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[pt] A energia eólica tem crescido de forma estável no Brasil nos últimos anos. Para impulsioná-la, é crucial considerar as mudanças climáticas, já que sua geração é altamente influenciada pelo clima. Por isso, é fundamental incorporar variáveis climáticas externas na modelagem das séries eólicas, contribuindo para reduzir as incertezas. Os Modelos Periódicos Autorregressivos com Variáveis Exógenas (PARX) representam uma abordagem viável para cumprir esse propósito, incluindo a variável exógena ENSO. No presente estudo, realizou-se a modelagem das séries de velocidade do vento nos estados do Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe, Rio Grande do Sul e Santa Catarina. Nesse sentido, foi considerada a covariância entre esses estados em cada região brasileira para avaliar a correlação espacial entre eles, criando a modelagem PARX-Cov. Além disso, a correlação entre os indicadores do fenômeno ENSO também foi considerada para viabilizar a previsão out-of-sample das variáveis climáticas, essa utilizada para a simulação de cenários de velocidade de vento. Ao comparar a modelagem do PARX e PARX-Cov, com o modelo vigente no setor elétrico brasileiro, observou-se um desempenho superior nos modelos propostos para a simulação de realizações futuras das séries de velocidade do vento. O modelo PARX-Cov com o índice ONI Acumulado é o mais adequado para Pernambuco, Rio Grande do Sul e Santa Catarina. O PARX-Cov com o índice SOI é mais apropriado para o Rio Grande do Norte. Para Alagoas e Sergipe, o PARX com o índice ONI Acumulado é o mais indicado, enquanto o PARX com Niño 4 Acumulado é melhor para a Paraíba. / [en] Wind energy has been steadily growing in Brazil in recent years. To boost its growth, it is crucial to consider climate change, as wind energy generation is highly influenced by the weather. Therefore, it is essential to incorporate external climatic variables into the modeling of wind series, helping to reduce uncertainties. Periodic Autoregressive Models with Exogenous Variables (PARX) represent a viable approach to achieve this, including the ENSO exogenous variable. In the present study, wind speed series were modeled in the states of Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe, Rio Grande do Sul, and Santa Catarina. In this context, the covariance between these states in each Brazilian region was considered to assess the spatial correlation among them, creating the PARX-Cov modeling. Furthermore, the correlation between ENSO phenomenon indicators was also considered to enable out-of-sample forecasting of climatic variables, used for simulating wind speed scenarios. When comparing the PARX and PARX-Cov modeling with the current model in the Brazilian electric sector, the proposed models showed superior performance in simulating future wind speed series. The PARX-Cov model with the Accumulated ONI index is most suitable for Pernambuco, Rio Grande do Sul, and Santa Catarina. The PARX-Cov model with the SOI index is more appropriate for Rio Grande do Norte. For Alagoas and Sergipe, the PARX model with the Accumulated ONI index is the most recommended, while the PARX model with Accumulated Niño 4 is better for Paraíba.

Suite à un stage avec la compagnie Hatch, nous possédons des jeux de données composés de séries chronologiques de vitesses de vent mesurées à divers sites dans le monde, sur plusieurs années. Les ingénieurs éoliens de la compagnie Hatch utilisent ces jeux de données conjointement aux banques de données d’Environnement Canada pour évaluer le potentiel éolien afin de savoir s’il vaut la peine d’installer des éoliennes à ces endroits. Depuis quelques années, des compagnies offrent des simulations méso-échelle de vitesses de vent, basées sur divers indices environnementaux de l’endroit à évaluer. Les ingénieurs éoliens veulent savoir s’il vaut la peine de payer pour ces données simulées, donc si celles-ci peuvent être utiles lors de l’estimation de la production d’énergie éolienne et si elles pourraient être utilisées lors de la prévision de la vitesse du vent long terme. De plus, comme l’on possède des données mesurées de vitesses de vent, l’on en profitera pour tester à partir de diverses méthodes statistiques différentes étapes de l’estimation de la production d’énergie. L’on verra les méthodes d’extrapolation de la vitesse du vent à la hauteur d’une turbine éolienne et l’on évaluera ces méthodes à l’aide de l’erreur quadratique moyenne. Aussi, on étudiera la modélisation de la vitesse du vent par la distributionWeibull et la variation de la distribution de la vitesse dans le temps. Finalement, l’on verra à partir de la validation croisée et du bootstrap si l’utilisation de données méso-échelle est préférable à celle de données des stations de référence, en plus de tester un modèle où les deux types de données sont utilisées pour prédire la vitesse du vent. Nous testerons la méthodologie globale présentement utilisée par les ingénieurs éoliens pour l’estimation de la production d’énergie d’un point de vue statistique, puis tenterons de proposer des changements à cette méthodologie, qui pourraient améliorer l’estimation de la production d’énergie annuelle. / Following an internship with the company Hatch, we have access to datasets that are composed of wind speed time series measured at different sites accross the world and over several years. The wind speed engineers from Hatch are using these datasets jointly with Environment Canada databases in order to ascertain the wind energy potential of these sites and to know whether it is worth installing wind turbines there. For a few years, some companies are also offering mesoscale simulations of wind speed based on different environmental characteristics from the site we want to evaluate. We would like to know if it is worth paying for those mesoscale datasets and if they can be used to provide better estimations of the wind energy potential. Among other things, these data could be used to provide a better estimation of the long term mean wind speed. Since we already possess measured datasets, we will also use them to test, with statistical methods, the methodology currently used and the different steps leading to an estimation of the wind energy production. First of all, we will see what are the different methods that could be used to extrapolate wind speed to a wind turbine’s height and we will evaluate those methods with the mean squared extrapolation error. Also, we will study wind distribution modelling by the Weibull distribution and consider its variability over time. Finally, cross-validation and block bootstrap will be used to see whether we should use mesoscale data instead of wind data from Environment Canada or whether it would even be beneficial to use both kind of data to predict wind speed. In summary, the whole methodology used by wind speed engineers to estimate the energy production will be tested from a statistical point of view and we will attempt to propose changes in this methodology that could improve the estimation of the wind speed annual energy production.

Le laboratoire TELE a développé une méthode d'évaluation des paramètres qui déterminent l'état de la surface de la mer, à partir de mesures effectuées à distance par une combinaison d'instruments hyperfréquences embarqués à bord de satellites. La résolution de ce problème nécessite de construire un modèle statistique de la surface de la mer comme fonction d'un nombre limité de paramètres pertinents, de développer le modèle de diffusion des ondes électromagnétiques par la mer rugueuse, de simuler, pour un ensemble donné d'états de mer, les mesures attendues des satellites et de mettre au point la méthode de calcul des paramètres descriptifs de l'état de la mer à partir des mesures des satellites (inversion). L'objectif de cette thèse est d'analyser, de développer et d'implémenter la modélisation statistique de la surface de la mer et de valider ce modèle, appelé UCL-3, à partir des données réelles. Notre recherche a permis de déterminer les quatre paramètres pertinents qui décrivent l'état de la mer. La structure des petites vagues résulte de la réaction instantanée de la surface au vent local et peut être décrite à l'aide de ce seul paramètre. Par contre, la structure des grandes vagues contient l'histoire de la vague ; c'est pourquoi, nous avons proposé de la décrire non seulement en fonction de la vitesse du vent mais aussi de la pente significative des vagues, de la distance d'action au vent et du nombre d'onde au pic du spectre des déplacements de la surface. La qualité de ce modèle a été confrontée avec des données de terrain, en particulier celles de la bouée BEATRICE (située au large de l'île d'Ouessant, France). Ensuite, le modèle a été validé à l'aide de données mesurées par des satellites. Nous avons porté une attention particulière à la mission TANDEM, qui combine en synergie des données provenant de divers senseurs à bord des satellites ERS-1 et ERS-2. Le modèle UCL-3 réduit la quantité des données pour lesquelles la procédure des précédentes recherches ne fonctionnait pas. Enfin, les grandeurs géophysiques obtenues ont été comparées avec des mesures simultanées « in situ » de bouées NOAA situées dans l'Océan Atlantique, l'Océan Pacifique Nord et le Golfe d'Alaska. Cette comparaison satellite – bouée montre que les résultats obtenus par l'inversion des mesures radars concordent avec ceux mesurés « in situ » par des bouées. / The Telecommunications and Remote Sensing Laboratory of UCL has developed a method to retrieve the sea surface state parameters, from remote sensing measurements collected by a combination of microwave satellite payloads. This approach has required to construct a rough sea surface statistical model (wave displacement spectrum, long wave slope probability density function, ... ) as a function of a limited number of relevant sea state parameters, to develop an electromagnetic scattering model suitable for the rough sea surface model, to simulate radar and radiometric measurements for a given set of sea states and to develop a computational inversion method to retrieve the sea state parameters from satellite data. The objective of this thesis has been to analyze, develop and implement the statistical modeling of the rough sea surface and to validate this model (called UCL-3) on real data. In this research, four parameters have been chosen as the minimum set required to provide a suitable enough description of the sea state for microwave remote sensing purposes. The small wave structure of the rough sea depends on the instantaneous local wind speed, therefore it may be described by this parameter only. On the other hand, the large sea wave structure which contains the wave history needs more degrees of freedom; therefore, we propose to describe these waves not only as a function of the wind speed but also of the wave significant slope, of the fetch and of the wavenumber at the peak of the surface displacement spectrum. With respect to previous researches made at UCL we have introduced an additional peak enhancement in the large sea wave spectrum. The quality of the resulting sea surface model has been confronted with “ground truth data” in particular those from the BEATRICE buoy (located near Ouessant Island, West of France). In a second step, the surface model, along with the electromagnetic scattering one, has then been validated on satellite data. In this thesis a particular attention has been paid to the TANDEM mission synergistically combining data from different sensors borne on two different satellites ERS1 and ERS2. The obtained geophysical retrievals have been compared with simultaneous "in situ" buoy measurements from a set of NOAA buoys located in the Atlantic Ocean, the Pacific Ocean and the Gulf of Alaska. This comparison allowed us to improve models previously derived at UCL and to reduce the percentage of retrieval failures i.e. the amounts of data points for which the retrieval procedure in the previous researches was failing. These sea surface results from inverted radar data agree with those derived from buoy data.

Ištirti mažos galios horizontaliosios ašies vėjo jėgainės energetines charakteristikas ir nustatyti efektyvumo didinimo galimybes. / Survey energy characteristics of little capacity horizontal axis wind power plant and identify efficiency increase potential.

A wind turbine needs to be controlled to ensure its safe and optimal operation, especially during high wind speeds. The most common control objectives are to limit the power and rotational speed of the wind turbine by using pitch control. Aero Energy is a company based in Potchefstroom, South Africa, that has been developing and manufacturing wind turbine blades since 2000. Their most popular product is the AE1kW blades. The blades have a tendency to over-speed in high wind speeds and the cut-in wind speed must be improved. The objective of this study was to develop an active pitch control system for wind turbines. A prototype active pitch control system had to be developed for the AE1kW blades. The objectives of the control system are to protect the wind turbine from over-speeding and to improve start-up performance. An accurate model was firstly developed to predict a wind turbine’s performance with active pitch control. The active pitch control was implemented by means of a two-stage centrifugal governor. The governor uses negative or stalling pitch control. The first linear stage uses a soft spring to provide improved start-up performance. The second non-linear stage uses a hard spring to provide over-speed protection. The governor was manufactured and then tested with the AE1kW blades. The governor achieved both the control objectives of over-speed protection and improved start-up performance. The models were validated by the results. It was established that the two-stage centrifugal governor concept can be implemented on any wind turbine, provided the blades and tower are strong enough to handle the thrust forces associated with negative pitch control. It was recommended that an active pitch control system be developed that uses positive pitching for the over-speed protection, which will eliminate the large thrust forces. Keywords: pitch control, wind turbine, centrifugal governor, over-speed protection, cut-in wind speed, blade element-momentum theory, rotor, generator, stall, feathering. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.

A wind turbine needs to be controlled to ensure its safe and optimal operation, especially during high wind speeds. The most common control objectives are to limit the power and rotational speed of the wind turbine by using pitch control. Aero Energy is a company based in Potchefstroom, South Africa, that has been developing and manufacturing wind turbine blades since 2000. Their most popular product is the AE1kW blades. The blades have a tendency to over-speed in high wind speeds and the cut-in wind speed must be improved. The objective of this study was to develop an active pitch control system for wind turbines. A prototype active pitch control system had to be developed for the AE1kW blades. The objectives of the control system are to protect the wind turbine from over-speeding and to improve start-up performance. An accurate model was firstly developed to predict a wind turbine’s performance with active pitch control. The active pitch control was implemented by means of a two-stage centrifugal governor. The governor uses negative or stalling pitch control. The first linear stage uses a soft spring to provide improved start-up performance. The second non-linear stage uses a hard spring to provide over-speed protection. The governor was manufactured and then tested with the AE1kW blades. The governor achieved both the control objectives of over-speed protection and improved start-up performance. The models were validated by the results. It was established that the two-stage centrifugal governor concept can be implemented on any wind turbine, provided the blades and tower are strong enough to handle the thrust forces associated with negative pitch control. It was recommended that an active pitch control system be developed that uses positive pitching for the over-speed protection, which will eliminate the large thrust forces. Keywords: pitch control, wind turbine, centrifugal governor, over-speed protection, cut-in wind speed, blade element-momentum theory, rotor, generator, stall, feathering. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.

This dissertation presents new methods for detecting dynamic and thermodynamic characteristics of Arctic sea ice using radar remote sensing. A new technique for sea ice motion detection from sequential satellite synthetic aperture radar (SAR) images was developed and thoroughly validated. The accuracy of the system is 0.43 km obtained from a comparison between SAR-derived ice motion vectors and in-situ sea ice beacon trajectories. For the first time, we evaluated ice motion tracking results derived from co-polarization (HH) and cross-polarization (HV) channels of RADARSAT-2 ScanSAR imagery and formulated a condition where the HV channel is more reliable than the HH channel for ice motion tracking. Sea ice motion is substantially controlled by surface winds. Two new models for ocean surface wind speed retrieval from C-band SAR data have been developed and validated based on a large body of statistics on buoy observations collocated and coincided with RADARSAT-1 and -2 ScanSAR images. The proposed models without wind direction input demonstrated a better accuracy than conventionally used algorithms. As a combination of the developed methods we designed a wind speed-ice motion product which can be a useful tool for studying sea ice dynamics processes in the marginal ice zone. To effectively asses the thermodynamic properties of sea ice advanced tools for modeling electromagnetic (EM) wave scattering from rough natural surfaces are required. In this dissertation we present a new analytical formulation for EM wave scattering from rough boundaries interfacing inhomogeneous media based on the first-order approximation of the small perturbation method. Available solutions in the literature represent special cases of our general solution. The developed scattering theory was applied to experimental data collected at three stations (with different snow thicknesses) in the Beaufort Sea from the research icebreaker Amundsen during the Circumpolar Flaw Lead system study. Good agreement between the model and experimental data were observed for all three case studies. Both model and experimental radar backscatter coefficients were considerably higher for thin snow cover (4 cm) compared to the thick snow cover case (16 cm). Our findings suggest that, winter snow thickness retrieval may be possible from radar observations under particular scattering conditions.

The abundance of gray whales along the coast of Flores Island, BC, varies on an annual basis. This thesis searches for a relationship between gray whale abundance in this area and environmental forcing factors. Regression analysis was used to search for relationships, using gray whale abundance as the dependent variable and sea-surface temperature, salinity, wind speed, upwelling indices and hours of bright sunlight. Independent variables were also lagged against gray whale abundance to search for time lags between variables. When combine in a multiple regression model, wind speed and upwelling lagged two years explained 89.6% (p = 0.004) of the variance in gray whale abundance. A possible pathway for this relationship may exist through local kelp populations, which have the ability to affect gray whale prey abundance.

Towards advancing the indices of hurricane energetics that are associated with potential damage, we develop a new methodology for calculating integrated kinetic energy (IKE) climatology. A simple, observation and dynamical - based radial wind speed model is used with the Extended Best Track Data Set to calculate IKE for North Atlantic Hurricanes from 1988 to 2008. The method is evaluated against previous methods of tropical cyclone intensity analysis, and the results are compared to traditional indices in terms of characterizing storm energetics and relating to storm surge. It is shown that the traditional indices are inaccurate measurements of hurricane energetics, and the assumptions that they are based on are not valid. Furthermore, in analyzing storm surge, it is possible that tropical cyclone damage is more strongly correlated with IKE rather than maximum wind speed.