Two-dimensional modeling of flow field and non-equilibrium sediment transport over irregular domains and topographies.

摘要

Flows and sediment movement in natural streams can be devastating. They can lead to the decrease of stream quality, aquatic life, and disruption of transportation infrastructures. Modeling flow field and sediment transport is necessary to design control structures and locate appropriate sites for construction. This dissertation presents a two-dimensional (2-D) computational model that simulates complex flows resulting from dam-break events, tide-induced floods, and flows occurring in open channels with variable geometries and bottom elevations. Suspended sediment, bed-load transport and bed deformation are also examined and discussed. Flow and sediment modules are computed on unstructured meshes using Finite Volume Methods (FVM).;In this study, the 2-D depth-averaged shallow-water equations, assuming hydrostatic pressure, are used to model the flow behavior. A cell-centered FVM based on Roe's approximate Riemann solver is implemented on unstructured grids to solve the system of mass and momentum equations. High order accuracy is achieved by applying the k-scheme flux limiter. The k-epsilon model is implemented to close the turbulence system. The sediment transport system includes 2-D advection-diffusion transport equations for suspended sediment and bed-load transport rates. The Exner equation is used to derive bed elevation formulation. The sediment-water system is solved following a semi-coupling procedure. It is an iterative method that consists in updating sediment transport and bed elevation changes using computed hydrodynamic values. The flow terms, in turn, are modified using the calculated bed change.;The flow model is validated by comparing results against 1-D analytical solutions and 2-D published results. The sediment-water system built in this study is verified by comparing with published experimental and numerical simulations. Satisfactory agreement is found with the test cases. Simulations reveal that the model also adapts adequately to time-varying geometries. From the different results obtained, it can be suggested that existing sediment transport formulae need complementary studies and adjustment to better estimate quantities of sediment carried by complex flows such as those resulting from dam failure over movable beds. The simulations and analyses run in this study show that the model built is capable of handling such studies. It is strong, flexible, and able to handle flows over complex topographies.