• Journal of Korean Society on Water Environment
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• v.28 no.5
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• pp.693-703
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• 2012

Load Duration Curve(LDC) is a useful tool for analyzing water quality characteristics under various stream flow conditions. This study investigated the methods to identify impaired waterbodies in the assessment of water quality goal attainment by using LDC for the management of Total Maximum Daily Loads (TMDLs). Three methods were proposed. Non-typical regime exclusion method is a method to exclude water quality observations in the non-typical extreme flow conditions in order to minimize the influence of non-ordinary water quality. Flow regime weighted average method is a method to calculate weighted mean water quality instead of arithmetic mean in order to consider water characteristics properly on stream flow regime in addition to the effect of Non-typical regime exclusion method. Load exceeded interval comparison method is a method to compare the intervals between the attained and non-attained load duration periods on the LDC. The assessment of water quality goal attainment can be performed more reasonably and precisely considering water quality variations on stream flow conditions by applying these proposed methods.

• Journal of Korean Society on Water Environment
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• v.37 no.6
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• pp.469-482
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• 2021

The recent climate change and urbanization have seen an increase in runoff and pollutant loads, and consequently significant negative water pollution. The characteristics of the pollutant loads vary among the different flow regime depending on their source and transport mechanism, However, pollutant load reduction based on flow regime perspectives has not been investigated thoroughly. Therefore, it is necessary to analyze the effects of concentration on pollutant load characteristics and reductions from each flow regime to develop efficient pollution management. As non-point pollutants continuously increase due to the increase in impervious area, efficient management is necessary. Therefore, in this study, 1) the characteristics of pollutant sources were analyzed at the Dalcheon Basin, 2) reduction of nonpoint pollution, and 3) reduction efficiency for flow regimes were analyzed. By analyzing the characteristics of the Dalcheon Basin, a reduction efficiency scenario for each pollutant source was constructed. The efficiency analysis showed 0.06% to 5.62% for the living scenario, 0.09 to 24.62% for the livestock scenario, 0.17% to 12.81% for the industry scenario, 9.45% to 38.45% for the land scenario, and 9.8% to 39.2% for the composite scenario. Therefore, various pollution reduction scenarios, taking into account the characteristics of pollutants and flow regime characteristics, can contribute to the development of efficient measurements to improve water quality at various flow regime perspectives in the Dalcheon Basin.

• Journal of Wetlands Research
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• v.21 no.spc
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• pp.1-8
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• 2019

River works for water utilization have substantially altered the natural flow regime, and it has resulted in deformation of healthy river ecosystems. In Korea, river restoration projects have conducted actively since 1990's. Major purposes of the river restoration are the rehabilitation of modified river channel, improvement of water quality, and creation of aquatic habitats as well as recreational spaces using natural material for river work. However, there have been little interests about the restoration of flow regime which influences to most aspects of river ecosystems. The restoration of natural flow regime has received much attention in preservation of aquatic ecosystems. It should be needed to explore the relationship between flow regime and river ecosystems, and the restoring flow regime is essential. This paper introduce the concept of environmental flow through the interrelation between flow regime and river ecosystem. It provides rolls of flow regime and addresses the method of establishing target flow regime using the RVA(Range of Variability Approach) that suggested by Richter et al.(1997) through analysis of altered flow pattern case of Han river basin.

• Journal of Environmental Science International
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• v.21 no.12
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• pp.1425-1433
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• 2012

Water temperature in the eastern part of the Yellow Sea (EYS) during winter (JFM) and summer (JJA) from 1964 to 2009 and Siberian High Pressure Index (SHI) and Arctic Oscillation index (AOI) during winter (JFM) from 1950 to 2011 were used to analyze long-term variation in oceanic and atmospheric conditions and relationship between winter and summer bottom water temperature. Winter water temperature at 0, 30 and 50 m had fluctuated highly till the late of 1980s, but after this it was relatively stable. The long-term trends in winter water temperature at both depths were separated with cold regime and warm regime on the basis of the late 1980s. Winter water temperature at 0m and 50m during warm regime increased about $0.9^{\circ}C$ and $1.1^{\circ}C$ respectively compared to that during cold regime. Fluctuation pattern in winter water temperature matched well with SHI and AOI The SHI had negative correlation with water temperature at 0 m (r=-0.51) and 50 m (r=-0.58). On the other hand, the AO had positive correlation with Winter water temperature at 0 m (r=0.34) and 50 m (r=0.45). Cyclic fluctuation pattern of winter water temperature had a relation with SHI and AO, in particular two to six-year periodicity were dominant from the early of the 1970s to the early of the 1980s. Before the late of 1980s, change pattern in winter water temperature at 0 and 50 m was similar with that in the bottom water temperature during summer, but after this, relationship between two variables was low.

• Journal of Korea Water Resources Association
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• v.43 no.4
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• pp.325-336
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• 2010

This study presents the alteration of flow regime by effects of dams and water use in the Geum River Basin. The surface water use rate and the Impounded Runoff (IR) index were examined to assess the pressure indicators of the flow alteration. We applied the flow duration curve, flow regime coefficient, flood and low-flow frequency analysis as well as Range of Variability Approach (RVA) to investigate the quantitative changes in natural flow regimes. The results indicate that the high flow decreased and low flow increased respectively compared to the natural flow regimes at eight gauging stations. The Geum river is regulated by 139 dams and reservoirs storing 24% of the annual mean discharge and has high surface water use rate of 36%. These indicators are main pressure factors to alter flow regimes.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.546-553
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• 2022

Narrow rectangular channels are employed in nuclear research reactors that use plate-type nuclear fuels, high heat-flux compact heat exchangers, and high-performance micro-electronics cooling systems. Two-phase flow in narrow rectangular channels is important, and it needs to be better understood because it is considerably different than that in round tubes. In this study, mechanistic models were developed for the flow regime transition criteria for various flow regimes in co-current air-water two-phase flow for vertical downward flow inside a narrow rectangular channel. The newly developed criteria were compared to a flow regime map of downward air-water two-phase flow inside a narrow rectangular channel with a 2.35-mm gap width under ambient temperature and pressure conditions. Overall, the proposed model showed good agreement with the experimental data.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1075-1079
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• 2004

Steam was vertically discharged into water through mini nozzles of various diameters (d=0.115, 0.520, 1.55mm). The condensation was observed and categorized into several types of condensation regimes for each of the nozzles. Compared with the regimes in the previous researches, the regimes of 'internal necking with attached bubble' and 'internal chug with detached bubble' were newly observed. Depending on a nozzle, some regimes expanded, shrank, or moved in the regime map. For the nozzle of 1.55mm, the regime map was similar to Chan and Lee (1982) except that the regime of 'internal chug' was not observed. For the nozzle of 0.115mm, the regime of 'internal chug' appeared even at high pool temperature.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.230-230
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• 2015

When and why do states cooperate in international basins? In recent years, there have been increasing attempts to apply international relations theories such as realism and neo-liberal institutionalism in understanding prospect of cooperation among sovereign states over shared rivers. Realists of hydropolitics argue that fate of cooperation resides in hands of hegemons and distribution of aggregate power among riparian states. Such pessimistic contention has been challenged by neo-liberal institutionalists, especially through regime theory. However, regime theory barely explains why and how cooperation emerges in the first place prior to regime formation. Therefore, the research suggests the game theory from neo-liberal institutionalism as an alternative theoretic approach. The accountability of Oye (1986)'s theoretical framework is illustrated through the case of cooperation in the Rhine River Basin.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.631-636
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• 2000

The experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow have been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.763-772
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• 1998

The effects of an inserted coil on flow patterns and heat transport performance for a horizontal rotating heat pipe have been studied experimentally. Especially, the present study is to see an internally inserted helical coil inside a RHP would lead to the same kind of results as internal fins. Visualization test conducted for an acryl tube, charged water with at a volumetric rate of 20%. When the flow kept pool regime at a low RPM(less than 1,000 RPM), the movement of coil forced the water to flow in axial direction. But this pumping effect of coil disappeared, when the pool regime changed to annular one which could be created by increasing RPM. The pumping effects for RHP with an inserted coil resulted enhancement both in condensation heat transfer coefficient and heat transport limitation, as obtained in case of using internal fins. But all these effects became negligible in the range of higher RPM(above 1,000∼1,200) with the transition of flow regime to annular flow.