Scielo RSS <![CDATA[Journal of Aerospace Technology and Management]]> http://www.scielo.br/rss.php?pid=2175-914620180001&lang=en vol. 10 num. lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Moving Forward: Continuous Article Publishing, Internationalization and Social Media Dissemination]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100100&lng=en&nrm=iso&tlng=en <![CDATA[Low Subsonic Wind Tunnel - Design and Construction]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100200&lng=en&nrm=iso&tlng=en ABSTRACT: This paper describes the design and the construction details of a medium size subsonic low-speed wind tunnel, which has been designed to achieve 90 m/s in the working section with expected low intensity turbulence level, making it available for researching in areas such as low speed aerodynamics (flight and terrestrial vehicles), sport activities, civil engineering applications, fundamental research in Fluid Mechanics and other possibilities. To accomplish such objectives a very detailed design was carried on using theoretical analyses, CFD simulations and semi-empirical methods, all of them applied to improve the flow quality along the wind tunnel sections. A very careful attention has been focused to the design of the fan blades and the electrical engine assembly, which has been inserted in a "pusher" configuration. Flow control and stabilization also took place using screens, honeycombs and corner vanes, all of them optimized to induce low turbulence levels in the working section. The design and construction of each wind tunnel section has been presented and discussed shedding light to the most relevant technical aspects and an attempt is made here to present some design and manufacture guidance for the main components of a low subsonic wind tunnel. <![CDATA[Space Propulsion: a Survey Study About Current and Future Technologies]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100201&lng=en&nrm=iso&tlng=en ABSTRACT: Current Space Launch Vehicles use chemical reactions (solid and liquid propellants) to achieve sufficient thrust to launch artifacts and humans into space. Propulsion technologies can be framed in three different categories: "escape propulsion", "in-space propulsion", and "deep space propulsion". The launch vehicles currently used for "escape propulsion" rely on mature technologies, which experienced only small incremental improvements over the last five decades, and breakthroughs for this kind of propulsion are not foreseen for the next two decades. This research gathered information on the main operational heavy-lift space launch vehicles with capacity over 5,000 kg that are used to reach GEO (Geostationary Earth Orbit) by the United States, Russia, Europe, China, Japan and India and compared their thrust capability. The results show that performance was improved mainly by adding boosters, increasing gross propellant weight, with larger diameter rocket motors and using more efficient liquid propellant pairs. Information regarding the frequency of published scientific articles and patents on Space Vehicles Propulsion Systems since the 1960s was also gathered, which demonstrates some progress in the last years, mainly in USA and Europe. "In-space" and "Deep space" spacecraft were also briefly examined in this article, resuming the main features of some new promising developments, mainly regarding the latter, which present prospects of significant technological advances; however, real progress in interplanetary missions will be possible only when technological breakthroughs towards other propulsion types become possible and feasible. So, two questions motivated the authors: why space propulsion development seems stagnant? Are there prospects for progress? <![CDATA[Ground-Based Microwave Radiometer Calibration: an Overview]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100202&lng=en&nrm=iso&tlng=en ABSTRACT This paper intends to briefly present some basic concepts on the microwave radiometry and radiometer calibration research in remote sensing applications and demonstrate results and analysis of the cryogenic calibration of a microwave ground-based radiometer currently deployed in scientific campaigns in Brazil. The equipment described in this text operates at 22 - 30 GHz and at 51 - 59 GHz frequency ranges and uses as the calibration standard a target cooled by liquid nitrogen. Since an accurate calibration (with observation errors below 0.5 K) is important to provide confidence in the retrieval of vertical temperature and humidity profiles, this work aims also to comment on some effects of the errors in calibration procedure on the atmospheric parameters of interest. <![CDATA[Susceptibility of GPS-Dependent Complex Systems to Spoofing]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100300&lng=en&nrm=iso&tlng=en ABSTRACT GPS-based systems have been widely used in different critical sectors, including civilian and military applications. Despite of being able to provide great benefits, under certain circumstances they show to be highly vulnerable to intentional interferences. In this context, this article aimed to evaluate the susceptibility of different complex GPS-dependent systems to intentional interferences, focusing on the technique known as spoofing. This technique presents a high complexity and a great potential for damaging/deceiving complex systems, besides being difficult to identify and to implement countermeasures. Complex systems, like mobile phones, automobile receivers and aircraft receivers were submitted to different levels of spoofing, in free space and in a semi-anechoic chamber, being corrupted with low power levels of interference. <![CDATA[Application of a Bibliometric Tool for Studying Space Technology Trends]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100301&lng=en&nrm=iso&tlng=en ABSTRACT: The statistical analysis of academic literature, also known as “bibliometrics”, is being increasingly applied to analyse research trends, to identify emerging areas of science and to find out where and how often specific articles are cited. The aim of this study was to identify technological innovation trend patterns in the aerospace sector applying bibliometric analysis over the period 2008 - 2015. In this study the keywords space technology, satellite, space launch vehicle, spacecraft, rocket and space station were used to scrutinize the database Web of Science (ISI). The obtained records were analysed using the Patent Insight Pro software (2015). It was observed that the researches related to aerospace technological development has been focused in satellites, giving also some directions for satellite launch vehicles. Bibliometric analysis revealed concern on new low-cost technologies development, and the applied logistic fit suggests that over the next five years the continuity on new space technologies development will be mostly related to small satellites, with also contributions associated with high-resolution imagery in order to improve Earth observation in low orbit. <![CDATA[One-Dimensional Thermal Analysis Model for Charring Ablative Materials]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100302&lng=en&nrm=iso&tlng=en ABSTRACT: This paper presents a one-dimensional model for the analysis of the charring ablative materials used in spacecraft thermal protection systems. The numerical method is based on an implicit finite difference formulation of the governing equations written for a system of mobile coordinates that accounts for the possible presence of surface recession. The maximum allowable operating temperature for the adhesive layer of the junction between the heat shield and the substructure is used as a design parameter for determining the minimum heat shield thickness. A case study on the re-entry of the Stardust capsule is presented. The model proposed as a useful dimensioning tool for the preliminary design phase of the heat shields of spacecraft entering the atmosphere. The model was validated through a survey of the literature related to the dimensioning of thermal shields, but based on numeric programs of highly representative industrial standards. <![CDATA[An Innovative Structural Fatigue Monitoring Solution for General Aviation Aircraft]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100303&lng=en&nrm=iso&tlng=en ABSTRACT: This article proposes a novel and effective solution for estimating fatigue life of General Aviation (GA) airframes using flight data produced by digital avionics systems, which are being installed or retrofitted into a growing number of GA aircraft. In the proposed implementation, a flight dynamics model is adopted to process the recorded flight data and to determine the dynamic loadings experienced by the aircraft. The equivalent loading cycles at fatigue-critical points of the primary structure are counted by means of statistical methods. For validation purposes, the developed approach is applied to flight data recorded by a fleet of Cessna 172S aircraft fitted with a Garmin G1000 integrated navigation and guidance system. Based on the initial experimental results and the developed uncertainty analysis, the proposed approach provides acceptable estimates of the residual fatigue life of the aircraft, thereby allowing a cost-effective and streamlined structural integrity monitoring solution. Future developments will address the possible adoption of the proposed method for unmanned aircraft structural health monitoring, also considering the accuracy enhancements achievable with advanced navigation and guidance architectures based on Global Navigation Satellite Systems (GNSS), Vision-Based Navigation (VBN) Sensors, Inertial Measurement Units (IMU) and Aircraft Dynamics Model (ADM) augmentation. <![CDATA[GPS Jamming Signals Propagation in Free-Space, Urban and Suburban Environments]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100304&lng=en&nrm=iso&tlng=en ABSTRACT: GPS-based systems have been widely used in different critical sectors, including civilian, military and commercial applications. Despite of being able to provide great benefits, under certain circumstances they show to be highly vulnerable to intentional interferences. In this context, this article aimed to evaluate the vulnerability range of this kind of systems, focusing on different kinds of environments and based on different propagation models, to which the simulations were performed. Results show high vulnerabilities of GPS-based systems even when operating in a well-protected urban environment, in a short range and under low-power sources of radiation. Graphs are presented with the range of effectiveness for different power levels of jammer in different situations. Evaluations are performed not only for the acquisition but also for the tracking processes of the GPS receivers, therefore being possible to establish a safe operation range for having a trustful GPS signal and mitigate malicious actions. The comparisons allow, as well, highlighting the importance of using the correct propagation model, in order to achieve consistent results, depending on the desired situation. <![CDATA[3D Printing and its Effect on Outsourcing: A Study of the Indian Aircraft Industry]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100305&lng=en&nrm=iso&tlng=en ABSTRACT: Indian Aircraft Industry has emerged as one of the rapid growing industrial endeavors in the world, with automation in most of its production and manufacturing areas. Technological advancements have led to this growth and, over the years, competitiveness has made the industry to efficiently look for avenues and other strategic alliances. In this direction, 3D printing technology has opened many opportunities. This study is focused on explaining the 3D printing technology utilization for production and servicing apart from developing a methodology to outsource various automated technologies to the tier-2/tier-3 companies basing themselves on specified parameters and capabilities by using the 3D printing. 3D printing in manufacturing industry, particularly in aircraft manufacture, has brought in novel prospective along with new challenges posturing new methodologies and innovative approaches to meet the global standards. In this line, the Indian Aircraft Industry has started redistributing its sourcing by outsourcing of certain non-strategic facilities and parts that can be manufactured with the use of 3D printing/additive manufacturing, computerization and automation to outsiders, aiming at development of capabilities in the partnership industry, to provide the scope for generating high volume at the affiliated industries to pave way for a win-win ground. Already playing a good role in aircraft engine manufacture at Indian aircraft industry, 3D printing is going to play a more vital role in the total aircraft manufacture and avionics in the next few years, if the present scenario is pragmatic in line with the industrial needs. With the advantage of "low or zero" waste, less impact on environment, apart from possibility of local manufacture and just-in-time delivery, with greater specification of the final product, outsourcing of the parts and products for the entire aircraft manufacture will be a reality as per the current research, thriving on improved production volumes of similar parts for various end users. Research further suggests that outsourcing configuration is looking to invest in the new methods and "timely production" would become an assurance with 3D printing. <![CDATA[DBD Plasma: Explicit Model with Integral Approximate Solution to Wall Jet]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100306&lng=en&nrm=iso&tlng=en ABSTRACT: This study aims to first introduce a formulation which is quite simple for obtaining dielectric-barrier discharge plasma spatial body force. This new model comprises a combination of an empirical model and a numerical one. Although there are still some limitations in the new model (restriction to specific geometry, maximum voltage amplitude of 30 kV, maximum frequency of 30 kHz, dielectric coefficient of 2.8 and Debye length of 0.0001 m), it is straightforward compared to the existing ones. The model possesses a high accuracy for the abovementioned band. It is proposed an approximate integral solution for the wall jet problem which is associated with the induced jet produced by dielectric barrier discharge plasma actuator. The approximate integral solution for the wall jet is verified by similarity, and the details are extensively discussed. <![CDATA[Design and Analysis of a Novel Spacecraft for Mitigating Global Warming]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100307&lng=en&nrm=iso&tlng=en ABSTRACT: A device called Huge Space Shield (HSS) has been put forward for mitigating global warming. This is a space tethers system, which use cables to connect a shielding surface and a mechanism control. In this study, orbital analysis was carried out to choose the best orbit for getting the best effect. Simulation studies were employed to understand the HSS at the beginning of entering the orbit, which were based on completely and semi-simplified model. Therefore, the force analysis gives rise to the system would not fail in the period of running on the orbit. All the results show that the HSS is stable at launch and operation, which can help ease global warming. <![CDATA[Dynamics of a Small Unmanned Aircraft Parachute System]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100308&lng=en&nrm=iso&tlng=en ABSTRACT: Parachute Systems (PS) can be readily used by small Unmanned Aircraft Systems (UAS) for risk mitigation and aircraft recovery. To date there has been limited research into the fundamental dynamics of parachutes at low Reynolds numbers, with existing studies focusing on larger parachutes. An understanding of the dynamics is needed to establish sound guidelines for parachute design and for their use during UAS operations. Existing design guidelines are reviewed and the key parachute design parameters are identifi ed. The validity of the existing guidelines applied to lower Reynolds number parachutes is explored through a series of wind-tunnel tests. It was found that existing design guidelines underpredict the key parameters of infl ation time and peak forces for parachute deployments at typical UAS operating speeds. The ramifi cations on the design and operation of small UAS are discussed. <![CDATA[Computational Investigation on the Effects of Two-Way Wing Morphing Strategy in the Critical Mach Number]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100309&lng=en&nrm=iso&tlng=en ABSTRACT: The elasto-flexible wing morphing is an advanced methodology to achieve higher lift-to-drag (L/D) ratio for the subsonic wing configurations at the given flow conditions. The present article describes mechanisms of continuous morphing of a swept back wing for achieving effective delay in the critical Mach number (Mcr) distribution over the wing surface with higher L/D ratio. Firstly, typical wing sweep angles of a Jet transport airplane ranging from 25º to 32º are considered for the present investigation towards sweep morphing. Then, the planform morphing is done by increasing the value of mean aerodynamic chord by 2.5% to 7.5% from its baseline value. A novel computational simulation technique is utilized to observe the value of Mcr over the wing at each 0.5% incremental chord values. The computational fluid dynamic analysis of a 3-D doubly tapered wing model is done at 0º angle of attack and free stream Mach number about 0.85. A NACA 6-series supercritical airfoil is selected for the wing design that resembles the wing configuration of an A300-B4 airplane. The outcome of the investigation has revealed reduced drag benefits near the transonic regime through the two-way wing morphing strategy and the results are presented with applications. <![CDATA[Run time Assessment for Gas Turbine Performance Simulation]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100310&lng=en&nrm=iso&tlng=en ABSTRACT: This article describes the run time characteristics of a gas turbine performance simulation using different solvers and components off-design performance database formats. Two different nonlinear systems of equation solvers, Newton-Raphson's and Broyden's, and two different formats of compressor and turbine off-design performance database (maps), tabulated values and fitted surface equations, were compared. Based on the results it is then possible to trade off and select the most appropriate combination of solver and component map type for the gas turbine performance simulation for real-time application. <![CDATA[Mode I+II Fatigue Crack Growth Delay by Stop-Holes]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100311&lng=en&nrm=iso&tlng=en ABSTRACT: The technique of retarding the growth of fatigue cracks by drilling holes on the crack tip is well known. Most of the research works on this subject are limited to fatigue cracks subjected to mode I loading conditions. In the present work the fatigue crack growth retardation by stop-holes of cracks under mode I+II loading is investigated. The proposed approximate solution is based on the implementation of a mixed-mode fatigue crack growth model and a multiaxial high cycle fatigue criterion. Numerical results for mode I+II fatigue crack growth retardation on Al-2024 thin plate are derived and the effect of the crack inclination angle, as well as the diameter of the stop-hole, are discussed and commented. <![CDATA[Performance Prediction of Microwave Absorbers Based on POMA/Carbon Black Composites in the Frequency Range of 8.2 to 20 GHz]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100312&lng=en&nrm=iso&tlng=en ABSTRACT: This paper presents a comparative study involving experimental and numerical behaviors of radar absorbing materials (RAM), based on conducting composites of poly(o-methoxyaniline) (POMA) and carbon black (CB). Samples of POMA/CB in epoxy resin matrix were prepared. First, these samples were experimentally characterized by electric permittivity and magnetic permeability measurements in the frequency range of 8.2 to 12.4 GHz. Afterwards, a linear extrapolation of these electromagnetic parameters until 20 GHz was carried out. These amounts were used as parameters for a set of simulations, developed from numerical implementation of theoretical predictions. The main advantage of the performed simulations is to know the behavior of the POMA/CB/epoxy resin as RAM in a wide range of frequencies (8.2-20 GHz), previously to the experimental work. The validation of the simulations with experimental reflection loss measurements showed a good fit and allowed predicting the material behavior as RAM. The results show that the studied RAM presents good return loss values in different frequencies, for example, -32 dB (~99.95% of absorption) at 14.6 GHz and -18 dB at 19.2 GHz, for samples with 7 and 9 mm-thickness values, respectively. The simulation tool used in this study was adequate to optimize the RAM production, contributing to the reduction of development costs and processing time of this kind of material. <![CDATA[Aircraft Preventive Maintenance Data Evaluation Applied in Integrated Product Development Process]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100313&lng=en&nrm=iso&tlng=en ABSTRACT: Initial Maintenance Review Board Report (MRBR) uses in service operation experience as a reference to define maintenance tasks intervals. However, in general, there is no structured data to compare systems performance and provide useful information to the analysts' decision-making. Even when engineering judgment is based on certification process, structural design, components intrinsic reliability and so on, the analysts responsible for maintenance tasks definitions tend to choose rather conservative proposals. This article presents a method to optimize preventive maintenance tasks intervals and use structured data based on interval optimization process to define maintenance intervals to those of similar systems under development. The method has been applied in an aircraft manufacturing company using current operation database after regulatory authorities' approval. As a result, it has been feasible to propose to the selected system, a maintenance task interval 100% higher than the one applicable to a similar system under operation. <![CDATA[An Evaluation of the Dielectric Barrier Discharge Treatment on the Mechanical, Structural and Morphological Properties of Carbon Fibers]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100314&lng=en&nrm=iso&tlng=en ABSTRACT: Carbon fibers (CFs) have been widely applied in the manufacture of polymeric composites. The mechanical properties of these composites depend on the adhesion in the matrix/CF interface. Since the CFs have poor adhesion properties, a surface treatment of the CFs becomes necessary. The plasma process used in this work was the dielectric barrier discharge (DBD). The DBD treatment of twill weave carbon fibers (2×2) was performed during 2.0; 5.0; 7.5 and 10.0 minutes. CF/polypropylene (PP) composites were produced by hot pressing method. The surface morphology, structure and mechanical properties of CFs were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, interlaminar shear test (ILSS) and dynamical mechanical analysis (DMA), respectively. SEM images show great changes on the CF surface after the treatment, AFM results show that the fiber treated for 2.0 min exhibited the highest roughness and Raman spectra revealed that the carbon fiber crystalline structure did not change after the treatment. The ILSS and DMA results show an increase of the mechanical strength and no major change in the glass temperature of the composites after the DBD treatment, respectively. Some results were compared to those obtained in our previous study, in which the plain weave fiber (1×1) was evaluated. <![CDATA[Analytical Solution for Optimal Low-Thrust Limited-Power Transfers Between Non-Coplanar Coaxial Orbits]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100315&lng=en&nrm=iso&tlng=en ABSTRACT: In this paper, an analytical solution for time-fixed optimal low-thrust limited-power transfers (no rendezvous) between elliptic coaxial non-coplanar orbits in an inverse-square force field is presented. Two particular classes of maneuvers are related to such transfers: maneuvers with change in the inclination of the orbital plane and maneuvers with change in the longitude of the ascending node. The optimization problem is formulated as a Mayer problem of optimal control with the state defined by semi-major axis, eccentricity, inclination or longitude of the ascending node, according to the class of maneuver considered, and a variable measuring the fuel consumption. After applying Pontryagin's maximum principle and determining the maximum Hamiltonian, short periodic terms are eliminated through an infinitesimal canonical transformation. The new maximum Hamiltonian resulting from this canonical transformation describes the extremal trajectories for long duration transfers. Closed-form analytical solution is then obtained through Hamilton-Jacobi theory. For long duration maneuvers, the existence of conjugate points is investigated through the Jacobi condition. Simplified solution is determined for transfers between close orbits. The analytical solution is compared to the numerical solution obtained by integration of the canonical system of differential equations describing the extremal trajectories for some sets of initial conditions. Results show a great agreement between these solutions for the class of maneuvers considered in the analysis. The solution of the two-point boundary value problem of going from an initial orbit to a final orbit, based on the analytical solution, is also discussed. <![CDATA[Proper Orthogonal Decomposition and Spectral Analysis of a Wall-Mounted Square Cylinder Wake]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100316&lng=en&nrm=iso&tlng=en ABSTRACT: The flow patterns over a finite square cylinder of aspect ratio of 3 were analyzed experimentally in a subsonic wind tunnel using the time-resolved particle image velocimetry (TR - PIV) techniques. The near wake flow structures and vortex shedding characteristics were investigated using mean flow analysis, spectral analysis and proper orthogonal decomposition (POD). The cylinders were fixed on a elliptical leading edge flat plate, creating a boundary layer which interacted with the cylinder wake. The 2D PIV measurements were conducted at a low horizontal plane, z/h = 0.3, to investigate possible boundary layer interactions. Due to the complexity of the phenomena, the flow was characterized both in terms of average behavior and time-resolved velocity fields. Both symmetrical and anti-symmetrical vortices structures occur in the cylinder wake, which can be identified based on the coefficients of the first four POD modes. The results indicated that the alternating Karman vortex structures are dominant, described by the first two POD modes. <![CDATA[Investigating Space Radiation Environment Effects on Communication of Razaksat-1]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100317&lng=en&nrm=iso&tlng=en ABSTRACT: This study attempted to identify whether space radiation sources could have affected the communication on RazakSAT-1 that was orbiting in a Low Earth Orbit-Near Equatorial (LEO-NEqO). Data on galactic cosmic rays (GCR), trapped protons, trapped electrons, and solar energetic particles (SEPs) obtained from Space Environment Information System (SPENVIS) are considered. The effects of these radiation sources are analyzed using the linear energy transfer (LET), total ionizing dose (TID), and solar cell degradation. Flux data from National Oceanic and Atmospheric Administration (NOAA) 15, 16, and 17 satellites, and the geomagnetic conditions during the time when RazakSAT-1's missing is also analyzed. Another two satellites, Satélite de Coleta de Dados (SCD-2) and Advanced Land Observation Satellite (ALOS), are compared with the performance of RazakSAT-1. Results showed that GCR dominated at a high energy range of 103 MeV and above in the LEO-NEqO, whereas the energies of the trapped protons and trapped electrons are less than 400 MeV and 4 MeV, respectively. There are no SEPs estimated during the mission period (2009 - 2011). Based on the SPENVIS, SCD-2 and ALOS are more exposed to higher radiation damage than RazakSAT-1. Thus, an analysis of space radiation environment effects on the RazakSAT-1 communication lost after one year of operation will be discussed further, as a platform to find the best strategy for future missions. <![CDATA[Direct Numerical Simulation Code Validation for Compressible Shear Flows Using Linear Stability Theory]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100318&lng=en&nrm=iso&tlng=en ABSTRACT: In order to simulate compressible shear flow stability and aeroacoustic problems, a numerical code must be able to capture how a baseflow behaves when submitted to small disturbances. If the disturbances are amplified, the flow is unstable. The linear stability theory (LST) provides a framework to obtain information about the growth rate in relation to the excitation frequency for a given baseflow. A linear direct numerical simulation (DNS) should capture the same growth rate as the LST, providing a severe test for the code. In the present study, DNS simulations of a two-dimensional compressible mixing layer and of a two-dimensional compressible plane jet are performed. Disturbances are introduced at the domain inflow and spatial growth rates obtained with a DNS code are compared with growth rates obtained from LST analyses, for each baseflow, in order to verify and validate the DNS code. The good comparison between DNS simulations and LST results indicates that the code is able to simulate compressible flow problems and it is possible to use it to perform numerical simulation of instability and aeroacoustic problems. <![CDATA[Minimum Activation Power of a Passive UHF RFID Tags: a Low Cost Method]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100319&lng=en&nrm=iso&tlng=en ABSTRACT: RFID is an automatic contactless identification method based on radio frequency (RF). The reading process depends of the power of electromagnetic signal received by a tag. Thus an accurate characterization of RFID tags is crucial for early adopter in aerospace industry. The present study shows the preliminary approach to characterize the reading distance for UHF RFID passive tag from the low-cost application test deployment. <![CDATA[A Statistical Dynamic Model for the Turbulent Transport of Kinetic Energy in Shear Layers]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100320&lng=en&nrm=iso&tlng=en ABSTRACT: Dynamic statistical equations for the turbulent fluxes of scalars and momentum in incompressible flows are derived after time wise integration of the equation for the oscillating transported property, decomposing the turbulent fluxes in terms representing distinct features of the main and fluctuating flow that influence the respective turbulent transport. These expressions provide a means for discussing the gradient diffusion hypothesis for the turbulent transport, for reconsidering the mixed length model in entirely continuous terms, and for seeking possible alternatives or corrections. Applying this methodology to the turbulent transport flux of kinetic energy, two dominating terms are found: one identified with a kinetic energy gradient model for shear layers; the other related to the main velocity gradient. Accordingly, a composed, Statistical Dynamic model is proposed for the turbulent transport of kinetic energy in shear layers, adding a velocity derivative term to Daly and Harlow's generalized gradient model. This velocity derivative term is calibrated in a nearly homogeneous turbulent shear flow, and the resulting Statistical Dynamic model is proved superior to Daly and Harlow's and other gradient models in channel and boundary layer flows. <![CDATA[Multi-objective Optimization Method For Repeat Ground-track Orbit Design Considering the Orbit Injection Error]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100321&lng=en&nrm=iso&tlng=en ABSTRACT: Considering the adverse effects of orbit injection error, a novel repeat ground-track orbit redesign approach is proposed to reduce the fuel consumption caused by the orbital maneuvering from the injection orbit to the nominal orbit. By introducing the performance indexes of revisiting accuracy and orbit injection maneuvering fuel consumption, the problem of repeat ground track orbit redesign considering the orbit injection error is transformed into a multi-objective optimization problem, which can be solved by multi-objective genetic algorithm. Finally, the numerical simulations show that the redesigned repeat ground-track orbits not only can meet the requirements of revisiting ground targets with high accuracy, but also can reduce the required fuel consumption significantly. <![CDATA[Fast Densification Process in Manufacturing Carbon/Carbon Using Vegetable Precursors]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100322&lng=en&nrm=iso&tlng=en ABSTRACT: The carbon/carbon composite manufacturing processes generally use flammable and toxic precursors. In order to make these processes safer, it is interesting to use less toxic and safer precursors to the environment and people. The present study investigates the types of pyrocarbon resulting from composite carbon/carbon densification produced by the technique of Film Boiling Chemical Vapor Infiltration using as carbon precursors: soybean oil, ethanol and hexane, the latter as control. The microstructure produced was analyzed through SEM techniques, PLOM, XRD and Raman. The pyrocarbons observed are Smooth Laminar, Rought Laminar and Regenerative Laminar types. Soybean oil resulted in porous bodies while other precursors resulted in denser bodies. The crystallites made with ethanol and hexane have preferential growth in the c direction, while those made with soybean oil grow preferentially in a direction. <![CDATA[Mini-channel Two Phase Flow of Hydrogen Peroxide: Decomposition with Silver Catalyst]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100323&lng=en&nrm=iso&tlng=en ABSTRACT Hydrogen peroxide is a chemical compound which is commonly used as a disinfectant at lower concentrations. The chemical is called as a green propellant for space applications. Water and oxygen are the products after self-decomposition of the compound at higher concentrations. The reaction rate at lower concentrations can be enhanced by using catalysts for faster reaction rates. In the present study, an experimental analysis of the reaction rate of hydrogen peroxide (6% by volume) with silver catalyst for varying flow rates is detailed. Reaction takes place in a long cylindrical borosilicate glass tube of diameter 2.50 mm. Separation of product mixture takes place in an enlarged tube of diameter 5.50 mm. Various two phase flow patterns formed after decomposition reactions are identified by images captured using high speed camera. Length of oxygen slug formed after catalytic reaction is measured by employing Image processing techniques. <![CDATA[A Comparative Study of the Heat Input During Laser Welding of Aeronautical Aluminum Alloy AA6013-T4]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100324&lng=en&nrm=iso&tlng=en ABSTRACT The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 µm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features. <![CDATA[Modeling and Analysis of a LOX/Ethanol Liquid Rocket Engine]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100325&lng=en&nrm=iso&tlng=en ABSTRACT This work studies the performance and dry mass of the under development LOX/Ethanol L75 liquid rocket engine. To this end, an object-oriented program written in C++ was developed. The program is intended to be versatile and easily extensible in order to analyze different configurations of liquid rocket engines. The UML (Unified Modeling Language) tool is used to model the architecture of the codes. UML diagrams help to visualize the code structure and the communication between objects, enabling a high degree of abstraction. The cryogenics Vulcain and HM7B engines power cycles along with the staged-combustion SSME engine perform the verification of the codes. Finally, the influence of changes in design parameters on the performance and dry mass of the L75 rocket engine is analyzed. <![CDATA[Preparation and Ablation Performance of Lightweight Phenolic Composite Material under Oxyacetylene Torch Environment]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100326&lng=en&nrm=iso&tlng=en ABSTRACT The present study investigates the influence of fiber content on thermal properties of short silica fiber (SSF) reinforced modified resole resin (MRR) composites. For this purpose, different SSF loading composites were prepared: 40, 55, and 65 wt.%. The ablation resistance related to mass loss parameters was quantified by testing under an oxyacetylene flame up to 2300 °C for 30 s. The thermal conductivity of the composite was studied via experimental steady state technique. Thermal stability of the composite material was estimated by means of thermo-gravimetric analysis (TGA), both in air and nitrogen atmosphere. The ablated composite material was characterized by different techniques (XRD, FTIR, and SEM). The results showed that the back-face surface temperature of SSF/MRR composites follows the typical variation curve, and linear ablation rate, mass ablation rate, and char yield decrease with increasing silica fiber content. This confirms that 55 and 65 wt.% SSF loading exhibited the best anti-ablation performance and the lowest percentage of char yield. XRD and FTIR analysis of the ablated specimen zone showed the absence of new phase. The thermo-gravimetric analysis confirmed the thermal resistance of SSF/MRR composites in comparison with MRR matrix and the decrease of char with increasing SSF loading. The thermal conductivity of these composites was significantly enhanced by the SSF into the modified resole matrix. This thermal conductivity follows both the rule of mixture and Maxwell models. The overall thermal characteristics of the SSF/MRR composites meet most of the necessary high temperature application criteria. <![CDATA[Effect of Convergent Section Contour on the Sonic Line in Rocket Engine Nozzles]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100327&lng=en&nrm=iso&tlng=en ABSTRACT This study made a numeric evaluation of the effect of convergent geometry on the position and profile of the sonic line in rocket engine nozzles. To validate the numerical solution, two conical nozzles, from which experimental results are available in the literature, were used as reference. The tested convergent geometries have the same values for throat radius (Rt), radius of curvature at the throat of the divergent section (Rc3), divergent length, and ratio of areas. The numerical solutions have shown that convergent geometry changes the shape of the sonic line, and nozzles with lower radius ratios (Rc2/Rt) are more sensitive to the shape of the convergent section. <![CDATA[A Reliable Method for Predicting the Specific Impulse of Chemical Propellants]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100328&lng=en&nrm=iso&tlng=en ABSTRACT The specific impulse (Isp) is an important performance parameter that describes energy efficiency of propellant combustion and is intimately related to the rocket engine thrust. In this study, it was possible by using only two variables, i.e., the heat of reaction (Q) and the number of moles of gaseous reaction products per gram of propellant (Ng) calculated according to [H2O-CO2] arbitrary decomposition assumption and constants derived from the ISPBKW code to predict the specific impulse of more than 165 compositions belonging to virtually all classes of propellants such as monopropellants, single-base, double-base, triple-base, and cast modified double-base (CMDB) propellants, pseudo-propellants, composite propellants, liquid mono- and bipropellants, and finally hybrid propellants. Further analysis reveals that for C-H-N-O containing propellants, the specific impulse values estimated using the new method should not deviate more than 5% from the output of the ISPBKW thermochemical code. <![CDATA[Synthesis of Graphene Oxide and Functionalized CNT Nanocomposites Based on Epoxy Resin]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100329&lng=en&nrm=iso&tlng=en ABSTRACT Lately, nanomaterials have been largely studied as reinforcements for epoxy resin. Although their usage is highly promising, the literature has reported some drawbacks regarding the improvement of mechanical properties in nanocomposites. These difficulties are usually due to dispersion of nanomaterials and its adhesion to the polymeric matrix. One approach to this problem is the functionalization of nanomaterials such as carbon nanotubes (CNTs) and graphene. In this work, we have studied the synthesis and functionalization process of CNTs and graphene oxide (GO) to be used as reinforcements for epoxy resin nanocomposites. CNTs were synthesized at 850 °C in a quartz furnace, from hexane and ferrocene vapor, and functionalized by acids and ethylenediamine treatments. GO was obtained by graphite exfoliation through a modified Hummer's method. The nanomaterials were characterized by Raman spectrum, FT-IR, XRD, and SEM images. Nanocomposites were prepared using these nanomaterials and evaluated by DMA. While both nanomaterials showed an improvement in mechanical properties, suggesting a chemical bond between nanomaterial and the epoxy matrix, it was clear that GO reinforced samples presented a higher storage modulus. <![CDATA[A New Approach for Robust Design Optimization Based on the Concepts of Fuzzy Logic and Preference Function]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100330&lng=en&nrm=iso&tlng=en ABSTRACT: In this study, an efficient methodology is proposed for robust design optimization by using preference function and fuzzy logic concepts. In this method, the experience of experts is used as an important source of information during the design optimization process. The case study in this research is wing design optimization of Boeing 747. Optimization problem has two objective functions (wing weight and wing drag) so that they are transformed into new forms of objective functions based on fuzzy preference functions. Design constraints include transformation of fuel tank volume and lift coefficient into new constraints based on fuzzy preference function. The considered uncertainties are cruise velocity and altitude, which Monte Carlo simulation method is used for modeling them. The non-dominated sorting genetic algorithm is used as the optimization algorithm that can generate set of solutions as Pareto frontier. Ultimate distance concept is used for selecting the best solution among Pareto frontier. The results of the probabilistic analysis show that the obtained configuration is less sensitive to uncertainties. <![CDATA[Direct Numerical Simulation of a Compressible Flow and Matrix-Free Analysis of its Instabilities over an Open Cavity]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100331&lng=en&nrm=iso&tlng=en ABSTRACT: This study takes a Jacobian-free approach based on the Arnoldi iteration to present a method to perform hydrodynamic instability analysis based on Direct Numerical Simulations. The method employs high order spatial and temporal discretizations for the flow simulation and has very low requirements of computational time and memory, compared to conventional matrix-forming methods. Details of the numerical treatment applied to guarantee consistency in the numerical solution are discussed, such as mesh and domain dependencies, and buffer zones for the open boundary conditions. The implementation presented here is applicable to any flow with Cartesian geometry, however, the method can be extended to complex geometries and three-dimensional flows. <![CDATA[Construction Methods and Comparative Evaluation of Metal Deployable Load-carrying Shell Structures]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100332&lng=en&nrm=iso&tlng=en ABSTRACT: This study describes the main regularities for the construction of deployable metal shells of a cylindrical type. The comparative analysis of the efficiency of compact folding methods of thin metal shells of cylindrical and conical types, capable of maintaining the initial load-carrying capacity after unfolding without applying the additional strengthening methods, is presented. The range of possible parameters of long-length structures, constructed on the basis of rigid deployable pressurized shells, is characterized. The paper gives the qualitative and quantitative evaluation of basic functional characteristics of folding inflatable metal structures of cylindrical and conical types under the action of a complex of characteristic external loads, close to the maximum allowable ones. The result of experimental operability confirmation of the proposed structures' configurations is presented. <![CDATA[Trajectory Optimization of Launch Vehicles Using Object-oriented Programming]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100333&lng=en&nrm=iso&tlng=en ABSTRACT: The aim of this study is to model launch vehicles with focus on 3-DOF trajectory optimization using a modular approach. Despite the large number of operational launch vehicles, they usually consist of basic components and subsystems. In other words, a launch vehicle is an assembly of stages, which in turn is divided into propellant system and engine, and the engine is an assembly of basic components such as pumps, turbines, combustion chamber, and nozzle. To allow future extension and reuse of the codes, a modular structure using object-oriented programming is used. Two formulations of state equations of the trajectory and two optimization methods are described. The launch vehicle performance will be measured by payload mass for a given mission. The simulations of the VLS-1, Ariane 5 and VLS-Alfa were performed and showed good agreement with the literature. <![CDATA[Aerodynamic Evaluation of Different Car Carrier Devices for Drag Reduction Using CFD]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100334&lng=en&nrm=iso&tlng=en ABSTRACT: Aerodynamic of commercial trucks has been extensively studied due to their impact on fuel efficiency; reducing consumption is one of the most important and challenging issues for the trucking industry. In this paper, several Computational Fluid Dynamic (CFD) simulations are performed to evaluate the drag of a standard car carrier and its different modifications. Therefore, several covers, which act as aerodynamic devices, are tested to determine their effectiveness in fuel consumption. The study compares the drag coefficients, velocity vectors, pressure contours, and turbulence kinetic energy of different fairing configurations. The results show that, although all covers reduce the drag coefficient compared to the conventional car carrier, two of them have significant drag reductions. <![CDATA[Copper/Iron Brake Friction for Military Aircraft Application]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462018000100400&lng=en&nrm=iso&tlng=en ABSTRACT: The present study assesses the influence of non-metallic constituents and manufacturing parameters, such as compaction pressure and sintering temperature, to produce a metal matrix composite (MMC) of copper/iron, based on the brake disc of aircraft AT-29 SuperTucano. The samples were produced with six different compositions, by varying the amount of abrasive particles (quartz and zirconia silicate) and the solid lubricant (graphite), with one of the compositions manufactured without the addition of graphite. The compaction pressures were 210 and 420 MPa, with sintering temperatures of 950 °C and 1050 °C in a furnace with controlled atmosphere of argon + 10% H2. After sintering, the effectiveness of the sintering process was evaluated through the apparent density (Archimedes's method), Brinell and Vickers hardness, and the microstructure by Scanning Electron Microscopy (SEM). The sintering process was severely affected by the solid lubricant (graphite): its reduction resulted in a density increase near 18%, and the hardness of the compound up to 62%. The hardness values demonstrated significant variation with compaction pressure, with a pronounced effect on compounds with less non-metallic elements. SEM analysis demonstrated that not only graphite, but also the ceramic particles affected the sintering process through the agglomeration of inclusions into the metal-metal interface. The samples without graphite exhibited almost the same value of pores after sintering, regardless of the compaction pressure, indicating that the graphite content affects directly the sintering process, regardless of the compaction pressure.