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ABSTRACT: This paper introduces a new approach to represent the rocket exhaust effluents into an atmospheric dispersion model considering the trajectory and variable burning rates of a Satellite Vehicle Launcher, taking into account the buoyancy of the exhausted gases. It presents a simulation for a Satellite Vehicle Launcher flight at 12:00Z in a typical day of the dry season (Sept 17, 2008) at the Centro de Lançamento de Alcântara using the Weather Research and Forecasting Model coupled with a modified chemistry module to take into account the gases HCl, CO, CO2, and particulate matter emitted from the rocket engine. The results show that the HCl levels are dangerous in the first hour after the launching into the Launch Preparation Area and at the Technical Meteorological Center region; the CO levels are critical for the first 10 min after the launching, representing a high risk for human activities at the proximities of the launching pad.Resumo em Inglês:
ABSTRACT: Because they are inexpensive platforms for satellites, CubeSats have become a low-cost way for universities and even developing countries to have access to space technology. This paper presents the ITASAT design, particularly the Attitude Determination and Control Subsystem, the Onboard Software, and the Assembly, Integration and Testing program. The ITASAT is a 6U CubeSat nano-satellite in development at the Instituto Tecnológico de Aeronáutica, in São José dos Campos, Brazil. The platform and its subsystems will be provided by industry while the payloads are being designed and developed by the principal investigators. The ITASAT Attitude Determination and Control Subsystem will rely on a 3-axis magnetometer, 6 analog cosine sun sensors, 3-axis MEMS gyroscopes, 3 magnetic torque coils, and 3 reaction wheels. The Attitude Determination and Control Subsystem operating modes, control laws, and embedded software are under the responsibility of the Instituto Tecnológico de Aeronáutica. A Kalman filter shall be employed to estimate the quaternion attitude and gyroscope biases from sensor measurements. The Attitude Determination and Control Subsystem operating modes are the nominal mode, with geocentric pointing attitude control and the stabilization mode, in which only the satellite angular velocity is controlled. The nominal mode will be split into 2 sub-modes: reaction wheel control plus magnetic wheel desaturation and 3-axis magnetic attitude control. Simulation results have shown that the attitude can be controlled with 1-degree accuracy in nominal mode with the reaction wheels, but these errors grow as much as 20 degrees or higher with the 3-axis magnetic control.Resumo em Inglês:
ABSTRACT: A sample of 152 accidents and incidents involving Remotely Piloted Aircraft Systems, more commonly referred to as "drones", have been analysed. The data was collected from a 10-year period, 2006 to 2015, conveniently sourced from a limited population owing to the scarcity of reports. Results indicate that safety occurrences involving Remotely Piloted Aircraft Systems (RPAS) have a significantly different distribution of contributing factors when sorted into distinct categories. This provides a thorough and up-to-date characterization of the safety deficiencies specific to RPAS. In turn, this contributes to the development of adequate safety management systems applicable to the RPAS sector. The majority of RPAS occurrences involved system component failures which were the result of equipment problems. Therefore, airworthiness instead of pilot licensing needs to be considered first when regulating the Remotely Piloted Aircraft System industry. "Human factors" and "loss of control in-flight" were found to be the second most common "contributing factor" and "occurrence category", respectively; Remotely Piloted Aircraft pilot licensing will help reduce the probability of these secondary occurrences. The most significant conclusion is that reporting systems must be implemented to address RPAS accidents and incidents specifically, such that more useful data is available, and further analysis is possible facilitating an improved understanding and greater awareness.Resumo em Inglês:
ABSTRACT: Uncertainty-based multidisciplinary design optimization considers probabilistic variables and parameters and provides an approach to account for sources of uncertainty in design optimization. The aim of this study was to apply a decoupling uncertainty-based multidisciplinary design optimization method without any dependence on probability mathematics. Existing approaches of uncertainty-based multidisciplinary design optimization are based on probability mathematics (transformation to standard space), calculating an approximation of the constraint functions in standard space and finding the most probable point, which is the best possible one. The current approach used in this paper was inspired on interval modeling, so it is good when there is insufficient data to develop a good estimate of the probability density function shape or parameters. This approach has been implemented for an existing Unmanned Aerial Vehicle (UAV, Global Hawk) designed for purposes of comparison and validation. The advantages of the provided approach are independence of probability mathematics, appropriate when there is insufficient data to approximate the uncertainties variables, appropriate speed to calculate the best reliable response, and proper success rate in the presence of uncertainties.Resumo em Inglês:
ABSTRACT: It is performed and presented an experimental and numerical investigation over the flow patterns around the fore-body section of a microsatellite launch vehicle in development at Instituto de Aeronáutica e Espaço. The experimental investigation with a VLM-1 model in 1:50 scale is carried out at the Brazilian Pilot Transonic Wind Tunnel, located in the Aerodynamics Division of the mentioned Institute, using the classical schlieren flow visualization technique. Schlieren images are obtained for nominal Mach number varying from 0.9 to 1.01. Numerical simulation using Stanford's SU2 code is conducted together with the experimental investigation in order to improve the understanding of the complex physical phenomena associated with the experimental results of this particular regime. The combination of the 2 techniques allowed the assessment of some important aspects on the flow field around the vehicle in the conditions considered in this study, such as shock wave/boundary-layer interaction. The numerical simulation is also very important, allowing the quantification of some important parameters and confirming the shock wave formation patterns observed in the simulation when compared with the schlieren images. A good agreement regarding the position of the shock wave, when compared with the schlieren images, with a maximum error of about 6%, is observed over the VLM model.Resumo em Inglês:
ABSTRACT: Flow field around rotors in axial flight is known to be complex especially in steep descent where the rotor is operating inside its own wake. It is often reported that, in this flight condition, the rotor is susceptible to severe wake interactions causing unsteady blade load, severe vibration, loss of performance, as well as poor control and handling. So far, there is little data from experimental and numerical analysis available for rotors in axial flight. In this paper, the steady Reynolds-Averaged Navier-Stokes Computational Fluid Dynamics solver Helicopter Multi-Block was used to predict the performance of rotors in axial flight. The main objective of this study was to improve the basic knowledge about the subject and to validate the flow solver used. The results obtained are presented in the form of surface pressure, rotor performance parameters, and vortex wake trajectories. The detailed velocity field of the tip vortex for a rotor in hover was also investigated, and a strong self-similarity of the swirl velocity profile was found. The predicted results obtained when compared with available experimental data showed a reasonably agreement for hover and descent rate, suggesting unsteady solution for rotors in vortex-ring state.Resumo em Inglês:
ABSTRACT: The addition of Gurney flap changes the nature of flow around airfoil by producing asymmetric Von-Karman vortex in its wake. Most of the investigations on Gurney flapped airfoils have modeled the flow using a quasi-steady approach, resulting in time-averaged values with no information on the unsteady features of the flow. Among these, some investigations have shown that quasi-steady approach does a good job on predicting the aerodynamic coefficients and physics of flow. Previous studies on Gurney flap have shown that the calculated aerodynamic coefficients such as lift and drag coefficients from quasi-steady approach are in good agreement with the time averaged values of these quantities in time accurate computations. However, these investigations were conducted in regimes of medium to high Reynolds numbers where the flow is turbulent. Whether this is true for the regime of ultra-low Reynolds number is open to question. Therefore, it is deemed necessary to examine the previous investigations in the regime of ultra-low Reynolds numbers. The unsteady incompressible laminar flow over a Gurney flapped airfoil is investigated using three approaches; namely unsteady accurate, unsteady inaccurate, and quasi-steady. Overall, all the simulations showed that at ultra-low Reynolds numbers quasi-steady solution does not necessarily have the same correlation with the time averaged results over the unsteady accurate solution. In addition, it was observed that results of unsteady inaccurate approach with very small time steps can be used to predict time-averaged quantities fairly accurate with less computational cost.Resumo em Inglês:
ABSTRACT: Recently, there has been a growing interest in studies concerning ionization sensors for aerospace applications, power generation, and fundamental research. In aerospace research, they have been used for studies of shock and detonation waves. Two key features of these sensors are their short response time, of the order of microseconds, and the fact that they are activated when exposed to high temperature air. In this sense, the present paper describes the development of an ionization sensor to be used in shock tube facilities. The sensor consists of 2 thorium-tungsten electrodes insulated by ceramic, with a stainless steel adapter for proper mounting, as well as 2 copper seal rings. An electrical circuit was also built with 2 main purposes: to provide the electrodes with a sufficient large voltage difference in order to ease ionization of the air and to assure a short time response of the sensor. The tests were carried out in a shock tube with the objective of observing the response of the sensor under stagnation conditions. For that, we chose initial driven pressures of 1.0; 1.2 and 1.5 kgf/cm2, with a constant driver pressure equal to 70 kgf/cm2. We analyzed the response of the sensor as a function of the initial driven pressure, stagnation temperature, and density. For the studied conditions, the results showed that the mean amplitude of the ionization sensor signal varied from 8.29 to 19.70 mV.Resumo em Inglês:
ABSTRACT: Cook-off tests are commonly used to assess thermal behaviour of energetic materials under external thermal stimuli. Numerical simulation became a powerful tool to reduce the costs with experimental tests. However, numerical simulations are not able to predict the violence of thermal response, but instead accurately reproduce radial heat flow in the test vehicle and satisfactorily predict the delay time to ignition and ignition temperature. This paper describes the slow cook-off simulation of 3 selected PBX based on RDX in a small-scale test vehicle, using the equilibrium equation of Frank-Kaminetskii and testing 2 kinetic models: Johnson-Mehl-Avrami (n) and Šesták-Berggren (m, n). The influence of successive addition of binder elements (HTPB, DOS, and IPDI) on slow cook-off results of selected PBX was assessed. The variation of ±10% in input data was performed to determine the influence on the slow cook-off results. Results showed that the addition of binder elements reduces the delay time to ignition as well as ignition temperature and that the Šesták-Berggren (m, n) kinetic model generates smaller values and with less deviation linked to the variation of input data. The selection of kinetic model as well as the variation of ±10% in input data had a negligible influence on the slow cook-off results of cured PBX.Resumo em Inglês:
ABSTRACT: Multifunctional composites combine structural and other physicochemical properties, with major applications in aeronautical, space, telecommunication, automotive, and medical areas. This research evaluates electromagnetic properties of multifunctional composites based on glass fiber woven fabric pre-impregnated with epoxy resin laminated together carbon fiber non-woven veil metalized with Ni. In this way, searching for possible application as radar absorbing structures or electromagnetic interference shielding structures. The scattering parameters, in the frequency range of 8.2 to 12.4 GHz, show that the epoxy resin/glass fiber prepreg allows the transmission of the electromagnetic waves through its microstructure, independently of the glass fiber reinforcement orientation (98% transmission, S24 = −0.09 dB). However, the carbon fiber/Ni veil shows highly reflector behavior (91% reflection, S22 = −0.43 dB). Energy dispersive spectroscopy of the veil, before and after nitric acid attacks, confirmed the Ni coating removal from the carbon fiber surface. Still, the scattering parameters show reflector behavior (77% reflection, S22 = −1.13 dB), attributed to the electrical conductivity of carbon fibers. Multifunctional composites based on glass fiber/epoxy/carbon fiber/Ni veil laminates were processed by hot compression molding. The scattering parameters show that the laminates do not behave as good radar absorbing structures. Nevertheless, the laminates present promising results for application as light weight and low thickness structural composites with electromagnetic interference shielding effectiveness (91.4% reflection for 0.36 mm thickness and 100% for ∼ 1.1 mm) for buildings, aircraft, and space components.Resumo em Inglês:
ABSTRACT: This study presents the complex index of refraction and the complex permittivity of a magnetic ceramic material made of copper, cobalt, and iron oxides. The index of refraction and the extinction coefficient of the CuCo-ferrite exhibit an almost frequency independent behavior and were averaged to n = 3.62 ± 0.05 and k = 0.06 ± 0.02, respectively, over the frequency range from 0.2 to 1 THz. The corresponding complex permittivity was ε' = 13.12 ± 0.35 for the real part and ε'' = 0.46 ± 0.15 for the imaginary one. The absorption coefficient and the transmittance of the CuCo-ferrite were also determined. The absorption coefficient exhibits a dip at ~0.35 THz, which corresponds to a peak in transmittance at this frequency. The impact of the observations on the potential realization of novel THz electronic devices is discussed.Resumo em Inglês:
ABSTRACT: The optical solar reflector is basically a mirror of second surface with low absorptivity/emissivity ratio and negligible degradation in the space environment, which makes it an excellent coating for thermal control of satellites. It works as a radiator and is used in particular parts of the external surfaces of the satellites in order to reject the undesirable heat to the deep space. In the Brazilian Space Programs, the radiators of the satellites are generally painted with special white paints in order to reject heat instead of the use of optical solar reflector. The problem of white-ink radiators is the high degradation of the thermo-optical properties that happen over the useful lives. Thus, a process of manufacturing and assembly of optical solar reflector was developed in Brazil. To validate this process in terms of mechanical and thermal properties, 3 types of optical solar reflector radiators were manufactured, and their absorptivity and emissivity properties at the temperature of 23 ºC were measured. Optical solar reflector coupons were mounted on aluminum plates to perform vibration, thermal vacuum and thermal-shock tests. A study was also done to optimize the thickness of the glue to fix the structure of the satellite on the optical solar reflector. It showed an excellent environmental stability and maintained its thermo-optical characteristics after the tests.Resumo em Inglês:
ABSTRACT: Resonant LCL-T converter can operate as stable voltage source, being fed from current, for instance, the photovoltaic battery. It is shown that LCL-T resonant tank has intrinsic ability to convert stable AC current into stable AC voltage thus parametrically regulating output voltage at a fixed value. This mode of operation is made possible by the use of active (synchronous) rectifier to recoup energy from the output back to the LCL-T resonant tank. Basic characteristics of resonant LCL-T converter regulated by phase shift between inverter and rectifier regardless of a solar battery current drift have been defined. It is shown that phase control guarantees 0 voltage and 0 current on switching; however, turn-off current could be substantial. Calculations and assumptions made in this study have been confirmed by simulation and hardware prototype.