Operations & Maintenance (O&M) contributes to about 25% of the total offshore wind farm costs which is rather large. It also influences the levelised production cost per kWh over the entire lifetime of the wind farm. Therefore, it is necessary to reduce the costs involved in O&M activities. One such activity is the logistics involved in O&M. The increasing logistical costs have been a challenge which can hamper the O&M market in the future. Therefore, it is important to take necessary steps to reduce the logistical costs. Wind farm operators have to take up logistical decisions to make optimal use of the available resources to maximise the wind farm availability. These decisions involve which turbines to repair, the route to follow considering constraints like weather conditions and vessel availability. A decision support tool aids in taking appropriate decisions to carry out the logistical activities. This calls for a testing tool which can assess the decisions taken by the planner or the decision support tool. Current research helps in developing a method to assess the quality of the decision taken by the decision maker or the decision support tool. This will help in making better decisions and reducing the costs involved in the logistics of O&M for Offshore Wind Farms (OWF). The objective of this graduation project is to set up guidelines for a test bench to examine the optimality of the decisions taken by the planner or the decision tool to carry out the logistical operations for a shorter duration.

Surrogate modeling is a family of engineering techniques that attracts great interest today and can be applied in many challenging fields. A big advantage of it is that surrogate models (models based on these techniques) offer reliable results by being computationally cheaper than other candidate models. The savings in computational time is usually paramount for problems that involve a lot of variables and parameters and many iterative processes.

In the wind energy industry in particular, the design of the best layout of the wind farm is a problem that has been presented in the literature as an optimization problem; that is, a problem to optimize the wind farm layout in respect to some objective the modeler deems appropriate. More often than not, maximizing the expected power of the layout is mainly considered as this objective. The layout's expected power is -- among other things -- heavily dependent on the layout and the wake interactions between the turbines. The iterative search among many layouts to find the best one can be done with the help of a well-known optimization tool, the binary genetic algorithm. However, this tool cannot work alone, it solely facilitates the search over an adequate number of candidate solutions. To make it work, the modeler should provide it with some model that assesses how good in terms of the objective that has been set.

In this thesis therefore, the theory, the development and the use of two models of interest are investigated: Gaussian Process Regression (a surrogate model) and the Monte Carlo Method (a method based on random sampling). Great care was given to compile the theoretical basis of these models in order to be a good reference point for the non-experienced reader. The nature of these two models differs quite a bit, but they both can be used by the modeler to yield interesting results. These results will be compared to each other and against a third model's results, a specific wake model. This third model is the Original Model which the Gaussian Process Regression model and the Monte Carlo Method model utilize and compare against. The reliability of the results and computational speed will be the measure of success and ranking for these three models.

Finally, the comparison of the three models continues in how potent they are to propose an optimized layout for a wind farm. Each of the three models is coupled with the binary genetic algorithm that is developed specifically to connect with them. Afterwards, the proposed best layouts are discussed. The results show that the Gaussian Process Regression model performs reliably and very fast in comparison to the Original model. On the other hand, the Monte Carlo model, although also fast when it is used to find an optimized layout, could not be verified that it performs reliably and therefore, its results cannot be trusted without going into further investigation. After the comparison, further discussion follows with some recommendations for future research.

Large turbines are a synonym of more energy harvested from the wind, but also of increment in the costs. This dilemma has led many researchers on the field of wind energy to wonder about the optimum size for wind turbines concerning the lowest cost of energy. This project studies the optimum turbine size for offshore applications through the modeling of the costs of the components that have the largest contribution to the Levelized Production Cost (LPC). Since at different power ratings different power densities are optimal, the turbine size is considered in terms of the rotor diameter and the turbine rated power. Therefore, the cost models developed in this work are a function of these two parameters. To develop the cost models, classical scaling approaches are used along with an offshore wind farm design emulator tool. Regarding that the optimum turbine size is not the same for all situations, two case studies of offshore wind farms are established. These case studies contrast some of the relevant characteristics of an offshore wind farm as the power installed capacity, the distance from shore, the water depth, and the wind and wave environment. The optimal size for large, far offshore wind farms was found to be in the range of 10-13 MW, while it was around 5-7 MW for small near shore farms. The optimum turbine size depends mostly on the reduction in the cost of the O&M and the increment in the costs of the turbines and support structure as the turbine scale employed in the wind farm becomes larger. Finally, the blades cost appears to be a limiting factor for the increment in the rotor diameter for the large turbines scales.

Material bend-twist coupling has been widely studied in the research community as a passive control mechanism for a wind turbine. However, there is a lack of research in incorporating it in the rotor design process, with little research being conducted for its application to small wind turbines. The present study focuses on this issue by including bend-twist coupling in the design of a 500W wind turbine by using a combination of parametric studies and a multidisciplinary constrained optimisation approach. By doing so, it aims to establish the effectiveness of bend-twist coupling as a tool for passive load alleviation in small wind turbines. The effectiveness is tested through obtaining a significant decrease in the flapwise blade root bending moment accompanied by only a marginal decrease in the AEP, when compared with the baseline uncoupled turbine. The reference blade is designed under limitations imposed by the rules of the Small Wind Turbine Design Contest. Bend-twist coupling is introduced in the blades with a fixed aerodynamic design. The rotor performance is analysed inHAWCStab2. The internal structure of the blade is created with the intention of producing flexible blades with a single composite material used throughout the blade. Carbon-epoxy and glass-epoxy FRPs are considered as the material to be chosen in the unidirectional laminae. The cross-sectional stiffness analysis is conducted using BECAS for a range of fibre layup angles in both carbon-fibre and glass-fibre blades. Carbon outperformed glass for all fibre angles with regard to the amount of coupling seen in the crosssections. Apart from flapwise bend-twist coupling, other secondary torsion couplings are also present. A load response study is carried out for varying positive fibre layup angles in both carbon-fibre and glass-fibre blades, under steady wind conditions for the operational wind speed range. An increase in the flapwise blade tip displacement and a reduction in the flapwise bending loads with increasing fibrelayup angles is observed for both glass-fibre and carbon-fibre blades. The HAWTOpt2 aero-structural design tool using OpenMDAO as its core is utilised to implement the optimisation. The spanwise fibre layup angle and laminate thickness distribution are the only design variables that were allowed to be manipulated by the optimiser. The objective function is comprised of two different individual objective functions weighed according to the situation. The optimisation cases failed due to inaccurate gradients of the objective function and constraints. Due to time constraints the manufacturing of the blade and, static load and wind tunnel testing were not carried out.

Modern multi-megawatt wind turbines are tall and may reach heights of 200 meter. Tall wind turbines require measurements above typical measurement mast height. As tall measurement masts are expensive and cumbersome to install, wind measurements at hub height are scarce. Currently, the use of lidars in wind measurement campaigns is increasing. Lidars provide wind measurements over the full wind turbine rotor, but lidars are not always available for an extended period. This thesis investigates the possibility of applying the measure-correlate-predict (MCP) method to short-term lidar measurements in order to extrapolate wind shear statistics.

The first step was to compare the wind shear derived from lidar measurements with wind shear derived from mast measurements because the instruments have a different measurement principle. Wind data from mast-lidar pairs at Høvsøre (DK) and Breezanddijk (NL) are used for the analyses. Subsequently, a detailed study of the seasonality of wind shear, as the seasonality becomes a concern
when the measurement period is shorter than one year. The MCP model has been implemented and validated using the commercially available software WindPRO. The data from the measurement sites have been used to test the new approach of estimating the mean wind shear exponent using short-term lidar measurements and MCP. Lastly, the uncertainty in the wind shear exponent is propagated
to uncertainty in the annual energy production.

Although the wind shear statistics are subject to seasonality, this thesis shows that the proposed method has the potential to significantly reduce the error in the estimate of the mean wind shear exponent. As the error in the mean wind shear exponent is decreased, the uncertainty in the vertical extrapolation of the wind resource can be reduced. This reduction ultimately leads to a decrease of the uncertainty in the annual energy production.

The application of stability checks in simulated offshore wind structures is performed through tools that are established in the offshore wind industry. In particular, the structure should fulfill certain strength and fatigue criteria among which Fatigue Limit States (FLSs) checks are critical. In terms of the process, fatigue assessment can be carried out in both time (TD) and frequency domain (FD), with the former being more popular in the offshore wind energy sector. Nevertheless, simplified tools in the FD have been suggested, since they yield results similar to those of the TD analysis. In order to decide upon the choice of tool in performing the FLS estimations, a relative comparison should be implemented. Particularly, fatigue assessment in the TD, fatigue assessment in the FD and a simplified type of fatigue assessment in the FD are examined. These types of fatigue assessment are conducted in three respective tools, with the TD type conducted in NREL’s FAST v8 and both the FD types simulated within MATLAB tools. The tools are judged upon the desirable levels of Modelling & Simulation (M&S) fidelity. A set of criteria are defined for the particular use case, in an attempt to express that fidelity. The criteria’s metrics are additionally provided in the proposed methodology and associated measurements are taken during simulations. Only after conducting further multi-criteria decision analyses (MCDA), the eventual levels of fidelity for the three types of fatigue assessment result to a consequent ranking among the tools. Therefore, the measured criteria lead to the quantification of these levels of fidelity for all three tools and the application of MCDA results to their ranking. The proposed fidelity framework is applied in a case study in order to evaluate the proposed methodology, as well as to select the type of fatigue assessment and consequent tool that should be used within an early design stage. The results indicate that the simplified fatigue assessment in the FD should be preferred over conventional fatigue assessment in both TD & FD. In addition, the criteria included in the fidelity framework seem to provide a multifaceted approach, since none of the tools is favored in all categories. Finally, similarities in results between relevant types of conducted comparisons as well as between different types of MCDA, enhance the consistency of the proposed fidelity methodology and increase its credibility.

Floating offshore wind energy is being widely implemented in deep-water sites thanks to its numerous advantages, which among others include the access to stronger and undisturbed wind resources. In addition, considering the fast-paced growth in size and power generating capacity of offshore wind turbines, the designs of floating foundations need to be continuously improved. Therefore, proper testing (at model-scale) is necessary.

To achieve this, several factors need to be taken into account. For instance, down-scaling for testing of floating structures brings challenges due to the so-called Reynolds effects, which degrade the aerodynamic response of the mounted turbine. Likewise, the rotation of the blades and the motions of the platform as a result of its interaction with waves, have an impact on the wind inflow acting upon the rotor. Thereby, modifying its instantaneous performance.

This Master thesis, carried out in cooperation with MARIN (Maritime Research Institute Netherlands), focuses on developing a reliable methodology that renders in the design of a scaled-down thrust-matched 10MW wind turbine rotor blade, for its further implementation in the testing of a floating offshore support structure.

For this purpose, the aforementioned effects are investigated, and a suitable set of design tools is selected and coupled, in order to realise an optimised blade geometry. For predicting the wind turbine behaviour, this implementation relies on the Blade Element Momentum Theory. Furthermore, the resulting blade's aerodynamic performance is validated using ReFRESCO (MARIN’s in-house CFD code), against the non-dimensional parameters of the DTU 10MW reference wind turbine.

Wind turbine design is subject to load calculation standards. These determine material use which in turn affects wind turbine costs. Wind turbine cost reductions are important as they contribute to the economic feasibility of wind turbines. Therefore careful evaluation of the load standards is paramount for wind turbine design. This thesis offers an evaluation of 50-year ultimate load estimates described in the IEC 61400-1 standard and a tool for wind turbine designers to manage the estimates...

As part of the effort to reduce the cost of offshore wind energy, this thesis addresses the problem of the design of the infield cable topology for offshore wind farms. The final outcome of the project is a tool that can be implemented in a more general optimization platform for offshore wind farm design. Therefore, the main objective is to approximate the optimal inter-array cable connections in affordable computation times. A review of the state of the art collection system designs indicates the radial and branched designs as the designs with the highest potential among the conceptual designs. The key target of the optimization procedure is the minimization of cable cost. Regarding the design constraints, cable capacities are respected and inter-array cable crossings are strictly avoided. The literature review of the related research reveals the complexity of the problem and pinpoints the use of heuristic methods. Planar Open Savings (POS) [1] and Esau-Williams (EW) [2] heuristics are chosen to treat the single cable radial and branched designs respectively. Both algorithms are saving heuristic methods, starting from a star design. At each iteration, the merging of two routes is considered that could yield to the maximum cost saving. After the implementation of the algorithms is validated, a methodology is proposed to allow the possibility for multiple cable types. The behaviour of the heuristics is evaluated both cost and time-wise in a wide range of instances. The results show that the parameters that differentiate their behaviour are the use of single or multiple cable types and the position of the substation, which can be located either centrally or outside the area of the farm. Moreover, a hybrid approach between POS and EW is developed that improves the performance of EW for multiple cable types. Finally, specific recommendations are made regarding the use of the best algorithm for each case. The practicality of the developed tool is enhanced by including the possibility to choose the switchgear configuration and by eliminating the crossings between inter-array cables and transmission lines. Last, modifications allow the minimization of crossings with pipelines/cables that are possibly laid on the seabed. Throughout the report, the comparison of results provided by the tool with the actually installed layouts shows the prospects of inter-array cable cost reductions.

In recent years, the research on Vertical Axis Wind Turbines (VAWTs) have been paving the way for the very large-scale (10-20 MW) floating offshore applications. For a cost effective utilization, VAWTs need to deliver superior aerodynamic and structural performance. Nowadays, the complex ow phenomenon of VAWTs have been better understood and the computational tools have reached to a mature level. It is time to explore the capabilities of this concept and improve its aerodynamic features by innovative design ideas. The main goal of this thesis is to enhance the performance of the lift-driven VAWTs by customized airfoil design and the active ow control with trailing edge aps. To achieve the research goals, four main lines of work are carried out: 1) performance exploration of an actuator cylinder, 2) design of the azimuthal flap control sequences, 3) comparison between the Actuator Cylinder Model and Panel Model in the presence of the active flap control and 4) airfoil design that is specified for effective flap operation on a VAWT blade. The flap control sequences are optimized with the use of the Actuator Cylinder Model for three aerodynamic objectives. These objectives are aiming to improve the power efficiency by maximizing the CP , provide a rated power control by minimizing the CP and decrease the cyclic load ranges by minimizing the CT . Whereas, RFOIL and NSGA-II genetic algorithm are coupled for the airfoil design, which aims for objectives such as superior single airfoil performance, extended flap sensitivity and high flap-wise bending stiffness. For a rotor solidity of 0.1 operating at tip speed ratio of 4, a 10% active flap is able to increase the CP by 7% , decrease the CP by 10% and alleviate 12% of the CT by sacrificing 3% of the CP . It is shown that depending on the solidity, tip speed ratio and the flap authority these figures could be increased. It is possible to brake the rotor with a relatively larger flap authority. The airfoils designed in this work are slightly cambered and span from 27% to 35% thickness, deliver higher maximum CP than a NACA 0018, show good performance in the dirty conditions and have high flap effectivity. Overall, the performance gains acquired by the new airfoils and flap control promises extensive improvements in multiple features of VAWTs such as power effciency, power control, load control that lead to reduced weight and decreased Cost of Energy.

Big wind farms with big wind turbines are more cost effective and produce greener electricity compared to smaller ones. This is one of the reasons for the growth of wind turbine size during the last 3 decades. However, as wind turbines become bigger, their blades become longer, thicker and heavier. This results in larger unsteady loads on blades which is an important limitation for their life time and their size growth. Flow control has emerged as the promising solution both for improving the aerodynamic efficiency and controlling the unsteady loads on wind turbine blades. DBD plasma actuator is an active flow control mechanism that has shown high potentials for unsteady load control with the capability to change lift coefficient to a significant amount with a very fast response time. The current research first intends to identify the variations of angle of attack and lift coefficient on wind turbine blades as a result of gravitational loads, mass and aerodynamic imbalances, turbulence, wind shear, yawed inflow and tower shadow and investigate their corresponding frequencies and the fatigue damage from the blade root bending moments. Then, (single and multi) DBD plasma actuator with different configurations will be used on three different trailing-edge shapes (round, half-round and sharp) of modified version of ’NACA64-2-A015’ airfoil to control the aerodynamic loads via circulation control. This is managed either by manipulation of Kutta condition or acting as a virtual Gurney flap. Furthermore, it is intended to investigate the correlation between the frequency of actuation, frequency of vortex shedding and the amount of lift enhancement.

The thesis is focused on designing a tip-region airfoil for a multi-MW wind turbine. It is approached with the objective of optimizing the geometry of the airfoil for the best trade-off between aero-acoustics and aerodynamic requirements. Using the wind turbine noise prediction tool SILANT it is established that trailing edge noise is the most dominant noise source. Reduction of airfoil self-noise should therefore focus on this noise mechanism. A modified version of the semi-empirical aero-acoustic prediction code by Brooks, Pope and Marcolini is used to compute this trailing edge noise. The panel code RFOIL is used for the boundary layer computations as well as the generation of the aerodynamic polars. A quality assessment of both codes is performed based on aerodynamic and acoustic wind tunnel measurements acquired by the Institut für Aerodynamik und Gasdynamik on the NACA 643-418 airfoil. The multi-objective optimization is executed using the genetic algorithm NSGA-II. The airfoil parameterization that is used is the Class Shape Transformation (CST) method by Kulfan. The results of the optimization are captured in the Pareto front and six individuals are assessed thoroughly. It is found that airfoils can be designed that fulfill all the aerodynamic requirements. Acoustically, only marginal differences can be observed and further research should be conducted on the topic.

Wind energy is one of the fastest growing types of renewable energy. Today, offshore wind represents 14% of the EU wind energy market, and has a huge potential for further growth [1]. Operations and Maintenance (O&M) accounts for 18-23% of the total lifetime cost in offshore wind farms, compared to 12% onshore [2]. The offshore O&M tasks are more costly, being influenced by distance offshore, harsh offshore conditions, wind farm size, wind turbine reliability and maintenance strategy [2]. Exchanges of main components, also known as major interventions, causes significant costs and has been indicated as the largest uncertaintywhen predicting O&M costs [3]. Major interventions are characterized by the need for a jack-up vessel to perform the exchange. No studies have been found on offshore major interventions. Echavarria has previously performed an analysis on the exchange rates of main components based on the onshore WMEP population, which had an average rated power of 233 kW [4]. Blades and generator were identified as most critical components, but it is not known how this reflects current exchange rates for larger turbines. The goal of this research is therefore to determine future failure rates and predict the cost of offshore major interventions.

The reduction of the Levelised Cost of Electricity (LCoE) in wind energy, and offshore in particular, is among the main objectives of research in the academia nowadays, and a demanding task as well. Offshore wind farms are capital intensive investments and lowering uncertainties and costs throughout design, planning, installation and operational phases will offer cheaper electricity production and a more competitive nature against fossil fuel powered energy.
Of course, a big part of the total cost of a wind farm is the wind turbines themselves. Innovations in the design and manufacturing processes are always welcome in order to further advance within the learning curve of the technology and achieve efficient economies of scale. Furthermore, the blades of the wind turbine rotor are its most important component because they express the most basic operation of the turbine, aerodynamics and energy capture. Yet they pose structural challenges. There are efforts to maximise energy output while keeping their mass low, which should subsequently drive down secondary costs. Additionally, another important factor is the increase of energy output in the farm level that can lead to a larger cost reduction.
This thesis aims to investigate the performance and feasibility of lightweight, low power density rotors. This investigation is made by acquiring a performance baseline with the reference rotor of the 10 MW INNWIND machine and comparing it with the proposed alternative rotor designs by means of parametrical modifications. The reference machine rotor radius is 89.166 m, with a blade mass of 41.7 tn and a rated power output of 10 MW operating at an optimal lambda of 7.5. All the new designs include an increase in rotor radius to 103 m. They also include differences in operational parameters such as rated rotational speed, blade slenderness and tip speed, while rated power stays the same. These designs result in different blade masses and allocation of energy production...

One of the main drawbacks of offshore wind energy is its high levelized cost of electricity (LCOE). One explanation for these high costs arises from the large amount of uncertainties that come with such complex projects. As a result of this complexity, it’s difficult to foresee the course of events in advance. Decisions made during the preliminary design phase are often based on limited data while having a great impact on project outcome. A tool is needed to assist engineers during these early stages of design. This tool should deliver good results using limited input data and require little computational time. An example of such a tool is TeamPlay; an engineering model that evaluates offshore wind farm design using automated optimization techniques. In its current state, only a monopile type foundation is analyzed within this process. Since the current trend in the industry is to build larger farms further from shore, this foundation type will become less popular in the future. A jacket type foundation is better suited for far-­‐shore application. In this thesis, a new stand-­‐alone engineering model is created which can be added to TeamPlay’s functionality to extend future use...

The EU goals to decrease wind energy prices are driving the wind energy industry to give more attention to monitoring and improving turbine performance. Meanwhile, as turbines grow bigger and more are placed offshore, performance monitoring costs are increasing, making it more interesting to consider novel devices to measure turbine performance. The purpose of this study was to investigate the applicability of these devices in power performance monitoring and evaluating the potential gains which can be achieved. A comparative study of the measurement accuracies was performed of the nacelle-based Lidar (WindIris) and a spinner anemometer (iSpins) against an IEC-compliant met-mast. Accuracies of both devices in measuring wind speeds, yaw misalignment and power curves were found to be comparable to a met-mast and therefore could be worthy replacements of met-masts for power performance measurements in the future. The impact of non-ideal wind conditions, like yaw misalignment, turbulence and wind shear, on power performance was also investigated using both experimental and Bladed simulated results. No conclusive results were found on the relationship between yaw misalignment and performance loss. The ideal yaw error was found to increase with increasing wind shear, caused by higher angles of attack in the top of the rotor area. The direct impact of turbulence intensity and wind shear on power curves was found to be wind speed dependent and not that significant on overall energy production. Finally, combining the knowledge acquired about yaw misalignment and device accuracies, a financial feasibility study was performed to evaluate future implementation of the novel devices for yaw misalignment correction. Since no conclusive evidence was presented that correcting for yaw misalignment could increase power performance significantly, current implementation of such a correction campaign is not recommended. If a deliberate yaw misalignment campaign were to be performed, however, the impact of yaw misalignment on turbine performance should be quantifiable and expectations are that implementation of novel devices should be financially feasible.

The main purpose of this project was the creation of a tool, based on the research performed by Scheldbergen [25] and Roscher [24], capable of performing Finite Element Analysis (FEA) on a Horizontal Axis Wind Turbine (HAWT) blade and minimize its weight by altering the various thicknesses locally, always satisfying a number of structural constraints. The first goal was the development of a geometry creation algorithm based on a Non Uniform Rational Basis Splines (NURBS) algorithm developed by Ferede [14], with a more complex spanwise/chordwise discretization technique in order to more accurately design a discretized HAWT blade. The second goal was the alteration of the material creation algorithm developed by Scheldbergen [25], so that different stacks at various blade locations can be assigned. Moreover, the aerodynamic loads generation algorithm of Scheldbergen [25] was modified to apply for different airfoils along the blade span. Also, Blade Element Momentum (BEM) theory was used for the calculation of the aerodynamic loads and the software XFOIL was used for the aerodynamic analysis of the airfoils (pressure distribution on the airfoil at corresponding angles of attack and Re numbers). An initial HAWT blade design was created, matching the SANDIA 5 MW wind turbine blade [23] geometry and materials. Furthermore, the apwise/edgewise stiffness, moments of inertia, mass and mode shapes were also validated. Additionally, the SANDIA blade was analyzed in DNV GL Bladed in order to validate the aerodynamic loads on the blade. Following, the tool was designed to process the geometry, the materials and the gravitational/ centrifugal/aerodynamic loads of the blade and translate them to an input for the FEA software MSC Nastran for Linear Static Analysis (SOL 101), Buckling Analysis (SOL 105) and Modal Analysis (SOL 103). The post processing algorithm of Scheldbergen [25] was modified to apply for a HAWT (instead of a VAWT), transforming the results of the FEA analysis into optimization constraints (ultimate load, buckling, tip deflection and fatigue). The final part of the algorithm involved the minimization of the blade's mass by altering the thickness at various locations, using the MATLAB function fmincon. Concluding, a case study of a smart rotor blade equipped with trailing edge ap (TRF) was examined. A _ 2 flap was used at 90-100% of the chord and 78-98% of the span. Two kinds of optimization were performed for the HAWT and smart rotor scenarios; one that included ultimate stress, tip deflection and fatigue constraints (UL-TD-FA) and one that also included buckling constraints (UL-BU-TD-FA). It was found that the buckling constraint was the limiting factor of the optimization and the fatigue constraint was the least dominant. The initial design of the smart rotor blade showed a 16.5% decrease of the maximum fatigue damage and a 2% decrease in the maximum stress. The optimized smart rotor blade mass was 0.5 % lower in the UL-TD-FA scenario and 2.5% in the UL-BU-TD-FA scenario compared to the HAWT blade. The tool created is capable of creating a flexible and fairly accurate representation of a HAWT and smart rotor blade. It also provides the ability to structurally analyze the blade under the most significant structural criteria and minimize the blade's weight under specific loading conditions. The tool constitutes a good starting point for more detailed structural analysis of smart rotors and more complex structural optimization of HAWT and smart rotor blades.

In this research work, the phenomenon of extreme wind events or gusts has been studied in detail and different aspects related to the nature of gusts are explored.
In order to detect wind gusts from a stochastic time series different gust detection techniques collected from previous research works and literature studies were compiled, refined, verified and compared against each other. In addition some important insight is also given regarding the setting up of appropriate values for various gust defining parameters.
The gust detection techniques are developed into computational codes and applied over different data sets. A comparison between these techniques highlights the pros and cons of each one of them. The peak to peak method and the velocity increment method provides accurate information about the maximum wind speed acceleration within a small time interval. Other methods like peak over threshold and the acceleration over threshold methods are useful to detect specific type of wind gusts above a certain threshold.
Wind data sets sampled at high frequency resolution and from different geographical locations were obtained and analyzed through these gust detections algorithms. Among these locations are the offshore wind farm at Egmond aan Zee (OWEZ), IJmuiden and the Cabauw Experimental Site for Atmospheric Research (CESAR) which are a representative of a near offshore, far offshore and an onshore location respectively. By using a uniform gust threshold criteria for peak over threshold and acceleration over threshold methods, a comparison between different locations reveal that the maximum gusts were detected for IJmuiden which generally has higher wind speeds throughout the year.
For each location, the total number of gusts detected have been combined to obtain a mean gust shape. Furthermore, the maximum wind gusts are selected from each month and compared with the standard IEC gust shapes.
The available high resolution wind data is for a duration of 1 year only which is not sufficient for the prediction of a maximum 50 year gust. However two different approaches are discussed to demonstrate the procedure. A statistical approach involving the extrapolation of data to predict the amplitude of maximum 50 year gust highlights the need for the availability of long term wind data. The analytical approach involving the calculation of the return period of different gusts is also explained and the results presented within this report are promising to continue further research within this domain.
The techniques, findings and conclusions obtained through this research work can be further tested and eventually utilized to compliment or improve upon the existing extreme load cases of the wind turbine design standards.

Low level jets (LLJs) are situations where wind speed maximums occurs close to the surface. Unfortunately, the influence of LLJs on wind turbine power production is still difficult and costly to quantify due to that the existing LLJ models are all time-based. The work that is done in this report addresses the research question should low level jets be included in offshore wind turbine design.
In this report, data from an offshore meteorology site IJmuiden is studied to analyze the occurrences and properties of LLJs. It is found that LLJs are frequent phenomena which occur at 1/3 of the days in a year. Most of the LLJs are observed when the atmosphere is very stable, which means stability is a crucial factor to LLJs. Based on the diabatic wind profile model, an assumption is made that the LLJ wind speed profile is related to friction velocity, Obukhov length and roughness length. The observed data is divided into groups by Obukhove length to find the relationship between these factors and the wind speed prole of a LLJ. It is found that the LLJ model can be fully dened by introducing an intersection height. The newly developed model is applied to wind turbine power analysis. The theoretical results agree with the simulations on Bladed, which show that power production variation due to the occurrence of LLJs depends on multiple factors, these are: Obukhov length, friction velocity, wind turbine hub height
and wind turbine rotor radius. The power production of 5 MW reference wind turbine due to the occurrence of LLJs diers from -0.27 to +0.31 MW compared to the expected power production considering constant wind speed across the rotor disc when Obukhov length varied from 60 to 180 m. The results also imply the applicability of the new LLJ model. It is recommended that wind turbine engineers should include LLJs in wind resource assessment. This LLJ model can be further improved by future research with data obtained from onshore meteorology sites. In addition, this research can be extended by applying this model to fatigue and load studies.