Autonomous take-off and landing of a tethered aircraft: a simulation study

The problem of autonomous launch and landing of a tethered rigid aircraft for airborne wind energy generation is addressed. The system operates with ground-based power conversion and pumping cycles, where the tether is repeatedly reeled in and out of a winch installed on the ground and linked to an electric motor/generator. In order to accelerate the aircraft to take-off speed, the ground station is augmented with a linear motion system composed by a slide translating on rails and controlled by a second motor. An onboard propeller is used to sustain the forward velocity during the ascend of the aircraft. During landing, a slight tension on the line is kept, while the onboard control surfaces are used to align the aircraft with the rails and to land again on them. A model-based, decentralized control approach is proposed, capable to carry out a full cycle of launch, low-tension flight, and landing again on the rails. The derived controller is tested via numerical simulations with a realistic dynamical model of the system, in presence of different wind speeds and turbulence, and its performance in terms of landing accuracy is assessed. This study is part of a project aimed to experimentally verify the launch and landing approach on a small-scale prototype.Comment: This is the longer version of a paper submitted to the 2016 American Control Conference 2016, with more details on the simulation parameter

Emerging renewable energy technologies: Survey, modeling, and simulations

This thesis approaches recent technologies to produce electric power from wind or water. The use of tethered kites for harnessing wind or water power and consequently transforming it into electric power is an idea which is starting to take off and with serious on-going developments. There are two types of major systems: Ground generation and on-board generation. The first one comprises a soaring kite tethered to a ground generator which generates electric power by means of reeling out the tether as the kite rises. This movement is controlled through the manipulation of its surface similar to the control of surfaces an aircraft. As for on-board generation, it is basically an aircraft with mounted generators on its wings, and tethered to the ground by a cable with the double function of securing and tethering the aircraft to the ground, as well as to bring the electric power from the aircraft to the grid. Both systems can be implemented on air and underwater. In the recent times there were serious developments in these technologies, one of them is the Makani Project powered by Google with a proven concept on-board generator of 600kW. Regarding underwater kite systems, there are several companies like Minesto (Saab spinoff) which also have a proven concept of 500kW. For these reasons and given the increasing power demand and accountability regarding energy sources, this work offers an overview of these ground-breaking technologies (compared against the conventional technologies) which can and will contribute to the decentralization of the electric energy production. In addition, this work provides a series of simulations and power estimates for kite systems to offer an unbiased view of this new type of electric energy harnessing.O uso de asas ou kites (vulgo papagaios) para aproveitar a força do vento ou da água e consequentemente transformá-la em energia elétrica é uma ideia que começa a ganhar forma nos últimos tempos e com desenvolvimentos muito significativos, que implicam um olhar mais atento sobre este tipo de tecnologia. Existem dois grandes grupos de sistemas: Geração no solo e em voo. A primeira consiste numa asa , ancorada a um gerador no solo através de um cabo, em que a energia elétrica é gerada pelo enrolar e desenrolar do cabo que o liga ao solo, à medida que a asa se movimenta ao sabor do vento, com a trajetória controlada através da alteração da superfície da asa de uma forma semelhante ao que acontece numa aeronave comum. Quanto à geração em voo, trata basicamente uma aeronave com geradores montados nas suas asas e ancorada ao solo através de um cabo com a função extra de efetuar a ligação elétrica entre a aeronave e a rede. Nos últimos tempos têm havido desenvolvimentos muito significativos nestas tecnologias, sendo que um deles chama especial atenção pela espetacularidade das imagens e por se tratar de uma empresa Google X – A Makani Project possui um conceito já provado de geração de 600kW. Da mesma forma e para geração subaquática, existem já diversas empresas entre elas a Minesto (constituída por engenheiros da Saab) com um conceito de 500kW. Por estas razões e dada a solicitação crescente a nível de energia elétrica e o aumento da responsabilização dos produtores de energia elétrica para o uso de fontes de energia renovável, este trabalho oferece um panorama geral sobre estas tecnologias inovadoras que terão um papel preponderante a desempenhar no futuro da descentralização do sistema elétrico-produtor

Autonomous Takeoff and Flight of a Tethered Aircraft for Airborne Wind Energy

A control design approach to achieve fully autonomous takeoff and flight maneuvers with a tethered aircraft is presented and demonstrated in real-world flight tests with a small-scale prototype. A ground station equipped with a controlled winch and a linear motion system accelerates the aircraft to takeoff speed and controls the tether reeling in order to limit the pulling force. This setup corresponds to airborne wind energy (AWE) systems with ground-based energy generation and rigid aircrafts. A simple model of the aircraft's dynamics is introduced and its parameters are identified from experimental data. A model-based, hierarchical feedback controller is then designed, whose aim is to manipulate the elevator, aileron, and propeller inputs in order to stabilize the aircraft during the takeoff and to achieve figure-of-eight flight patterns parallel to the ground. The controller operates in a fully decoupled mode with respect to the ground station. Parameter tuning and stability/robustness aspect are discussed, too. The experimental results indicate that the controller is able to achieve satisfactory performance and robustness, notwithstanding its simplicity, and confirm that the considered takeoff approach is technically viable and solves the issue of launching this kind of AWE systems in a compact space and at low additional cost

Estimate of energy production in aerial systems of Wind Energy

O impacto ambiental resultante da produção de energia elétrica através de combustíveis fósseis determinou uma mudança na forma de obtenção desta energia aparecendo assim as energias renováveis.Nesta dissertação é abordada uma forma de produção de energia elétrica eólica utilizando um AWES (Airborne Wind Energy System), mais especificamente um Pumping Kite Generator. O sistema apresenta uma asa presa a um cabo que a liga a um gerador elétrico através de um tambor, produzindo energia elétrica através da tensão no cabo enquanto a asa se move numa trajetória aproximadamente ortogonal à direção do vento. Quando o comprimento máximo do cabo é atingido, a asa é controlada de forma a minimizar a tensão no cabo e é recolhida até uma posição inicial da qual reinicia o ciclo de produção.Com base no perfil dinâmico da asa e para efeitos de cáculo da produção de energia durante um ciclo, as fases de largada e de recolha são analisadas. São introduzidos parâmetros adimensionais que ajudam a descrever a eficiência do ciclo. As velocidades de largada e de recolha são calculadas e usadas para o cáculo da potência ao longo de um ciclo. A potência máxima obtida durante um ciclo é calculada através de duas etapas sendo que a primeira é para velocidades de vento abaixo da velocidade nominal e a segunda etapa são para velocidades acima da nominal. Através de uma seleção de vários parâmetros é também construída uma curva de potência do sistema.É ainda obtida a produção de energia anual teórica num determinado local com base em dados de vento reais.The environmental impact resulting from the production of electricity through fossil fuels has led to a change in the way this energy is obtained, thus giving rise to renewable energies.This dissertation discusses a way to produce wind power using an AWES (Airborne Wind Energy System), more specifically a Pumping Kite Generator. The system presents a wing attached to a cable that connects it to an electric generator through a drum, producing electric energy through the tension in the cable while the wing moves in a path approximately orthogonal to the direction of the wind. When the maximum cable length is reached, the wing is controlled so as to minimize the tension in the cable and is withdrawn to an initial position from which it restarts the production cycle.Based on the dynamic profile of the wing and for the purpose of calculating energy production during a cycle, the reel in and reel out phases are analyzed. Dimensional parameters are introduced to help describe the efficiency of the cycle.Reel in and reel out speeds are calculated and used to calculate power over a cycle. The maximum power obtained during a cycle is calculated through two steps, the first one being for wind speeds below the nominal speed and the second step for speeds above the nominal. Through a selection of several parameters a system power curve is also constructed.The theoretical annual energy production is also obtained in a given location based on actual wind data

Ground Gen Airborne Wind Energy Conversion Systems: Tools for Conceptual Design and Rapid Prototyping

Airborne Wind Energy System (AWES) are quickly coming to fruition, with increased energy production while reducing the cost of implementation and materials. This thesis develops a new computational model for a tethered AWES and characterizes a new rapid prototyping method with the objective of supporting the design and rapid prototyping complex geometries to increase stiffness and strength. Vortex lattice method (VLM) code efficiently estimated the aerodynamic coefficients and wind tunnel tests showing little discrepancy from the VLM model. The power model showed similar results to other researched models from Myles Loyd, and Fchener. Furthermore, the model showed that a bridle can add a significant increase in pitch stability and the ability to increase pitch authority without a horizontal stabilizer. Wind tunnel results confirm high lift capabilities of the delta wing geometry with angle of attack up to 90°, although the power generation is not optimal due to the small aspect ratio of the main element. Using 3D printed nylon (PA12) and carbon fiber reinforced polymer (CFRP), thermal and mechanical properties were characterized to determine the feasibility of using the 3D printed structure as a core and a mold. It was determined that the weight percent composition of the PA12 had about 1.5% water and 14% carbon platelet, which the water can adversely affect chemical adhesion and the carbon improves mechanical properties. Additionally, the PA12 also had the thermal stability to withstand the cure temperatures of the CFRP. Through tensile tests, it was determined that within the linear region the PA12 exhibited isotropic behavior. However, for ultimate failures, the PA12 exhibited anisotropic behavior, using the coordinate system of the 3D printer, with the X direction absorbing 2.4 times more energy with a higher strain and ultimate failure. It was shown that stronger adhesion occurred between the PA12 and the CFRP using a lower cure temperature and vacuum. The lower temperature avoids residual stresses caused by the difference in coefficient of thermal expansion. The adhesion strength verified that the 3D printed PA12 structure can be used as a core and mold for rapid prototyping applications. Further development of AWES are then discussed

Airborne Wind Energy Conference 2019 : (AWEC 2019)

[Book of Abstracts from the Airborne Wind Energy Conference 2019.

High resolution aerial and field mapping of thermal features in Ragged Hills, Yellowstone National Park

High resolution aerial images taken in a cost and time effective way from low-flying platforms were used to map a hydrothermal area in the Yellowstone National Park. The mapping area called Ragged Hills is located in the Norris Geyser Basin, a major hydrothermal basin of the Park famous for its great diversity and number of thermal features. Because of an increasing thermal activity since the early 1990s numerous hydrothermal features of different sizes developed in Ragged Hills. Various changes in size and chemistry of the thermal features were observed during sporadic ground surveys. No detailed maps of the thermal inventory existed because of the difficulties in mapping this rapidly changing area by standard ground survey methods. Mapping the features in a short time to get a status quo of the feature’s form and size was the goal of the present work. Two different low-flying platforms were used during this project – a helium filled balloon and a single engine airplane (Cessna 172). To be able to georeference the aerial photos later a grid of ground control points was laid out and the points were surveyed by differential GPS as well as by theodolite. Deviations between both methods were on average 37 cm (Northing) and 61 cm (Easting). The overflights with the airplane were more cost intensive, requiring aircraft rental and trained pilots. Because the obtained images were in most cases blurred, they were served as overview only. Nevertheless the pixel resolution was quiet good with an average of 6 cm. Besides the true color images taken by a digital camera, also thermal pictures were taken from the airplane with a spatial resolution of 1.2 m. The balloon survey provided a costeffective and easy-to-handle alternative. Major restrictions are only the transport of the helium bottles to the study site, and the requirements for calm wind conditions. From an altitude of 50 to 80 m sharp and high resolution images were obtained. About 45 pictures were used to create a mosaic of the whole study area with a pixel resolution of 2.5 cm. No high-resolution thermal pictures could be taken from the balloon because the weight of the camera (3.9 kg) exceeded the balloon’s lifting capacity (1.5 kg). The created high-resolution aerial overview was included in a digital atlas together with topography and geological maps, older lowresolution aerial pictures, and hydrochemical data. The following diploma thesis gives an overview about available low-flying platforms and their individual advantages and disadvantages, describes the methods used in detail and evaluates them regarding expenditure and time it took to realize the individual working steps. Furthermore an interpretation of mapping and hydrochemical data is presented.Förderkreis Freiberger Geologie e.V.researc