Modelling the three-dimensional tidal flow structure in semi-enclosed basins

Duin, Olav J.M. van (2009) Modelling the three-dimensional tidal flow structure in semi-enclosed basins.

Abstract:Coastal areas are generally intensely used areas with high population density and economic activity. On a basin scale the tide directly determines water levels and currents in a basin. These flow characteristics furthermore determine the shape of the basin itself, for example the forming and evolution of tidal sandbanks, which in turn influences the flow pattern. Because of its importance for various human and natural activities the modelling of tidal flow has been studied by many authors in the past. This has lead to depth-averaged (2DH) and 3D models amongst others The first analytical 3D-model that describes tidal flow in a semi-enclosed basin using Kelvin and Poincaré modes with partial slip was created for this research. For this the method devised by Mofjeld (1980) for 3D tidal flow along a single coast with viscosity and no-slip was extended, thereby following Taylor’s approach (1921). As a reference situation the Northern Part of the North Sea was modeled and the properties of the Kelvin and Poincaré modes described. Also the flow and shear stress properties were studied. The flow properties were also compared to an equivalent 2DH model but for this first values for the friction parameter had to be determined. For this various methods were adopted with varying success in approximating the 3D properties. It is clear that that 3D structure is important to be able to precisely determine the flow properties. The value for the friction parameter that gives the best results of the methods employed was that be found by fitting the Kelvin dissipation factor of the 3D model (using viscosity and slip parameters) with the 2DH model (using a friction parameter). The fitting of the Kelvin dissipation factor lead to a friction parameter of 1.7*10-3 m/s for the reference case (the 3D model had a slip parameter of 0.005 m/s and a viscosity parameter of 0.09 m2/s). With this parameter the 2DH model results were compared with the 3D model results, showing that 3D structure is indeed important. Eventually this friction lead to an average error in predicting 3D longitudinal bottom shear stress amplitude with a 2DH model of 13% while the theoretically best result would have been 3%. This all leads to the conclusion that continued research in this area can further improve 3D and 2DH modeling.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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