Resumo em Inglês:

Abstract: Hypergolic reactions may be useful in civil and military applications. In the area of rocket propulsion, they constitute a potential field due to the reduced weight and complexity of fuel injection systems, allowing yet controlled use of the propulsors. This manuscript aimed at presenting different hypergolic systems and their particularities, comparing them with chemical propulsion svstems, which are most commonly employed in rocket motors, for example.

Resumo em Inglês:

Abstract: Atomic vapor laser isotope separation has been studied at the Institute for Advanced Studies for nuclear purposes since 1982, and recently it has been questioned about its potentialities for the aerospace area. Many applications from nuclear propulsion to electricity generation and space navigation have been found, which justify the study of isotope separation for aerospace applications. One of the key process, and the first step for atomic vapor laser isotope separation, is the production of a neutral vapor jet. This paper discussed the potentiality of using laser ablation as a tool to generate neutral metal vapor jet for isotope separation purposes. The basis for the discussion is a set of experimental results obtained at the Institute for Advanced Studies. The experiments were described, the results were analyzed using basic theoretical treatment found in the literature, and it was concluded that laser ablation is a potential tool for the generation of a neutral vapor jet for atomic vapor laser isotope separation purposes.

Resumo em Inglês:

Abstract: In the aerospace industry, laser beam welding has been considered as one of the most promising routes among the new manufacturing processes. Substitution of riveting by laser beam welding of aircraft structures has contributed to weight and cost savings. Concurrently, new aluminum alloys have been developed with the addition of lithium with better mechanical properties and lower density. The Al-3.5%Cu-1.1%Li alloy (AA2198) is one of these new generation alloys. However, laser beam welding of Al-alloys expectations might be greatly reduced by the occurrence of two main defects: porosity and hot cracking. Porosity is mainly caused by the entrapment of lithium gases, followed by rapid solidification. On the other hand, hot cracking happens due to the conjunction of tensile stresses, which are transmitted to the mushy zone by the coherent solid underneath, and to an insufficient liquid feeding to compensatefor the volumetric changes. This work intended to contribute towards the knowledge of AA2198 'welding metallurgy, utilizing a 2-kW-ytterbium-dopedfiber laser. The T-joint configuration welds were performed autogenously or with the addition of an AA4047 filler ribbon. Ali the weld beads presented high porosity level, but with a decreasing tendency when welding from both sides. The use of the filler material could solve hot cracking problem. The best results are observed using two runs (both sides) with filler and a speed of 2 m/min and power of 1,200 W. The T-pull tensile strength obtained under these conditions was 178 MPa, which is below the tensile strength of the unwelded AA2198 sheet but higher than the AA6013 welded in similar conditions.

Resumo em Inglês:

Abstract: Multidisciplinary design optimization is a promising field in aerospace engineering. However, advances in this field have not been applied yet to improve Brazilian sounding rockets, such as the VS-40. Therefore, to give a perspective of the multidisciplinary design optimization in this context, this work presented a case study of this rocket, which consists ofthe shape optimization of its fins. To achieve this goal, a special tool called MDO-SONDA, which is the main contribution of this work, was developed. Its current version interacts with two high-fidelity executable codes, one of aerodynamics and another of trajectory, exploiting the synergy between both disciplines. The MDO-SONDA is based on a multiobjective genetic algorithm whose real operator was originally designed in this work. By using the proposed tool, it was found that the drag due to the rocket fins could be reduced up to 29% without increasing the chances of adverse effects that could lead to unstable behaviors.

Resumo em Inglês:

Abstract: Dynamic mechanical analysis is a unique technique that measures the modulus and damping of materiais as they are deformed under periodic stress. Propellants, which are viscoelastic in nature, are subjected to time, temperature, and frequency effects during the analysis to determine their dynamic and transient properties. The choice of parameters during the experiments like temperature, frequency, strain (%), and stress level is very crucial to the results obtained since the propellant behaves differently under different conditions. A series of experiments like strain and temperature ramp/ frequency sweeps, creep, stress relaxation, etc. have been conducted using high burning rate composite propellant (burn rate ~20 mm/s at 7,000 kPa), in order to determine the precise effects of such parameters on the results obtained. The evaluated data revealed that as the temperature increases the storage modulus, loss modulus, and tan delta curves with respect to the frequency shift towards the lower side. Moreover, there is equivalency between the increase in the temperature and the decrease in the frequency, which can be used for the time-temperature superposition principles. Further, in transient tests, the relaxation modulus has been found to decrease when increasing strain levels in the given time range. Also, relaxation modulus versus time curves were found to shift towards the lower side with increasing temperature while creep compliance decreases with the increase in stress and decrease in temperature. The glass transition value of the composite propellant increases when there is an increase in the heating rate.

Resumo em Inglês:

Abstract: Deployable structure technology has been used in aerospace and civil engineering structures very popularly. This paper reported on a recent development of numerical approaches for the kinematic analysis of the deployable truss structures. The dynamic equations of the constrained system and the computational procedures were summarized. The driving force vectors of the active cables considering the friction force were also formulated. Three types of macroele-ments used in deployable structures were described, including linear scissor-link element, multiangular scissor element, and rigid-plate element. The corresponding constraint equations and the Jacobian matrices of these macroelements were formulated. The accuracy and efficiency of the proposed approach are illustrated with numerical examples, including a double-ring deployable truss and a deployable solar array.

Resumo em Inglês:

Abstract: Centro de Lançamento de Alcântara is the main Brazilian launching center. In spite of presenting several desirable aspects, due to its proximity to the Equator, it has a peculiar topography because of the existence of a coastal cliff, which modifies the characteristics of the atmospheric boundary layer. This may affect rocket-launching operations, especially when associated with safety procedures. This work is a continuation of previous experimental studies about the airflow pattern at this launching center. An improved way of simulating the atmospheric boundary layer in a short-test section wind tunnel using passive methods is presented here. It is also presented a preliminary analysis of the airflow pattern in Centro de Lançamento de Alcântara, at specific positions as the edge of cliff and around the mobile integration tower, from wind tunnel measurements using particle image velocimetry. Three values of Reynolds number, based on the coastal cliff height, l, ranging from 6.8×105 to 2.0×106, were considered.

Resumo em Inglês:

Abstract: The present paper has discussed investigations about the propeller slipstream effects on the aerodynamics of a generic unmanned air vehicle platform in the wind tunnel for a broad advance ratio range. The propeller-induced effects for small unmanned air vehicles are more significantly pronounced than general aviation aircraft, because of their high propeller-diameter-to-wing-span-ratio. The stall angle of attack of the small unmanned air vehicle is generally delayed under slipstream effects. The study evaluated the shift in stall angle of attack as a function of propeller-diameter-to-wing-span and advance ratios of the propeller. The aerodynamics of the unmanned air vehicle platform is estimated through wind-tunnel experiments. The study reported in this paper is part of an effort to develop the framework for the analysis of propeller-wing interactionfor small/micro unmanned air vehicles at an early design stage. Specifically, the slipstream effects on the aerodynamics of a generic small unmanned air vehicle are studied in the wind tunnel for the shift in the aircraft stall angle of attack. The lift-curve slope of the aircraft is independent from the variation of advance ratio. The stall characteristics show strong dependence on the advance ratio. Therefore, the relationship is modeled accurately using inverse-quadratic relationship. This empirical trend of the stall behavior with advance ratio can be useful in the analysis and simulation of the resulting flight and estimation of performance envelopes.

Resumo em Inglês:

Abstract: Fluids in a dielectric barrier glow discharge at atmospheric pressure have attracted interest from communities of thermo and fluid dynamics, as well as control. This work investigated the effects of a plasma actuator, operating at 8.0 kV and 4.4 kHz, on the pressure distribution around a polyvinyl chloride circular cylinder in low-velocity airflow. The experiment was repeated with the actuator at various angles. The results show an acceleration of the flow demonstrated by a 60% lower pressure coefficient at the actuator area. The flow separation was also delayed by an angle of as much as 30°. These effects were shown to be greater when the actuator was positioned at an angle closer to the separation area.

Resumo em Inglês:

Abstract: This paper described an architecture that is able to emulate the behavior of the imaging transfer system proposed for the PLATO satellite - PLAnetary transits and oscillations of stars. It was conceived to accurately represent flight operation as to validate the satellite digital processing unit on its development phase. Details related to the mission, its architecture, and the implementation technical details are presented in this article.