Nowadays the demands for floating offshore wind (FOWT) have exceeded 5MW with the rapidly growing wind market. The aerodynamic environment of FOWT is more complex than onshore or fixed offshore wind turbine due to the large motions of floating platforms. The platform motion, especially pitch and surge motions, increase aerodynamic unsteadiness, wake interactions and other complex flow phenomena. These conditions influence the velocities and accelerations at the rotor sections along the blade. However, a limited simulation and load estimation capability make aerodynamic analysis a challenge. It is questionable whether some industry aerodynamic analysis codes like conventional Blade Element Momentum (BEM) theory and Generalised Dynamic Wake theory are accurate. Results indicate that current methods for predicting the aerodynamic loads may be inadequate. Aerodynamic flow effects cannot be accurately modelled using traditional BEM theory with common corrections in such a complex condition. So compared with traditional potential theory, CFD method provides more physically realistic simulation. The applying and validation of CFD method will be outlined in this dissertation. The commercial multi-purpose CFD solver STAR CCM+ 9.02 is employed for calculation of the flow using Reynolds-Average Navier-Stokes (RANS) equations in conjunction with different turbulent models. Finally, results from CFD simulations of various offshore floating wind turbines under different load conditions will be presented. CFD simulation is accurate, but time consuming. So, an optimization method will be detected to get a more accurate result and saving time. 2D CFD RANS data was instead of commonly 2D data. However, not result in the desired improvements when compared to BEM results. Therefore, a 2D airfoil data obtained by post-processing of 3D CFD computations was used. 3D results were used to estimate 2D airfoil characteristics to modify two important parameters in BEM codes: the axial and the tangential induction factors by applying the reduced axial velocity method by getting the local angle of attack from CFD solutions. This thesis will demonstrate that the aerodynamics of offshore floating wind turbines is sufficiently different from conventional offshore and onshore wind turbines, warranting the use of higher fidelity analysis approaches. It is obvious that thexxiiiplatform motions will have a great effect on unsteady aerodynamic performance of the wind turbine rotor. This thesis will study and explain the rules and reasons of this phenomenon in detail. Future offshore floating wind turbine designs should strive to either minimize platform motions or be complementarily optimized, via higher fidelity aerodynamic analysis techniques, to account for them. It is believed that this dissertation is the first in-depth study of offshore floating wind turbine aerodynamics and the applicability of various analysis methods.

This study concerns the potential sociotechnical transition of the current UK centralised alternating current (AC) electricity system to one where distributed direct current (DC) systems may proliferate. The development of the new distributed DC system has the potential to address a number of global challenges including the UN’s 17 Sustainability Challenges, particularly in terms of city and disaster resilience, energy security and energy independence. With the development of renewables and small-scale storage, among other technologies, this transition becomes a technical possibility. As transitions theory identifies energy systems as sociotechnical, transitions are a complex and people-centred process, an issue that has been identified that creates barriers to technical transitions. The multi-level perspective (MLP) is used as the theoretical framework and its applicability for future transitions is considered. The research proposes a “bottom-up” approach, focused on the demand side within the built environment, to avoid the transition developing into a wicked problem. Using a mixture of primary interview data, analysed using thematic analysis, supported by data, from published academic and industry/governmental literature, a multi-method case study approach is used to develop a transitions model between the “as is” state and the potential future state with DC systems. Also identified were the institutions within the social and technical networks of the electricity regime, barriers and enablers to the transition, boundary points between the networks and the structurations of institutions within these networks. Key findings are a lack of interdisciplinary thinking among different academic disciplines, a lack of DC standards and home appliances, and that DC is in focus for the office rather than the home. Knowledge dissemination especially via education, government procurement and energy policy, and the importance of independence from the market are key components for a successful proliferation. A conundrum connecting renewable generation, the carbon debate and energy policy, is identified. With a deeper understanding of the regime, landscape and with a multi-systems approach, a tentative solution is provided. Contributions to knowledge are: the transitions model; the sociotechnical characterisation of the electricity system; a better understanding of how liability, living standards, disaster risk reduction and city resilience can be impacted by failure chains associated with power cuts; and a deeper understanding of the MLP model.

Lightning protection is an issue of safety for humans and their properties. Although humans may be protected against a direct lightning strike if they are situated into a modem structure, electrical and electronic appliances, which equip the structure may suffer fatal damages. These damages can be avoided by taken the necessary protective measures. Depending on the low voltage distribution system that connects the structure, the necessary protective measures may vary due to different risks that are associated with each low voltage distribution system. Most of the low voltage distribution systems that can be found in Europe were examined considering the effects that can occur when a customer connected to them becomes a victim of a direct lightning strike. The majority of this work was based on theoretical research, by using software simulations, which has focused on the risk and the technical issues that need to be considered when designing a lightning protection system for a low voltage installation. The impact of various elements that are part of a low voltage distribution system such as cables and earthing systems was assessed. More emphasis was given .to the requirements that low voltage surge protection devices should fulfil. The practical part of this research has examined the validation of the simulation results by comparing them with scaled down experiments. High voltage and current generators were used for testing surge protection devices and low voltage plant equipment such as cables, fuses etc. The main objective of this research project was to contribute into the understanding and modelling of the transient behaviour of low voltage systems due to a direct lightning strike and into the necessary precautions that need to be taken.

No description available.

No description available.

The design of liberalised electricity markets (e.g., the energy, capacity and ancillary service markets) is a topic of much debate, regarding their ability to trigger adequate investment in generation capacities and to incentivize flexible power system operation. Long-term generation investment (LTGI) models have been widely used as a decision-support tool for generation investments and design of energy policy. Of particular interest is quantification of uncertainty in model outputs (e.g., generation projections or system reliability) given a particular market design while accounting for uncertainties in input data as well as the discrepancies between the model and the reality. Unfortunately, the standard Monte Carlo based techniques for uncertainty quantification require a very large number of model runs which may be impractical to achieve for a complex LTGI model. In order to enable efficient and fully systematic analysis, it is therefore necessary to create an emulator of the full model, which may be evaluated quickly for any input and which quantifies uncertainty in the output of the full model at inputs where it has not been run. The case study shows results from the Great Britain power system exemplar which is representative of LTGI models used in real policy processes. In particular, it demonstrates the application of Bayesian emulation to a complex LTGI model that requires a formal calibration, uncertainty analysis, and sensitivity analysis. In power systems with large amounts of variable generation, it is important to provide sufficient incentives for operating reserves as a main source of generation flexibility. In the traditional unit commitment (UC) model, the demand for operating reserves is fixed and inelastic, which does not reflect the marginal value of operating reserves in avoiding the events of load shedding and wind curtailment. Besides, the system-wide reserve constraint assumes that the operating reserve can be delivered to any location freely, which is not true in real-world power system operations. To recognize the value and deliverability of operating reserves, dynamic zonal operating reserve demand curves are introduced to an enhanced deterministic UC model for co-optimizing the day-ahead schedules for energy and operating reserves. In the case study on the RTS-73 test system, comparisons are made between the choices of reserve policies (e.g., single, seasonal or dynamic zones) and of different reserve zonal partitioning methods. Results suggest that the enhanced deterministic UC model produces on average lower operational cost, higher system reliability and higher energy and reserve revenues than the traditional one. Finally, we discuss future directions of methodological research arising from current energy system challenges and the computer models developed for better understanding of the impacts of market incentives on power system planning and operations.

The increase in the anthropogenic greenhouse gases has severely damaged the environment in terms of pollution and global climate change. It is capturing the carbon dioxide from the present and future power plants that could save the climate. The post-combustion CO2 capture system using amine wet scrubbing is investigated in detail for natural-gas fired power plant from pilot-scale to commercial-scale level. The research work is focused on the investigation of the different innovative modifications to the micro gas turbine (MGT) including exhaust gas recirculation (EGR), steam injection and humid air turbine. The process models are developed for both MGT and pilot-scale amine-based CO2 capture plant. The MGT model is tuned and validated with extensive experimental data at different part load conditions for base case, CO2, steam and simultaneous CO2 and steam injection to the default MGT. The thermodynamic behaviour, emissions, system efficiency and the sensitivity of the base case MGT for ambient conditions are explored. The robust model is extended for EGR, steam injection and humid air turbine system models; and process system performance comparison for the different modifications is assessed for possible recommendation. In addition, the impact of the operating conditions and locations of the EGR on the performance of the MGT is also analysed. Further, the effect of the enhanced CO2 on the extensively validated pilot-scale amine-based CO2 capture plant integrated with MGT is examined. In addition, the sensitivity analysis of the pilot-scale amine-based CO2 capture model is studied to quantify the effect of the operating parameters on the system performance and to estimate the optimum operating envelope. The EGR at 55 % resulted in a 20.5 % decrease in specific reboiler duty from the pilot-scale amine-based CO2 capture plant at the CO2 capture rate of 90 % for monoethanolamine at 30 wt. % aqueous solution. Furthermore, a techno-economic process design and/or scale-up of the commercial-scale amine-based CO2 capture system to service about 650 MWe of the natural gas-fired power plant system with and without EGR is investigated for varying EGR percentage. Finally, thorough comparative potential for the natural gas, coal, biomass fired and co-firing of coal and biomass power plants integrated with CO2 capture and CO2 compressions system are explored for different cases of each power plant. The biomass firing resulted in about 40 % increase in fuel flow rate for the constant heat input case while it resulted in 30 % derating of the power output for the constant fuel flow rate case. The comparative potential of gas-CCS, coal-CCS and BECCS has shown that the NGCC with EGR resulted in the least efficiency penalty on integration with CO2 capture and compression system due to the higher net efficiency. However, coal and biomass fired power plant resulted in the least specific losses per unit of the CO2 capture on integration with CO2 capture and compression system due to the higher specific CO2 capture.

It is well known that the torque density in electrical machines is limited by magnetic saturation and thermal constraints on the winding insulation and permanent magnets (PMs). In particular, doubly salient electrically-excited machines with the armature and DC windings on the stator, for example, the variable-flux machine (VFM), have (a) limited stator slot area for both windings, (b) severe magnetic saturation due to the DC excitation, and (c) negligible reluctance torque, and may exhibit high copper loss and high magnetic saturation. A novel method to alleviate magnetic saturation in the stator of VFMs is proposed. It is achieved by pre-magnetizing the stator core using PMs placed in the stator slots. The PM effects and performance improvements are analyzed by the finite element method based on the frozen permeability (FP) method. The developed novel VFM with PMs is a hybrid excited stator slot PM (HSSPM) machine. The basic operation principle and the electromagnetic performance with different stator and rotor pole combinations having double (all pole wound concentrated windings) and single layer (alternate pole wound concentrated windings) windings are investigated. HSSPM machines have improved electromagnetic performance and also retain the good flux regulation capability of VFMs. They can also be operated without the DC excitation, i.e. only with the armature and PM excitation. Thus, a new machine configuration – stator slot PM machine (SSPM) is further developed and investigated in terms of the influence of stator/rotor pole combinations and double and single layer windings. The newly developed SSPM machine also has the potential for fail-safe capability in the event of drive faults, and in addition, the requirements on the DC inverter and controller can be eliminated. The finite element predicted electromagnetic performances of HSSPM and SSPM machines are experimentally validated. Finally, the PM- and iron losses in HSSPM and SSPM machines having different stator/rotor pole combinations with single and double layer windings and their demagnetization ratio are analyzed. The influence of leading design parameters on their machine losses and efficiency is further investigated and their electromagnetic performance compared.

This thesis reports on research undertaken to investigate the end-of-life management of solid oxide fuel cells (SOFC), through the definition of a framework and the development of a multicriteria evaluation methodology which together support comparison of alternative end-of-life scenarios. The primary objective of this research is to develop an understanding of the challenges and opportunities arising during the end-of-life phase of the technology, such that any conflicts with end-of-life requirements might be addressed and opportunities for optimising the end-of-life phase fully exploited. The research contributions can be considered in four principal parts. The first part comprises a review of SOFC technology and its place in future sustainable energy scenarios, alongside a review of a growing body of legislation which embodies concepts such as Extended Producer Responsibility and Integrated Product Policy. When considered in the context of the life cycle assessment literature, which clearly points to a lack of knowledge regarding the end-of-life phase of the SOFC life cycle, this review concludes that the requirement for effective end-of life management of SOFC products is an essential consideration prior to the widespread adoption of commercial products. The second part of the research defines a framework for end-of-life management of SOFCs, which supports clarification of the challenges presented by the SOFC stack waste stream, as well as identifying a systematic approach for addressing these challenges through the development of alternative end-of-life management scenarios. The framework identifies a need to evaluate the effectiveness of these end-of-life scenarios according to three performance criteria: legislative compliance; environmental impact; and economic impact. The third part of the research is concerned with the development of a multi-criteria evaluation methodology, which combines conventional evaluation methods such as life cycle assessment and cost-benefit analysis, with a novel risk assessment tool for evaluating compliance with current and future legislation. A decision support tool builds on existing multi-criteria decision making methods to provide a comparative performance indicator for identification of an end of-life scenario demonstrating low risk of non-compliance with future legislation; low environmental impact; and a low cost-benefit ratio. Finally, the validity of the framework for end-of-life management is tested through the completion of two case studies. These case studies demonstrate the flexibility of the framework in supporting a reactive end-of-life management approach, whereby end-of-life management is constrained by characteristics of the product design, and a proactive approach, whereby the impact of design modification on the end-of-life phase is explored. In summary, the research clearly highlights the significance of the end-of-life stage of the SOFC life cycle. On the one hand, failure to manage end-of-life products effectively risks undermining the environmental credentials of the technology and is likely to lead to the loss of a high-value, resource-rich material stream. On the other hand, the early consideration of aspects identified in the research, especially while opportunities remain to influence final product design, represents a real opportunity for optimising the end-of-life management of SOFC products in such a way as to fully realise their potential as a clean and efficient power generation solution for the future.

Solar sails are spacecraft that utilise the Solar Radiation Pressure, the force generated by impinging photons, to propel themselves. Conventional actuators are not suitable for controlling the attitude of solar sails therefore specific attitude control methods have been devised to tackle this. One of these methods is to change the centre of pressure with respect to the center of mass thus creating a torque. Reflectivity Control Devices (RCDs) have been proposed and successfully used to change the centre of pressure. Current methods that utilise RCDs have control authority over two axis only with no ability to control the torque about the normal of the sail surface. This thesis extends the state of the art and demonstrates 3-axis control by generating arbitrary torque vectors within a convex polyhedron. Two different RCD materials are considered, transmission and diffusion technologies both compatible with the proposed concept. A number of metrics have been developed which facilitate the comparison of different sail configurations. One of these metics is the sun map which is a graphic representation of the sun angles for which control authority is maintained. An iterative design process is presented which makes use of the metrics developed and aids in the design of a sail which meets the mission requirements and constraints. Moreover, the effects of different parameters on the performance of the proposed control concept are discussed. For example it is shown that by alternating the angle between the edge and middle RCDs the control authority increases. The concept's scalability has been investigated and a hybrid control scheme has been devised which makes use of both RCDs and reaction wheels. The RCDs are complemented by the reaction wheels to achieve higher slew rates while in turn the RCDs desaturate the reaction wheels. Finally, a number of simulations are conducted to verify the validity of the proposed concept.