• Journal of Korea Water Resources Association
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• v.34 no.6
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• pp.605-615
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• 2001

SMAC method, one of the numerical simulation techniques, is modified from the original MAC method for the time-dependent variation of fluid flows. The Navier-Stokes equations for incompressible time-dependent viscous flow is applied, and marker particles which present the visualization of fluid flaws are used. In this study, two-dimensional numerical simulations of the water column collapse are carried out by SMAC method, and the simulation results are compared with Martin and Moyce's experimental data and result of the MPS method. A good results are obtained. This numerical simulation could also be applied to the breaking phenomenon of hydraulic structures such as dam break.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.624-628
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• 2008

Two-dimensional flow analysis is a way to provide good estimates for complex flow features in flow around islands and obstructions, flow at confluence and flow in braided channel. One of difficult problems to develop a two-dimensional hydraulic model is to analyze dry and wet area in river channel. Dry/wet problem can be encountered in river and coastal engineering problems, such as flood propagation, dam break analysis, tidal processes and so on. The objective of this study is to develop an accurate and robust two-dimensional finite element method with dry/wet technique in complex natural rivers. The dry/wet technique with Deforming Grid Method was developed in this study. The Deforming Grid Method was used to construct new mesh by eliminating of dry nodes and elements. The eliminated nodes and elements were decided by considering of the rising/descending velocity of water surface elevation. Several numerical simulations were carried out to examine the performance of the Deforming Grid Method for the purpose of validation and verification of the model in rectangular and trapezoidal channel with partly dry side. The application results of the model were displayed reasonable flow distribution.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1619-1623
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• 2008

현재 섬진강 수계에서는 댐방류에 따른 하류하천의 하도추적은 수문학적 모형에 의해 운영되고 있으나, 하구의 조위 및 하천내 존재하는 수공구조물의 영향 그리고 지류에 의한 흐름분석을 위해서는 정교한 수리학적 모형이 필요하게 된다. 섬진강으로 유입하는 대표수계는 경천, 요천, 그리고 보성강이 있으며, 보성강의 상류에는 주암댐이 보성강의 유하량을 조절하게 되는 데 이를 반영한 모형구축을 지속적으로 수행할 예정이다. 또한 섬진강 하구유역에서는 조위에 의해 본류의 홍수위가 영향을 받게 되므로 이에 대한 영향도 분석하였다. 섬진강 하구에서는 여수관측소와 광양조위지점이 있는데, 두 지점 모두 일년치의 예측이 가능하게 되며 여수지점에서는 실시간 조위관측이 수행되고 있기 때문에 향후 두 지점의 조위결과값을 이용한 최적의 조위산정방법을 결정하게 된다. 본 모형은 하천에서 발생하는 부정류 수리학적 해석모형에 의해 다양한 수행결과를 제시하게 된다. 각각의 관측수위표지점과 비교한 결과 전체적인 경향에서는 합리적인 결과를 나타냄으로서 모형의 적합성을 확인할 수 있었다. 본 연구를 통하여 대상구간의 전체하도에 대한 적용절차 및 분석기법 등을 참조하여 다른 수계로의 확장이 가능하게 되었다. 단면변환 및 경계조건 산정방법, 모형의 수행 및 결과 분석 등이 댐방류 또는 지류의 유입을 고려한 합리적인 하천관리를 위한 방향을 제시할 것으로 판단된다.

• Journal of Environmental Science International
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• v.17 no.7
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• pp.733-741
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• 2008

The object of this study is the safety insurance of the dam to provide for the extraordinary flood. The safety insurance of the reservoir was taken by the preparatory discharge using the temporary division tunnel used during the reservoir construction. In this study, the Sungju reservoir was simulated. The existing discharge facilities of the intake tower of the Sungju reservoir could nat have influence on the flood control. When the Sungju reservoir operated to begin preparatory discharge for 48 hrs by the temporary diversion tunnel that have discharge of an 20-years frequency, the water level was lowered about 20 cm. When the Sungju reservoir operated to begin the continuous discharge after the preparatory discharge, the water level was lowered over 1m but the downstream at risk was caused by the resulted. If it is possible to operate to begin the preparatory discharge of the reservoir for 24 hrs by the temporary diversion tunnel, that will improve the flood control faculty of the reservoir without other hydraulic structure and safety of the Sungju reservoir will be higher.

• Journal of Korea Water Resources Association
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• v.30 no.1
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• pp.35-44
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• 1997

Petrov-Galerkin finite element model for analyzing dynamic wave equation is applied to gradually and rapidly varied unsteady flow. The model in verified by applying to hydraulic jump, nonlinear disturbance propagation in frictionless horizontal channel and dam-break analysis. It shows stable and accurate results compared with analytical solutions for various cases. The model in applied to a surge propagation in a frictionless horizontal channel. Three-dimensional water surface profiles show that the computed result converges to the analytical one with sharp discontinuity. The model is also applied to the Taehaw River to analyze unsteady floodwave propagation. The computed results have good agreements with those of DWOPER model in terms of discharge and stage hydrographs.

• Journal of Environmental Impact Assessment
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• v.18 no.6
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• pp.331-346
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• 2009

The serious problem facing two-dimensional finite element hydraulic model is the treatment of wet and dry areas. This situation is encountered in most practical river and coastal engineering problems, such as flood propagation, dam break analysis and so on. Especially, dry areas result in mathematical complications and require special treatment. The objective of this study is to investigate the wet and dry parameters that have direct relevance to model performance in situations where inundation of initially dry areas occurs. Several numerical simulations were carried out, which examined the performance of the marsh porosity method of RMA-2 model to investigate for application of parameters. Experimental channel with partly dry side slopes, straight channel with irregular geometry and Han river were performed for tests. As a result of this study, effectively applied marsh porosity method provide a reliable results for flow distribution of wet and dry area, it could be further developed to basis for extending to water quality and sediment transport analysis.

• Journal of Korean Society on Water Environment
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• v.20 no.5
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• pp.473-479
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• 2004

A sedimentation basin (SB) at the inlet of an irrigation reservoir which was constructed using an auxiliary dam was monitored to evaluate its pollutant removal efficiency. Water sampling at three points, i.e., inflow stream, upstream and downstream of the reservoir, were taken 5 times before and after the construction of the SB in 1999 and 2003, respectively. No significant water quality variations in inflow stream were observed during these periods. The COD, T-N, T-P and SS removal efficiencies were 38, 24, 35 and 49%, respectively. The results indicated that those removal efficiencies significantly increased during the rainy season and COD removal efficiency, especially, was higher than others studies. The scale of SB in this study was rational as aspects of pollutant removal efficiency and hydraulic detention time. And it is recommended that SB, at inlet of an reservoir, should be constructed as completely separated structure from reservoir water body and having SAR Index from 0.7% to 1.0%.

• 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.

• Smart Structures and Systems
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• v.21 no.2
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• pp.195-205
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• 2018

Research on Lamb wave-based damage identification in plate-like structures depends on precise knowledge of dispersive wave velocity. However, boundary reflections with the same frequency of interest and greater amplitude contaminate direct waves and thus compromise measurement of Lamb wave dispersion in different materials. In this study, non-reflecting boundaries were proposed in both numerical and experimental cases to facilitate time-frequency characterization of Lamb wave dispersion. First, the Lamb wave equations in isotropic and laminated materials were analytically solved. Second, the non-reflecting boundaries were used as a series of frames with gradually increased damping coefficients in finite element models to absorb waves at boundaries while avoiding wave reflections due to abrupt property changes of each frame. Third, damping clay was sealed at plate edges to reduce the boundary reflection in experimental test. Finally, the direct waves were subjected to the slant-stack and short-time Fourier transformations to calculate the dispersion curves of phase and group velocities, respectively. Both the numerical and experimental results suggest that the boundary reflections are effectively alleviated, and the dispersion curves generated by the time-frequency analysis are consistent with the analytical solutions, demonstrating that the combination of non-reflecting boundary and time-frequency analysis is a feasible and reliable scheme for characterizing Lamb wave dispersion in plate-like structures.

• Geomechanics and Engineering
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• v.13 no.6
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• pp.1027-1044
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• 2017

Membrane penetration is the most important factor influencing the measurement of volume change for triaxial consolidated-drained shear test for coarse-grained soil. The effective pressure p, average particle size $d_{50}$, thickness $t_m$ and elastic modulus $E_m$ of membrane, contact area between membrane and soil $A_m$ as well as the initial void ratio e are the major factors influencing membrane penetration. According to the membrane deformation model given by Kramer and Sivaneswaran, an analytical solution of the membrane penetration considering the initial void ratio is deduced using the energy conservation law. The basic equations from theory of plates and shells and the elastic mechanics are employed during the derivation. To verify the presented solution, isotropic consolidation tests of a coarse-grained soil are performed by using the method of embedding different diameter of iron rods in the triaxial samples, and volume changes due to membrane penetration are obtained. The predictions from presented solution and previous analytical solutions are compared with the test results. It is found that the prediction from presented analytical solution agrees well with the test results.