Numerical Simulation Of Estuarine Cohesive Sediment Transport

Un-equilibrium transport of sediment is the key of bed evolution of rivers and estuaries. The factors in sediment transport are very complex, for flows with sediments in nature are often turbulent flows. It is quite hot demanded in building reservoirs, navigation channels and river channel control works that understanding of transport rules of sediment, evaluation of changes of sediment transport after projects, prediction of river bed evolution in future and evaluation of effects of these changes on environment and ecologic systems to evaluate the benefit life of the projects. Based on sediment transport dynamics, rive bed evolution and fluid dynamics, numerical simulation of sediment transport became a powerful tool to understand rules of sediment transport in some water bodies.Studies on theories and methods of numerical simulation of estuarine cohesive sediment transport are carried out in this paper. Firstly, according to the characteristics of estuarine bed, a layers self-weight consolidation conceptional river-bed model is proposed to describe the dynamics process of river-bed more really. An experiential expression to describe the sediment aggregation based on characteristics of floe in Yangtze River estuary. The expression explains how turbulence constrains the aggregation when flow velocity exceeds the breaking velocity. Fractal dimension of floe is decided according to the measured falling velocity of floes. The falling velocity decided by the fractal dimension agrees well with which decided by Rouse method. Secondly, efficient numerical methods are adapted to promote the efficiency of FEM in unsteady flow simulations. Now it is possible for numerical simulation with FEM of long time sediment transport process on PC. Lastly, an experiential expression to evaluate the depth averaged vertical viscous coefficient is proposed. For there are no turbulent models, simulation with this easily method become quite stable, efficient.Based on the theories and methods developed by the author, a 2D model in plane and a 3D model based on a-coordinate system is developed. The two mathematical models are applied to simulate the cohesive sediment transport in Yangtze River estuary, and the results agree with field data well.