• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.839-846
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• 1994

This paper presents a simultaneous solution algorithm for one-dimensional unsteady flow routing through a dendritic channel system. This simulations solution algorithm is based on the double-sweep method and utilizes separate recursion equations for continuity, momentum and energy equations for each of the individual components of a dendritic channel system. Through separate recursion equations for each of the components. the new algorithm converts a dendritic channel network problem into a single-channel problem. The new algorithm is utilized in conjunction with a linearized unsteady flow model using full dynamic flow equations. The required computer storage for the coefficient matrix of the whole system is reduced significantly from the $2N{\times}2N$ matrix to a $2N{\times}4$ matrix, where N is the number of cross sections used in the computation of flow variables in a dendritic channel system. The algorithm presented in this paper provides an efficient and accurate modeling of unsteady flow events through a dendritic channel system.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.75-79
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• 2005

GSSHA(Gridded Surface Subsurface Hydrologic Analysis) 모형은 미 공병단 연구개발센터(USACE ERDC; US Army Corps of Engineers Engineering Research and Development Center)체서 개발된 물리적인 개념의 공간 분포형(PBSD; Physically Based Spatially Distributed) 수문모형으로, CASC2D 모형(Ogden 와 Julien, 2002; Downer 등, 2002)을 개선, 확장한 모형이다. GSSHA 모형의 실행에는 Brigham Young 대학의 컴퓨터그래픽공학연구실에 의해 개발된 미 국방성 WMS(Watershed Modeling System) 인터페이스를 사용하며, 이를 통해 많은 입력과 출력조건을 가지는 분포형 모형의 복잡한 모의 과정을 효과적으로 처리할 수 있다. 본 연구에서는 GSSHA 모형을 이용하여 경안천 유역의 물순환 양상을 분석하였다. GSSHA 모형은 유역을 균일한 유한 차분 격자로 나누어 각각의 격자를 기본 단위로 모의한다. 모형의 주요 모의 모듈은 강우 분포, 융설, 차단, 침투, 증발산, 지표면 저류, 2차원 표면류 추적, 1차원 하도 추적, 불포화 층 모의, 2차원 포화 지하 대수층 흐름, 지표면 유사 침식, 하천 유사 추적 등이 포함된다.

• Journal of Korea Water Resources Association
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• v.38 no.2
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• pp.155-166
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• 2005

Upwind schemes are very well adapted to the discontinuous flow and have become popular for applications Involving dam break flow, transcritical Slow, etc. However, upwind schemes have been applied mainly to the idealized problems not to the natural channels with irregular geometry so far because of the error due to source terms. In this paper, the new type of upwind discretization of source terms, which uses the normalized Jacobian to discretize the source terms, is proposed. As results of tests to flows with source terms by the upwind models, the method proposed in this paper is proved as efficient and accurate. This generalized method for differencing source terms is simple and might beapplicable to diverse type of flux upwind discretization scheme in finite difference method.

• Journal of Korea Water Resources Association
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• v.38 no.2
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• pp.133-142
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• 2005

The settling concentration of fine suspended solid particles(alumina(Al$_2$O$_3$) and quartz(SiO$_2$)) is investigated with the physico-chemical effects(initial concentration, pH and NaCl). Laboratory tests have confirmed the significant influence of increasing initial concentration and salinity which can lead to flocculation due to the intermolecular attraction. Furthermore, the influence of the pH value on the concentration-time corves of alumina has been on firmed. Besides a numerical model to predict the behaviour of cohesive deposit under still water is analyzed by solving the unsteady one-dimensional diffusion-advection equation with a explicit, implicit, Crank-Nicolson and finite difference scheme. The model predicts the existence of an equilibrium concentration. Application of the model with implicit centered difference to data from settling experiments shows a similar distribution.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.02a
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• pp.81-84
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• 2008

김재겸은 2005년 한국 멀티미디어 학회 논문지에 새로운 이차원 셀룰라 오토마타 설계 방법을 소개하고 이 설계 방법으로 구성된 이차원 셀룰라 오토마타를 이용한 해쉬함수를 제안하였다. 본 논문에서는 이 해쉬함수에 대한 첫 번째 분석 결과를 소개한다. 이 해쉬함수는 8 라운드로 구성되고 한 라운드는 두 개의 비선형 연산 부분을 포함하고 있으며, 메시지는 두 비선형 연산 부분에 모두 사용된다. 메시지 차분이 비선형 연산 부분을 거친 뒤 사라질 확률은 $2^{-14}$이다. 따라서 1 라운드 후 약 $2^{-28}$의 확률로 이 해쉬함수의 충돌쌍을 찾을 수 있다. 본 논문의 분석 결과를 통하여 이 해쉬함수는 매우 취약함을 알 수 있다.

• 한국해양학회지
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• v.28 no.2
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• pp.86-100
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• 1993

Three-dimensional baroclinic hydrodynamic model, BACHOM-3, is developed using ADI finite difference scheme. The model is applied to a uni-nodal standing wave in a rectagular basin. The model results for the surface elevation and velocities coincide with the analytical results. To verify the field applicability of the model and to investigate the flow patterns of the Suyoung Bay in Pusan, Korea, the model is applied to the bay. The numerically predicted velocity predicted velocity fields during spring tide at normal river flow are compared with field measurements, the comparisons show good agreement. A clockwise residual circulations at the first level (depth = 0∼2m) and the second level (depth=2∼5 m) of the central part of the bay occur, and the ebb flow is stronger than the flood flow. Computed velocity fields show that the phase difference of velocities between the surface layer and bottom layer occurs and the phase lag increases with height from the bottom. Then, the model is applied successfully for the computation of flow fields considering flood river flow and wind effects. When the wind is blowing toward the land from the sea, the flow patterns at the surface layer correspond with the wind direction, but the flow patterns at the near solid boundary of the lower layer show opposite currents to the wind direction.

• Journal of the Korean Association of Geographic Information Studies
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• v.3 no.4
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• pp.33-49
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• 2000

This research demonstrates the application of GIS to the selection of the waste landfill site through the case study of a urban area. The estimation factors for the suitability analysis of the waste landfill site were determined. The database was built through collection, input, and transformation of data. The recent land cover classification data and NDVI data which were obtained through processing of satellite imagery were incorporated into GIS data as estimation factors. The relative weights of importance among 2nd category estimation factors were determined by the pairwise comparison method. Also relative weights of 1st category estimation factors which are divided into the social-economical factor and the natural environmental factor were combined with those of 2nd category estimation factors. As the results of this case study, the suitability analysis was conducted in accordance with various estimation criteria. The highest suitability index was obtained in the case where we considered the relative weights of 2nd category estimation factors as different in the viewpoint which regards the social economical factor as important.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.42-42
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• 2015

사행수로에서의 원심력은 비선형적인 압력분포를 야기하여 이차류, 편수위 등과 같은 불규칙하고 복잡한 흐름을 발생시킨다. 일반적으로 이들 흐름은 난류이고 매우 3차원적이며 자유수면과의 상호작용이 중요한 역할을 할 수도 있다. 환경, 유사이동, 지형 변화와 관련된 환경 수리학적 관점에서 사행수로에서의 흐름을 이해하고 설계하기 위해서는 이러한 복잡한 3차원 흐름을 정확하게 계산하는 것이 매우 중요하다. 이 연구에서는 유한차분법에 근거한 3차원 흐름해석 모형을 이용하여 사행수로에서의 난류 흐름을 모의하고자 한다. 지배방정식은 3차원 비정상 RANS(Reynolds averaged Navier-Stokes) 방정식이며, 난류 해석을 위해서 공학적으로 널리 이용되고 있는 난류 모형 중 k-omega 모형을 이용한다. 수치모형은 시간과 공간에 대해서 2차 정확도의 이산화 기법을 적용한다. 자유수면의 변동은 이상(two-phase) VOF (volume of fluid) 기법을 이용하여 계산한다. 수치모형의 적용 대상은 기존 문헌에서 제시되어 있는 키노시타 사인곡선을 이용하여 만든 폭 60cm의 사행수로에서 후르드수 0.23 그리고 레이놀즈수 41,700의 조건에서 발생시킨 난류 흐름이다. 적용한 난류모형들을 이용하여 해석한 결과들을 유속벡터분포와 수위의 항으로 비교분석하여 사행수로에서 발생되는 이차류와 편수위 변화 재현에 대한 수치모형의 적용성을 평가하고 각 난류모형들의 특성을 제시한다.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.317-324
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• 1994

The circulation of Lake Paldang is analysed numerically as an ultimate goal to develop a vehicle predicting the dispersion and concentration of pollutants and sediment flowed into the lake. In finite difference formulation of 2-D depth averaged governing equations. Abbott's 3-time level scheme is employed and for nonlinear terms time centering iteration technique in time and space is used. Model parameters for shear stresses and eddy diffusivities are determined through measured data in and near the lake. Predicted velocities for steady flow are shown to be close to the measured velocities and further improved by taking into account of wind effect. This indicates that the wind effect is needed for proper circulation analysis and it calls for the inclusion of the wind effect. Simulated results of unsteady flow caused by flood inflows and release through Paldang dam are found to characterize the flow features quite well as expected. This implies that the developed model can be used as a tool to analysing the circulation in the lake.