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You searched for subject:(nonuniform sediment). Showing records 1 – 3 of 3 total matches.

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1. Lin, Qianru. Three-Dimensional Numerical Modeling Of Multiple-Sized Sediment Transport Modeling Under Current And Waves.

Degree: PhD, Mechanical Engineering, 2014, University of Mississippi

In this study, a three-dimensional numerical model of multiple-sized sediment transport under current and waves is developed. The coastal circulations are described by a three-dimensional hydrodynamic model, which is governed by the three-dimensional phase-averaged shallow water flow equations coupled with wave radiation stresses. Methods are also developed to determine the bed shear stress due to current only, waves only, and coexistence of current and waves, accounting for the nonlinear interaction of the current and waves on bed shear stresses. Meanwhile, empirical formulas for bed-load transport capacity, suspended-load transport capacity, and near-bed suspended-load concentration under current and waves are established for multiple-sized sediments. These formulas are used to close the sediment transport model. The flow and sediment transport equations are solved using a finite volume method on non-staggered grid. The computational mesh is composed of quadtree rectangular grid on the horizontal plane and sigma coordinate in the vertical direction. The SIMPLEC algorithm with Rhie and Chow's momentum interpolation is used to couple the flow velocity and water level. A coupled solution procedure is used to solve the discretized sediment transport, bed change and bed material sorting equations together. The empirical formulas for bed-load and suspended-load transport rates and the near-bed suspended-load concentration have been tested intensively using a large volume of single- and multiple-sized sediment transport data under current and waves. Statistics show that more than 50% of the cases are predicted within a factor of 2 of the measured values and more than 80% of the cases are within a factor of 5. The hydrodynamic model has been validated using two laboratory cases and two field cases, which demonstrate the reliability of the flow model and its coupling with wave model. The multiple-sized sediment transport sediment transport model has been validated using three laboratory cases and one field case. The predications of the model are in good agreement with the measurements. Sensitivity analyses have also been conducted for the bed friction coefficient, suspended-load scale factor, Schmidt Number, bed-load adaptation length, and roughness height constant. The developed sediment model has been demonstrated its capability of predicting morphologic behavior through the test cases. Advisors/Committee Members: Mustafa S. Altinakar, Bing Wei, Yan Ding.

Subjects/Keywords: Bed Load; Near-Bed Sediment Concentration; Nonuniform Sediment Transport; Numerical Modeling; Suspended Load; Engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Lin, Q. (2014). Three-Dimensional Numerical Modeling Of Multiple-Sized Sediment Transport Modeling Under Current And Waves. (Doctoral Dissertation). University of Mississippi. Retrieved from https://egrove.olemiss.edu/etd/440

Chicago Manual of Style (16th Edition):

Lin, Qianru. “Three-Dimensional Numerical Modeling Of Multiple-Sized Sediment Transport Modeling Under Current And Waves.” 2014. Doctoral Dissertation, University of Mississippi. Accessed January 26, 2021. https://egrove.olemiss.edu/etd/440.

MLA Handbook (7th Edition):

Lin, Qianru. “Three-Dimensional Numerical Modeling Of Multiple-Sized Sediment Transport Modeling Under Current And Waves.” 2014. Web. 26 Jan 2021.

Vancouver:

Lin Q. Three-Dimensional Numerical Modeling Of Multiple-Sized Sediment Transport Modeling Under Current And Waves. [Internet] [Doctoral dissertation]. University of Mississippi; 2014. [cited 2021 Jan 26]. Available from: https://egrove.olemiss.edu/etd/440.

Council of Science Editors:

Lin Q. Three-Dimensional Numerical Modeling Of Multiple-Sized Sediment Transport Modeling Under Current And Waves. [Doctoral Dissertation]. University of Mississippi; 2014. Available from: https://egrove.olemiss.edu/etd/440


Universiteit Utrecht

2. Walgreen, M. Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting.

Degree: 2003, Universiteit Utrecht

The work presented in this thesis concerns the dynamics of shoreface-connected ridges and tidal sand ridges. These large-scale bedforms are observed on the inner and outer shelf of coastal seas in water depths of 10-20m. The motivation of this work is to improve the understanding of the mechanisms related to their formation and the processes that determine their main characteristics. This is done with the use of idealised morphodynamic models. The basic assumption underlying these models is that large-scale sand ridges can solely form as free instabilities on a flat sea bottom. Mathematical methods based on a stability analysis are applied, whereas analytical and numerical methods are used to solve the equations. Existing models are extended with new physical processes, in particular including the role of grain sorting. An important part of this thesis concerns the unresolved question about the origin of the observed mean grain size pattern over the ridges. It explores the hydrodynamic processes that can lead to sediment sorting and the formation of large-scale sand ridges. The model results indicate that the dynamics for different forcing conditions strongly differ. Shoreface-connected sand ridges mainly form during storm conditions, whereas if fair weather conditions prevail the more offshore located tidal sand ridges develop. A probabilistic formulation of these two realisation of the model is used to find conditions for which both types of large-scale bedforms occur simultaneously, as is the case in the southern North Sea. These conditions turn out to be a low storm fraction and the presence of both tidal and storm-driven currents. The transport of non-uniform sediment is described by formulations for both bed load and suspended load, both of which account for dynamic hiding effects. A one-layer model for the bed evolution is used and two grain size classes (fine and coarse sand) are considered. The results of the model for storm conditions indicate that the observed phase shift between bed topography and mean grain size for shoreface-connected ridges (finest sand on seaward flanks) is due to the selective transport via suspended load of grains with different sizes. Parameter values are based on the sand ridges along the Atlantic coast of North America. A net stabilising effect on the initial growth and an enhanced migration is predicted. A physical explanation for the model results is given. During fair weather or tidally dominated conditions, when bed load transport of sediment is dominant, the results indicate an increase in initial growth and migration rates of tidal sand ridges for a bimodal sediment mixture. A symmetrical tidal current results in a grain size distribution, with the coarsest sand found at the crest of the ridges. Results are compared with the tidal ridges on the Belgian coastal shelf. The investigation of the long-term evolution of shoreface-connected ridges focuses on storm-dominated micro-tidal shelves. It is shown that, starting from an initial state without bedforms, a pattern…

Subjects/Keywords: Natuur- en Sterrenkunde; shoreface-connected sand ridges; tidal sand ridges; coastal shelf; morphodynamic model; stability analysis; sediment transport; nonuniform sediment; grain sorting; storm-driven current; tidal current

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Walgreen, M. (2003). Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting. (Doctoral Dissertation). Universiteit Utrecht. Retrieved from http://dspace.library.uu.nl:8080/handle/1874/703

Chicago Manual of Style (16th Edition):

Walgreen, M. “Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting.” 2003. Doctoral Dissertation, Universiteit Utrecht. Accessed January 26, 2021. http://dspace.library.uu.nl:8080/handle/1874/703.

MLA Handbook (7th Edition):

Walgreen, M. “Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting.” 2003. Web. 26 Jan 2021.

Vancouver:

Walgreen M. Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting. [Internet] [Doctoral dissertation]. Universiteit Utrecht; 2003. [cited 2021 Jan 26]. Available from: http://dspace.library.uu.nl:8080/handle/1874/703.

Council of Science Editors:

Walgreen M. Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting. [Doctoral Dissertation]. Universiteit Utrecht; 2003. Available from: http://dspace.library.uu.nl:8080/handle/1874/703

3. Walgreen, M. Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting.

Degree: 2003, University Utrecht

The work presented in this thesis concerns the dynamics of shoreface-connected ridges and tidal sand ridges. These large-scale bedforms are observed on the inner and outer shelf of coastal seas in water depths of 10-20m. The motivation of this work is to improve the understanding of the mechanisms related to their formation and the processes that determine their main characteristics. This is done with the use of idealised morphodynamic models. The basic assumption underlying these models is that large-scale sand ridges can solely form as free instabilities on a flat sea bottom. Mathematical methods based on a stability analysis are applied, whereas analytical and numerical methods are used to solve the equations. Existing models are extended with new physical processes, in particular including the role of grain sorting. An important part of this thesis concerns the unresolved question about the origin of the observed mean grain size pattern over the ridges. It explores the hydrodynamic processes that can lead to sediment sorting and the formation of large-scale sand ridges. The model results indicate that the dynamics for different forcing conditions strongly differ. Shoreface-connected sand ridges mainly form during storm conditions, whereas if fair weather conditions prevail the more offshore located tidal sand ridges develop. A probabilistic formulation of these two realisation of the model is used to find conditions for which both types of large-scale bedforms occur simultaneously, as is the case in the southern North Sea. These conditions turn out to be a low storm fraction and the presence of both tidal and storm-driven currents. The transport of non-uniform sediment is described by formulations for both bed load and suspended load, both of which account for dynamic hiding effects. A one-layer model for the bed evolution is used and two grain size classes (fine and coarse sand) are considered. The results of the model for storm conditions indicate that the observed phase shift between bed topography and mean grain size for shoreface-connected ridges (finest sand on seaward flanks) is due to the selective transport via suspended load of grains with different sizes. Parameter values are based on the sand ridges along the Atlantic coast of North America. A net stabilising effect on the initial growth and an enhanced migration is predicted. A physical explanation for the model results is given. During fair weather or tidally dominated conditions, when bed load transport of sediment is dominant, the results indicate an increase in initial growth and migration rates of tidal sand ridges for a bimodal sediment mixture. A symmetrical tidal current results in a grain size distribution, with the coarsest sand found at the crest of the ridges. Results are compared with the tidal ridges on the Belgian coastal shelf. The investigation of the long-term evolution of shoreface-connected ridges focuses on storm-dominated micro-tidal shelves. It is shown that, starting from an initial state without bedforms, a pattern…

Subjects/Keywords: shoreface-connected sand ridges; tidal sand ridges; coastal shelf; morphodynamic model; stability analysis; sediment transport; nonuniform sediment; grain sorting; storm-driven current; tidal current

Record DetailsSimilar RecordsGoogle PlusoneFacebookTwitterCiteULikeMendeleyreddit

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Walgreen, M. (2003). Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting. (Doctoral Dissertation). University Utrecht. Retrieved from https://dspace.library.uu.nl/handle/1874/703 ; URN:NBN:NL:UI:10-1874-703 ; 1874/703 ; URN:NBN:NL:UI:10-1874-703 ; https://dspace.library.uu.nl/handle/1874/703

Chicago Manual of Style (16th Edition):

Walgreen, M. “Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting.” 2003. Doctoral Dissertation, University Utrecht. Accessed January 26, 2021. https://dspace.library.uu.nl/handle/1874/703 ; URN:NBN:NL:UI:10-1874-703 ; 1874/703 ; URN:NBN:NL:UI:10-1874-703 ; https://dspace.library.uu.nl/handle/1874/703.

MLA Handbook (7th Edition):

Walgreen, M. “Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting.” 2003. Web. 26 Jan 2021.

Vancouver:

Walgreen M. Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting. [Internet] [Doctoral dissertation]. University Utrecht; 2003. [cited 2021 Jan 26]. Available from: https://dspace.library.uu.nl/handle/1874/703 ; URN:NBN:NL:UI:10-1874-703 ; 1874/703 ; URN:NBN:NL:UI:10-1874-703 ; https://dspace.library.uu.nl/handle/1874/703.

Council of Science Editors:

Walgreen M. Dynamics of sand ridges in coastal seas: the effect of storms, tides and grain sorting. [Doctoral Dissertation]. University Utrecht; 2003. Available from: https://dspace.library.uu.nl/handle/1874/703 ; URN:NBN:NL:UI:10-1874-703 ; 1874/703 ; URN:NBN:NL:UI:10-1874-703 ; https://dspace.library.uu.nl/handle/1874/703

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