drying does little or no impact on the generation of asymmetric flow. Strong bottom friction stress makes ebb-dominant flow clearly. Change of tidal flat into land swells ebb- dominant flow, and change of tidal flat into sea disappears ebb-dominant flow. Nonlinear tides play a decisive role in the generation of asymmetrical tidal flow. Non-linear tides should be included in the open boundary conditions of hydrodynamic modeling in the Mokpo coastal zone.

• Journal of Korean Society on Water Environment
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• v.36 no.6
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• pp.508-520
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• 2020

Dam reservoirs have been reported to contribute significantly to global carbon emissions, but unlike natural lakes, there is considerable uncertainty in calculating carbon emissions due to the complex of emission pathways. In particular, the method of calculating carbon dioxide (CO2) net atmospheric flux (NAF) based on a simple gas exchange theory from sporadic data has limitations in explaining the spatiotemporal variations in the CO2 flux in stratified reservoirs. This study was aimed to analyze the spatial and temporal CO2 distribution and mass balance in Daecheong Reservoir, located in the mid-latitude monsoon climate zone, by applying a two-dimensional hydrodynamic and water quality model (CE-QUAL-W2). Simulation results showed that the Daecheong Reservoir is a heterotrophic system in which CO2 is supersaturated as a whole and releases CO2 to the atmosphere. Spatially, CO2 emissions were greater in the lacustrine zone than in the riverine and transition zones. In terms of time, CO2 emissions changed dynamically according to the temporal stratification structure of the reservoir and temporal variations of algae biomass. CO2 emissions were greater at night than during the day and were seasonally greatest in winter. The CO2 NAF calculated by the CE-QUAL-W2 model and the gas exchange theory showed a similar range, but there was a difference in the point of occurrence of the peak value. The findings provide useful information to improve the quantification of CO2 emissions from reservoirs. In order to reduce the uncertainty in the estimation of reservoir carbon emissions, more precise monitoring in time and space is required.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.6
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• pp.70-78
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• 1998

The changes of tidal characteristics of Kyonggi-Bay Region after the Large Reclamations in the Inchon Coastal Area have been studied by the numerical modelling. The constructions of Inchon International Airport and Sihwa Seadike were considered as the main reclaimation projects in this region. A two dimensional hydrodynamic model was used for this study, and it was composed in relatively high resolution with curvilinear orthogonal coordinate. As the results, at the Inchon harbor and Palmido, where a deep channel is developed, the semi tidal ranges(Z$_0$) were decreased in 8 cm after the two reclamations. However, the Z$_0$ values in the outside of the deep channel were decreased only in 2~4 cm, so that the tidal changes in the deep channel were greater than in the outside of it. After the reclamations, the maxmum velocity was increased 17% at the Inchon harbor, however it was decreased from 1. 55 m/s to 1.10 m/s at the Palmido. This is because the available area in which the stream may spread out was largely reduced after the reclamations. An Asan-bay region, the Z$_0$ was decreased in 5 cm at the Punyang-man and Asan-man stations located after the reclamations in Inchon coastal area. However the changes of Z$_0$ were very little at the outside of Asan-bay. In Asan-bay, the current velocity and direction were little influenced by the reclamations in Inchon coastal area.

• Journal of Korean Society on Water Environment
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• v.27 no.6
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• pp.743-753
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• 2011

One of the most important water management issues of Soyang Reservoir, located in North Han River in Korea, is a long term discharge of turbid water to downstream during flood season. Installation of a selective withdrawal structure (SWS) is planned by the reservoir management institute as a control measure of outflow water quality and associated negative impacts on downstream water use and ecosystem. The objective of the study was to explore the effectiveness of the SWS on the control of outflow turbidity under two different hydrological years; one for normal flood year and another for extreme flood year. A two-dimensional (2D), laterally averaged hydrodynamic and water quality model (CE-QUAL-W2) was set up and calibrated for the reservoir and used to evaluate the performance of the proposed SWS. The results revealed that the SWS can be an effective method when the ${\Theta}$ value, the ratio between the amount of turbid water that containing suspended sediment (SS) greater than 25 mg/L and the total storage of the reservoir, is 0.59 during the normal flood year. However, the effectiveness of the SWS could be marginal or negative in the extreme flood year when ${\Theta}$ was 0.83. The results imply that the SWS is an effective alternative for the control of turbid water for moderate flood events, but not a sufficient measure for large flood events that are expected to happen more often in the future because of climate change.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.8
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• pp.813-821
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• 2005

This paper presents a modeling study of thermal dynamics and turbid current in the Obong Lake, Kangreung. The lake formed by the artificial dam in 1983 for agricultural water supply, is currently under consideration of reconstruction in order to expand the volume of reservoir for water supply and flood control in downstream area. The US Army Corps of Engineers' CE-QUAL-W2, a two-dimensional laterally averaged hydrodynamic and water quality model, was applied to the lake after reconstruction as well as the present lake. The model calibration and verification were conducted against surface water levels and temperature of the lake measured during the years of 2001 and 2003. The model results showed a good agreement with fold measurements both in calibration and verification. Utilizing the validated model, an impact of dam reconstruction on vertical temperature and hydrodynamics were predicted. The model results showed that steep temperature gradient between epilimnion and hypolimnion would be formed during summer, along with extension of cold deep water after reconstruction. During winter and spring seasons, however, the vertical temperature profiles was predicted to be quite similar both before and after reconstruction. This results indicated that thermal stratification would become stronger during summer and stay longer after dam reconstruction. From the examination of predicted water movements, it was noticed that the upstream turbid current would infiltrate into the interface between metalimnion and hypolimnion and then suspended solids would slowly settle down to the bottom before reconstruction. After reconstruction, however, it was shown that the upstream turbid current would stay longer in metalimnion with similar density due to strong stratification. The model also predicted that dam reconstruction would make suspended solids near the dam location significantly decrease.

• 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.

• Journal of Korea Water Resources Association
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• v.37 no.11
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• pp.915-927
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• 2004

The purpose of this paper is to estimate the instream flow of the South Han River Basin to ensure an adequate supply of suitable quality of water for preservation and enhancement of aquatic ecosystems. Proposed methods is Physical Habitant Simulation System of Instream Flow Incremental Methodology. Accurate estimation on a water depth and a velocity distribution was acquired by applying a two dimensional hydrodynamic model for a simulation of a hydraulic parameter necessary for the habitat evaluation to be used in a physical habitat simulation system. The Habitat Suitability Criteria with the application of univariate curve on zacco platypus as a representative fish was able to be established by conducting a field investigation. The establishment of a hydrological materialistic balance between upper and lower streams was confirmed by conducting a simulation simultaneously together with a mainstream section, which was excluded from the considered sections for the inhabitation evaluation of fish.

• Journal of Convergence for Information Technology
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• v.9 no.8
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• pp.155-163
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• 2019

Laminar mixed convection of a nanofluid consists of water and $Al_2O_3$ in a horizontal circular tube has been studied numerically. Two-phase mixture model has been used to investigate hydrodynamic and thermal behaviors of the nanofluid with variables physical properties. Three dimensional Navier-Stokes, energy and volume fraction equations have been discretized using the finite volume method. The Brownian motions of nanoparticles have been considered to determine the thermal conductivity and dynamic viscosity of $Al_2O_3$-Water nanofluid, which depend on temperature. The calculated results show good agreement with the previous numerical data. Results show that in a given Reynolds number (Re), increasing solid nanoparticles volume fraction and Richardson number (Ri) increases the convective heat transfer coefficient and wall shear stress.