Converting energy from ocean waves is an exciting concept aimed at reducing our dependency on fossil fuels. Ocean energy devices must convert the large forces and relatively small movements from ocean waves into electrical power with a minimum carbon and energy intensity in order to be economically viable. The research herein focuses on the Oyster, a flap-type pitching wave energy converter developed by Aquamarine Power. A device that has the minimal carbon or energy intensity is not necessarily the most mechanically efficient. A commercially viable wave energy converter should have a competitive cost of energy and be as carbon negative as possible. In order to expedite the route to commercialisation, successive designs should iterate towards a minimum lifetime cost of energy. The sheer complexity of wave energy converter systems makes for a vast optimisation problem to determine the system parameters that exhibit the minimum carbon and energy intensities. This thesis presents a study of the oscillating flap-type wave energy converter to determine the trends between design parameters, total power output and carbon and energy throughput. The minimum carbon and energy intensities have been shown to be strongly dependent on minimising maintenance requirements. In order to determine the design criterion a range of flap widths and system pressures are investigated and their effect on component service lives assessed. The results are then converted to lifetime carbon and energy intensities for a direct comparison. To achieve this, fundamental research on the maintenance requirements of critical components such as the hinge bearings and hydraulic power system is required. A hydrodynamic model describes the dynamic response and links the system energy inputs to its modelled energy output. This work is intended to help guide developers of flap-type wave energy converters towards commercialisation. It enhances the understanding of the routes to failure and service life predictions, providing avenues to balance service lives to optimise maintenance and maximise uptime. This will assist in the development of more energy efficient wave energy converters over their lifetime. This information will better enable the marine energy sector to offset our fossil fuel dependence, ultimately reducing our impact on the environment and leading to a ‘greener’ future.

Numerical modeling of extreme flooding in an urban area in eastern Iowa is presented. Modeling is performed using SRH-2D, an unstructured grid, finite volume model that solves the depth-averaged shallow-water equations. Data from a photogrammetric stereo compilation, contour maps, a hydrographic survey and building records were used to create a digital elevation model depicting the river channel and floodplain. A spatially distributed Manning coefficient based on land cover classification, derived from aerial photography is also used. The model is calibrated with high-resolution inundation depth data derived from a 1 m light detection and ranging survey, collected during the falling limb of the flood hydrograph, and discrete global positioning system measurements of water surface elevation at a bankfull condition. The model is validated with discrete high water marks collected immediately after the flood event. Results show the model adequately represents the water surface elevation in the main channel and floodplain and that exclusion of the discharges from minor creeks did not affect simulation accuracy. Reach scale results are not affected by the presence of buildings, but local inconsistencies occur in shallow water if buildings are not removed from the mesh. An unsteady hydrograph approximates flood hydrodynamics better than a steady-state simulation, but extreme computation time is not feasible for most investigations. The two-dimensional model was also compared to a comparable one-dimensional model of the study reach. The 1D model suffered from an inability to accurately predict inundation depth throughout the entire study area.

Le sujet de cette thèse s'inscrit dans le cadre de l'étude de la matière active. Ces systèmes sont composés de "particules actives" capables de s'organiser spontanément (transition de phase), et de manière autonome (sans application d'un champs extérieur), créant ainsi des dynamiques complexes comme les transition de phase dynamiques, synchronisation, instabilités etc...De nombreuses études tendent à montrer le rôle important des interactions entre particules active dans l'émergence de ces dynamiques. Nous avons abordé ces questions à travers l'étude d'une suspension de micro-algues Chlamydomonas reinhardtii. Il s'agit d'un système modèle de micro-nageur couramment utilisé pour l'étude des suspensions actives. Nous avons notamment étudié un phénomène de migration spontanée de la suspension, permettant de concentrer des micro-algues grâce à une source de lumière. Puis nous avons étudié le processus de dispersion d'un amas concentré de micro-algues. Nous avons notamment mis en évidence le rôle des interactions hydrodynamiques entre micro-algues dans cette dynamique de dispersion. / The subject of this thesis is part of the study of the active matter. These systems are composed of "active particles" capable of organizing themselves spontaneously (phase transition), and autonomously (without application of an external field), thus creating complex dynamics such as dynamical phase transition, synchronization, instabilities etc ...Numerous studies tend to show the important role of interactions between active particles in the emergence of these dynamics. We have addressed these issues through the study of a suspension of microalgae Chlamydomonas reinhardtii. It is a model system of micro-swimmer commonly used for the study of active suspensions. We studied in particular a phenomenon of spontaneous migration of the suspension, allowing to concentrate micro-algae thanks to a light source. We then studied the dispersal process of a concentrated bloom of microalgae. In particular, we have highlighted the role of hydrodynamic interactions between micro-algae in this dispersion dynamics.

This thesis presents analysis of the hydrodynamic and sedimentation changes of the Causeway Lake, Queensland. It was created in 1939 when a causeway and bridge construction was built across the estuary entrance. Since the construction, significant sediment retention has occurred in the lake. The sediment study presented in this thesis was undertaken based on historical data, field data measurement and numerical modelling, supported by theoretical analysis. Based on bathymetry data for the period from 1986 and 2003, an average of 2500 m3/year of sediment has settled in the estuary. To verify the sources of sedimentation, field measurements were undertaken at selected sections at two upstream boundaries (Mulambin and Shoal Creeks), and at the downstream boundary under the bridge. Four sets of field measurements with tidal elevation up to 4.5 m (0.8 m above the bridge sill) were analysed. Results showed that sediment transport in from the sea side was about 1050 m3/year and from the catchments area was in the order of 1100 m3/year (wash load was not included). Implementation of numerical modelling using RMA required calibration using field data. The predicted sediment transport was in order of 2900 m3/year. The calibrated model was used to simulate the sedimentation pattern for the next 10 years. Four scenarios were analysed, and the resulting recommendation was to dredge out about 141,000 m3 sediment from the Mulambin Creek branch area. Other solutions were also suggested: improvement of lake management and possibility to raise the sill level (water gate).

The objective of this research is to identify the circulation patterns of the water and sediment fluxes in coastal and estuarine zones, where the shoaling processes correlate with tide generating flow patterns. The research provides a better understanding of the characteristics of spatial and temporal variability of currents. An important deviation from previous research is the inclusion of the baroclinic term, which becomes very important in density driven flows. The understanding of this process provides a basis for determining how the water circulation three-dimensionally controls the hydrodynamics of the system and ultimately transports the suspended and soluble materials due to combined currents and waves. A three-dimensional circulation model is used to calculate the water circulation. The model is based on the three-dimensional (3D) version of Advanced Circulation (AD-CIRC) Hydrodynamic Model with extending the Sediment Transport module. The model is based on the finite element method on unstructured grids. The output of the hydrody-namic model is used to estimate spatial and temporal advections, dispersions and bottom shear stress for the erosion, suspension, deposition and transport of sediment. The model development includes extending the existing three-dimensional (3D) ADCIRC Model with (1) baroclinic forcing term and (2) transport module of suspended and soluble materials. The transport module covers the erosion, material suspension and deposition processes for both cohesive and non-cohesive type sediments. The inclusion of the baroclinic demonstrates the potential of over or underpredicting the total net transport of suspended cohesive sediment under influence of currents. The model provides less than 6% error of theoretical mass conservation for eroded, suspended and deposited sediment material. The inclusion of the baroclinic term in stratified water demonstrates the prevailing longshore sediment transport. It is shown that the model has an application to the transport of the cohesive sediments from the mouth of the Mississippi River along the north shore of the Gulf of Mexico towards and along the Texas coast. The model is also applicable to determine the design erosion thickness of a cap for isolating contaminated dredged material and to evaluate the appro-priate grain size of cap sediments to minimize the erosion.

In this paper, a global existence result of smooth solutions to the multidimen- sional nonisentropic hydrodynamic model for semiconductors is proved, under the assumption that the initial data is a perturbation of the stationary solutions for the thermal equilibrium state. The resulting evolutionary solutions converge to the stationary solutions in time asymptotically exponentially fast.

The steady problem of free convective heat transfer from an isothermal inclined elliptic cylinder and its stability is investigated. The cylinder is inclined at an arbitrary angle with the horizontal and immersed in an unbounded, viscous, incompressible fluid. It is assumed that the flow is laminar and two-dimensional and that the Boussinesq approximation is valid. The full steady Navier-Stokes and thermal energy equations are transformed to elliptical co-ordinates and an asymptotic analysis is used to find appropriate far-field conditions. A numerical scheme based on finite differences is then used to obtain numerical solutions. Results are found for small to moderate Grashof and Prandtl numbers, and varying ellipse inclinations and aspect ratios. <br /><br /> A linear stability analysis is performed to determine the critical Grashof number at which the flow loses stability. Comparisons are made with long-time unsteady solutions.

This thesis studies two important carbon structures, graphene and carbon nanotubes, with the purpose of understanding how their three-dimensional electron density distribution affects the way fast ions interact with them. <br /><br /> A brief introduction to research in pure carbon structures is made. We then use different models to calculate the equilibrium electron density distribution in graphene and carbon nanotubes. <br /><br /> In the second part of the thesis we investigate fast ions moving parallel to a graphene sheet and experiencing forces due to the dynamic polarization of carbon valence electrons. Using the three-dimensional electron density distribution of graphene, we calculate the force directly opposing the ion's motion (stopping force), as well as the force which bends the ion's trajectory towards the sheet (image force). It is our purpose to compare these results with those based on a two-dimensional hydrodynamic model of graphene, which approximates the electron distribution of graphene by a charged fluid confined to the two-dimensional plane of the sheet. <br /><br /> The results obtained for interactions of ions with a single graphene sheet should be useful for a further analysis of ion channeling through carbon nanostructures.

The steady problem of free convective heat transfer from an isothermal inclined elliptic cylinder and its stability is investigated. The cylinder is inclined at an arbitrary angle with the horizontal and immersed in an unbounded, viscous, incompressible fluid. It is assumed that the flow is laminar and two-dimensional and that the Boussinesq approximation is valid. The full steady Navier-Stokes and thermal energy equations are transformed to elliptical co-ordinates and an asymptotic analysis is used to find appropriate far-field conditions. A numerical scheme based on finite differences is then used to obtain numerical solutions. Results are found for small to moderate Grashof and Prandtl numbers, and varying ellipse inclinations and aspect ratios. <br /><br /> A linear stability analysis is performed to determine the critical Grashof number at which the flow loses stability. Comparisons are made with long-time unsteady solutions.

In this study, we design different inscribed/circumscribed circular torus-type microchannels to investigate the stretching behavior of DNA molecules. Strain rate and relaxation time play an important role in DNA stretching. In order to perform an analysis of the coil-stretch transition of DNA, we develop a method of stretching DNA molecules by using £gPIV and CLSM measurements. £gPIV is designed to measure the velocity distribution, after which the local strain rate can be estimated. The hydrodynamic stretching of DNA molecules in the elongation flow is observed using a confocal laser scanning microscope (CLSM). The relaxation time of the DNA molecules is then estimated according to the CLSM images analysis. At present, our experiments using the electro-osmotic flow (EOF) driven at various electric fields and viscosities to stretch DNA molecules show how one can investigate the influence of hydrodynamic interactions in the case of stretching of DNA molecules.