• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.4
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• pp.229-239
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• 2019

A model of landslides is developed using the shallow water equations to simulate time-dependent performance of landslides. The shallow water equations are derived using the (b, s) coordinate system which can be applied in both river and ocean. The finite volume scheme employing the HLL approximate Riemann solver and the total variation diminishing (TVD) limiter is applied to deal with the numerical discontinuities occurring in landslides. For dam-break water flow and debris flow, numerical results are compared with analytical solutions and experimental data and good agreements are observed. The developed landslide model is successfully applied to predict subaerial and submarine landslides. It is found that the subaerial landslide propagates faster than the submarine landslide and the speed of propagation becomes faster with steeper bottom slope and less bottom roughness.

• 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.

• 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 Korea Water Resources Association
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• v.42 no.4
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• pp.271-279
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• 2009

The objective of this study is to develop the scheme to apply one-dimensional finite volume method (FVM) to natural river with complex geometry. In the previous study, FVM using the Riemann approximate solver was performed successfully in the various cases of dam-break, flood propagation, etc. with simple and rectangular cross-sections. We introduced the transform the natural into equivalent rectangular cross-sections. As a result of this way, the momentum equation was modified. The accuracy and applicability of newly developed scheme are demonstrated by means of a test example with exact solution, which uses triangular cross-sections. Secondly, this model is applied to natural river with irregular cross-sections and non-uniform lengths between cross-sections. The results shows that the aspect of flood propagation, location and height of hydraulic jump, and numerical solutions of maximum water level are in good agreement with the measured data. Using the developed scheme in this study, existing numerical schemes conducted in simple cross-sections can be directly applied to natural river without complicated numerical treatment.

• Water for future
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• v.21 no.1
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• pp.67-76
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• 1988

Analyzed was the circulation phenomena in the open channel with sudden expansion, by applying the Galerkin's finite element method to the depth-averaged 2-dimensional continuity and momentum equations. Wave tests were done in the simplified channel in order to review the validity of this newly developed model and the computed results were within 0.5% of $L_2$-norm error, and application of this model to the simulation of simplified dam-break gave very close results compared with the analytical solution, thus, it can be concluded that this model is valid and efficient. The main flow in the expanded channel was defined as a new initial condition with given velocity and the flow in the expanded portion was at rest in simulating the circulation, and besides the Neumann's condition the slip boundary condition for lateral wall was found to be proper condition than the no-slip condition. It can be concluded, from the numerical tests in the sudden expension, that the circulating phenomena depend mainly on the convective inertia and the effect of turbulence due to bottom shear and lateral shear is insignificant.

• Journal of Korea Water Resources Association
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• v.38 no.5 s.154
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• pp.333-343
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• 2005

The upwind model is well known to simulate shockwaves, but it is rarely applied to natural rivers because of problems caused by the source terms. Although several methods have been developed to deal with the source terms, none of them has been applied to natural rivers. This paper deals with application of the upwind model to the natural river. An implicit upwind model is applied to a hypothetical irregular channel and a natural river with highly irregular bed, width, and hydraulic structures. Different types of the flows including steady-state flow, flood wave, dam-break wave, and bore are simulated to test accuracy and applicability of the implicit upwind model. It is proved that the model can simulate various types of flows in natural rivers with high accuracy and robustness.

• Journal of Korea Water Resources Association
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• v.36 no.5
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• pp.777-785
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• 2003

A numerical model for the solution of two-dimensional free surface flow is developed on unstructured grid. By using fractional step method, the two-dimensional shallow water equations (SWE) are treated as two one-dimensional problems. Thus, it is possible to simulate computational hydraulic problems with higher computational efficiency. The one-dimensional problems are solved using upwind TVD version of second-order Weighted Averaged Flux (WAF) scheme with HLLC approximate Riemann solver. The numerical oscillations which are common with second-order numerical scheme are controlled by exploiting WAF flux limiter, Some idealized test problems are solved using this model and very accurate and stable solutions are obtained. It can be concluded as an efficient implement for the computation of SWE including dam break problems that concerning discontinuities, subcritical and supercritical flows and complex domain.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5B
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• pp.575-589
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• 2008

In the present work, we investigate the hydrodynamic behavior of a turbulent bore, such as tsunami bore and tidal bore, generated by the removal of a gate with water impounded on one side. The bore generation system is similar to that used in a general dam-break problem. In order to the numerical simulation of the formation and propagation of a bore, we consider the incompressible flows of two immiscible fluids, liquid and gas, governed by the Navier-Stokes equations. The interface tracking between two fluids is achieved by the volume-of-fluid (VOF) technique and the M-type cubic interpolated propagation (MCIP) scheme is used to solve the Navier-Stokes equations. The MCIP method is a low diffusive and stable scheme and is generally extended the original one-dimensional CIP to higher dimensions, using a fractional step technique. Further, large eddy simulation (LES) closure scheme, a cost-effective approach to turbulence simulation, is used to predict the evolution of quantities associated with turbulence. In order to verify the applicability of the developed numerical model to the bore simulation, laboratory experiments are performed in a wave tank. Comparisons are made between the numerical results by the present model and the experimental data and good agreement is achieved.

• Journal of Korea Water Resources Association
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• v.40 no.10
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• pp.833-840
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• 2007

The experimental study was carried out to investigate propagation distance of flood wave due to levee breach in a flat inundation area without obstacle. Hitter solution was considered to formulate the experimental results and a representative form was written referring to existing researches. As a result of experiments, it was found that the propagation velocity of the wave front in inundation area was significantly influenced by the initial water level in a channel, which was similar to flow in a channel due to dam break. An empirical formula was also suggested using the experimental results. The dimensionless propagation distance L can be written as the power function of dimensionless time T Coefficients k and m were varied with the dimensionless time T whereas k and m in Ritter solution were 2 and 0, respectively. The variation of coefficients in the relationship between L and T was influenced by the water depth in the inundation area and the fact proved that the changing points of L in the slope of relationship between L and T are the same to those of relationship between the dimensionless maximum water depth in the inundation area, $h_{max}$ and L.