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ABSTRACT Birds are known for their agility, manoeuvrability, and flexibility during flight. These features allow their ability to fly under a large range of flight conditions. Bio flyers and bio aerodynamic/fluid surfaces have inspired many to perform experiments and simulations as well as to relate their results to engineering applications. Wings specifically have been the most inspirational element. Aerodynamic forces, structure, unsteady flow, fluid-structure interaction, flow control, flow adaptive elements and mechanisms, flow vortices, flapping mechanisms, and hovering flight of birds are examples of research interests. This paper presents an overview of prior analyses and experiments on the aerodynamic performance and mechanical properties of birds in steady non-flapping flight.Resumo em Inglês:
ABSTRACT Fourier transform infrared spectroscopy techniques, associated or not to others, are a well-studied subject used for characterizing polymers/energetic materials that have been employed mainly in aerospace industries. However, the infrared analyses are usually qualitative and performed using the mid-infrared. This paper discusses the Fourier transform infrared spectroscopy qualitative and quantitative methodologies, coupled or not with thin layer chromatography and thermogravimetric analysis, for characterization of aerospace polymer systems, in some cases, using mid-infrared, near-infrared and far-infrared regions, by traditional accessories and the latest generation spectra mode, universal attenuated total reflection. This short review was made based on methodologies developed during the last two decades and published by many scientific and industrial research groups, emphasizing studies usually carried out in the last five years. A critical assessment and future trends were included.Resumo em Inglês:
ABSTRACT Carbon fibers have been widely used as structural reinforcement in aeronautical composites, because of their exceptional mechanical properties. However, carbon fibers present few polar groups on their surfaces inducing a weak interaction with some thermosetting and thermoplastic matrices. Surface treatments, such as thermal and electrochemical oxidation, are generally followed by sizing in order to improve interfacial adhesion between carbon fibers and some matrices. The precise surface characterization, by means of its chemical groups and radical identification, has been pointed out as an effective tool of carbon fibers finishing assessment process. Goniometry and Fourier transforminfrared spectroscopy are widely used to characterize some materials applied in industry, but not for carbon fibers, mainly because of their filamentary shape and the high concentration of carbon even in their near surface. In this paper, unsized and sized Torayca T300 carbon fibers were characterized by goniometry tests to evaluate hydrophilic or hydrophobic character. Qualitatively, it was noticed the effect of sizing on carbon fibers by their hydrophilic behavior, which has not been observed in unsized samples. Chemical analysis was performed by Fourier transform-infrared spectroscopy using different setups: photoacoustic, attenuated total reflectance and universal attenuated total reflectance. The Fourier transform-infrared spectroscopy/attenuated total reflectance/Germanium was shown to be the most promising technique to analyze carbon fibers surface, despite the low level of relative intensities of some bands. By this technique, it was possible to observe differences between unsized and sized carbon fibers spectra.Resumo em Inglês:
ABSTRACT The objective of this research was to design pilot helmets and to perform analysis of designed ballistic helmet against impact strength of bullet in Solidworks and Laminator software. The material used for construction of the helmet is fiber reinforced polymer matrix composite in which polymer matrix is made of nylon, a thermoset resin, and the fibers are aramid, an aromatic polymide resin developed by E.I. duPont de Nemours and Company and sold under the trademarks “Kevlar®” and “Nomex®”. The design of the helmet is done by deciding the stacking sequence of various laminae which are oriented with main material directions at different angles to the global laminate axes in order to produce a structural element in the form of a shell. The simulation of the helmet in Solidworks and Laminator is done with an 8-g AK 47 bullet, hitting it with a velocity of 710 m/s. The model is validated against published data and a good correlation is observed. The result of this project is that a 1.30 kg helmet with shell thickness of 7 mm is obtained, which is economical, light weight and is able to give high-performance protection against ballistic shrapnel and bullets.Resumo em Inglês:
ABSTRACT In order to study stealth strike-fighter, an analysis on stealth-aerodynamic integration and conceptual design is conducted. A conceptual 3-D digital model with internal antiship missiles and air-to-air missiles is designed in CATIA software. Based on the physical optics and equivalent electromagnetic current methods, using the self-programmed RCSAnsys software, the Radar Cross Section (RCS) characteristics and characteristics of scattering intensity distribution of the model are numerically simulated. Based on the turbulence theory of standard k-ε equations, using Fluent software, the pressure, velocity and lift-to-drag characteristics of the conceptual aircraft are numerically simulated. The simulation results show that the stealth and aerodynamic characteristics of the conceptual aircraft can be designed through integration analysis process, which can provide technical support to the design of the advanced operational aircrafts.Resumo em Inglês:
ABSTRACT This paper describes the polycarbonate acrylic laminated development that can be applied in aeronautics and aerospace transparencies. The case studied is a laminated double-curved transparency (bubble form) used in an observation side window of a military aircraft. Side windows need strength and specific characteristics, similar to windshields, allowing the perfect visualization and image capture. Laminated transparencies composed by different materials have better qualities than the monolithic ones. This kind of transparency can offer high mechanical and chemical resistance, high transparency, no fragmentation and easy maintenance or recovery. A significant amount of information about materials and processes was jointed in order to build the reinforced transparency and validate this study. The final results were analyzed based on two points of view: mechanic resistance and, especially, optical quality.Resumo em Inglês:
ABSTRACT Under conditions of the influence of space environment factors, the thin-walled load-carrying transformable-volume structures are subjected to volumetric deformation and long-time exposure to external loads, close to maximum permissible design values. The required functional properties of transformable-volume structures are ensured on the basis of applying surface engineering methods, whose effectiveness is difficult to confirm as there is no possibility to reproduce the space environment factors complex under the terrestrial conditions. The method for verification of applied technologies regarding the modification of surface properties was described. It was based on the comparison of finite-element and experimental-computational models of displacements in equivalent fragments of the transformablevolume structures surface. Qualitative and quantitative evaluation of methods is given, allowing changing the rigiditystrength characteristics of transformable-volume structures for space applications without alteration of their mass and compactness.Resumo em Inglês:
ABSTRACT In this paper, different feedback linearization schemes are studied to address the motion planning problem of fixed-wing unmanned aerial vehicles. For a unmanned aerial vehicle model with second-order dynamics, several schemes are studied to make the vehicle (i) fly over and (ii) make a loitering around the objective position. For each scheme, comparisons are made to illustrate the advantages and disadvantages. Lyapunov stability analysis is used to prove the stability of the proposed schemes, and simulation results for some case studies are included to show their feasibility.Resumo em Inglês:
ABSTRACT In this paper, a systematic method to synthesize parallel mechanisms for feed support mechanisms based on screw theory is proposed. First, the motion requirement of the feed support mechanism is studied. Then, a class of parallel mechanisms having a translational motion with different degrees of freedom is synthesized based on the constraint-synthesis method. Then, these parallel mechanisms are modified based on the specificities of deployable mechanisms, and two kinds of mechanisms are selected as the unit for the feed support mechanism. Finally, the deployment ratio of two kinds of mechanisms is optimized. The configurations obtained in this paper can enrich the types of feed support mechanisms.Resumo em Inglês:
ABSTRACT The non-linear estimators are certainly the most important algorithms applied to real problems, especially those involving the attitude estimation of spacecraft. The purpose of this paper was to use real data of sensors to analyze the behavior of Unscented Kalman Filter (UKF) in attitude estimation problems when it is represented in different ways and compare it with the standard estimator for non-linear estimation problems. The robustness of the estimation was performed when this was subjected to imprecise initial conditions. The attitude parametrization was described in Euler angles, quaternion and quaternion incremental. The satellite China-Brazil Earth Resources Satellite and measurements provided by the Satellite Control Center of the Instituto Nacional de Pesquisas Espaciais were considered in the study. The results indicate that the behaviors for both estimators were equivalent for such parameterizations under the same conditions. However, comparing the Unscented Kalman Filter with the standard filter for non-linear systems, Extended Kalman Filter (EKF), it was observed that, in the presence of inaccurate initial conditions, the Unscented Kalman Filter presented a fast convergence whereas Extended Kalman Filter had problems and only converged later on.Resumo em Inglês:
ABSTRACT In CubeSats, because the size is limited, the estimation of the incident solar energy according to the orbital parameters and satellite attitude is more critical for the design process of the electrical power system. This estimation is helpful either for sizing of the power sources and energy storage or for defining the operation modes of the CubeSat with the energy available. This paper describes the kinematic and dynamic equations to derive the CubeSat attitude; similarly, the mathematical models of solar cells and batteries are also derived to calculate the energy harvested and stored. By determining the attitude of a 3U CubeSat over one orbit, we estimated the incident solar energy and thus the energy generated by the solar cells and energy stored in batteries when a direct energy-transfer architecture is used. In addition, these estimations where performed for three orientation scenarios: nadir-pointing, Sun-pointing and free-orientation. The estimated incident average solar energy for the three scenarios indicated that the Sun-pointing and free-orientation scenarios harvest more energy than the nadir-pointing one. This estimation is also helpful to predict the state of charge of the batteries in standby mode, allowing for determination of the time required for charging the batteries and, hence, the operating modes of the CubeSat. We expect to include the consumed energy while considering all of the operating modes of the satellite as well as different orbital parameters.Resumo em Inglês:
ABSTRACT This article deals with the problem of Earth’s magnetic field sensors calibration in the context of low-cost nanosatellites’ navigation systems. The attitude of space vehicles can be determined from the state estimation using information from three-axis inertial and non-inertial sensors. This study considers a three-axis solid-state magnetometer. In the vehicle itself, the presence of ferrous materials and electronic devices creates disturbances, distorting the measured field. The sensor precision can be enhanced through calibration methods which calculate the systematic error. The objective here is to study and implement calibration combining a geometric method and the TWOSTEP algorithm. The methodology is based on numerical simulations, with the development of a database of the Earth’s magnetic field along the vehicle orbit, and experimental tests using a nanosatellite mockup, containing an embedded processor Arduino MEGA 2560 platform and the magnetometer HMC5843.