<p> The thesis contains an experimental verification of a paper by D. G. Huber dealing with a solution to the problem of the irrotational motion of two fluid strata towards a line sink. Friction was assumed negligible in the theoretical analysis and, as a result, the experimental values deviated somewhat from the theoretical expectations. The largest deviation occurred at the point of incipient drawdown where the theoretical and experimental values of the Froude number differed by 48%. The trends obtained in the experiment verify the theoretical solution. The effect of viscosity at the point of incipient drawdown for two different interface height to width ratios was determined.</p> <p> The work of Harleman et al. in submerged sluice control was extended and showed that the Froude number of the lower layer at the point of incipient drawdown with high rates of flow was much larger than expected. The reason for the change was explained using the Khafagi-Hammad relationships.</p> / Thesis / Master of Engineering (MEngr)

Utilising tidal currents as a renewable energy resource is presently under consideration to meet the requirements of increasing worldwide energy demand and the need to reduce carbon emissions. In this respect, in-stream tidal devices are proposed to convert the kinetic energy of currents into useful extractable power. In order to extract a useful amount of energy from tidal currents, the proposed devices need to be deployed in an array or farm-like format. Due to the thrust exerted by the devices within an array, the natural flow regime will inevitably be changed. In light of this, this study aims to estimate the maximum power that can be extracted by tidal turbine arrays and assess the far-field effects of energy extraction in the designated areas around the UK for various array configurations. In this thesis, the ocean tides are modelled using the long wave equations, commonly referred as the shallow water equations (SWEs). A numerical solver based on a Runge-Kutta discontinuous Galerkin finite element method is employed to solve the SWEs. One main advantage of the discontinuous Galerkin method is that it approximates the solution individually at each element, which allows for discontinuities within the solution system while ensuring mass conservation locally and globally. The selected numerical solver has been verified against several benchmark tests. It is then modified to include a line discontinuity to represent the effect of tidal turbine array(s) in a coastal basin. The algorithm implemented in the numerical solver involves a sub-grid model, which is based on Linear Momentum Actuator Disk Theory (LMADT) to approximate the local flow-field in the presence of the turbines. This near-field approach allows the flow velocity at the turbine to be estimated with a greater accuracy. As the power available to the turbines is related to the velocity at the turbine blades, the characterisation of the designated tidal site as a resource using LMADT may be more accurate than previously proposed methods. An additional advantage of using LMADT is that it provides a distinction between the power extracted by the turbines and the total amount of power that is removed from the tidal stream, including the wake mixing losses. The methodology employed in this thesis has been applied to two tidal basins around the UK; the Anglesey Skerries (a headland) and the Bristol Channel (an oscillating bay). A comprehensive unstructured triangular finite element model has been constructed to simulate the naturally occurring tides at these regions. The constructed model has then been validated against field measurement. The validated model is used to conduct parametric studies, which evaluate the importance of tidal array locations, configurations and operating conditions on the available power at the Anglesey Skerries and the Bristol Channel sites. The parametric study aims to evaluate a realistic upper limit of available power at each site considered. This study also provides a unique analysis to examine the potential tidal farm interactions by deploying several tidal arrays at both Anglesey Skerries and the Bristol Channel.

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This thesis is primarily focused on flow-field upstream of hydropower intakes, with emphasis on the use of temperature control curtains and predicting the flow acceleration zone. By reviewing the available literature, it is concluded that the flow-field upstream of hydropower intake systems can be modeled by potential flow theory. The understanding of near intake flow-field can be useful in fish entrainment studies and in designing fish repulsion systems. To control downstream river temperatures, a flexible curtain was installed upstream of several dams in California. Flow downstream of the curtain was analyzed using a Computational Fluid Dynamic (CFD) solver with rigorous validation by experimental data. The experiment was conducted with a 4 beam Acoustic Doppler Velocimeter (ADV) probe. The study shows that wall jet properties downstream of the curtain are affected by the water depth and the inlet Reynolds number. Empirical expressions were developed to predict jet properties and the wall shear stress. Flow upstream of the curtain was analyzed using potential flow theories with validation by the CFD solver. In this part, a theory based on Schwarz-Christoffel transformation was developed to predict the flow-field upstream of the curtain without accounting for any density stratification in the water body. It is observed that the acceleration zone upstream of the curtain can be affected by sink opening size, its location and water depth. The effect of boundaries on flow upstream of a line sink and the interaction of multiple sinks were analyzed. The effect of stratification on a line sink is also analyzed. A theory is developed to predict the incipient withdrawal condition when a sink is located on the horizontal bottom. The theory is also extended to a tilted bottom. The effect of boundaries on the incipient withdrawal condition is analyzed. When only one layer is being withdrawn, it is shown that a homogenous equation can be applied to a stratified condition by assuming an upper layer boundary at the interface. In addition to these works, a despike algorithm for ADV data is developed, and a numerical analysis on central difference scheme is presented. / Water Resources Engineering