• Journal of the Society of Naval Architects of Korea
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• v.33 no.2
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• pp.1-12
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• 1996

Hydrodynamic characteristics of shipping water on deck are investigated by using a simplified two-dimensional model. Formulation of the shipping water on deck leads to a nonlinear hyperbolic system of equations based on the shallow-water wave theory. Time-domain solution of these equations are obtained numerically using a finite difference method which adopts predictor-corrector method for time-marching and 2nd upwind differencing method for convection term calculation. To confirm the validity of the present numerical method, we calculated some shallow-water wave problems accompanying a bore and compared the obtained results with the analytic solutions. We found good agreements between them. Though the calculation results of shipping water on deck, we show that the shipping water flows into the deck as a rarefying wave arid grows into a bore after colliding with a deck structure. Also we examined the effects of acceleration and slope of deck and found that they have significant influences on the flow of shipping water.

• Journal of the Korean Solar Energy Society
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• v.32 no.2
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• pp.19-27
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• 2012

This paper describes an experimental study on efficiency of solar collector in solar water heating system connected to hourly water heating load. In general, the functional form of solar efficiency is expressed as a function of fluid temperature entering solar collector, ambient temperature, and solar irradiance. When energy saving from solar heating of water heating system is analyzed on along-term basis such as one year with given solar irradiance data, simplified analysis is more convenient han detailed system simulation for quick assessment. However, the functional form of the efficiency is not convenient for approximately simplified energy analysis because the inlet temperature can be obtained through a detailed system simulation. In the study, solar collector efficiency is obtained with various daily water heating load sand daily solar irradiance using experimental tests. The study also considers large residential buildings such as apartment buildings for application of solar water heating systems. From test results, it is found that daily solar collector efficiency is proportional to daily water heating loads and daily solar irradiance. The data obtained from the study can be utilized to find a functional relation between daily solar irradiance and daily heating load in stead of collector inlet temperature for application of solar collector efficiency to long-term approximated energy analysis of solar heating system.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1174-1178
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• 2005

In this study, flood inundations have been simulated by using the numerical model FLUMEN solving the shallow-water equations with a finite volume method. Before applying to a real problem, the numerical model is first applied to simplified problems. Obtained numerical results are verified by comparing to available analytical solutions and laboratory measurements. Reasonable agreements are observed. The model is then applied to a simulation of flood events with real geometries. The results of the present study provide basic informations for a flood inundation map.

• Journal of the Korean Society of Marine Environment & Safety
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• v.3 no.1
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• pp.85-92
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• 1997

To understand the dynamics of a drifting object, an analysis based on fluid dynamics theory is presented. A simplified analysis shows a consistency with the linear formula currently used for search and rescue mission. Also an experiment using miniatured human models has been conducted to study the drift characteristics of Person-in-Water. The tests were carried out at the water channel facility and the models were tested in different positions and styles. The measured drag coefficients for human body ranged over 0.4-1.2.

• Journal of the Korean Society of Safety
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• v.33 no.3
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• pp.92-98
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• 2018

The flow of cooling water in a passive containment cooling system (PCCS), used to remove heat released in design basis accidents from a concrete containment of light water nuclear power plant, was conducted in order to investigate the thermo-fluid equilibrium among many parallel tubes of PCCS. Numerical simulations of the subcooled boiling flow within a coolant loop of a PCCS, which will be installed in innovative pressurized-water reactor (PWR), were conducted using the commercially available computational fluid dynamics (CFD) software ANSYS-CFX. Shear stress transport (SST) and the RPI model were used for turbulence closure and subcooled flow boiling, respectively. As the first step, the simplified geometry of PCCS with 36 tubes was modeled in order to reduce computational resource. Even and uneven thermal loading conditions were applied at the outer walls of parallel tubes for the simulation of the coolant flow in the PCCS at the initial phase of accident. It was observed that the natural circulation maintained in single-phase for all even and uneven thermal loading cases. For uneven thermal loading cases, coolant velocity in each tube were increased according to the applied heat flux. However, the flows were mixed well in the header and natural circulation of the whole cooling loop was not affected by uneven thermal loading significantly.

• Journal of Korean Society on Water Environment
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• v.21 no.5
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• pp.448-457
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• 2005

The conventional activated sludge processes were operated as a combined organic substrate removal and nitrification. So, it was necessary to provide with oxygen for both carbon and ammonia removal. But, in the BNR processes, nitrification is separated from carbon removal that causes fast ammonia oxidation and reduced oxygen demands. And most of the substrate is utilized by denitrification organisms and phosphorus accumulating organisms. with these appearances, mathematical model for BNR processes different from IWA ASM can be simplified and applied. In this study, it was performed that the existing equations as McKinney model, nitrification model published by U.S. EPA and oxygen demands from stoichiometry and the relationship between NUR and OUR were applied to full-scale BNR processes and the results were compared with the measured. and it is possible to make out the optimum design parameter from those equations.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.411-420
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• 2020

Numbers fitting-curve equations have been proposed to predict soil-water retention curve (SWRC) whose parameters have no definitude physical meaning. And these methods with precondition of measuring SWRC data is time-consuming. A simplified directly method to estimate SWRC without parameters obtained by fitting-curve is proposed. Firstly, the total SWRC can be discretized into linear segments respectively. Every segment can be represented by linear formulation and every turning point can be determined by the pore-size distribution (PSD) of Mercury Intrusion Porosimetry (MIP) tests. The pore diameters governing the air-entry condition (AEC) and residual condition (RC) can be determined by the PSDs of MIP test. The PSD changes significantly during drying in SWR test, so the determination of AEC and RC should use the PSD under corresponding suction conditions. Every parameter in proposed equations can be determined directly by PSD without curve-fitting procedure and has definitude physical meaning. The proposed equations give a good estimation of both unimodal and bimodal SWRCs.

• Journal of Korean Society on Water Environment
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• v.31 no.5
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• pp.491-506
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• 2015

Distributed models represent watersheds using a network of numerous, uniform calculation units to provide spatially detailed and consistent evaluations across the watershed. However, these models have a disadvantage in general requiring a high computing cost. Semi-distributed models, on the other hand, delineate watersheds using a simplified network of non-uniform calculation units requiring a much lower computing cost than distributed models. Employing a simplified network of non-uniform units, however, semi-distributed models cannot but have limitations in spatially-consistent simulations of hydrogeochemical processes and are often not favoured for such a task as identifying critical source areas within a watershed. Aiming to overcome these shortcomings of both groups of models, a hybrid watershed model STREAM (Spatio-Temporal River-basin Ecohydrology Analysis Model) was developed in this study. Like a distributed model, STREAM divides a watershed into square grid cells of a same size each of which may have a different set of hydrogeochemical parameters reflecting the spatial heterogeneity. Like many semi-distributed models, STREAM groups individual cells of similar hydrogeochemical properties into representative cells for which real computations of the model are carried out. With this hybrid structure, STREAM requires a relatively small computational cost although it still keeps the critical advantage of distributed models.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.456-465
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• 1988

The performance of the cold latent heat storage is investigated by experiment and by a simplified analytic approach. The heat storage tank has eight horizontal circular tubes and one path of refrigerant evaporating tube. The phase change material in the heat storage tank is water which is frozen by evaporating refrigerant of refrigeration system and melts by the warm air in the heat storage tank. In the experiment, the performance has been studied by the various conditions including the initial water temperature on solidification and flow rate and temperature of air. The rate of recovered heat has been simulated by a simplified model and the results shows a good agreement. In solidification process, initial water temperature causes time delay corresponding to the sensible heat and it is found that the shape of evaporator is important. In melting process, the recovered heat rate from the heat storage tank is proportional to $Re^{0.8}(T_{bi}-T_f)$ of air where $T_{bi}$ and $T_f$ indicate temperatures of inlet air and phase change, respectively. And the deminishing rate of the recovered heat is higher for the higher heat rate.

• Korean Journal of Hydrosciences
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• v.8
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• pp.97-110
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• 1997

Quantifying water balance components is crucial to understanding the basic hydrology and hydrochemistry. An importance of water balace studies has been emphasized from the need to grasp the actual condition of water resources and environmental changes including climatic changes. This paper proposes a method for evaluating water balance components based on the vegetation monitor using remote sensing data. Here, the evapotranspiration model adopts a direct method by using NDVI(Normalized Difference Vegetation Index) calculated from NOAA/AVHRR data and a detailed descriptionof water balance by using the evapotranspiration over the Korean Peninsula. In the study, areal distribution data sets of water balance components are produced using NDVI and a simplified water balance model. This method enables one to discuss the hydrological problems for North Korea where insufficient meteorological and hydrological data exist. The results obtained indicate the specific regional features on water inventory and fluctuation in water balance.