Tidal Energy is one of the growing renewable energy technologies that is aimed at tackling global energy challenges. The Horizontal Axis Tidal Turbine (HATT) is an in-stream Tidal Energy Converter (TEC) which extracts kinetic energy from tidal flows. These tidal turbines face many reliability challenges due to their complexity, harsh operating environment and low accessibility. One of the component contributing significantly to the reliability of a TEC is the bearing supporting the rotating shaft within the nacelle. The reliability assessment of this component is essential during the design process and before their eventual deployments. This work is describes shaft bearing reliability assessment procedures. In recent years, the Offshore Renewable Energy (ORE) Catapult’s National Renewable Energy Centre has developed a dedicated multi axis test facility for full scale testing of tidal turbine nacelles and components (i.e. Nautilus). This work presents a methodology for testing tidal turbine shaft bearings in a representative manner in the full scale nacelle test rig, Nautilus. Two aspects are considered, namely the damage assessment and the damage replication in an accelerated manner. The damage assessment process considers the global loading on the shaft bearing and a Rigid Dynamics (RD) model has been applied to identify the local bearing loads. Local loads are converted to stress enabling the identification of stress-life relationship and bearing damage. The damage replication process is aimed to evaluate the 20 year damage and the Acceleration by Phase-shift (AbP) method has been developed to accelerate the cumulative damage. The AbP method enables the assessment of performance characteristics of shaft bearings in a laboratory environment, reducing failure rates, validate performance in a cost effective manner by reduced testing times. Within this work, novel processes for shaft bearing reliability assessments and demonstration are suggested and it concludes with the presentation of a recommended test plan for carrying out accelerated tests on a full scale bearing.

Utilizar fuentes de energía renovable es el desafío para el mundo civilizado del siglo XXI. Una fuente que ha sido poco explorada en Chile es la energía mareomotriz. Esta fuente depende de factores como el efecto gravitacional de la luna y el sol, fuentes que están aseguradas por muchos millones de años más. Además, las energías no renovables se están encareciendo cada día más, por lo que se espera que algún día estas nuevas fuentes de energías sean rentables. Por esto es importante estudiar el recurso de las mareas en nuestro país, y prepararse para cuando eso suceda. En este estudio se investiga acerca del fenómeno de las mareas y se estudia este recurso en Chile, haciendo así un diagnóstico del potencial mareomotriz que existe en este país. Además se analizan los lugares más propicios para el desarrollo de las diversas formas de explotar este recurso en Chile. Se exponen distintas tecnologías para aprovechar el potencial energético de las mareas, tanto las que aprovechan su energía potencial como las que utilizan la energía cinética generada por las corrientes de mareas. Se pone especial énfasis en esta última debido a que es una forma ambientalmente muy favorable de obtener electricidad. Para analizar la factibilidad económica de la explotación energética de este recurso se estudia la eficiencia energética de las distintas tecnologías analizando su factor de planta y el costo de la energía producida, se analiza la central mareomotriz más emblemática que es la central de La Rance, Francia. Además, se diseña un posible proyecto en Chile, utilizando la tecnología que aprovecha la energía cinética de las mareas y haciendo la evaluación económica de él.

This thesis considers the effect of disruptive waves and turbulence on a horizontal axis tidal stream turbine (TST), in terms of performance and survivability. The TST reaction to transient fluid flow is modelled analytically using Blade Element Momentum Theory (BEMT). Standard BEMT corrections are evaluated for the TST application and an alternative optimisation method is proposed for the steady state BEMT, improving compatibility with transient and depth dependent inflow, as well as the non-dimensionalisation constant needed to calculate the performance coefficients. Also, an alternative BEMT tip and hub loss implementation has led to a significant improvement of the turbine axial force prediction and in the high induction region. Validation studies are presented for BEMT coupled with regular, nonlinear wave theory and good agreement is found with published experimental data. A novel method to simulate irregular sea states is developed to couple with BEMT and a combined reactive coupling of waves and current is implemented. The TST performance in an irregular sea state is considered against turbine performance with real ADCP data and a good agreement is found. This work evaluates the BEMT implementation for the specific application of modelling TST's and significantly improves the fundamental theory, applicability and quality of results in this case.

This thesis contains an experimental campaign on the practical implementation of oscillating-foil technologies. It explores two possible engineering applications of oscillating-wings: thrust-generation, and energy-extraction. The history of, benefits of, and difficulties involved in the use of oscillating-foils is discussed throughout. Many existing technologies used for thrust generation and hydrokinetic energy extraction are based on rotating blades or foils, which have evolved over decades of use. In recent years, designs that use oscillating-foils, with motions analogous to the flapping of a fish’s tail or a bird’s wing, have shown increased hydrodynamic performance compared to the traditional rotary technologies. However, these systems are complex, both in terms of the governing unsteady fluid dynamics, and the methods by which kinematics are prescribed. Simply put, system complexity and cost need to be reduced before these devices see wide-spread use. For this reason, the work contained within this thesis explores possible methods of reducing the complexity of oscillating-foil systems in an effort to contribute to their development. For thrust-generation applications, this entailed using flexible foils to create passive pitching kinematics. This was parametrically studied by testing foils of different structural properties under a range of kinematics. The results suggested that properly tuning the flexibility of the foil could enhance both the thrust generation, and the efficiency of the propulsive system. With respect to energy-harvesting applications, the reliability of a novel fully passive turbine was assessed. The prototype tested had no active control strategy, and the degreesof-freedom were not mechanically linked, greatly simplifying the design. The prototype was subjected to real-world conditions, including high turbulence levels and the wake of an upstream turbine, and displayed robust performance in most conditions. In both applications, the hydrodynamic performance of the oscillating-wings was directly measured, and particle image velocimetry was used to observe the flow topology in the wakes and boundary layers of the foils. The vortex and stall dynamics were highlighted as key flow features, and are studied in detail. / Graduate

Master of Science / Department of Geology / Allen W. Archer / The Morrowan middle Bloyd sandstone of northwest Arkansas records a fluvial to estuarine transition in a drowned incised valley system. Lower portions of outcrops contain fluvially deposited, planar-tabular cross-stratified sandstone with a uni-directional southwest paleoflow. Intervals with dune scale, intricately interwoven trough cross-stratification with northeastern paleoflow is attributed to strong tidal and wave influence in the outer estuary. Upwards the middle Bloyd changes into a muddy mid-estuarine interval with heterolithic bedding and a bi-directional northeast-southwest paleoflow. Overlying this interval a marine sand about one meter in thickness can be found containing bryozoan and crinoid fossils. Overlying the middle Bloyd, the marine Dye Shale member of the Bloyd Formation marks the transition to a dominantly marine setting.

Managed realignment is now widely seen as an important part of coastal management strategy, as an environmentally sustainable, cost-effective alternative to traditional, hard defences. However, the trajectory of salt marsh development in managed realignment schemes remains uncertain and it is unclear how sites should be managed to fulfil both coastal defence and biodiversity objectives. In this study, the overarching aim is to find out ways in which we can create salt marshes that are self-sustaining and function as closely to natural ecosystems as possible, by considering the linked biogeomorphological processes in salt marsh ecosystems. Such an approach will improve predictions of habitat development and recommendations for future practice in managed realignment schemes. The first important question is: How do pre-alignment plant species growing within managed realignment sites respond to salt water inundation upon re-exposure to flooding? Understanding the responses of the terrestrial vegetation community to initial seawater flooding may improve predictions of the short-term transition into salt marsh vegetation. To answer this, the effects of seawater inundation on pre-existing vegetation are initially examined in a greenhouse experiment in Chapter 3. It was demonstrated that one common plant species component of many coastal grasslands, Trifolium repens, responds poorly to simulated seawater soil flooding, but the response is population-, i.e. ecotype-, specific; therefore, the species consequently has an adaptive capacity to withstand short periods of soil inundation by seawater. In addition, I look at how and why the vegetation community of a restored site transitions following the reintroduction of tidal water, including the response of the original community of non-salt marsh plant species to salt water inundation and subsequent salt marsh plant community reassembly. After three years of tidal inundation at South Efford managed realignment site (SEM), terrestrial vegetation had decreased in cover and nearly all species recorded on the adjacent natural marsh had colonised. However, the cover of salt marsh species was limited by waterlogging, caused by modifications to the tidal regime by a self-regulating tidal gate. This leads on to the second question: How do new engineering techniques alter the tidal regime and what specific aspects of the new regime drive plant community reassembly and sedimentation patterns? In Chapters 4, 5 and 6, three years of ecological and geomorphological development are investigated in response to a variable inundation regime imposed by regulated tidal exchange at SEM. Inundation of the marsh surface was very regular, but water levels were not deep enough to encourage sufficient morphological development, sedimentation nor hydrochory. In contrast, ecological development was limited by waterlogging. Balancing the tidal regime with the drainage efficiency of managed realignment sites may be the most likely scenario under which restored salt marsh will develop with maximum biodiversity benefits. Otherwise, further management techniques, such as the excavation of tidal channels, may need to be employed to improve site drainage. Consequently, the final question is: How can biodiversity be maximized on realignment sites through the use of different management techniques and site design? Tidal channels on a range of managed and natural sites were shown to improve the drainage efficiency of adjacent soils (particularly channels of greater width and/or higher Strahler order). Plant species diversity was generally higher on channel banks in managed realignment sites. On sites with highly reduced soils, the colonisation and establishment of halophytes could be advanced on the banks of tidal channels. Additionally, topographic heterogeneity introduced by tidal channels created a variety of habitat niches, which allowed a range of salt marsh species to establish in the absence of highly competitive species, such as Elymus repens. Results from this study could contribute to the generation of a number of recommendations for the implementation of managed realignment schemes, particularly regarding the excavation of tidal creek networks.

No description available.

In the quest to reduce the release of carbon dioxide to limit the effects of global climate change, tidal-in-stream energy is being investigated as one of many possible sustainable means of generating electricity. In this scheme, turbines are placed in a tidal flow and kinetic energy is extracted. With the goal of producing maximum power, there is an ideal amount of resistance these turbines should provide; too little resistance will not a develop a sufficient pressure differential, while too much resistance will choke the flow. Tidal flow in a strait is driven by the difference in sea-level along the channel and is impeded by friction; the interplay between the driving and resistive forces determines the flow rate and thus the extractible power. The use of kinetic energy flux, previously employed as a metric for extractible power, is found to be unreliable as it does not account for the increased resistance the turbines provide in retarding the flow. The limits on extraction from a channel are dependant on the relationship between head loss and velocity. If head loss increases with the square of the velocity, a maximum of 38% of the total fluid power may be extracted; this maximum decreases to 25\% if head loss increases linearly with velocity. Using these values, the estimated power potential of BC's Inside Passage is 477MW, 13% of previous assessments. If a flow has the ability to divert through a parallel channel around the installed turbines, there are further limits on production. The magnitude of this diversion is a function of the relative resistance of impeded and diversion channels. As power extraction increases, the flow will slow from its natural rate. This reduction in velocity precipitously decreases the power density the flow, requiring additional turbine area per unit of power. As such, the infrastructure costs per watt may rise five to eight times as additional turbines are installed. This places significant economic limitations on utility-scale tidal energy production. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Since the first discovery of an extrasolar planet around a solar-type star, observers have detected over 500 planets outside the solar system. Many of these planets have Jovian masses and orbit their host stars in orbits of only a few days, the so-called 'Hot Jupiters'. At such close proximity to their parent stars, strong tidal interactions between the two bodies are expected to cause significant secular spin-orbit evolution. This thesis tackles two problems regarding the tidal evolution of short-period extrasolar planets. In the first part, we adopt a simple model of the orbit-averaged effects of tidal friction, to study the tidal evolution of planets on inclined orbits. We also analyse the effects of stellar magnetic braking. We then discuss the implications of our results for the importance of Rossiter-Mclaughlin effect observations. In the second part, we study the mechanisms of tidal dissipation in solar-type stars. In particular, internal gravity waves are launched at the interface of the convection and radiation zones of such a star, by the tidal forcing of a short-period planet. The fate of these waves as they approach the centre of the star is studied, primarily using numerical simulations, in both two and three dimensions. We find that the waves undergo instability and break above a critical amplitude. A model for the tidal dissipation that results from this process is presented, and its validity is verified by numerical integrations of the linear tidal response, in an extensive set of stellar models. The dissipation is efficient, and varies by less than an order of magnitude between all solar-type stars, throughout their main-sequence lifetimes, for a given planetary orbit. The implications of this mechanism for the survival of short-period extrasolar planets is discussed, and we propose a possible explanation for the survival of all of the extrasolar planets currently observed in short-period orbits around F, G and K stars. We then perform a stability analysis of a standing internal gravity wave near the centre of a solar-type star, to understand the early stages of the wave breaking process in more detail, and to determine whether the waves are subject to weaker parametric instabilities, below the critical amplitude required for wave breaking. We discuss the relevance of our results to our explanation for the survival of short-period planets presented in the second part of this thesis. Finally, we propose an alternative mechanism of tidal dissipation, involving the gradual radiative damping of the waves. Based on a simple estimate, it appears that this occurs even for low mass planets. However, it is in conflict with current observations since it would threaten the survival of all planets in orbits shorter than 2 days. We discuss some hydrodynamic instabilities and magnetic stresses which may prevent this process.

Shippagan Gully is a highly dynamic tidal inlet located on the Gulf of St-Lawrence near Le Goulet, New Brunswick. This tidal inlet is highly unusual due to the fact that the inlet has two open boundaries with phase lagged tidal cycles that drives flow through the inlet. Over the past few decades, the shipping activities through the inlet have been threatened due to the narrowing of the navigation channel caused by deposited sediment on the east side of the channel. Many engineering projects have been undertaken at Shippagan Gully in order to try and mitigate the deposition problem. However, these attempts have either been unsuccessful or the engineered structures have deteriorated over the years. This study uses the CMS-Flow and CMS-Wave numerical models to provide guidance concerning the response of the inlet to various potential interventions aimed at improving navigation safety.