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ABSTRACT: This article analyses the main candidate topologies for power supply for low earth orbit satellite applications, which are considered from the standpoint of energy continuity and power balance. The system components are dealt with as energy port elements through which energy is exchanged along the system. A comparative study and selection of the optimal topology were carried out, according to a criteria of mass/volume reduction and system efficiency improvement. The comparison was made between a three-domain controlled (fully regulated) and a two-domain controlled (also called hybrid) bus topology. After selection, a description of the design of the system control was given, considering the battery charge regulator (BCR) and battery discharge regulator (BDR) as a unified battery power conditioning equipment integrated into a single bidirectional converter. The system design was validated with a Simulink based model with the selected topology being controlled in closed loop to provide a regulated 28 V primary power bus. Finally, the article presents the current prototyping under development.Resumo em Inglês:
ABSTRACT: This paper aims to assess the progress made towards the implementation of a Single European Sky (SES). It examines the program’s four main key performance indicators - environmental impact, safety, cost efficiency and capacity - and depicts in more detail the sequence of changes in each problematic area, thereby providing a better visualization of the main milestones and the issues hindering proposed reforms. The paper concludes that the overall process of reforming European airspace within SES has been slow and delayed, partly due to a lack of cooperation and commitment from air navigation service providers and states to deliver the information needed and apply desired amendments. The paper recommends several actions, which could improve the SES performance, including among others the implementation of incentives to meet the program’s objectives, as well as penalties for lack of cooperation, and the introduction of a common en-route charging rate at the European level.Resumo em Inglês:
ABSTRACT Natural (Terrestrial & Space) Environment (NE) phenomena play a significant role in the design and flight of aerospace vehicles and in the integrity of the associated aerospace systems and structures. Both the terrestrial environment (0-90 km altitude) and the space environment (Earth orbital altitudes) parameters and their engineering application philosophy are given with emphasis on launch vehicle-affected terrestrial environment elements. This paper will describe the key terrestrial and space environment sources: wind; atmospheric; and orbital models used in the design and development of launch/space vehicles.Resumo em Inglês:
ABSTRACT Since atmospheric winds play the most critical natural enviroment (NE) role as input into the design and development of an aerospace launch vehicle, this paper provides a more detailed description of the wind environment and its interaction with engineering design in launch and space vehicle development applications at Kennedy Space Center (KSC).Resumo em Inglês:
ABSTRACT: Using the 1951-2017 historical series of the Atlantic Meridional Mode (AMM) index and the monthly number of sunspots, it was possible to observe a significant association between them. The use of wavelet and cross-wavelet analysis showed the presence of multidecadal cycles pronounced in eleven years, as well as cycles of 2.66 and 5.33. AMM index showed, in the part of the Sea Surface Temperature (SST), the presence of a weak signal of 21.33 years. Influence and association of sunspot variability on surface temperature in Northern and Northeastern regions of Brazil were investigated. Using a non-parametric statistical correlation test, the historical series of surface temperature anomalies in five locations (Belém, São Luiz, Fortaleza, Fernando de Noronha, and Natal) were compared with the monthly solar-series anomalies. The temperature series used were the minimum monthly average, the monthly average, and maximum monthly average temperatures, with their respective anomalies in relation to the mean. However, among all the series (except for São Luiz), the analyzed minimum temperature anomalies showed a negative correlation with sunspots. As a preliminary result, the analyzed climatic indexes present an apparent degree of memory associated with the variability of sunspot activity.Resumo em Inglês:
ABSTRACT: This paper aims to investigate the side force on a cone-cylinder geometry at different angles of attack (α) by adopting experiments and computations. The cone-cylinder configuration had a length to diameter ratio (L/D) of 10, and a base diameter (D) of 25 mm. The nose shape had a fineness ratio of approximately 3. Results indicated that the side force increases with the increasing of the angle of attack. A circular ring was used to reduce the side force at different angles of attack. Using a smaller height ring (2% of local diameter) in the initial portion of the body did not reduce the side force significantly at lower angles of attack. However, a ring with larger height (5% of local diameter) placed at 2.5 times the diameter of the body from the tip reduced the side force at almost all the angles of attack.Resumo em Inglês:
ABSTRACT: Modifications to the critical parameters, such as the exhaust nozzle area, are sometimes done during maintenance of aircraft engines. These modifications are done either to increase the design thrust or to compensate for the reduction of thrust due to leakage in the variable area jet nozzle. There is a trade-off between several performance parameters when such critical parameters are changed during maintenance. A tuned aerothermodynamic simulation model that agrees well with the experimental data from the original engine is required to study the effect of these changes. In the present work, a multipoint map scaling approach and a parameter estimation method are used to develop a simulation model that agrees well with the experimental data from the original turbojet engine. The design modifications are then incorporated in the model, and the effect of the modification on the various performance parameters is studied. The effect of leakage in the nozzle flaps and the corresponding reduction required in the nozzle throat area are calculated. It is shown that the tuned model developed with experimental testbed data enables the identification of ancillary effects of a change in a design parameter, such as the nozzle throat area.Resumo em Inglês:
ABSTRACT: A high-resolution simulation of a real case is carried out in Eastern Amazon (Northeastern coast of State of Pará) with the Weather Research and Forecasting (WRF) model in order to analyze/detect local circulation features in the region. To this end, we simulated a case with low interference of synoptic weather systems and precipitation aiming to eliminate the effects of convective systems in local circulations. The performance of the model for the day studied was evaluated and the existence of circulations found in the simulation was confirmed through observational data. The model performance evaluation showed that the model was able to capture most of the patterns for the studied area. The simulation captured the presence of three main circulations: the Sea Breeze (SB), on the coast; the Land Breeze (LB), also on the coast; and the Bay Breeze (BB), which forms on both banks of Marajó Bay. In addition to these three major circulations, the high-resolution simulations also revealed the presence of a river breeze (RB) from Guamá River and a fan-shaped circulation on the entrance of Guajará Bay. The observational data confirmed the presence of Guamá River breeze from the Southeast, which is more active from July to September.Resumo em Inglês:
Abstract: In the context of the cooperative development of the L75 Liquid Rocket Engine (with 75 kN of thrust) and in the frame of a global enlargement of competence in the field of turbomachines for liquid rocket propulsion systems, Institute of Space Propulsion of the German Aerospace Center (DLR; in German, Deutsches Zentrum für Luft- und Raumfahrt), in Lampoldshausen, and the Brazilian Institute of Aeronautics and Space (IAE; in Portuguese, Instituto de Aeronáutica e Espaço) have managed to produce its first flight ready components for pumps in liquid rocket propulsion systems. Among these components was a series of prototyped shrouded impellers for the oxidizer pumps manufactured in different materials and by different fabrication processes executed by four independent Brazilian and German workshops. Non-destructive and destructive testing methods have been applied for impellers materials validation, and for manufacturing processes verification. A special attention was given to the spin tests results and analysis, which included verification at maximum operational speed and burst testing, in order to determine the failure speed. Each tested impeller reached the required specification for the application in the L75 turbopump. Spin test logic and test results are discussed later on. Therefore, the scope of the present study is to investigate several traditional and cutting-edge processes applied for shrouded turbopump impellers manufacturing. A verification and validation of these processes will also be discussed.Resumo em Inglês:
ABSTRACT: The choice for using a fighter fuselage in a fighter jet design affects a vortex generation advantageous in maneuverability. To study the effect of straight-body-type-fuselage (SBTF) on the vortex dynamic, a computational fluid dynamics (CFD) method is used, in order to simulate a model of SBTF fighter. The simulation uses Q-criterion to probe vortices, and a logarithmic grid to emphasize the micro-gridding effect of the turbulent boundary layer. The results show detailed quantitative velocity, pressure, trajectory of the vortex core, and wing negative surface pressure distribution (SPD), providing clear pictures of opportunity for performance improvement, better lift, agility, and maneuverability of a fighter if a model requires a new design.Resumo em Inglês:
ABSTRACT: This paper presents a solver for the CFD (computational fluid dynamics) modeling of catalytic chambers in monopropellant thrusters based on the open-source OpenFOAM® (Open Field Operation and Manipulation) framework. A model was formulated and used to simulate the physical and thermochemical processes taking place inside the catalytic chambers of the monopropellant thrusters. The code integrates reacting gas flow in porous media, with mass and heat transport. The most important implemented functionalities were the separation of two reactive gases, one transient reactive gas flowing between the catalyst bed interstices (interstitial gas), and another static reactive gas on the surface of catalyst particles, or pellets (surface gas). Homogeneous and heterogeneous reactions occur on the interstitial gas and the catalyst particle, respectively. A flexible definition of porous properties, a calculation of multicomponent diffusion-flux mass, a diffusion mass coeffcient, a mass transfer coeffcient, and a heat transfer coeffcient were implemented as well. Experimental and analytical studies about hydrazine monopropellant thrusters in the literature were used to the case tests and verification of the solver. Temperature and mass fraction fields were simulated and compared. The results of the temperature profile are in agreement with experimental and theoretical studies found in the literature, and mass fraction presents some differences.Resumo em Inglês:
ABSTRACT: In this paper, a code is developed in C++ programming language aiming to select and introduce a well-chosen propulsion system for appropriate operation in an aircraft. By using a suitable turbocharged engine, the inlet pressure of the engine manifold will increase to a level equal to the pressure at sea level. Therefore, the aircraft engine will not notice the drop of pressure caused by the increase in altitude. Consequently, the engine power will not be reduced. On the other hand, at high altitude, using only one turbocharger is not adequate to supply engine inlet pressure and flow rate equivalent to sea level conditions, requiring the use of more turbochargers. The code developed in this study will be able to introduce the appropriate turbocharged engine based on the flight altitude and the required power engine of an air vehicle. The altitude defined in this code ranges from 5 to 30 kilometers, which leads to a selection of one to three turbochargers plus a number of intercoolers, according to user input parameters. The objective function of this optimization problem is defined as a function of turbochargers efficiency. However, this objective function can be modified according to the user requests and requirements.Resumo em Inglês:
ABSTRACT: This paper exposes initially the motivations for developing a TRL online calculator by AEB (Brazilian Space Agency; in Portuguese, Agência Espacial Brasileira). Such motivations demand the tool to be a way not only to assess the TRL condition of operational space missions and systems, but also as a method of evaluating and sharing proposals with new technological content. The TRL methodology and its relation to risk management are discussed. The development phases of the IMATEC Lite application are then described, with emphasis to the data handling structure capable of storing the user product model. A result of technology assessment using the software is detailed by presenting the PBS of the SERPENS 1 mission nanosatellite. The prospects of using the tool for judging the acceptability of new missions and projects are discussed, as well as some of the encountered difficulties.Resumo em Inglês:
ABSTRACT: This paper proposes a methodology to harvest the benefits of camber morphing airfoils for small unmanned aerial vehicle (SUAV) applications. Camber morphing using discrete elements was used to morph the base airfoil, which was split into two, three, and four elements, respectively, to achieve new configurations, into the target one. . In total, thirty morphed airfoil configurations were generated and tested for aerodynamic efficiency at the Reynolds numbers of 2.5 × 105 and 4.8 × 105, corresponding to loiter and cruise Reynolds numbers of a typical SUAV. The target airfoil performance could be closely achieved by combinations of 5 to 8 morphed configurations, the best of which were selected from a pool of thirty morphed airfoil configurations for the typical design specifications of SUAV. Interestingly, some morphed airfoil configurations show a reduction in drag coefficient of 1.21 to 15.17% compared to the target airfoil over a range of flight altitudes for cruise and loiter phases. Inspired by the drag reductions observed, a case study is presented for resizing a SUAV accounting for the mass addition due to the morphing system retaining the benefits of drag reduction.Resumo em Inglês:
ABSTRACT: One of the most important features of an aerospace vehicle design is its shape, especially the forebody part, since it defines the main characteristics of the vehicle aerodynamic. In this context, the present work has the purpose of investigating the transonic aerodynamic regime in typical vehicle models, with different frontal geometry configurations, using the experimental techniques pressure sensitive paint (PSP) and Schlieren. The aim is to get more insights about the flow patterns over the selected models, regarding the transonic regime, in terms of qualitative density field evaluation, and the identification of important aerodynamic parameters, such as shock wave positioning and pressure gradients over the model, as well as the influence of the forebody configuration in the flow pattern. The test campaign was carried out in the Pilot Transonic Wind Tunnel of the Institute of Aeronautics and Space (IAE; in Portuguese, Instituto de Aeronáutica e Espaço), varying Mach numbers from subsonic to low supersonic. Five forebody configurations mounted in a cylindrical body having the standard cone-cylinder shape as baseline was considered. A description of the phenomena occurring around and on the models surface for all five models is presented, through analyses of the Schlieren images and PSP results.Resumo em Inglês:
ABSTRACT: Ceramic matrix composites have attracted the interest of turbine manufacturers for use in coating hot sections because of their higher capacity to withstand high temperatures and because they have a lower requirement for air cooling. One of the most commonly used ceramic coatings is zirconia-yttria. However, its main disadvantage is the inherent fragility of ceramics, which limits the use of these materials in mechanical structures and industrial applications. Ceramics are generally reinforced with the incorporation of additives to reduce their brittleness and increase their mechanical strength and toughness. It is known that La2O3 which are potential source for stabilization of zirconia composites. In this context, ZrO2-Al2O3-La2O3 based ceramic matrix composites were developed for deposition of a thermal barrier coating on the substrate of exhaust nozzles of aerospace turbines varying the content of La2O3 by 5, 7 and 10 wt%. The composites were produced by a thermomechanical process and sintered at 1385 °C. The properties of these composites were studied by X-ray diffraction, relative density, scanning electron microscopy, and Vickers microhardness tests. The results indicate that the composite with 10% La2O3 has great potential for use as ceramic coatings of turbine exhaust nozzles in the aerospace industry.Resumo em Inglês:
ABSTRACT: This paper discusses the method for propellant combustion studies with embedded thermocouple and imaging method at ambient pressure. In this study, three different propellant compositions are experimentally evaluated for surface temperature, flame zone temperature with embedded thermocouple, and reaction zone thickness with high-speed imaging of propellant during combustion at ambient pressure. Preheat zone and flame zone temperature profiles are recorded with time and surface temperature is determined with available models. Observation of these experiments gives the difference between combustion mechanism of double-base propellant with diethylene glycol dinitrate (DEGDN) and 2,4-dinitrotoluene (DNT), composite propellant (CP) and CP with energetic binder. Scanning electron microscope (SEM) images analysis for pristine and quenched sample is also presented.Resumo em Inglês:
ABSTRACT: Long-haul low-cost carrier (LHLC) business models are generating considerable interest from the aviation practitioners and academics. Despite the high interest for the LHLC business model, only few have compared the LHLC business model to hybrid carrier business model and studied how airlines can compete with LHLCs. This paper analyses the differences of hybrid and long-haul low-cost carrier models and shows how Aer Lingus airlines has secured its dominant position in the Irish-US market. Product comparison with the help of in-depth interviews with key aviation practitioners as well as secondary data about the capacity and demand of the two carriers in question proves the differences between the two models. Porter five forces model provides an overview of the external competitive environment where the airlines in question operate. The research concluded that the hybrid and long-haul low-cost business model characteristics have many similarities, but also significant differences. It was also discovered that LHLC lack capacity and frequency as well as feeder traffic are very important elements for the transatlantic market. Robust route network including interline traffic and low operating cost, elements present in the hybrid airline business model, ensure profitability.Resumo em Inglês:
ABSTRACT: This paper studies the influence caused by a vortex generator (VG) on a wing section with NACA 0015 airfoil when this generator is located before and after a recirculation bubble caused by the boundary layer detachment. The study was numerically carried out and concentrated under conditions of flow with Rec = 2.38 × 105 and angles of attack AoA = 3 and 6, characterized by the fact that they undergo detachment of the boundary layer before and after the location of the VG, respectively. The use of the generator in AoA = 3 strongly influenced the reduction of the recirculation bubble, leading to a drag reduction of 1.43%. In AoA = 6 with a bubble recirculation, the effect was much lower, with no well-defined formation of longitudinal vortices, resulting in increased drag and lift at 0.33 and 0.35%, respectively.Resumo em Inglês:
ABSTRACT: An optimal thruster configuration for attitude control subsystem of a spacecraft is presented in this paper. The optimal configuration is designed according to minimum number of required thrusters for satisfying desired reliability with specific redundancy level. The genetic algorithm is employed for optimization process and feasibility of the results is evaluated using algebraic and geometry methods. The main feature of the proposed configuration among feasible configuration with minimum number of required thrusters, which has held to optimal configuration, is that this configuration has maximum reliability and minimum fuel consumption. In addition to feasibility, attitude control performance of some configurations is also examined through the simulation. The results of simulation confirm that the proposed configuration has desirable performance. It is noteworthy to mention that the configuration with maximum number of required thrusters, which is a conventional configuration such that each thruster belongs to only one control channel, has less fuel consumption than optimal configuration. However, the total mass of optimal configuration is less than that of conventional configuration due to a smaller number of thrusters.Resumo em Inglês:
ABSTRACT: This work describes the aerodynamic characteristics of an aircraft wing model with a Rüppell’s griffon vulture (RGV)-type winglet. A computational fluid dynamics (CFD) study using ANSYS 15.0 was conducted to study the effect of the RGV winglet on a rectangular wing. The NACA 65(3)-218 wing consists of 660 mm span and 121 mm chord length where the aspect ratio is 5.45. Eight different winglet configurations have been studied. Furthermore, the study is extended to study effect of cant angle and different angles of attack (AOA) to the winglet. A comparative study is done on aerodynamic features such as lift coefficient (CL), drag coefficient (CD), lift/drag ratio (CL/CD) and tip vortices to get the best RGV winglet design. The RGV winglet achieved highest CL compared to other types of winglets configuration. Based on contour plot analysis, the RGV winglet shows lower vortex formation compared to without winglet. The results show about 15 to 30% reduction in drag coefficient and 5 to 25% increase in lift coefficient by using an RGV winglet.Resumo em Inglês:
ABSTRACT: An experimental study to determine the dependence of the viscosity and shear stress of hydroxyl-terminated polybutadiene (HTPB) and dimeryl diisocyanate (DII) liner on curing time is presented. Viscosity and shear-stress were measured by HAAKE RheoStress 600 rheometer with parallel disks configuration at a constant temperature of 65 °C. The viscosity and shear-stress change were monitored for 8 h. Analysis of data showed that the liner viscosity and shear-stress dependency on time matched to pseudoplastic fluid model. For low shear-rates, the viscosity build-up is highest, with the logarithm of the viscosity being practically linear with time and the viscosity increases by more than two orders of magnitude for these cases. When the shear rates increase, the viscosity build-up slows down considerably with time and the viscosity is increased only by one order of magnitude.Resumo em Inglês:
ABSTRACT: Background: There is an increase in the number of flight travellers and with it comes the risks of developing in-flight dental conditions that evokes pain at higher altitudes. The knowledge about such conditions are necessary among the dentists to prevent such phenomena. Aim: To assess the knowledge and familiarity about aviation dentistry among dentists. Methodology: A cross-sectional questionnaire-based study conducted among 170 postgraduates and dental professionals in a private dental institution. A pilot study was conducted among 30 individuals, and the questionnaire was validated. Data was analysed by SPSS package 20. Descriptive statistics and chi-square tests were used. Results: 61.8% of the individuals were not familiar with the term aviation dentistry. A statistically significant association was found between familiarity with aviation dentistry and the qualification of the dentists and also between familiarity with aviation dentistry and years of experience of the dentists with a p value < 0.05. Conclusion: The study result shows the lack of knowledge about aviation dentistry among postgraduates and dental professionals.Resumo em Inglês:
ABSTRACT: Effect of Mach number on coflowing jet at lip thickness of 0.2 Dp, 1.0 Dp and 1.5 Dp (where Dp is primary nozzle exit diameter, 10 mm) at Mach numbers 1.0, 0.8 and 0.6 were studied experimentally. It was found that an increase in Mach number does not have any profound effect on axial total and static pressure variation for 0.2 Dp. Decreasing the mean diameter is due to the geometrical constraints. In this study, the primary nozzle dimension and secondary duct is maintained constant for comparison. For the case of 0.2 Dp, static pressure is almost equal to atmospheric pressure for all Mach numbers. Whereas for other two lip thickness, increase in Mach number marginally influences axial total pressure and profoundly varies static pressure. It is noted that it varies considerably up to 11.1% in the axial direction and up to 17% in the radial direction for Mach number 1.0. For lower Mach numbers, such variation is not observed. Increase in Mach number increases static pressure variation in the coflowing jet flow field with lip thickness 1.0 Dp and 1.5 Dp.Resumo em Inglês:
ABSTRACT: A mathematical model is established using the space coordinates of nodes and vector matrix of components to study the construction method and lightweight nature of single-layer tensegrity structures on the basis of their geometric parameters. Connection matrix and configuration of the single-layer tensegrity structures are built using MATLAB software. The force balance equations of nodes of a three-bar tensegrity structure are established by introducing the force-density method, and the force-density relationship amongst the components is analysed. Thus, the configuration principle of single-layer tensegrity structure is verified. The force-density relationship between the components in the single-layer tensegrity structure is obtained. The change rule of the force-density relationship in different single-layer tensegrity structures is also analysed. Notably, p-1 stable configurations are present in the p-bar tensegrity structure. The force-density relationships of these p-1 configurations are in symmetrical distribution, that is, the j-th and (p-j)th configurations have the same force-density relationship. The lightweight nature of the structure is studied using the force-density relationship between the components, and the optimal structural parameter relationship is obtained when the structure has the lightest mass.Resumo em Inglês:
ABSTRACT: This work presents a computational tool for preliminary analysis of hypersonic vehicles, based on local surface inclination methods: the HipeX. This program was developed for reading standard triangulation language (STL) geometry files and calculating pressure coefficient and temperature distributions over vehicle’s surface using the Newtonian, modified Newtonian or tangent-wedge methods. Validations were made with a cylinder and a sphere, where only the Newtonian method was applied, and with experimental data from Apollo capsule at Mach 10, where the Newtonian and the modified Newtonian methods were applied. These validations presented the code capability to read geometries as well as to estimate aerodynamic force coefficients. A preliminary application was to predict the aerodynamic force coefficients of a generic hypersonic vehicle over constant dynamic pressure trajectories of 23,940, 60,000 and 95,760 N/m2 with zero angle of attack. With a fixed dynamic pressure of 60,000 N/m2, this vehicle was tested over several Mach numbers and with angle of attack variation from -10 to 10 deg. Zero angle of attack investigation showed minor changes on the force coefficients with altitude, while the variation of angle of attack produced more pronounced variations on these parameters. Maximum flow temperatures over vehicle’s surface were estimated ranging from 850 to 5,315 K.Resumo em Inglês:
ABSTRACT: The performance enhancement of aircraft coupled with the development of increasingly lightweight and flexible materials has led designers to use smaller structural safety factors along the time, which can make aerodynamic surfaces more susceptible to aeroelastic phenomena, including flutter. This kind of occurrence must be carefully investigated by ground and flight tests during aircraft development and certification, which requires suitable instrumentation in order to predict the occurrence of unwanted vibrations. The sensors in this kind of application must be less intrusive as possible, in order to not modify the dynamic or aerodynamic behavior of the system. This work proposes the use of infrared imaging as a tool for flutter detection, analyzing the suitability of the technique for this application. For this purpose, a literature review was performed by presenting infrared technology concepts; then, some preliminary tests were performed in a structure to predict flutter characteristics, and finally wind tunnel tests were executed in the same structure, validating this technique and highlighting its positive points and points that need improvement.Resumo em Inglês:
ABSTRACT: The field of data compression has evolved over the last decades. In this way, several techniques to reduce the amount of acquired data from the sensor required to be transmitted have been developed. Those techniques are usually classified by lossless or lossy, where, for the lossless techniques, all acquired data is recovered, while the lossy techniques introduce errors to these data. Each of these techniques presents advantages and drawbacks, being the analyst responsible for choosing the appropriate technique for a specific application. This work presents a comparative study using lossy audio formats to be applied on a launch vehicle on-board acoustic data. The Opus format achieved a higher compression rate in comparison with standard compression techniques by saving up to 254 times the required amount of data to be transmitted through a telemetry link on launcher vehicle, and the lowest discrepancy from original data measured by the mean square error metric.Resumo em Inglês:
ABSTRACT: This work deals with the problem of the design of an autonomous redundant system for the attitude determination of nanosatellites. The system consists of a circuit board equipped with three microcontrollers, a magnetic field sensor in three axes, and complementary commercial-of-the-shelf (COTS) components and connectors to provide data signal exchange the vehicle on-board computer. The main goal of this system, named SDATF (of the acronym in Portuguese Sistema de Determinação de Atitude com Tolerância a Falhas), is to provide autonomously the vehicle attitude from the information collected from the onboard computer (OBC) and the magnetometer. The adopted attitude determination algorithm is based on the well-known QUEST method, and the goal of this system is to get accurate attitude computations to low-orbit CubeSat satellites using COTS electronic components, and to provide highly reliable data and high availability levels using fault tolerance tools to avoid the harmful consequences of spatial radiation and its faults known as single event upsets (SEU). The article presents the general design of the fault-tolerant systems and experimental tests using bit flip injection methodology.Resumo em Inglês:
ABSTRACT: The choice of fleet by a given airline must consider different elements associated with both the aircraft and the airports to be operated, making it necessary a method to assist the aircraft choice process. This study assesses the take-off runway distance requirement of different aircraft models and compares the requirement to the take-off runway distance available at a group of airports. Using the Herfindahl-Hirschman index (HHI), the methodology consider the analysis of take-off runway length available on 80 Brazilian airports and compared it to the take-off distance required for 108 combinations of aircraft model, engine model and flight range, considering the take-off performance of the aircraft models with maximum payload weight. In total, 536 routes of four Brazilian airlines has been adopted to simulate the most profitable operating scenario. The result presents the take-off performance of different aircraft models and allows a performance comparison between them. In addition, this research investigates which is the most common flight range in Brazil, and what influence it exerts in the aircraft take-off performance, and contributes to a better match between the aircraft used and the airport operated in fleet optimization.Resumo em Inglês:
ABSTRACT: Increased flight time of multirotor drones is a key enabler for further adoption and industrial use of drones. A model for analyzing the performance of a fuel cell hybrid system for a multirotor drone is presented and applied for a case with an X8 multirotor drone with a maximum take-off mass of 25 kg. Endurance is the main performance parameter, and the model can be used to quantify the relative performance between different power sources. The model aims to determine if a specific hybrid fuel cell system is a viable option for a given multirotor drone and if it will provide better endurance than when powered by batteries. The model can also be used in system optimization and sensitivity analysis. In a case study, a fuel cell hybrid system with a 7.2 L cylinder with hydrogen at 300 bar is found to increase the flight time by 43 minutes (+76%) from the currently used LiPo-batteries. A plot identifies the energy system mass threshold for when the fuel cell hybrid system gives better endurance than batteries to be 7.3 kg. Based on current technology status, the cost of a fuel cell hybrid system is about 12 times that of LiPo-batteries.Resumo em Inglês:
ABSTRACT: The Dempster-Shafer (D-S) theory is widely applied in various fields involved with multi-sensor information fusion for radar target tracking, which offers a useful tool for decision-making. However, the application of D-S evidence theory has some limitations when evidences are conflicting. This paper proposed a new method combining the Pignistic probability distance and the Deng entropy to address the problem. First, the Pignistic probability distance is applied to measure the conflict degree of evidences. Then, the uncertain information is measured by introducing the Deng entropy. Finally, the evidence correction factor is calculated for modifying the bodies of evidence, and the Dempster’s combination rule is adopted for evidence fusion. Simulation experiments illustrate the effectiveness of the proposed method dealing with conflicting evidences.Resumo em Inglês:
ABSTRACT: In this paper, a robust optimization method is developed to solve the Satellite Launch Vehicle (SLV) trajectory design problem in the presence of uncertainties. Given these uncertainties in the actual SLV ascent trajectory, it is important to find an optimal trajectory that is resistant to these uncertainties, as it results in increased flight performance, reduced steering-control system workload and increased SLV reliability. For this purpose, the optimization problem is first considered by applying to maximize the payload mass criterion as an objective function and three-dimensional equations of motions as the governing constraints. Then by adding mean and standard deviation parameters of uncertainties, the robust optimizer model is developed and the genetic algorithm is used to execute the model. Monte Carlo simulation is also used to analyze the results of uncertainties and its continuous feedback to the optimizer model. Finally, an optimal trajectory is obtained that is robust to the uncertainties effects such as aerodynamic coefficients, dry mass and thrust errors of the SLV. The results of the simulation show the validity of this claim.Resumo em Inglês:
ABSTRACT: This paper presents an LMI (Linear Matrix Inequalities) application for the design of robust controllers for multivariate systems that have multiple points of operation. Some systems change their parameters along time, then, it is necessary to switch the control for different operational points. The purpose of this controller is to ensure the stability and performance requirements of the system for different operating points with the same controller. The method uses the following concepts of predefined structures controller, LMI region, and polytopic systems. To validate the controller a linearized model of a helicopter was used. These helicopters belong to a system class of MIMO (Multiple-Input Multiple Outputs) type and present a complex dynamic in their flight modes, therefore, due to these features, this type of helicopter is a good model to implement and test the efficiency of the described method in this work. The results were satisfactory. Some limitations in its implementation were found and discussed. An LQG (Linear-Quadratic-Gaussian) controller was also designed for the same model of the helicopter just for comparison. Analyzing the settling time properties, the LMI controller presented a better response than the LQG controller.Resumo em Inglês:
ABSTRACT: The mass properties of aircraft directly influence their performance and costs, and are particularly subject to high uncertainties in the early phases of the development process. As aircraft systems become more detailed, their mass properties are iteratively updated. Those updates, in turn, may lead to rework on aircraft systems. To avoid excessive iterations, aircraft manufacturers employ the mass properties management (MPM) process during their development processes. However, even when this approach is adopted, the continuous cycle of increasing weight and redesigning aircraft structures represents a significant challenge, which may lead to the cancellation of programs. One of the causes of this problem is inefficient integration between MPM and the aircraft development process. We propose a concept to significantly enhance the integration between MPM and aircraft development processes, suggesting feasible practices to support its implementation. The research methodology combines a review of the literature, an exploratory case study, a three-year longitudinal case study, and verification by experts. The results describe a concept for integrating aircraft MPM and development, supported by 16 practices. They also include a characterization of the MPM process based on literature and practices, which lists 17 characteristics divided into four categories: Goals/Strategy, Activities/Information, Resources/Tools, and Organization/Roles and Responsibilities.Resumo em Inglês:
ABSTRACT: Modifications achieved in the ignition delay time of shellac-based pyrotechnic igniter using different additives of varying particle size are observed and compared. 40 different pyrotechnic compositions were prepared using five additives i.e. aluminium, magnesium, red iron oxide, naphthalene and activated carbon. Four particle sizes i.e. <75 µm, 75-150 µm, 150-300 µm, 300-600 µm and two weight percentages of the additives i.e. 3% and 5% were investigated. A base composition, without any additive, was also prepared to compare and investigate the effects of additives and their particle size on the ignition delay time of the composition. The incorporation of additives significantly reduced the ignition delay time of the base composition. Addition of 5% red iron oxide having a particle size of <75 µm, delivered the maximum decrement in ignition delay time i.e. by 49.7%. Naphthalene of particle size of <75 µm added as 3% in the composition weight, provided the minimum reduction in the ignition delay time i.e. by 13.7%. It was also observed that all of the additives exhibited a similar manner of decrement in ignition delay time as the particle size decreased, except for naphthalene which exhibited an opposite trend.Resumo em Inglês:
ABSTRACT: The purpose of this paper is to construct a new general vehicle model as an open fundamental material for the guidance and control research. In this study, parameterized configuration, aerodynamics calculation, control-oriented modeling, stability analysis, and nominal trajectory design are performed for the general vehicle model. First, the aerodynamic configuration is parameterized as an axisymmetric body with a power-law revolution nose. Then, an engineering method considering inviscid flow, base drag and skin friction is used for the aerodynamics calculation, and a control-oriented fitting model of longitudinal aerodynamics is established based on the analysis of the correlation between aerodynamic force and the parameters of Mach number, attack angle, elevator deflection and height. Next, the aerothermodynamic environment prediction of power-law revolution axisymmetric hypersonic vehicle (PRAHV) is discussed, and the nose heating rate formula of PRAHV is established. The stability analysis and nominal trajectory design of PRAHV is performed based on the fitting model and the heating rate formula. The stability analysis shows that both the static stability and dynamic stability of the vehicle are unstable. The nominal trajectory of unpowered longitudinal maneuvering is achieved by the hp-adaptive pseudospectral method, which demonstrated that the availability of the control-oriented model established in this paper. In conclusion, this work provides a fundamental object for further study of vehicle guidance, control, and evaluation.Resumo em Inglês:
ABSTRACT: Aerodynamic performance of a full span NACA 641-412 airfoil with a circular-shaped damage at various attack directions has been numerically investigated in this study. To assess the aerodynamic effects of different penetration angles in which threats such as projectiles can pass through the wings, attack directions of 30°, 60°, -30° and -60° relative to the normal axis of the chord line has been studied and compared with attack direction of 0°. To validate with published studies about damaged wing, the 200 mm chord airfoil was simulated with the damage hole diameter of 20% chord at the midspan and midchord location in Reynolds number of 500,000. Quantitative and qualitative results of this numerical study had a good agreement with published experimental data due to appropriate structured mesh and turbulence modelling. In addition to lift, drag and pitching moment coefficient, surface pressure distribution around the damage hole has been studied. Results show that, if the penetration angle becomes more negative, aerodynamics performance of the wing will be further decreased; therefore, attack directions of threat mechanisms such as “ahead and above” or “below from the rear” have severe negative impact than other directions on aerodynamic performance of the damaged infinite wing.Resumo em Inglês:
ABSTRACT: In this paper, a new form of open traveling salesman problem (OTSP) is used for path planning for optimal coverage of a wide area by cooperated unmanned aerial vehicles (UAVs). A hybrid form of particle swarm optimization (PSO) and genetic algorithm (GA) is developed for the current path planning problem of multiple UAVs in the coverage mission. Three path-planning approaches are introduced through a group of the waypoints in a mission area: PSO, genetic algorithm, and a hybrid form of parallel PSO-genetic algorithm. The proposed hybrid optimization tries to integrate the advantages of the PSO, i.e. coming out from local minimal, and genetic algorithm, i.e. better quality solutions within a reasonable computational time. These three approached are compared in many scenarios with different levels of difficulty. Statistical analyses reveal that the hybrid algorithm is a more effective strategy than others for the mentioned problem.Resumo em Inglês:
ABSTRACT: Correlations for the supersonic jet characteristics, the mean shock cell length and the supersonic core length, have been obtained in terms of the jet parameters. The jet parameters considered in this study are the exit diameter of the nozzle (de), the design Mach number (Me), the nozzle pressure ratio (NPR) and the ratio of specific heats of the medium (γ). The parameters were varied as follows: exit diameters, from 0.5 to 25 mm; Mach number from 1 to 3; the NPR from 2.14 to 35. Initially, working fluid used is cold air and then effect of variation of γ is taken into consideration. The computational model has been validated and then used for all the numerical simulations. A quadratic fit for both characteristics has been obtained which is applicable to any supersonic jet. The correlations developed are valid within the respective ranges of the parameters stated above.Resumo em Inglês:
ABSTRACT: The preliminary design of geostationary communication satellite solar array is presented in this work. Based on the power requirements, power margin requirements and performance requirements, the number of panels, strings and cells to be used on the solar array were defined. The main objective of this study was to optimize the power generated from the satellite solar array and the extraction of the parameters of a photovoltaic module, which is subject to the space environment and under a series of practical constraints, in order to extract the desired performance parameters for multiobjective functions, taking into account the solstice and equinox periods during temperature operation. A gravitational search algorithm based on the law of gravity and mass interactions was introduced. This algorithm has proved its effectiveness in optimizing system parameters in the literature. From the results obtained in this work, the total power of the optimized system was reduced by 181 W. The degradation and output power characteristics of the solar panels were calculated for different temperature values.Resumo em Inglês:
ABSTRACT: The energy characteristics and theoretical performance of the hybrid rocket fuels are discussed in this paper. Aluminum (Al) and boron (B) metal additives were used to increase the energy density of the paraffin-based solid fuels. To predict the energy characteristics, the heat of combustion was evaluated by adiabatic bomb calorimetry. Theoretical performance parameters such as specific impulse (Isp), flame temperature, and characteristic velocity were obtained with NASA Chemical Equilibrium with Applications (CEA) code. Calorimetric test results revealed that paraffin/polyethylene/boron (P/PE/B)-based fuel formulations exhibited the highest heat of combustion among all the tested fuels. The heat of combustion value of the P/PE/B sample at 25 wt% B loading was found to be 9612 ±16 cal/g and 9293±17 cal/g for the P/PE/Al fuel formulation. The CEA results showed that the addition of Al to paraffin is noneffective in improving specific impulse performance. When B loading increased from 5 to 25 wt% in the P/PE/B, the Isp increased by 47 s compared to pure paraffin. A specific impulse increase implies the possible propellant mass saving. The reduction of the oxidizer and fuel masses may yield increased payload performance for given boundary conditions. The P/PE/B25 formulation has reported the highest value of characteristics velocity (C*) compared to other paraffin-based formulation.Resumo em Inglês:
ABSTRACT: In this work, the aerodynamic performance of four types of bird’s airfoils (eagle, stork, hawk, and albatross) at low Reynolds number and a range of angles of attack during fixed (unflapping) gliding flight was numerically investigated utilizing open-source computational fluid dynamics (CFD) code Stanford University unstructured (SU2) and K-ω Shear Stress Transport (K-ω SST) turbulence model. The flow of the simulated cases was assumed to be incompressible, viscous, and steady. For verification and comparison, a low Reynolds number man-made Eppler 193’s airfoil was simulated. The results revealed that stork has the greatest aerodynamic efficiency followed by albatross and eagle. However, at zero angle of attack, the albatross aerodynamic efficiency exceeded all the other birds by a significant amount. In terms of aerodynamics efficiency, stork’s and albatross’s airfoils performed better than Eppler 193 at angles of attack less than 8°, while at a higher angle of attack all studied birds’ airfoils performed better than Eppler 193. The effect of surface permeability was also investigated for the eagle’s airfoil where the permeable surface occupied one-third of the total airfoil surface. Permeability increased the generated lift and the aerodynamic efficiency of the eagle’s airfoil for angles of attack less than 10°. The increase reached 58% for the lift at zero angle of attack. After the specified angle, the permeability had an adverse effect on the flow which may be due to the transition to turbulent ahead of the permeable section.Resumo em Inglês:
ABSTRACT The article explores the reuse of technical processes in the manufacturing of space systems, from the perspective of establishing a database of technical manufacturing processes for use by space organizations. It will be argued that the reuse of processes is made feasible when a database of processes is implemented and that the reuse of technical manufacturing processes provides gains in time, cost, and reliability. A proposal for the organization of project technical processes into a database is presented. The article addresses the following topics: technical process concepts, control and use of technical manufacturing processes practiced by space agencies, identification of technical manufacturing processes, and their organization in a database. Finally, an example of the application of reuse is presented, and the main consequences of the reuse of technical manufacturing processes with the aid of a database are discussed.Resumo em Inglês:
ABSTRACT For studies of hypersonic flows and supersonic combustion in ground test facilities, three devices can be used as ram accelerators, shock tunnels and supersonic combustor test benches. These devices can reproduce, on the ground, similar conditions to those in real flight at a certain altitude and speed. In the case of the supersonic combustor test bench (SCTB), it simulates the same flow conditions inside the combustor of a scramjet. The SCTB consists basically of a combustion chamber or vitiated air generator unit, where the air is heated, and a nozzle, where the air is accelerated to the desired test speed. The supersonic combustor to be tested is directly coupled to the nozzle exit of the SCTB. Ultimately, it was necessary to use a transition piece to connect the nozzle to the combustor to be tested, because the nozzle exit has a circular section and the combustor entrance has a rectangular one. This work aims to present the process of characterizing the cold flow along the SCTB of the Institute for Advanced Studies (IEAv) using the schlieren technique. The interference of the transition piece in obtaining the required flow conditions at the exit of the SCTB or the entrance of the combustor was mainly evaluated.Resumo em Inglês:
ABSTRACT: This paper deals with the implementation of a version of the MIT LFM-CW radar at the Ecuadorian Space Institute. The effects of near and very near ranges, and free space loss in the performance of the image processing is theoretically revised. Subsequently, the implemented radar is tested in an imaging campaign on a small probing polygon, and very congruent results are obtained.