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ABSTRACT: In this work, the Techno-economic Environmental Risk Analysis framework, a multi-disciplinary optimisation tool developed by Cranfield University, is utilised in conjunction with an in-house optimiser to carry out aircraft engine cycle optimisation processes. The central point here is the evaluation of the capabilities of the in-house optimiser for performing this type of optimisation processes. Simplifying hypotheses are thus considered when both defining the aircraft flight trajectory and modelling the different engine configurations analysed. Accordingly, several optimum engine cycles minimising separately three objective functions, (i) specific fuel consumption in cruise, (ii) fuel burned, and (iii) oxides of nitrogen emitted, are determined. The cycle optimisation processes carried out yield results reflecting the general trends expected when optimising according to these objective functions. It follows then that the in-house optimiser is suitable for carrying out gas turbine power plant optimisation processes. It is expected that this optimiser be utilised in future for both optimising the preliminary design of gas turbine engines and determining optimum and "greener" aircraft engine cycles.Resumo em Inglês:
ABSTRACT: Design and development of gas turbine components are a complex multidisciplinary process. At the beginning of the power class definition and engine configuration it is necessary to conduct a market study. The results obtained are used in gas turbine thermodynamic cycle calculations and analysis in order to define the gas turbine design point. Several possible design points are evaluated during this procedure. After this step, the gas turbine components are designed, including: compressor, combustion chamber and turbine. For industrial gas turbine purposes, it is common to use a free turbine after the gas generator, also commonly named power turbine. In this work, a power turbine was initially designed by meanline techniques, considering internal loss mechanisms, to obtain the main dimensions. The geometries of the components were generated in a 3-D environment to make possible the mesh generation, process to discretize the physical domain into a computational domain and use a 3-D Computational Fluid Dynamics tool. The results from the meanline approach and from the 3-D turbulent flow numerical simulations were compared to verify the turbine operational conditions and its predictions at design and off-design conditions. The gas turbine under study is a project, derived from a low thrust turbojet previously developed by Instituto de Aeronáutica e Espaço. The power turbine project uses the same turbojet gas generator, already designed and currently under tests.Resumo em Inglês:
ABSTRACT: The influence of variable-sweep wing on the aircraft's radar cross section (RCS) characteristics has been studied to reduce the aircraft's RCS as well as its detection probability by the hostile radar. With the help of CATIA, a 3-D digital model of the variable-sweep wing aircraft is built to generate a series of digital grids. Using MATLAB, a numerical simulation on the RCS of variable-sweep wing aircraft is conducted based on physical optics (PO) method and equivalent currents method (ECM). The results of mathematical statistics and comparative analysis show that: (i) the RCS peak value in the head direction of the aircraft decreases non-linearly with the sweep angle of the wing's leading edge; (ii) the azimuth angle corresponding to one of the peak values of the aircraft's RCS is equal to the leading edge's sweep angle; (iii) when the leading edge's sweep angle is 33º, the arithmetic average value of the RCS values in the head direction of the aircraft is 0.644% of the average value when the sweep angle is 0º; (iv) the larger the sweep angle is, the lower the probability that the aircraft is detected.Resumo em Inglês:
ABSTRACT: Joints in deployable structures can degrade the stiffness and the stability of spacecraft. In this study, the nonlinear stiffness of spherical joints is investigated. The traditional contact model of spherical joints based on non-conforming contact assumption is presented. A new contact model for spherical joints based on the Winkler model and geometric constraints is established to calculate the stiffness of spherical joints with small clearances. The finite element model (FEM) of spherical joints is built to evaluate the accuracy of the theoretical model. The effects of the clearance and the contact force of spherical joints on the deformation of joints are investigated. When compared with FEM results, the error of the new spherical model is smaller than that of the traditional contact model when the clearance of spherical joint is not excessively large. The new contact model for spherical joint is more accurate than the traditional contact model when the clearance of spherical joint is large.Resumo em Inglês:
ABSTRACT: In recent years, advances in aeronautical engineering field include, among others, the development of increasingly lightweight and flexible materials, allowing better performance of systems in applications such as Unmanned Aerial Vehicles, photographic model airplanes, light weight aircraft etc. This progress, however, can cause difficulties in design and various types of tests, such as those performed in modal analysis, since the instrumentation weight and shape can influence the behavior of very light and aerodynamic structures. This paper proposes a new technique to perform modal analysis in simple structures, eliminating the use of accelerometers, which must be numerous in this type of analysis and have significant weight; the whole structure can be analyzed at the same time, and this is an advantage in comparison with other techniques as vibrometer laser, that analyses one point at a time. The technique in question makes use of infrared imaging, detecting, through the heat, the structure deformation, allowing the trace of its modal shape. For this, a theoretical analysis and a thermomechanical modeling of a known structure are performed, with subsequent test to be validated, and finally the conclusions and suggestions for future work are presented.Resumo em Inglês:
ABSTRACT: The potassium nitrate (KNO3)/sucrose (C12H22O11) propellant, known as KNSu, is traditionally used in rocket studies by amateur groups. Performance tests of KNSu, whose composition is 65 wt% KNO3 and 35 wt% C12H22O11, cold-manufactured by mechanical press, are presented in this paper. The study determines the behaviour of density (ρ) and burning rate (r) as function of compression pressure (Pc) for the propellant grain manufacturing. Forty-four samples were prepared and tested, for seven different values of Pc. It was observed that ρ and r depend on Pc, according to quadratic polynomial functions, and the mass flux per unit area is a constant.Resumo em Inglês:
ABSTRACT: The goal of this study is twofold. The first one is to assess the applicability of approaches based on dynamic-mechanical analysis to investigate the viscoelastic properties of a self-adhesive synthetic rubber. The second goal is to identify the parameters of a viscoelastic model which accurately represents the frequency-dependent mechanical properties. For that purpose, the time-temperature superposition principle is successfully applied to build the master curves of the material up to 1 MHz. The thickness of the samples and the thermal expansion effects are found to have a negligible influence on the mechanical properties measured by dynamic-mechanical analysis. The parameters of a generalized Maxwell model and a fractional derivative model are identified from the obtained master curves and lead to an accurate representation of the frequency-dependent mechanical properties of the rubber.Resumo em Inglês:
ABSTRACT: The atmospheric hypersonic flight of sub-orbital and space vehicles generates aerodynamic heating and high wall heat fluxes, inducing high temperatures on the vehicle's structures and affecting their mechanical behavior, besides degrading the operation of board equipment. Furthermore, since payload preservation is always mandatory, the use of efficient Thermal Protection Systems (TPS) is a key-requirement for any spacecraft design. As an outcome, designing the TPS is a critical aspect of any rocket development program, since an undersized system may result in catastrophic failure, and an oversized one implies increased mass and cost. Sub-orbital platforms are a low-cost alternative for microgravity research. A sub-orbital platform (SARA) is being developed by Instituto de Aeronáutica e Espaço (IAE) for such an application, and its current design uses a conventional layer of cork as TPS to protect its lateral surface, with the trade-off of large mass. Alternatively, a Thermally Integrated Structural Sandwich Core (TISSC), which consists of a structural sandwich panel in a three-layer plate with two face sheets and the core, presents advantages such as lightweight, low maintenance, insulation as well as load bearing capabilities, and low life-cycle cost. In this work, a TISSC is proposed to replace SARA's current TPS. The main contribution of the presented methodology is to couple the aerodynamic heating, heat transfer in porous insulation and thermo-structural analyses of the proposed configuration in order to evaluate the TISSC TPS performance. The results are compared with those obtained for the current SARA TPS design, showing improvements in thermal insulation and structural strength, as well as a remarkable mass reduction.Resumo em Inglês:
ABSTRACT: In this paper, we develop a parametric model method and simulate the deployment mechanism of inflatable antenna structures. Different folded methods are developed for the primary members of inflatable antenna structures, which include inflatable tubes, an inflatable torus, a reflector etc. The unstressed configuration and the folded configuration of these members are modeled parametrically using the developed folded methods. A simulation software is developed for the deployment mechanism of inflatable structures by the improved spring-mass system. The driving forces in the deployment process, i.e. the gas pressure and the moment of the fold hinges, are analyzed for each member. During the development process, self-contact or collision with the membrane occurs. A rule for identifying self-contact elements is applied, and a penalty function method is developed to solve this challenging problem. Finally, the equation of motion is solved using finite difference method. The developed simulation software is validated by simulating a cylindrical inflatable tube that is folded in half, and the simulation agrees well with the experiment. The deployment mechanism of the antenna model similar to that for the Inflatable Antenna Experiment (IAE) is modeled, analyzed and estimated. The deployed configurations and the dynamic parameters of each node are obtained. The numerical simulation results show that the simulation software for the deployment mechanism can correctly predict the deployment process of inflatable antenna structures.Resumo em Inglês:
ABSTRACT: The use of digital simulation has become an essential activity during the development and operation of launch vehicles, due to the complexity of such systems. Of particular interest is the flight dynamics simulation, which investigates the behavior of the vehicle in flight subjected to forces and moments. This work presents a simulation tool suited to perform six degrees-of-freedom flight dynamics investigations of launch vehicles. Developed at the Instituto Nacional de Pesquisas Espaciais (INPE) and the Instituto de Aeronáutica e Espaço (IAE) in Brazil, the tool was implemented following the requirement for flexibility, so that it can be used to simulate different types of launch vehicles. The assessment of the vehicle performance and the vehicle payload capacity are some examples of analysis that can be performed with the tool. A modular programming strategy was employed to assure the tool flexibility. Therefore, the models presented in the tool were implemented as separate modules. The combination of these models can originate flight models of different launch vehicles. Two flight scenarios of Brazilian rockets were simulated and the results were verified against simulation tools already employed by aerospace community. The developed tool showed good agreement with respect to the simulators used to perform the comparison.Resumo em Inglês:
ABSTRACT: This study examines the development of a system that assists in planning flight activities of the Academia da Força Aérea (AFA) so that meteorological data can be used to predict the occurrence of fog. This system was developed in MATLAB 8.0 by applying multilayer perceptron-type artificial neural networks and using an error correction algorithm called backpropagation. The methodology used to implement the network comprises eight input variables, five neurons in the intermediary layer, and one neuron in the output layer, which corresponds to the presence or absence of fog. The fog phenomenon is very important for the study and definition of flight strategic planning. Data taken from 1989 to 2008 and related to the input variables were used for the training and validation of the proposed network. Consequently, the multilayer perceptron network has a 95% reliability compared with the data collected. This high level of reliability is an exceptional result for the management, planning, and decision making team of the AFA strategic group. Thus, it can be concluded that the proposed system is efficient and will subsidize, with good safety margin, AFA's flight activity planning and could also be applied to other air activities in Brazil.Resumo em Inglês:
ABSTRACT: The sensitivity of the planetary boundary layer (PBL) parameterizations is investigated using the hybrid Fifth Generation Penn State University/National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) and its results were compared with observations from two field campaigns held during the dry and wet seasons at the Centro de Lançamento de Alcântara (CLA). The comparisons were made using the integrated zonal and meridional components of observed and forecasted winds. Initially, three boundary layer parameterizations, in addition to the current parameterization, were selected for evaluation: Blackadar (BLK), Medium Range Forecast (MRF), Janjic (ETA) and Burk-Thompson (BT). The MRF and BLK schemes produced better results than the ETA and BT schemes. Nevertheless, MRF and BLK underestimate the zonal and meridional wind components by around 16% in the rainy season and overestimate them by on average 18% in the dry season.