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Abstract: Preliminary studies on field emission (FE) arrays comprised of carbon nanotubes (CNT) as an electron source for electric propulsion system show remarkably promising results. Design parameters for a carbon nanotube (CNT) field-emission device operating on triode configuration were numerically simulated and optimized in order to enhance the e-beam focusing quality. An additional focus gate (FG) was integrated to the device to control the profile of the emitted e-beam. An axisymmetric finite element model was developed to calculate the electric field distribution on the vacuum region and a modified Fowler-Nordheim (FN) equation was used to evaluate the current density emission and the effective emitter area. Afterward, a FE simulation was employed in order to calculate the trajectory of the emitted electrons and define the electron-optical properties of the e-beam. The integration of the FG was fully investigated via computational intelligence techniques. The best performance device according to our simulations presents a collimated e-beam profile that suits well for field emission displays, magnetic field detection and electron microscopy. The automated computational design tool presented in this study strongly benefits the robust design of integrated electron-optical systems for vacuum field emission applications, including electrodynamic tethering and electric propulsion systems.Resumo em Inglês:
Abstract: The present work is concerned with the numerical simulation of hypersonic blunt body flows with chemical non-equilibrium. New theoretical and numerical formulations for coupling the chemical reaction to the fluid dynamics are presented and validated. The fluid dynamics is defined for a stationary unstructured mesh and the chemical reaction process is defined for "finite quantities" moving through the stationary mesh. The fluid dynamics is modeled by the Euler equations and the chemical reaction rates by the Arrhenius law. Ideal gases are considered. The thermodynamical data are based on JANNAF tables and Burcat's database. The algorithm proposed by Liou, known as AUSM+, is implemented in a cell-centered based finite volume method and in an unstructured mesh context. Multidimensional limited MUSCL interpolation method is used to perform property reconstructions and to achieve second-order accuracy in space. The minmod limiter is used. The second order accuracy, five stage, Runge-Kutta time-stepping scheme is employed to perform the time march for the fluid dynamics. The numerical code VODE, which is part of the CHEMKIN-II package, is adopted to perform the time integration for the chemical reaction equations. The freestream reacting fluid is composed of H2 and air at the stoichiometric ratio. The emphasis of the present paper is on the description of the new methodology for handling the coupling of chemical and fluid mechanic processes, and its validation by comparison with the standard time-splitting procedure. The configurations considered are the hypersonic flow over a wedge, in which the oblique detonation wave is induced by an oblique shock wave, and the hypersonic flow over a blunt body. Differences between the solutions obtained with each formulation are presented and discussed, including the effects of grid refinement in each case. The primary objective of such comparisons is the validation of the proposed methodology. Moreover, for the hypersonic flow over a blunt body, solutions obtained for two meshes are shown, compared and analyzed. The numerical solutions are also compared with experimental data.Resumo em Inglês:
Abstract: A stationary experiment was performed to study the degradation of carbon-based materials by immersion in a plasma jet. In the experiment, graphite and C/C composite were chosen as the target materials, and the reactive plasma jet was generated by an air plasma torch. For macroscopic study of the material degradation, the sample's mass losses were measured as function of the exposure time under various temperatures on the sample surface. A microscopic analysis was then carried out for the study of microscopic aspects of the erosion of material surface. These experiments showed that the mass loss per unit area is approximately proportional to the exposure time and strongly depends on the temperature of the material surface. The mass erosion rate of graphite was appreciably higher than the C/C composite. The ablation rate in the carbon matrix region in C/C composite was also noticeably higher than that in the fiber region. In addition, the latter varied according to the orientation of fibers relatively to the flow direction. These tests indicated an excellent ablation resistance of the C/C composite, thus being a reliable material for rocket nozzles and heat shielding elements of the protection systems of hypersonic apparatuses from aerodynamic heating.Resumo em Inglês:
Abstract: 2,2’, 4,4’, 6,6’- hexanitrostilbene (HNS) is an energetic material, a nitroaromatic compound, with thermal and chemical stabilities, which is employed in the aerospace industry. In this work, the Arrhenius parameters (activation energy and pre-exponential factor) of thermal decomposition reaction were studied and the results were compared with the values reported in the literature. The Kissinger method, applied to DSC’s nonisothermal data of the decomposition temperature was chosen for this study. The activation energy determined for the thermal decomposition of HNS revealed values from 428 kJ.mol-1 to 477 kJ.mol-1, under the experimental conditions employed.Resumo em Português:
Resumo: A adição de partículas metálicas nanométricas em sistemas de propulsão, tais como propelentes sólido, líquido, híbrido e de motores aspirados, "ramjet", tem sido recentemente mais pesquisada. Significante aumento na velocidade de queima e no impulso específico são algumas das vantagens do uso de nanopartículas de materiais energéticos em diferentes tipos de sistemas de propulsão. O alumínio tem sido largamente empregado como aditivo metálico em materiais energéticos, e recentemente em um novo sistema de propulsão (aluminum/ice propulsion, Alice). Estudos mostram que a vantagem do uso de nanopartículas de alumínio em substituição das partículas micrométricas facilita a ignição de sistemas e permite melhor incorporação dos componentes nas formulações, melhorando sua homogeneidade. Alguns dos processos de combustão que requerem altas pressões e temperaturas podem ocorrer em condições moderadas devido ao aumento da área superficial dos reagentes, nesse caso, de aditivo metálico.Resumo em Inglês:
Abstract: The addition of nanosized metal particles in propulsion systems such as solid and liquid propellants, hybrid propellant and ramjet motors has recently became a major focus of research. Significant increases in the burning velocity and in the specific impulse are some of the advantages of using nano-scale energetic materials in many different types of propulsion systems. Aluminum has been largely employed as a metallic additive in energetic materials, also in a recently new propulsion system (aluminum/ice propulsion, "Alice"), and some studies show that the advantages of using nanosized aluminum instead of microsized aluminum are facilitating the ignition of the systems and allowing better incorporation of the components in the formulations and improving its homogeneity. Some of the combustion processes that require high pressures and even higher temperatures can occur in moderate conditions due to the increase of the surface area of the reactants, in this case, the metallic additive.Resumo em Inglês:
Abstract: The chemical compatibility of explosives, pyrotechnics and propellants with those materials is studied to evaluate potential hazards when in contact with other materials during production, storage and handling. Compatibility can be studied by several thermal methods as DSC (differential scanning calorimetry), TG (Thermogravimetry), VST (Vacuum stability test) and others. The test methods and well defined criteria are the most important elements when a compatibility study is being accomplished. In this paper, the compatibility of two very important high explosives used in ammunition, RDX (Cyclo-1,3,5-trimethylene-2,4,6-trinitramine) and HMX (Cyclotetramethylene tetranitramine) was studied with the materials: fluoroelastomer (Viton) and powdered aluminum (Al), using DSC and VST methods. The criteria to judge the compatibility between materials is based on a standardization agreement (STANAG 4147, 2001), and the final conclusion is that explosives and this materials are compatible, but in DSC it was observed that the peak of decomposition temperature of the admixture of RDX with Al decreased in 3º C and another peak appeared after the decomposition peak.Resumo em Inglês:
Abstract: The complex dielectric permittivity (e) and magnetic permeability (m) of Radar Absorbing Materials (RAM) based on metallic magnetic particles (carbonyl iron particles) embedded in a dielectric matrix (silicon rubber) have been studied in the frequency range of 2 to 18 GHz. The relative permeability and permittivity of carbonyl iron-silicon composites for various mass fractions are measured by the transmission/reflection method using a vector network analyzer. The concentration dependence of permittivity and permeability on the frequency is analyzed. In a general way, the results show that e´ parameter shows a more significant variation among the evaluated parameters (e", m", m'). The comparison of dielectric and magnetic loss tangents (e"/e" and m"/m', respectively) shows more clearly the variation of both parameters (e and m) according to the frequency. It is also observed that higher carbonyl iron content fractions favor both dielectric and magnetic loss tangents.Resumo em Inglês:
Abstract: This paper presents the processing and characterization of electromagnetic radiation absorbing paints and sheets based on magnetic and dielectric materials dispersed in polymeric matrices. Two different paint formulations containing carbonyl iron and/or polyaniline, using polyurethane as matrix, were prepared. Silicone sheets were also produced with polyaniline conducting polymer as filler. Measurements of the electric permittivity and magnetic permeability of the materials were also carried out. Simulations for the silicone sheets were performed in order to correlate the electromagnetic parameters with the material thickness. The paints absorbed 60 to 80% of the incident electromagnetic radiation and the silicone sheets absorbed 90%, indicating the material's radar absorbing potential.Resumo em Português:
Resumo: Este artigo apresenta uma comparação das características relevantes observadas nos clusters aeroespacial e automobilístico do Vale do Paraíba Paulista e analisa o adensamento das cadeias produtivas e tecnológicas. Para tanto, os procedimentos metodológicos adotados eram de natureza qualitativa, empregados por meio de pesquisa documental. Os resultados indicam que o governo estabeleceu, em meados de 1945, o atual Departamento de Ciência e Tecnologia Aeroespacial (DCTA), como centro de Pesquisa e Desenvolvimento (P&D) e, em 1979, a Embraer, como indústria estatal de construção aeronáutica. Procurou-se também gerar condições para que empresas nacionais surgissem ao seu redor e substituíssem a dependência do fornecedor internacional para fornecimento de sistemas e subsistemas aeroespaciais, desenvolvendo capacidade tecnológica própria. Por seu lado, o cluster automobilístico em estudo iniciou-se no Vale do Paraíba Paulista (VPP) pela regionalização de empresas multinacionais de construção automobilística migradas da região do grande ABC Paulista à procura de espaço físico para o seu crescimento, contando também com incentivos fiscais favoráveis. Os resultados da pesquisa indicam que, a despeito de diferenças fundamentais em relação ao adensamento de suas cadeias produtivas, mostraram resultados adversos semelhantes.Resumo em Inglês:
Abstract: This paper presents a comparison of the relevant characteristics of São Paulo State's Vale do Paraíba automotive and aerospace clusters observed and analyzes the technological and productive chains strengthening. In order to accomplish it, the adopted methodological procedures are of qualitative nature, by means of documentary research. The results pointed out that the government established, in the mid-1945, the currently named Departamento de Ciência e Tecnologia Aeroespacial (DCTA), as a research and development (R&D) center and, by 1979, Embraer, a state-owned aeronautical construction industry. It was also sought to generate conditions so that domestic companies could emerge around and replace the dependency on aerospace systems and subsystems international suppliers by developing indigenous technological capacities. The automotive cluster under study started in the São Paulo State's Vale do Paraíba (PPV) by means of the regionalization of multinational automotive construction firms migrated from ABC Paulista region looking for physical space for their growth, also relying on tax benefits. The survey results indicate that, in spite of fundamental differences with regard to their productive chains strenghtening processes, they showed similar adverse results.Resumo em Português:
Resumo: O presente estudo descreve o processo de gestão de projetos de pesquisa e desenvolvimento (P&D) de uma instituição pública de pesquisa do setor aeroespacial, integrante do parque tecnológico e industrial do Vale do Paraíba Paulista, o Comando-Geral de Tecnologia Aeroespacial - CTA. A pesquisa exploratória conduzida visa identificar a aplicação de financiamento empregada pelo governo federal e FINEP, como também os instrumentos e as ferramentas disponíveis na instituição incorporando os planos, leis, diretrizes, normas e relatórios que permeiam o processo de gestão de projetos de P&D. Este estudo examinou as atividades de planejamento, acompanhamento e controle de casos reais de projetos. A partir das informações qualitativas e quantitativas coletadas, foram apresentadas as considerações e recomendações, de modo a melhorar a eficácia e a eficiência da gestão desses projetos.Resumo em Inglês:
Abstract: The present study describes the research and development (R & D) project management process in an aerospace sector public research institution, belonging to the São Paulo State Paraiba River Valley technological and industrial park, the General Command for Aerospace Technology (Comando - Geral de Tecnologia Aeroespacial - CTA). The exploratory research undertaken aimed to identify the application of federal government and FINEP funding, as well as the instruments and tools available to the institution, including its planning, its regulations, guidelines, standards and reports which pervade the R & D project management process. This study examined the planning, follow-up and monitoring activities associated with real case studies. From the qualitative and quantitative information collected, observations and recommendations were made in order to improve the efficient management of these activities.Resumo em Inglês:
Abstract: This paper aimed to compare the wind measurements in two different types of anemometer: classical aerovane and modern sonic anemometer. The two sensors were installed at Alcântara Launch Center during a dry period of 2008 at 10 m height. The analysis compared the average and maximum wind speed for one- and ten-minute time intervals for each anemometer. The results showed that, considering the range of the measurements (from 3.0 up to 6.5 m/s), the average and maximum wind speed are different by roughly 0.5 and 1.0 m/s, respectively. There is no significant difference between the results from one- and ten-minute time intervals. The substitution of the sensors at the Anemometric Tower at Alcântara Launch Center will lead to an increase of the average and maximum wind speed.