The Coulomb propulsion system has no exhaust plume impingement problem with neighboring spacecraft and does not contaminate their sensors because it requires essentially no propellant. It is suitable to close formation control on the order of dozens of meters. The Coulomb forces are internal forces of the formation and they influence all charged spacecraft at the same time. Highly nonlinear and strongly coupled equations of motion of Coulomb formation makes creating a Coulomb control method a challenging task. Instead of positioning all spacecraft, this study investigates having a sensor craft be sequentially controlled using dedicated drone craft. At least three drone craft are required to control a general sensor craft position in the inertial space. However, the singularity of a drone plane occurs when a sensor craft moves across the drone plane. A bang-bang control method with a singularity check can avoid this problem but may lose formation control as the relative distances grow bounded. A bang-coast-bang control method utilizing a reference trajectory profile and drone rest control is introduced to increase the control effectiveness. The spacecraft are assumed to be floating freely in inertial space, an approximation of environments found while underway to other solar system bodies. Numerical simulation results show the feasibility of sensor craft control using Coulomb forces. / Master of Science

Chrysopelea paradisi, also known as the flying snake, possesses one of the most unique forms of aerial locomotion found in nature, using its entire body as a dynamic lifting surface without the use of wings or membranes. Unlike other airborne creatures, this species lacks appendages to aid in controlling its flight trajectory and producing lift. The snake exhibits exception gliding and maneuvering capabilities compared with other species of gliders despite this lack of appendages. While gliding, C. paradisi morphs its body by expanding its ribs, essentially doubling its width and utilizing its entire length as a reconfigurable wing. Its cross-sectional shape transforms into a thick, airfoil shape with a concave ventral surface, outwards protruding lips at the leading and trailing edges, a somewhat triangular dorsal surface with a round apex, and fore-aft symmetry. This study investigated the aerodynamic performance of this unique shape by simulating a single, static segment of the snake's body over a wide range of Reynolds numbers (3,000 to 15,000) and angles of attack (-10 to 60o) to simulate the full range of the snake's flight kinematics. This is the first study on an anatomically accurate snake model, and few aerodynamic studies have been performed in this low Reynolds number regime. Load cell measurements and time-resolved digital particle image velocimetry (TRDPIV) were performed on a 2D anatomically accurate model to determine the lift and drag coefficients, wake dynamics, and vortex shedding characteristics. This geometry produced a maximum lift coefficient of 1.9 and maximum lift to drag ratio of 2.7, and maintained increases in lift up to 35o. Overall, this geometry demonstrated robust aerodynamic behavior by maintain significant lift production and near maximum lift to drag ratios over a wide range of test parameters. These aerodynamic characteristics may enable the flying snake to glide at steep angles and over a wide range of angles of attack, often encountered in gliding trajectories. This geometry also produced larger maximum lift coefficients than many other bluff bodies and airfoils in this low Reynolds number regime. This thesis is organized as follows. The first section contains a broad introduction on gliding flight and C. paradisi's unique mode of gliding. The following section is a manuscript that will be submitted to a journal and contains the experimental analysis on the snake's cross-sectional shape. Several appendices attached to the end of this thesis contain additional analysis and work performed throughout the duration of this project and unique Matlab algorithms developed during this research. / Master of Science

Os veículos aéreos não tripulados (VANTs) vêm apresentando destaque crescente no setor aeronáutico mundial, tanto no desenvolvimento dos mesmos quanto nas diferentes aplicações desses veículos, devido ao seu grande potencial de utilização. Em muitas aplicações, a utilização de múltiplos VANTs apresenta várias vantagens sobre um VANT sozinho. No entanto, o agrupamento pode experimentar problemas inerentes à comunicação sem fio, podendo originar novos problemas como inviabilizar a coordenação e a execução cooperativa de uma missão, por exemplo. Em um cenário não colaborativo, VANTs com algum nível de autonomia e que partilhem do mesmo espaço aéreo também deverão ser capazes de trocar informações entre si, principalmente informações sobre posicionamento e rota de voo, e também estarão suscetíveis aos distúrbios da comunicação sem fio. Para balancear as vantagens e as desvantagens, esses robôs precisarão se comunicar cientes das restrições e utilizando a rede de modo otimizado, por meio da aplicação de algoritmos que equilibrem adequadamente técnicas de difusão de informações e técnicas de mitigação de retransmissões. Neste projeto de doutorado foi feita a investigação sobre o método de disseminação de dados, por meio de broadcasting, em uma rede móvel ad hoc entre VANTs, denominada Flying Ad hoc Networks (FANETs). FANETs são um novo paradigma que pode superar as restrições de missões de um único VANT. As FANETs são compostas por vários VANTs que cooperam para realizar alguma missão crítica (por exemplo, uma missão de busca e resgate). Para manter a coordenação, todos os VANTs devem continuamente enviar ou retransmitir mensagens através do canal sem fio para garantir que todos os membros da rede saibam o estado da rede. Geralmente, a troca de dados necessários para manter a sincronização da missão exige o uso de broadcast para que todos os membros da rede possam recebê-los. No entanto, quando essa troca de mensagens é feita arbitrariamente, isso pode causar o problema da tempestade de broadcast (BSP), levando o meio sem fio a um estado inoperante. Apesar de alguns esforços relatados na literatura para o provimento de técnicas gerais de mitigação do problema BSP, o desafio de agregar novas informações ou conhecimento a receptores que estejam voando, ao invés de apenas espalhar os dados na rede, tem recebido menos atenção. Nesta tese, além de demonstrar que o problema BSP intensifica a contenção de rede à medida que o número de VANTs aumenta, também foi criado um método que se prova mais eficiente que os existentes até então. Tal técnica, denominada de Algoritmo Baseado em Vizinhança Dinâmica para o Problema da Tempestade de Broadcast (DNA-BSP), foi desenvolvida e validada com base em experimentos de mundo real e em simulações computacionais. Ele pode mitigar o problema BSP, que é um desafio real nas FANETs, reduzindo a redundância de mensagens em mais de 98% e tornando a entrega de mensagens 99,5% mais rápida do que no cenário de flooding, superando as técnicas gerais de mitigação do BSP quando aplicado em FANETs. Os resultados detalhados neste texto também poderão orientar trabalhos futuros ao fornecer informações úteis para o planejamento e otimização de redes ad hoc móveis para VANTs. / Unmanned aerial vehicles (UAVs) have been showing increasing notoriety in the global aviation scene, both on their development and on the different applications for these vehicles, due to their high potential of use. In many applications, using multiple UAVs has several advantages over a single UAV. However, a cluster of UAVs may experience issues inherent to wireless communication, which may lead to new complications such as making mission coordination and cooperative execution impractible. In a non-collaborative scenario, UAVs with some level of autonomy which share the same airspace should also be able to exchange information among themselves, especially positioning and flight path information, and may also be susceptible to wireless communication disturbances. These robots have to use the network fairly and should communicate under restrictions, appropriately adjusting techniques that disseminate information and that mitigate broadcasts, in order to balance the advantages and disadvantages of being a group. This Ph.D. research investigates how broadcasting is used to disseminate data throughout ad hoc mobile networks between UAVs called Flying Ad hoc Networks (FANETs). FANETs are a new paradigm that can overcome the mission constraints of single UAVs. FANETs are composed of several UAVs that cooperate to accomplish a critical mission (e.g., hazardous area monitoring). Aiming to maintain UAVs coordination, all aircraft must continuously retransmit or relay messages through the wireless channel to assure that every member knows the FANET status. However, when this message exchange is done blindly, it may cause the broadcast storm problem (BSP), leading the wireless medium to a dysfunctional state. Despite some efforts reported in the literature for providing general techniques to mitigate the broadcast storm problem, the challenge of aggregating new information or knowledge to receivers, instead of just spreading the information in the network, has received less attention. In this research, it has been proved that the broadcast storm problem causes network contention as the number of UAVs increases, and the innovative Dynamic Neighborhood-based Algorithm for the Broadcast Storm Problem (DNA-BSP) has been provided as a countermeasure, which was developed and validated based on computer simulations and outdoor experiments. It can mitigate the broadcast storm problem, which is a real challenge in FANETs, reducing message redundancy in more than 98%, and making message delivery 99,5% faster than in flooding scenario, outperforming classical broadcast storm mitigation techniques when applied in FANETs. Our detailed results can also guide future researches and provide useful insights for engineers planning and optimizing mission-critical mobile ad hoc network with support of UAVs.

Orientador: Carlos Alberto Canesin / Resumo: No presente trabalho de dissertação, é analisado e desenvolvido um conversor ressonante com o objetivo de produzir ozônio, aplicado à água de processos de higienização industrial. Na atualidade, no ano de 2018, dois dos fatores de grande importância no desenvolvimento de conversores para geração de ozônio são: a eficiência energética, isto é, quanta energia é aproveitada em relação à energia total fornecida ao conversor, e a outra é a produção de ozônio fazendo uso dessa energia aproveitada. Os dois fatores não necessariamente estão relacionados, por exemplo, para dois conversores distintos com a mesma energia disponível, pode acontecer que em um deles possa ser produzido maiores concentrações de ozônio com um menor aproveitamento de energia. Portanto, este trabalho enfatiza a melhoria da eficiência energética na produção de ozônio, empregando comutação suave nas estruturas envolvidas do conversor ressonante proposto, o que resulta em uma eficiência energética de 91,57%. A estrutura do conversor proposto apresenta dois estágios em cascata, o primeiro deles, um conversor que é responsável por gerar um barramento CC estável de 400,5 V e que atende aos requisitos de fator de potência e distorção harmônica total com valores de 0,994 e 5,79%(para a corrente de entrada), respectivamente, e o segundo, um inversor ressonante capaz de fornecer uma tensão de 4,4 kV com uma frequência de 10 kHz que atua como fonte de alimentação de um reator conformado por câmaras de descarga usadas em ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In the present dissertation, it is studied and developed a resonant converter in order to produce ozone, applied in water treatment for cleaning processes. Currently, in the year 2018, two of the factors of great importance in the development of converters for ozone generation are: energy efficiency, that is, how much energy is used in relation to the total energy supplied to the converter, and the other is the production of ozone making use of this energy harnessed. The two factors are not necessarily related, for example, for two different converters with the same energy available, it can happen that in one of them can be produced higher concentrations of ozone with a lower use of energy. Therefore, this work emphasizes the improvement of energy efficiency in the production of ozone using soft switching in the involved structures of the proposed resonant converter, which results in an energy efficiency of 91.57%. The structure of the proposed converter has two stages in cascade, the first one, a converter that is responsible for generating a stable DC bus of 400.5 V and that meets the requirements of power factor and total harmonic distortion with values of 0.994 and 5.79% (for the input current), respectively, and the second, a resonant inverter capable of providing a voltage of 4.4 kV with a frequency of 10 kHz which acts as a power supply for a reactor formed by discharge chambers used in ozone generation applications by electric discharge. Naturally, relevant ozone info... (Complete abstract click electronic access below) / Mestre

Les aubes TuHP équipant le M88 subissent des contraintes thermomécaniques extrêmes qui provoquent l’amorçage et la propagation de fissures. Ces fissures peuvent évoluer rapidement et devenir critiques pour la sécurité. Actuellement, ces aubes sont inspectées in-situ au moyen d’un endoscope ou d’un vidéoscope dans le domaine du visible. Cependant, ce mode d’inspection par voie visuelle laisse souvent planer un doute sur la présence ou non d’une fissure ou sur sa criticité. Le démontage du module pour une inspection approfondie au microscope est alors nécessaire,augmentant le coût et le délai de la maintenance.L’objectif de la thèse est double. Il s’agit d’une part de valider un nouveau moyen de détection, sans démontage, de la fissuration des aubes HP en complément de l’inspection visuelle classique in-situ, et d’autre part d’utiliser les données expérimentales pour simuler la propagation d’une fissure et évaluer le caractère prédictif du modèle utilisé (direction et vitesse de propagation). La solution proposée pour réduire, voire supprimer le démontage des aubes, consiste à détecter les fissures par thermographie active flying spot dans le très proche infrarouge, de 1 à 2 microns (bande SWIR) au travers d’un endoscope classique. Le premier volet de la thèse a consisté à mettre au point le dispositif flying spot dans une configuration représentative d’un endoscope, puis à valider ce procédé d’inspection par des essais sur des aubes TuHP en retour d’expérience.Le deuxième volet de la thèse est davantage tourné vers la simulation. Le travail a tout d’abord consisté à intégrer un modèle de propagation de fissures en régime de fatigue prenant en compte les effets du temps et de l’environnement, dans le code de calcul par éléments finis ZeBuLon. Ce modèle a ensuite été utilisé pour simuler la propagation de fissures dans des aubes TuHP soumises à des cycles de chargement et de température complexes et représentatifs d’une mission réelle. La dernière partie du travail a consisté à comparer les résultats des simulations numériques avec les observations réalisées sur des aubes TuHP en retour d’expérience, afin d’évaluer le caractère prédictif du modèle de propagation pour cette application (direction et vitesse). / High pressure turbine blades undergo heavy thermomechanical constraints which drive initiation and propagation of cracks. These cracks may propagate rapidly and become critical for safety. The inspection of blades is currently conducted with endoscopes or videoscopes in the visible range. However, this kind of control is not sufficient to distinguish a crack from a surface defect, and it can be difficult to assess the criticality of a crack. In these cases, the dismantling of the engine for an accurate inspection with a microscope is necessary but this operation is time consuming and costly.This study has two aims. The first aim consists in validating a new inspection system complementary to the observations in the visible range. The second aim consists in using the experimental results to simulate the propagation of a crack and evaluate the ability of the model to predict the trajectory of a crack in a blade.The proposed solution to improve the detection of cracks in situ was to use the flying spot active thermography process in the SWIR range (1-2μm – short wavelength infrared) through a classical endoscope. The first aim of the experimental work was to develop the flying spot process to work on an industrial endoscope, and to validate it with tests on a series of cracked blades. The second part of this study is focused on the numerical simulation of the cracks. First, this work consisted in integrating a fatigue crack propagation model which takes into account the effects of creep and oxidation, in the finite element software ZeBuLoN. Then, this model was used to simulate the propagation of a crack in blades undergoing a complex load and thermal cycle representative of a real aircraft mission. The last part of this work consisted in comparing the numerical results with the experimental observations on cracked blades, to check the ability of themodel to predict the direction and the velocity of a crack in a blade.

The purpose of this thesis is to conduct an analysis of whether the printed circuit boards from Ericsson can be tested using an automatic probing system or what changes in the design are required, to be a viable solution. The main instrument used for analyzing the printed circuit board was an oscilloscope. The oscilloscope was used to get the raw data for plotting the difference between the theoretical and actual signals. Connected to the oscilloscope was a 600A-AT probe from LeCroy. The programs used for interpreting the raw data extracted from the oscilloscope included Python, Matlab and Excel. For simulations on how an extra via in the signal path would affect the end results we used HFSS and ADS. The results were extracted into different Excel sheets to get an easier overview of the results. The results showed that the design of a board must almost become completely rebuilt for the changes, and it is therefore better to implement in a new circuit board rather than in an already existing one. Some of the components have to either be smaller or placed on one side of the board, where they cannot be in the way of the probe. The size of the board will become larger since the rules of via placements will be limited compared to before. The most time demanding part was the simulations of the extra via in the signal path, and the results showed that if a single-ended signal is below two gigahertz the placing of the via does not make a big difference, but if the signal has a higher frequency the placement is mostly dependent on the type of the signal. The optimal placement is generally around four millimeters away from the receiving end. / Målet med detta examensarbete är att göra en analys av huruvida Ericssons kretskort kan testas med hjälp av ett automatiskt probe system eller om det kräver stora förändringar i designdelen av kretskorten och om, vad för förändringar det i sådant fall kan vara. Till hjälp att analysera kretskorten har vi haft oscilloskop för att få ut rådata om skillnaderna mellan de teoretiska och verkliga signalerna. För att kunna tyda oscilloskopets samplade signaler har olika programmeringsspråk som Python, Matlab samt Excel använts. En extra via i signalens väg har även simulerats i HFSS och ADS med olika sorts probar för att se hur signalens beteende påverkas. Resultaten extraherades sedan in i olika Excel ark för att få en lätt överskådlig bild av resultaten. Resultatet vi fick visade att utformningen av ett kretskort med ändringarna skulle vara lättare att göra med en ny design istället för en redan existerande då större delar av kortet skulle behöva göras om. Vissa stora komponenter behöver antingen göras om, hitta mindre men likvärdiga eller sättas på ena sidan av kortet där de inte är i vägen för proben. Kretskorten som kommer använda flygande probesystem kommer antagligen bli lite större då viornas placering är mer begränsade än tidigare. Det mest tidskrävande arbetet var att simulera olika placeringar av en extra via i signalens väg. Detta visade att på en single ended signal under två gigahertz så gör det ingen större skillnad vart i signalens väg som den extra vian placeras. Då en högre frekvens används så är själva signalens karaktär det viktigaste än placeringen av en via, men om man inte vet den exakta karaktären så är fyra millimeter bort från mottagarens sida att rekommendera då närmare placering av viorna gör att signalerna börjar störa varandra.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / AFRIKAANSE OPSOMMING: Hierdie proefskrif handel oor die natuurlike balanserings meganismes van veelvlakkige en modulêre omsetters wat fase-skuif dragolf puls wydte modulasie gebruik. Die meganismes kan in twee hoof groepe verdeel word: ‘n swak balanserings meganisme wat afhanklik is van die oorvleuling van die skakelfunksies en ‘n sterk meganisme wat voorkom ongeag of die skakelfunksies oorvleul al dan nie. Die sterk meganisme verdeel verder in twee subgroepe, ‘n direkte oordrag van onbalans energie en ‘n meganisme wat afhang van die verliese in die stelsel. Elkeen van die meganismes word aan die hand van ‘n omsetter topologie waarin die spesifieke meganisme oorheers beskryf en ontleed. In die ondersoek word klem geplaas op die daarstelling van uitdrukkings om die tydskonstantes van herbalansering na ’n afwyking vir elk van die omsetter toplologieë te beskryf. / ENGLISH ABSTRACT: This thesis investigates the natural balancing mechanisms in multilevel and modular converters using phase shifted carrier pulse width modulation. Two groups of mechanisms are identified; a weak balancing mechanism that is only present when the switching functions are interleaved and a strong mechanism that occurs irrespective of the interleaving of the switching functions. It is further shown that the strong balancing mechanism can be divided into a balancing mechanism that depends on the direct exchange of unbalance energy and a loss based balancing mechanism. Each of the mechanisms is discussed and analysed using a converter where the specific mechanism dominates as example. Emphasis is placed on the calculation of the rebalancing time constant following a perturbation. Closed form expressions for the rebalancing time constants for each of the analysed converters are presented.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis investigates the viability of constructing a solid-state transformer (SST) with a series-input, parallel-output connection of full-bridge, three-level ying-capacitor converters. It focusses on the active recti er front-end of the SST which is used to control the input current to be sinusoidal and in-phase with the sinusoidal input voltage. A stack of two converters are built and tested. The input current, as well as the ying capacitor voltages of the two active recti ers in the stack, are actively controlled by a nite-state model-based predictive (FS-MPC) controller. The use of multiple ying-capacitor converters poses a problem when using FS-MPC because of the large number of possible switching states to include in the prediction equations. Three FS-MPC control algorithms are proposed to attempt to overcome the problem associated with the large number of switching states. They are implemented on an FPGA digital controller. The algorithms are compared on the bases of voltage and current errors, as well as their responses to disturbances that are introduced into the system. The simulation and experimental results that are presented shows that by interleaving the control actions for the two converters, one can obtain fast and robust responses of the controlled variables. The viability of extending the interleaving control algorithm beyond two converters is also motivated. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die moontlikheid van volbrug, drievlak vlieënde-kapasitoromsetters wat gebruik word om 'n serie-intree, parallel-uittree drywingselektroniese transformator (DET) te bou. Dit fokus op die aktiewe gelykrigter van die DET wat gebruik word om die intreestroom te beheer om sinusvormig en in fase met die sinusvormige intreespanning te wees. 'n Stapel van twee omsetters word gebou en getoets. Die intreestroom, sowel as die vlieënde kapasitorspannings van die twee aktiewe gelykrigters in die stapel, word aktief beheer met behulp van 'n eindige-toestand, model-gebaseerde voorspellende beheerder (ET-MVB). Die gebruik van veelvuldige vlieënde-kapasitoromsetters bemoeilik die implementering van 'n ET-MVB-beheerder as gevolg van die groot aantal skakeltoestande wat in die voorspellende vergelykings in ag geneem moet word. Drie ET-MVB-algoritmes word voorgestel om te poog om die probleme, wat met die groot aantal skakeltoestande geassosieer word, te oorkom. Die algoritmes word in 'n FPGA digitale verwerker geïmplementeer. Die algoritmes word vergelyk op grond van hul stroom- en spanningsfoute, asook hul reaksie op steurings wat op die stelsel ingevoer word. Die simulasie en praktiese resultate toon dat, deur die beheeraksies vir die twee omsetters te laat oorvleuel, die gedrag van die beheerde veranderlikes vinniger en meer robuust is. Die moontlikheid om die oorvleuelende beheeraksies uit te brei tot meer as twee omsetters word ook gemotiveer.

The Multiple Simultaneous Specification controller design method is an elegant means of designing a single controller to satisfy multiple convex closed loop performance specifications. In this thesis, the method is used to design pitch and roll attitude controllers for a Zagi flying-wing unmanned aerial vehicle from Procerus Technologies. A linear model of the aircraft is developed, in which the lateral and longitudinal motions of the aircraft are decoupled. The controllers are designed for this decoupled state space model. Linear simulations are performed in Simulink, and all performance specifications are satisfied by the closed loop system. Nonlinear, hardware-in-the-loop simulations are carried out using the aircraft, on-board computer, and ground station software. Flight tests are also executed to test the performance of the designed controllers. The closed loop aircraft behaviour is generally as expected, however the desired performance specifications are not strictly met in the nonlinear simulations or in the flight tests.

The Multiple Simultaneous Specification controller design method is an elegant means of designing a single controller to satisfy multiple convex closed loop performance specifications. In this thesis, the method is used to design pitch and roll attitude controllers for a Zagi flying-wing unmanned aerial vehicle from Procerus Technologies. A linear model of the aircraft is developed, in which the lateral and longitudinal motions of the aircraft are decoupled. The controllers are designed for this decoupled state space model. Linear simulations are performed in Simulink, and all performance specifications are satisfied by the closed loop system. Nonlinear, hardware-in-the-loop simulations are carried out using the aircraft, on-board computer, and ground station software. Flight tests are also executed to test the performance of the designed controllers. The closed loop aircraft behaviour is generally as expected, however the desired performance specifications are not strictly met in the nonlinear simulations or in the flight tests.