• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.5
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• pp.43-50
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• 2018

The temperature of underground water generally remains constant regardless of the season. therefore, it is possible to get plenty of energy if we use characteristics of underground water for both cooling and heating. This study evaluates efficiency of real size coaxial and U-tube type complex geothermal system which is combined with underground water well. This study also evaluates relative efficiency/adaptability through comparison with existing geothermal systems(vertical closed loop system, open loop system(SCW)). The heat exchange capacity of complex geothermal system according to temperature difference between circulating water and underground water shows very high significance by increasing proportionally. The temperature change of underground water according to injection energy, shows very high linear growth aspect as injection thermal volume heightens. As a result of evaluation of heat exchange volume between complex geothermal system and comparative geothermal system, coaxial type has 26.1 times greater efficiency than comparative vertical closed type and 2.8 times greater efficiency than SCW type. U-tube type has 26.5 tims greater efficiency than comparative vertical closed type and 2.8 times greater than SCW type as well. This means complex geothermal system has extremely outstanding performance.

• Journal of Korean Society on Water Environment
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• v.23 no.1
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• pp.122-130
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• 2007

This study was conducted to evaluate water treatment characteristics according to vegetated wetland(V) and open water(O) arrangements in free water surface constructed wetland. Three pilot-scale wetlands, V-V, O-V and V-O, were built and operated. $BOD_5$ was a slightly reduced at all the arrangements because the influent concentration was so low as background concentration of constructed wetlands. While T-N and T-P removal efficiency showed higher than 50% for all cases. The O-V arrangement showed the highest removal efficiency: 20% for $BOD_5$, 56% for SS, 59% for T-N and 72% for T-P. Effluent concentration of the O-V were significantly low compared with those from the V-O. O-V arrangement would be beneficial in the light of pollutant removal efficiency as well as construction cost.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.769-769
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• 2005

• Journal of Korean Society of Water and Wastewater
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• v.23 no.3
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• pp.345-352
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• 2009

The purpose of inlet baffle is to distribute the flow uniformly over the entire cross-sectional area of the sedimentation basin. The goal when designing this baffle is to achieve some head loss while keeping the velocity gradients through the ports equal to the velocity gradient in the end of the flocculator, so as to not break up the flocs. Sedimentation tank performance is strongly influenced by hydrodynamic and physical effects such as inlet design. This study was conducted to evaluate the effect of open ratio of the inlet baffle on hydraulic behavior within a rectangular sedimentation basin using CFD simulation and ADV technique. In order to verify the CFD simulation, we measured the factual velocity at 18 points in the full-scale sedimentation basin at Y water treatment plant. Good agreement was obtained between the CFD predictions and the experimentally measured data. From the simulation results of the existing basin with 7.4 % open ratio, it was investigated that extreme decrease in velocity occurred in the middle of basin. Since then, flow features was unstable. The region which the velocity decrease rapidly moved forward to the flow direction in proportion to the increase of inflow velocity. Also, it was investigated that the flow characteristic of 6.0 % open ratio was significantly different from 7.4 % open ratio at the same configuration condition. These results are a clear indication that inflow momentum and open ratio are the parameters affecting the characteristics of hydraulic patterns. The influence of these parameters on the sedimentation performance requires further study.

• Journal of Environmental Impact Assessment
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• v.12 no.3
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• pp.161-170
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• 2003

To investigate the characteristics of 17 solid waste landfills in the upper drainage basin of Lake Daechong, the landfill sites were surveyed, the leachate of these landfills were analyzed, and the analysis results were assessed from standpoint of water contamination. Sanitary landfills which are now being operated are relatively well equipped with facilities such as leachate collection, daily soil cover and landfill gas treatment devices. But a few of open-dumping landfills were leaking leachate apparently and were supervised improperly and neglectfully by local governments. Some of sanitary landfills exceeded the COD permission criteria of leachate effluent, and some of open-dumping landfills exceeded SS, T-P, Pb, As, Fe, Mn permission criteria of leachate effluent. To improve the water quality of Lake Daechong which is utilized for supplying drinking water, agricultural water, and industrial water to the great part of Chungchong area, the adequate and prompt measures for preventing Daechong Lake water contamination from landfills leachate is necessary.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.77-83
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• 2009

In this study, we conducted resistance and propulsion performance test of ship composed of the Resistance Test, Propeller Open Water Test and Self Propulsion Test using the CFD(Computational Fluid Dynamics). We used commercial RANS(Reynolds Averaged Navier Stokes equation) solver, as a calculating tool. The unstructured grids were used in a bow and stern of ship, having complex shape, for a convenience of generating grids, and the structured grids were adopted in a central hull and rest of hull having a relatively simple shape which is called hybrid grid method. In addition, The sliding mesh method was adopted to rotate a propeller directly in the Propeller Open Water and Self Propulsion Test. The Resistance Test and Self Propulsion Test were calculated using Volume of Fluid (VOF) model and considering a free surface. And all The three cases were applied realizable k-epsilon model as the turbulence model. The results of calculations were verified for the suitability of calculations by comparing MOERI's EFD results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.1
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• pp.22-37
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• 2016

This article investigates numerical modeling of surface piercing propeller (SPP) in unsteady open water condition using boundary element method. The home code based on BEM has been developed for the prediction of propeller performance, unsteady ventilation pattern and cross flow effect on partially submerged propellers. To achieve accurate results and correct behavior extraction of the ventilation zone, finely mesh has generated around the propeller and especially in the situation intersection of propeller with the free surface. Hydrodynamic coefficients and ventilation pattern on key blade of SPP are calculated in the different advance coefficients. The values obtained from this numerical simulation are plotted and the results are compared with experiments data and ventilation observations. The predicted ventilated open water performances of the SPP as well as ventilation pattern are in good agreement with experimental data. Finally, the results of the BEM code/experiment comparisons are discussed.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.2
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• pp.61-69
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• 2004

In this study, flow around rudder is analyzed by utilizing the numerical calculation, and the rudder open water test is performed to validate the calculation. The aim of this study is to design the new rudder shape to improve manoeuvring performance. In first, flow around two-dimensional rudder section is analyzed to understand the characteristics of section profile. And the calculation for all-movable rudders is performed and compared with results of rudder open water test. It is hard to numerically predict the drag force because the value is sensitive to the turbulence modeling and grid spacing near the wall. However, the lift force is predicted well. And we can prove that concave profile of the rudder section produce more lift and torque than convex one as a experiment. However PANEL method that ignore viscous effect cannot distinguish the difference of them. So, we can look for the numerical tool to be developed the new rudder shape.

• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.369-376
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• 2022

In this study, the stability of an anion exchange membrane water electrolyzer (AEMWE) cell was evaluated in an on-off cycling operation with respect to an applied electric bias, i.e., a current density of 500 mA cm^-2, and an open circuit. The ohmic and polarization resistances of the system were monitored during operation (~800 h) using electrochemical impedance spectra. Specific consideration was given to the ohmic resistance of the cell, especially that of the membrane under on-off cycling conditions, by consistently feeding the cell with KOH solution. Owing to an excess feed solution, a momentary increase in the polarization resistance was observed immediately after the open-circuit. The excess feed solution was mostly recovered by subjecting the cell to the applied electric bias. Stability tests on the AEMWE cell under on-off cycling with continuous feeding even under an open circuit can guarantee long-term stability by avoiding an irreversible increase in ohmic and polarization resistances.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.49-60
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• 2015

Open-water sediment disposal has many applications in costal construction. Dumping of sediment in open water can be divided into descending stage under water and sedimentation stage on the seabed, and retained rate is evaluated from analyzed results of these two successive stages. Descending particle cloud have two distinct thermal and swam phase, and trajectory equations for each phase are derived to describe settling velocity and radius of particle cloud. For sedimentation stage, a numerical simulator is used to calculate growth factors for particle fiction angle and current velocity. Retained rate is defined as a mass rate of remained sediment inside the circle which has a center at dumping point on the sea level and user-defined effective radius. Retained rate map for Singapore coast is presented with water depth of 20 m, current velocity of 0.0~1.5 m/s, and effective radius of 5 m. It will decrease sediment mass loss during disposal operation and minimize surrounding environmental pollution.