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In recent years, kites are beginning to be considered as viable alternatives to oshore wind turbines, due to the potential reduction in levelised cost of energy and the increase in exploitable resource due to versatility of kite based generators. This thesis focuses on the kite carousel design, which consists of a ground based vertical axis generator with a number of kites attached. The kites are flown in a pattern that induces motion in the generator and thus produces power. This method of energy harvesting allows substantial scaling of devices. Device output depends not only on the available ow and kite size, but is further influenced by the length of the kite tether, the radius of the carousel structure, and the number of kites attached. Although kites have been studied extensively in recent years, there is no consensus on the optimum design and configuration of the carousel. The thesis presents a minimum order model of a kite carousel. This numerical model is used to indicate the driving principles of the carousel and the importance of flightpath design on output. The presented model can be applied to various ow conditions. However, due to the definition of dimensionless power used, there is a scaling dependency of the model outputs regarding the kite tether length. An alternative method of describing the swept area of the carousel, based on the swept area of the kite flightpath, is used to mitigate this and indicate device efficiency in power extraction. The flightpath optimisation and parameter study illustrate this scaling dependency and highlight the effect of the carousel radius and tether length on the optimized flightpath. These results then inform a case study for a carousel placed in a representative tidal flow. The case study describes a device with 8 kites attached to a 5 m diameter carousel that produces 64 kW over a representative tidal cycle with a peak flow of 2.2 m/s.

Wind turbine operation in icing conditions has been researched for the last 30 years because of the impact of icing on both wind projects' profitability and financial viability for wind sites, which offer abundance of wind kinetic energy. Much work has been published on modelling ice induced energy losses and quantifying the impact of icing on the overall performance of wind turbines. However, these findings have not led to universally integrated solutions and approaches to adapt wind turbines to different icing events by advanced operational strategies. This project used the numerical modelling approach for wind turbines subjected to icing to investigate how wind turbine performance in icing conditions can be improved through the design of different ice mitigation operational strategies. Icing events with variable duration, wind speed, ambient temperature and icing parameters were defined to obtain expected energy losses and ice mass accumulation for evaluating different operational strategies for ice mitigation. Wind tunnel experimental measurements were conducted to facilitate the comparison of XFoil and Fluent for estimating aerodynamic degradation and quantifying the sensitivity of predicted energy losses to aerodynamic modelling tools. For preliminary studies and conceptual design of operational strategies it was concluded that XFoil can be used for a range of icing events. Thus, it was used in combination with lewINT ice accretion code and blade element momentum method to demonstrate a novel approach for selecting the best operational strategy or set of strategies to achieve maximum energy generation during periods of icing. Derating by tip-speed ratio modification during icing was investigated with a focus on its application and advantages. Thus, unlike other studies, a systematic method for choosing modified tip-speed ratio values was developed based on the installed electrical generator and energy payback time scheme. The strategy was found extremely favourable for short and extreme icing events with reduction of icing losses up to 23 %, and accumulated ice mass up to 30 %. The method for comparison outlined in this project allowed derating to be compared against other operational strategies. It was established that for longer and milder icing events the design strategy should be maintained. Non-optimised anti-icing systems was found to be a preferred operational strategy for ambient temperatures above -5ºC providing the cost of the system was no higher than 2 % of the turbine's capital cost and there were more than 43 short extreme or 26 long mild icing event occurrences per year. For the selected icing events, the operational shutdown strategy was not found to be a viable option. The presented method allows for the comparison of other ice mitigation strategies providing their cost for implementation and operation can be incorporated into the viability and performance analysis. The work covered in this project proposed a more holistic approach on studying ice mitigation strategies, which would facilitate integrated solutions and higher fidelity studies to develop novel ice mitigation techniques or advance current solutions. Further development of the presented methods would be needed to transfer the results that can be obtained from this analysis from preliminary conceptual design stage to prototype and test stages. However, this is one of the first studies to attempt advancing and designing different operational strategies together to achieve more effective adaption of wind turbines in cold climates.

Concerning the fact that the number of wind turbines is increasing worldwide, it seems necessary to implement monitoring systems. To respond to this demand, this PhD thesis studies different fault diagnosis techniques in order to improve the reliability and reduce maintenance costs. Based on the fact that a considerable amount of data is stored via SCADA in every industry nowadays, the methods developed on historical data (called data-driven methods) can be very beneficial. By analysing the historical data, the changing trends of a nonlinear dynamics, such as a wind turbine, can be predicted. Moreover, by applying suitable approaches, one can distinguish different faults based on the output of the system. The first part in this research reviews a neural network identification method by decoupling linear and nonlinear parts of a wind turbine model. As for the linear part, a Luenberger observer is designed, while for the nonlinear part, a neural network observer is proposed. By having an identification model for a wind turbine system, residual-based fault detection is studied. The second part in this research proposes a novel neuro-robust fault estimation method to deal with the occurred faults on actuators or sensors. The challenge in this method is environmental disturbances and sensor noises. To overcome these problems and simultaneously estimate the faults and the states, an augmented system is proposed in different scenarios of actuator faults or sensor faults. Then, a neural network updating rule is calculated along with the robust performance index to fully achieve this goal. The stability of the augmented system is guaranteed by having a Lyapunov function and input-to-state stability criteria. The third and final part in this research studies different structures of Convolutional Neural Networks for the problem of fault classification in a wind turbine. As working with time-series signals is challenging in deep learning classification, a pre-processing analysis is applied to prepare the data of system outputs for the input of the model. Each proposed method is applied to a 4.8 MW wind turbine benchmark and obtained results are illustrated and discussed to validate the accuracy and performance of the approach.

The increased demand for sustainable energy sources has resulted in a boom for the wind energy industry. The industry therefore wants to manufacture wind turbine blades at higher production rates and for the blades themselves to be more efficient. The project undertaken assessed anhydride-cured epoxy resins alongside a novel manufacturing process, vascular curing, to develop both material and manufacturing capabilities to achieve these goals. This study initially characterised three anhydride-cured epoxy resins developed by Hitachi Chemical Company Ltd. These resins were shown to offer increased interfacial adhesion to glass fibres over an amine-cured epoxy industry benchmark, with an increase in interfacial shear strength of 24-66% depending on the anhydride. Preliminary trials on carbon fibre were conducted due to demand for larger blades to increase energy efficiency, this again showed improved performance was attained for the anhydride-cured epoxy resin, with a 34% increase in interlaminar shear strength over the industry benchmark. Composite wind turbines are currently manufactured using long and low temperature cure cycles to prevent thermal gradients developing in the part which lead to manufacturing defects, ultimately limiting the production rate and incurring manufacturing costs. A proof-of-concept setup to experimentally validate vascular curing for thick composite sections (50 mm) was developed. This novel manufacturing process embedded a secondary heating mechanism within the part. It was shown both experimentally that the embedment of a vascule network reduced the observed peak exotherm on average by 25 °C. Overall, this work has furthered knowledge of anhydride-cured epoxies and showcased that they could have much wider use, due to the improved interfacial adhesion to both glass and carbon fibres. The vascular cure laboratory-scale setup has been developed and shown exciting preliminary results. With further development both these resins and processing methods could both be integrated into current industrial processes to enable better quality wind turbine blades to be made at higher production rates to meet demand.

Scaling up of rotor technology is a key challenge faced by industry for future turbines. Larger rotors provide greater total energy capture, but also suffer increased loads on the blades and, subsequently, accelerated wear of all components of the turbine. To reduce the wear, load alleviation techniques have received significant interest from both academia and industry. Various authors have proposed both active and passive solutions, and one prominent technique is the implementation of Bend-Twist Coupling (BTC). When used to induce twist towards feather under flap-wise bending, BTC has been shown to reduce the maximum loads on the turbine drastically. While the advantages of BTC are well documented, the underlying modelling approaches are still mostly unvalidated. Code-to-code comparisons and validation exercises between techniques have shown significant discrepancies. It has also been demonstrated that at least some of the difference can be traced to small discrepancies in inputs and cross-sectional representation. This thesis contributes to the body of research on cross-sectional modelling of wind turbine blades through both numerical and experimental work. Using two cross-sectional modellers (i.e. BECAS and VABS) and 3D Finite Element Models in ABAQUS, a numerical sensitivity study has been carried out. Comparison of the compliance terms for three typical turbine blade cross-sections highlights the innate performance variability caused by manufacturing tolerances and modelling simplifications. The results show the importance of the Trailing Edge (TE) bondline, previously unstudied, to the accurate prediction of the stiffness of compliant and coupled beams. The TE bondline is also shown to contribute meaningfully to the disagreement observed between 3D shell and solid model predictions. The numerical insights are supported by experimental work through testing of several demonstrators, designed to contain BTC, under cantilever loading. Each of demonstrator has a different cross-sectional design, capturing the influence of various common features of wind-turbine blade cross sections. Together, these demonstrators help validate the modelling techniques investigated and provide important practical insights for cross-sectional properties of compliant and coupled beams. As such, this work helps establish best practices for modelling and testing of bend-twist coupled beams. In doing so, it also provides reliable experimental data for validation and benchmarking purposes of current and future numerical and/or analytical modelling techniques.

The present work investigates the influence of properties variation of Diesel fuel in the range of injection pressures from 60MPa to 450MPa on nozzle flow and cavitation. The PC-SAFT equation of state is utilised to derive physical property predictions of a grade no.2 Diesel emissions certification fuel. Four candidate multicomponent Diesel surrogates are modelled. Density, viscosity and volatility predictions are compared to experimental data from several other Diesel fuels and against Peng Robinson. PC-SAFT calculations are performed using different sources for the pure component parameters, namely LC and GC methods. An eight-component surrogate yields the best match for Diesel properties with a combined mean absolute deviation of 7.1% from experimental data found in the literature for conditions up to 373 K and 500 MPa. The vapour-liquid equilibrium of this surrogate is then calculated with a novel algorithm, which uses as independent variables the mixture composition, density and temperature. This algorithm is based on unconstrained minimisation of the Helmholtz Free energy via a combination of the successive substitution iteration and Newton-Raphson minimisation. The reliability of two different methods presented in the existing literature is assessed for 7 different cases. The properties of the eight component surrogate are derived and put onto tables to be used in simulations. These simulations are performed on a tapered heavy-duty Diesel engine injector at a nominal fully open needle valve lift of 350μm. Two approaches have been followed: (i) a barotropic evolution and (ii) the inclusion of wall friction-induced thermal effects. Results indicate a significant increase in the mean vapour pressure of the fuel and an unprecedented decrease of cavitation volume inside the fuel injector with increasing injection pressure. This has been attributed to the shift of the pressure drop from the feed to the back pressure inside the injection hole orifice as fuel discharges. The study links friction-induced thermal effects to the preferential cavitation of the fuel components. Lighter fuel components are found to cavitate to a greater extent than heavier ones, independently of the initial fuel composition. Moreover, the final vapour cloud composition was found to differ with injection pressure, as the components within vaporise at their respective rhythm according to their molecular structure and global pressure/temperature conditions.

In order to improve the aerodynamic performance of the vertical axis wind turbines (VAWTs), the presented research seeks to use the novel idea of three different flow control techniques, Gurney flaps (GF), passive micro vortex generators (MVGs) and leading-edge protuberances to extend the operating range and to suppress aerodynamic instabilities for a small-scale H-type VAWT. Two dimensional simulations are used to assess the impact of various GFs on the isolated aerofoil. It is found that the GFs can enhance the aerodynamic performance of the aerofoil by generating more lift and delaying the onset of stall. The benefit of having GF of 1%c and 2%c height is also shown for H-VAWT achieving significant power improvement at low tip speed ratios (TSRs). The main function of the MVGs is to transfer momentum from outside into the inner boundary layer, leading to the suppression of flow separation. In this study, a set of properly designed MVGs is found to increase the lift and reduce the drag of the isolated aerofoil beyond the stall angle. The VAWT with MVGs control shows significant enhancement in power generation at high TSR ranging from 2 to 3.5. The optimum configuration of the MVGs is found to be located at 20% chord length of the blade, having a rectangular shape and a mounting angle of 16◦. Sinusoidal wave protuberances of the leading edge are numerically investigated to obtain the detailed flow fields for analysis and visualization. The results show that leading-edge protuberances with proper design can improve the lift of the blade near the stall angle and the power generation of the VAWT at TSR ranging from 1 to 2.5. The three passive flow controls have been numerically investigated to show their ability to improve the aerodynamic performance of VAWTs and their strong potential for this sector.

Floating offshore wind technology has high potential due to the renewable energy goals and the vast deep water ocean areas, however, still faces several challenges until achieving commercial market uptake. Floating concepts have to gain economic competitiveness and deal with more complex coupled system dynamics and greater uncertainties. This makes modeling, simulation, and reliability-based design optimization indispensable. However, reliability assessment and design optimization of floating wind turbines has not yet been coupled. - This is precisely the focus of this thesis. The overall aim is to derive guidelines for reliability-based design optimization of floating wind turbine support structures, taking target safety levels and failure mechanisms from existing standards into account and applying them in such novel concepts. To achieve this, reliability methods applied in the offshore and marine renewable energy industry are reviewed, classified, and investigated with respect to suitable procedures for reliability assessment of offshore wind turbine systems. Addressing the aspect of floating wind, the large diversity of existing floating support structures is assessed, focusing on their suitability for offshore wind farm deployment. Based on this, a reference floating wind turbine system is defined, for which an aero-hydro-servo-elastic coupled model of dynamics is developed and verified. Additionally, a holistic framework for automated simulation and optimization is developed and applied to different design optimization tasks: based on global limit states, addressing innovative design solutions or the future trend towards larger MW-class wind turbines, and finally including reliability criteria. The developed model, framework, and approaches - especially the concept for combining floating wind turbine design optimization with reliability assessment in a computationally and time-efficient manner - are of high value for both research and industry. The knowledge and outcomes of this thesis offer a broad range of future applications and pave the way towards economic and reliable floating support structure designs.

This thesis encompasses a holistic review of the development trends in wind turbine technology (onshore and offshore) and the challenges perceived at the stages of design, construction and operations of modern-day wind energy technology (Friedrich and Lukas, 2017). The main focus of this study is to evaluate the risks associated with offshore wind farm development (OWFD). This is achieved by first estimating those perceived risks, understanding the relative importance of each individual risk, and carrying out an assessment using a specialist analytical tool known as AHiP-Evi. AHiP-Evi was developed through a combination of application of Analytic Hierarchy Process (AHP) and Evidential Reasoning (ER) techniques. The AHP was used to ascertain the weighting of the respective risk variables according to their relative importance, while the ER was used to evaluate the aggregated influence of the collective risk variables associated with the OWFD. Finally, a specific modelling tool known as BN-SAT (Bayesian Network Sensitivity Analysis Technique) was developed to evaluate the probabilities of occurrence of the variable nodes and their overall impacts on the decision node (OWFD). The BN-SAT is comprised of a combination of Bayesian networks (BNs) concepts and a sensitivity analysis (SA) approach. The AHiP-Evi model initially developed in this study is transformed into the BN structure in order to compute the conditional and unconditional prior probability for each starting node using the NETICA analytical software to determine the aggregated impact of the specific risk variables on the OWFD. The outcome from this modelling analysis is then compared to the initial assessment carried out by the application of the AHiP-Evi modelling tool in order to validate the robustness of both modelling tools. In the case study of this research, the percentage difference of the outcomes of the two models is insignificant, which demonstrates the fact that both systems are effective. The Fuzzy Analytic Hierarchy Process (FAHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) were integrated to develop a specific model for the selection of best-case risk management technique (RMT). Based on the decision makers’ (DMs) aggregated judgements, it was possible to compute the values and determine the best-case RMT dependent on the decision variables driving the decision - for example, costs and benefits, through the developed integrated model known as FAHP-FTOPSIS. The outcome of this selection model has been seen to be reasonably practical and a successful conclusion of the research contribution. Awareness of the aggregated impact of the risk variables is important in making the decision about appropriate investments in a strategic improvement of risk management and efficient resource allocations to the offshore wind industry.

Due to the challenging wind potential and the increasing energy demand, it is important to design the future wind turbines to operate efficiently at low wind speeds. The focus of this thesis is about the small scale straight-bladed Vertical Axis Wind Turbine (VAWT) due to its competitive advantages and promising market. This thesis aims to provide an in-depth understanding of the aerodynamics of small VAWTs and the effect of blade pitch in the turbine performance at low wind speed conditions. Moreover, this thesis proposes a novel procedure for the analysis of turbine performance and the estimation of the Angle of Attack (AOA). This enables the design of the most appropriate fixed pitch and variable pitch configurations. Based on the unsteady Reynolds-Averaged Navier-Stokes (uRANS), the state-of-the-art Computational Fluid Dynamics (CFD) simulation is utilised as a modelling approach and this enables high fidelity analysis with a reasonable computational cost. In order to find the most appropriate CFD methodology for the modelling of a VAWT, detailed verification and validation studies are carried out and this includes the comparisons of the CFD predictions against detailed instantaneous experimental data.

This thesis is a compilation of three studies that give a detailed understanding of the impact of manufacturing variability on high pressure turbine rotor blade aerodynamic and proposes several means by which the effects of manufacturing variability can be mitigated. A prerequisite for the aerodynamic studies is the ability to process the measurements of real blades. Structured-light scanning was used measure the manufactured blades and geometry processing scripts were developed to extract the manufacturing variability once the blades were aligned to the design-intent coordinate system. The extracted manufacturing variability were then mapped to computational fluid dynamics (CFD) models and assessed aerodynamically. For the first study, blade sections were analysed using MIT's Multiple Blade Interacting Streamtube Euler solver (MISES). The distribution of blade surface curvature was found to influence the blade surface velocity distributions, which consequently affect the development of the boundary layers, ultimately contributing to changes in momentum deficit and aerodynamic blockage. The recommendation here was to measure the blades with sufficient resolution to resolve curvature in order for a meaningful performance assessment to be made. The second study analysed the measured blades using Reynolds-Averaged Navier-Stokes (RANS) CFD. From this study, an exit flow angle-based blade reorientation procedures and a functional sentencing methodology were proposed. For a statistically non-representative sample, these changes to the manufacturing process reduces the spread in stage capacity from ~±0.5% to ~±0.15% while increasing the manufacturing yield rate from ~68% to ~97%. The third and final study was performed using RANS CFD to understand the multi-passage behaviour of assembled HPT rotor blade rows. This study included the shroud and the flow structures around the tip of the blade were found to be the result of the interaction between the horse-shoe vortex and the pressure fields of the blades. In a multi-passage environment where periodicity is relaxed, the flow structures were also dependent on how the blades interacted with one another. However, despite the change in flow structures, averaging results obtained from single-passage CFD models gave good approximations of multi-passage stage capacity and mass-averaged exit flow angle.

The impact of corrosion and biofouling on offshore wind turbines is considered to be a key issue in terms of operation and maintenance (O&M) which must be better addressed. Early design assumptions for monopile foundations anticipated low, uniform corrosion rates in a sealed compartment that would be completely air- and water-tight. However, operational experience has shown that in practice it is very difficult to maintain a fully sealed compartment, with seawater and oxygen ingress frequently observed within many monopiles across the industry. A key concern is that this situation may accelerate corrosion of the internal surfaces. On the external surfaces, the accumulation of biofouling is known to impede the safe transfer of technicians from vessel to transition piece (TP) and requires frequent cleaning. It is also likely to influence the dynamic behaviour of the foundation due to the added weight and the hydrodynamic loading due to thickness and surface roughness changes. There is sufficient evidence to suggest that the current offshore wind guidelines on biofouling could be improved to optimise the design margins. This thesis investigated the influence of internal monopile corrosion and external biofouling growth on the turbines at Teesside Offshore Wind Farm (owned and operated by EDF Energy). At Teesside, the primary drivers of internal monopile corrosion are identified as temperature, oxygen, pH and tidal variation. The influence of each of these parameters on the corrosion rate of monopile steel were investigated in a series of laboratory experiments and in-situ monopile trials. The experimental study was conducted at EDF laboratories in France using 186 corrosion coupons that were exposed to various treatments simulating internal monopile conditions. At Teesside, 49 coupons were suspended at various internal monopile locations across 5 foundations. In both cases, the weight loss measurement of coupons over time was used to determine the corrosion rates. Results suggest that tidal (wet/dry cycles) low pH and oxygen ingress have the greatest influence on the corrosion degradation of unprotected monopile steel. Internal tidal variations create a particularly aggressive corrosion environment. A decision tree matrix has been developed to predict corrosion rate classification (high/medium/low) under a range of environmental conditions. In parallel, a biofouling assessment was conducted at Teesside Offshore Wind Farm to determine the type and extent of marine growth on the intertidal and submerged zones of turbines. This has enabled a better understanding of the species diversity and community morphology but has also facilitated the development and testing of two sampling methodologies for the intertidal and subsea regions of offshore wind turbines; scrape sampling and remotely operated vehicle (ROV) surveying, respectively. The results of the assessment suggest a zonation pattern of marine growth with depth that is consistent with findings from other offshore wind farms and platforms. A super abundance of the non-native midge species T. japonicas at the intertidal zone has also been observed at other offshore wind farms in Belgium and Denmark, however, this is first evidence of its existence at a UK offshore wind farm. Removal of biofouling from the intertidal zones and jet-washing has now been optimised to coincide with peak settlement periods of mussels and barnacles. Image analysis and 3D mapping was conducted on the subsea ROV video footage to estimate thickness, roughness and added weight of biofouling. This research provides an initial investigation into the effects of internal corrosion and external biofouling on monopile foundations at Teesside Offshore Wind Farm. The methodologies developed for this investigation and the results are critically discussed in the context of asset life assessment and improvements are suggested in further work.

Metrological features like vertical gradients in wind speeds, wind direction, and turbulence intensity are becoming more decisive in design and deployment of wind turbines (WT). This has fueled a need for new measurements techniques to collect the specific parameters for structural health monitoring (SHM) of the wind mast and blades. Importantly it has led to an increase in non-contact measurement techniques as well as the need for better-validated modelling techniques that address problems of (a) flutter and (b) type and component certification of WT blades and masts. One such novel approach is the use of Ground-Based Radar (GBR) as a non-contact SHM sensor. GBR are increasingly being used either as a vibration‐based or as guided‐wave‐based SHM sensors for monitoring of WT blades and masts. The study contributes to the monitoring of blades and masts during design, testing, and in-field operation. The optimal monitored condition parameters (CP's) that the GBR can utilise are identified as the component modal frequencies and deflection at blade tips and tower nacelle. The research gap and subsequently novelty being addressed include: First, the apparent lack of singular studies that consider a portable GBR for SHM of in-field blades and masts of level 1 damage detection while the WT is operating normally under international IEC standards 61400-1 Design load conditions (DLC) 1.1. to 1.5. Secondly, the apparent lack of studies for utilising GBR under SHM framework for WT operating in actual conditions. Previous studies (and not under SHM framework) focussed on WT in a parked position or under laboratory set-ups. This research thus sought two main objectives (a) GBR determination of the two SHM Condition Parameters (CP), modal frequencies and flapwise deflection, for an operating in-field wind turbine blade and masts and (b) Integration of GBR into the 3-tier framework and its validation thereof. In achieving these research objectives and answering the research questions, a conceptual framework cognisant with type and component certification for the blade and mast design (IEC 61400-1, IEC 61400-2) and full blade SHM under IEC 61400-23. Using simplified Sammon mapping, 2D visualization techniques, Operational Modal Analysis (OMA's) and three set of multi-sensor experiments the objectives of the research were progressively achieved. The first experiment involved GBR determination of the frequency on a Steel I-beam hit by an impact hammer with an accelerometer as the ground-truth. The second involved use of a custom-made rotating arm to acquire deflection of a beam structure in a rotating motion. Third experiments focussed on the CP acquisitions from an operating in-field WT. The main WT components being the WT blades and tower. The GBR results were in the first experiment validated using a Geographical Positioning System (GPS). The aim of these 2 experiments was primarily to assess the capability of the GBR to acquire CP's, the accuracy of the acquired values and most importantly CP's acquisitions by GBR within a 3-tier SHM framework. Correction of the GBR results was also undertaken using Welch Power Spectrum estimation and Group delay response for the frequencies results. The third experiment had its resulted validated using an OMA's in form of a Campbell diagram under a 3-tier SHM framework. The key results from the 3 cluster experiments were as follows: 1.I-Beam experiment: - Comparisons between the GBR results with those of an accelerometer indicated a divergence of ±0.1% from accelerometer results when a correction was applied, and ±3% without correction. 2.Rotating arm experiment: - Employing a rotating beam structure with GPS Leica AR 25 choke antenna attached at the tip, the system was used to model a rotary structure. The deflection characterization was done using a portable GBR and the output from the GPS. Using Sammons mapping, GBR results were processed and thereafter compared those of a GPS, which indicated a maximum divergence of ± 3% 3.Operational in-field WT: - The GBR was able to acquire both the both CP's (modal frequencies and flap wise deflections) for the blade and mast. The validation results were obtained from OMA Campbell diagram. An accuracy of 3-7% was achieved when the GBR results were compared WT design parameters as provided by the Campbell diagram. This experiment, was the focus of this thesis, by demonstrating the actual deployment of a GBR for WT blade and mast monitoring The above three sets of experiments were thus able to demonstrate the ability of GBR for SHM of WT blades and masts, while also enabling its integration as a 3-tier SHM framework. Thus, providing significance of this research to the wider wind energy industry and monitoring the world for (a)Flutter through the acquisition of SHM condition parameters (CP's) that can be used to verify the results of the flutter design process for optimization of WT blades. (b)Easing the Type and component certification process for WT blades and masts by the implementation of a 3-tier SHM framework to address the (i).Deficiency of current fatigue damage metrics in blade-tip monitoring as well as, (ii).Insufficient understanding of the structural behaviour of FRPC materials under long-term real operating conditions. In conclusion, using GBR for onshore infield WT during real-time operations provides data to enable validation and improvement of current aeroelastic models for flutter analysis. Thus, providing significant information towards flutter analysis and improvement of future flutter models. The thesis also entrenches the use of GBR as a non-contact sensor in level 1 damage detection for infield WT composite blades within a 3‐tier SHM framework. This work suggests additional work be done regarding whirling mast movements monitoring using GBR. This will particularly support the development of a flutter analysis model. Further work may also need to be done in the application of GBR monitoring within a 3-tier SHM framework for off-shore WT where vertical subsidence of the sea plays a key role.

With the increased world population, fossil fuel consumption and Co2 emissions, solutions are being sought to provide for the increase in energy demands and to reduce emission levels. One promising approach is the use of renewable energy and waste heat sources to drive thermo-mechanical conversion systems, such as Stirling engines. Recently, interest in developing efficient and cost effective Stirling engine technology has increased, particularly in many academic and industrial organizations. In this context, this thesis has first focused on the development of thermodynamic and numerical simulations for the V-type alpha Stirling engine. Secondly, the development of efficient regenerator that can improve the engine performance, it is a new non-annulus segmented micro-channels regenerator of parallel geometry. Using non-ideal adiabatic analysis approach, a successful thermodynamic model was developed for a V-type alpha Stirling engine, and it was validated using published experimental data available for the engine prototype. Also, the development of a detailed 3D CFD model for V-type alpha Stirling engine was carried out and its results were validated using the developed thermodynamic model. The results have shown good agreement in the estimation of the engine indicated power. The combination of the thermodynamic analysis with the 3D CFD modelling to predict the engine performance was an advantage of this work. The effects of different design parameters and operating conditions have been investigated on the performance of a V-alpha type Stirling engine by using the developed CFD model. Those parameters including the dead volume, cold/hot ends temperatures, charge pressure, porosity and matrix wire diameter of regenerator. The PV diagram for the engine was used to predict the power output contributed by each parameter. The maximum power output in this parametric study was achieved 162 W by using a wire matrix diameter of 0.02 mm, porosity of 80%, cold side temperature of 20 0C, and hot side temperature of 600 0C. Also, results predicted that, further increase of the heater and the cooler heights (up to 140 mm) pushed the power output to reach 170 W. A detailed 3D CFD model for segmented micro-channel regenerator was developed and its results were validated against experimental measurements showing maximum deviation of 10.6% and 6.03% for both unidirectional and oscillatory flows respectively in terms of measuring the outlet temperature. The validated CFD model was used to carry out an investigation on the effect of increasing the number of segmentations on the regenerator effectiveness and engine performance. The effects of changing the micro-channel diameter on the regenerator performance in terms of heat transfer and pressure loss was also investigated. The micro- channels regenerator with diameter of 0.5 mm and 32 segments performed better than all other configurations investigated in this study including the Random Fibre matrix. In order to reduce the time and cost for Stirling engine development, this work investigated the route to upgrade commercially available V-type compressor to develop V-type alpha Stirling engine through detailed 3D CFD modelling. The correlations of Nusselt number and friction factor for the developed segmented regenerator were used as porous media parameters in the CFD model for the developed Stirling engine. Also, a new concept for the engine cooler design was modelled and integrated in the overall engine model, showing improved performance for the engine due to lowering of the coolant temperature. The maximum indicated power observed from the developed engine using the 32-segmented regenerator with 0.5 mm micro-channel diameter was 132.89 W. This is higher by 18.33% and 44.4% than those of the two commercial matrix regenerators, namely the Random fibre and the Screen woven respectively.

The Diffuser Augmented Wind Turbine (DAWT) combines a diffuser and a Horizontal Axis Wind Turbine (HAWT). This set-up was designed with the intention to accelerate upstream wind speeds to the wind turbine rotor using a diffuser thereby generating more power at a given upstream wind speed. The purpose of this research was to investigate the DAWT in terms of optimising performance through diffuser design and testing the effect of building integration on performance. Numerical studies were used to evaluate performance parameters: turbine disk loading, pressure coefficients, tip speed ratio and power coefficient. Augmentation factors quantified the improvement in wind turbine performance when applied with a diffuser using measured wind speeds and pressures. The first study observed the drop in performance between a free stream and roof-mounted DAWT. Following this, two 'shrouds' were compared where the diffuser outperformed the concentrator with an augmentation factor of 2.94 versus 1.87 respectively. Numerical studies then focussed on diffuser design by testing eight aerofoil cross-sectional profiles and applying design area (At/Ae) and length-to-diameter (L/D) ratios. The 'Optimum DAWT' design was identified as the A5 (FX60 PR281 At/Ae 0.25 L/D 2.5) model. The augmentation factor was an average of 1.42 and 7.43 based on the ratio of wind speeds. A study then tested the roof-mounted A5 model in four Atmospheric Boundary Layer's (ABL) each representing the wind speed profile of a different urban terrain. The change in ABL was found to have little influence on augmentation. The Optimum DAWT restored wind speeds otherwise lost at the rotor due to building presence. Higher wind speeds and a favourable pressure drop across the roof-mounted rotor in the direction of wind flow were better controlled and distributed with the diffuser. From experimental testing of the Optimum DAWT it was found that wind speeds to the test rotor increased by 136% from 1.02m/s to 2.41m/s. The augmentation ratio was 8.32 based on the ratio of wind speeds. The Optimum DAWT exhibited better responsive behaviour than the test bare wind turbine in terms of matching the expected output power profile and a smaller response time for output power in relation to changing in wind speeds.

Two limiting conditions of burning rate are considered, culminating in either flame extinction, or transition to a detonation. A 2D schlieren technique, for flame imaging of quenching kernels has been employed, supported by 3D swinging sheet measurements. The study was able, for the first time, to determine the kernel mean diameters at the point of quench. It was found that the burning regime on the U/K diagram covered higher values of K and strain rate Markstein numbers, Ma_Sr, than previously reported. Hydrogen, methane, n-butanol and i-octane air mixtures were studied at different pressures and temperatures, up to 1 MPa and 365 K. Kernel mean diameters are normalised with laminar flame thicknesses, and correlated, through measurement of turbulent length scales, with K and Ma_Sr. It is also shown how the quenching, through blow-off, of jet flames is closely related to that of single kernel quenching of premixed flames. Just as excessive air entrainment causes quenching of jet flames, entrainment of pilot flame gases by a highly turbulent mixture, can ensure its survival. As a part of the assessment of H2 as a fuel, its autoignition and transition to detonation were studied, with emphasis on laminar flow. This necessitated micro-tubes for flame acceleration. Stoichiometric H2/O2 mixtures were studied at pressures where autoignition delay times are short. The probability of a purely laminar propagation leading to a detonation is marginal only when the initial temperature is raised to 375 K, do purely laminar detonations become possible, in tubes of between about 0.5 and 1.35 mm diameter. The tendency of mildly turbulent mixtures to auto-ignite, for an initial temperature of 300 K is greater than with laminar flames on the same initial conditions and tube sizes. A further related study demonstrates a proposed detonation engine for the laminar transition to detonation, but this reveals practical design limitations.

This doctoral thesis concerns itself with the simulations of turbulent fluid flows with heat transfer about serpentine tube boiler geometries, with the aim of developing the tools necessary to tackle research questions put forward by the EDF Energy R&D UK Centre with regard to their continued use beyond their original decommissioning date in a safe manner. This is in support of the Plant Lifetime Extension, or PLEX, scheme currently being implemented by EDF to safely lengthen the operational lifespan of their Advanced Gas-Cooled Reactor (AGR) fleet, which provide a significant portion of the UK's energy demands, without large-scale reactor deployments to replace them. Among the key components that ageing affects most significantly are the serpentine boiler systems used by some of the newer AGR designs, where fatigue and corrosion damage have forced operators to plug individual tube platens to prevent feedwater escaping and coming into contact with the graphite core. The primary coolant is CO 2 , which is heated by the reactor core before coming into thermal contact with the boiler tubes, producing steam. The flow domain is an in-line tube bank with alternating longitudinal pitch, and so this report utilises Code Saturne, a general-purpose Computational Fluid Dynamics package developed by the wider EDF R&D teams, on an idealised square in-line tube bank validation case assuming flow periodicity, along with supporting software packages. Chapter 1 contains a discussion on AGR technology, introduces the problem definition, and the main research outcomes expected by EDF Energy by the doctorate's end. Chapter 2 documents a review of pertinent literature concerning flows about cylinders and tube banks, and the heat transfer processes which occur across them. Chapter 3 outlines the software packages and the methods used to simulate fluid problems via the Finite Volume Method, along with the reasons for their selection. Chapter 4 is entirely dedicated to turbulence modelling and explores in detail many of the strategies used to account for it, though it is not exhaustive. Chapter 5 introduces the concept and underlying reasoning behind the Analytical Wall Function (AWF) of Suga et al. (2006), which enables the possibility of improved near-wall behaviour for high-Reynolds number turbulence modelling approaches and an extension to account for augmented surface roughness. Chapter 5 also documents precisely how this AWF modelling approach has been implemented in Code Saturne for the first time as part of this research work. Chapter 6 presents the methodology behind simulating a square in-line tube bank using flow periodicity, and the results obtained from 2D and 3D appraisals using Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) approaches, with temperature operating as a passive scalar while thermal fluid properties are held constant, both with and without the AWF implementation. Chapter 7 addresses a similar methodology, except on a problem of greater interest to the application, a spanwise-periodic platen geometry consisting of four tube platens with ten passes through the flow domain, with confining walls, where tube blanking is represented and the properties of carbon dioxide can now vary freely with temperature. Attempts are made also to definitively quantify the effect of blanking and augmented roughness on impairments of heat transfer through the system, to give some indication as to its safe operational lifespan. Finally, the conclusions from each chapter are presented, along with a discussion on potential avenues for further exploration. Appendices A and B list some of the more lengthy formulations and derivations used within the AWF implementation respectively, while Appendix C contains some supplementary results from Chapter 7 not critical to the discussion taking place there. The findings here indicate that in a worst-case scenario, at current reactor capacity, approximately 30% of heat transfer is negatively impacted by blanking of tubes and near-wall roughness effects.

The current medical fitness standard guidelines issued by Renewable UK for wind turbine technicians were adopted from the UK Fire and Rescue service. However, on the face of it, the two industries have different demands. This thesis aimed to ascertain the day-to-day nature of the role of a wind turbine technician - specifically, it aimed to understand the effect of external loads on vertical ladder ergometer climbing, the effect of a climb assist device and the effect of space restriction on ladder climbing. A further aim was to understand the difference between climbing a pitched and vertical ladder ergometer. Using an online survey, it was found that 50% of respondents climbed wind turbines on four, five or six days per week. The median turbine height climbed was 36 m whilst carrying external loads up to 15 kg. Finally, of the specific wind turbines involved, only 25% contained climb assist devices. This thesis ascertained that vertical ladder ergometer climbing was significantly (p < 0.05) more demanding than pitched ladder climbing, with a large effect on V̇O2 (d = 1.7 – 3.3) and heart rate (HR)(d = 1.5 – 1.9). The change in pitch leads to the mean V̇O2 across all speeds increasing from 39.1 ml.kg.min-1 to 45.5 ml.kg.min-1, and mean HR increasing from 148 bpm to 170 bpm. The use of a climb assist device significantly (p < 0.05) decreased mean V̇O2 from 28.3 ml.kg.min-1 to 22.0 ml.kg.min-1, mean HR from 134 bpm to 114 bpm, and the rate of perceived exertion (RPE) from a median of 3 to a median of 1. Furthermore, descending a vertical ladder has a significantly lower energetic cost than that of ascending, with a significant (p < 0.05) decrease in V̇O2 from 28.3 ml.kg.min-1 to 15.3 ml.kg.min-1, mean HR from 134 bpm to 111 bpm, and RPE reduced from a median of 2.5 to a median of 1. Climbing vertically with 5 kg significantly increased V̇O2 (36.4 versus 38.1 ml.kg.min-1) and HR (162 versus 167 bpm) compared to a no-load condition, while climbing vertically with 10 kg also significantly increased V̇O2 and HR compared to no load (36.4 versus 40.1 ml.kg.min-1; 162 versus 170 bpm) and 5 kg condition (38.1 versus 40.1 ml.kg.min-1; 162 versus 170 bpm). In comparison to results in unrestricted conditions, there was no significant (p > 0.05) change in the horizontal space required for climbing when a space constraint was applied to participants (0.88 m, 1.03 m or 1.23 m). This thesis found that, depending on the speed and/or the presence of an external load, the intensity of vertical ladder ergometer climbing exceeds that of the medical fitness guidelines. This thesis therefore proposes that future work should re-examine the medical fitness standard - the research also highlights that more studies are needed in order to create an evidence base from which to design a bespoke industry fitness standard.

Cooling techniques for solid parts in the combustor and turbine are essential for both the performances and the life time of jet engine components. Experiments of the jet engine components are costly to set up, and it is sometimes difficult to access the 3D flow structures and heat transfer in key regions. Due to the fast development of high performance computing in recent decades, Large-Eddy Simulation (LES) is widely used not only in fundamental studies of the flow structures and heat transfer, but also to help the design and optimisation of jet engine components. This thesis focuses on the development of an LES based approach and the prediction of effusion cooling schemes for combustor liners. In this work, a novel hybrid LES-RANS approach based on wall proximity is further developed based on an existing in-house code to extend its capability, especially for unsteady heat transfer studies. Two synthetic methods for free-stream turbulence generation are studied. The hybrid LES-RANS approach is first validated by a canonical unsteady heat transfer case, a heated square cylinder in cold crossflow. The accuracy of the approach in predicting the unsteady flow field and surface heat transfer is assessed by comparison with relevant measurements. Analysis of turbulent structures is performed to help understand their effects on the surface heat transfer, as well as show how well those structures are resolved on modest grids. Free-stream turbulence is introduced in the heated cylinder case to study the effects of inflow turbulence on both the flow field and surface heat transfer. Two effusion cooling cases are studied using the hybrid LES-RANS approach. A singlerow film cooling configuration is first studied. Results of the simulations are validated against the experimental dataset. Good prediction is obtained for velocity and surface adiabatic cooling effectiveness. A multi-row effusion cooling configuration under scaled representative combustor conditions is also investigated. Agreement with the measurements and further studies of turbulent structures suggest that the hybrid LES approach is a promising tool for the investigation of complex industrial configurations with highly unsteady flow features.

The depletion of fossil fuel and the increase of fuel consumption globally create an increased demand for the use of renewable energy. Vertical axis tidal turbines are a promising renewable energy device which needs to be improved. One problem appears in its operation is the structural instability and noise coming from the vibration of the long slender vertical axis blades. The vibration is a result of fluid structure interaction between turbine blades and the unsteady tidal current. This interaction of the tides and the blade generates vortical features which can excite the turbine blades to vibrate and causes a tonal noise known as singing. The aim of this work is to predict the blade response and locked-in condition by controlling the vortex shedding. The vortex is controlled by modifying blade’s trailing edge shape. The modifications include truncated, sharp and rounded trailing edge shapes. The response is modeled by vibrations using a spring damper system. A 2D numerical model of a vertical axis tidal turbine blade is developed to resolve the vibration using OpenFOAM 2.2. The blade has 0.75 m chord length and 3.07×106 Re. The model employs the equivalence incoming velocity method which represents the actual unsteady tidal current by time varying velocity magnitude and angle of attack of the model incoming flow. The problem is examined by observing the force applied to a static blade, and a rotating three bladed vertical axis turbine primarily. This is to confirm that the mesh topology and selected boundary conditions are sufficient and robust to resolve the blade response model. The locked-in condition is clarified by the blade main frequencies, pressure distribution, displacement, and force coefficients. In addition to the reference trailing edge, three different trailing edge shapes were studied. From the results it can be seen that the response is sensitive to pitching motion, high blade initial angle of attack, high tidal velocity and low spring and damping constant blade material. The results also show that the blunt (conventional truncated) foil has the largest ability to control the turbine blade response which is demonstrated by the smallest amplitude and the least frequent turbine blade’s vibration. For all three trailing edge shapes, along with a more limited investigation of an asymmetric trailing edge all are shown to be able to shift the frequency of the resonant response. This will allow the designer to study the likely behaviour of their design. Overall, the developed methodology using a two-dimensional, three degree of freedom solution of the unsteady CFD around the foil is shown to provide useful insight to the tidal turbine designer at a reasonable computational cost.

Internal diesel injector deposits (IDIDs) have become a prolific issue in the last decade, increased number of incidences have occurred since the introduction of ultra-low sulfur diesel and biodiesel. The IDIDs have caused concerns for customers such as injector systems misfiring or blocking, increased emissions and fuel consumption. Interest into the origins of the deposits has steadily grown, with identified possible causes including contaminants, degraded additives, or thermal and pressure stresses of the engine. Most examples in previous studies only provide surface analysis of IDIDs, however, the surface only provides a relatively small part of the story. In order to understand how an IDID has formed the history needs to be explained, to do this the lower layers of the IDID need to be analysed. Outcomes of this research include the first example of focused ion beam and secondary ion mass spectrometry being used in combination to analyse IDIDs and clearly shows different chemical layers, demonstrating that these deposits are made up of multiple complex chemistries. Raman spectroscopy can provide graphitic content information for IDIDs giving evidence of formation however, a method to remove fluorescence from carbonaceous structures was first devised and validated in order to allow this to be performed. The jet fuel thermal oxidation test (JFTOT) has been proven to be an effective method of replicating deposits on comparison with IDIDs from failed field engines, and key chemistries have been identified for B20 biodiesel and ultra-low sulfur diesel (ULSD). This work has used existing analytical methods to understand IDIDs and found novel insights that have not been previously observed in the literature.

This work considers the value of flexible power provision from natural gas-fired combined cycle (NGCC) power plants operating post-combustion carbon dioxide (CO2) capture in low carbon electricity markets. Specifically, the work assesses the value of the flexibility gained by varying CO2 capture levels, thus the specific energy penalty of capture and the resultant power plant net electricity export. The potential value of this flexible operation is quantified under different electricity market scenarios, given the corresponding variations in electricity export and CO2 emissions. A quantified assessment of natural gas-fired power plant integrated with amine-based post-combustion capture and compression is attempted through the development of an Aspen Plus simulation. To enable evaluation of flexible operation, the simulation was developed with the facility to model off-design behaviour in the steam cycle, amine capture unit and CO2 compression train. The simulation is ultimately used to determine relationships between CO2 capture level and the total specific electricity output penalty (EOP) of capture for different plant configurations. Based on this relationship, a novel methodology for maximising net plant income by optimising the operating capture level is proposed and evaluated. This methodology provides an optimisation approach for power plant operators given electricity market stimuli, namely electricity prices, fuel prices, and carbon reduction incentives. The techno-economic implications of capture level optimisation are considered in three different low carbon electricity market case studies; 1) a CO2 price operating in parallel to wholesale electricity selling prices, 2) a proportional subsidy for low carbon electricity considered to be the fraction of plant electrical output equal to the capture level, and 3) a subsidy for low carbon electricity based upon a counterfactual for net plant CO2 emissions (similar to typical approaches for implementing an Emissions Performance Standard). The incentives for variable capture levels are assessed in each market study, with the value of optimum capture level operation quantified for both plant operators and to the wider electricity market. All market case studies indicate that variable capture is likely to increase plant revenue throughout the range of market prices considered. Different market approaches, however, lead to different valuation of flexible power provision and therefore different operating outcomes.

The development of reduced chemical mechanisms in a systematic way has emerged as a potential solution to the problem of incorporating the increasingly large chemical mechanisms into turbulent combustion CFD codes. In this work, Rate-Controlled Constrained Equilibrium (RCCE) is linked with different systematic methods for identifying the major species in different detailed mechanisms. As a result, a methodology is proposed for developing reduced mechanisms with RCCE via a Computational Singular Perturbation (CSP) analysis of counterflow non-premixed flamelets for different scalar dissipation rates, by integrating over mixture fraction space a modified CSP pointer and weighting the local ordering for each strain rate. RCCE simulations with the derived reduced mechanisms for methane with 16 species and for propane with 27 species are compared with the integration of the detailed mechanisms GRI 1.2 and USC-Mech-II respectively. The last, and most complex, problem under investigation is a detailed mechanism for a realistic surrogate fuel for kerosene, for which two reduced mechanisms are developed via the RCCE-CSP methodology with 17 and 42 species. The applicability of the methodology is demonstrated in non-premixed flames for several strain rates, in non-premixed flames ignited with a pilot to test the dynamic behaviour, in premixed flames for different equivalence ratios and subsequently in perfectly stirred reactors for ignition delay times for varying temperature, pressure and equivalence ratio. An additional combustion regime, studied here, is a laminar non-premixed flamelet, with time-dependent strain rate at high pressure, to test the dynamic behaviour of the reduced mechanisms compared to the full model. Overall very good agreement is obtained, indicating that the methodology can produce reliable mechanisms for different fuels and for a wide range of conditions, combining a remarkable degree of reduction in computational time.

In this research a spectral element method is used to perform direct numerical simulation (DNS) and implicit large-eddy simulation (LES) of flows induced by centrifugal buoyancy in rotating cavities. These flows occur, for instance, in the compressor cavities of gas turbines internal air systems, in which cooling air is used to extract heat from compressor disks. Buoyancy-induced flows are inherently challenging to study using computational fluid dynamics (CFD), since turbulence models based on the Reynolds-averaged Navier-Stokes (RANS) equations are not able to provide an accurate description of the phenomena induced by the interplay between buoyancy and rotation. For this reason, model-free approaches are desirable, since they can provide an accurate description of the flow physics. First, the method is applied to a rotor/stator configuration, in which regions of laminar, transitional and fully turbulent flow coexist, and the results are compared with experimental data from the literature. Subsequently, flow induced by centrifugal buoyancy in a sealed rotating annulus is investigated using linear stability analysis, DNS and LES. It is shown that the onset of convection for a rotating cavity is similar to that for the problem of Rayleigh-Bénard convection. Analysing flow statistics for different values of the Rayleigh number, it is shown that the disk boundary layer behaves as a laminar Ekman layer, both in terms of its thickness and of its velocity profiles. This is observed even when instantaneous profiles are considered, despite the unsteadiness of the solution. The results also show that the shroud thermal boundary layer scaling is consistent with that of natural convection under gravity. Introducing an axial throughflow of cooling air, some features observed in the sealed cavity are maintained, however a strong reduction in the core temperature and a corresponding increase in the shroud heat transfer occur. The axial throughflow also promotes a significant increase in the range of frequencies observed inside the cavity.

The objective of this work is the creation of a novel Wind Turbine Emulation (WTE) technique to support the needs of a new generation of multi-bladed vertical-axis wind turbine (VAWT) designs aimed at the urban environment. The scheme, presented in this thesis, uses Computational Fluid Dynamics (CFD) data, from the analysis of such devices, as the basis of its operation. CFD methods are used for the analysis of wind turbine performance but CFD models do not incorporate physical system inertial response or provide a physical test bed. WTE must, therefore, continue to play a role in the support of wind turbine design, research and development. Ongoing work, on enhancing wind turbine designs for use in the urban environment, is leading towards the use of complex, drag-based, multi-bladed, vertical-axis devices to deal with the problems inherent in the urban situation. Current WTE systems are found to be incapable of modelling the complex torque output of these devices adequately, since they are based on the use of a steady-state model modulated by an approximating analytical function. The WTE technique developed in this thesis uses CFD profiles mapped to a two-dimensional array to generate torque coefficient values in real time. Initially a standard inertia-compensation scheme, based on an acceleration observer, is used, but testing shows that this method is inadequate due to the requirement for a low-pass filter in the feedback path. To achieve the performance necessary to accurately model the output from a multi-bladed VAWT, a novel inertia-compensation scheme is designed and implemented. The improved technique eliminates the filter induced performance degradation by dynamically manipulating z-plane pole positions based on real-time observation of system stiffness and incorporating an adaptive `lag-lead' pre-filter at the input to the torque compensation control loop. System behaviour is approximated by an s-plane model and pole manipulation is achieved by dynamic modulation of the wind turbine (WT) moment of inertia quantity used in the feedback path. Tests show that the novel inertia compensation scheme meets the requirements for accurate emulation of VAWT performance. Mean torque and power output tests confirm that, for all profiles used, the output accurately reflects those predicted by the original CFD analyses. Time and frequency domain analyses of generator load current signals confirm that the technique facilitates the analysis of generator output signals on a WTE test bed for the development of fault diagnosis and Condition Based Maintenance (CBM) strategies.

This thesis leads to a framework for micrositing, the process through which the specific location for mounting micro wind turbines in urban environments is determined. It can be used as a guidance on how to model an area of interest, find the optimum location for micro wind turbines installation and calculate the annual energy production, commenting on the accuracy that can be expected from the results. Essentially, it is composed of three parts, each one deals with different set of tasks associated with model development and simulation. The first part investigates the computational practices to the fields of turbulence in urban environments implemented in the open-source CFD library OpenFOAM. It examines the performance of a turbulence model, known as DES, which has not been previously used for external flows in complex urban environments and concludes that this approach offers improved robustness and accuracy over a range of wind conditions. It offers improved prediction of flows in wake regions compared to RANS methods and is less computationally demanding than full LES approaches. The validity of DES implementation is tested using data sets derived from both wind tunnel experiments and field measurements. In the second part, a procedure is developed to identify the optimum location for mounting wind turbines, based on the spatial variations in mean annual wind speed and the corresponding annual energy production (AEP). The procedure utilizes one year of measured wind data for one site to extrapolate (using the `Wind Atlas Methodology') the annual wind speed at the site of interest. Then combining the climate data with the CFD results and the power characteristics of the micro wind turbines, it estimates the mean wind speed and the annual energy yield. Essentially, this methodology leads to the formation of three dimensional fields of the average annual wind speed and the AEP (3d wind maps), which will enable identification of the effects of the complex urban topography on the wind flow, and the potential locations for micro wind turbines installation. The third part examines the accuracy that can be expected from the annual energy production estimation techniques and provides guidelines on the calculations. In particular, it investigates the validity of the standard power curves for the site-specific air density and evaluates their effect on the annual energy production estimations. Differences of the order of 10-3 between the default and the site specific mean air density (ρ), do not change substantially the energy production. However, for higher discrepancies of the order of 10-2 the power output can differ more than 10%. Turbulence affects the wind energy in two ways: through power performance impacts and through effects on turbine loads and fatigue. In the operational range of each turbine, TI increases the output at low wind speeds, while in the transition region to rated power it decreases the power output. In the context of this study, the DES approach was implemented to examine the flow at the De Montfort university campus in Leicester. The 3d wind maps for the mean wind speed and the annual energy production were developed and the optimum locations for micro wind turbines installation were identified. Although the rooftops of the higher buildings have mostly the potential for wind energy applications, the effect of the urban topography on the wind potential is not always apparent. Lower building can occasionally have higher potential for micro wind turbines installation than taller and roofs of the same height and close each other may differ substantially in their predicted energy output. Using the field measurements by two 3d ultrasonic anemometers placed in the campus, the site specific air density and turbulence intensity were considered to correct the energy yield estimations and evaluate their effect on the results.

Blades are designed to have good rigidity to be able to minimise the destruction that could be caused by rapid wind load and gust. The increase in length of the wind turbine contributes to the susceptibility of the wind turbine blade to the unpredictable destruction caused by random gusts. One of the ways to effectively increase the blade flexibility as well as increase its unloading effect led to the focus of this research on adaptive wind turbine blades. The project aims to investigate the potential benefits of flapping blades in the extraction of wind energy and proposing an analytical model for the prediction of the normalised induced twist with the sole purpose of having a robust tool for optimal design of adaptive wind turbine blades. In order to achieve these goals, the project is carried out in two aspects. Firstly, a proof of concept of a flapping blade; this report presents the preliminary results of the numerical simulation of a flapping-pitching rectangular flat plate in a uniform air flow. Various combinations of flapping amplitude, flapping frequency and pitching amplitude are analysed and their effect on the instantaneous and maximum lift coefficient is presented. The change in the flapping frequency and amplitude were shown to have considerable effect on the lift coefficient. It can be deduced from the results that the lift coefficient is influenced by the flapping frequency and flapping amplitude combination. The lift coefficient is most affected by the flapping amplitude when compared to the flapping frequency. The results indicate that the pitching amplitude initially enhances the lift coefficient. However, excessive pitching amplitude results in low lift coefficient. The second aspect is to develop a robust analytical model for the prediction of the normalised induced twist of an adaptive blade. Wind turbine adaptive blade design is a coupled aero-structure (CAS) design process, in which, the aerodynamic performance evaluation requires structural deformation analysis of the adaptive blade. However, employing finite element analysis (FEA) based commercial packages for the structural deformation analysis as part of the aerodynamic objective evaluation process has been proven to be time consuming. In order to develop the robust tool for the prediction of the normalised induced twist, the effect of shell thickness distributions, fibre angle distributions and materials are investigated using arbitrary lay-ups configurations. The structural/material configurations and the analyses of the adaptive blades are performed using an auxiliary software tool developed via MATLAB codes for implementing structural deformation analysis. The results are generated in ANSYS Parametric Design Language (APDL), which are read using ANSYS for the extraction of the results. Static and dynamic analyses are carried out for several cases, and the results are used to develop the analytical model for the prediction of the normalised induced twist. The proposed analytical model performance is validated by comparing the normalised induced twist predicted using the proposed model with those obtained using the ANSYS and the results suggest that the proposed model is efficient in predicting the normalised induced twist of an adaptive blade.

There is a constant requirement to understand scour especially regarding its prevention, due to the potential impact and disastrous consequences. The installation of offshore wind turbines is haunted by scour mitigation and at the start of the offshore wind turbine boom in the early 2000’s this was achieved using overzealous amounts of rock armour. However, as investment and cost efficiency has increased, protection methods have been refined, but, there remains significant room for improvement. Research into offshore sediment dynamics has benefited greatly by computational advancements providing a greater understanding of processes and the driving mechanisms; leading to protection method improvements and reductions in environmental impact. The premise of this study is to push this knowledge further, by developing and validating a novel scour model within CFD software that can be used to simulate and analyse offshore scour; specifically, the scour around complex, new offshore wind turbine foundation geometries.

Wind turbines are leading the way in helping to reduce the dependency on fossil fuel energy sources. However to compete with other energy sources there is a need to reduce the cost of energy from wind turbines. It has been shown in the literature that as wind turbines increase in size their reliability decreases. As wind turbines move further offshore and into deeper water this becomes more of an issue as carrying out maintenance becomes more challenging and costly. One way of improving the reliability of wind turbines is through the use of condition monitoring systems (CMS) which can continually monitor the health of the machine and allow more optimised maintenance and repair scheduling. Although the benefits of using a CMS may seem evident, operators have been slow in the uptake of such systems. One reason for this is due to issues with the reliability of CMS themselves. As stated in the literature, CMS must accurately detect 60-80% of faults to be economically justifiable. Not detecting faults or the occurrence of false alarms is detrimental to the effectiveness of CMS. The work presented in this thesis aims to address the issue of CMS reliability. Through the installation of two CMS in operational wind turbines the author of this thesis has gained valuable insight into the design, build and installation of CMS which has facilitated the novel contributions from this work. The first contribution comes from the formulation of an engineering design process which incorporates five categories of robustness which were identified by the author through Failure-Mode Effects Analysis on a wind turbine CMS that was installed in an operational wind turbine. The engineering design process incorporating the robustness categories will allow wind turbine CMS to be designed which are capable of operating reliably in the harsh environment they are subjected to. The second contribution comes from the development of three techniques which will increase CMS reliability by reducing false alarms and introducing the ability to detect erroneous data.

Thousands of load calculations for wind turbine design have been calculated by manufactures, consultants and certification bodies. These have been done as required to develop and validate specific designs. However, there has not been a general systematic study of trends in loads related to key wind turbine design parameters and external operating conditions. The aim of this thesis is parameterise and quantify trends of extreme and fatigue loads based on systematic modifications of wind turbine characteristics. This thesis is in two main parts. The first part provides an overview of loads calculation methods, flow modelling and approach adopted also considering scaling rules, comparing scaling with similarity and the scaling evident in from commercial world turbines data. The second part presents and evaluates loading trends for extreme and fatigue loads related to systematic alterations of key wind turbine parameters. Three chapters of results investigate the load impacts of blade structural properties, rotor solidity and up-scaling respectively. The chapter on blade structural properties demonstrates that the self-weight of blades is a major component influencing loads of the blade root and hub. The chapter on rotor solidity shows that significant load reduction can result for blade root, shaft and yaw bearing in reducing the solidity of rotor. However, the aerodynamic damping reduces with reducing solidity, which is crucial for tower base fore-aft loads; therefore the reducing rotor solidity has an adverse impact on the tower base fore-aft loads. The chapter on up-scale demonstrates that up-scaling with similarity method can give good prediction of loads with an error of ±10% and ±15% for extreme and fatigue loads of large wind turbines (up to 10MW) at the mean wind speed within power production range. Additional, the chapter of up-scaling showed that the up-scaled wind turbines reduce the sensitivity to turbulence with the size of rotor.

This thesis deals with topics concerning both passive and active control of stirred tanks. Regarding passive flow control, the effect of certain turbine blade modifications is investigated, most notably that of the blade perimeter increase in a fractal manner, applied on a conventional radial turbine stirring an unbaffled tank. It is found that the tested modifications show potential for applications, as by applying them, a drop in power consumption, an increase of the bulk turbulence intensity and the mass flow rate, and a suppression of the shed blade vortices' intensity and coherence is achieved. The latter, in particular, is argued to be a potential cause of the above-mentioned drop in torque/power consumption. Additional material from this section are the detailed comparison of fractal and perforated bluff bodies and a characterisation of the form drag distribution of radial turbines stirring unbaffled tanks. The latter was achieved by employing a novel pressure measuring technique. Regarding the active flow control, this thesis focuses on the prediction of stirred tank power consumption in situations where the shaft speed is not constant, but rather time dependent. The motivation for this is that such speed control has been shown to promote mixing in the tank. Employing first principles, qualitative scaling laws and empirical correlations, analytical models for the prediction of the torque response, when the shaft speed undergoes smooth, or step changes are developed. The predictions are then experimentally validated using torque measurements. The above models could find application in the design process of variable speed systems.

Autoignition is a multi-physics phenomenon that occurs in wide-ranging engineering applications, such as diesel engines, gas turbines and jet-engine afterburners. In these applications, autoignition occurs in the presence of flow inhomogeneities and turbulence. Further, liquid fuel autoignition presents a case of chemically reacting flow where processes such as jet break-up, atomisation, droplet evaporation (interfacial heat and mass transfer), turbulent mixing and chemical reaction occur simultaneously in the presence of important flow, mixture and phase inhomogeneities. The multi-scale nature and direct coupling between these various contributing processes, present a challenging fundamental problem which cannot be understood by extrapolation from homogeneous, inhomogeneous (gaseous) and even single droplet combustion studies. This thesis presents an experimental study on autoignition of polydispersed droplets generated by single liquid jets of pure liquid n-heptane and n-pentane injected axisymmetrically from a circular nozzle into a confined turbulent hot coflow of air at atmospheric pressure. Distinct phenomena are identified concerning the emergence of various autoignition regimes --- no autoignition, random spots and continuous flame; the occurrence of these regimes depends on the reaction conditions of air temperature, air velocity, and liquid fuel injection velocity. In the random spots regime, autoignition appears in the form of well-defined localised spots occurring randomly along the length of the reactor. Optical measurements of these random spots are made from which the autoignition lengths/locations are measured and are used to infer average delay (or residence) times from injection. At higher air temperatures and lower liquid fuel injection velocities, autoignition is observed to move closer to the injector; the corresponding delay times also decrease. With increasing air velocity and hence turbulent fluctuations, autoignition moves downstream but the delay times decrease. The shorter delay times are also associated with faster evaporation of the liquid fuel. The results from this work suggest that turbulent inhomogeneous autoignition of liquid fuels cannot be directly predicted from chemical delay times from homogeneous studies and that the effects of evaporation, and turbulent mixing, as quantified by the mixture fraction and conditional scalar dissipation rate must be accounted for. The results also provide insights into the flow conditions leading up to the various observed autoignition phenomena for liquid fuels, and constitute a valuable data-set that can contribute towards developing and validating models of advanced multiphase turbulent combustion and chemically reacting flows.

Modern gas turbine design continues to drive towards improved performance, reduced weight and reduced cost. This trend of aero-engine design results in thinned blade aerofoils which are more prone to aeroelastic problems such as flutter. Whilst extensive work has been conducted to study the flutter of isolated turbomachinery blades, the number of research concerning the unsteady interactions between the blade vibration, the resulting acoustic reflections and flutter is very limited. In this thesis, the flutter of such embedded blade rows is studied to gain understanding as for why and how such interactions can result in flutter. It is shown that this type of flutter instability can occur for single stage fan blades and multi-stage core compressors. Unsteady CFD computations are carried out to study the influence of acoustic reflections from the intake on flutter of a fan blade. It is shown that the accurate prediction of flutter boundary for a fan blade requires modelling of the intake. Different intakes can produce different flutter boundaries for the same fan blade and the resulting flutter boundary is a function of the intake geometry in front of it. The above finding, which has also been demonstrated experimentally, is a result of acoustic reflections from the intake. Through in-depth post-processing of the results obtained from wave-splitting of the unsteady CFD solutions, the relationship between the phase and amplitude of the reflected acoustic waves and flutter stability of the blade is established. By using an analytical approach to calculate the propagation and reflection of acoustic waves in the intake, a novel low- fidelity model capable of evaluating the susceptibility of a fan blade to flutter is proposed. The proposed model works in a similar fashion to the Campbell diagram, which allows one to identify the region (in compressor map) where flutter is likely to occur at early design stages of an engine. In the second part of this thesis, the influence of acoustic reflections from adjacent blade rows on flutter stability of an embedded rotor in a multi-stage compressor is studied using unsteady CFD computations. It is shown that reflections of acoustic waves, generated by the rotor blade vibration, from the adjacent blade rows have a significant impact on the flutter stability of the embedded rotor, and the computations using the isolated rotor can lead to significant over-optimistic predictions of the flutter boundary. Based on the understanding gained, an alternative strategy, aiming to reduce the computational cost, for the flutter analysis of such embedded blades is proposed. The method works by modelling the propagation and reflection of acoustic waves at the adjacent blade rows using an analytical method, whereby flutter computations of the embedded rotor can be performed in an isolated fashion by imposing the calculated reflected waves as unsteady plane sources. Computations using the proposed model can lead to two orders of magnitude reduction in computational cost compared with time domain full annulus multi-row computations. The computed results using the developed low-fidelity model show good correlation with the results obtained using full annulus multi-row models.

The necessity for increasing the efficiency of combustion engines whilst simultaneously reducing the emissions of various pollutants is widely accepted. With reference specifically to premixed spark ignition (SI) engines, the turbulence/flame interaction is of particular relevance as it not only determines the maximum possible burning rate in such an engine, but also if flames are likely to extinguish (quench). The present study describes a three-dimensional laser imaging technique which has been developed to study turbulent premixed flames in a fan-stirred combustion bomb. This has, for the first time, allowed the full 3D structure of flames developing at engine-like conditions to be analysed without the assumptions required in previous works using 2D flame imaging techniques. Methane/air mixtures at a starting temperature and pressure of 298K and 0.1 MPa respectively and an equivalence ratio with respect to stoichiometry of 0.6 were centrally ignited using a laser ignition system at various root-mean-square (RMS) turbulence velocities, where for each explosion, a 3D image of the growing flame was captured at various instants in time. The flame images were quantitatively characterised to yield flame surface area, burned gas volume, reaction progress variable and flame surface density. From the flame surface areas and burned gas volumes, turbulent burning velocities were directly measured from surface area ratios and compared with correlations of turbulent burning velocities made previously at Leeds using 2D flame imaging techniques. This tested the assumption that flame structure observed with 2D imaging techniques gave a good representation of the overall 3D flame structure. An excellent agreement was found between the datasets, indicating that such assumptions were valid under the conditions employed in the present work. The surface area ratio data obtained in the present work were also compared with the predictions of direct numerical simulation (DNS) studies conducted at Cambridge University, where it was found that the experimentally derived results typically exhibited slightly higher flame surface area ratios. This was attributed to the combustion chamber geometry in the DNS study and differences in mixture properties between the two studies, with more work at similar starting conditions required to elucidate the exact cause of the differences. Reaction progress variable was calculated for the 2D laser sheet images obtained in the present work and their 3D counterparts. Although a good agreement was seen where the central laser sheet image in a 3D reconstruction was analysed, disparities were observed when laser sheet images at a fixed position in the combustion bomb was used at high root mean square turbulence velocities. This indicates that the use of fixed position laser sheet imaging techniques, such as particle image velocimetry, are of limited use for highly turbulent flame analysis.

De-centralised renewable energy power generation is proposed to be a significant part of the future of electricity generation technology, with wind energy playing a significant role. With half of the global population residing in urban and suburban areas, the opportunity for individuals or small organisations to generate power locally facilitates the decrease in losses associated with long distance electricity generation and transmission. Small-scale wind turbine applications within suburban/urban areas are exposed to high level of gust and turbulence compared to flow over less rough surfaces (e.g. coastal/offshore areas, open grasslands, rural areas, etc.). There is, therefore, a need for such systems not only to cope with, but to thrive under such rapidly fluctuating, complex urban wind conditions. Assessing the potential of a proposed urban wind turbine project is hindered by insufficient assessment of both the urban wind resource and power capabilities of certain turbine designs within a potential suburban/urban site. This, however, requires estimation of important factors such as local atmospheric turbulence, total energy available to the turbine system and the potential power output to be generated should a certain turbine system design be installed within a potential site. The research presented in this thesis proposes a methodology for scoping the potential of small wind turbines within a built environment through effective assessment of the urban wind resource and power capabilities of small turbine systems. The aim is to address the lack of accurate and affordable methods for site viability assessment of small wind turbines within a built environment. This methodology encompasses three sub-models which estimate the local atmospheric turbulence (represented by the turbulence intensity, T.I.), additional energy within the gusty urban wind (represented by the excess energy content, EEC) and the turbine power capability at different heights within a potential site. Firstly, to quantify the influence of location on the total energy available to a small wind turbine at a potential site, an in-depth evaluation of the urban wind resource is completed. This includes the development of methods to predict the local atmospheric turbulence at a given turbine mast height, and the additional energy available to the turbine which is usually under represented when using assessments based only on mean wind speeds. This is achieved using high temporal resolution wind measurement datasets from eight potential turbine sites within the urban and suburban environments and LiDAR building height datasets from three major UK cities namely, Leeds, Manchester and London. Subsequently, new analytical models are developed that allow the mapping of atmospheric turbulence and excess energy at different heights over Leeds, Edinburgh, Manchester and London by combining the T.I. and EEC estimation models with currently available methods of predicting mean wind speeds over urban areas. The results from these two models highlight the importance of including building height variation and changes in wind direction within the assessment, and also the value of employing detailed building geometric data as model inputs. A simple low-cost 2-D multiple streamtube vertical axis wind turbine (VAWT) model capable of simulating turbine performance in a fluctuating wind isdeveloped. Combining this VAWT model with dynamic stall features and variable speed control strategy, enables a system based design of wind turbines operating within suburban/urban environment. A method of estimating the performance of a turbine operation within an urban wind resource is developed by assessing the power capabilities of the VAWT model using high-resolution wind measurement datasets as model inputs. This is combined with the T.I. and EEC estimation models in developing a new model known as the turbine power estimation (TPE) model used in mapping turbine performance at different heights over Leeds, Edinburgh, Manchester and London. Comparison between the TPE model and a generic power curve is made, hence suggesting the possibility of using a simple model to estimate the power capabilities of a certain turbine design while accounting for local turbulence within an urban wind resource. Finally, the investigation of the cumulative potential of small wind turbine power generation in Leeds, Edinburgh, Manchester and London indicates a largely untapped wind resource available (represented by high EEC values estimated within small distances in each city) which could be harnessed if gust tracking solutions were to be commercially available. It also highlights the importance of site viability assessment and its financial implications illustrated by capacity factor maps over the four cities, which has practical value for turbine manufacturers and urban planners alike. Thus, for urban wind applications to achieve their optimum deployment potential, this research study proposes a simple, effective and affordable tool for preliminary scoping the potential of certain small wind turbine designs within a suburban/urban environment, and hence encouraging effective carbon savings. In order to maximize the impact of this research study, it would be valuable that these maps be extended to other towns/cities and made available and easily accessible to individuals and interested parties, and hence this is a major objective of future work.

Calculation of the blade tip clearances of the high-pressure-compressor rotors in aeroengines involves calculating the radial growth of the corotating compressor discs. This requires the calculation of the thermal growth of the discs, which in turn requires a knowledge of the disc temperatures and Nusselt numbers for the buoyancy-induced flow in the cavity between the discs. This is a strongly conjugate problem in which the equations for the fluid flow and the disc temperature are coupled. In this thesis, the buoyancy-induced flow and heat transfer inside the compressor rotors is modelled assuming laminar Ekman-layer flow on the discs and compressible flow in the fluid core between the Ekman layers; conduction in the discs is modelled using a one-dimensional fin equation. The theoretical predictions are compared with Nusselt numbers and temperatures obtained from two independent sets of temperature measurements, obtained on a multi-cavity compressor rig, and the ‘experimental’ Nusselt numbers were calculated using a Bayesian model for the inverse solution of the fin equation. For most of the experimental cases, with Grashof numbers up to 1012, mainly good agreement was achieved between the theoretical predictions and experimental values of the disc temperatures and Nusselt numbers. As predicted by the model, increasing the rotational Reynolds number can, under certain conditions, cause a decrease in the Nusselt numbers. Importantly, the results suggest that laminar Ekman-layer flow could occur even at the high Grashof numbers found in the compressor rotors of aeroengines. An extension of the buoyancy model included empirical correlations for the Nusselt numbers for the compressor shroud and disc cobs. This extended model was used to predict the temperature rise of the axial throughflow of cooling air in the compressor rotor, and reasonable agreement was achieved between the predicted and measured throughflow temperatures. This is the first time a theoretical model (rather than CFD) has been used to predict the temperatures of a compressor disc and the axial throughflow, and the model takes only seconds to predict the temperatures that would take days or even weeks to predict using CFD. Some suggestions are made for future research to improve the extent and accuracy of the model.

Servo valves are used in a broad variety of flow modulation applications. In the field of aerospace, servo valves are used in aero engines to meter fuel flow. The existing valves are labour intensive to manufacture and highly optimised such that to achieve improvements in performance requires a novel design. This research investigates smart material actuators and valve concepts. Specifically, a prototype pilot stage nozzle flapper valve is developed for the purpose of actuating a main stage spool. The typical nozzle flapper type servo valve uses a torque motor to actuate the flapper. In this research project, the torque motor has been substituted for two piezoelectric ring bender actuators. A novel mounting mechanism has been developed to secure the ring benders within the valve. Analytical and finite element models have been made to understand the displacement mechanism of a ring bender and the effects of the mount on the displacement and force from a ring bender, and the results were compared with experiment. The mounting stiffness at the inner and outer edges was found to decrease the displacement of the ring bender and it was found that the stiffness of the mount at the outer edge has a greater negative effect on displacement than the stiffness of the mount at the inner edge. The displacement of a ring bender was tested across the operational temperature range of an aero engine. It was found that the displacement of the ring bender is reduced at low temperatures and increases at high temperature. The variation of stiffness of the elastomeric mount was also tested with temperature and it was found that the displacement of a ring bender is significantly reduced when the mounting elastomer approaches its glass transition temperature. A prototype valve was built to test the pressures and flows that could be achieved at two control ports by using a ring bender as actuator. A single ring bender and two ring benders, mounted in tandem to provide redundancy, have been tested. An analytical model was developed and the predictions are compared with experimental results for pressures and flow. The full stroke of the valve was 300m when mounted and reduced to 150m when mounted in tandem with an inactive ring bender. The hysteresis of the valve is +/-10%. The pressures and flow at and between the control ports of the valve are consistent with the predictions.

Thermal energy accounts for 49% of the National annual energy budget of the United Kingdom. In a typical household, the consumption of thermal energy makes up to 77% of its annual energy consumption, made of space heating and hot water production. Intermittent renewable energy sources are often used to reduce the domestic energy expenditure of national energy systems such as the electric grid or the natural gas network. Energy storage, and increasingly heat storage, is often described as one way to overcome the unpredicatable nature of many renewable energy systems. This thesis investigates the use of a latent heat storage system, which uses the enthalpy of transition between two physical states, as a means to store thermal energy at a low thermal loss. To achieve this, a phase change material (PCM), a material with a high enthalpy of transition, is allowed to supercool and enter a metastable state. A novel trigger mechanism is presented and refined to initiate nucleation in the supercooled PCM, beginning the phase transition and releasing the enthalpy of transition. From over 150 PCMs which are described in the literature, four are investigated in detail for their suitability in this application. A particular PCM, CaCl2.6H2O is investigated further and its issue of incongruent melting is successfully suppressed. The trigger mechanism presented uses a Peltier heat pump to locally cool a small amount of PCM, contained within a latent heat store. The supercooled PCM was cooled to a critical point, its autonucleation temperature, where a stable nucleus is spontaneously formed through heterogeneous nucleation. The trigger mechanism was demonstrated to work on multiple PCMs. The trigger mechanism was then implemented into a latent heat storage system, reffered to as a heat battery. The heat battery was filled with a characterised eutectic PCM mixture, CaCl2.6H2O + 5% KCl (w.t.). The trigger mechanism was demonstrated to initiate nucleation within the heat battery. The work demonstrates the ability for a heat battery to operate using a supercooled PCM and activation mechanism, and then highlights the limitations of such an approach. Future work is identified, which must first be tackled in order to construct a fully technically viable system.

The Doubly-fed induction generator (DFIG) is one of the most popular generators used in variable speed wind turbines with the merits of high efficiency and using small-scale power electronic converter. To improve the reliability and stability of power grids with high penetration of wind power, low-voltage ride through (LVRT) requirements for wind turbines have been introduced by many countries in their grid codes. Wind turbines are required to stay connected to the grid during voltage dips and provide reactive power support. The standard vector control (VC) is challenged to fulfill those LVRT requirements as it does not provide a satisfactory transient response for DFIG-WTs. The DFIG is sensitive to grid disturbances as its stator terminals are directly connected to the power grid. Using advanced control strategies is a cost-effective way that can improve the dynamic performance of the DFIG-WTs based on existing hardware. This thesis aims to develop control algorithms for DFIG-WT in order to improve the dynamic performance of DFIG-WT and enhance the its robustness against uncertainties and disturbances. The performance of VC with different controlled variables of DFIG has been evaluated at first. An external-loop for stator flux is proposed to accelerate the damping of stator flux and improve the terminal voltage control during voltage dip. Performance of the proposed controller is verified via simulation and experiment tests in comparison with the standard VC-based active/reactive power control and terminal voltage control. As VC can only provide asymptotically decoupled control of active and reactive power due to its constant assumption of stator voltage and flux, feedback linearisation control (FLC) is designed for DFIG to provide a fully decoupled control and maintain a consistent control performance among different operation points. The FLC of different controlled variables have been proposed, and the transient response of DFIG with those FLCs during voltage dips has been investigated by simulation. The FLC requires accurate system model and parameters, and full-state feedbacks are needed. The parameter uncertainty could strongly degrade the performance of FLC. The disturbance observer based FLC (DOFLC) is proposed to improve its robustness against parameter uncertainties, but only constant or slow timevarying disturbances can be handled. A perturbation estimation based nonlinear adaptive control (NAC) for the decoupled control of the active and reactive power of DFIG is proposed. Perturbation observer (PO) is designed to estimate fast timevarying perturbations, including system nonlinearities, parameter uncertainties, unmodelled dynamics, and unknown disturbances. With compensation of system perturbations, the fully decoupled control of active and reactive power is realised. The dynamic performance and robustness against uncertainties and disturbances is verified via both simulation and experiment tests in comparison with the VC and DOFLC. Perturbation estimation based NAC is applied to the speed and terminal voltage control for the DFIG-WT. Choosing the rotor speed and stator flux as system outputs, two second-order-represented input-output linearised relationship with relative degree 4 are obtained. Two third-order perturbation observer are designed for the second-order subsystems. Time-varying perturbations, including all system nonlinearities, unmodelled dynamics, and unknown disturbances, can be estimated as a lumped term. Simulation results are carried out to verify the performance of the proposed controller during voltage dips and voltage swells and the robustness against parameter uncertainties. Unbalanced grid voltages have frequently occurred due to an imbalance of line impedances, unbalanced loads, and some asymmetric grid faults. The conventional solution with VC under unbalanced grid conditions requires four control loops in both positive- and negative- sequence dq reference frame. A Perturbation estimation based NAC for the power control to DFIG operation under unbalanced grid conditions is developed in stationary aß references frame, with which the separated control in positive and negative sequence dq reference frame is not required. Perturbation observer is designed to estimate sinusoidal time-varying perturbations. By compensating those perturbations with PO, tracking control of the rotor currents with linear output feedback controller is realised. To eliminate the active power oscillations when grid voltage is unbalanced, rotor current references are given based on the current-power relationship modelled under unbalanced grid conditions. The results presented in this thesis address the problems mentioned above. When the stator flux is controlled during a voltage dip, the DFIG shows improved performance in damping the oscillated natural flux and maintaining a good terminal voltage profile. FLC based DFIG controllers are designed to achieve the fully decoupled control of the DFIG such that better dynamic performance is obtained than using the VC. To overcome the drawbacks of FLC on its weak robustness of the FLC against uncertainty, perturbation observer based nonlinear adaptive control is proposed so the dynamic performance of the DFIG can be improved when there are parameter uncertainty, unknown dynamics, and external disturbances, etc.

The offshore wind market has grown rapidly over recent years. The most widely used foundation type for offshore wind turbines is the monopile. Current design guidance for monopile foundations dates back to the 1950s and 1960s and was originally developed for the oil and gas industry, where both the pile dimensions as well as the design load conditions are different than for offshore wind. The PISA project was aimed at investigating the behaviour of monopile foundations and reducing the conservatism in design. The project used state of the art numerical modelling, which was validated through a field testing campaign. The numerical modelling was focused on capturing the monotonic response of the foundation to failure. The field testing provided valuable additional data for the rate effects and the cyclic behaviour of monopile foundations. Data analysis methods are presented to accurately interpret the foundation response. The data analysis is focused on capturing the ground level foundation response as well as the pile behaviour below ground. Additionally, the cyclic behaviour is analysed in detail. These results are used as a basis for the development of numerical models for capturing the observed behaviour in the field tests. This thesis outlines plasticity models which are integrated in a generalised Winkler model. The model development makes use of the Hyperplasticity framework. These numerical models include: (1) the kinematic hardening model to capture plastic unloading; (2) the rate effect model to capture increased foundation capacity with increasing load rate; (3) the ratcheting model to capture accumulated rotation under cyclic loading; (4) the combined rate and ratcheting model and (5) the gapping model to capture gapping on the active side of the pile. Each of the models is calibrated to the PISA eld tests illustrating the capabilities and limitations of the models for capturing the eld test response. Finally, the kinematic hardening model is integrated in software to calculate the dynamic behaviour of an operating wind turbine. Integrating more accurate soil-structure interaction models could lead to improved predictions of the turbine behaviour and reduce the cost of monopiles.

Vertical Axis Tidal Turbines (VATTs) have become the subject of increased interest in recent decades, but the development of this type of hydrokinetic turbine has faced several challenges that have not yet been overcome. The influence of rotor parameters on turbine performance is one of these challenges. No axiom can be found in the literature about the effect of these parameters on the turbine behaviour, and sometimes research projects even show contradictory results. As a consequence, parameters that define turbine rotors may differ substantially from each other but have performed similarly in terms of efficiency. In relation to this matter, experimental modelling has been carried out in the School of Engineering facility at Cardiff University. Using small-scale set-ups, experimental testing provided useful and reliable information that shed light into these design uncertainties. Blade roughness has been found to have a great impact on the turbine behaviour, and the influence of this parameter has been tested and analysed in depth in a subsequent chapter of the thesis. Apart from the parametric analysis, a mechanical and an electrical system were utilised for the turbine set up. Thanks to these different systems of energy conversion, it was possible to compare the extracted power and to evaluate their inherent losses. Electricity was generated from the electrical approach, which was very useful in order to accurately evaluate the turbine efficiency. Taking into account the results coming from physical testing, an optimised prototype of a VATT was designed and manufactured; estimated to be a 1:15 scale device. Not just the rotor but the whole super structure was built, in order to analyse both the efficiency and the performance of the rotor, as well as the 1 structural response of the entire device. Performing experimental testing without removing the effect that a blocked channel provides to the turbine rotation is no trivial issue, and intermediate scale tests will become a fundamental step for recognition of the technology. Aiming to achieve a reliable source of information, the manufactured tidal turbine prototype has been tested in a water sports centre (White Water Rafting Centre, Cardiff). There is a clear lack of information in the literature about testing tidal turbines on an intermediate scale, and the chance to test a tidal turbine is a very valuable opportunity. The experiments were accomplished in a very similar environment to a real tidal stream, but with the related advantages of complete control over the turbine deployment. Thus, these experiments are considered to provide very useful data for scientific knowledge and also the tidal stream energy sector. Finally, the study of the hydrodynamic turbine wake in small scale was carried out. Not only velocity measurements were collected at the turbine operating point, but also water elevations upstream and downstream were measured by using depth gauges based on water conductivity. At the time of writing and to the best of the authors’ knowledge, not many research articles have studied the wake characteristics of vertical axis tidal stream turbines, and none have used this equipment. The quality of the data is deemed to be excellent and the following process of the information described perfectly the near and far wake. This could be extremely useful for a future scale-up of the turbine, and the development of an array.

Wind turbines (WTs) are a proven source of clean energy with wind power energy harvesting technologies supplying about 3% of global electricity consumption in 2014. However there is an increasing demand on maintenance and operational improvements since turbines have been plagued with downtime problems ofmajor components e.g. gearboxes, which in particular are known to have a higher downtime per failure than other WT subassemblies. This is as a result of two reasons. First, WT gearboxes have historically suffered from early failures due to the underestimation of operational load conditions. Second, WT gearboxes have very complex repair procedures needing heavy lifting equipment such as external cranes for repair and replacement. This downtime results in revenue loss for the customer. Hence, for a company like Vestas Wind Systems AlS, who designs, manufactures and services WTs dealing with the gearbox downtime issue is of great importance. This thesis focuses on the gearbox challenge specific to Vestas organisational context based on a research journey undertaken by the author whilst embedded in Vestas as an employee. It focuses on the 2MW fleet of gearboxes serviced by Vesias globally. Furthermore, the thesis addresses two dimensions of the industrial problem - (i) investigating the gearbox problem, i.e. the issue with reliability and maintainability, and identifying solutions for improving these, and (ii) improvement of Vestas internal processes which contribute to delivering maintenance and repair solutions for gearboxes e.g. the capturing and reusing of maintenance and repair data for failure and reliability analysis. These two strands of the research equip decision makers within Vestas with tools and techniques for making decisions concerning the maintenance and repair challenges. Hence, enabling the company to improve performance of the gearboxes and extending the life of gearboxes. The main outcomes of this thesis are the development of new and novel in-service decision-making models (and tools) which are currently adding 'value to Vestas. First, a preventive maintenance optimisation model was developed by applying state of the art approaches used in industries like aerospace and marine, to historical gearbox in-service data from Vestas operational WTs. This model estimates the optimal interval for preventive replacements, repair and inspections of gearboxes. The benefit to Vestas is that the model helps WT managers to make timely decisions regarding planning and scheduling maintenance, which can reduce the downtime considerably and avoid consequential failures, hence resulting in cost savings for the company. Second, a novel extreme vibration model was developed using the automated condition monitoring data from operational gearboxes. This model can help in detecting failures on the high speed and intermediate speed stages of the gearbox as early as one month in advance. The model was recently developed and validated and is soon to be implemented in the organisation but it is expected to help avoid consequential failures and reduce downtime due to the ability to plan and schedule maintenance early as soon as a fault is detected. Third, a decision support framework (with an accompanying tool) for repair cost estimation, gearbox damage classification and feedback of repair data to design, was developed using a soft systems approach. In addition, a data repository has been created which contains repair statistics that is used for analysis purposes for guiding repair decisions and of the design of new gearboxes. The developed models, framework and tools are now being used across the organisation by engineers and service personnel, and by Vestas external repair providers, which has led to savings for Vestas in the order of hundreds of thousands of Euros yearly.

This thesis explorers the reasons for power shortage and the level of maintenance implementation in Iraqi power plants, furthermore, it examines the current organisational culture in Iraqi power plants, and its effect on maintenance implementation factors. Currently the active power plant units in Iraq are producing only 54% their designed capacity, which is in turn only supplying 50% of the countries’ demand. Therefore, to try and understand the reasons for this low level of efficiency, this research uses an exploratory sequential mixed method design, starting with semi-structured interviews (qualitative) with nine power plant managers or their representatives, followed by a questionnaire survey (quantitative), receiving 484 responses from the employees of those nine power plants. The reasons for power shortage in Iraq were identified, Furthermore, the level of maintenance implementation in the Iraqi power plants, was examined found to be at a medium level. In terms of organisational culture, not enough attention has been paid in the literature. This lack of research in the area of cultural effect on maintenance implementation was one of the main motivators for this study to answer the following question; to what extent do organizational culture profiles effect maintenance implementation factors in organisations. Structural equation modelling (SEM) technique was used to examine the relationship between organisational culture and maintenance implementation factors. Furthermore, based on the research findings, maintenance improvement framework was developed and detailed plans for implementation were formulated. The framework was built on the basis that improving organisational culture will improve the factors affecting maintenance and these factors will facilitate Total Productive Maintenance (TPM) implementation in Iraqi power plants.

Over the last couple of decades, there has been increased interest in environmentally friendly technologies. One of the renewable energy sources that has experienced huge growth over the years is wind power with the introduction of new wind farms all over the world, and advances in wind power technology that have made this source more efficient. This recognition, together with an increased drive towards ensuring the sustainability of wind energy systems, has led many to forecast the drivers for future performance. This study aims to identify the most sustainable wind turbine design option for future grid electricity within the context of sustainable development. As such, a methodology for sustainability assessment of different wind turbine design options has been developed taking into account environmental, data uncertainty propagation and economic aspects. The environmental impacts have been estimated using life cycle assessment, data uncertainty has been quantified using a hybrid DQI-statistical method, and the economic assessment considered payback times. The methodology has been applied to a 1.5 MW wind turbine for an assessment of the current situation and potential technology improvement opportunities. The results of this research show that overall, the design option with the single-stage/permanent magnet generator is the most sustainable. More specifically, the baseline turbine performs best in terms of embodied carbon and embodied energy savings. On the other hand, the design option with the single-stage/permanent magnet generator performs best in terms of wind farm life cycle environmental impacts and payback time compared to the baseline turbine. With respect to the design options with increased tower height, it is estimated that both designs are the least preferred options given their payback times. Therefore, the choice of the most sustainable design option depends crucially on the importance placed on different sustainability indicators which should be acknowledged in decision making and policy.

Significant advances in wind turbine technology have increased the need for maintenance through condition monitoring. Indeed condition monitoring techniques exist and are deployed on wind turbines across Europe and America but are limited in scope. The sensors and monitoring devices used can be very expensive to deploy, further increasing costs within the wind industry. The work outlined in this thesis primarily investigates potential low-cost alternatives in the laboratory environment using vibration-based and modal testing techniques that could be used to monitor the condition of wind turbine blades. The main contributions of this thesis are: (1) the review of vibration-based condition monitoring for changing natural frequency identification; (2) the application of low-cost piezoelectric sounders with proof mass for sensing and measuring vibrations which provide information on structural health; (3) the application of low-cost miniature Micro-Electro-Mechanical Systems (MEMS) accelerometers for detecting and measuring defects in micro wind turbine blades in laboratory experiments; (4) development of an in-service calibration technique for arbitrarily positioned MEMS accelerometers on a medium-sized wind turbine blade. This allowed for easier aligning of coordinate systems and setting the accelerometer calibration values using samples taken over a period of time; (5) laboratory validation of low-cost modal analysis techniques on a medium-sized wind turbine blade; (6) mimicked ice-loading and laboratory measurement of vibration characteristics using MEMS accelerometers on a real wind turbine blade and (7) conceptualisation and systems design of a novel embedded monitoring system that can be installed at manufacture, is self-powered, has signal processing capability and can operate remotely. By applying the conclusions of this work, which demonstrates that low-cost consumer electronics specifically MEMS accelerometers can measure the vibration characteristics of wind turbine blades, the implementation and deployment of these devices can contribute towards reducing the rising costs of condition monitoring within the wind industry.

The uptake of renewable energy sources has increased dramatically in recent decades, in response to the contribution to climate change attributed to CO2 emissions from the burning of fossil fuels, the need for governments to maximise the use of domestic energy forms with depleting conventional sources, and to reduce exposure to fuel price volatility. Renewable energy targets set by the European Union have been supported by legislation and economic incentives, and have resulted in a sharp increase in installed wind power capacity in particular. Wind power is seen as a particularly attractive source of renewable energy capacity in the UK due to favourable resources and a competitive cost of energy for onshore sites, with 8.8 GW of capacity currently installed [1]. Constraints from visual and environmental impacts, together with improved wind resources, have led to the acceptance of greater financial costs and the exploitation of offshore sites, with over 5 GW installed to date [1]. Both onshore and offshore, the wind industry now has significant operational experience, with some of the earliest wind farms approaching the end of their design life. Material fatigue is a design critical factor which dictates the safe operational life of wind turbines, but is subjected to numerous areas of uncertainty in the level of environmental loading and structural response, as well as material properties and manufacturing methods. Therefore, a conservative design must be ensured from the outset, which presents the potential for fatigue life extension of installed assets if improved knowledge of their operational experience can be obtained. This thesis details the methodology for a fatigue load assessment of operational offshore wind turbine support structures using measured data, and attempts to quantify areas of loading which contribute to total fatigue damage. The methodologies developed build on existing recommendations for onshore wind turbines to incorporate the additional effects of the offshore environment. Results from measured loading suggest that design fatigue levels can be reduced if operational monitoring is included. Operational experience can allow design conservatism, which is necessary due to uncertainties in structural properties and in levels of stochastic loading, to be more accurately quantified.

The current trends for next generation turbofan engines are towards shorter nacelles and increased distances between the fan and the outlet guide vanes. This leads to an overall reduction in lined surface areas as well as an increase in the relative importance of the interstage liner, which is the liner placed between the rotor blades and the stator vanes. The interstage is different in that the liner is subject to a mean flow with a strong swirl component and shear. This project will contribute to understanding and predicting the effect of the swirl on liner attenuation and consists of 4 steps: To model an eigenvalue problem that includes sheared and swirling mean flows and acoustic absorption, to develop a code based on this eigenvalue problem and to validate it, to compare results from this code with experimental results and to carry out a parametric study to evaluate how the swirling flow afects liner attenuation and optimum impedance. Two models were developed. The first one considers a ducted sheared mean flow and is based on the Pridmore-Brown equation and the second one takes into consideration a mean flow with swirl and shear and is based on the Linearized Euler Equations. For both cases an eigenvalue problem was obtained by applying the normal mode analysis to the governing equations together with the impedance boundary condition. Both models were discretized using a Finite Difference Method. The codes were exhaustively validated against predicted values obtained by other methods for uniform, sheared and swirling mean flows and hard-walled and lined ducts. The swirling mean flow, when present, is a combination of rigid body and vortex swirl. A cross-validation between the Finite difference code based on the Linearized Euler Equation and the JM66 code from Rolls-Royce was carried out for a more realistic case. Axial wavenumbers and pressure and velocity eigenvectors obtained with the JM66 code were compared with the current predictions. A comparison has been conducted of predictions from the current Finite Difference code with measured data at a single frequency for a range of spinning mode numbers. Qualitative agreement is obtained for the measured Power Transmission loss (TL) but the low Mach numbers and modest TL levels meant that the effect of swirl was small nad it was difficult to validate the accuracy at the Finite Difference code specifically for the swirl case. Finally, a parametric study was undertaken for hard-walled and lined ducts for realistic interstage conditions to evaluate the effect sound propagation in swirling flows. This confirmed that the effect of swirl is higher for radial modes near cut-off and tends to vanish for higher radial mode orders. The swirl strongly changes the modal content. When swirl is included, the modal distribution for positive and negative azimuthal mode orders is no longer symmetrical. The higher the swirling flow magnitude, the more the modal content is shifted to negative circumferential mode orders. Co-rotating modes become more cut-on and contra-rotating modes become more cut-off. When acoustic absorptive liners are considered, the swirl changes the liner optimum resistance and reactance and affects the optimum insertion loss. The optimum resistance becomes considerably higher and the change in optimal liner reactance is not as pronounced. The swirling flow also reduces attenuation; the insertion loss is lower when swirl is considered. As a conclusion, swirling flow should be considered when designing liners.

Floating wind technology has the potential to produce low-carbon electricity on a large scale: it allows the expansion of o shore wind harvesting to deep water, indicatively from 50-60 to a few hundred metres depth, where most of the worldwide technical resource is found. New design specifi cations are being developed for floating wind in order to meet diverse criteria such as conversion effi ciency, maintainability, buoyancy stability, and structural reliability. The last is the focus of this work. The mechanics of floating wind turbines in wind and waves are investigated with an array of numerical means. They demand the simulation of multiple processes such as aerodynamics, hydrodynamics, rotor and structural dynamics; understanding their interaction is essential for engineering design, verifi cation, and concept evaluation. The project is organised in three main parts, presented below. Aero-hydro-mechanical simulation, characterising the rigid-body motions of a floating wind turbine. An investigation of multi-physical couplings is carried out, mainly through EDF R&D's time-domain simulator CALHYPSO. Wave forces are represented with the potential- ow panel method and the Morison equation. Aerodynamic forces are represented by a thrust model or with the blade element momentum theory. Main fi ndings: Exposure of fi nite-angle coupling for semi-submersible turbines with focus on heave plate excursion; characterisation of the aerodynamic damping of pitch motion provided by an operating vertical-axis turbine. Dynamic mooring simulation, focussed on highly compliant mooring systems, where the fluid-structure interaction and mechanical inertial forces can govern line tension. EDF R&D's general-purpose, finite-element solver Code Aster is confi gured for this use exploiting its nonlinear large-displacement and contact mechanics functionalities. Main findings: Demonstration of a Code Aster-based work ow for the analysis of catenary mooring systems; explanation of the dynamic mooring eff ects previously observed in the DeepCwind basin test campaign. Aeroelastic analysis of vertical-axis rotors, aimed at verifying novel large-scale floating wind turbine concepts in operation, when aeroelastic-rotordynamic instabilities may occur. The finite-element modal approach is used to qualify rotor vibrations and to estimate the associated damping, based on the spinning beam formulation and a linearised aerodynamic operator. Main fi ndings: Characterisation of the vibration modes of two novel vertical-axis rotor concepts using the Campbell diagram; estimation of the related aerodynamic damping, providing information on the aeroelastic stability of these designs.

Perception of scale is important to our activity within a space and to our experience of a landscape. This presents a problem if people cannot predict or convey the scale effects of large structures proposed in a landscape, as has been the case for recent wind turbine proposals in Scotland. To address this problem, this research explored how people perceive scale and scale effects in a landscape. It took wind turbines as an example structure and analysed how different scales of windfarm create different scale effects in different landscapes, as well as how to best assess and communicate these effects. The research applied three methods to address the research questions: Landscape and Visual Impact Assessment (LVIA), which is a standard, structured process applied by professional landscape architects; experiential landscape assessment, which included semi-structured interviews with local people in addition to site assessment; and public attitude and preference study, which included Adaptive Choice-Based Conjoint analysis (ACBC). These different methods allowed the research questions to be explored in different ways, while overlapping in some aspects and providing triangulation. The research findings revealed that our perception of scale and scale effects in a landscape is influenced by numerous attributes and depends on how these are experienced together. Building upon the theoretical background, an important difference between visual scale and spatial scale was highlighted, as well as alternative ways in which scale references are made. Throughout the research, the need for clear communication was emphasised and the findings included identifying the specific words that people use to describe scale effects in the most discriminating way. This research supported other studies in finding that consultation with local people (professionals and the public) was vital to understand in sufficient depth how a landscape was perceived, experienced and valued. In addition, the innovative development of Conjoint Analysis demonstrated how this method can reveal how people judge the relative importance of different attributes that influence landscape and visual effects and, by doing so, offer new possibilities as a tool in landscape research. Building upon the general findings concerning scale, specific findings regarding the scale effects of windfarms included: greater influence of the proximity of a windfarm than size or numbers of wind turbines; greater importance for being in private and/or fixed locations that offer a sense of refuge compared to public locations and/or when moving; the importance of collective effects perceived and experienced by a community; the importance of perceived spatial separation between a viewer and a windfarm (affecting sensitivity to scale effects within open settings); and differences in how people judge the importance of horizontal scale effects compared to vertical scale effects. The research findings contribute to the knowledge and understanding of people’s perception of scale and scale effects in a landscape and they counter some common assumptions and current practice in landscape architecture. They can be applied in practice and policy to help assess scale effects, convey more clearly to people the type of scale effects and how these will affect them, and minimise the adverse scale effects of windfarms through siting and design. The thesis also identifies how to build upon these findings in the future, including recommendations for additional research, new approaches to assessment (including the use of prompt lists) and thresholds for acceptability of scale effects.