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ABSTRACT: Smokeless propellants have been studied and manufactured for many decades. They can exist in various physical forms and also can have different properties according to the use of each propellant. One important form of smokeless powders is the ball powder, which has spherical grains. The manufacture process of the ball powder has many advantages over the usual way to manufacture a smokeless powder. For example, unstable and even deteriorated nitrocellulose, after being stabilized again, can be used to produce spherical powders. Also, the process to produce them requires less water and energy, which can result in a cheaper way to manufacture powders. In this review, the spherical powders manufacturing process is described, as well as the characteristics and advantages of this specific form of a double-base powder.Resumo em Inglês:
ABSTRACT: A microcontroller-based programmable electronic switching module is designed and developed. For supplying power to this module, thermoelectric generators (TEGs) are electrically integrated to the switching module. This integrated switching module is carried out to develop a Thermoelectric-sourced Programmable Electronic Switching Module (TPESM), which has many applications in the defence, space and many other fields. This module can also be used to charge batteries and to operate some microelectronic devices. The main objective of this paper was to use the available heat sources in armament stores for some needful applications. This module was successfully developed and proved to ignite electro-explosive devices (EED) at pre-programmed timing using programmable electronic switching module, which operates by the generated voltage of TEG. This paper discusses the applications, development, operation, experiments and results of this module.Resumo em Inglês:
ABSTRACT: Numerical modeling of premixed combustion is important for a wide range of machines and systems focusing on compliance with the increasing pollutants reduction requirements. However good industrial numerical combustion models need a practical requiring, in this way, a balance between speed and accuracy. The flamelet models are suitable for this purpose providing a decoupling of the reactive and fluid dynamic problems, and an important model of this family is the b-Ξ flame surface wrinkling model. A specially challenging experiment to test this combustion model is the ORACLES test rig whose two independent parallel inlet channels consistently influence the turbulent combustion, injecting fuel and oxydizer at different equivalence ratios. The b-Ξ flamelet combustion model is known by the sensibility to numerical schemes and boundary conditions and, based on this, the present study proposes to investigate the coupling with the important SST k-ω turbulence model and achieve good balance among accuracy, boundedness, stability and efficiency using the ORACLES experiment.Resumo em Inglês:
ABSTRACT: In the last decades, hybrid rocket engines have been increasingly studied and used in space vehicles. However, the low regression rates and specific impulses still represent major drawbacks to this technology. The objective of this study was to quantify the relative improvement of regression rate values with the use of a swirling flow injector in comparison to an axial injector. Seven tests were conducted with axial injection and seven with swirl injection. Regression rate results were compared, and it was found that swirl injection improved regression rates in 50% for mass fluxes higher than 45 kg·s-1·m-2. It was possible to see radiation, kinetic and diffusion theory on the logarithmic plot of regression rate per oxidizer flux yielded by both injectors. A strong agreement with experimental findings of regression rates in the literature parameters is reported.Resumo em Inglês:
ABSTRACT: A series of geometric models of lobed nozzles with a central plug was created by different scalloping positions and widths. The shapes of lower and upper edges, cutting depth were kept unchanged. In this study, by the use of numerical simulation, the effects of scalloped width and position on the performance of jet mixing in the pumping condition were analyzed. The results indicated that, as the position of scalloped lower edge kept constant, the radial position of the accelerated mixing region of sidewalls did not change. The accelerated mixing region is enlarged as scalloped width increased, while the growth rate of enlarged region is less than the growth rate of scalloping width. When the scalloped region with the same width moved outward in the radial direction, the mixing rate of the region of the lobe outer edges increased. However, the distance for complete mixing of the primary stream in the core region was increased. It was also found that inward moving of scalloped lower edge enhanced the effect of strengthening streamwise vortices but induced more pressure loss.Resumo em Inglês:
ABSTRACT: Bird's formation flight is one of the best types of cooperation in nature. The bird's flight was the motivation of humans for flying. After one century of flight development, bird's formation flight was the motivation of humans for aircraft's formation flight. The closeness of aircrafts in formation flight and the effect of disturbances such as vortex make the formation flight control a challenging issue for control designers. This paper introduces a novel integration between guidance commands and system controller inputs. In recent papers the control system inputs were derived from approximate equations, and this approximation caused maneuver limitation. To tackle this problem, a new method is introduced, which employs proportional-integral-derivative (PID) controller in the integration block. This integrated guidance and control system employs the pure pursuit guidance to determine the unmanned aerial vehicle's acceleration command. A two-loop dynamic inversion technique is used for designing attitude and velocity controller, while the acceleration feedback control is used between the guidance system and attitude controller, which leads to increase in maneuverability of unmanned aerial vehicle's formation flight. The simulation results show that the proposed method can control the UAV's formation with sufficient accuracy in severe maneuvers.Resumo em Inglês:
ABSTRACT: The objective of this paper is to study the problem of the robotic manipulator operating on a non-fixed base by considering two dynamics scenarios. One in which the base is free to react in response to the robotic manipulator motion and the other in which the robotic manipulator moves its links in such a way to compensate the reaction forces on the platform so as to keep it stable. This approach is passive in the sense that no additional control effort has to be done to compensate the effects of the reaction forces on the platform. The methodology to approach the problem includes lab experiments aiming the dynamics analysis of a robotic manipulator operating on an ice platform on a glass table. The mathematical model of a satellite like a robotic manipulator is developed and then implemented in a computer by using the MATLAB software environment. The results of the computer simulations confirm that the control effort for the attitude control is larger for the case in which the links are in operation compared to the case in which the robotic manipulator is not working. For the passive case, the results confirm the attitude stability of the robotic manipulator platform when it is working. The passive case is that in which the robotic manipulator links are moving in a synchronized configuration and in a reverse sense.Resumo em Inglês:
ABSTRACT: The main goal of this paper is to analyze if it is feasible to employ a trained shape memory alloy wire as a linear actuator to modify the camber of a morphing wing rib. In order to achieve this purpose, a morphing rib with a compliant trailing edge was proposed, developed, and subjected to structural analyses to ensure its flexibility. After the rib configuration was set, it was manufactured by a 3-D printer. The NiTi wire used as actuator was trained by a thermomechanical procedure based on a cycling process with a constant load application to present the two-way shape memory effect. In that way, the wire presents a determined length at its low-temperature phase and a shorter one at its high-temperature phase. Since the wire contraction and the torque applied by it are two crucial factors to define the camber curvature, it was decided to study two different wire lengths: 103.5 and 152.1 mm. The aerodynamic performance of the morphing cambered airfoils was studied using XFOIL software and compared to that of conventional airfoils with single hinged flap. The results show that both morphing airfoils present better aerodynamic performance for small angles of attack.Resumo em Inglês:
ABSTRACT: Terminal area is an important part of airspace system. Its operation efficiency is related to the safety, order and efficiency of the entire air traffic. So the assessment of the terminal route network operation efficiency is needed. Considering the aspects of route segment capacity, flight flow, workload and operation stability, the paper analyzes the influent factors on the operation efficiency of terminal area route network, constructs the calculation parameters of operating efficiency, and establishes the calculation model of operating efficiency of the route segment. An assessment model for the operation efficiency of terminal area route network based on flight demand is built using comprehensive weighted method. Finally, the feasibility of the assessment model is verified by analyzing a case. The model can be used to assess not only the operation efficiency of a single route segment based on different flight demands in the terminal area, but also the real-time efficiency of the terminal area route network.Resumo em Inglês:
ABSTRACT: This study has proposed and empirically tested for the first time genetic algorithm optimization models for modelling Australia's domestic airline passenger demand, as measured by enplaned passengers (GAPAXDE model) and revenue passenger kilometres performed (GARPKSDE model). Data was divided into training and testing datasets; 74 training datasets were used to estimate the weighting factors of the genetic algorithm models and 13 out-of-sample datasets were used for testing the robustness of the genetic algorithm models. The genetic algorithm parameters used in this study comprised population size (n): 200; the generation number: 1,000; and mutation rate: 0.01. The modelling results have shown that both the quadratic GAPAXDE and GARPKSDE models are more accurate, reliable, and have greater predictive capability as compared to the linear models. The mean absolute percentage error in the out of sample testing dataset for the GAPAXDE and GARPKSDE quadratic models are 2.55 and 2.23%, respectively.Resumo em Inglês:
ABSTRACT: This study explores the potential deployment of small satellites for maritime interdiction and security applications by investigating the available solutions and formulating a generic proposal to optimize the use of those short-lived space assets in support of these operations. The operational background is analyzed with respect to the potential use of these systems by field officers. An analysis for operational micro and picosatellite characteristics is executed, and a brief outlook on the vulnerabilities of those for Low Earth Orbits is given. Moreover, a real scenario has been implemented, and the obtained computational results provide useful insight into how these space systems can be used for maritime security operations. Particular reference is given to the state-of-the-art status of propulsion systems capable of enhancing the lifetime of the satellites. Similarly, a literature survey has been conducted collecting all available picosatellites in orbit today that deal with maritime security applications. The study also explores the application of Lambdasat picosatellite (currently in orbit) to demonstrate the capability of exchanging alert messages between ground stations in Greece and in the US and vessels in the middle of the ocean. With these experiments we will demonstrate the ability magnitude of a picosatellite to support maritime operations.Resumo em Inglês:
ABSTRACT: This article introduces a numeric model, developed in a MATLAB environment, in order to monitor NAVSTAR GPS performances concerning accuracy effects and interference phenomenon. The model will be presented as a starting point for a future production of an open-source software, shareable and enlargeable, which will be able to provide real-time information about navigation satellite system performance. a sequence of analysis and comparisons with existing owners of the software will be possible using real data acquired with a high-performance monitoring station, in order to validate numeric models compiled.