• Water for future
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• v.29 no.4
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• pp.209-221
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• 1996

It may be difficult to make exact estimates of peak discharge or runoff depth of a flood and to establish the proper measurement for the flood protection since water stages or discharges have been rarely measured at small river basins in Korea. Three small catchments in the Su-Young river basin in Pusan were selected for the study areas. Various runoff parameters for the study areas were determined, and runoff analyses were performed using three different runoff models available in literatures; the storage function method, the discrete, linear, input-output model, and the linear reservoir model. The hydrographs calculated by three different methods showed good agreement with the observed flood hydrographs, indicating that the models selected are all capable of sucessfully modeling the flood events for small watersheds. The storage function method gave the best results in spite of its weakness that it could not be applicable to small floods, while the linear reservoir model was found to provide relatively good results with less parameters. The capabilities of simulating flood hydrographs were also evaluated based on the effective rainfall from the storage function parameters, the $\Phi$-index method, and the constant percentage method. For the On-Cheon stream watershed, the storage function parameters provided better estimates of effective rainfall for regenerating flood hydrographs than any others considered in the study. The $\Phi$-index method, however, resulted in better estimates of effective rainfall for the other two study areas.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.75-75
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• 2019

첨두홍수량 자료는 홍수예경보 및 치수계획수립 등 하천관리에 있어서 매우 중요한 요소이다. 그러나 대규모 홍수가 발생 시 악천후가 동반된 기상상황이나, 현장 접근이 어려운 환경적 조건과 예산 및 인력 부족 등에 의한 불가피한 문제로 첨두홍수량을 측정하는데 어려움 있다. 따라서 일반적으로 수위-유량관계곡선식을 이용하여 첨두홍수량을 산정하지만 단순 고수위 외삽 추정을 통해 개발된 곡선식을 이용한 첨두홍수량 산정에 있어서는 주의가 필요하다. 이러한 경우 홍수가 지나간 후 현장조사를 통해 획득한 위치, 표고, 횡단면적 등 홍수흔적(flood marks)을 가지고 경사면적법(slope-area method)과 같은 간접적인 방법으로 첨두홍수량을 추정할 수 있다. 본 연구에서는 2018년 큰 호우사상이 발생한 내성천의 지류인 서천의 영주시(월호교) 지점과 남강의 산청군(하촌리) 지점에서 홍수흔적 조사를 통해 지점별 두 개의 단면을 선정하였다. 영주시(월호교) 지점의 두 단면 간 거리는 약 90m, 높이차는 약 0.21m로 조사되었고, 산청군(하촌리) 지점의 두 단면 간 거리는 약 330m, 높이차는 약 0.47m로 조사되었다. 경사면적법을 이용한 첨두 홍수량 추정에 적용된 조도계수는 '서천 하천기본계획(2014)', '남강 하천기본계획(2013)'에서 계획 홍수량 산정에 적용된 조도계수 0.029와 0.025를 적용하였다. 영주시(월호교) 지점은 2018년 9월 4일 발생한 호우사상의 첨두수위 5.59m에서 수위-유량관계곡선식을 이용하여 산정된 유량은 $1,127.8m^3/s$이고 경사면적법을 이용하여 추정된 유량은 $1,105.9m^3/s$로 약 -1.98%의 편차율이 발생하였다. 산청군(하촌리) 지점은 2018년 8월 26일 발생한 호우사상의 첨두수위 6.75m에서 수위-유량관계곡선식을 이용하여 산정된 유량은 $3,435.0m^3/s$이고 경사면적법을 이용하여 추정된 유량은 $3,233.3m^3/s$로 약 -6.24%의 편차율이 발생하였다. 경사면적법을 이용하여 추정된 첨두홍수량은 수위-유량관계곡선식을 이용하여 산정된 유량과 편차율이 지점별 ${\pm}10%$ 이내의 근사한 범위로 산정되었다. 따라서 경사면적법을 이용한 첨두홍수량 추정 방법의 적용에 있어서 적절한 것으로 판단된다.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.147-156
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• 2011

The purpose of multipurpose reservoir operation in flood season is to reduce the peak flood at a control point by utilizing flood control storage or to minimize flood damage by controlling release and release time. Therefore, the most important thing in reservoir operation for flood season is to determine the optimal release and release time. In this study, goal programming is used for the optimal reservoir operation in flood season. The goal programming minimizes a sum of deviation from the target value using linear programming or nonlinear programming to obtain the optimal alternative for the problem with more than two objectives. To analyze the applicability of goal programming, the historical storm data are utilized. The goal programming is applied to the reservoir system operation as well as single reservoir operation. Chungju reservoir is selected for single reservoir operation and Andong and Imha reservoirs are selected for reservoir system operation. The result of goal programming is compared with that of HEC-5. As a result, it was found that goal programming could maintain the reservoir level within flood control level at the end of a flood season and also maintain flood discharge within a design flood at a control point for each time step. The goal programming operation is different from the real operation in the sense that all inflows are assumed to be given in advance. However, flood at a control point can be reduced by calculating the optimal release and optimal release time using suitable constraints and flood forecasting system.

• Ecology and Resilient Infrastructure
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• v.6 no.1
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• pp.23-33
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• 2019

Naeseong Stream is a sand-bed river that flows through the northern area of Gyeongbuk province. It is characterized by dynamic sandy bedforms developed in response to the seasonal hydrological fluctuation and by its unique riverine landscape called "white river." However, changes including construction of Yeongju Dam from 2010 and the extensive vegetation establishment around 2015 occurred along the Naeseong Stream. This paper aims to analyze climate, hydrology, and water quality as factors and to examine the possibility of channel changes accordingly. The second least precipitation during the last 60 years happened in 2015, which led to the lowest peak discharge in 50 years. The sediment characteristics of Naeseong Stream were not significantly different along the upstream and downstream reaches, but it was confirmed that annual minimum water level of the stream decreased continuously regardless of the dam construction. This suggests that intermittent drought and change in water quality are likely to provide favorable conditions for riparian vegetation establishment and the resulting physical changes have affected riverbed degradation. Therefore, it is necessary to conduct diversified monitoring in connection with river vegetation change in order to analyze the causes of river changes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.2
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• pp.187-192
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• 2019

Hybrid power storage system with emergency power function for demand management and power outage minimizes the investment cost in the building of buildings and factories requiring emergency power generation facilities, We propose a new business model by developing technology that can secure economical efficiency by reducing power cost at all times. Normally, system power is supplied to load through STS (Static Transfer Switch), and PCS is connected to system in parallel to perform demand management. In order to efficiently operate the electric power through demand forecasting, the EMS issues a charge / discharge command to the ESS as a PMS (Power Management System), and the PMS transmits the command to the PCS controller to operate the system. During the power outage, the STS is rapidly disengaged from the system, and the PCS becomes an independent power supply and can supply constant voltage / constant frequency power to the load side. Therefore, it is possible to secure reliability through verification of actual system linkage and independent operation performance of hybrid ESS, By enabling low-carbon green growth technology to operate in conjunction with an efficient grid, it is possible to improve irregular power quality and contribute to peak load by generating renewable energy through ESS linkage. In addition, the ESS is replacing the frequency follow-up reserve, which is currently under the charge of coal-fired power generation, and thus it is anticipated that the operation cost of the LNG generator with high fuel cost can be reduced.

• Applied Chemistry for Engineering
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• v.33 no.1
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• pp.58-63
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• 2022

Graphite has been used as an anode material for lithium-ion batteries for the past 30 years due to its low de-/lithiation voltage, high theoretical capacity of 372 mAh/g, low price, and long life properties. Recently, all-solid-state lithium-ion batteries (ASSLB), which are composed of inorganic solid materials with high stability, have received great attention as electric vehicles and next-generation energy storage devices, but research works on graphite that works well for ASSLB systems are insufficient. Therefore, we induced the performance improvement of ASSLB anode electrode graphite material by removing the amorphous carbon present in the carbon material surface, acting as a resistive layer from the graphite. As a result of X-ray diffraction (XRD) analysis using heat treated graphite in air at 400, 500, and 600 ℃, the full width at half maximum (FWHM) at (002) peak was reduced compared to that of bare graphite, indicating that the crystallinity of graphite was improved after heat treatment. In addition, the discharge capacity, initial coulombic efficiency (ICE) and cycle stability increased as the crystallinity of graphite increased after heat treatment. In the case of graphite annealed in air at 500 ℃, the high capacity retention rate of 331.1 mAh/g and ICE of 86.2% and capacity retention of 92.7% after 10-cycle measurement were shown.

• Clean Technology
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• v.16 no.3
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• pp.191-197
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• 2010

Repair reaction of plasma damaged porous methyl doped SiOCH films was carried out with silylation agents dissolved in supercritical carbon dioxide ($scCO_2$) at various reaction time, pressure, and temperature. While a decrease in the characteristic bands at $3150{\sim}3560cm^{-1}$ was detectable, the difference of methyl peaks was not identified apparently in the FT-IR spectra. The surface hydrophobicity was rapidly recovered by the silylation. In order to induce effective repair in bulk phase, the wafer was heat treated before reaction under vacuum or ambient condition. The contact angle was slightly increased after the treatment and completely recovered after the subsequent silylation. Methyl groups were decreased after the plasma damage, but their recovery was not identified apparently from the FT-IR, spectroscopic ellipsometry, and secondary ion mass spectroscopy analyses. Furthermore, Ti evaporator was performed in a vacuum chamber to evaluate the pore sealing effect. The GDS analysis revealed that the open pores in the plasma damaged films were efficiently sealed with the silylation in $scCO_2$.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4102-4110
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• 2022

Aiming at high-power and long-pulse operation up to 1000 s, some improvements have been made for both 2.45 GHz and 4.6 GHz lower hybrid (LH) systems during the recent 5 years. At first, the guard limiters of the LH antennas with graphite tiles were upgraded to tungsten, the most promising material for plasma facing components in nuclear fusion devices. These new guard limiters can operate at a peak power density of 12.9 MW/m². Strong hot spots were usually observed on the old graphite limiters when 4.6 GHz system operated with power >2.0 MW [B. N. Wan et al., Nucl. Fusion 57 (2017) 102019], leading to a reduction of the maximum power capability. With the new limiters, 4.6 GHz LH system, the main current drive (CD) and electron heating tool for EAST, can be operated with power >2.5 MW routinely. Long-pulse operation up to 100 s with 4.6 GHz LH power of 2.4 MW was achieved in 2021 and the maximal temperature on the guard limiters measured by an infrared (IR) camera was about 540 ℃, much below the permissible value of tungsten material (~1200 ℃). A discharge with a duration of 1056 s was achieved and the 4.6 GHz LH energy injected into the plasma was up to 1.05 GJ. Secondly, the fully-active-multijunction (FAM) launcher of 2.45 GHz system was upgraded to a passive-active-multijunction (PAM), for which the density of optimum coupling was relatively low (below the cut-off value). Good coupling with reflection coefficient ~3% has been achieved with plasma-antenna distance up to 11 cm for the new PAM. Finally, in order to eliminate the effect of ion cyclotron range of frequencies (ICRF) wave on 4.6 GHz LH wave coupling, the location of the ICRF launcher was changed to a port that is located 157.5° toroidally from the 4.6 GHz LH system and is not magnetically connected.

• Ecology and Resilient Infrastructure
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• v.10 no.4
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• pp.217-225
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• 2023

This study analyzed the effect of flood level reduction in the case of creating and operating offline storage for the Jangdong district, which can be used as a flood buffer space for the Geumgang River, through one-dimensional unsteady flow numerical simulation. In particular, the sensitivity analysis of changes in the height and width (length) of transverse weirs on flood level changes was performed to provide quantitative information necessary for flood control facility (embankment) design. As a result of analyzing the flood control effect of the offline storage based on the peak flood discharge and level, spatially, the flood control effect at the planned flood buffer space site and the downstream end was confirmed, and it was confirmed that the flood reduction effect at the downstream occurred the most. By design conditions of the transverse overflow weir, the greatest flood reduction effect was found under the condition that the overflow weir height based on the 50-year frequency flood level and the transverse overflow weir width (length) of 125 m were considered. The effect of delaying the time to reach the maximum flood due to the operation of the offline storage site was also presented based on unsteady flow modeling.

• Journal of Korean Society of Forest Science
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• v.90 no.2
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• pp.197-209
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• 2001

TOPMODEL, semi-distributed hydrological model, is frequently applied to predict the amount of discharge, main flow pathways and water quality in a forested catchment, especially in a spatial dimension. TOPMODEL is a kind of conceptual model, not physical one. The main concept of TOPMODEL is constituted by the topographic index and soil transmissivity. Two components can be used for predicting the surface and subsurface contributing area. This study is conducted for the validation of applicability of TOPMODEL at small forested catchments in Korea. The experimental area is located at Gwangneung forest operated by Korea Forest Research Institute, Gyeonggi-do near Seoul metropolitan. Two study catchments in this area have been working since 1979 ; one is the natural mature deciduous forest(22.0 ha) about 80 years old and the other is the planted young coniferous forest(13.6 ha) about 22 years old. The data collected during the two events in July 1995 and June 2000 at the mature deciduous forest and the three events in July 1995 and 1999, August 2000 at the young coniferous forest were used as the observed data set, respectively. The topographic index was calculated using $10m{\times}10m$ resolution raster digital elevation map(DEM). The distribution of the topographic index ranged from 2.6 to 11.1 at the deciduous and 2.7 to 16.0 at the coniferous catchment. The result of the optimization using the forecasting efficiency as the objective function showed that the model parameter, m and the mean catchment value of surface saturated transmissivity, $lnT_0$ had a high sensitivity. The values of the optimized parameters for m and InT_0 were 0.034 and 0.038; 8.672 and 9.475 at the deciduous and 0.031, 0.032 and 0.033; 5.969, 7.129 and 7.575 at the coniferous catchment, respectively. The forecasting efficiencies resulted from the simulation using the optimized parameter were comparatively high ; 0.958 and 0.909 at the deciduous and 0.825, 0.922 and 0.961 at the coniferous catchment. The observed and simulated hyeto-hydrograph shoed that the time of lag to peak coincided well. Though the total runoff and peakflow of some events showed a discrepancy between the observed and simulated output, TOPMODEL could overall predict a hydrologic output at the estimation error less than 10 %. Therefore, TOPMODEL is useful tool for the prediction of runoff at an ungaged forested catchment in Korea.