Numerical simulation of flood waves in contraction channels with different cross section profiles (original) (raw)
Related papers
2006
This study is devoted to the flood wave propagation modelling corresponding to a realistic situation. The equations that governs the propagation of a flood wave, in natural rivers, corresponds to the free surface flow equations in the Shallow Water case. The obtained two dimensional system, known as Saint Venant's system, is derived from the three-dimensional incompressible Navier Stokes equations by depth-averaging of the state variables. This system is written in a conservative form with hyperbolic homogeneous part. The discretization of the convection part is carried out by the use of the finite volume method on unstructured mesh. To increase the accuracy of the scheme, the MUSCL technique is used. The diffusive part is discretized using a Green-Gauss interpolation technique based on a diamond shaped co-volume. For the numerical experiment, we have studied a realistic channel of the Ourika valley which is located in Morocco. The flood occurred on August 1995 is simulated with...
Flood routing was studied here has many applications in engineering projects and helps designers in understanding the flood flow characteristics in river flows. Floods were taken unsteady flows that vary by time and location. Equations governing unsteady flows in waterways are continuity and momentum equations which in case of one-dimensional the Saint-Venant hypothesis were considered. Dynamic wave model as one of the flood routing methods was examined for flooding operations because of its high accuracy. The best numerical methods and various schemes was the main challenge for optimal modeling of dynamic waves and predicting flooding behavior. A 78-km reach of Ghare-Aghaj River hydrometric Station was investigated and hyperbolic nonlinear partial differential equations were solved. Preissmann Implicit Scheme and Mac-Cormak Explicit Scheme were modeled using finite difference numerical methods. Developed models were also compared to one of the most reliable Mike series computer program. It was aimed to find the most suitable numerical finite difference scheme based on computing skills and coding output results. The results confirmed the superiority of Preissmann Implicit Scheme in predicting flood wave characteristics for the studied area.
Numerical Simulation of a Dam-Break Flood Wave
In this paper, the propagation of a flood wave after the break of a reinforced concrete dam is simulated numerically, assuming one-dimensional (1D) unsteady flow. Two numerical models are developed based on the 1D Shallow Water Equations (SWE) or Saint-Venant's Equations, using the numerical schemes Lax-Wendroff and McCormack, respectively. In order to validate the simulation results, a comparison with experimental data is made. The experimental set-up consists of a water tank that simulates the reservoir of a dam, followed downstream by a horizontal dry bottom section, a triangular bottom sill with high slopes and a small pool of water at rest that ends up in a vertical diaphragm. The algorithms can simulate successfully the flow over the triangular bottom sill with a high negative value of slope, without any complicate considerations. The comparison of experimental and numerical data shows a high degree of convergence. The use of an artificial diffusion factor is favorable for...
A numerical model for routing of flood wave in a part of meandering river is presented. It is based on a modified form of the complete one-dimensional Saint-Venant equations of unsteady flow. These equations were modified such that flows in the meandering river channel, left over bank flood plain, and right over bank flood plain were all identified separately. Thus, the differences in hydraulic and geometric properties and flow-path distances were considered for all three divisions of the valley cross-section. This development differs from conventional one-dimensional treatment of unsteady flows in rivers with flood plain wherein the flow is either averaged across the total cross-sectional area (channel and flood plain) or the flood plain is treated as off-channel storage, and the reach lengths of the channel and flood plain are assumed to be identical. The weighted four-point implicit finite difference method is selected to solve a modified Sain-Venant equations for its versatility and computing efficiency. The numerical model was applied to the Euphrates river at the reach between Haditha dam and Hit city along (124.4 km) to make a sensitivity analysis of the following parameters: maximum flood wave discharge, maximum flood wave elevation, lag time of the peak discharge, lag time of the peak level, and time of arrival of flood wave to a seven major cities along the Euphrates river in a case study and comparing it with a same parameters produced when a conventional one-dimensional treatment of unsteady flows in river with flood plains where the meandering in river is neglected.
Canadian Journal of Civil Engineering, 2008
Velocity gradient between main channel and flood plains in compound channels leads to the formation of a large shear layer and secondary currents between these two subsections. These phenomena in the interaction region bring about a complex three-dimensional nature of the flow in compound channels. To cope with these flows, many numerical investigations have utilized three-dimensional formulations with advanced turbulence models. However, the free surface in many of these models is fixed and rigid-lid assumption has been used. In the present research, three-dimensional shallow water equations were used to calculate the flow field in compound channels. Three-dimensional equations were integrated in layers and were combined with the continuity equation. In this formulation, free-surface elevation was calculated without the need to solve any additional equations. Velocity and bed shear stress distribution and the stage–discharge relationship in compound channels with smooth and rough b...
Flood wave propagation in a steep mountain river: comparison of four simulation tools
2009
Most of the recent developments concerning efficient numerical schemes to solve the shallow-water equations in view of real world flood modelling purposes concern the two-dimensional form of the equations or the one-dimensional form written for rectangular, unit-width channels. Extension of these efficient schemes to the onedimensional cross-sectional averaged shallow-water equations is not straightforward, especially when complex natural topographies are considered. This paper presents different formulations of numerical schemes based on the HLL solver, and the adaptation of the topographical source term treatment when cross-sections of arbitrary shape are considered. Coupled and uncoupled formulations of the equations are considered, in combination of centred and lateralised source term treatment. These schemes are compared to a numerical solver of Lax Friedrichs type based on a staggered grid.
A Numerical Study of Wave Run-Up Over a Bank
2012
A two-dimensional numerical model is developed to solve Nonlinear Shallow Water Equations. In order to appropriately describe the strongly nonlinear hydrodynamics, a high-order TVD-MacCormack scheme is implemented. For avoiding the occurrence of spurious oscillations, surface gradient method is utilised. Additionally, with incorporating a simple wetting and drying method, the model is able to accurately reproduce the phenomenon of wave propagation on dry bed. Model capabilities are confirmed through comparison with existing analytical studies including the dambreak problems, run-up and back-wash on a sloping bathymetry. The model is then applied to the study of wave run up over banks of a curved channel with a parabolic cross-section. .
River Flood Propagation Simulation
International Journal of Advance Research and Innovative Ideas in Education, 2020
In many cases, the shallow water equation give a very sufficient account of the evolution of flood waves in the rivers. The numerical resolution of these equations was achieved using the MATLAB calculator, using the finite differences method. Initial and boundary conditions were varied to compare results in flood calculations and the impact on the river’s flood height. Also, it is assumed that the flood waves diffuse, hence the use of the model of Barre Saint Venant on the principle of the diffusing wave. The benefits of these simplified processes can be seen primarily in the development of flood forecasting systems. The results obtained take account of the variation.
On the Use of Shallow Water Equations in Hydraulics
2017
Shallow water equations are widely used in inundation analysis as they are known to be successful in computation of flood inundations over wide terrains. Flood propagation in between buildings in urban areas and flows around hydraulic structures such as bridges may not satisfy the assumptions of shallow flow and may display markedly more 3-Dimensional (3D) flow characteristics. However, shallow flow equations can be used for such 3D flows also to allow fast numerical solution and a useful output may be obtained. In this study, shallow water equations are applied to flows with prominent 3D characteristics and results are evaluated. Water depths and velocity field in horizontal plane were calculated satisfactorily, surface waves in supercritical flow involving shocks were described in detail. However, in flows passing around more than one obstruction, there is a cumulative increase in error in the computed water depths. In case of uniform flows with boundary layer characteristics, vel...