Marine energy is a renewable source that has not been exploited widely. Fetching the off-shore marine energy requires a lot of investments, thus, maximizing the power delivered by the marine current system is important. Marine current power generation may be limited during certain periods due to weather situation and far distance power transmission that makes failure rate arise and repair time long. In this thesis, using marine current speed recorded at Taiwan coastline, we analyze the reliability and not-delivery energy indices of different off-shore power collection topologies and transmission system by using fault tree analysis and network reduction method. Model parameter uncertainty effects on the system reliability are studied and economic assessments of these configurations are also conducted.

Field and laboratory measurements characterize the performance of vertical axis hydrokinetic turbines operating in uniform and non-uniform inflow conditions for river applications. High sampling frequency velocity measurements, taken at 200 Hz upstream of a stopped and operating 25-kW H-type vertical axis hydrokinetic turbine in the Winnipeg River, show the existence of large eddies with an order of magnitude of the turbine’s diameter. Scaling laws allow modeling river conditions in the laboratory for more detailed investigations. A small-scale, 30 cm diameter, squirrel-cage vertical turbine designed, manufactured and equipped with a torque and position sensors is investigated for the detail behavior of the turbine subjected to different inflow conditions in a laboratory setting to study the effect of flow and fluid structures. The adjustable design of the laboratory turbine enables operations with different solidities, 0.33 and 0.67, and preset pitch angles, 0°, ±2.5°, ±5° and ±10°. Tests are first performed with uniform inflow condition to measure the sensitivity of the turbine to solidity, preset pitch angle, free-surface, and Reynolds number to obtain the optimum operating conditions. During the free-surface testing a novel dimensionless coefficient, clearance coefficient, is introduced that relates the change in turbine efficiency with change in the free-surface height. High-speed imaging at 500 fps of semi-submerged blades visualizes the vortex-shedding pattern behind the blades and air entrainment. High-speed imaging results of large eddy pattern behind the vertical turbine are consistent with theory and measurements. Subsequently, cylinders of different diameters create non-uniform inflow conditions in the water tunnel by placing them at different longitudinal and lateral locations upstream of the model turbine. Thus, the effects of non-uniform inflow generated under controlled settings shows the impact of eddies and wake on the turbine performance. High sampling frequency measurements of torque and position at 683 Hz enables investigating the impact of flow variations on turbine performance in the frequency domain. These results are also useful for fatigue analysis. Finally, entrained air bubbles in the flow—in river and laboratory settings—affect turbulence quantities, as measured using an acoustic Doppler velocimeter, and successfully addressed by implementing a new hybrid filter developed for this application.

Field and laboratory measurements characterize the performance of vertical axis hydrokinetic turbines operating in uniform and non-uniform inflow conditions for river applications. High sampling frequency velocity measurements, taken at 200 Hz upstream of a stopped and operating 25-kW H-type vertical axis hydrokinetic turbine in the Winnipeg River, show the existence of large eddies with an order of magnitude of the turbine’s diameter. Scaling laws allow modeling river conditions in the laboratory for more detailed investigations. A small-scale, 30 cm diameter, squirrel-cage vertical turbine designed, manufactured and equipped with a torque and position sensors is investigated for the detail behavior of the turbine subjected to different inflow conditions in a laboratory setting to study the effect of flow and fluid structures. The adjustable design of the laboratory turbine enables operations with different solidities, 0.33 and 0.67, and preset pitch angles, 0°, ±2.5°, ±5° and ±10°. Tests are first performed with uniform inflow condition to measure the sensitivity of the turbine to solidity, preset pitch angle, free-surface, and Reynolds number to obtain the optimum operating conditions. During the free-surface testing a novel dimensionless coefficient, clearance coefficient, is introduced that relates the change in turbine efficiency with change in the free-surface height. High-speed imaging at 500 fps of semi-submerged blades visualizes the vortex-shedding pattern behind the blades and air entrainment. High-speed imaging results of large eddy pattern behind the vertical turbine are consistent with theory and measurements. Subsequently, cylinders of different diameters create non-uniform inflow conditions in the water tunnel by placing them at different longitudinal and lateral locations upstream of the model turbine. Thus, the effects of non-uniform inflow generated under controlled settings shows the impact of eddies and wake on the turbine performance. High sampling frequency measurements of torque and position at 683 Hz enables investigating the impact of flow variations on turbine performance in the frequency domain. These results are also useful for fatigue analysis. Finally, entrained air bubbles in the flow—in river and laboratory settings—affect turbulence quantities, as measured using an acoustic Doppler velocimeter, and successfully addressed by implementing a new hybrid filter developed for this application.

Every marine energy source presents advantages and disadvantages. For example, they are not atthe same stage of maturity. Tidal range power is fully mature but the limited number of sitesavailable, combined with the large environmental impacts and investment costs limit itsdevelopment. The idea of artificial lagoons that will be offshore tidal range plant could create a newinterest for this technology. But for the moment, no plant of this type has been constructed yet. Tidalstream power is the next mature technology of marine energy after tidal range. Its development willrequire public subsidies but is supposed to be commercial in 2015. Systems are already indemonstration in several countries (UK, France and Canada). Wave power is less mature but it willbenefit from the development of tidal stream power and will probably be commercial in 2020. Somesystems are also in demonstration but challenges seem greater in wave power than in tidal power.Wave power conversion systems have to extract energy from the waves, even the largest ones, butat the same time resist to them. Contrary to tidal stream which has a predictable resource, waves areway less predictable and systems will have to be able to resist and valorize waves. OTEC (OceanThermal Energy Conversion) has been studied for years but it is still not mature. Its development forelectricity production needs technology research to develop cheaper and more compact systems(heat exchangers, pipes…). Air conditioning applications are developing and also require the use ofpipes and heat exchangers. Advances in this utilization could maybe help the development of OTECsystems for electricity production. Osmosis is the less mature and the most challenging technology. Atechnological breakthrough in the membrane could allow a rapid development. This breakthroughwill probably come from other sectors so it is important for the industries to get ready in order todevelop the system as soon as this technological improvement will be made.

Tidal current and wave power, as emerging forms of renewable generation, represent innovations that are confronted by significant technological and financial challenges. Currently, the marine energy sector finds itself in a decisive transition phase having developed full-scale technology demonstrators but still lacking proof of the concept in a commercial project environment. After the decades-long development process with larger than expected setbacks and delays, investors are discouraged because of high capital requirements and the uncertainty of future revenues. Although ideas for improving the investment climate can be found, there is a lack of well-founded arguments and coordinated strategies to work towards a breakthrough in the marine energy market. The objective of this research is to provide stakeholder-specific prioritised strategy options for de-risking the commercialisation of tidal current and wave power technologies. A key principle applied is to integrate a wide knowledge spectrum comprising the technology, policy and financing sectors and to compile the information in a holistic and transparent manner. To gain a broad understanding of the characteristics of presently ongoing marine energy activities and the correlated strategic planning, a comprehensive survey was conducted. Based on this multidisciplinary attempt, an all-encompassing appraisal was possible by avoiding over-concentration on stakeholder-specific views or interests. System dynamics modelling was employed to develop a series of cause-effect relationship diagrams of the key interactions and correlations in the field. It was revealed that the circular relationship between two major risks for array-scale projects - reliability and funding - requires coordinated action to overcome. As funding is necessary for improving system reliability (and vice-versa), showcasing 'array-scale success' was identified as the game-changing milestone towards commercial generation. Furthermore, it was found that a number of comparably competent manufacturing firms is required to implement major marine energy projects. This would result from fostering a multi-company market breakthrough concept, based on intensified knowledge sharing and trustful collaborative interaction between competitors. Additionally, effective separation of complexity into 'detail' and 'dynamically complex' constituents was found to be fundamental for identifying long-term, effective solutions. It is decisive to accept this primary classification, as measures appropriately applied on one type of complexity can be counterproductive if applied on the other. Most of the available planning tools and analytical methods do not address the management of dynamic complexity, necessary in innovative environments where flexibility and tolerance of vagueness are indispensable. Successful application of several strategies to deal with both types of complexity in comparable innovation-driven environments was considered suitable for de-risking the commercialisation of marine energy. The challenges for strategy-finding in a demandingly complex and increasingly dynamic environment are addressed in this research by exploiting a case-specific expert knowledge database. The structured information compression and subsequent strategy-finding process is realised based on calculated rankings of impact factors by systems dynamics software and substantiated by representative interview statements. The analysis makes use of multi-level expert knowledge and the application of a control-loop-based methods. The systems approach as applied in this research comprises the combination of interview-based (bottom-up learning) processes and the application of prioritised strategy options in the form of concerted management action (top-down planning). The approach of processing multi-level interview data by system dynamics modelling represents a powerful method to detect and assess ongoing developments and thus to advance strategy-finding. The systematic and unbiased approach to identify the top-level drivers for commercialising marine energy supports the long-term creation of investor confidence, based on a concept of transparency and credibility.

In recent years, much research has focused on the possibility of using arrays of turbines to generate clean and predictable power from tidal currents. The first such array is now in development but a number of important questions remain unanswered. Among these, how should turbines be arranged within a tidal stream to maximise their collective performance? And what impacts will such devices have on the marine environment? In beginning to address these questions, this thesis takes two important steps toward establishing best practice in the design of tidal turbine arrays. In the first part of the thesis, the social and ecological impacts of marine energy development are reviewed. This review highlights the importance of communication and public engagement in securing support for a marine energy project and identifies the effects of increasing noise and collision risk on marine life as the most pressing ecological issues to be addressed. In the second part, theoretical models of tidal turbines are examined and a simple numerical model is used to extend existing theories on optimal turbine arrangement. The shallow water equations are used to simulate flow through an idealised channel and an actuator disc model is used to represent a single row of tidal turbines as a line sink of momentum. Optimal turbine arrangements are then sought for different and increasingly realistic flow conditions. Results provide new and important insights into the dynamics of flow through partial-width arrays and suggest that arranging turbines unevenly within the flow cross-section can increase considerably their collective power output.

The study’s main purpose is to propose a governance framework that meets the priority of sustainable development for the regulation of offshore renewable resources in the OECS region. The study develops an analytical framework for evaluating the recently adopted “Round 3 model of governance” for the regulation of offshore wind and other marine activities in the United Kingdom. The focus is on the licensing procedures applicable to offshore wind development. Thereafter, the study examines the appropriateness of the application of the Round 3 model to the regulation of marine renewables in the OECS, and makes recommendations in that regard. Additionally, through the study of marine renewable resource development, this thesis looks at general conditions for effective ocean governance. In this regard, the thesis argues that strict hierarchical governance of the marine environment is not a desirable approach to effective ocean governance.

Wave energy generation is a promising renewable energy source but it faces certain challenges before it can become commercially viable. In comparison to conventional energy generation it is expensive, furthermore it has been plagued by reliability challenges due to the harsh operating demands of the marine environment. This Thesis investigates the reliability of wave energy devices, and specifically focuses on mooring system reliability. Two major themes are developed: Firstly, an assessment is conducted on a conventional mooring component, reviewing safety factors suggested in mooring system design guidelines and investigating whether there is a potential to reduce these safety factors (and in so doing, reduce system costs). Numerical modelling, laboratory testing and field testing demonstrate that excessively large safety factors are published in design guidance for static loading scenarios. However, when considering fatigue loading regimes (a critical aspect of wave energy generation), the proposed safety factors are found to be appropriate. In fatigue design, the importance of selecting an appropriate stress concentration factor for use with generic S-N curves is highlighted. These findings indicate the publication of additional stress concentration factors and a standard approach for mean stress adjustment would be a valuable addition to mooring system design guidance for fatigue. The second theme introduces a novel mooring component, The Exeter Tether, designed to reduce mooring loads and thus reduce system costs. The introduction of any novel technology brings new reliability considerations, and a reliability assessment of the tether and sub-components is presented in this Thesis. Following a failure modes and effects analysis, a bespoke range of physical tests is developed to investigate reliability concerns unique to this novel component. Laboratory testing of the tether assembly shows promising fatigue performance, however field trials highlight concerns regarding bio-fouling and marine debris ingress. Sub-component testing of the EPDM (Ethylene propylene diene monomer) polymer core suggests an increase in material stiffness with both marine ageing and repeated compression cycles. This finding supports results from assembly trials in the laboratory and at sea, where tether assembly dynamic axial stiffness is observed to increase over time. The overarching design philosophy behind the Exeter Tether is to reduce mooring system loads, so establishing the `worked' operating profile of the tether is crucial for the design intentions to be realised without compromising the reliability of the overall mooring system. Trials on the anti-friction membrane establish optimum performance when using two layers of UHMWPE (Ultra high molecular weight polyethylene) tape. Further areas requiring research are highlighted, and suggestions are made to improve the reliability of future design iterations of The Exeter Tether. The two reliability approaches presented demonstrate the potential for cost reduction in mooring system design and highlight the importance of physical component testing, both in the field and in laboratory conditions, to optimise component design whilst ensuring overall system reliability.

Point absorber style marine energy harvesters have been investigated based on their structure, energy harvesting efficiency, and reliability along with costs. However, due to the continuously varying ocean conditions and climates, the system usually suffers low power output and reliability from low input and high Peak to Average Ratio (PAR). Therefore, a Mechanical Motion Rectifier (MMR) based point absorber is introduced in this thesis to promote the harvesting efficiency and reduce the PAR by unifying the input rotation, and allow disengagement inside the gearbox during low power output phase. A 1:20 scale full system was then designed, prototyped, and tested based on the MMR. The bench test results show that the proposed MMR based point absorber could improve the energy conversion efficiency by 10 percent, which brings feasibility to the implementation. Traditional Wave Energy Converter(WEC) can only harvest ocean waves while ocean current is also one of the significant energy sources widely existing in ocean. In order to further increase the energy harvesting efficiency, one individual energy input source shows its limits. A vast majority of places around the world tends to co-exist both marine waves and current, and extracting energy from both sources could potentially increase the electric power output. Therefore, the Hybrid Wave and Current Energy Harvester (HWCEC) is introduced along with the hybrid gearbox. It is capable of harvesting energy from both ocean waves and current simultaneously so that the electric power output is significantly higher from a combined system. Tank test data shows 38-79 percent of electric power output promotion of an HWCEC compared to a regular WEC, and 70 percent reduced PAR in irregular wave condition. After that, system electric damping has been thoroughly investigated on both electrical side and mechanical side. The best power output corresponding electrical resistance is identical to the generator internal resistance while the best gear ratio of 3.5 is determined via both simulation and tank test. Furthermore, the system's PAR has been investigated by analyzing the trend of the peak occurrence. Tank test data shows the HWCEC's output power peak occurrence is at roughly 20 percent located at its PAR average. Therefore, the HWCEC system can promote energy harvesting efficiency to the combined system design, and improve its reliability from a significantly reduced peak to average ratio. It also gives HWCEC a large variety of deployable locations compared to a regular WEC under more marine environment. Furthermore, a new design of the Hybrid model, Hybrid LITE, is then developed, which not only features the HWCEC features, but also a lightweight, immersive and inflatable design for fast deployment and transportation. Since the system is built with an open water chassis, the overall system robustness is significantly improved since no water sealing is required on the powertrain compared to the HWCEC. / Master of Science / Ocean contains enormous amount of Marine Hydrokinetic (MHK) energy including ocean waves, tidal streams, and ocean current. Marine energy was investigated due to its continuous, massive and high-density hydrokinetic power output. In order to better serve the needs for ocean surface applications and take advantage of high energy density compared to other renewable energy sources, Wave Energy Converters (WEC) has been investigated, which harvests energy from the ocean wave. In the past years of study, it came to our attention that places such as the west coast of the U.S., northern Europe, and the Mediterranean area tend to have both abundant marine wave and current energy. Therefore, a new design of the Hybrid Wave and Current Energy Converter (HWCEC) is investigated for higher power output. In order to combine the energy sources from waves and current, a Hybrid Gearbox was selected to joint the power and unifies the motion from the wave for a higher efficiency. Simulations and 1:10 ratio co-existing wave and current basin test have been conducted for the HWCEC. By using the same system, single wave or current input are used as the baselines and the dual input HWCEC has demonstrated great benefit and potential. The electric damping and the gearbox ratio of the HWCEC are studied for the best power output in both simulation and tank test. The result shows that the HWCEC could promote up to 38-71 percent of electricity output in a regular wave condition, and 79 percent in irregular wave condition. The Peak to Average Ratio (PAR) is a key factor for system's mechanical reliability. The testing shows that the HWCEC can reduce 70 percent of the peak motion and contribute to the average, which is an indirect indicator of the system's better reliability. Furthermore, to align the needs of the design for real-life applications, The Hybrid LITE Converter idea was then developed for special deployment requirements for the future application of the Hybrid system. It has a novel open-system design with the implementation of a newly designed hybrid gearbox. This converter has the potential of promoting the reliability, deployability and weight reduction for easy transportation from its open system design compared to HWCEC. The system modeling could be done as future work varies from the changing deployment locations for higher electric power output.

Direct drive Permanent Magnet Linear Generators (PMLGs) are used in energy converters for energy harvesting from marine waves. Greater reliability and simplicity can be achieved for Wave Energy Converters (WECs), by using direct drive machines linked to the power take-off device, in comparison with WECs using rotational generators combined with hydraulic or mechanical interfaces to convert linear to rotational torque. However, owing to the relatively low velocities of marine waves and the desire for significant energy harvesting by each individual unit, direct drive PMLGs share large permanent magnet volumes and hence, high magnetic forces. Such forces can generate vibrations and reduce the lifetime of the bearings significantly, which is leading to an increase in maintenance costs of WECs. Additionally, a power electronics converter is required to integrate the generator‘s electrical output to meet the requirements for connection to the national grid. This thesis is concerned mainly with the fundamental investigation into the use PMLGs for direct drive WECs. Attention is focused on developing several new designs based on tubular long stator windings topologies and optimisation for flat PMLGs. The designs are simulated as air- and iron-cored machines by means of Finite Element Analysis (FEA). Furthermore, a new power electronics control system is proposed to convert the electrical output of the long stator generators. Various wave energy-harvesting technologies have been reviewed and it has been found that permanent magnet linear machines demonstrate great potential for integration in WECs. The main reason is the strong exaltation flux provided by the high number of permanent magnets. Such flux, combined with design simplicity, can deliver high induced voltage as well as structural integrity. In the thesis, a flat single and double structured iron-cored PMLG is studied and optimised. Several magnetic force mitigation techniques are investigated and an optimisation is conducted. The optimisation is concerned mainly with increasing electrical output power and reducing the magnetic forces in the generators. As a result, an optimal design introducing the idea of separated magnetic cores has been proposed. The FEA simulations reveal that magnetic separation in the yoke can increase significantly the energy-harvesting capability of PMLGs. Furthermore, the concept of the design of long stator windings for tubular PMLGs is studied. Two long stator generators having different magnetisation topologies and similar sizes to existing machine are modelled and compared to the existing machine. The similar-sized existing and proposed PMLGs are simulated by FEA. In this way, settings such as different boundary conditions, symmetry boundaries and material properties are used to gain confidence in the simulated results of the proposed machines. Moreover, the simulated results for the existing PMLG are verified against previously performed numerical simulations and practical tests delivered and published as part of other research. The outcome for the proposed PMLGs reveals several advantages for the long stator design, such as lower cogging forces and higher energy harvesting and a lower price of the raw structural materials. Additionally, the thesis proposes and simulates a new design for an air-cored PMLG. To boost the output power, the proposed design is based on a long stator topology adopting two sets of permanent magnet rings sandwiching copper windings in a tubular structure. The design is compared with a current machine in FEA and the results show significant reduction in radial forces and an increase in energy harvesting. Finally, a novel power electronics control system, bypassing inactive coils is suggested and simulated as part of the grid integration system for the long stator PMLGs. The new system achieves a reduction in the thermal losses in the power electronics switches in comparison with existing systems. The power electronics system and the generator have been simulated in Matlab coupled externally with FEA (JMAG Designer).