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This thesis describes the development of a Predictive Control to SISO and multivariable linear and nonlinear models of Dinorwig pumped storage hydroelectric power station. The results show that Generalised Predictive Control (GPC) offers significantly better performance across the plant's operating range when compared with classic PI controllers. The GPC controller produces a faster response when the station is operating with a single unit while preserving stability as the operating conditions change when multiple units are on-line. Inclusion of constraints in the GPC controller yields a fast, well-damped response in the common case when only a single Unit is in operation, without compromising stability when multiple Units are on-line. Simulation has also shown that improved power delivery is obtained when the plant is operated in frequency control mode. In the final part of the work a Mixed Logical Dynamical (MLD) predictive control was developed and applied to a MIMO nonlinear elastic model of Dinorwig. The results show that MLD predictive control is faster and less sensitive than the constrained GPC. The MLD predictive control can also be integrated with high-level plant functions.

Tidal barrages could contribute to mitigating climate change, but their deployment is not without potential welfare costs attributable to the degradation of ecosystem services. Economic valuation of natural resources provides a common metric for quantifying the disparate costs and benefits of barrage construction in a way that provides transparency when trade-offs are considered. However, very little is currently known about the value of environmental impacts associated with tidal barrages. Using the Taw Torridge estuary in North Devon as a case study, this research proposes an Environmental Benefits Assessment methodology that supports application of the ecosystem services concept to local environmental impact appraisal, and facilitates economic valuation. This methodology is novel in that it evaluates benefits, as opposed to services, and considers a comprehensive suite of benefits in a single assessment: an approach rarely attempted in practice, but essential if ecosystem services approaches are to fully support resource management needs. The subsequent empirical valuation uses stated preference techniques to examine the different ways people use and value the estuary ecosystem, determine how strongly they rank different costs and benefits of tidal barrages, and elicit willingness to pay (WTP) to reduce the habitat loss resulting from a tidal barrage development. The study provides the first empirical valuation of UK estuarine mudflats, but makes a further contribution to the environmental economics discipline by deploying both contingent valuation and choice experiment methods. Additionally, a novel application of the Analytic Hierarchy Process (AHP) is used to examine the consistency of WTP with expressed preferences for habitat protection in relation to other barrage attributes. The alternative stated preference techniques result in comparable WTP values and the importance attached to habitat loss (as measured by the AHP) is strongly associated with WTP and also with its scope sensitivity, indicating that WTP is largely driven by environmental preferences.

After many years of slow but progressive development, the wave energy industry is on the cusp of breaking through the economic and technical barriers to full scale deployment of wave energy electrical generating devices. As the major obstacles in device design are solved, and with several devices in the water, the scope for increasing their efficiency through advanced control techniques is now becoming clearer. In some cases, it would be advantageous to integrate an advanced prediction of wave behaviour (of some tens of seconds into the future) into these control methods. Past research on wave prediction has focused on utilising the Fourier theorem to deconstruct wave records and then make predictions ahead in space, with published results indicating promise. However, predicting ahead in time has so far not been achieved. This thesis takes the Fourier theorem method of prediction to its logical conclusion by exploring its limitations in predicting over both time and space. A discussion as to why these limits should exist, and possible work into the solution of the wave prediction problem, are also presented. A review of current devices under development, and the history and emergence of the wave generating industry (which is a comparatively recent technology and still in its infancy), are also included as appendices to the main thesis in order to put the work into context.

As management of the environment becomes more complex and the number of potentially conflicting issues to be balanced expands, there will be increasing and more intense debates about the course(s) of action(s) to be taken. Navigation of conflict determines trade-offs established and decisions taken, and will become progressively important, as the need to unify incompatible uses grows. Both definition and management of environmental conflict is ambiguous, lacking in understanding and mechanisms to effectively handle disputes. Interdisciplinary consideration of conflict highlights its potential to yield functional and dysfunctional aspects, recognising dispute is not inherently negative. Framing environmental debates as conflict situations may yield substantial management benefits. Using case studies (UK), this research identifies the impact of stakeholder conflict on achieving sustainable decision-making, and, seeks to develop conceptual tools to aid exploration of disputes, using the issue of hydropower development. Growing environment awareness has simultaneously emphasised the benefits of hydroelectric power and its environmental costs. In a changing policy climate, where renewable energy generation potential and environmental protection are needed, conflict between stakeholders is considerable. To meet practitioner’s needs, an understanding of conflict is needed. Findings highlight the existence and nature of stakeholder conflict. Environmental conflict is epitomized by: parameters of the problem, characteristics of the stakeholders and dispute process. Conflict is recognised as a platform for expression which may yield functional or dysfunctional consequences for decision-making. The impact of the individual is significant; variables such as perceptions, behaviours and personalities, alongside facets of the problem, characterise disputes. Assessment of conflict at a range of spatial and temporal scales, established capacity for escalation, stagnation and the development of impasses, each with differential impacts on decision-making. A conceptual framework illustrating the impact of conflict on decision-making, and role in the facilitation of change is generated. Conflict is recognised as a critical management point for facilitating sustainable decisions. From a management perspective, it is important to manage conflict at this critical point to achieve the best decision. This research outlines an alternative approach to the conceptualisation and management of environmental conflict, and highlights the significant impact of the individuals involved. The identification, application and further development of methodologies have yielded a number of conceptual tools for conflict management. Recognising the important role of conflict as a mechanism for change may be crucial for the future of environmental management.

Over the past decade within the renewable energy sector a strong research and development focus has resulted in the growth of an embryonic tidal stream energy industry. Previous assessments of the tidal stream resource appear to have neglected shallow tidal flows. This resource located in water depths of 10-30m is significant because it is generally more accessible for energy extraction than deeper offshore tidal sites and hence a good location for first generation tidal stream arrays or fences. The close proximity to shore may lead to improvements in construction feasibility and economic prospects. The objective of this project is to investigate several aspects concerning the exploitation of shallow tidal flows for energy extraction. Fundamental to this project is the importance of developing research alongside and in conjunction with industrial shallow water prototype projects. The key objectives are: (1) The development and understanding of the use of artificial flow constraint structures in the form of specifically-shaped foundations (herein described as “rampfoundations”) that constrain the flow leading to an increase in the magnitude and quality of power from marine current energy convertors (MCEC) operating in shallow tidal flows. (2) The investigation of seabed and free-surface proximity effects on the downstream wake structure of a MCEC. (3) Commercial shallow water device optimisation; utilising project results to aid with the design and development of full-scale commercial demonstrators. Through theoretical and scaled experimental modelling, and commercial collaboration the project has concluded ramp foundations could be utilised to locally increase tidal flow velocities and increase MCEC output across a tidal cycle in shallow flows. Predicted power benefits are in the region of 5-22% depending on lateral and vertical ramp channel blockage ratios. The ramp width or overall array width must therefore be tuned to the channel width to maximise power benefits. Rampfoundations will thus only be technically viable in relatively narrow channels or ideally in MCEC arrays or tidal fences. Results have shown that the downstream wake length is dependent on and varies with the vertical flow constraint and it is critical that the downstream array spacing of MCECs are tuned to the local flow depth. An optimum device height to flow depth ratio to minimise wake length has been identified. It is hoped that this ramp-foundation concept and the relationship between boundary proximity and wake length will continue to help with the development of a niche shallow tidal energy market

This study presents a numerical investigation of a generic horizontal axis cross-flow marine turbine. The numerical tool used is the commercial Computational Fluid Dynamics package ANSYS FLUENT 12.0. The numerical model, using the SST k-w turbulence model, is validated against static, dynamic pitching blade and rotating turbine data. The work embodies two main investigations. The first is concerned with the influence of turbine solidity (ratio of net blade chord to circumference) on turbine performance, and the second with the influence of blockage (ratio of device frontal area to channel crosssection area) and free surface deformation on the hydrodynamics of energy extraction in a constrained channel. Turbine solidity was investigated by simulating flows through two-, three- and four-bladed turbines, resulting in solidities of 0.019, 0.029 and 0.038, respectively. The investigation was conducted for two Reynolds numbers, Re = O(10^5) & O(10^6), to reflect laboratory and field scales. Increasing the number of blades from two to four led to an increase in the maximum power coefficient from 0.43 to 0.53 for the lower Re and from 0.49 to 0.56 for the higher Re computations. Furthermore, the power curve was found to shift to a lower range of tip speed ratios when increasing solidity. The effects of flow confinement and free surface deformation were investigated by simulating flows through a three-bladed turbine with solidity 0.125 at Re = O(10^6) for channels that resulted in cross-stream blockages of 12.5% to 50%. Increasing the blockage led to a substantial increase in the power and basin efficiency; when approximating the free surface as a rigid lid, the highest power coefficient and basin efficiency computed were 1.18 and 0.54, respectively. Comparisons between the corresponding rigid lid and free surface simulations, where Froude number, Fr = 0.082, rendered similar results at the lower blockages, but at the highest blockage an increase in power and basin efficiency of up to 7% for the free surface simulations over that achieved with a rigid lid boundary condition. For the free surface simulations with Fr = 0.082, the energy extraction resulted in a drop in water depth of up to 0.7%. An increase in Fr from 0.082 to 0.131 resulted in an increase maximum power of 3%, but a drop in basin efficiency of 21%.

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).

The Fabriconda wave energy converter is a submerged tube lying perpendicular to incoming wave fronts. The tubeconsists of a series of smaller fabric tubes, called cells, joined together longitudinally to form a larger central tube. The cells and central tube are flooded with water. Cross-sectional area changes with pressure due to the cells changing shape. The Fabriconda is therefore distensible, enabling it to extract energy from external waves. Waves induce a series of travelling bulges, and an internal oscillatory flow, in both the central tube and cells. If the speed of these bulges is close to the phase speed of the external wave, energy is progressively transferred to this flow. A power take-off system terminates the tube at the stern. A 1D mathematical model has been developed to predict the power captured by the Fabriconda, based on the application of the conservation of momentum and mass to the flow in both the central tube and cells. An analytical solution of this model has been found using an assumption of harmonic behaviour. A time-stepping finite difference solution was also derived and found to agree with the analytical solution. The results from these models have been compared with measurements. The cross sectional shape of the Fabriconda depends on the ratio between cell and central tube pressure, while the free bulge speed is dependent on the sum of the central tube and cell distensibilities. Both �ndings were supported by measurements. Measurements found that power generally peaked closer to the resonance frequency than predicted and was dependent on initial pressure. The effect of tube length on the frequency dependency of power capture and the presence of secondary peaks led to the conclusion that normal mode effects are significant to the Fabriconda's performance. This work has determined the operating principles of the Fabriconda and demonstrated that it can extract energy from waves. Predictions of full scale performance and commercial viability are not considered.

Marine renewable energy promises to provide a significant contribution to the future electricity supply. It is estimated that 17% of today's UK electricity demand could be generated from wave and tidal sources. The ambition to harvest this resource is in the public interest, as it eases the pressures on energy security, holds the potential to reduce carbon emissions and has the prospect to create a new UK industry sector worth £15 billion. From an engineering perspective, marine energy is one of the least developed renewable energy technologies and has to be regarded as unproven. The reliability of components and devices in the harsh marine environment is one of the main engineering challenges. Reliability assessments and the assurance of acceptable reliability levels are dependant on the adequacy of failure information, which is scantily available for marine energy. This thesis shows that large failure rate uncertainties impede the reliability assessment for wave energy converters and how a suite of experimental, numerical and statistical methods can be applied to improve scarcely available reliability information. The analysis of component load conditions identifies fatigue as failure mode of concern and the fatigue life of mooring lines and marine power cables is quantified in a floating wave energy application. A Bayesian statistical approach and dedicated service-simulation component testing is proposed, and implemented to improve the quality of reliability estimates and to provide relevant data and assurance. The methods presented, along with the results, will assist reliability assessment and design during early development stages, and will inform the prediction of maintenance requirements during operation. Reliable marine energy systems will be the technical enabler for the successful transition of prototype devices to a commercially viable marine energy industry.