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"This report describes the theoretical principles of three-dimensional sediment transport and bed-evolution processes, and numerical solution of the appropriate governing equations. It also includes technical documentation and user's instructions for the sediment-operations program module developed as an integral part of the CH3D code."--P. ii.
This research project focuses on the analysis and prediction of flow structures and sediment transport process in open channels by using three-dimensional numerical models. The numerical study was performed using the open source computational fluid dynamics (CFD) solver based on the finite volume method (FVM) – OpenFOAM. Turbulence is treated by means of the two main methodologies; i.e. Large Eddy Simulation (LES) and Reynolds-Averaged Navier–Stokes (RANS). The free surface is tracked using the Volume of Fluid method (VOF). In addition, a new multi-dimensional model for sediment transport based on the Eulerian two-phase mathematical formulation is applied. The results obtained from the different numerical configurations are verified and validated against experimental data sets published in important research journals. The main characteristics of the flow structures are studied by using three set-up cases in steady and unsteady-state (transient) hydraulic flow conditions. On the other hand, the new multi-dimensional model for sediment transport is applied to predict the local scour caused by submerged wall jet test-case. Non-uniform structured elements are used in the grid configuration of the computational domains. A mesh sensitivity analysis is performed in each test-case study in order to obtain independent grid results. This analysis provides a balance between accuracy and optimal computational time. The results demonstrate that the three-dimensional numerical configurations satisfactorily reproduce the temporal variation of the different variables under study with correct trends and high correlation with the experimental values. Regarding the analysis and prediction of the flow structures, the results show the importance of the turbulence approach in the numerical configuration. On the other hand, the results of the new multi-dimensional two-phase model allow to analyze the full dynamics for sediment transport (concentration profile). Although the numerical results are satisfactory, the application of three-dimensional numerical models in field-scale cases requires a high computational resource.
The central concern of the book is to study flows and sediment phenomena through hydraulic structures in a regulated reservoir. The flow patterns in and around most hydraulic structures are complex, three-dimensional, and highly turbulent. For these reasons, in order to understand the impact of hydraulic structures on the hydrodynamic, sediment transport processes and morphological changes in regulated reservoirs it is often necessary to investigate these processes in three dimensions. In design a real and complex water regulated reservoir both physical and numerical models are applied. In the numerical sections, explain the governing equations of the hydrodynamic (including turbulence), sediment transport and morphodynamic process, respectively. Besides, mathematical solutions for the different equations are given in detail in a separate chapter. In next chapters, the capability of the numerical model is evaluated with two sets of experimental data. Also, one chapter presents the application of the numerical model to the experiment explained in physical modelling part and comparisons made between the physical and numerical model results. Final chapter summarises the main findings.
Concentration in the corresponding z-level of the water column. Secondly, the horizontal concentration difference was determined. Finally, the horizontal pressure gradient in the water column was directly calculated from the horizontal concentration gradient. A stepwise bottom boundary condition was adopted for steep slopping bottom boundary. The algorithm has been used to enhance the EFDC model. The model code has been tested in three test cases: 1) flat bottom basin, 2) steep sloping channel, and a coastal shelf. Results indicate that conventional approach in current EFDC dealing with horizontal pressure gradient terms causes spurious surface elevation and velocity field. In comparison, the employment of the algorithm presented in this study this study significantly reduced numerical errors in predicting surface elevation and currents in navigation channels and coastal shelves.
This dissertation, "Three-dimensional Modelling of Hydrodynamics and Tidal Flushing in Deep Bay" by Aiguo, Qian, 乾愛國, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled "Three-Dimensional Modelling of Hydrodynamics and Tidal Flushing in Deep Bay" submitted by QIAN Aiguo for the degree of Master of Philosophy at the University of Hong Kong in December, 2003 Deep Bay is a semi-enclosed shallow bay on the eastern side of the Pearl Estuary, between Shenzhen to the north and the New Territories of Hong Kong to the south. As a result of large-scale development in Shenzhen, Deep Bay has experienced severe water quality deterioration in recent years. Some isolated water quality studies of Deep Bay have been conducted. However, Deep Bay is a unique embayment which exhibits large seasonal salinity variation, and no three-dimensional (3D) modeling of the tidal flushing process has yet been done. The flushing time, a key parameter that governs water quality and biological processes, needs to be quantified using a robust 3D hydrodynamic model. In the present study, a 3D hydrodynamic model of Deep Bay is developed and the 3D salinity and tidal circulation of the bay are systematically discussed. The flushing and dispersion features are studied, and the tidal flats in inner Deep Bay are simulated. The Environmental Fluid Dynamic Code (EFDC) is used to develop the 3D hydrodynamic model of Deep Bay. The topographical configuration, space and time scales, boundaries and boundary conditions are selected based on physical consideration and extensive numerical tests. The model is calibrated and verified against two different field data sets respectively for the dry and wet season. The effect of salinity on velocity field is also examined via a numerical experiment by eliminating any salinity gradient from the measured wet season tidal conditions. The analysis of field measurements and numerical modeling is synthesized, and it is demonstrated that the flows within Deep Bay are characteristic of a well mixed/weakly stratified estuary. The small freshwater flows make insignificant contribution to the salinity structure of the outer Deep Bay area, which is mainly influenced by the inflow introduced from the Pearl Estuary. Based on the validated hydrodynamic model, the tidal flushing is studied using a 3D conservative mass transport model. The flushing times of different parts of Deep Bay are quantified via systematic numerical simulation including: i) real tidal forcing on Deep Bay model and ii) typical M2 tides on a local model with only one tidal open boundary. It is demonstrated that the flushing rate is approximately 0.04 per day (flushing time 25 days) in the inner bay, and increases beyond the middle bay rapidly, to 0.3-0.4 per day at the outer end. The flushing rate is significantly affected in both the dry and wet season by salinity gradients. The dispersion of a continuous pollutant source into Deep Bay is also studied. It is demonstrated that this dispersion conforms to the flushing features within the bay. The source remains in the inner bay area with a high concentration, but is rapidly diluted beyond the Shekou cape cross section of middle Deep Bay. It is therefore demonstrated that severe water quality deterioration in Deep Bay occurs mainly in its inner bay area, and that any "red tide" occurring from time to time in inner Deep Bay will not spread to the bay as a whole. DOI: 10.5353/th_b2979900 Subjects: Hydrodynamics - Computer sim