Made available in DSpace on 2014-06-11T19:28:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-03-06Bitstream added on 2014-06-13T20:18:22Z : No. of bitstreams: 1 silva_mr_me_guara.pdf: 974660 bytes, checksum: 8f80690ebfe32f2752005d78330dde96 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Esta dissertação apresenta uma metodologia para a otimização de manobras de atitude de satélites artificiais estabilizados por rotação, utilizando-se algoritmos genéticos. Primeiramente, é simulado o controle inicial da manobra, dado por uma lei de controle baseada em uma função de chaveamento, conforme a teoria de Shigehara (1972). Em seguida, com base nos resultados obtidos pela lei de controle inicial, aplica-se o algoritmo genético na otimização dos intervalos e polaridades de funcionamento de um atuador, tipo bobina magnética. Durante este procedimento, nas diferentes manobras, a otimização global e por período foram simuladas. Na implementação do algoritmo genético, o problema de otimização de manobra considera uma função multi-objetivo definida pela minimização dos erros dos ângulos da manobra e o tempo final. A exequibilidade desta metodologia utilizando algoritmos genéticos se verifica na comparação entre os resultados obtidos por Gamarra Rosado e Rios Neto (1992a; 1992b), obtidas no processo de subotimização da manobra. Da análise das simulações realizadas, observou-se que o algoritmo genético conseguiu minimizar o tempo final da manobra, entretanto, em todos os casos analisados, os ângulos finais de declinação e ascensão reta sofreram pequenas diferenças nos valores finais em comparação com a condição final da manobra estabelecida / This dissertation presents a methodology for the optimization of attitude maneuvers of a satellite stabilized by rotation, using genetic algorithms. First, the initial control is simulated maneuver, given by a control law based on a switching function, as the theory of Shigehara (1972). Then, based on the results obtained by the initial control law, applies the genetic algorithm in optimization of intervals and polarities of operation of an actuator, solenoid coil type. During this procedure, the different maneuvers, and global optimization period were simulated. In the implementation of genetic algorithm, the optimization problem maneuvering considering a multiobjective function defined by minimizing the errors of the angles of the maneuver and final time. The feasibility of this methodology using genetic algorithms is verified when comparing the results obtained by Gamarra Rosado and Rios Neto (1992a; 1992b), obtained in the process of sub-optimization of the maneuver. The analysis of the simulations, it was observed that the genetic algorithm able to minimize the end time of the operation, however, in all cases examined, the final angles of declination and right ascension experienced slight differences in the final values in comparison to the final condition of maneuver established

Orientador: Víctor Orlando Gamarra Rosado / Banca: Maria Cecilia França Zanardi / Banca: Luiz Eduardo Nicolini do Patrocínio Nunes / Resumo: Esta dissertação apresenta uma metodologia para a otimização de manobras de atitude de satélites artificiais estabilizados por rotação, utilizando-se algoritmos genéticos. Primeiramente, é simulado o controle inicial da manobra, dado por uma lei de controle baseada em uma função de chaveamento, conforme a teoria de Shigehara (1972). Em seguida, com base nos resultados obtidos pela lei de controle inicial, aplica-se o algoritmo genético na otimização dos intervalos e polaridades de funcionamento de um atuador, tipo bobina magnética. Durante este procedimento, nas diferentes manobras, a otimização global e por período foram simuladas. Na implementação do algoritmo genético, o problema de otimização de manobra considera uma função multi-objetivo definida pela minimização dos erros dos ângulos da manobra e o tempo final. A exequibilidade desta metodologia utilizando algoritmos genéticos se verifica na comparação entre os resultados obtidos por Gamarra Rosado e Rios Neto (1992a; 1992b), obtidas no processo de subotimização da manobra. Da análise das simulações realizadas, observou-se que o algoritmo genético conseguiu minimizar o tempo final da manobra, entretanto, em todos os casos analisados, os ângulos finais de declinação e ascensão reta sofreram pequenas diferenças nos valores finais em comparação com a condição final da manobra estabelecida / Abstract: This dissertation presents a methodology for the optimization of attitude maneuvers of a satellite stabilized by rotation, using genetic algorithms. First, the initial control is simulated maneuver, given by a control law based on a switching function, as the theory of Shigehara (1972). Then, based on the results obtained by the initial control law, applies the genetic algorithm in optimization of intervals and polarities of operation of an actuator, solenoid coil type. During this procedure, the different maneuvers, and global optimization period were simulated. In the implementation of genetic algorithm, the optimization problem maneuvering considering a multiobjective function defined by minimizing the errors of the angles of the maneuver and final time. The feasibility of this methodology using genetic algorithms is verified when comparing the results obtained by Gamarra Rosado and Rios Neto (1992a; 1992b), obtained in the process of sub-optimization of the maneuver. The analysis of the simulations, it was observed that the genetic algorithm able to minimize the end time of the operation, however, in all cases examined, the final angles of declination and right ascension experienced slight differences in the final values in comparison to the final condition of maneuver established / Mestre

As part of a continuous trend of the space sector for obtaining higher performance space science and Earth observations, there is an increasing demand for higher requirements in pointing accuracy and disturbance prediction. The Space Rider System (SRS) is a Low Earth Orbit (LEO) reusable vehicle that aims at answering to that demand. It is a real science platform for short orbital missions, and its service module is being developed for European Space Agency (ESA) by Italian company AVIO S.p.A. The module possesses several rotating parts such as the solar arrays and the reaction wheels, that both create vibration disturbances that might jeopardize the Micro-Gravity (MG) requirements set on the project. At the same time, these reaction wheels were found to be failing to complete certain slew maneuvers, although they are the preferred actuator for most attitude controls. In a perspective to studying these aspects and exploring possible enhancements, this study develops two generic models to simulate the vibration disturbances from Solar Array (SA) and Reaction Wheel (RW). Furthermore, the optimization routine of a different guidance approach using a quaternion shape method is developed to tackle the Reaction Wheels Assembly (RWA) saturation. Through extensive validation work coupled with research and simulations, the developed models were found to enable a good estimation of the vibrations on the spacecraft, and enhance the ability of the company to validate requirements in a more agile way. Furthermore, an optimization algorithm was developed and has shown great performance in desaturating all the problematic maneuvers using reaction wheels during orbital phases, with low computational requirements. / Som en del av rymdsektorns kontinuerliga strävan att uppnå högre prestanda inom rymdvetenskap och jordobservationer ökar kraven på högre precision i riktningen och störningsförutsägelser. Space Rider System (SRS) är en återanvändbar farkost för låg jordbana (LEO) som syftar till att uppfylla dessa krav. SRS är en vetenskapsplattform för korta rymduppdrag i omloppsbana, och dess servicemodul utvecklas för ESA av det italienska företaget AVIO S.p.A. Modulen har flera roterande delar, t.ex. solpanelerna och reaktionshjulen, som båda skapar vibrationsstörningar som kan äventyra de krav på mikrovibrationer som ställs på projektet. Samtidigt konstaterades det att reaktionshjulen inte klarar av att genomföra vissa svängningsmanövrar, trots att de är det föredragna manöverdonet för de flesta attitydkontroller. För att studera dessa aspekter och utforska möjliga förbättringar utvecklas i denna studie två generiska modeller för att simulera vibrationsstörningar från solpanelerna och reaktionshjulen. Dessutom utvecklas optimeringsrutinen för en annan styrningsmetod med hjälp av en kvaternion-formmetod för att hantera mättnaden av reaktionshjulen. Genom ett omfattande valideringsarbete med forskning och simuleringar visade sig de utvecklade modellerna möjliggöra en god uppskattning av vibrationerna på rymdfarkosten och förbättra företagets förmåga att validera krav på ett smidigare sätt. Vidare utvecklades en optimeringsalgoritm som har visat stor prestanda när det gäller att avmätta alla problematiska manövrar med hjälp av reaktionshjul under omloppsfaserna, med låga beräkningskrav.

Approved for public release; distribution in unlimited. / Spray cooling is a promising means of dissipating large steady state heat fluxes in high density power and electronic systems, such as thermophotovoltaic systems. The present study reports on the effectiveness of spray cooling in removing heat fluxes as high as 220 W/cm2. An experiment was designed to determine how the parameters of spray volumetric flow rate and droplet size influence the heat removal capacity of such a system. A series of commercially available nozzles were used to generate full cone water spray patterns encompassing a range of volumetric flow rates (3.79 to 42.32 L/h) and droplet Sauter mean diameters (17.4 to 35.5 micrometers). The non-flooded regime of spray cooling was studied, in which liquid spreading on the heater surface following droplet impact is the key phenomenon that determines the heat transfer rate. The experimental data established a direct proportionality of the heat flux with spray flow rate, and an inverse dependence on the droplet diameter. A correlation of the data was developed to predict heat flux as a function of the studied parameters over the range of values tested in this. / Lieutenant, United States Navy

The recent interests in the necessity of high maneuverability and vertical launching triggered namely the unconventional control design techniques that are effective at high angle of attack flight regimes. For most of missile configurations, this interest required thrust vector control together with conventional aerodynamic control. In this study, nonlinear modeling and dynamical analysis of a surface to air missile with both aerodynamic and thrust vector control is investigated. Aerodynamic force and moment modeling of the presented missile includes the challenging high angle of attack aerodynamics behavior and the so called hybrid control, which utilizes both tail fins and jet vanes as control surfaces. Thrust vector and aerodynamic control effectiveness is examined during flight envelope. Different autopilot designs are accomplished with hybrid control. Midcourse and terminal guidance algorithms are implemented and performed on target sets including maneuverable targets. A different initial turnover strategy is suggested and compared with standard skid-to-turn maneuver. Comparisons of initial roll with aerodynamic and thrust vector control are examined. Afterwards, some critical maneuvers and hybrid control ratio is studied with a real coded genetic algorithm. Rapid turnover for low altitude targets, intercept maneuver analysis with hybrid control ratio and lastly, engagement initiation maneuver optimization is fulfilled.