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Dive into the research topics where Sam S. Y. Wang is active.

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Featured researches published by Sam S. Y. Wang.


Journal of Hydraulic Research | 2000

Nonuniform sediment transport in alluvial rivers

Weiming Wu; Sam S. Y. Wang; Yafei Jia

A correction factor has been developed in this paper to account for the hiding and exposure mechanism of nonuniform sediment transport. This factor is assumed to be a function of the hidden and exposed probabilities, which are stochastically related to the size and gradation of bed materials. Based on this concept, the formulas to calculate the critical shear stress of incipient motion and the fractional bed-load and suspended load transport rates of nonuniform sediment have been established. These formulas have been tested against a wide range of laboratory and field data and compared with several other existing empirical methods. The predictions by these newly proposed formulas are very good.


Journal of Hydraulic Research | 2001

The applications of the enhanced CCHE2D model to study the alluvial channel migration processes

Jennifer G. Duan; Sam S. Y. Wang; Yafei Jia

This paper is to report a newly developed numerical-empirical model, the Enhanced CCHE2D (EnCCHE2D), and its application to simulating the alluvial channel migration phenomena. EnCCHE2D model is capable of predicting quasi-three-dimensional (3D) flow field and shear stress distribution on the bed, because a set of empirical functions of 3D flow characteristics formulated by results of a 3D model, CCHE3D, was integrated with CCHE2D, a depth-averaged hydrodynamic model, the predecessor of EnCCHE2D. The processes of sediment transport and meander migration were predicted based on these quasi-3D flow solutions. The advance or retreat of bank is calculated by considering not only the hydraulic erosion of bank surface and toe, but also the mass balance of sediment flux in the near-bank zone. As a result, the simulation of bank erosion, bar/pool formation and shifting, bank advance and retreat, channel widening and migration and meander evolution phenomena agree well with the available measurements of physical experiments.


Water Resources Research | 2005

A depth-averaged two-dimensional model for flow, sediment transport, and bed topography in curved channels with riparian vegetation

Weiming Wu; F. Douglas Shields; Sean J. Bennett; Sam S. Y. Wang

[1] A depth-averaged two-dimensional numerical model has been developed to simulate flow, sediment transport, and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris. The effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth-averaged two-dimensional momentum and suspended-sediment transport equations and by adjusting the bed load transport angle. The governing equations are discretized using the finite volume method on a nonstaggered, curvilinear grid. Model validity has been assessed using experimental data observed in both fixed- and movable-bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation. In general, mean flow velocities, sediment transport rates, and changes in bed topography predicted by the model agree well with the experimental observations. For laboratory and field cases, root-mean-square relative errors for velocities were less than about 13% and 44%, respectively, and about 50% of errors for changes in bed topography were less than 14.5% and 8% of the flow depth, respectively.


Journal of Hydraulic Research | 1995

Verification of a three-dimensional numerical model simulation of the flow in the vicinity of spur dikes

R. Mayerle; Sam S. Y. Wang; F. M. Toro

The objective of this paper is to show the results of simulations of the flow near spur dikes using a three dimensional numerical model. Special attention was given to the simulation of the wake formed downstream of the dyke and the influence of the eddy viscosity field on velocities, flow depths and reattachment lengths. The most important features of the model are described. Comparisons with flume measurements conducted at the Franzius Institute in Hannover, Germany are also presented.


Journal of Hydraulic Research | 2008

One-dimensional explicit finite-volume model for sediment transport

Weiming Wu; Sam S. Y. Wang

A 1D finite-volume model has been established to simulate the nonequilibrium transport of nonuniform sediment with transient flows, such as dam-break flow and overtopping flow, over movable beds. The effects of sediment transport and bed change on the flow are considered in the flow continuity and momentum equations. An explicit algorithm is adopted to solve the governing equations. The model has been tested preliminarily in several experimental cases, including an experiment on wedge development due to sediment overloading under transcritical flow conditions, an experiment on dam surface erosion due to overtopping flow, and two experiments on dam-break flow over movable beds. The model performs quite well in the cases of wedge development and overtopping flow, but significantly under-predicts the bed erosion due to dam-break flow. A modification has thus been made by considering the effects of sediment concentration on sediment settling and entrainment in the case of dam-break flow over movable beds. The present model has been compared with the traditional movable-bed “clear-water” model that ignores the effects of sediment on the flow. It has been found that the present model provides more reasonable predictions, and the “clear-water” model has larger errors when sediment transport is stronger and may even fail in the case of dam-break flow.


Journal of Hydraulic Research | 2009

A three-dimensional distinct element model for bed-load transport

Abbas Yeganeh-Bakhtiary; Behnam Shabani; Hitoshi Gotoh; Sam S. Y. Wang

A three-dimensional model is developed to simulate bed-load transport using Distinct Element Method (DEM). The model describes the bed-load transport as dynamically interdependent motions of individual sediment particles under the flow action. A steady logarithmic velocity distribution over the flow depth is considered to represent fluid motion, while turbulent intensities are also included within the closure model. The present model accounts for both fluid–particle and particle–particle interactions, which are the predominant micro-mechanisms of bed-load transport under low and high tractive forces, respectively. Characteristic features of bed-load transport, previously reported by experimental observations, are numerically reproduced. The concept of vertical momentum transfer is exploited to describe features of concurrently present of saltation and sheet-flow layers. It is concluded that the vertical motion of particles is not significantly active in sheet-flow layer and the particle momentum is preserved. Consequently the interparticle collisions is the predominant mechanism of bed-load transport at high fluid tractive forces.


International Journal of Computational Fluid Dynamics | 2005

Identification of Manning's roughness coefficients in channel network using adjoint analysis

Yan Ding; Sam S. Y. Wang

In this paper, a numerical method based on optimal control theories and adjoint analysis for identifying Mannings roughness coefficients in the full nonlinear de Saint Venant equations is presented. In order to make the parameter identification applicable to most natural river flows, special attention to a complex channel network is paid. The adjoint equations of the one-dimensional (1D) full nonlinear de Saint Venant equations in a channel network are obtained by means of variational approaches. To solve the adjoint equations in a channel network with confluences, the internal boundary conditions for confluences in the channel network are also derived from variational approaches and specified at the nodal points of confluences. In the present identification approach, one set of distributed parameters with spatial variation along river reaches can be identified, which insures the minimum simulation error along the whole channel network. By imposing the internal boundary conditions on confluences, the optimal estimations of the distributed roughness coefficients in unsteady channel network flows are achieved. In addition, the Limited-Memory Quasi-Newton (LMQN) method is utilized for enhancement of effectiveness of identification procedure. The bound constraints for Mannings roughness coefficients are taken into account. The constraints are capable of preserving the physical meaning of the estimated parameters throughout the identification process. This identification approach can be applied to estimate the spatial distribution of Mannings roughness coefficients in natural channel network flows.


Journal of Hydrodynamics | 2006

NUMERICAL MODELING OF SUSPENDED SEDIMENT TRANSPORT IN CHANNEL BENDS

Suiliang Huang; Yafei Jia; Sam S. Y. Wang

An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distributions of flow velocities and suspended sediment concentrations along water depth, it significantly enhanced the applicability of 2D models in simulating open channel flows, especially in channel bends. Preliminary numerical experiments in a U-shaped and a sine-generated experimental channel indicate that the proposed method performs quite well in predicting the change of bed-deformation in channel bends due to suspended sediment transport. This method provides an effective alternative for the simulations of channel morphodynamic changes.


Engineering Applications of Computational Fluid Mechanics | 2009

MODELING DAM-BREAK FLOWS USING FINITE VOLUME METHOD ON UNSTRUCTURED GRID

Xinya Ying; Jeff Jorgeson; Sam S. Y. Wang

Abstract This study aims to develop a robust, accurate, and computationally efficient numerical model for dam-break flows. The model is based on the finite volume method on an unstructured triangular grid. The intercell flux is computed by the HLL approximate Riemann solver. The model employs the form of the shallow water equations in which the effects of pressure and gravity are included in one source term. Such a choice can simplify the computation and eliminate numerical imbalance between source and flux terms. The accuracy and computational efficiency of the newly developed model are demonstrated through several test problems, including oblique hydraulic jump, a laboratory partial dam-break case, and a real-life dam-break case. It is found that the model is robust and capable of accurately predicting dam-break flows that may occur over complicated terrain and involve subcritical flows, supercritical flows, and transcritical flows.


World Water and Environmental Resources Congress 2003 | 2003

Numerical Simulation of Flood Inundation due to Dam and Levee Breach

Xinya Ying; Sam S. Y. Wang; Abdul A. Khan

A numerical model has been developed to simulate flood inundation due to dam and levee breach. The model solves the conservative form of the two-dimensional shallow water equations using a finite volume method. The intercell flux is computed by upwind method and the water-level-gradient is evaluated by weighted average of both upwind and downwind gradient. The newly developed model is tested with various types of examples, including a partial dam-break problem, oblique hydraulic jump due to contraction of a side boundary, and a real life case of flood wave propagation in the Toce River Valley. It is found that the scheme is inherently robust and stable, and is able to predict complex flow phenomena that involve subcritical flows, supercritical flows, transcritical flows, overland flows, and overtopping flows.

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Yafei Jia

University of Mississippi

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Yan Ding

University of Mississippi

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Yaoxin Zhang

University of Mississippi

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Xiaobo Chao

University of Mississippi

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Zhiguo He

University of Mississippi

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F. Douglas Shields

Agricultural Research Service

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Xinya Ying

University of Mississippi

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Charles M. Cooper

Agricultural Research Service

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