• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.3
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• pp.69-78
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• 2007

In this study, a time-dependent aspect of an embankment failure is considered to simulate a flood inundation map and calculate overtopping discharge induced by an embankment failure. A numerical model has been developed by solving the two dimensional nonlinear shallow water equations with a finite volume method on unstructured grids. To analyze a Riemann problem, the HLLC approximate Riemann solver and the Weighted Averaged Flux method are employed by using a TVD limiter and the source term treatment is also employed by using the operator splitting method. Firstly, the numerical model is applied to a dam break problem and a sloping seawall. Obtained numerical results show good agreements with experimental data. Secondly, the model is applied to a flow induced by an embankment failure by assuming that the width and elevation of embankment are varied with time-dependent functions. As a result of the comparison with each numerical overtopping discharge, established flood inundation discharges in the previous studies are overestimated than the result of the present numerical model.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.428-432
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• 2007

댐 제방 등의 붕괴로 인하여 발생하는 급격한 유량의 변화와 흐름영역의 변화로 인한 천이류 및 도수의 발생, 불규칙한 하천단면에서 갈수기 저수기의 흐름해석은 기존의 수치해법의 한계로 인하여 수리모형실험 및 경험식 또는 단면의 단순화 등에 의존하고 있는 실정이다. 본 연구에서는 자연하천에서 비선형 흐름율 계산에 불연속초기조건의 해석해인 Riemann 근사해법을 사용하여 수치적으로 안정되고 정확한 1차원 모형을 개발하고자 한다. 이를 위하여 유한체적법을 사용하였고, 수위와 유량의 계산을 위하여 요구되는 유한체적을 유출입하는 흐름율의 계산에 HLL Riemann 해법을 사용하였으며, MUSCL 기법으로 2차 정확도기법으로 확장하였다. Riemann 해법을 통하여 계산된 비선형의 흐름율과 보존 특성을 만족시켜줄 수 있는 하상 및 하폭변화로 인한 생성항을 처리하는 기법을 제안함으로서 새로운 1차원 수치해석모형을 개발하였다. 개발된 모형의 실제하천의 적용성을 확인하기 위하여 하상과 하폭이 변화하는 부정류 흐름에 적용하여 모형의 적용성 및 정확성을 검증하였다.

• Journal of Korea Water Resources Association
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• v.50 no.5
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• pp.289-302
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• 2017

DFB (Divergence Form for Bed slope source term) was rigorously derived and the error of mDFB using mean water depth at the cell face in DFB was clearly demonstrated. In addition, DFB technique turned out to be an exact method to the bed slope source term. The existing volume/free-surface relationship to the PSC (Partially Submerged Cell) has been corrected. It was discussed that treatment for the partially submerged edge is required to satisfy the C-property in PSC. It is expected that this study will provides a more accurate means in analyzing the shallow water equations with the approximate Riemann solver.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.21-27
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• 2012

The HLLL scheme, proposed by T. Linde, determines all the wave speeds from the initial states because the middle wave is evaluated by the introduction of a generalized entropy function. The scheme is considered a genuine successor to the original HLL scheme because it is completely separated form the Roe's linearization scheme unlike the HLLE scheme and does not rely on the exact solution unlike the HLLC scheme. In this study, a numerical model was configured by the HLLL scheme with the total energy as a generalized entropy function to solve governing equations, which are the one-dimensional shallow water equations without source terms and with an additional conserved variable relating a concentration. Despite the limitations of the first order solutions, results to three cases with the exact solutions were generally accurate. The HLLL scheme appeared to be superior in comparison with the other HLL-type schemes. In particular, the scheme gave fairly accurate results in capturing the front of wetting and drying. However, it revealed shortcomings of more time-consuming calculations compared to the other schemes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2B
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• pp.121-129
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• 2009

In this study, dam-break flows are simulated numerically by using an efficient and accurate Cartesian cut-cell mesh system. In the system, most of the computational domain is discretized by the Cartesian mesh, while peculiar grids are done by a cutcell mesh system. The governing equations are then solved by the finite volume method. An HLLC approximate Riemann solver and TVD-WAF method are employed to calculation of advection flux of the shallow-water equations. To validate the numerical model, the model is applied to some problems such as a steady flow convergence on an ideal bed, a steady flow over an irregular bathymetry, and a rectangular tank problem. The present model is finally applied to a simulation of dam-break flow on an experimental channel. The predicted water surface elevations are compared with available laboratory measurements. A very reasonable agreement is observed.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1961-1971
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• 2006

A soft recovery system (SRS) is a device that stops a high speed projectile without damaging the projectile. The SRS is necessary to verify the shock resistant requirements of microelectronics and electro-optic sensors in smart munitions, where the projectiles experience over 20,000 g acceleration inside the barrel. In this study, a computer code for the performance evaluation of a SRS based on ballistic compression decelerator concept has been developed. It consists of a time accurate compressible one-dimensional Euler code with use of deforming grid and a projectile motion analysis code. The Euler code employs Roe's approximate Riemann solver with a total variation diminishing (TVD) method. A fully implicit dual time stepping method is used to advance the solution in time. In addition, the geometric conservation law (GCL) is applied to predict the solutions accurately on the deforming mesh. The equation of motion for the projectile is solved with the four-stage Runge-Kutta time integration method. A small scale SRS to catch a 20 mm bullet fired at 500 m/s within 1,600 g-limit has been designed with the proposed method.

• Ecology and Resilient Infrastructure
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• v.1 no.1
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• pp.1-7
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• 2014

In this study, a numerical simulation technique for coastal area where wave and current interactions are observed is proposed. Considering the spatial scale of coastal area and the coastal processes such as wave, current, shoaling, wave breaking, and inundation processes, boussinesq equation model is used. A depth-integrated transport model based on the consistent assumption with the boussinesq equation model is used for the prediction of solute transport. To solve the equations, finite volume method with an approximate riemann solver is used. The proposed model is applied to a coastal area and reasonable computational results are obtained.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1332-1336
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• 2007

댐 제방 붕괴파는 갑작스러운 유량의 증가가 발생하여 불연속적인 흐름특성을 가지는 충격파(shock wave)가 전파되며, 갈수기 저수기에는 중소하천의 상류, 여울과 소에서의 흐름 또는 낙차공이나 보, 댐 여수로 등의 수공구조물에서 부분적인 사류 흐름이 발생된다. 이 때 흐름은 한계수위를 통과하게 되므로 기존 수치해법의 적용에 어려움이 존재한다. 본 연구에서는 실제하천에 적용될 수 있는 1차원 HLL, Roe Riemann 근사해법들을 간단히 소개하고, 시간공간적으로 2차의 고정확도 기법으로 확장하는 방법에 대하여 소개하였다. 각 기법을 정확해가 존재하는 댐붕괴 및 마른하도 전파의 경우에 적용하여 각 기법의 적용성 및 정확성을 비교하였다. 그리고 기존 Lax-Friedrichs 기법과 Lax-Wendroff 기법의 적용결과를 비교하였다. 적용결과 Lax-Friedrichs 기법을 제외한 모든 기법이 정확해와 잘 일치하였으며 특히 HLL 기법을 2차 정확도로 확장한 WAF 기법이 가장 높은 정확도로 계산되었다. 그러나 비선형 생성항이 존재하는 실제하천에 있어서 MUSCL 기법을 이용한 2차 정확도 기법이 합리적일 것으로 판단된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5B
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• pp.429-439
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• 2009

When Catastrophic extreme flood occurs due to dam break, the response time for flood warning is much shorter than for natural floods. Numerical models can be powerful tools to predict behaviors in flood wave propagation and to provide the information about the flooded area, wave front arrival time and water depth and so on. But flood wave propagation due to dam break can be a process of difficult mathematical characterization since the flood wave includes discontinuous flow and dry bed propagation. Nevertheless, a lot of numerical models using finite volume method have been recently developed to simulate flood inundation due to dam break. As Finite volume methods are based on the integral form of the conservation equations, finite volume model can easily capture discontinuous flows and shock wave. In this study the numerical model using Riemann approximate solvers and finite volume method applied to the conservative form for two-dimensional shallow water equation was developed. The MUSCL scheme with surface gradient method for reconstruction of conservation variables in continuity and momentum equations is used in the predictor-corrector procedure and the scheme is second order accurate both in space and time. The developed finite volume model is applied to 2D partial dam break flows and dam break flows with triangular bump and validated by comparing numerical solution with laboratory measurements data and other researcher's data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.479-492
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• 2014

In this study, was proposed a numerical scheme imposing exact solutions as the internal boundary conditions for the shallow-water flows over a discontinuous transverse structure such as a step. The HLLL approximate Riemann solver with the MUSCL was used for the test of the proposed scheme. Very good agreement was obtained between simulations and exact solutions for various problems of the shallow-water flows over a step. In addition, results by the numerical model showed good agreement with those of dam-break experiments over a step and stepped chute one. Developed model can simulate the shallow-water flows over discontinuous bottom such as a drop structure without additional rating curve or topography smoothing. Given the proper evaluations for the flow resistance by a step and the energy loss by the nappe flow in the future, could be simulated flooding and drying of the shallow-water flows over discontinuous topography such as a weir or the river road with retaining wall.