The West Coast of Vancouver Island (WCVI), with an average gross wave energy flux of 40-50 kW/m at the continental shelf, possesses one of the most energetic wave climates in the world and has the potential to meet the electric demands of the utility grid on Vancouver Island and numerous coastal remote communities. However, the development of wave energy sites has the potential to interrupt other existing marine activities and wave energy operations could damage the sensitive marine ecosystems. The objective of this thesis is to identify strategically important sites for wave energy – sites that have great economic potential in an energy generation context yet have minimal impacts on existing economic uses and minimal ecological impacts. Wave energy technology agnostic frequency and directional filters were developed based on a unionized representation of Wave Energy Converter (WEC) performance generated by combining four types of WEC performance characteristics. These two filters improved the quantification of extractable wave resources by accounting for the technological limits of wave frequencies and directions. Subsequently, a detailed economic evaluation was developed to estimate the influence of the distance to the coastline and transmission network, electricity market sizes, and a technology agnostic description of WEC farm physical layout on the selection of wave energy sites. The technology-agnostic description of WEC farm physical layouts was designed based on the cable properties, cable termination/distribution, and cable protection used in real-world projects. The WEC farm capacities are constrained by the transmission cable to minimize the cost for developing wave energy sites. Lastly, a multi-criteria analysis, which includes four stakeholder perspective scenarios, was developed to identify the strategically important sites for future wave energy development along the WCVI. A total of 16 regions, covering an area of 392 km2 and having an average of 35.68 kW/m wave energy flux, were identified as strategically important sites for wave farms. These regions show the potential to meet the electric demand of Vancouver Island, and they are worth further investigated when selecting a location for future wave energy development. / Graduate

This thesis presents an assessment of a modular flap-type wave energy converter. Comparisons are made to an equivalent width rigid device. All quoted relative difference results here use the rigid device as the reference point. The variables that are evaluated are the power capture and surge and yaw foundation loads. The power capture is evaluated at both module and device level, while the foundation loads are assessed just at the device level. The investigation is carried out through testing of a 30th scale physical model in a wave tank. A key output from the work is the development of the physical model. The model consists of six flap modules, mounted on a common base structure. Each module contains a highly controllable and compact power take off system. The devices are tested in a range of conditions, primarily consisting of regular waves of different period and direction. The damping strategy employed is the simplest approach available, setting the achievable damping level on each module to be the same. For the modular device in head-on regular waves, the results show that the power capture increases significantly moving from the outer to the central modules. On average, the central pair of modules produce 68 % of the total mean power, the inner modules 25 % and the outer modules only 7 %. Between the devices, it is shown that the power captures in head-on waves are similar, with a mean relative difference of -3 %, with +/-5 % uncertainty. Thus, no statistically significant change in power capture is shown. In off-angle waves, the mean relative difference is –1 %, with +/-4 % uncertainty. However, for the highest wave direction that was tested in, 27.5 degrees, the modular device outperforms the rigid flap, by 10 %, with uncertainty of +/-1 %. The surge foundation loads are shown to be very similar for the two devices - in head-on waves, the mean relative difference is +2 %. Depending on the level of applied damping, however, significant differences in the yaw foundation loads are shown. Using damping where the power capture is maximised, the yaw loads increase by a mean of 10 %; using damping where the power to load ratio is instead maximised, the modular yaw loads are 26 % lower. Finally, the economics of the power production is estimated through division of the power capture with a cost metric, the foundation loads. While this does not provide a full techno-economic assessment, it effectively captures the interdependency of the power capture and foundation loads for the devices. The mean relative differences in the power per load ratios of the devices are found to be similar across the wave conditions. In the head-on waves, the differences are between –8 and –0.4 %, depending on damping strategy; in the off-angle waves, the differences are between –6 and +10 %. For both sets of wave conditions, the modular flap performs better when the damping is set to maximise the ratio of power capture to foundation loads. The work concludes that the modular and rigid devices produce power and experience foundation loads at similar levels in head-on waves. Given the high power capture efficiency, nearshore location, simple mode of operation and high survivability of the flap-type WEC, this suggests that the modular device is a viable stand-alone concept. The work also finds that in off-angle waves, some benefits can be achieved with an appropriately damped modular system, notably in improved power capture and reduced yaw foundation loads. These could reduce the sensitivity that flap-type devices have in off-angle waves and allow expansion of the width and hence capacity of machines. Further work should extend the wave conditions tested in, by using more irregular and directional waves, and investigate more damping strategies and geometries. Economic assessment should also be carried out.

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.

The sustainable development of the offshore wind and wave energy sectors requires optimising the exploitation of the resources, and it is in relation to this and the shared challenge for both industries to reduce their costs that the option of integrating offshore wind and wave energy arose during the past decade. The relevant aspects of this integration are addressed in this work, and in particular the evaluation of the Wave Energy Converter (WEC) sub-system of a hybrid wind-wave energy converter: the state of the art of combined technologies; the definition of a novel hybrid prototype, based on a preliminary feasibility analysis of a conceptual proposal; and the evaluation of a simplified version of this prototype by means of physical and numerical modelling as a mean to set the reference and define new tools and methods for future evaluation and optimisation of the prototype. Because of the novelty of combined wave and offshore wind systems, fundamental knowledge was lacking as, for example a comprehensive review and classification, which was published as a journal paper framed in the present work. In particular, the core of this PhD thesis deals with the WEC sub-system of a hybrid device that integrates an Oscillating Water Column (OWC) device into the typical monopile substructure of an offshore wind turbine. A new prototype of the hybrid energy converter has been proposed, and a patent application was filled. Furthermore, an experimental set-up was designed, built and tested at a wave flume. On the basis of this experimental campaign the performance of the device is analysed. Finally, a full 3D-numerical mirror of the experimental set-up, including the hybrid energy converter, is defined and validated, and the flume enclosure effects studied for regular waves.

The original aim of the research project was to investigate the mechanism of power capture from sea waves and to optimise the performance of a vee-shaped floating Wave Energy Converter, the Floating Clam, patented by Francis Farley. His patent was based on the use of a pressurised bag (or ‘reservoir’) to hold the hinged Clam sides apart, so that, as they moved under the action of sea waves, air would be pumped into and out of a further air reservoir via a turbine/generator set, in order to extract power from the system. Such “Clam Action” would result in the lengthening of the resonant period in heave. The flexibility of the air bag supporting the Clam sides was an important design parameter. This was expected to lead to a reduction in the mass (and hence cost) of the Clam as compared with a rigid body. However, the present research has led to the conclusion that the Clam is most effective when constrained in heave and an alternative power take-off is proposed. The theoretical investigations made use of WAMIT, an industry-standard software tool that provides an analysis based on potential flow theory where fluid viscosity is ignored. The WAMIT option of Generalised Modes has been used to model the Clam action. The hydrodynamic coefficients, calculated by WAMIT, have been curve-fitted so that the correct values are available for any chosen wave period. Two bespoke mathematical models have been developed in this work: a frequency domain model, that uses the hydrodynamic coefficients calculated by WAMIT, and a time domain model, linked to the frequency domain model in such a way as to automatically use the same hydrodynamic and hydrostatic data. In addition to modelling regular waves, the time domain model contains an approximate, but most effective method to simulate the behaviour of the Clam in irregular waves, which could be of use in future control system studies. A comprehensive series of wave tank trials has been completed, and vital to their success has been the modification of the wave tank model to achieve very low values of power take-off stiffness through the use of constant force springs, with negligible mechanical friction in the hinge mechanism. Furthermore, the wave tank model has demonstrated its robustness and thus its suitability for use in further test programmes. The thesis concludes with design suggestions for a full-scale device that employs a pulley/counterbalance arrangement to provide a direct connection to turbine/generator sets, giving an efficient drive with low stiffness and inherently very low friction losses. At the current stage of research, the mean annual power capture is estimated as 157.5 kW, wave to wire in a far from energetic 18 kw/m mean annual wave climate, but with scope for improvement, including through control system development.

Wave energy has the potential to contribute considerably to the UK's energy mix. The marine environment is already subjected to many anthropogenic pressures. There is a need to develop the industry as sustainably as possible. A key concern is the potential for underwater noise to affect marine life. A wave energy converter (WEC; BOLT Lifesaver, Fred Olsen Ltd.) was deployed at the Falmouth Bay marine renewable energy test site (FaBTest). The underwater sound levels were recorded at this site for a two week baseline period, a five-day installation period and intermittent operational and non-operational activity from March 2012 - November 2013. The recordings were also analysed for the Marine Strategy Framework Directive (MSFD) indicator third octave bands of 63-Hz and 125-Hz for shipping noise. The median and modal sound levels in Falmouth Bay were found to be loudest in the frequency range 100 Hz - 1 kHz and affected by local shipping activity. During installation activity, the sound levels were louder at all frequencies recorded as compared to similar periods with no installation activity, with a mean difference of 6.9 dB Hz-1 in the range 10 Hz to 48 kHz. Long term marine renewable energy construction projects may affect the MSFD indicator bands. There was little overall difference in the average sound levels for the operational and non-operational periods as the median PSD levels were louder by an average of 0.04 dB Hz-1 during the operational activity as compared to the non-operational activity. The results of this study indicate that the effect of a single WEC device on the overall sound levels in Falmouth Bay is relatively low considering the substantial presence of shipping in the area. However, in the immediate vicinity of the device (<200 m), the sound produced was found to be of significance to marine animals. It therefore requires considering in future deployments, particularly at a site with little anthropogenic activity.

This thesis discusses the development of a Numerical Wave Tank (NWT) capable of describing the coupled behaviour of Wave Energy Converters (WECs) and their moorings under extreme wave loading. The NWT utilises the open-source Computational Fluid Dynamics (CFD) software OpenFOAM(R) to solve the fully nonlinear, incompressible, Reynolds-Averaged Navier-Stokes (RANS) equations for air and water using the Finite Volume Method (FVM) and a Volume of Fluid (VOF) treatment of the interface. A method for numerically generating extreme waves is devised, based on the dispersively-focused NewWave theory and using the additional toolbox waves2Foam. A parametric study of the required mesh resolution shows that steeper waves require finer grids for mesh independence. Surface elevation results for wave-only cases closely match those from experiments, although an improved definition of the flow properties is required to generate very steep focused waves. Predictions of extreme wave run-up and pressure on the front of a fixed truncated cylinder compare well with physical measurements; the numerical solution successfully predicts the secondary loading cycle associated with the nonlinear ringing effect and shows a nonlinear relationship between incident crest height and horizontal load. With near perfect agreement during an extreme wave event, the reproduction of the six degree of freedom (6DOF) motion and load in the linearly-elastic mooring of a hemispherical-bottomed buoy significantly improves on similar studies from the literature. Uniquely, this study compares simulations of two existing WEC designs with scale-model tank tests. For the Wavestar machine, a point-absorber constrained to pitch motion only, results show good agreement with physical measurements of pressure, force and float motion in regular waves, although the solution in the wake region requires improvement. Adding bespoke functionality, a point-absorber designed by Seabased AB, consisting of a moored float and Power Take-Off (PTO) with limited stroke length, translator and endstop, is modelled in large regular waves. This represents a level of complexity not previously attempted in CFD and the 6DOF float motion and load in the mooring compare well with experiments. In conclusion, the computational tool developed here is capable of reliably predicting the behaviour of WEC systems during extreme wave events and, with some additional parameterisation, could be used to assess the survivability of WEC systems at full-scale before going to the expense of deployment at sea.

The Wave Hub facility in Cornwall (South West UK) is a marine renewables test site, predominantly designed for the purpose of trialling wave energy converters prior to commercialisation. Beach water-users such as bathers and surfers are of economic importance to tourism in Cornwall, and during theWave Hub consultation there were concerns among stakeholders that wave energy extraction would reduce the height and quality of coastal waves for sur ng, as well as a ecting sediment transport and beach morphology. This thesis investigates the interaction between wave conditions, beach morphology, and beach water-users, and proposes how a wave climate altered by wave energy extraction is likely to alter these interactions. A multidisciplinary research approach is adopted, involving the collection of qualitative and quantitative social data, the collection of over 5 years of physical wave and beach morphology data, and predictive modelling of the e ects of an attenuated wave climate. Quantitative, structured interview data from 403 water-users, collected at two beaches (Perranporth and Porthtowan) in the lee of Wave Hub, indicate that the population of water-users in the area is predominantly made up of surfers (53%), but bodyboarding and swimming/bathing are also popular activities (29% and 11%, respectively). In-depth semi-structured interviews reveal that water-user perceptions of wave energy extraction and its potential coastal impacts are constructed using intuitive risk perceptions, rather than technical understanding. These risk perceptions are constructed through a weighing of their perception of wave energy devices ('technology') and their perception of the coastal environment ('nature'). To investigate how waves are perceived, nearshore wave buoy measurements collected in 14 m water depth and transformed to breaking height, are compared to concurrent visual observations of mean breaker height and period. On average water-users underestimated signi cant wave height and period by 48% and 17%, respectively. Accounting for variations in wave perception, the wave preferences of di erent water-user groups are determined. Water-users are found to share a common preference towards wave v periods of 9 - 20 s, but di erent water-user groups are found to have di erent ranges of preferred wave height, which is found to govern whether wave energy extraction will decrease or increase the occurrence of preferred waves. Previous research indicates that three-dimensional (3D) beach morphology with crescentic bar and rip features is the primary controller of surf-zone hazard, and also strongly in uences the quality of sur ng waves at the coast. A dataset of 5.5 years of quasi-weekly bar measurements, and quasi-monthly intertidal surveys from Perranporth beach is used to quantify seasonal to inter-annual changes in threedimensionality. Integrated, cumulative uctuations in wave steepness, wave power, and relative tide range that occur over seasonal time scales are shown to be well correlated to seasonal uctuations in beach three-dimensionality. 3D morphology is well related to a disequilibrium term that predicts increases or decreases in threedimensionality by examining the di erence between instantaneous wave conditions and a temporally varying equilibrium condition, based on a weighted average of antecedent waves. This indicates that periods of wave regime change between erosive winter conditions with high steepness waves and accretive summer conditions with low steepness waves are related to the growth of 3D features, and vice versa, while extended periods with similar wave conditions drive the beach towards equilibrium. Using a range of realistic and extreme coastal wave height attenuation scenarios determined from previous Wave Hub modelling studies, it is predicted that none of the scenarios will have a universally positive or negative e ect on the occurrence of wave conditions preferred by water-users. When used to predict beach threedimensionality at Perranporth beach, the attenuated wave climates are found to reduce the variability in three-dimensionality. Even an extreme and unrealistic level of wave energy extraction (100% energy capture) was shown to have an insigni cant e ect on the occurrence of preferred waves, and only under an extraction scenario where the impact was not varied with wave frequency did this level of attenuation have a signi cant e ect on the predicted beach three-dimensionality. The inshore wave attenuation from Wave Hub is therefore likely to have an insigni cant e ect on wave conditions and beach morphology of relevance to beach water-users. A number of observations and recommendations are discussed for the development of a sound and robust methodological approach, which can be used to investigate the e ects of wave energy extraction on beach water-users at future wave farm sites.

Commercial viability of Wave Energy Converters (WEC) depends on addressing not only the energetic effciency, but also in solving the practical issues related to manufacturing methods, access to technology, handling, transportation and installation, operation and maintenance, impact on marine life and most importantly the cost per kW-h. The UFCAP WEC is one concept which has the potential to facilitate handling, manufacturing, and installation activities as well as to be able to lower the current wave energy cost per kW-h, however its feasibility had not been properly assessed nor proved. It consists of multiple interconnected Oscillating Water Columns (OWC) chambers, it is modular, and simple, with no-moving parts in contact with the water and can use a simpler one-direction turbine which is more economic, and more effcient than self-rectifying turbines used in most of the OWCs devices. Testing of the device to fully assess its feasibility required a low pressure check-valve, and a customized turbine which were developed during the present work. Check-valves are widely used in the industry for medium or high-pressures, but were not available at all for large-flows with low-pressure-differences. A novel check-valve was devised for this application, along with the scaled UFCAP prototypes developed to be tested in a wave-flume and in the ocean to validate UFCAPs concept feasibility, and identify critical design parameters and features such as the conduit/air-chamber ratio. Ocean tests allowed to observe performance at component and assembly levels, learning new failure-modes and stablishing best-practices for future deployments. Testing confirmed the UFCAP WEC is not only an idea, but a concept which works and can generateing electricity at a competitive cost. / Graduate

There is a demand for renewable energy in today’s society. Wave energy is a nearly untapped source of renewable energy. Ocean Harvesting Technologies AB (OHT) is currently developing a device that can be used to convert wave energy into electricity. The device is a Wave Energy Converter of the type point absorber. Their concept is a floating buoy that is connected to the seafloor via a Power Take-Off (PTO) unit. The PTO unit is equipped with generators, which are used to convert kinetic energy of the buoy into electricity. The objective of this thesis is to control the generators to optimize the performance of the system. OHT was interested in knowing how their system performs under the influence of a controller based on MPC. Hence an MPC-controller is constructed in this thesis. The developed controller functions by predicting the states (position and velocity) of the buoy over a finite time (e.g. $5s$). Then the controller uses the predictions to find a control force that makes the system behave optimally for the next $5$ seconds. A requirement from the company is that the controller should find the control force based on how the buoy is predicted to move in 3 Degrees Of Freedom (DOF). Further, the controller should be able to operate in real-time. To meet the company’s requirements, the following is done. A linear 3ODF model of the system is derived. This is used to predict the states of the buoy in the controller. An MPC algorithm is constructed. In this, the linear model and constraints of the system are included. Then, a simulation environment is built. This is including a non-linear model of OHT’s system. The performance of the controller is tested in the simulation environment. Real-time implementation is an important aspect of the controller. The computational time required by the controller is measured in the simulations. The results imply that the controller stands a chance of being real-time implementable. However, make sure that it can be run in real-time it should be tested on the control unit that OHT plans to use in their system. A linear model of the system is used in the controller to predict the future states o the buoy. It is important that the predictions are accurate for the controller to control the system in an optimal way. Hence, the validity of the linear model is investigated. The controller is managing to predict some states better than others. However, the controller is doing a fine job with controlling the system in terms of generated power. Thus the linear model is considered to be valid for the application. An advantage with controllers based on MPC is the simplicity of tuning the controller. Changes of settings in the controller have a predictable effect on the results. For the settings found in this thesis, the system is performing fine in terms of power generation. However, more work is needed to find more optimal settings.