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Title: Theoretical frameworks for the upscaling of physical interactions in aquatic mobile-boundary flows
Author: Papadopoulos, Konstantinos
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2017
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The objective of this thesis is the development of a unifying framework for the integration and upscaling of the fluid mechanical, ecological and biomechanical processes occurring in aquatic flows. Particular focus is on the interactions of the fluid motion with aquatic plants and sediments in aquatic systems. Appropriately formulated coupled conservation equations are developed for fluid, sediment, and plant motions. The starting points for their derivation are the continuity and momentum equations written for instantaneous local field variables, for fluid, sediment and aquatic plants. The equations of motion for fluid, sediment and plants (at the stem scale) are averaged over time and space to cope with the temporal and spatial heterogeneity of the flow field near the interfacial boundary and couple the fluid and non-fluid equations of motion. To deal with the possible discontinuity of the time-averaged fields within the averaging time, appropriate definitions and theorems for time-averaging are proposed. Time-averaging is then applied on the equations of motion for each phase to obtain the respective time-averaged equations. Time-averaged equations for the second-order velocity moments are also proposed for mobile-boundary flows. The application of consecutive time-space averaging on the continuum equations led to the development of the double-averaged equations of motion for each phase. Double-averaged continuity and momentum equations have been recently proposed for mobile-boundary flows. In this thesis, the coupled double-averaged continuity and momentum equations are proposed for the sediment material and aquatic plants at the reach scale. Double-averaged equations for the second-order velocity moments have been derived for the case of fluid and sediments. By applying the double-averaging methodology (i) the governing equations are upscaled to the scales relevant to applications, (ii) the fluid motion is rigorously coupled with the non-fluid (plants or sediments) motions, and (iii) the effect of the moving interfacial boundary is introduced explicitly in the governing averaged equations. The derived second-order hydrodynamic double-averaged equations are applied to the analysis of extensive data from Direct Numerical Simulations of turbulent open-channel flows over mobile granular beds (the simulations were performed in the Dresden Technical University by Professor J. Fröhlich's Group). The use of the double-averaged equations provides significant data reduction and assists in the data interpretation. The key physical mechanisms involved in the energy transfers between the fluid mean, form-induced and turbulent fields as well as sediment motions are identified based on the assessment of the terms in the double-averaged balances of kinetic energy.
Supervisor: Not available Sponsor: European Union's Seventh Framework Programme
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Fluid dynamics ; Sediments (Geology) ; Aquatic organisms