• Tunnel and Underground Space
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• v.30 no.5
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• pp.446-461
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• 2020

Numerical simulations of CIEMAT column test in Spain are performed to investigate the coupled thermo-hydro-mechanical (THM) behavior of MX80 bentonite pellets using TOUGH2-FLAC3D. The heater power and injection pressure of water in the numerical simulations are identical to those in the laboratory test. To investigate the applicability of the thermo-hydraulic (TH) model used in TOUGH2 code to prediction of the coupled TH behavior, the simulation results are compared with the observations of temperature and relative humidity with time. The tendencies of the coupled behavior observed in the test are well represented by the numerical models and the simulator in terms of temperature and relative humidity evolutions. Moreover, the performance of the models for the reproduction and prediction of the coupled TH behavior is globally satisfactory compared with the observations. However, the calculated stress change is relatively small and slow due to the limitations of the simple elastic and swelling pressure model used in numerical simulations. It seems that the two models are insufficient to realistically reproduce the complex coupled THM behavior in the bentonite pellets.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1039-1049
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• 2015

The inflow estimation at large multipurpose dam reservoir is carried out by considering the water balance among the discharge, the storage change during unit time interval obtained from the observed water level near dam structure and area-volume curve. This method can be ideal for level pool reservoir but include potential errors when the inflow is influenced by the water level slope due to backwater effects from upstream flood inflows and strong wind induced by typhoon. In addition, the other uncertainties arisen from the storage reduction due to sedimentation after the dam construction and water level noise due to mechanical vibration transmitted from the electric power generator. These uncertainties impedes the accurate hydraulic inflow measurement requiring exquisite hydrometric data arrangement for reservoir waterbody. In this study, the distributed hydrologic model using UBC-3P boundary setting was applied and its feasibility was evaluated. Finally, the modeling performance has been verified since the calculated determination coefficient has been in between 0.96 to 0.99 after comparing with observed peak inflow and total inflow at Namgang dam reservoir.

• Journal of Korea Water Resources Association
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• v.51 no.6
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• pp.481-490
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• 2018

Recently, the spatiotemporal patterns of flood disasters have become more complex and unpredictable due to climate change. Flood hazard map including information on flood risk level has been widely used as an unstructured measure against flooding damages. In order to product a high-precision flood hazard map by combination of hydrologic and hydraulic modeling, huge digital information such as topography, geology, climate, landuse and various database related to social economic are required. However, in some areas, especially in developing countries, flood hazard mapping is difficult or impossible and its accuracy is insufficient because such data is lacking or inaccessible. Therefore, this study suggests a method to delineate large scale flood-prone area based on topographic factors produced by linear binary classifier and ROC (Receiver Operation Characteristics) using globally-available geographic data such as ASTER or SRTM. We applied the proposed methodology to five different countries: North Korea Bangladesh, Indonesia, Thailand and Myanmar. The results show that model performances on flood area detection ranges from 38% (Bangladesh) to 78% (Thailand). The flood-prone area detection based on the topographical factors has a great advantage in order to easily distinguish the large-scale inundation-potent area using only digital elevation model (DEM) for ungauged watersheds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.659-667
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• 2017

This study analyzes the changes in the flow characteristics due to the difference in inflow discharges from the main channel and tributary at the confluence of the Nakdong and Geumho Rivers. The analysis was done using a two-dimensional numerical method. The study site has complicated flow patterns because of the discharge variation from the main stream and tributary. The study section has a meandering main channel, and the hydraulic characteristics cannot be defined with simple conditions such as the confluence angle of the channels or the ratio of the channel widths. An actual flood event in 2012 was applied in the numerical simulation. The maximum velocity occurred in the meandering section after passing the confluence, where a rapid change was expected. A high velocity and large bed change in this section were observed in the simulation results. The variation of discharges from the main channel and tributary was a more dominant factor in the flow and bed changes for the normal flow conditions than the flood event. This indicates that countermeasures for channel stabilization should be considered in the meandering section downstream of the confluence section, and countermeasures for the study section should be investigated.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.1
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• pp.9-23
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• 1997

A numerical study of a two-layer, stratified flow is investigated, using the implicit finite difference method in one dimension. The results of computational method have been tested and, in case of lock exchange flow, compared with the results of experimental data. The results of model experiments with various interfacial, bottom friction coefficients along with various time weighting factor of numerical scheme and dissipative interface are shown and discussed. Two-layer model experiment has been also carried out to investigate the generation and propagation characteristics of internal tidal wave over the steep bottom topography under stratified condition. The internal wave seems to well radiate through the downstream boundary under the experiments adopting radiation conditions both at two layers and only at upper layer, confirming the applicability of radiational boundary condition in stratified flows. It is also shown that the internal wave through the downstream boundary propagates more actively with increasing thickness of lower layer in the downstream. This implies that the potential tidal energy in the interface will depend upon the thickness of lower layer for the constant thickness of upper layer.

• Journal of the Korean GEO-environmental Society
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• v.13 no.10
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• pp.15-23
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• 2012

A numerical model and field monitoring data are used to estimate a change in groundwater level at a borrow site, which will be constructed at the mountainous area with a large ground excavation in the study area, Hwaseong city. Lithologic data and hydraulic coefficients are collected at 9 boreholes and also groundwater levels are measured at these boreholes and existing wells in the study area. Additionally, groundwater recharge rate for the type of land cover is estimated using water budget analysis; 133.34mm/year for a mountainous area, 157.68mm/year for a farming area, 71.08mm/year for an urbanized area, and 26.06mm/year for a bedrock exposure area. The change in groundwater level in and around a borrow site is simulated with Modflow using these data. The result of a transient model indicates that a removal of high ground (over 40El.m) by an excavation will produce a decrease in groundwater levels, up to 1 m, around a borrow site in 10 years. It also explains that this ground excavation will bring about the decreases of 9.4% and 7.0% for groundwater recharge and surface runoff, respectively, which are the factors causing groundwater level's change. This study shows that it is required to construct the groundwater monitoring wells to observe the change of groundwater near a borrow site.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.3 s.22
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• pp.69-76
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• 2006

An hydraulic and hydrologic analysis procedure was proposed to reduce the inundation damage of highway in urban stream, that could contribute the EAP and Traffic control planning of Dongbu highway in the Jungrang stream basin which is one of the representative urban area in Korea. We performed the HEC-HMS runoff analysis, and the UNET unsteady flow modeling to decide the inundation reaches and their characteristics. The high inundation risk areas were of Emoon railway bridge and the Wollueng bridge, which are inundated in the case of 10 year and 20 year frequency flood respectively. We also analyze the inundation characteristics under the various conditions of the accumulation rainfall and the duration. Flood elevation at the Wolgye-1 bridge exceed over Risk Flood Water Level(EL.17.84 m) when the accumulation rainfall is over 250 mm and shorter duration than 7 hr. When neglecting backwater effect from the Han river, inundation risk are highly at the reach C2(Wolgye-1 br. ${\sim}$Jungrang br., left bank), C1(Wolgye-1 br. ${\sim}$Jungrang br., right bank), D(Jungrang br. ${\sim}$Gunja br.) in order, but when consider the effect, the inundation risk are higher than the others at the reach D2(Jungrang br. ${\sim}$Gunja br., left bank) and E(Gunja br. ${\sim}$Yongbi br.), which are located downstream near confluence.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.793-797
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• 2010

물리적 녹조저감 기술인 커튼형 수류차단막은 유입 하천과 저수지 천이부에서 높은 영양염류와 조류를 포함한 표층 수류의 차단 또는 우회를 통해 본류 수역의 녹조발생을 저감하는 대책이다. 본 연구에서는 2009년 5월 회남대교 약 2 km 상류에 시범 설치된 대청호의 수류차단막 효과를 분석하고자 선행연구에서 보정한 2차원 횡방향 평균 수리 및 수질 모델을 최근의 수문사상인 2009년 6~8월까지 적용하여 검보정하고 수치모의를 실시하였다. 저수지 수위와 실측수위를 비교한 결과, 7월 중순 유입량 증가에 따른 수위 상승을 잘 반영하였고, 결정계수값($R^2$)이 0.997로 나타나 모델은 저수지 물수지 계산에 있어서 높은 신뢰도를 보였다. 댐앞과 회남수역에서 수심별 수온예측 오차는 AME 0.258~$1.584^{\circ}C$, RMSE 0.393~$2.548^{\circ}C$의 범위로 실측값을 잘 반영하는 것으로 나타났다. 회남, 댐, 추동, 문의 수역의 표층에서 $PO_4$-P 및 Chl-a 농도에 대한 모의값과 실측값의 시계열 비교 결과, 모델은 저수지내 각 측정지점에서 실측값의 시계열 변화를 잘 모의하였고, 회남수역에서 7월 중순 홍수 유입에 따라 증가하였다. 특히, $PO_4$-P 농도가 0.06 mg/L까지 증가하는 것으로 나타났다. 이는 홍수기에 높은 영양염류를 포함한 탁수가 수류차단막 하단을 통과하여 수리학적 도수현상(Hydraulic jump)을 일으킨 것이 원인이라 판단된다. 수류차단막 설치에 따라 회남수역의 표층에서 Chl-a 농도의 저감 효과가 두드러졌으나, 댐, 추동 및 문의수역에서의 제어 효과는 미미하였다. 이와 같이 회남수역에서 효과가 큰 이유는 2009년 수문사상의 영향과 저수지 지형특성상 유입수의 영향을 직접받기 때문으로 판단된다. 또한, 회남수역에서 수류차단막 설치에 따른 T-N 및 T-P 평균 저감 효율(수류차단막이 설치되지 않은 경우에 대한 설치 후 농도 저감 비)은 각각 10.8% 및 19.1%이었으며, 평균 저감농도는 모의값을 기준으로 각각 1.637 mg/L에서 1.461 mg/L 및 0.047 mg/L에서 0.038 mg/L로 나타났다. DIN 및 $PO_4$-P 평균 저감 효율은 각각 6.4% 및 24.6%이었고, Chl-a 평균 저감 효율은 25.5%이었으며, 평균 저감농도는 모의값을 기준으로 0.025 mg/L에서 0.018 mg/L로 나타났다. 모의결과를 종합해 볼 때, 대청호에 시범 설치된 조류제어용 수류차단막은 2009년의 수문사상에서 회남수역의 녹조발생 저감에 기여한 것으로 판단된다. 또한 대청호에서 유사한 수문사상을 보인 2006년(62일간)에 비해 2009년(28일간)에 조류주의보 발령 일수가 대폭 줄었다는 사실도 차단막의 효과를 간접적으로 확인해 준다.

• Journal of Korea Water Resources Association
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• v.51 no.9
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• pp.747-759
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• 2018

Multivariate regional frequency analysis has advantages of regional and multivariate framework as adopting a large number of regional dataset and modeling phenomena that cannot be considered in the univariate frequency analysis. To the best of our knowledge, the multivariate regional frequency analysis has not been employed for hydrological variables in South Korea. Applicability of the multivariate regional frequency analysis should be investigated for the hydrological variable in South Korea in order to improve our capacity to model the hydrological variables. The current study focused on estimating parameters of regional copula and regional marginal models, selecting the most appropriate distribution models, and estimating regional multivariate growth curve in the multivariate regional frequency analysis. Annual maximum rainfall and duration data observed at 71 stations were used for the analysis. The results of the current study indicate that Frank and Gumbel copula models were selected as the most appropriate regional copula models for the employed regions. Several distributions, e.g. Gumbel and log-normal, were the representative regional marginal models. Based on relative root mean square error of the quantile growth curves, the multivariate regional frequency analysis provided more stable and accurate quantiles than the multivariate at-site frequency analysis, especially for long return periods. Application of regional frequency analysis in bivariate rainfall-duration analysis can provide more stable quantile estimation for hydraulic infrastructure design criteria and accurate modelling of rainfall-duration relationship.

• Transactions of the KSME C: Technology and Education
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• v.5 no.2
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• pp.135-143
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• 2017

The domestic unique research reactor, HANARO (Hi-flux Advanced Neutron Application ReactOr), has been constructed with the open-pool, the core is submerged in, for the multi-purpose neutron application. The reactor has a primary cooling system to remove the fission heat from the core and its connected fluidic systems. Since the works are required at the reactor pool top as a characteristic of the research reactor, the radiation shall be minimized with the operation of the hot water layer system to avoid unnecessary radiation exposure on the workers during work at the pool top. Moreover, the pool water management system is connected to the reactor pool to maintain the pool temperature below $50^{\circ}C$ to minimize the uprising radioactive gas or impurity from the colder pool bottom. For the efficient flow rate of the PWMS, the thermal capacity of heat exchanger is selected with 260 kW in the normal operation condition. In this paper, the modeling is formulated to figure out whether or not each pool temperature maintains below the temperature limit and the calculation results show that the designed PWMS heat exchanger has enough capacity with the design margin regardless of the reactor operation mode.