Resumo em Inglês:

ABSTRACT: Iron oxide is a mineral compound that shows different polymorphic forms, including hematite (α-Fe2O3), magnetite (Fe3O4) and maghemite (γ-Fe2O3). Solid propulsion technology nanoparticulate materials, such as hematite and maghemite, exhibit high performance on thermal decomposition of ammonium perchlorate. The enhanced catalytic effect of metallic iron oxide nanoparticles is attributed to their particle size, more active sites and high surface area, which promotes more gas adsorption during thermal oxidation reactions. Nowadays, metallic iron nanoparticles can be synthesized via numerous methods, such as co-precipitation, sol-gel, microemulsion, or thermal decomposition. Although there are data on these synthetic methods in the literature, there is a lack of details related to nanoparticulate oxides and to their characterization techniques. In this context, this short review based on scientific papers, including data from the last two decades, presents methods for obtaining nanoparticulate iron oxides as well as the main aspects of the different characterization techniques and also about the decomposition aspects of these nanomaterials. Morphologies and structures of iron oxides can be characterized through transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. As for textural properties, they are usually determined by physical adsorption techniques.

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ABSTRACT: Composite propellant mainly consists of two parts, binder matrix (prepolymer, plasticizer, cross linker, antioxidant and curative etc.) and solid ingredients (oxidizer, metal fuel, burn rate modifier, combustion stabilizer etc.). Its processing involves several stages like ingredient preparation (grinding, 1.1 Hazard Division - 1.1 HD), mixing (1.1 HD), casting (1.1 HD), curing (1.3 HD) and extraction (1.3 HD). Each and every process is very hazardous. Removal of any of the mentioned step will be a great achievement for solid rocket motor processing. Mandrel is used to give proper grain geometry. But for metal mandrel, its extraction process (1.3 HD) is very dangerous. Proper safety precaution should be taken to perform the said operation. Also, for a metal mandrel, it is very difficult to develop intricate grain geometry due to extraction problem. This paper mainly deals with casting techniques of propellants (case bonded or cartridge loaded) with a chemically collapsible mandrel. This mandrel is collapsed in presence of suitable chemicals, hence extraction step (1.3 HD) becomes simpler. As the extraction process is very easy, intricate grain geometry can be developed in solid rocket motor. The mandrel is cheap, recycleable and relatively lightweight compared to the metal mandrel, thus handling becomes very easy. The mandrel material and the dissolution solvent have no effect on the propellant, which will be confirmed by evaluation of physicochemical as well as ballistic properties measurement.

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ABSTRACT: During field trials, it was observed that the delay of ignition of electro-explosive devices (EED) depends on ratings of power supplies or dynamo and also on the firing cable lengths. The change in ignition delay of EEDs due to altered supplied current will detoriate the repeatability of sequence of actions in time-critical armament applications. In order to study, supplement and analyze this observation, the measurement of electrical energy required for EEDs ignition is necessary. The electrical energy of EEDs has been determined experimentally by instrumentation and measurement setup using hall sensor and photo detector. The hall sensor is used to measure the actual current passing through EEDs when power supply is applied to them. Photo detector is used to detect the flash produced during EED ignition. By conducting repeated trials, it was observed that this method is reliable to determine the electrical energy required for EEDs ignition. With this parameter, the actual current to be supplied and the pulse width of supplied current for repeated ignition delays can be determined. Knowing the electrical energy of a particular EED by the proposed method, the required firing cable length and power supply for ignition of critical delay applications can be selected. This method also helps to design explosive-based ignition systems in defence applications.

Resumo em Inglês:

ABSTRACT: The focus of this study is to evaluate the effect of carboxyl and amino functionalization of multiwalled carbon nanotubes on the mechanical property of the epoxy resin filled with modified carbon nanotubes. The carbon nanotubes were treated with sulfuric and nitric acids and also with hexamethylenediamine. The presence of acid and amine chemical groups on the carbon nanotube surface was confirmed by X-ray photoelectron spectroscopy. The composites were produced with epoxy resin and modified carbon nanotubes. Vickers hardness tests were carried out on the composites and neat resin. The results showed an increase of hardness in the composite prepared with functionalized carbon nanotubes. This phenomenon is due to the fact that the chemical interaction between modified carbon nanotube and epoxy resin is much stronger than between pristine carbon nanotube and epoxy resin. This stronger interaction is related to the presence of functionalized carbon nanotubes.

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ABSTRACT: The electromechanical impedance method has been seen as a promising tool for structural health monitoring regarding different types of structures and purposes. Most importantly, this method can be used in real-time applications. Frequently, massive, high-cost, single-channel impedance analyzers are used to process the time domain data, aiming at obtaining the complex, frequency-dependent electromechanical impedance functions and therefore infer about the presence, position and extent of an existing damage. However, for large structures, it is desirable to deploy an array of piezoelectric transducers over the area to be monitored and interrogate these transducers successively, in order to increase the probability of successful detection of damage at an early phase. The literature describes many miniaturized systems that can monitor large structures, however, presenting serious restrictions on data acquisition capabilities. This paper presents a hardware that is not limited to any data acquisition restriction, exhibiting an innovative way to measure the electromechanical impedance of multiplexed bonded transducers. Each logical block of the proposed architecture is presented in detail. The proposed system not only avoids costly fast Fourier transform analyzers/ algorithms, but also evades high-speed data acquisition hardware. A prototype using inexpensive integrated circuits and a digital signal processor was built and tested for two different types of structures: an aluminum beam and an aircraft aluminum panel. Simulated damages were introduced to each structure, and the detection performance of the prototype was tested. The actual prototype uses a universal serial bus connection to communicate with a personal computer.

Resumo em Inglês:

ABSTRACT: Through electromagnetic simulation, the present work reports on a comparative study of the enhanced radiation properties of a standard X-band horn antenna loaded by a wire medium. Acting as an artificial dielectric, the wire medium consists of an array of parallel metallic wires installed into the antenna with the wires oriented in the direction of the incident electric field. As compared with the properties of the air horn antenna, the wire-medium antenna produces an appreciable reduction in the side-lobe levels with an improvement of 10 dB at 8.87 GHz in the first side lobe. For the wire-medium antenna, the E -and H -plane radiation patterns look similar, a property desired for precision radar and radiometric mapping systems.

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ABSTRACT: The original radar cross section data or some rough models are often used to estimate a given aircraft target detection probability. The calculation results may not be very accurate as targets are different from one another and the real radar detection process is complex. A new method for radar cross section model generation is proposed and it takes the random factors like air turbulence into account; this makes it conform to the reality. In addition, this radar cross section model can be directly applied to the radar detection process to calculate the detection probability of a specific aircraft at any attitude. Four typical aerial vehicles are taken as examples to demonstrate this method and information such as detection probability, signal to noise ratio and detection distance. Target's instantaneous probability of being tracked, which corresponds to target's detection probability, can also be calculated. Using these calculation results, we can compare two different aircrafts' stealth performance in detail or optimize an aircraft's flight path.

Resumo em Inglês:

ABSTRACT: The present article deals with the identification, at the same time, of aircraft stability and control parameters taking into account dynamic damping derivatives. Such derivatives, due to the rate of change of the angle of attack, are usually neglected. So the damping characteristics of aircraft dynamics are attributed only on pitch rate derivatives. To cope with the dynamic effects of these derivatives, authors developed devoted procedures to estimate them. In the present paper, a complete model of aerodynamic coefficients has been tuned-up to identify simultaneously the whole set of derivatives. Besides, in spite of the employed reduced order model and/or decoupled dynamics, a six degrees of freedom model has been postulated without decoupling longitudinal and lateral dynamics. A recursive non-linear filtering approach via Extended Kalman Filter is proposed, and the filter tuning is performed by inserting the effects of dynamic derivatives into the mentioned mathematical model of the studied aircraft. The tuned-up procedure allows determining with noticeable precision the stability and control derivatives. In fact, either by activating maneuvers generated by all the control surfaces or by inserting noticeable measurement noise, the identified derivatives show very small values of standard deviation. The present study shows the possibility to identify simultaneously the aircraft derivatives without using devoted procedures and decoupled dynamics. The proposed technique is particularly suited for on-line para-metrical identification of Unmanned Aerial Systems. In fact, to estimate both state and aircraft parameters, low power and time are required even using measurement noises typical of low-cost sensors.

Resumo em Inglês:

ABSTRACT: In this study, an accurate computational algorithm in the context of immersed boundary methods is developed and used to analyze an incompressible flow around a pitching symmetric airfoil at Reynolds number (Re = 255). The boundary conditions are accurately implemented by an iterative procedure applied at each time step, and the pressure is also updated simultaneously. Flow phenomena, observed at different oscillation frequencies and amplitudes, are numerically modeled, and the physics behind the associated vortex dynamics is explained. It is shown that there are four flow regimes associated with four wake structures. These include three symmetric flow regimes, with adverse, favorable and no vortex effects, and an asymmetric flow regime. The phenomena associated with these flow regimes are discussed, and the critical or transitional values of the Strouhal (St) and normalized amplitude (AD) numbers are presented. It is shown that, at the fixed pitching amplitude, AD = 0.71, the transition from adverse (drag generation) to favorable (thrust generation) symmetric flow regime occurs at St = 0.23. Moreover, at this particular amplitude, transition from symmetric to asymmetric regime occurs at St = 0.48. It is also shown that, at St = 0.22, the wake is always deflected and the flow is asymmetric for large enough amplitudes AD > 2. The dipole vortices and lift generation are two characteristics of asymmetric vortex street. This numerical study also reveals that the initial phase angle has a dominant effect on the appearance of dipole vortices and vortex sheet deflection direction. Numerical results are in good agreement with the available experimental data.

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ABSTRACT: A two-dimensional second-order positivity-preserving finite volume upwind scheme is developed for a semi-coupled algorithm involving the air and droplet flow fields in the Eulerian frame, which shares the grid for each phase. Special emphasis is placed on the computational modeling, which is induced from a strongly-coupled algorithm that satisfies the strict hyperbolicity and its numerical scheme based on the Harten-Lax-van Leer-Contact solver preserving the positivity to handle multiphase flow in the Eulerian frame. The proposed modeling associated with the semi-coupled algorithm including the Navier-Stokes and droplet equations takes into account different boundary conditions on the solid surface for each phase. The verification and validation studies show that the new scheme can solve the air and droplet flow fields in fairly good agreement with the exact analytical solutions and experimental data. In particular, it accurately predicted the maximum value of the droplet impingement intensity near the stagnation region and the droplet impingement area.

Resumo em Inglês:

ABSTRACT: The interannual variability of precipitation in El Niño/Southern Oscillation-neutral years was studied for the Centro de Lançamento de Alcântara region. Monthly precipitation, sea surface temperature, wind at 925 hPa and outgoing longwave radiation data from various gridded datasets for the 1951-2010 period (60 years) were used. The data grouping was based on terciles. For the Centro de Lançamento de Alcântara in El Niño/Southern Oscillation-neutral years, March is the month of the rainy quarter (March to May) when the interhemispheric gradient of the sea surface temperature anomalies over the Atlantic (GRAD) and the atmospheric circulation at 925 hPa over the Centro de Lançamento de Alcântara were able to best explain the variability of precipitation. In this month, the wind direction at 925 hPa was the factor that explained the highest fraction of precipitation variance (40%), followed by GRAD (30%) and the wind magnitude (20%). For the Centro de Lançamento de Alcântara, in general, above-average precipitation was related to weak north-northeasterly low-level winds and southward GRAD, while below-average precipitation was related to strong east-northeasterly low-level winds and northward GRAD. These features were related to an eastward expansion of the Amazon convection towards the northern Northeast Brazil and might be related to a slight southward displacement of the Intertropical Convergence Zone in above-average precipitation years.

Resumo em Inglês:

ABSTRACT: This paper brings the first results concerning a new analytic model to evaluate atmospheric dispersion in rocket launch scenarios, namely Generalized Integral Laplace Transform Technique for Rocket effluent dispersion model. The model is constituted by three different modules, being two pre-processors (micrometeorological parameters and deposition parameters) and the dispersion program. The dispersion calculations are made through the Generalized Integral Laplace Transform Technique solution of the two-dimensional, time-dependant, advectiondiffusion-deposition equation. The results show a set of simulations using data from the Chuva Project from the Centro de Lançamento de Alcântara for both stable and unstable planetary boundary layers, in order to evaluate model performance and illustration.