Three-dimensional numerical modelling of sediment and heavy metal transport in surface waters

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Three-dimensional numerical modelling of sediment and heavy metal transport in surface waters

 

Author: Jiang, Yuwu
Title: Three-dimensional numerical modelling of sediment and heavy metal transport in surface waters
Degree: Ph.D.
Year: 2003
Subject: Hong Kong Polytechnic University -- Dissertations
Sediment transport -- Mathematical models
Department: Dept. of Civil and Structural Engineering
Pages: xxi, 282 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1740396
URI: http://theses.lib.polyu.edu.hk/handle/200/3648
Abstract: Accurate and efficient hydrodynamic and water quality numerical models are very useful in providing various types of information for hydraulic engineering and environment protection projects. In this study, three-dimensional (3D) models for hydrodynamics and the fate and transport of cohesive sediment and heavy metals have been developed and coupled together to study surface water systems. As one of the major tasks of this study, a cohesive sediment transport model which includes the sediment aggregation and breakup processes has been developed based on the work of Winterwerp (1999). With the accurate prediction of cohesive sediment concentration, a simple metal kinetic model has been included. Two types of metal kinetic mechanisms, i.e. the one-stage and two-stage adsorption and desorption mechanisms, have been considered and tested for this model. The computed results suggested that when there is not enough data to depict the two-stage mechanism, the one-stage mechanism can still perform reasonably well. The hydrodynamic model is a 3D parallel finite element model whose algorithm is proposed by Wai and Lu (2000). In this study the model has been upgraded as follows: 1) efficient parallelized solvers for large linear equation systems are used in this model, making the model perform 50 times faster than the original Wai and Lu's model; 2) the Level 2.5 turbulence closure sub-model is included to improve the accuracy of the vertical eddy viscosity coefficient estimation; 3) in the vertical direction, the finite element method instead of finite difference methods is used to solve the vertical diffusion term, which gives velocity information at the exact water bottom; 4) both the 9-node quadrilateral and the 6-node triangular elements can be used to discretize the complex spatial domain; 5)the parallel algorithm is revised to fit the Beowulf distributed memory computer system and the efficient linear equation solver, and many more. With these upgrades, this model is more versatile and efficient to deal with real world situations. Furthermore, some new strategies and techniques have also been introduced in this study, e.g. a new approach for computing drying-wetting processes which can improve mass conservation and numerical stability in 3D modelling. This coupled hydrodynamic-sediment-metal model has been applied to Xiamen Bay and the Pearl River estuary, China. The simulation results show that the model is robust in representing the hydrodynamic and sediment processes in estuaries. The present one-stage metal model successfully reveals the non-conservative behavior of dissolved metals in the Pearl River estuary, particularly in the dry season. It has been shown that this model has considerable potential in providing hydraulic and water quality information for various types of engineering construction and environment protection activities.

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