Thesis (MEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Support tower structures of Wind Energy Conversion Systems (WECS) are major cost items and by means of integrated design and optimization, the Life-Cycle Cost (LCC) can be reduced substantially. In this thesis, Horizontal Axis Wind Turbine (HAWTs) tower structures are investigated by means of a technique or tool that can bene t in decision making related situations to reduce the LCC of such WECS support towers from inception to disposal. Often, during the conceptual design phase a certain level of uncertainty or fuzziness exists and plays a role. The central focus in this project is on lattice type towers; however an account on tapered, tubular monopole towers is given as well. The problem is identi ed to be of a multi-objective nature, where a variety of criteria or objectives that are identi ed play a role in the possible reduction of the total LCC of the structure. The study also entails the delineation and discussion of the factors and components that a ect the LCC of a steel structure. The decision maker has control over only a few of these factors and components as identi ed, and these can be formulated by means of an objective to be minimized (or maximized in several other cases). Some of the objectives are incommensurable and others are commensurable with each other. In other words, several of these objectives either `compete' or don't `compete' against each other, respectively. The investigation resulted in the development of a multi-objective LCC optimization using the λ-formulation (or min-max formulation) as the objective aggregating approach for the four objectives identi ed (varied during analysis for sensitivity checks). The objectives are user-de ned in terms of membership functions that grade the degree of membership from total acceptance to total rejection by means of boundary values. This formulation is Non-Pareto based and the decision maker obtains the best trade-o or best compromise solution. The detailed discussion around these objectives is included in the literature study. The objectives in the multi-objective study are weight, cost, perimeter and nodal deflections, and a weighting of the objectives is possible but this is excluded from this study. A Genetic Algorithm (GA), coded in MATLAB, is implemented as the optimization tool or technique. The algorithm uses a quadratic penalty function approach and a natively written Finite Element Analysis (FEA) tool is used for the response model in the tness evaluation process, where the performance for stability, capacity and overall deflections of an individual in the population is quanti ed. A GA has the advantage that it operates on an entire population of individuals using basic principles such as genetics, crossover, mutation, selection and survival of the ttest from biology and Darwinian principles. GAs are very robust and e ective global search methods that can be applied to most elds of study. GAs have previously been e ectively applied in structural, single objective optimization (structural weight) problems. The GA is adopted and modi ed and veri ed with results on academic problems obtained from literature. Satisfactory performance was observed, although room for improvement is identi ed. A case study on a full scale model is performed, using circular hollow sections and equal leg angle sections. These are commonly used steel profi les for lattice type towers. The results obtained are as expected. The structural mass was used as a measure to compare the results. A heavier structure is obtained using the equal leg angle sections compared to the CHS structure with a di fference of up to 20% in weight. The best compromise solutions are feasible and near optimal, given the conditions of the equally weighted objectives in this study. The membership function defi nition and boundary value determination still remains a key issue when using fuzzy logic to incorporate the preference information of the decision maker. / AFRIKAANSE OPSOMMING: Toringstrukture van windturbines is belangrike kostekomponente van `n windkragopwekking stelsel. Deur middel van geï ntegreerde ontwerp en optimalisering kan die lewensikluskoste aansienlik verminder word. In hierdie tesis word horisontale-as windturbinetoringstrukture ondersoek. Deur middel van `n tegniek of hulpmiddel wat kan baat vind by besluitneming situasies, word die lewensiklus-koste van sodanige windturbine ondersteuning torings vanaf voorgebruik-fase tot lewenseinde-fase verminder. Dikwels, tydens die konseptuele ontwerp-fase, speel `n sekere vlak van onsekerheid of verwarring ook `n rol. Die sentrale fokus in hierdie projek is op staal vakwerk tipe torings gelê. `n Vereenvoudigde ontleeding van buisvormige torings is ook benader. Die probleem is van multikriteria aard, waar `n verskeidenheid van kriterie of doelwitte ge denti seer was. Hulle speel `n rol in die moontlike vermindering van die totale lewensiklus-koste van die struktuur. Die studie behels ook die bespreking en afbakening van die faktore en komponente wat die lewensiklus-koste van 'n staal struktuur bepaal. Die besluitnemer het slegs beheer oor sekere van hierdie faktore en komponente, en hierdie word deur middel van `n saamgevoegde doel-funksie gede neer wat dan geminimeer word. Sommige van die doelfunksies kompeteer met mekaar en sommige kompeteer nie met mekaar nie. Die ondersoek het gelei tot die ontwikkeling van `n multikriteria lewensiklus-koste optimalisering met behulp van die λ-formulering (of min-max formulering). Hierdie is `n tegniek wat die kriterie in vorm van `n verteenwoordigende doel-funksie saamvoeg. Daar is vier doelwitte wat geï denti seer was. Die gebruiker de nieer spesiale, lineêre doel-funksies wat van totale aanvaarding tot totale verwerping streek. Dit word deur middel van randwaardes gedoen. Hierdie formulering is nie Pareto gebaseer nie, en die besluitnemer verkry die `best trade-off ' of die beste kompromis oplossing. Die detailleerde bespreking rondom hierdie doelwitte is in die literatuurstudie ingesluit. Die doelwitte wat in die multikriteria studie gebruik word is gewig, koste, omtrek van die snitpro el en strukturêle defleksie. `n Gewig kan aan elke kriterium toegeken word, maar dit word van hierdie studie uitgesluit. `n Genetiese algoritme (GA), geï mplementeer in MATLAB, word as die optimalisering instrument en tegniek gebruik. Die algoritme gebruik `n kwadratiese `straf-funksie' en `n MATLAB Eindige Element Analise (EEA) word gebruik vir die gedragsmodel in die `fi ksheid' evalueringsproses. Die prestasie vir stabiliteit, kapasiteit en algehele verlegging van `n individu in die GA bevolking word daardeur gekwanti seer. `n GA het die voordeel, dat dit met `n hele bevolking van individue werk. Dit is gebaseer op beginsels van genetika en Darwin se beginsels. GAs is baie stabiel en ook e ektiewe globale soek metodes wat van toepassing in verskillende studierigtings is. GAs is al e ektief toegepas in strukturêle optimalisering (veral strukturêle gewig optimalisiering). Die GA in hierdie studie was aangepas en die gedrag en prestasie is bevestig met resultate van akademiese probleme uit die literatuur. Bevredigende prestasie is waargeneem, maar ruimte vir verbetering is ook geï denti seer. `n Gevallestudie oor `n grootskaal model is uitgevoer, en die gebruik van ronde holpro ele en gelykbenige hoekpro ele is uitgevoer. Dit is algemeen gebruikte staalpro ele vir vakwerk tipe torings. Die resultate wat verkry is, is soos verwag. Die strukturêle massa is gebruik as `n maatstaf om die resultate te vergelyk. `n Swaarder struktuur is die resultaat wanneer gelykbenige hoekpro ele gebruik word in vergelyking met die ronde holpro el struktuur. `n Verskil tot 20% in gewig is waargeneem. Die beste kompromis oplossing is haalbaar en naby-optimaal, gegewe die omstandighede van die gelyk geweegde doelfunksies in hierdie studie. Die doel-funksie de nisie, die voorkeur van die besluitnemer en die bepaling van die randwaardes bly steeds `n belangrike kwessie by die gebruik van hierdie benadering.

Large wind turbine blades, manufactured from fibre reinforced laminated composite materials, are key structural components of wind turbine systems. The demands for efficient and accurate modelling techniques of these composite blades have significantly increased. Over past decades, although complex computational models have been widely developed, more analytically based models are still very much desired to drive the design and optimization of these composite blades forward to be lighter, stronger, efficient and durable. The research work in this thesis aims to develop such more analytically based aerodynamic, structural and aero-elasticity models for large wind turbine blades manufactured from fibre reinforced laminated composite materials. Firstly, an improved blade element momentum (BEM) model has been developed by collectively integrating the individual corrections with the classic BEM model. Compared to other existing models, present BEM model accounts for blade tip and root losses more accurately. For laminar flow, the 3-D cross-flow is negligibly small. In this case, present BEM model with statically measured 2-D aerodynamic coefficients agrees closely to experimental measurements. However, stall delay correction is required for a 3-D rotating blade in stall. A new stall delay model is developed based on Snel s stall delay model. Verifications are performed and discussed for the extensively studied NREL UAE phase-VI test. The predictions of distributive and collective factors, e.g. normalised force coefficients, shaft torque and etc. have been compared to experimental measurements. The present BEM model and stall delay model are original and more accurate than existing models. Secondly, significant deficiency is discovered in the analytical thin-walled closed-section composite beam (TWCSCB) model proposed by Librescu and Vo, which is widely used by others for structural modelling of wind turbine blades. To correct such deficiency, an improved TWCSCB model is developed in a novel manner that is applicable to both single-cell and multi-cell closed sections made of arbitrary composite laminates. The present TWCSCB model has been validated for a variety of geometries and arbitrary laminate layups. The numerical verifications are also performed on a realistic wind turbine blade (NPS-100) for structural analysis. Consistently accurate correlations are found between present TWCSCB model and the ABAQUS finite element (FE) shell model. Finally, the static aero-elasticity model is developed by combining the developed BEM model and TWCSCB model. The interactions are accounted through an iterative process. The numerical applications are carried out on NPS-100 wind turbine. The numerical results show some significant corrections by modelling wind turbine blades with elastic coupling.

This thesis develops design methodologies for megawatt(MW)-scale yokeless and segmented armature (YASA) generators for wind turbine applications. The methodologies include the electromagnetic, the structural and the thermal designs of a YASA generator. The design process starts with developing an analytical method to generate preliminary machine designs for a megawatt-scale YASA generator. This analytical approach considers both electromagnetic and structural aspects of a generator, the parameters of which were obtained and visualised on a design reference map. This new concept of displaying machine parameters is useful for a designer to identify the relationship between them. An optimisation tool using pseudo-weight approach is integrated into the analytical tool to determine a optimum machine design. This is a flexible optimisation tool, allowing the user to give priorities to each objective function. The analytical calculation has reduced the design space for suitable machine candidates to be applied in further finite element analysis (FEM). In finite element analysis of an optimised YASA machine, the electromagnetic performance of a 1 MW YASA generator was produced and verified with analytical and experiment results. This is followed by structural optimisation with finite element method, where a spider wheel with a support ring geometry is applied to the rotor plate. This reduces the structural weight by more than 50% while the structure retain strong stiffness. Finally, the cooling system of the stator of the YASA generator is studied and the cooling channels design is proposed. Simulation results show that the stator of a 1 MW YASA generator can be effectively cooled with forced air.

Le but de ce travail consiste à concevoir et développer des outils de commande et de contrôle pour des systèmes à structures variables comprenant plusieurs sources d’énergie (photovoltaïque, éolienne…). L’approche proposée vise à développer les modèles appropriés pour la commande et la gestion de chaque partie du système. Les différents modèles tiendront comptes du caractère aléatoire de la production d’énergie issue des différentes sources en présence tout en veillant à assurer une gestion globale optimale. L’intérêt principal d’un tel système est la cohabitation des ressources et du stockage dans le but de sécuriser l’approvisionnement au consommateur. La thèse traite trois phases principales : Une phase de modélisation et de mise en place des commandes, suivies d’une phase de simulation puis une phase de validations et de tests. Ainsi le modèle de chaque sous-système de production a été élaboré en tenant compte des différentes caractéristiques (physique et géométrique) de la source considérée, pour la partie commande et contrôle des approches classiques en automatique ont été appliqué afin d’assurer la maximisation de la production, la stabilité de l’ensemble et le bon fonctionnement du système. Une fois les commandes validées, nous avons procédés à des simulations Hardware In the Loop, en implémentant les stratégies de maximisation d'énergie sur la banc d'essai en temps réel, et ce à l'aide d'une carte DSPACE1104, puis nous avons assemblés les différentes sources d'énergies en les couplant via le programme de gestion d'énergie proposé et mis au point. / The objective of this work is to design and develop tools for monitoring and control systems with variable structures with multiple energy sources (wind, solar, ...). The proposed approach aims to develop appropriate models for the control and management of each part of the system. The different models take into account of the random nature of the production of energy outcome from different available sources, while ensuring optimum overall management of system. The main advantage of this system is the coexistence of resources and storage system in order to secure the supply to the consumer. The thesis deals with three main phases: a phase of modeling and implementation of controls, followed by a simulation phase and a phase of validation and testing. So the model of each subsystem production was developed with consideration of its different characteristics (physical and geometrical), for the control section conventional approaches were applied automatically to ensure the maximization of the production, the stability of the assembly and the functioning of the system. for the part concerning the management and control, conventional approaches in automatic have been applied to ensure the maximization of production, the stability of the overall system and its proper functioning. Once control strategies validated, we have processed in simulations Hardware In the Loop, by implementing strategies to maximize energy on the benchmark in real time, using a DSPACE1104 card, then we assembled the different sources of energy by coupling them through the program of energy management proposed and developed.

Wind power is one of the fastest growing production methods of electric energy. The expansion of wind power in Sweden are focused to northern counties. There are advantages as good wind conditions and large unexploited areas to build wind farms in the north, but there are also problems caused by the long winters. Due to the long periods of cold climate, ice and snow accumulation on blades are a safety risk, induces production losses and causes wear at wind turbine components. The commercial de-icing systems are not fulfilling the demands of being cost effective and are mainly focusing the heating to the leading edge. Therefore a new de-icing system based on infrared radiation has been investigated. This system is supposed to be placed at the wind turbine tower and de-ice one blade at a time. Experiments with this new de-icing system has been performed in small and full scale at a section of a real wind turbine blade. The experiments were carried out in facilities of Arctic Falls in Piteå. Different parameters as power demand of the heaters, distance between blade and heaters, wavelength of the radiation, influence by the surrounding temperature and total de-icing time were evaluated. Results showed that the largest impact of the efficiency and de-icing time were induced by the distance and width of the radiation spectrum for the heaters. Three types of filaments with different peaks of wavelengths were investigated and the most efficient de-icing was achieved when using a combination of heaters. Measurements of intensity together with de-icing experiments showed that the optimal distance from the blade was 1.5 m for heaters with standard reflectors. The main conclusion from the experiments with an infrared de-icing system is that it works. But not efficient enough to compete with the commercial systems of today even though it manage to de-ice the whole blade instead of just the leading edge. But this de-icing system has good potential if the heaters first of all are developed to radiate a more concentrated beam of radiation that is only focusing at the blades. The new method is estimated to be an lower investment due to that the techniques of infrared heaters are already well implemented in other areas. But more economic calculations has to be done to further motivate the work.

L’énergie éolienne est une source d’énergie propre et renouvelable qui fait partie des moyens pour réduire les émissions de gaz à effet de serre et contrer le réchauffement climatique dans le domaine de la production électrique.L’objectif de la thèse est d’optimiser la production d’énergie éolienne par la réduction des fluctuations de charge induites par la turbulence de la couche limite atmosphérique. Ces fluctuations augmentent la fatigue des pales et réduisent la durée de vie des rotors.Cette réduction des fluctuations de charge est réalisée par le biais d’une approche expérimentale et à l’échelle du laboratoire. Deux actionneurs non conventionnels sont étudiés et testés au sein d’un écoulement contrôlé ensoufflerie: il s’agit d’actionneurs plasma et de jets fluidiques. L’objectif est d’effectuer un contrôle de circulation par une action proche du bord de fuite arrondi de la pale afin de modifier la portance du profil.Dans le cadre du projet SMARTEOLE, les deux stratégies sont d’abord testées en parallèle sur un profil bidimensionnel. Pour cette thèse, les actionneurs plasma sont implémentés autour du bord de fuite arrondi afin d’augmenter ou de réduire la portance. Les performances aérodynamiques ont été modifiées dans la partie linéaire de la courbe de portance. Pour des raisons d’efficacité et de fiabilité, le projet est poursuivi avec des jets fluidiques pour aller vers l’étude des pales et du contrôle d’écoulement en rotation. Ces pales sont préalablement testées dans une configuration translationnelle pour évaluer l’effet du contrôle sans les effets de la rotation. Finalement,les pales sont montées sur le banc éolien du laboratoire. Les effets du contrôle sont mis en évidence par les mesures de pression pariétale et de moment de flexion en pied de pale. Le contrôle induit des réductions importantes de fatigue qui motivent la poursuite des travaux dans le domaine du contrôle d’écoulement appliqué aux pales d’éolienne. / Wind energy is a clean and renewable source of energy that remains one of the solutions to cut carbon emissions and curb global warming in the field of power generation. The present thesis objective is the optimisation of wind energy production by the all eviation of blade load fluctuations induced by shear and turbulence in the atmospheric boundary layer. These fluctuations increase the blade fatigue and reduce the life duration of the rotors.This load fluctuation all eviation is assessed with an experimental approach and at a laboratory scale. Two not conventional flow control strategies, plasma actuators and fluidic jets, are implemented and tested in the controlled environment of a wind-tunnel to perform a circulation control by acting in the vicinity of the rounded trailing-edge of the blade in order to modify its lift force.In the scope of the SMARTEOLE project, both plasma and fluidic strategies are, as a first step, tested in parallel on a 2D-airfoil. For this thesis, plasma actuators are implemented over the airfoil trailing-edge to increase ordecrease the lift force. Airfoil performances are indeed modified in the linear part of the lift curve. For efficiency and reliability reasons, it is chosen to pursue the work towards the rotational configuration with the fluidic strategy. Blades are then manufactured and tested first in a translational configuration to evaluate the potentialof the fluidic actuation without rotational effects. Then, blades are mounted in the wind turbine bench of the laboratory. The effects of the actuation are demonstrated through surface pressure and flapwise bending moment measurements. Actuation shows important fatigue reduction motivating the pursue of the investigations on active flow control applied to wind turbine blades.

Com a busca pela sustentabilidade no abastecimento de energia elétrica, a fonte eólica tem ganhado grande destaque na matriz energética global por possuir modelo de negócio consolidado, pois conta com aerogeradores modernos, naceles instalados em alturas cada vez maiores, geradores elétricos mais potentes e com sistemas de controle altamente tecnológicos. No Brasil, a energia eólica vem sendo a grande vencedora dos leilões de energia, aumentando de forma significativa seu portfólio pela viabilidade na construção de grandes complexos que devido à elevada potência instalada, realiza seu acesso ao Sistema Interligado Nacional (SIN) em níveis de tensão cada vez maiores, ou seja, em pontos mais sensíveis do sistema de transmissão. Motivado por esse crescimento e pela representatividade dos novos parques em pontos vitais do SIN, o objetivo desta dissertação é avaliar as diferentes metodologias e conceitos adotados como premissa no projeto do sistema de proteção aplicado a uma Central de Geração Eólica (CGE), apresentando como conclusão, além dos diagramas de sequência a serem utilizados no cálculo das correntes de curto-circuito, uma metodologia completa de definição dos ajustes de proteção para atender as especificidades construtivas dessas instalações. / Through the search for sustainability in electric power supply, the Eolic source has gained distinction in the global energetic matrix, as it has a consolidated business framework, which counts on modern wind turbines, nacelles installed at higher and higher altitudes, more powerful electric generators with high-technology control systems. In Brazil, Eolic energy has been the great winner in energy auctions, which has increased significantly its portfolio, due to its viability in the construction of large complexes. Having a high installed power capacity, these large projects enable access to the Sistema Interligado Nacional - SIN (National Interconnected System) at higher and higher voltage levels, that is, at more sensitive points of the transmission system. Motivated by all this development and by the representativeness of the new wind farms, installed at vital points of the SIN, the objective of this dissertation is to assess the different methodologies and concepts adopted as premise in the protection system project applied to a Central de Geração Eólica CGE (Eolic Generation Center). The conclusion presented herein, besides the sequence diagrams for the short circuit calculations, provides a complete methodology of definition of the protection adjustments required to comply with the building specificities of these installations.

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.

Esta Tese apresenta o desenvolvimento de um modelo de sistema capaz de monitorar, adquirir, armazenar e transmitir dados remotamente utilizando diversos sensores e rede de celulares 3G para ser aplicada no projeto de pequenos aerogeradores, tendo como meta gerar um produto que apresente boa relação custo/eficiência, com emprego de materiais e processos de manufatura adaptados à realidade mundial. É apresentado um novo modelo de sistema para aquisição de dados, baseado na integração das novas tecnologias da informação e comunicação e de técnicas de processamento analógico e digital de sinais, visando estudar o desempenho de parâmetros gerados em um pequeno aerogerador de bancada. Através deste modelo será possível monitorar continuamente, dentro dos intervalos previstos de amostragem, a ocorrência de mudanças dos parâmetros analisados através de sensores instalados no aerogerador. Os resultados das análises destes sensores podem ser adquiridos e transmitidos remotamente através da Rede 3G, diretamente para uma sala de operações ou ainda ser disponibilizada na WEB através das novas tecnologias e mídias sociais. As informações aqui estudadas mostram resultados que podem ser úteis para qualquer segmento do mercado e para todas as áreas científicas, econômicas e ambientais, que queiram conhecer e aplicar o modelo de um sistema de aquisição e monitoração de dados para o gerenciamento de aerogeradores de pequeno porte. Apesar de no experimento ter sido utilizado variáveis de um aerogerador, são mostradas outras aplicações possíveis de aquisição de dados, monitoramento e experimentos remotos utilizando-se o canal de comunicação celular 3G e a integração das novas tecnologias de informação e comunicação. / This thesis presents the development of model system that can monitor, acquire, store and transmit data remotely using various sensors and 3G cellular network to be applied in the design of small wind turbines, aiming to generate a product that presents a cost-efficient through use of materials and manufacturing processes adapted to the reality world. It presented a new model system for data acquisition based on the integration of new information technologies and communication and processing techniques of analog and digital signals, to study the performance of parameters generated in a small wind turbine bench and remote. Through this model will be possible to monitor continuously, within the ranges provided for sampling, the occurrence of changes of parameters measured by sensors installed in the turbine. The results of analysis of these sensors can be acquired and transmitted remotely via the 3G network, directly to an operating room or be available on the Web with new technologies and social media. The information studied here show results that may be useful for any market segment and for all scientific, economic and environmental issues, willing to learn and apply the model of an acquisition system and data monitoring for management of small wind turbines. Although the experiment has been used variables of a wind turbine, are shown other possible applications of data acquisition, remote monitoring and experiments using the 3G mobile communication channel and the integration of new information technologies and communication.

The paper compares electricity production between the semi-submersible and the spar-buoy floating wind turbine systems under normal, stochastic and extreme wind conditions at Utsira Nord site located on the Norwegian continental shelf in the North Sea. The analysis of complex behavior of the floating wind turbine system and the fluid-structure interaction is performed in aero-servo-hydro-elastic code ASHES. The results indicate a slightly better energy performance of the semi-submersible than the spar in all load cases but one. The pitch and heave degrees of freedom are evaluated as the most relevant for the power output. It is shown that pitch and heave platform motions have smaller displacement in the semi-submersible floater than in the spar under average environmental conditions and at the rated wind speed operating range. The simulation also confirmed that the energy yield is very sensitive to the magnitude of the loads: the spar performed best under mild environmental conditions, while the semi-submersible was better under medium environmental conditions. Small difference in energy yield is attributed to the same baseline blade and external controller properties used for both floaters where generator torque was kept constant to limit the power excursions above the rated power. The method proposed under this paper has demonstrated that a good approximation of the energy performance of the floating wind turbine system can be performed in a fast and effective manner.