• Journal of Korea Foundry Society
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• v.34 no.2
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• pp.54-59
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• 2014

In this study, the extruded Al-6.3Zn-2.4Mg alloys were selected among the 7000 series aluminum alloys sensitive to hydrogen environment in order to examine the effects of both the aging conditions and the length of hydrogen charging period on the mechanical properties of the alloy. The specimens were aged for 24hours at $100^{\circ}C$ (under aging (UA)), $120^{\circ}C$ (peak aging (PA)), and $160^{\circ}C$ (over aging (OA)), respectively. Charging tests were performed at RT for 12, 24, 36 hours under potentiostatic conditions (-2000 mV vs (Ag/AgCl)) for 12, 24 and 36 hours in 1M $H_2SO_4$ and 0.1%$NH_4SCN$ solution. The fracture surface was examined by scanning electron microscopy (SEM). X-ray diffraction (XRD) pattern in peak aged sample was obtained before and after hydrogen charging from extruded Al-6.3Zn-2.4Mg alloys. The decreasing rate of tensile strength and elongation is represented in order of over aging < under aging < peak aging, and it is believed that the hydrogen recharge is more sensitive to elongation than tensile strength. The formation of $AlH_3$ in hydrogen charged Al-6.3Zn-2.4Mg alloys has been confirmed by X-ray diffraction studies.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.237-237
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• 2011

효율적인 지하수 관리를 위해서는 시공간적인 변동성을 고려한 지하수 함양률의 정량적 산정이 필수적이다. 본 연구에서는 지표수-지하수 연동해석이 가능하며 토지이용 특성과 국내 토양특성을 가장 잘 표현할 수 있는 한국형 장기 유출 모형 SWAT-K를 이용하여 진천지역의 분포형 지하수 함양량을 산정하였다. 행정경계와 수자원단위지도에서 제시하는 표준단위유역을 기준으로 하여 진천군을 포함하는 미호천유역을 SWAT-K 구동을 위한 모델영역으로 설정하여 주하도를 따라 34개의 소유역으로 구분하였다. SWAT-K를 구동하기 위해서는 기상 및 수문자료를 구축해야 하는데 강우량을 비롯하여 기온, 풍속, 일사량, 상대습도 등의 기상자료가 요구된다. 본 연구에서는 대상유역 내에 위치한 청주, 충주, 대전, 이천, 보은, 천안 기상관측소의 자료를 이용하여 기상자료를 구축하였으며, 모형의 계산시간, 모형결과의 정확도 등을 판단하여 30m 공간해상도를 가지는 DEM을 300m 공간 해상도로 가공하여 사용하였다. 토지이용도는 모의시 다양한 토지이용상태를 반영할 수 있도록 중분류(1:25,000) 토지이용도를 사용하였다. 토양도는 국립농업과학원에서 토양도 전산화 사업을 통해 구축된 1:25,000 축척의 정밀토양도를 사용하였다. SWAT-K를 이용하여 진천군을 포함한 미호천 전체유역에 대해 지표수-지하수 통합 물수지 분석 결과(2004년~2009년) 연평균 강수량 대비 유출률은 66.6%, 증발산률은 34.6%, 함양률은 20.8%로 나타났다. 지표수 유출과정과 지하수위 변동을 동시에 고려하여 산정한 소유역별 연간 함양량 결과를 산정하였고, 총 34개의 소유역별 연간 지하수 함양량을 제시하였다. 또한 SWAT-K 모형을 이용한 모델 영역중 진천군에 속하는 행정구역별, 표준권역별 연평균 함양량을 산출하였으며, 그 분석 결과 진천군 평균 함양률은 20.5%로 산정되었다.

• Journal of Soil and Groundwater Environment
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• v.20 no.3
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• pp.41-50
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• 2015

Hydrogeologic environment of the Mega City such as Seoul, suffers from rapid changes caused by urbanization, construction of underground subway or buildings, and contaminant loading by diverse anthropogenic activities. Understanding the present condition of groundwater environment and water budget is necessary to prevent natural and manmade disasters and to prepare for sustainable water resource management of urban environment. In this study, regional groundwater flow and water budget status of Seoul was analyzed using numerical simulation. Modeling result indicated that groundwater level distribution of Seoul generally followed the topography, but the significant decreases in groundwater level were observed around the subway network. Steady-state water balance analysis showed groundwater recharge by rainfall and leakage from the water supply network was about 550,495 m³/day. Surface water inflow and baseflow rate via Han River and major streams accounted for 799,689 m³/day and 1,103,906 m³/day, respectively. Groundwater usage was 60,945 m³/day, and the total groundwater leakage along the subway lines amounted to 114,746 m³/day. Modeling results revealed that the subway could decrease net groundwater baseflow by 40%. Our study result demonstrated that the subway system can have a significant influence on the groundwater environment of Seoul.

• Journal of Drive and Control
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• v.17 no.3
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• pp.26-32
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• 2020

In modern society, the energy-saving problem of industrial vehicles is economically and environmentally critical. Energy savings using the potential energy of forklifts are one of the viable solutions to resolving this problem. The basic concept of this study is to operate the hydraulic motor and recharge the battery using the flow rate from the cylinder when loading heavy objects and lowering the fork. To save energy, the torque and rotational speed of the generator should be optimized according to the load and descent speed to increase efficiency. To this end, we propose a system that optimizes energy saving efficiency by controlling the swashplate angle of the variable hydraulic motor through the GA(Genetic-Algorithm). The results were verified by building and comparing fixed motor models and variable motor models using the AMEsim. The results of the study show that the proposed optimized swashplate angle increases the energy saving efficiency by approximately 6%-8%, depending on the working conditions.

• Journal of Korea Water Resources Association
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• v.33 no.5
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• pp.611-622
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• 2000

In this study, MODFLOW model is used to analyze the groundwater flow system of Seoguipo area in Cheju island, The final parameters of permeability coefficient and storage coefficient of target area can be obtained by trial and error method using the measured data of pumping rate as initial values. And it is found that the applicability for groundwater flow system is reflected well from the simulation result of the model. Seoguipo area spring water is thought to appear by relatively stable groundwater recharge below EL. 400m according to head distribution through the analysis of observed data considering topographic and geological characteristics, Lee's study(996), and the simulation result. Also it is known that point II, III, and VI show relatively large velocity vectors, and groundwater flows through the movement path which is distributed in various directions of I, II, III, IV, V, VI, and VIl form the result of velocity vector analysis using head distribution result values to analyze the groundwater flow path under unsteady flow condition.dition.

• Journal of Korea Water Resources Association
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• v.37 no.2
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• pp.97-108
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• 2004

Recently the ground-water development using the ground-water dam was proposed for the efficient use of the limited water resources especially for islands or seaside area. But in operating the ground-water dam adjacent to seaside an excessive pumping causes the sea-water intrusion which is caused by the drawdown of ground-water level. In this study, the effect of the recharging well method to reduce the sea-water intrusion was evaluated, and was applied to the downstream of the Ssangcheon ground-water dam site. The SUTRA model was used to simulate the salinity transport in the unsaturated and saturated zone. As the results, the effect of recharging method on the downstream of the ground-water dam was proven to be very efficient to reduce the salinity in the pumping well, and especially the best result was shown at the case that the recharging well is located at 40∼60m from the cutoff wall and the recharging rate is up to 6∼7％.

• Journal of Korea Water Resources Association
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• v.50 no.12
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• pp.889-896
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• 2017

In the present study, an integrated SWAT-MODFLOW model was implemented to analyze the method of supplying groundwater abstraction contributing to Musimcheon stream. Various simulations of supply of groundwater to streamflow with current and maximum groundwater abstraction have been explored for 5 years (2011-2015). In 2015, when the severe drought happened, the monthly discharge change rate due to groundwater supply was ranged from 23% in current abstraction to 68% in maximum abstraction. In terms of annual groundwater recharge, these quantities could be applicable recharges ranged from 75 mm (6.2% of annual mean precipitation) to 290 mm (24% of annual mean precipitation) which could be stable annual supply. Since surface water is vulnerable to drought, the water supply using groundwater could be an effective alternative for stream deficiency.

• Economic and Environmental Geology
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• v.37 no.5
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• pp.499-508
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• 2004

Changwon City first constructed riverbank filtration plants in Book-Myeon and Daesan-Myeon in Korea in the year 2001. This study evaluated hydrogeological characteristics and groundwater flow simulation between the Nakdong River and the fluvial aquifers adjacent to the river in Book-Myeon, Changwon City. The groundwater simulation calculated the influx rate from the Nakdong River and the fluvial aquifers to pumping wells through the riverbank filtration system. The groundwater flow model utilized drilling, grain size analysis, pumping test, groundwater level measurements, river water discharge and rainfall data. Hydraulic heads calculated by the steady-state model closely matched measured heads in pumping and observation wells. According to the transient flow model, using a total pumping amount of 14,000 $m^3$/day, the flux into the pumping wells from the Nakdong River accounts for 8,390 $m^3$/day (60%), 590 $m^3$/day (4%) is from the aquifer in the rectilinea. direction to the Nakdong River, and 5,020 $m^3$/day (36%) is from the aquifer in the parallel direction to the Nakdong River. The particle tracking analysis shows that a particle from the Nakdong River moves toward the pumping wells at a rate of about 1.85 m/day and a particle from the aquifer moves toward the pumping wells at a rate of about 0.75 m/day. This study contributes to surface water/groundwater management modeling, and helps in understanding, how seasonal change affects pumping rates, water quality, and natural recharge.

• Journal of Environmental Policy
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• v.10 no.1
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• pp.49-70
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• 2011

The numerous efforts have been made in understanding generation and transportation mechanism of nonpoint source pollutants from agricultural areas. Also, the water quality degradation has been exacerbated over the years in many parts of Korea as well as other countries. Nonpoint source pollutants are transported into waterbodies with direct runoff and baseflow. It has been generally thought that groundwater quality is not that severe compared with surface water quality. However its impacts on groundwater in the vicinity of stream quality is not negligible in agricultural areas. The SWAT model has been widely used in hydrology and water quality studies worldwide because of its flexibilities and accuracies. The spatial property of each HRU, which is the basic computational element, is not presented. Thus, the SWAT HRU mapping module was developed in this study and was applied to the study watershed to evaluate recharge rate and $NO_3-N$ loads in groundwater. The $NO_3-N$ loads in groundwater on agricultural fields were higher than on forests because of commercial fertilizers and manure applied in agricultural fields. The $NO_3-N$ loads were different among various crops because of differences in crop nutrient uptake, amount of fertilizer applied, soil properties in the field. As shown in this study, the SWAT HRU mapping module can be efficiently used to evaluate the pollutant contribution via baseflow in agricultural watershed.

• Journal of Soil and Groundwater Environment
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• v.9 no.3
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• pp.38-48
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• 2004

Natural attenuation of petroleum hydrocarbon was investigated at an industrial complex about 45 Km away from Seoul. The three-years monitoring results indicated that the concentrations of DO, nitrate, and sulfate in the contaminated area were significantly lower than the background monitoring groundwater under the non-contaminated area. The results also showed a higher ferrous iron concentration, a lower redox potential, and a higher (neutral) pH in the contaminated groundwater, suggesting that biodegradation of TEX(Toluene, Ethylbenzene, Xylene) is the major on-going process in the contaminated area. Groundwater in the contaminated area is anaerobic, and sulfate reduction is the dominant terminal electron accepting process in the area. The total attenuation rate was about 0.0017∼0.0224day$^{-1}$ and the estimated first-order degradation rate constant(λ) was 0.0008∼0.0106day$^{-1}$ . However, the reduction of TEX concentration in the groundwater was resulted from not only biodegradation but also dilution and reaeration through recharge of uncotaminated surface and groundwater. The natural attenuation was, therefore, found to be an effective, on-going remedial process at the site.