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1

Improved HLL Scheme for 1D Dam-Break Flows over Complex Topography

Ying X., Wang S. S. Y.

Archives of Hydro-Engineering and Environmental Mechanics

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2010

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Vol. 57, nr 1

31-41

EN

It has been discovered that the shallow water model based on approximate Riemann solvers can produce unrealistic flows in the case of uneven topography and inaccurate solutions of discharge near hydraulic jumps. To overcome these deficiencies, we proposed a new approach to implement the HLL Riemann solver for open channel flows, including: (1) adopting a form of Saint Venant equations which have only one source term representing driving forces; (2) defining discharge at interface and evaluating it according to the flux obtained by the HLL Riemann solver. In this paper, the performance of this new method is evaluated by means of dam-break flows over a channel with triangular cross-section and a natural river valley with complex topography, respectively. Comparisons of computed results with analytic solutions and data measured from the physical model show that the proposed method is capable of satisfactorily reproducing dam-break flows over complex topography.

2

On the methodology to develop reliable models for water system research

Wang S. S. Y., Frederick A. P., Jia Y.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 4

487-499

EN

Highly sophisticated computational models are demanded to conduct re-search, optimize engineering design and make management decisions of highly complex water systems to meet the needs of today's society. The reliability of the computational models to be adopted for the research of the water resources systems is of great importance. Both professionals in the field and their professional societies have devoted a great deal of efforts in the development of better methodologies for verifying and validating computational model's correctness, convergence, accuracy, validity and reliability. The latest most rigorous methodology for verification and validation of the three-dimensional free-surface flow models has just been developed and its effectiveness has just been demonstrated by the American Society of Civil Engineers Task Committee. This paper is to present a few selected examples to show how to develop a reliable model for conducting water resources sys-tem research.

3

Simulation of flood event in a reach of the Nile River using CCHE2D model

Khan A. A., Wang S. S. Y.

Archives of Hydro-Engineering and Environmental Mechanics

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2003

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Vol. 50, nr 4

329-341

EN

The impact of design flood in terms of water surface level and maximum velocity in a reach on the Nile River is studied, using a depth-averaged two-dimensional model. The reach includes a proposed site for a shipyard maintenance harbour. The CCHE2D model, a depth-averaged two-dimensional model, is selected to perform both the steady state computation, for calibration purposes, and flood routing through the reach to obtain maximum water surface level and velocity information. Manning's coefficient was obtained by matching the computed and measured water surface level in the reach under steady flow conditions. The computed results of velocity and water surface profiles agreed satisfactorily with the measured data. The verified model was then used to simulate a flood event within the same reach. Stage-discharge relationships for various sections within the reach were obtained. The peak water surface level at each section was compared with the flow stage under normal flow conditions. The peak stage was found to be well below the proposed elevation of the construction site. The estimation of the peak velocity and water surface level might be useful for bank protection work.

4

Simulation of three-dimension side discharge into an open channel

Jia Y., Czernuszenko W., Wang S. S. Y.

Archives of Hydro-Engineering and Environmental Mechanics

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2002

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Vol. 49, nr 1

3-21

EN

A three-dimensional computational model, solving Reynolds equations with the ke turbulence closure, has been presented to simulate the flow field in an open channel near a side-discharge channel. The purpose of this study was to exam this model's applicability for simulating the three-dimensional recirculation velocity field in the vicinity of the side discharge channel. The numerical simulations show that both the height and length of the recirculation zone were correctly predicted when compared with laboratory measurements. The predicted trend of the shape of the recirculation zone under different flow conditions agrees with experimental data. It was confirmed that the SMART upwinding scheme performs better than QUICK and HYBRID schemes, since it induces less numerical diffusion and no oscillations. It was found in this study that the SMART scheme needs some minor modifications for complex flow computations.