Current Issue : October - December Volume : 2017 Issue Number : 4 Articles : 5 Articles
The shape-based method can provide suitable initial guesses for trajectory optimization, which are useful for quickly converging\na more accurate trajectory. Combined with the optimal control theory, an optimized shape-based method using the finite Fourier\nseries is proposed in this paper. Taking the flight time-fixed case and the time-free case into account, respectively, the optimized\nshape-based method, which considers the first-order optimal necessary conditions, can guarantee that not only an orbit designed\nduring the preliminary phase is optimal, but also the thrust direction is not constrained to be tangential. Besides, the traditional\nshape-based method using the finite Fourier series, in which the thrust direction is constrained to be tangential, is developed for\nthe time-free case in this paper. The Earth-Mars case and the LEO-GEO case are used to verify the optimized shape-based method�s\nfeasibility for time-fixed and time-free continuous low-thrust trajectory design between circular coplanar orbits, respectively.The\noptimized shaped-based method can design a lower cost trajectory....
The aim of this paper is the evaluation of several pilot models found in the literature, suited for helicopter pilot-assisted and\npilot-induced oscillations analyses.Three main topics are discussed: (i) sensitivity of rotorcraft-pilot couplings simulations on the\napplication of the different pilot models available in the literature; (ii) effect of vehiclemodeling on active pilotmodeling; (iii) effects\nof interactions between active and passive pilot models.The focus is on hovering flight, where a specific adverse rotorcraft-pilot\ncoupling phenomenon, the vertical bounce, may occur. Pilot models are coupled with a comprehensive aeroservoelastic model of a\nmid-weight helicopter.The numerical investigations are performed in frequency domain, in terms of eigenanalysis and frequency\nresponse analysis....
TheBrazilian hypersonic scramjet aerospace vehicle 14-X B is a technological demonstrator of a hypersonic airbreathing propulsion\nsystem based on the supersonic combustion (scramjet) to be tested in flight into the Earthââ?¬â?¢s atmosphere at an altitude of 30 km\nand Mach number 7. The 14-X B has been designed at the Prof. Henry T. Nagamatsu Laboratory of Aerothermodynamics and\nHypersonics, Institute for Advanced Studies (IEAv), Brazil.The IEAv T3 Hypersonic Shock Tunnel is a ground-test facility able to\nproduce high Mach number and high enthalpy flows in the test section close to those encountered during the flight of the 14-X B\ninto the Earthââ?¬â?¢s atmosphere at hypersonic flight speeds.A1mlong stainless steel 14-X Bmodel was experimentally investigated at T3\nHypersonic Shock Tunnel, for freestreamMach numbers ranging from7 to 8. Static pressuremeasurements along the lower surface\nof the 14-X B, as well as high-speed Schlieren photographs taken from the 5.5âË?Ë? leading edge and the 14.5âË?Ë? deflection compression\nramp, provided experimental data. Experimental data was compared to the analytical theoretical solutions and the computational\nfluid dynamics (CFD) simulations, showing good qualitative agreement and in consequence demonstrating the importance of these\nmethods in the project of the 14-X B hypersonic scramjet aerospace vehicle....
In this study, the distribution of surface heat transfer induced by dual side-jets injected into a hypersonic flow has been visualized\nusing a temperature sensitive paint. The experiments were performed in both tandem and parallel injector arrangements, and\nthe spacing between the injection holes was taken as a parameter in each arrangement. As a result, the aerodynamic heating in\nthe separated region of the boundary layer and in the horseshoe vortex was clearly visualized. In the tandem arrangements, heat\ntransfer remarkably increased immediately upstreamof the front injector.Thedistributions and the intensity of surface heat transfer\nwere similar to those caused by the single injection. On the other hand, in the parallel arrangements, the extent of the separation\nnearly doubled, and the maximum heat flux decreased to less than half of that from the single injection. The global distribution\nof heat transfer varied significantly as the injector spacing was changed. When the injectors were positioned with a large spacing,\nthe interaction between the side-jets was relatively lowered, and thus distribution, as for the single injector, was induced around\neach injection hole individually. In contrast, with a short spacing, the dual injection behaved as a single obstacle.The most effective\nreduction of maximum heat flux was achieved with an intermediate injector spacing....
Spinsonde is a chute-free vertical retardation technique specifically developed\nfor fixed-wing unmanned aircraft to acquire accurate measurement of vertical\nwind speed profile for meteorological applications. Key advantages of spinsonde\nover the expendable chute-operated dropsondes are the ability to acquire\nmulti-cycle measurement, efficient use of payload capacity and cost-effectiveness.\nThis work proposes the concept of ââ?¬Å?rotosondeââ?¬Â, which is the\nspinsonde equivalent for unmanned helicopters. Computer simulations are\ncarried out to evaluate the performance of the rotosonde and results indicate\nthat the measured speed generally correlates with the wind speed to within Ã?±3\nkmÃ?·hâË?â??1 even for intensities in excess of 180 kmÃ?·hâË?â??1. The profound implication\nof this work is that unmanned helicopters can now be considered for important\nfield of studies such as cyclogenesis given their reliability to operate in\ngusty wind conditions in remote oceans, particularly during docking and\nlaunching from carriers....
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