The majority of offshore wind farms utilize monopile substructures. As these wind farms are typically located in water depths less than 30 meters, the effect of breaking waves on these structures is of great concern to design engineers. This research investigation examines many of the practical considerations and alternative ways of estimating breaking wave forces. A survey of existing European wind farms is used to establish a realistic range of basic design parameters. Based upon this information a parametric study was pursued and a series of realistic design scenarios were evaluated. Comparisons include the sensitivity to the wave force model as well as to analytical and numerical wave theories used to evaluate the wave kinematics. In addition, the effect of different kinematics stretching techniques for linear waves is addressed. Establishing whether the bathymetry will induce spilling or plunging wave breaking is critical. Spilling wave breaking can be addressed using existing wave and wave force theories; however for plunging wave breaking an additional impact force must be introduced. Dimensionless design curves are used to display pertinent trends across the full range of design cases considered. This research study provides insight into the evaluation of the maximum breaking wave forces and overturning moment for both spilling and plunging breaking waves as a function of bottom slope.

Wind energy is recognized as a sustainable source of energy that is both reliable and capable of dramatically reducing pollution to the environment and dependency on non-renewable fuels, leading to research on wind turbines. Nowadays, the demand for electricity increases. Considering that the greater the distance from shore, the greater the wind, more electricity will be generated along the coast. It is necessary and beneficial to study large scale offshore wind turbines. The National Renewable Energy Lab (NREL) 5-MW offshore wind turbine is simulated using a three-dimensional computational fluid dynamics (CFD) model in this article. A realizable k-ε viscous model is used to simulate turbulence flow. The work is validated by comparing the torque with published simulated data, and satisfied consistency is observed. Further simulation and comprehensive analysis demonstrate the flow features and aerodynamic performances of 5-MW offshore wind turbine under various wind and rotor speeds. The velocity profiles, total pressure distribution, pressure coefficient, rotor thrust, torque and aerodynamic properties are obtained in detail.

The installed capacity of European Offshore Wind Turbines (OWT) is likely to rise from the 2014 value of 7GW to 150GW in 2030. However maintenance of OWT is facing unprecedented challenges and cost 35% of lifetime costs. This will be equivalent to £14billion/year by 2030 if current OWT maintenance schemes are not changed. However the complexities around OWT operation require tools and systems to optimise OWT maintenance. The design of optimal OWT maintenance requires failure analysis of over 10,000 components in OWT for which there is little published work relating to performance and failure. In this work, inspection reports of over 400 wind turbine gearboxes (source: Stork Technical Services) and SCADA data (source: Shetland Aerogenerators Ltd) were studied to identify issues with performance and failures in wind turbines. A modified framework of Failure Mode Effects and Criticality Analysis (i.e. FMECA+) was designed to analyse failures according to the unique requirements of OWT maintenance planners. The FMECA+ framework enables analysis and prediction of failures for varied root causes, and determines their consequences over short and long periods of time. A software tool has been developed around FMECA+ framework that enables prediction of component level failures for varied root causes. The tool currently stores over 800 such instances. The need to develop a FMECA+ based Enterprise Resource Planning tool has been identified and preliminary results obtained from its development have been shown. Such a software package will routinely manage OWT data, predict failures in components, manage resources and plan an optimal maintenance. This will solve some big problems that OWT maintenance planners currently face. This will also support the use of SCADA and condition monitoring data in planning OWT maintenance, something which has been difficult to manage for a long time.

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No description available.

This thesis summarizes the simulation and analysis performed for the MassCEC project described herein. The intent was to perform a “dry run” of the new IEC offshore wind turbine design standard, IEC 61400-3-1 and to illustrate the use of that standard in the Massachusetts Offshore Wind Energy Area. IEC 61400-3-1 is a design standard used to ensure wind turbine structural performance over the design life of the machine. Each installed wind turbine must be certified by a Certified Verification Agent using this standard before installation. The certification process typically uses a structural dynamics model to predict a turbine’s structural response in the presence of a range of operational conditions and meteorological oceanographic conditions, which are codified into Design Load Cases. The area in question is located approximately 24 km of south of Martha’s Vineyard with an assumed water depth of 40 m. The National Renewable Energy Laboratory’s FAST software (V8.12) was used to perform simulations of a large subset of the DLCs. Wind data files were generated using NREL’s TurbSim and IECWind. This thesis discusses the instructions of the standard, preparation for simulation of Design Load Cases, and analysis of results. Results from simulations show the application of the standard in detail as applied to a reference turbine. Limitations and ambiguities of the standard in the simulation of control failure cases are analyzed. The application of the standard to hurricane loading is also analyzed alongside an example case for a Category 5 hurricane. The standard is found to be fundamentally reasonable in application to a reference turbine in the Massachusetts Offshore Wind Energy Area.

Dans le contexte actuel de transition énergétique, les acteurs de la production électrique (dont EDF) s'orientent de plus en plus vers les technologies "bas carbone", permettant de développer leur mix énergétique et d'assurer une production toujours plus respectueuse de l'environnement. Parmi l'ensemble des alternatives progressivement industrialisées au cours de ces dernières décennies, l'énergie éolienne voit son développement s'accélérer. De nouveaux projets voient le jour, notamment avec le développement de parcs éoliens posés en mer le long des côtes françaises.Afin de garantir une sécurité maximale des installations vis-à-vis des défaillances mécaniques, les ingénieurs doivent mettre en place un ensemble de vérifications ayant pour but d'assurer l'intégrité structurelle pendant une durée de vie donnée. Cette étape, nécessaire à la certification et donc à l'industrialisation du projet, exige un investissement numérique important. Dans le cas particulier de l'estimation de l'endommagement à durée de vie, un ensemble complet d'analyses doit être effectué afin de simuler les réactions structurelles en différents points de la conception et ce, pour l'ensemble des conditions environnementales de chargement possibles (cas de charge). Au total, quelques milliers de simulations correspondant à l'ensemble des situations probables sont à prévoir pour la seule estimation de l'endommagement à durée de vie. De plus, la prise en compte des différents phénomènes physiques du problème (aérodynamique, hydrodynamique, mécanique élastique), ainsi que la considération des non-linéarités des réponses liées à l'asservissement de la turbine, impliquent l'utilisation de codes de résolution temporels et multi-physiques coûteux pour chacune des situations de chargement à simuler.Afin de réduire l'investissement lié à l'estimation de cet endommagement, l'utilisation de méthodes numériques de substitution (également appelées métamodèles) est une alternative prometteuse. Ces méthodologies ont montré leur efficacité dans divers domaines de l'ingénierie permettant d'approcher, par diverses hypothèses statistiques, la réponse de modèles numériques en ne considérant qu'un nombre réduit de simulations.Ce travail de thèse s'est focalisé sur le développement d'outils numériques pour le dimensionnement efficace des structures éoliennes en mer et plus particulièrement sur l'utilisation des métamodèles de Krigeage (ou méthode de régression par processus gaussien) pour l'estimation de l'endommagement mécanique. Sous certaines hypothèses, cette méthode de substitution se prête particulièrement bien à l'approximation des réponses de modèles physiques, notamment grâce à la mise en place facilitée d'architectures itératives d'enrichissement ("active learning strategy"). Deux domaines ont principalement été étudiés : l'estimation rapide des quantités d'endommagement structurel par le développement de la méthode "Adaptive Kriging for Damage Assessment" (AK-DA) et les possibilités d'utilisation de cette dernière dans le cadre d'études de la fiabilité conceptuelle au regard de la tenue à l'endommagement. L'applicabilité de ces méthodes a été illustrée via l'utilisation d'exemples numériques inspirés du contexte industriel et de ses contraintes. / The mechanical certification of wind turbine structures is required for the funding of newoffshore projects on the French coasts. In order to ensure a maximal safety level of installations,a series of structural analyzes are required by the certification bodies. Amongst all, thedamage based computations represent an important numerical effort for EDF. The presentedworks focus on the applicability and the performances of Kriging metamodels for the estimationof the lifetime cumulated damage of offshore wind turbine structures (AK-DA approach)and the damage based reliability assessment of new designs (AK-MCS/AK-DA coupling).

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The trend of offshore wind power is bigger and bigger wind turbines. Turbines are now becoming so big that existing installation vessels no longer are feasible and new bigger installation vessels are needed. Ship owners hesitate to order new vessels worried that the rapid turbine growth will continue and make also the new vessels obsolete in a few years. This can create a bottleneck in the offshore wind market.   This thesis assignment attempts to develop a telescopic tower as an alternative way of installing offshore wind turbines. A telescopic tower can decrease overall height and COG during marine installation, giving opportunity to install the largest wind turbines also with existing vessel fleet.   The method for developing the telescopic tower is to first find the main problems and functions of the concept. A design basis based on a 12 MW reference wind turbine is developed. Based on this reference turbine different solutions to the main problems and functions are developed by creative thinking, literature research, modelling, calculations and analysis. A cost/benefit analysis is performed to investigate if there is any economic potential in the developed solution. To complete the study other installation methods and telescopic tower concepts are investigated for benchmark comparison.   The telescopic tower will have two sections. Shoulders are welded to the inner wall of the lower tower. The upper tower fit inside the lower tower and a telescopic mechanism is installed below to lift the assembly as the mechanism climb the shoulders of the lower tower. The telescopic mechanism works much like a pin and hole mechanism used for jack-up rigs. The pins engage/disengage with the shoulders by the movement of linear actuators. The vertical climbing motion is provided by hydraulic cylinders. The power source is an HPU placed on the wind turbine external platform.   To connect the upper and lower tower permanently a friction connection with long slotted holes is used. This connection is developed for assembly of onshore towers in an EU-sponsored project called Histwin. The walls of the lower and the upper tower overlap at the connection and are pressed together by pretensioned bolts to create a friction surface that hold the loads from the upper tower.   The conclusion is that the telescopic tower is technically feasible and can be installed by the existing installation vessel fleet. The economic feasibility is dependent on the specific project characteristics, but there are scenarios where the telescopic tower can have great economical upside.

Für Offshore-Windenergieanlagen (OWEA) wird die Überwachung mittels Monitoringsystemen immer wichtiger für den effizienten Betrieb. Problematisch ist, dass nicht nur die OWEA selbst, sondern auch die Monitoringsysteme altern. Für verlässliche Monitoringsysteme müssen daher auch deren Alterungsprozesse analysiert werden, damit das System lebensdauerumfassend an der OWEA verwendbar ist. Hierfür wurden Laser-Triangulationssensoren untersucht, die unterschiedlichen Temperaturen und Luftfeuchten ausgesetzt wurden. Das Messsignal wurde temperaturkompensiert und hinsichtlich seiner Messunsicherheit bewertet. Ferner ergaben erste Alterungsversuche, dass noch keine signifikanten Alterungserscheinungen aufgetreten sind.