Three-dimensional Numerical Simulation of Sediment Flushing from Reservoirs, Anglais PDF Download
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Author: Seyed Hossein Ghoreishi Najafabadi
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Category :
Languages : en
Pages :
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Author: Seyed Hossein Ghoreishi Najafabadi
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Category :
Languages : en
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Author: Miodrag Spasojevic
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Category : Bed load
Languages : en
Pages : 172
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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.
Author: Markus Burkow
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Languages : en
Pages :
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Author:
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Languages : en
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In this thesis, the theory of three dimensional numerical modeling of transport and re-suspension of fine sediments is studied and a computer program is develped for simulation of the three dimensional suspended sediment transport. The computer program solves the three dimensional advection-diffusion equation simultaneously with a computer program prepared earlier for the simulation of three dimensional current systems. This computer program computes the velocity vectors, eddy viscosities and water surface elavations which are used as inputs by the program of fine sediment transport. The model is applied to Bay of Izmir for different wind conditions.
Author: Irina Klassen
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Category :
Languages : en
Pages :
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Author: Shao-ou Chin
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Category : Fluid dynamics
Languages : en
Pages : 446
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Author: Anu Acharya
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ISBN:
Category :
Languages : en
Pages : 384
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The intensive research on sediment transport indicates a need of an appropriate equation for predicting the total sediment load in rivers to manage reservoirs, operate dam and design in-stream hydraulic structures. None of the available equations in sediment transport has gained universal acceptance for predicting the total sediment transport rate. These facts indicate the need of a general formula to represent all these formula for predicting the sediment transport rate. The first goal of this dissertation is to find a unified total sediment transport equation for all rivers. On the other hand, scour around hydraulic structures such as spur dikes and bridge piers can be a serious problem that weakens structural stability. An investigation on the turbulent flow field and turbulence distribution around such hydraulic structures is essential to understand the mechanism of local scour and to determine which turbulence properties affect the local sediment transport. In addition, a universal turbulent model that is valid for all cases of turbulent flow in open channels does not exist. This dissertation thoroughly examined the turbulent flow field and turbulence distribution around a series of three dikes. The goal is to determine the significant turbulent properties for predicting the local sediment transport rate and to identify the appropriate turbulence model for simulating turbulent flow field around the dikes. To develop a general unified total load equation, this study evaluates 31 commonly used formulae for predicting the total sediment load. This study attributes the deviations of calculated results from different formulae to the stochastic properties of bed shear stresses and assumes that the bed shear stress satisfies the log- normal distribution. At any given bed shear stress, Monte Carlo simulation is applied to each equation, and a set of bed shear stresses are randomly generated. Total sediment load generated from each Monte Carlo realization of all the equations are assembled to represent the samples of total sediment load predicted from all the equations. The statistical properties of the resultant total sediment loads (e.g. standard deviation, mean) at each given bed shear stress are calculated. Then, a unified total sediment load equation is obtained based on the mean value from all the equations. The results showed the mean of all the equations is a power function of dimensionless bed shear stress. Reasonable agreements with measurements demonstrate that the unified equation is more accurate than any individual equation for predicting the total sediment load. An experimental study and numerical simulation of the flow field and local scour around a series of spur dikes is performed in a fixed flat bed and scoured bed condition. A micro-Acoustic Doppler Velocimeter (ADV) is used to measure the instantaneous velocity field in all the three spatial directions and the measured velocity profiles are used to calculate the turbulence properties. Results show that the local scour develops around the first dike. Turbulence intensity together with the mean velocity in the vertical direction measured at the flat bed closely correlates to the scour depth. In addition, the maximum bed shear stress, occurring at the tip of the second dike in the three-dike series, does not correspond to the maximum scour. Large bed load transport due to bed shear stress may not initiate bed scouring, but turbulence bursts (e.g. sweeps and ejections) will entrain sediment from bed surface and develop the local scour. A three-dimensional numerical model FLOW-3D is used to simulate the turbulent flow field around a series of spur dikes in flat and scoured bed. This study examines Prandtl's mixing length model, one equation model, standard two-equation model, Renormalization-Group (RNG) model, and Large Eddy Simulations (LES) turbulence model. The Prandtl's mixing length model and one equation model are not applicable to flow field around dikes. Results of mean flow field by using the standard two-equation model, and RNG turbulence model are close to the experimental data, however the simulated turbulence properties from different turbulent model deviate considerably. The calculated results from different turbulence models show that the RNG model best predicts the mean flow field for this series of spur dikes. None of the turbulence closure models can predict accurate results of turbulence properties, such as turbulence kinetic energy. Based on those results, this study recommends the use of RNG model for simulating mean flow field around dikes. Further improvements of FLOW-3D model is needed for predicting turbulence properties near this series of spur dikes under various flow conditions.
Author: Aiguo Qian
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ISBN: 9781374720015
Category :
Languages : en
Pages :
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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
Author: Cahyono
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ISBN:
Category :
Languages : en
Pages : 0
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Details are given herein of the development, refinement and application of a higher-order accurate 3-D finite difference model for non-cohesive suspended sediment transport processes, in non-stratified estuarine and coastal waters. The velocity fields are computed using a 2-D horizontal depth-integrated model, in combination with either an assumed Iogarithmic velocity profile or a velocity profile obtained from field data. Also, for convenience in handling variable bed topographies and for better vertical resolution, a sigma-stretching co-ordinate system has been used. In order to gain insight into the relative merits of various numerical schemes for modelling the convection of high concentration gradients, in terms of both accuracy and efficiency, thirty six existing finite difference schemes and two splitting techniques have been reviewed and compared by applying them to the following cases:....
Author: Sergio Everardo Adeff
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ISBN:
Category : Hydrodynamics
Languages : en
Pages : 1054
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