The need for sustainable energy sources becomes greater each year due to the continued depletion of fossil fuels and the resulting energy crisis. Solutions to this problem are potentially in the form of wind turbines which have been receiving increased support at a micro level. At present a number of wind turbines are being developed that are of cross-flow vertical axis operation which have shown significant increases in performance compared to existing technologies. From an extensive literature review a number of key issues have been highlighted which are concerned with design, operation and diagnostics of this new wind power technology which have been used to formulate the scope of this research. A design procedure for a cross-flow machine that features both a multi-blade rotor and fixed outer stator guide vanes has been derived in which both rotor and stator blade profiles have been generated for a low wind speed urban application. Using these blade profiles a prototype wind turbine has been fabricated and used for full scale development testing. In the presented work both experimental and numerical investigations have been carried out to determine the operational characteristics of this new technology. The experimental data obtained under controlled laboratory conditions has been used to validate a Computational Fluid Dynamic (CFD) model which has been used throughout. A flow field analysis of the machine has highlighted large asymmetries in both pressure and velocity about the central axis of the machine in both stationary and rotating frames of reference. This has identified primary inefficiencies within the design which limit the torque generating capability of the rotor due to blockage effects and downstream blade interactions. This asymmetry has been quantified in the form asymmetry ratio and used to determine downstream rotor effects and the optimum location of multiple wind turbines which is seen to be x/D >10 in order to minimize performance reductions. The torque and power generation capabilities of the machine have been characterised at both 'design' and ‘offdesign' conditions in which individual blade torque contributions have been quantified. This has highlighted specific energy transfer zones within the turbine namely at a few key blades on the windward side of the rotor. It has also shown counter-rotating torques generated on the leeward side of the machine at specific blade positions during the cycle. Overall performance has been quantified in which a maximum CT = 1.7 and CP = 0.24 has been observed which has some similarities to the Savonius rotor. Geometric effects on torque and power response have been quantified in which a strong dependence on stator blade number is noticed. Further, maximum performance output of the machine is generated at the baseline design condition. Using torque response data a multiple regression model has been developed in which a design equation for crossflow rotor torque has been derived which can be used during the conceptual design phase. Finally, the effectiveness of a two-dimensional transient CFD model to predict cross-flow wind turbine rotor blade loss has been evaluated against full scale experimental data. It has shown that from analysis in the frequency domain specific blade faults can be recognised which agrees well with experimental data obtained. The use of this model for wind turbine performance emulation has been described.

Wind turbines are the largest contributor to renewable energy both in Britain and the rest of Europe. With a rise in the installed capacity and an increase in offshore wind energy due to governments green targets by 2020, there has been a large development in new wind turbines for optimized performance. The present thesis deals with the uncertainties in regards to the lightning phenomenon on wind turbines with emphasis on the rotor blades. Rotor blades are the most expensive part to replace in the event of lightning related damage. The research presents results based on lightning data analysis on wind turbines, backed up by finite element analysis testing of wind turbine systems. The final chapters include the testing and improving of lightning protection systems installed on modern day rotor blades. The first part of the thesis deals with the theoretical understanding of the lightning phenomenon and its effect on wind turbine systems. The core work of the research begins with the analysis of lightning data collected over Nysted wind farm and different wind turbines installed over the world. The data analysis helps in identifying the parts of the wind turbine that are at high risk to lightning attachment and related damage. The peak current levels of the lightning strikes seen on the wind turbine are compared with those in modern day lightning standards, and show that historic data in the standards are not an exact match to the real case scenarios. The lightning data analysis also sheds light into the importance of upward initiated lightning, which will become important for large wind turbines, especially in their new offshore environment. A full scale 3D FEA model of a wind turbine, with lightning protection systems installed in its rotor blades, is subjected to electrical stresses to find likely attachment points in regards to upward initiated lightning, and these results are later compared to those found in the data analysis. The second half of the thesis deals with the testing of new materials and prototype blades, to be introduced to reduce their radar cross section. The new materials include a large amount of carbon content which affects the efficiency of the lightning protection system. High voltage and high current tests backed up with finite element analysis have been performed to find how these new materials affect the performance of the lightning protection system. The results indicate that further work needs to be done before these new materials can be integrated into the blade, as they increase the risk of lightning related damage to the blade.

Wind is a fluctuating source of energy and, therefore, it can cause several technical impacts. These can be tackled by forecasting wind speed and thus wind power. The introduction of several statistical models in this field of research has brought to light promising results for improving wind speed predictions. However, there is not converging evidence on which is the optimal method. Over the last three decades, significant research has been carried out in the field of short-term forecasting using statistical models though less work focuses on longer timescales. The first part of this work concentrated on long-term wind speed variability over the UK. Two subsets have been used for assessing the variability of wind speed in the UK on both temporal and spatial coverage over a period representative of the expected lifespan of a wind farm. Two wind indices are presented with a calculated standard deviation of 4% . This value reveals that such changes in the average UK wind power capacity factor is equal to 7%. A parallel line of the research reported herein aimed to develop a novel statistical forecasting model for generating monthly mean wind speed predictions. It utilised long-term historic wind speed records from surface stations as well as reanalysis data. The methodology employed a SARIMAX model that incorporated monthly autocorrelation of wind speed and seasonality, and also included exogenous inputs. Four different cases were examined, each of which incorporated different independent variables. The results disclosed a strong association between the independent variables and wind speed showing correlations up to 0.72. Depending on each case, this relationship occurred from 4- up to 12-month lags. The inter comparison revealed an improvement in the forecasting accuracy of the proposed model compared to a similar model that did not take into account exogenous variables. This finding demonstrates the indisputable potential of using a SARIMAX for long-term wind speed forecasting.

Floating wind turbines (FWTs) are considered a new lease of opportunity for sustaining growth from offshore wind energy. In recent years, several new concepts have emerged, with only a few making it to demonstration or pre-commercialisation stages. Amongst these, the spar-buoy based FWT has been extensively researched concept with efforts to optimise the dynamic response and reduce the costs at acceptable levels of performance. Yet, there exist notable lapses in understanding of these systems due to lack of established design standards, operational experience, inaccurate modelling and inconsistent reporting that hamper the design process. Previous studies on spar-buoy FWTs have shown inconsistencies in reporting hydrodynamic response and adopted simplified mooring line models that have failed to capture the coupled hydrodynamic behaviour accurately. At the same time, published information on drive-trains for FWTs is scarce and limited to geared systems that suffer from reliability issues. This research was aimed at filling the knowledge gaps with regard to hydrodynamic modelling and drive-train research for the spar-buoy FWT. The research proceeds in three parts, beginning with numerical modelling and experimental testing of a stepped spar-buoy FWT. A 1:100 scale model was constructed and tested in the University of Edinburgh’s curved wave tank for various regular and irregular sea states. The motion responses were recorded at its centre of mass and nacelle locations. The same motions were also simulated numerically using finite element method based software, OrcaFlex for identical wave conditions. The hydrodynamic responses were evaluated as Response Amplitude Operator (RAO) and compared with numerical simulations. The results showed very good agreement and the numerical model was found to better capture the non-linearities from mooring lines. A new design parameter, Nacelle Magnification Factor, was introduced to quantify coupled behaviour of the system. This could potentially encourage a new design approach to optimising floating wind turbine systems for a given hub height. The second part of the research was initiated by identification of special design considerations for drive-trains to be successfully integrated into FWTs. A comparative assessment of current state of the art showed good potential for directdrive permanent magnet synchronous generators (PMSG). A radial flux topology of the direct-drive PMSG was further examined to verify its suitability to FWT. The generator design was qualified based on its structural integrity and ability to ensure minimal overall impact. The results showed that limiting the generator weight without compromising air-gap tolerances or tower-foundation upgrades was the biggest challenge. Further research was required to verify the dynamic response and component loading to be at an acceptable level. The concluding part of research investigated the dynamic behaviour of the directdrive generator and the various processes that controlled its performance in a FWT. For this purpose, a fully coupled aero-hydro-servo-elastic model of direct-drive FWT was developed. This exercise yet again highlighted the weight challenge imposed by the direct-drive system entailing extra investment on structure. The drive-train dynamics were analysed using a linear combination of multi-body simulation tools namely HAWC2 and SIMPACK. Shaft misalignment, its effect on unbalanced magnetic pull and the main bearing loads were examined. The responses were found to be within acceptable limits and the FWT system does not appreciably alter the dynamics of a direct-drive generator. Any extra investment on the structure is expected to be outweighed by the superior performance and reliability with the direct-drive generator. In summary, this research proposes new solutions to increase the general understanding of hydrodynamics of FWTs and encourages the implementation of direct-drive generators for FWTs. It is believed that the solutions proposed through this research can potentially help address the design challenges of FWTs.

This thesis presents Computational Fluid Dynamics (CFD) simulations of renewable turbines akin to those used for wind, hydro, and tidal applications. The models developed took the form of actuator discs with the solution of incompressible Reynolds-Averaged Navier-Stokes equations with the k-ω SST turbulence models. Simulations were initially conducted of a single turbine in water and air and then two axially aligned turbines to study the flow field interactions. These models were compared with previous theoretical, experimental and numerical data evident in the literature. Generally, good agreement was found between these models and other analogous data sources in terms of velocity profiles in the far wake. The actuator disc method was underpinned using the transient actuator line method, which showed good agreement from a quantitative and qualitative viewpoint. However, it required significant additional computational time when compared to the actuator disc method. Each of the models were developed and solved using complimentary commercially available CFD codes, ANSYS-CFX and ANSYS-Fluent. For this type of study, a critical evaluation of these codes was in all probability performed for the first time, where it is shown that for the studies investigated in this thesis ANSYS-CFX performed better than ANSYS-Fluent with respect to the computational effort (i.e. time and lines of code).

Stop signal task of response inhibition, I find that response inhibition (stopping) is slowed in the presence of angry facial expressions, and such slowing is greater in individuals high in trait neuroticism. Further, as predicted, the influence of neuroticism is moderated by individual differences in emotion regulation, such that good emotion regulation ‘buffers’ the impact of neuroticism. The implications of these findings for current cognitive models of threat-processing are discussed.

This thesis investigated the capability of multi-terminal high voltage direct current (HVDC) networks based on voltage source converter (VSC) technology to transfer power generated from offshore wind farms to onshore grids and interconnect the grids of different countries. Variable speed wind turbines and other low-carbon generators or loads that are connected through inverters do not inherently contribute to the inertia of AC grids. A coordinated control scheme for frequency support from multi-terminal VSC-HVDC (MTDC) scheme was designed to transfer additional power to AC grids from the kinetic energy stored in the wind turbine rotating mass and the active power transferred from other AC systems. The wind turbine inertia response limited the rate of change of AC grid frequency and the active power transferred from the other AC system reduced the frequency deviation. The wind turbines recovered back to their original speed after their inertia response and transferred a recovery power to the AC grid. An alternative coordinated control scheme with a frequency versus active power droop controller was designed for frequency support from MTDC schemes, in order to transfer the recovery power of wind turbines to other AC systems. This prevented a further drop of frequency on the AC grid. The effectiveness of the alternative coordinated control scheme was verified using the PSCAD simulation tool and demonstrated using an experimental test rig. A scaling method was demonstrated for a multi-terminal DC test rig to represent the equivalent steady state operation of different VSC-HVDC systems. The method uses a virtual resistance to extend the equivalent DC cable resistance of the test rig through the action of an additional DC voltage versus DC current droop controller. Three different VSC-HDC systems were modelled using the PSCAD simulation tool and demonstrated on the DC test rig with virtual resistance, showing good agreement.

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.

Recent in-flight instances of aircraft engine power loss involving hail ingestion have forced the manufacturers to demonstrate successful engine operation whilst ingesting hail. The main objective of this research project has been to obtain an understanding of the basic characteristics of hailstone impacts. A hail gun was designed to fire simulated hailstones at speeds up to 175 m/s. Three measurement techniques were used to determine the impact characteristics of the hailstones, i.e: patternator, high speed cine-photography, and still photography with short duration flashes. Using these techniques, the basic impact characteristics in terms of post-impact particle size, velocity and mass distribution were obtained for a variety of target configurations. The influence of seemingly important parameters on the impact characteristics were investigated, including approach angle and velocity, target curvature, and target rotation. Studies were further made into multiple impacts, and the effect of target curvature and rotation on the impact characteristics. Based on the experimental results, a set of empirical rules and a mathematical model describing hailstone break-up were defined.

The need for sustainable energy sources becomes greater each year due to the continued depletion of fossil fuels and the resulting energy crisis. Solutions to this problem are potentially in the form of wind turbines, for sustainable urban environment, that have been receiving increased support. At present, a number of wind turbines have been developed that show significant increase in performance compared to existing technologies. From an extensive literature review, a number of key issues have been highlighted which are concerned with the design, optimisation and diagnostics of Vertical Axis Wind Turbines (VAWTs) that have been used to formulate the scope of this research. A design procedure for a vertical axis wind turbine, that features both multi-blade rotor and fixed outer stator guide vanes, has been derived, in which both rotor and stator blade profiles have been generated for a low wind speed application. In the presented work, numerical investigations have been carried out extensively to determine the optimised design of the VAWT. Sliding mesh technique has been used for the rotation of rotor blades. This new technique captures the transient flow phenomena that occur when the rotor and the stator blades interact with each other. Hence, the results predicted by CFD using this technique are much superior in accuracy. Furthermore, a detailed flow field analysis of the VAWT has highlighted large asymmetries in both pressure and flow velocity about the central axis of the VAWT in both the stationary and the rotating frames of references. Various geometric parameters associated with the design of the VAWT have been investigated over a wide range in order to analyse the effect of these parameters on the performance output of the VAWT. These geometric parameters are the blade angles, the number of blades in the VAWT and the size of the rotor/stator sections of the VAWT. It has been shown that all these parameters considerably affect the performance output of the VAWT and hence have been optimised in the present study for maximum performance output of the VAWT. One of the key elements of this study is the development of a performance prediction model of the VAWT that takes into account the effects of the aforementioned geometric parameters of the VAWT. This novel prediction model is both robust, user-friendly and has shown to predict the performance output of the VAWT with reasonable accuracy. Hence, the prediction model can be used by the designers of the VAWT. Nowadays, condition based health monitoring of mechanical systems is topic of vast research. Most of the studies in this field use experimental facilities and conventional toolboxes to handle the output data from the sensors. With the advent of advanced CFD tools, it has now become possible to use CFD as an effective tool for fault detection in VAWTs. An attempt has been presented in this study regarding condition monitoring of VAWTs for sustainable urban environment. Various faults like missing blade and slits in blade have been investigated and analysed. It has been shown that CFD can detect these faults and show the effects of these faults on local flow parameters such as pressure and velocity.