• Journal of Korea Water Resources Association
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• v.41 no.8
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• pp.761-772
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• 2008

The object of this study is to develop the model that solves the numerically difficult problems in hydraulic engineering and to demonstrate the applicability of this model by means of various test examples, such as, verification in the gradually varied unsteady condition, three steady flow problems with the change of bottom slope with exact solution, and frictional bed with analytical solution. The governing equation of this model is the integral form of the Saint-Venant equation satisfying the conservation laws, and finite volume method with the Riemann solver is used. The evaluation of the mass and momentum flux with the HLL Riemann approximate solver is executed. MUSCL-Hancock scheme is used to achieve the second order accuracy in space and time. This study introduce the new and simple technique to discretize the source terms of gravity and hydrostatic pressure force due to longitudinal width variation for the balance of quantity between nonlinear flux and source terms. The results show that the developed model's implementation is accurate, robust and highly stable in various flow conditions with source terms, and this model is reliable for one-dimensional applications in hydraulic engineering.

• The Journal of Engineering Geology
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• v.5 no.3
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• pp.289-300
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• 1995

At the initial stage of the underground reservoir design one should thoroughly consider surface and subsurface hydrology, hydrogeologic characteristics of aquifer system, and the function of cut - off wall because it is linked to the effective management. In this study, three dimensional finite difference model was applied to analyse the function of Ian underground reservoir at Kyungbuk Province. The steady and unsteady state conditions after construction of the underground dam were simulated through the model, and from these results the groundwater budget and the safe yield were determined. The model simulation indicates the infiltration of irrigation water to be one of the major factors of seasonal fluctuation of groundwater level. The recharge rates of irrigation water were estimated as 4.3mm/d during May and June, and 1.7mm/d during July and Agust. Groundwater recharge from the watershed area estimated to about $0.04m^3/s$, almost consistent through the year. In 1984, groundwater discharge through the transverse section of the dam was $0.002m^3/s$ and the optimum yield for two momths(July and Aguest)was $254000m^3$, however, the discharge became $0.013m^3/s$ in1993, implying the failure of cut -off function. without appropaiate of the cut - off wall, optiumum yield during the irrigaton period would be $93, 000m^3$.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.201-213
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• 2017

Water is removed from crude oil containing water by using oil separator. This study aims to develop a three-dimensional (3D) Eulerian computational fluid dynamics (CFD) model to predict the separation efficiency of air-water-oil separator. In the incompressible, isothermal and unsteady-state CFD model, air is defined as continuous phase, and water and oil are given as dispersed phase. The momentum equation includes the drag force, lift force and resistance force of porous media. The standard k-${\varepsilon}$ model is used for turbulence flow. The exit pressures of water and oil play an important role in determining the liquid level of the oil separator. The exit pressures were identified to be 6.3 kPa and 5.1 kPa for water and oil, respectively, to keep a liquid level of 25 cm at a normal operating condition. The time evolution of volume fractions of air, water and oil was investigated. The settling velocities of water and oil along the longitudinal separator distance were analyzed, when the oil separator reached a steady-state. The oil separation efficiency obtained from the CFD model was 99.85%, which agreed well with experimental data. The relatively simple CFD model can be used for the modification of oil separator structure and finding optimal operating conditions.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.269-279
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• 2015

Nowadays, the world has suffered by natural disaster of climate change due to global warming. Korea has also faced with similar situation. To prevent these natural disaster, Four Major River Management has conducted. One of conducted content in Four Major River Management is the levee maintenance which classified into fill-up the inland, levee of reinforcement and so on. These maintenances may make the characteristics of groundwater flow change and affect to the levee safety (piping phenomenon). Therefore, analysis on groundwater fluctuation according to level of riverside and inland should be required. This study focus on levee of Hoe stream, which is connected to Nakdong river, and piping safety factor in the levee analyzed by using pore water pressure. Besides, groundwater fluctuation, which is depended on level of riverside and inland, is simulated by using the SEEP/W (2D ground water model). This simulation considered steady flow and unsteady flow. As a result, piping safety factor increased due to rising the inland level. Piping safety factor of riverside was effected by only river water level. Therefore, external levee factor considering inland level raising and suitable control of river water level is need to increase piping safety factor.

• Journal of Korea Water Resources Association
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• v.52 no.6
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• pp.411-420
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• 2019

The objective of this study is to evaluate the appropriateness of methodology for designing urban sewer system using a rational method-based model, Makesw and an urban runoff model, SWMM. The Gunja basin was selected as a study area and precipitation, runoff, vegetation, soil, imperviousness data were used to estimate floods. The appropriateness of methodology was evaluated based on comparison analysis between floods estimated from Makesw and SWMM. The comparison analysis was conducted between floods estimated from Makesw and SWMM, which were simulated using design rainfall and measured rainfall from past inundation events. The comparison results showed that in the case of design rainfall, the rational method-based floods were larger than that based on SWMM in all main lines. However in several branch lines, the rational method-based floods were smaller than thoes based on SWMM. In addition, for the case of measured rainfall from past inundation events, it was easily to find the main and branch lines where the rational method-based floods were smaller than SWMM based ones. Especially, the lines where rational method-based floods were underestimated, were mostly main, $1^{st}$, $2^{nd}$ lines. It was concluded that the rational method-based results were not conservative. Based on rational method (steady flow analysis) and SWMM (unsteady flow analysis), the more conservative results the method provides, the more highly it is recommended to use in designing an urban sewer system.

• Journal of Korea Water Resources Association
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• v.54 no.8
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• pp.629-641
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• 2021

In this study, a two-dimensional numerical model (Nays2DH) was applied to analyze the process of morphological changes in the river channel bed depending on the changes in the amount of flooding after fully opening the Sejong weir, which was constructed upstream of the Geum River. For this, numerical simulations were performed by assuming the flow conditions, such as a non-uniform flow (NF), unsteady flows (single flood event, SF), and a continuous flood event (CF). Here, in the cases of the SF and CF, the normalized hydrograph was calculated from real flood events, and then the hydrograph was reconfigured by the peak flow discharge according to the scenario, and then it was employed as the flow discharge at the upstream boundary condition. In this study, to quantitatively evaluate the morphological changes, we analyzed the time changes in the bed deformation the bed relief index (BRI), and we compared the aerial photographs of the study area and the numerical simulation results. As simulation results of the NF, when the steady flow discharge increases, the ratio of lower width to depth decreases and the speed of bar migration increases. The BRI initially increases, but the amount of change decreased with time. In addition, when the steady flow discharge increases, the BRI increased. In the case of SF, the speed of bar migration decreased with the change of the flow discharge. In terms of the morphological response to the peak flood discharge, the time lag also indicated. In other words, in the SF, the change of channel bed indicates a phase lag with respect to the hydraulic condition. In the result of numerical simulation of CF, the speed of bar migration depending on the peak flood discharges decreased exponentially despite the repeated flood occurrences. In addition, as in the result of SF, the phase lag indicated, and the speed of bar migration decreased exponentially. The BRI increased with time changes, but the rate of increase in the BRI was modest despite the continuous peak flooding. Through this study, the morphological changes based on the hydrological characteristics of the river were analyzed numerically, and the methodology suggested that a quantitative prediction for the river bed change according to the flow characteristic can be applied to the field.

• Journal of Korea Water Resources Association
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• v.42 no.7
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• pp.579-589
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• 2009

Hwang River in South Korea, has experienced channel adjustments due to dam construction. Hapcheon main dam and re-regulation dam. The reach below the re-regulation dam (45 km long) changed in flow regime, channel width, bed material distribution, vegetation expansion, and island formation after dam construction. The re-regulation dam dramatically reduced annual peak flow from 654.7 $m^3$/s to 126.3 $m^3$/s and trapped the annual 591 thousand $m^3$ of sediment load formerly delivered from the upper watershed since the completion of the dam in 1989. An analysis of a time series of aerial photographs taken in 1982, 1993, and 2004 showed that non-vegetated active channel width narrowed an average of 152 m (47% of 1982) and non-vegetated active channel area decreased an average of 6.6 km2 (44% of 1982) between 1982 and 2004, with most narrowing and decreasing occurring after dam construction. The effects of daily pulses of water from peak hydropower generation and sudden sluice gate operations are investigated downstream of Hapcheon Dam in South Korea. The study reach is 45 km long from the Hapcheon re-regulation Dam to the confluence with the Nakdong River. An analysis of a time series of aerial photographs taken in 1982, 1993, and 2004 showed that the non-vegetated active channel width narrowed an average of 152 m (47% reduction since 1982). The non-vegetated active channel area also decreased an average of 6.6 $km^2$ (44% reduction since 1982) between 1982 and 2004, with most changes occurring after dam construction. The average median bed material size increased from 1.07 mm in 1983 to 5.72 mm in 2003, and the bed slope of the reach decreased from 0.000943 in 1983 to 0.000847 in 2003. The riverbed vertical degradation is approximately 2.6 m for a distance of 20 km below the re-regulation dam. It is expected from the result of the unsteady sediment transport numerical model (GSTAR-1D) steady simulations that the thalweg elevation will reach a stable condition around 2020. The model also confirms the theoretical prediction that sediment transport rates from daily pulses and flood peaks are 21 % and 15 % higher than their respective averages.

• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.3 s.10
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• pp.151-163
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• 2003

In this study, the algorithm of groundwater flow process was established for koreanized groundwater program development dealing with the geographic and geologic conditions of the aquifer have dynamic behaviour in groundwater flow system. All the input data settings of the 3-DFM model which is developed in this study are organized in Korean, and the model contains help function for each input data. Thus, it is designed to get detailed information about each input parameter when the mouse pointer is placed on the corresponding input parameter. This model also is designed to easily specify the geologic boundary condition for each stratum or initial head data in the work sheet. In addition, this model is designed to display boxes for input parameter writing for each analysis condition so that the setting for each parameter is not so complicated as existing MODFLOW is when steady and unsteady flow analysis are performed as well as the analysis for the characteristics of each stratum. Descriptions for input data are displayed on the right side of the window while the analysis results are displayed on the left side as well as the TXT file for this results is available to see. The model developed in this study is a numerical model using finite differential method, and the applicability of the model was examined by comparing and analyzing observed and simulated groundwater heads computed by the application of real recharge amount and the estimation of parameters. The 3-DFM model is applied in this study to Sehwa-ri, and Songdang-ri area, Jeju, Korea for analysis of groundwater flow system according to pumping, and obtained the results that the observed and computed groundwater head were almost in accordance with each other showing the range of 0.03 - 0.07 error percent. It is analyzed that the groundwater flow distributed evenly from Nopen-orum and Munseogi-orum to Wolang-bong, Yongnuni-orum, and Songja-bong through the computation of equipotentials and velocity vector using the analysis result of simulation which was performed before the pumping started in the study area. These analysis results show the accordance with MODFLOW's.

• The Korean Journal of Nuclear Medicine
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• v.4 no.1
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• pp.27-36
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• 1970

적혈구(赤血球) 수명의 측정에는 $^{51}Cr$-표지적혈구법(標識赤血球法)이 임상적(臨床的)으로 이용(利用)되고 있으며 이는 이론상(理論上) steady state 즉(卽) 측정기간(測定期間)동안 순환(循環) $^{51}Cr$량(量)-적혈구량(赤血球量)이 일정(一定)할 때에 한(限)하여 유효(有效)하며 unsteady state 때는 true red cell survival을 알기 위하여서는 측정치에 영향을 주는 요인(要因)에 대하여 각각(各各) 교정(校正)해 줄 필요(必要)가 있다. 이 요인(要因)중에 특히 실혈(失血)로 인(因)한 영향에 관(關)하여는 계통적인 연구(硏究)가 적다. 이에 저자(著者)들은 $^{51}Cr$표지적혈구법(標識赤血球法)을 이용(利用)하여 실혈(失血)이 적혈구(赤血球) 수명측정(測定)에 미치는 영향을 인체(人體)에서 실험 관찰하여 몇가지 성적을 얻었다. 연구대상(硏究對象)은 총(總) 56명(名)의 청장년(靑壯年)으로 급성실혈군(急性失血群)과 만성실혈군(慢性失血群)으로 구분(區分)하여 급성실혈군(急性失血群)은 위장출혈등(胃腸出血等)이 없는 2대(代)의 의대생(醫大生)으로 $^{51}Cr$표지적혈구법(標識赤血球法)을 사용하여 적혈구(赤血球) 수명을 측정하는 동안($10{\sim}14$ 일간(日間)) 1일당(日當) 10ml(6명(名)), 25ml(4명(名)), 50ml(4명(名)), 75ml(4명(名)), 100ml(6명(名))를 각각(各各) 사혈(瀉血)한 군(群)과 10일간(日間) 1,000ml를 사혈한 군(群) 즉 200ml씩 5회(回)(4명(名)), 500ml씩 2회(回)(4명(名))로 세분(細分)하였으며 만성실혈군(慢性失血群)은 직업적인 공혈자(供血者)로 반복사혈로 생긴 9명(名)의 빈혈자와 십이지장충증(十二指腸蟲症)에 감염(感染)되어 구충(驅蟲)한 중등도(中等度)의 철결핍성 빈혈환자 7명(名)으로 나누어 관찰하였다. 측정(測定) 방법(方法)으로는 Gray 및 Sterling법(法)을 개설한 방법(方法)으로 $^{51}Cr$표지적혈구(標識赤血球)의 계측시료(計測試料)로서 전혈(全血) 및 적혈구(赤血球)를 사용(使用)하였다. 실험(實驗)성적은 1. 1일당(日當) 실혈량(失血量)이 증가(增加)할수록 적혈구(赤血球)수명($T\frac{1}{2}$)은 짧아짐을 알 수 있었다. 즉(卽) 1일당(日當) $20{\sim}50ml$ 사혈군에서는 $T\frac{1}{2}$이 현저히 짧아지는 rapid phase을 나타내고 1일당(日當) 50ml이상(以上) 사혈군에서는 짧아지는 정도(程度)가 완만한 slow phase을 나타낸다(Fig. 6). 2. 1일량(日量) 10ml 및 25ml식(式) 사혈한 군(群)의 적혈구수명(赤血球壽命)을 측정(測定)하는데 있어 적혈구(赤血球)를 사용하였을 때에는 $T\frac{1}{2}$측 정치에 유의한 차(差)가 없었으며 이 범위 내에서는 Hct., Hb. 및 혈청철치(血淸鐵値)도 역시 유의한 차(差)가 없었다. 3. 1일량(日量) 50ml 및 75ml, 100ml씩 사혈한 군(群)에서는 적혈구(赤血球)만을 사용(使用)하였을 때와 전혈(全血)을 시료(試料)로 하였을 때 사이에 $T\frac{1}{2}$의 측정치에 유의한 차(差)가 있었으며 이 때는 Hct., Hb. 및 혈청철치(血淸鐵値)에도 변화(變化)가 있었다. 즉(卽), 전혈(全血)을 사용한 적혈구(赤血球) 수명($T\frac{1}{2}$)의 측정치가 적혈구(赤血球)만를 사용(使用)한 적혈구(赤血球) 수명($T\frac{1}{2}$)의 측정치 보다 짧았다. 4. 일정(一定)기간(10 일(日)) 사혈의 총량(1000ml)이 같을 매는 200ml를 5회(回) 사혈한 군(群)이나 500ml를 2회(回) 사혈한 군(群) 사이에 적혈구(赤血球) 수명($T\frac{1}{2}$)에 유의(有義)한 차(差)를 볼 수 없었다. 5. 직업적 공혈자의 반복사혈로 인(因)한 만성(慢性) 빈혈환자 9명(名)에서의 $^{51}Cr$적혈구(赤血球)수명($T\frac{1}{2}$) 측정치는 평균(平均) 19.2일(日)로 짧아져 있으나 적혈구수명측정전후(赤血球壽命測定前後)에 충분(充分)한 철제(鐵劑)를 투여(投與)하여 Hct., Hb. 및 혈청철치(血淸鐵値)를 증가(增加)시켰으며 이때 볼 수 있었든 Hct치(値)를 규준(規準)하여 교정한 적혈구(赤血球)수명($T\frac{1}{2}$)은 거의 정상(正常)범위 안에 있어(27.6일(日)) 이러한 인자(因子)를 고려하지 않으면 잘못 이해할 수가 있다. 6. 구충자충(鉤蟲仔蟲)을 구충한 7명(名)의 중등도(中等度) 철(鐵)결핍성 빈혈환자에서의 적혈구(赤血球)수명($T\frac{1}{2}$) 측정치는 25일(日)$\sim$31일(日)로 평균(平均) 28일(日)이었으며, 이때 장 출혈량은 1일(日) $1.0{\sim}3.5ml$이었다. 단시일내의 급성실혈시에는 이와같은 소량의 실혈(失血)도 적혈구(赤血球)수명($T\frac{1}{2}$) 측정치에 영향을 보여 줌을 알 수 있었다. 따라서 이러한 정도의 실혈은 실험오차에 기인하는 것인지 아니면 장기 출혈에서는 이러한 소량의 실혈이 적혈구(赤血球)수명($T\frac{1}{2}$) 측정에 영향을 미치지 않는 것인지는 아직 확실히 말할 수 없다. 8. $^{51}Cr$-표지적혈구(標識赤血球)로 측정한 적혈구(赤血球)수명($T\frac{1}{2}$)은 측정시의 실혈량(失血量)에 큰 영향을 받음을 알 수 있으며 저자(著者)들은 $^{51}Cr$표지적혈구(標識赤血球)를 이용(利用)한 적혈구(赤血球) 수명 측정때 검사기간중 실혈량이 적혈구수명치(赤血球壽命値)에 미치는 관계를 상술(上述)한 실험치(實驗値)를 기초(基礎)로 하여 다음과 같을 교정식(校正式)을 고찰(考察)해 보았다. $^{51}Cr\;T\frac{1}{2}=17.0e^{-0.0495}+18.4e^{-0.000924x}$ 단(但) X : 1일(日) 실혈량(失血量)(단위(單位) ml)