Resumo em Inglês:

ABSTRACT This paper presents an analysis of the scenario of small satellites and its correspondent launch vehicles. The miniaturization of electronics, together with reliability and performance increase as well as reduction of cost, have allowed the use of commercials-off-the-shelf in the space industry, fostering the Smallsat use. An analysis of the launched Smallsats during the last 20 years is accomplished and the main factors for the Smallsat (r)evolution, outlined. Based on historic data, future scenarios for different mass categories of Smallsats are presented. An analysis of current and future launch vehicles reveals that we are currently in a phase of transition, where old launch vehicles get retired and new ones enter the market. However, the satellite launch vehicle business has been established to carry payloads of thousands of kilos into low Earth orbit and has not adjusted itself to the market of Smallsats. As a result, there is only 1 launch vehicle for dedicated Smallsat launches commercially available, but it carries a high price tag. Several small low-cost launch vehicles under development are identified and the challenges to overcome, discussed. Since these small launch vehicles have similar complexity as huge launch vehicles, high development costs are intrinsic, leading to a high specific price (USD/kg payload).

Resumo em Inglês:

ABSTRACT In this study conservation equations were implemented along the boundaries via ghost control-volume immersed boundary method. The control-volume finite-element method was applied on a cartesian grid to simulate 2-D incompressible flow. In this approach, mass and momentum equations were conserved in the whole domain including boundary control volumes by introducing ghost-control volume concept. The Taylor problem was selected to validate the present method. Four different case studies of Taylor problem encompassing both inviscid and viscous flow conditions in ordinary and 45º rotated grid were used for more investigation. Comparisons were made between the results of the present method and those obtained from the exact solution. Results of the present method indicated accurate predictions of the velocity and pressure fields in midline, diagonal, and all boundaries. The agreement between the results of the present method and the exact solution was very good throughout the whole temporal domain. Furthermore, comparison of the rate of kinetic energy decay in viscous case showed same level of agreement between the results.

Resumo em Inglês:

Abstract: The present paper investigates the high-order spectral finite volume method with emphasis on applicability aspects for compressible flows. The intent is to improve the understanding and implementation of numerical techniques related to high-order unstructured grid schemes. In that regard, a hierarchical moment limiter and high-order mesh capability are developed for a 2-dimensional Euler spectral finite volume solver. The limiter formulation and geometry interpreter for high-order mesh generation are new contributions for the spectral finite volume method. Literature test cases are evaluated to assess the interaction of curved mesh, limiter and spatial reconstruction features of the spectral finite volume scheme. An order-of-accuracy study is presented along with steady and unsteady problems with strong shock waves and other discontinuities typical of compressible flows. Moreover, second, third and fourth-order spatial resolution analyses are explored and the spectral finite volume results are compared with those from different numerical methods.

Resumo em Inglês:

ABSTRACT In the present study relative state transition matrix was obtained. It matches the relative motion of 2 satellites while including the oblate perturbation. The used formulation applies the geometric approach and is in Cartesian frame. The relative state transition matrix uses absolute state transition matrix of individual satellites. Thereon, simplification in computing methods and on-board implementation at controls are explored in a leader/follower coordination method. Numerical experiments illustrate the accuracy when the baseline separation is equal to 2 km and eccentricity is 0.005 and 0.05 for all the inclinations.

Resumo em Inglês:

ABSTRACT In this paper, 12 new aerofoils with varying thicknesses for an aft-swept flying wing unmanned air vehicle have been designed using a MATLAB tool which has been developed in-house. The tool consists of 2 parts in addition to the aerodynamic solver XFOIL. The first part generates the aerofoil section geometry using a combination of PARSEC and Bezier-curve parameterisation functions. PARSEC parametrisation has been used to represent the camber line while the Bezier-curve has been used to select the thickness distribution. This combination is quite efficient in using an optimisation search process because of the capability to define a range of design variables that can quickly generate a suitable aerofoil. The second part contains the optimisation code using a genetic algorithm. The primary target here was to design a number of aerofoils with low pitching moment, suitable for an aft-swept flying wing configuration operating at low Reynolds number in the range of about 0.5 × 106. Three optimisation targets were set to achieve maximum aerodynamic performance characteristics. Each individual target was run separately to design several aerofoils of different thicknesses that meet the target criteria. According to the set of result obtained so far, the initial observation of the aerodynamic performance of the newly designed aerofoils is that the lift/drag ratio in general is higher than that of the existing ones used in many current-generation high-altitude long-endurance aircraft. Another observation is that increasing the maximum thickness of the aerofoil leads to a decrease in the maximum lift/drag ratio. In addition, as expected, this ratio sharply drops after the maximum value of some of these aerofoils.

Resumo em Inglês:

ABSTRACT Industry and universities around the world invest time and money to develop digital computer programs to predict gas turbine performance. This study aims to demonstrate a brand new digital model developed with the ability to simulate gas turbine real time high fidelity performance. The model herein described run faster than 30ms per point, which is compatible with a high-definition video refresh rate: 30 frames per second. This user-friendly model, built in Visual Basic in modular structure, can be easily configured to simulate almost all the existing gas turbine architectures (single, 2 or 3 shaft engines mixed or unmixed flows). In addition, its real time capability enables simulations with the pilot in the loop at earlier design phases when their feedback may lead to design changes for improvements or corrections. In this paper, besides the model description, it is presented the model run time capability as well as a comparison of the simulated performance with a commercial gas turbine tool for single, 2 and 3 shaft engine architecture.

Resumo em Inglês:

ABSTRACT This article presents a retirement analysis model for aircraft fleets. By employing a greedy algorithm, the presented solution is capable of identifying individually weak assets in a fleet of aircraft with inhomogeneous historical utilization. The model forecasts future retirement scenarios employing user-defined decision periods, informed by a cost function, a utility function and demographic inputs to the model. The model satisfies first-order necessary conditions and uses cost minimization, utility maximization or a combination of the 2 as the objective function. This study creates a methodology for applying a greedy algorithm to a military fleet retirement scenario and then uses the United States Air Force A-10 Thunderbolt II fleet for model validation. It is shown that this methodology provides fleet managers with valid retirement options and shows that early retirement decisions substantially impact future fleet cost and utility.

Resumo em Inglês:

ABSTRACT The breeze potential along the Brazilian northern and northeastern coast was studied using wind data from the Climate Forecast System Reanalysis for the period between 1980 and 2010. March and September were considered, which are representative of the rainy and dry (or less rainy) periods, respectively. The Brazilian northern and northeastern coast is composed by meridionally oriented coastlines (Amapá State coast and eastern coast of Northeast Brazil) and a zonally oriented coastline (Brazilian northern coast east of Marajó Island). Along the meridionally oriented coastlines, the breeze potential was mainly related to the zonal wind and extended inland over 1 - 2° from the shore. The daily zonal wind cycle maximum (minimum), which represents the land (sea) breeze potential, occurred at ~0700 UTC (~1900 UTC). Along the zonally oriented coastline, the breeze potential was mainly related to the meridional wind and extended inland and offshore over 2 - 3° from the shore. At the shore, the daily meridional wind cycle maximum (minimum), which represents the land (sea) breeze potential, occurred at ~1000 UTC (~2200 UTC). Phase propagation occurred from the shore inland in March and September and also offshore in September. In general, for the entire Brazilian northern and northeastern coast, the breeze potential frequency was higher in September (20 - 25 days per month). In March, while the frequency slightly decreased over the meridionally oriented coastlines (to 15 - 20 days per month), the frequency sharply decreased over the zonally oriented coastlines to 5 - 10 days per month in landside coastal areas and vanished in seaside coastal areas. Higher frequency was generally related to lower interannual variability, and there was significant correlation between the interannual variability of the frequency and oceanic indices, along specific coastal areas. The features of the breeze potential areas obtained in this study complement the results from others and provide a more complete depiction of breeze features along the entire Brazilian northern and northeastern coast.

Resumo em Inglês:

ABSTRACT: This study aims to evaluate the dynamic mechanical properties of a binder, used in composite propellants, with increasing amount of different solid fillers. Dynamic Mechanical Analysis (DMA) is performed to determine the region of glass-rubber transition temperature (Tg). Further parameters were obtained from the description of the loss factor curves (tanδ) with models based on exponentially modified Gauss (EMG) distribution function. Polyurethane binders employing the polyol HTPB and diisocyanate were filled with 20, 40, and 60 mass-% of ammonium perchlorate (AP), aluminum (Al) or cyclotrimethylene trinitramine (RDX) particles, using fine and coarse mean sizes. A special turning device manufactured by Fraunhofer ICT was installed inside the curing oven in order to avoid sedimentation during curing. The cured composites were characterized by DMA in torsion mode from -100 °C to 70 °C. The good homogeneous distribution of fillers in the samples was evaluated by computational X-ray micro-tomography. The data on tanδ showed a complex structure describable at first with 2 overlapping peaks. The peak at lower temperatures is due to mobility of unrestricted binder parts (Tgunr) and the second broader peak at high temperature is due to mobility of restricted binder parts (Tgres). Results of tanδ, calculated areas of EMG curves and apparent activation energies of the distinct relaxation processes indicate that Al particles have higher interaction with HTPB-based polyurethane than AP and RDX. Probably Al is bonded to the binder network via isocyanate coupling with OH groups present in the surface. Ammonium perchlorate and cyclotrimethylene trinitramine particle sizes and its morphology influenced the viscoelastic properties. AP and RDX cause more changes in intensity of first peak of loss factor than Al. Increasing amount of these both particles enhances storage (G’) and loss (G”) shear moduli. As a whole tanδ intensity is lowered in the main peak and Al showed an intensity increase in the second apparent peak.

Resumo em Inglês:

ABSTRACT: Sandwich structures are nowadays widely used due its excellent characteristics of matching light weight with high bend stiffness. However the complex nature of its composition turns the estimation of its mechanical elastic properties challenging. The objective of the present article is to propose an analytical/experimental model to estimate the orthotropic elastic properties of this composite material. To accomplish this objective a theory of anisotropic plates is used together to an extensometric experimental approach. A sandwich laminate specimen, instrumented with strain gages, was submitted through pure bending loading by a mechanical testing machine on a 4-point bending apparatus. The result of this research was the determination of 4 orthotropic elastic properties of the sandwich laminate specimen, namely: the longitudinal and transversal Young moduli, the shear modulus, and the Poisson's ratio.

Resumo em Inglês:

ABSTRACT: Composite laminates display a complex mechanical behavior due to their microstructure, with a through-thickness variation of the displacement and stress fields that depends on the fiber orientation in each layer. Aiming to develop reduced-order numerical models mimicking the real response of composite structures, we investigated the capability and accuracy of finite element analyses coupling layered shell and solid kinematics. This study represents the first step of a work with the goal of accurately matching stress evolution in regions close to possible impact locations, where delamination is expected to take place, with reduced computational costs. Close to such locations, a 3-D modeling is adopted, whereas in the remainder of the structure, a less computationally demanding shell modeling is chosen. To test the coupled approach, results of numerical simulations are presented for a quasi-statically loaded cross-ply orthotropic plate, either simply supported or fully clamped along its boundary.