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Title: Large-Eddy Simulation for wind and tidally driven sea circulation in coastal semi-closed areas.
Authors: Galea, Anthony
Supervisore/Tutore: Armenio, Vincenzo
Issue Date: 23-Apr-2014
Publisher: Università degli studi di Trieste
A novel high-resolution, eddy-resolving numerical model (LES-COAST) is used to investigate currents, mixing and water renewal in Barcelona harbour and Taranto bay. These environmental sites are of particular importance due to the interplay between touristic and commercial activities, requiring detailed and high-definition studies of water quality within the harbour. We use Large Eddy Simulation (LES) which directly resolves the anisotropic and energetic large scales of motion and parametrizes the small, dissipative, ones. Small-scale turbulence is modelled by the Anisotropic Smagorinsky Model (ASM) which is employed in presence of large cell anisotropy. The complexity of the harbour is modelled using a combination of curvilinear, structured, non-staggered grid and the Immersed Boundary Method (IBM). Both computation grids and harbour structures are purposely constructed for these applications by appropriate programs. Boundary conditions for wind forcing at the free surface and currents at the inlets of the port are obtained from in-situ measurements (for the case of Barcelona harbour) or by nesting this numerical model into a coastal model (Taranto bay). In this dissertation thesis an important modification to LES-COAST is implemented and is proposed as a prototype scheme, namely the possibility to consider the effect of surface waves in coastal semi-closed areas. Particularly, a linear formulation of the free surface boundary condition is considered, which would be able to reproduce the presence of seiches and tides on the dynamics of the area under investigation. The methodology is validated against analytical solution for a stationary oscillating surface wave in a simple computational grid.In both harbours considered, first- and second-order statistics, such as the mean velocity field, turbulent kinetic energy, and horizontal and vertical eddy viscosities are calculated and their spatial distribution is assessed. Water residence time is also considered for the two coastal semi-closed areas examined. Finally, the LES solution is validated against available field data.The study shows the presence of sub-surface elongated rolling structures (with a time scale of a few hours), contributing to the vertical water mixing. The time-averaged velocity field reveals intense upwelling and downwelling zones along the walls of the harbours. The analysis of second-order statistics in these harbours shows strong inhomogeneity of turbulent kinetic energy and horizontal and vertical eddy viscosities in the horizontal plane, with larger values in the regions characterized by stronger currents. The water renewal within the port is quantified for particular sub-domain regions, showing that the complexity of the harbour is such that certain inner basins of Barcelona harbour have a water renewal of over five days, including its yacht marina area, and over seven days for Taranto bay. For the Barcelona simulation, the LES solution compares favourably with available current-meter data; it is also compared with a RANS solution obtained in literature for the same site under the same forcing conditions, the comparison demonstrating a large sensitivity of properties to model resolution and frictional parametrization.
Ciclo di dottorato: XXVI Ciclo
Keywords: Large-Eddy-simulationBarcelona HarbourTaranto Bayturbulent mixingcoastal modellingwater renewalfree surfacesea circulation
Type: Doctoral
Language: en
Settore scientifico-disciplinare: ICAR/01 IDRAULICA
NBN: urn:nbn:it:units-12587
Appears in Collections:Ingegneria civile e architettura

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