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The vertical distribution of suspended sediment concentration and velocity plays a major role in the study of the transport rate and the transport capacities of a river. Many suspended sediments concentration and velocity profiles exist in the literature, having ambiguous conditions of application. In addition, it is not easy to conduct in - situ measurements. This reveals, not only the utility of using numerical profiles, but also the responsibility of choosing an optimal one.The present thesis aims to conceive new tools for studying the vertical velocity and concentration distribution. In this context, we present two new sediment diffusivity coefficients obtained by the introduction of correction operator on the parabolic diffusivity coefficient. These models are implemented in the convection diffusion equation to generate two analytical concentration profiles and using the Boussinesq assumption, they lead to two analytical velocity profiles. Also, we conceive a method for choosing between different mathematical representation of a same physical phenomenon, and two methods for the intersection between these representations when more than one is applicable and for the extension of the representations to the cases where no model is applicable. We apply this method on the study of the vertical velocity profile and the sediment distribution in steady and uniform sediment laden open channel flows, and we develop the expert system for the vertical sediment concentration distribution code_ERESA.In an appendix, we test the use of the finite volume code_Saturne for the study of the vertical velocity distribution and suspended sediment concentration in open channel flows.
Comprehensive text on the fundamentals of modeling flow and sediment transport in rivers treating both physical principles and numerical methods for various degrees of complexity. Includes 1-D, 2-D (both depth- and width-averaged) and 3-D models, as well as the integration and coupling of these models. Contains a broad selection
The Coastal Inlets Research Program (CIRP) is developing predictive numerical models for simulating the waves, currents, sediment transport, and morphology change at and around coastal inlets. Water motion at a coastal inlet is a combination of quasi-steady currents such as river flow, tidal current, wind-generated current, and seiching, and of oscillatory flows generated by surface waves. Waves can also create quasi-steady currents, and the waves can be breaking or non-breaking, greatly changing potential for sediment transport. These flows act in arbitrary combinations with different magnitudes and directions to mobilize and transport sediment. Reliable prediction of morphology change requires accurate predictive formulas for sediment transport rates that smoothly match in the various regimes of water motion. This report describes results of a research effort conducted to develop unified sediment transport rate predictive formulas for application in the coastal inlet environment. The formulas were calibrated with a wide range of available measurements compiled from the laboratory and field and then implemented in the CIRP's Coastal Modeling System. Emphasis of the study was on reliable predictions over a wide range of input conditions. All relevant physical processes were incorporated to obtain greatest generality, including: (1) bed load and suspended load, (2) waves and currents, (3) breaking and non-breaking waves, (4) bottom slope, (5) initiation of motion, (6) asymmetric wave velocity, and (7) arbitrary angle between waves and current. A large database on sediment transport measurements made in the laboratory and the field was compiled to test different aspects of the formulation over the widest possible range of conditions. Other phenomena or mechanisms may also be of importance, such as the phase lag between water and sediment motion or the influence of bed forms. Modifications to the general formulation are derived to take these phenomena into account. The.
The flow after the rupture of a dam on an inclined plane of arbitrary slope and the induced transport of non-cohesive sediment are analysed using the shallow-water approximation. We observe the development of free-surface instabilities in the numerical results, hereafter called roll waves. Subsequently, the present monograph presents a novel Continuum Mechanics model which allows us to study the transport of sediment both in laminar and turbulent, non-hydrostatic free-surface flow, avoiding the intrinsic limitations of flow depth averaged models. Finally, this model is applied to solve the dam-break problem against an isolated obstacle and to predict the transport of sediment after the rupture of a horizontal dam. It is demonstrated that models based on depth-averaged variables (e.g. generalisations of the one-dimensional Saint-Venant equations to predict morphological changes) are superseded by more sophisticated and accurate procedures valid for non-hydrostatic shallow water flows over bed of arbitrary bottom slopes (e.g. the model described herein).
Transport of sediments creates a variety of environmental impacts because it not only induces erosion and deposition problems, but also transfers contaminants or viruses adhered or coupled with the sediments. A better understanding of the fundamental sediment transport processes is significant for environmental researchers to provide practical and scientifically sound solutions to hydraulic engineering problems. Stochastic characteristics of sediment transport have been identified from experiment data. The trajectory of a sediment particle is stochastic due to the probabilistic nature of the flow and sediment conditions. The main goal of the study is to develop a stochastic model governing suspended sediment transport. In this research, several issues related to stochastic modelling of suspended sediment transport are discussed: the numerical scheme for the Fokker-Planck equation; suspended sediment transport in regular surface flows; and suspended sediment transport in extreme flow environments. A fourth-order accurate numerical scheme has been developed for the two-dimensional advection-diffusion (A-D) equation in a staggered-grid system. The first-order spatial derivatives are approximated by the fourth-order accurate finite-difference scheme, thus all truncation errors are kept to a smaller order of magnitude than those of the diffusion terms. For the time derivative, the fourth-order accurate Adams-Bashforth predictor-corrector method is applied. The stability analysis of the proposed scheme is carried out using the Von Neumann method. It is shown that the proposed algorithm has good stability. The proposed numerical scheme can provide more accurate results for long-time simulations validated against analytical and/or numerical solutions. A stochastic partial differential equation based model has been derived based on the law of conservation of mass and the Langevin equation of particle displacement to simulate suspended sediment transport in open-channel flows. The proposed model, explicitly expressing the randomness of sediment concentrations, has the advantage of capturing an instantaneous profile of sediment concentrations including not only the mean but also the variance compared with the deterministic A-D equation. As a result, the probability distribution of the sediment transport rate can be characterized based on a number of realizations obtained in the numerical experiments. The lattice approximation is applied to solve the SPDE of suspended sediment transport in open channel flow. The ensemble mean sediment concentration of the proposed SPDE, obtained by the Monte Carlo simulation, agrees well with that of the deterministic A-D equation. This study proposed a stochastic jump diffusion model in response to extreme flows to describe the movement of sediment particles in surface waters. The proposed approach classifies the movement of particles into three categories - a drift motion, a Brownian type motion due to turbulence in the flow field for example, and jumps due to occurrence of extreme events. In the proposed stochastic diffusion jump model, the occurrence of the extreme flow events is modeled as a Poisson process. The frequency of occurrence of the extreme events in the stochastic diffusion jump model can be explicitly accounted for in the evaluation of movement of sediment particles. The ensemble mean and variance of particle trajectory can be obtained from the proposed model. As such, the stochastic diffusion jump model, when coupled with an appropriate hydrodynamic model, can assist in developing a forecast model to predict the movement of particles in the presence of extreme flows.