Current Issue : April - June Volume : 2015 Issue Number : 2 Articles : 5 Articles
This paper develops a novel autopilot design method for blended missiles with aerodynamic control surfaces and lateral jets. Firstly,\nthe nonlinear model of blended missiles is reduced into a piecewise affine (PWA) model according to the aerodynamics properties.\nSecondly, based on the equivalence between the PWA model and mixed logical dynamical (MLD) model, the MLD model of\nblended missiles is proposed taking into account the on-off constraints of lateral pulse jets. Thirdly, a hybrid model predictive\ncontrol (MPC) method is employed to design autopilot. Finally, simulation results under different conditions are presented to show\nthe effectiveness of the proposed method, which demonstrate that control allocation between aerodynamic control surfaces and\nlateral jets is realized by adjusting the weighting matrix in an index function....
We developed a global model aiming to study discharges in CO2 under various conditions, pertaining to a large spectrum of\npressure, absorbed energy, and feeding values. Various physical conditions and form factors have been investigated. The model\nwas applied to a case of radiofrequency discharge and to helicon type devices functioning in low and high feed conditions. In\ngeneral, main charged species were found to be CO2\n+ for sufficiently low pressure cases and O? for higher pressure ones, followed\nby CO2\n+, CO+, andO2\n+ in the latter case.Dominant reaction is dissociation of CO2 resulting into COproduction. Electronegativity,\nimportant for radiofrequency discharges, increases with pressure, arriving up to 3 for high flow rates for absorbed power of 250W,\nand diminishes with increasing absorbed power. Model results pertaining to radiofrequency type plasma discharges are found in\nsatisfactory agreement with those available from an existing experiment. Application to low and high flow rates feedings cases of\nhelicon thruster allowed for evaluation of thruster functioning conditions pertaining to absorbed powers from50Wto 1.8kW.The\nmodel allows for a detailed evaluation of the CO2 potential to be used as propellant in electric propulsion devices....
Chaotic and periodic motions of an FGM cylindrical panel in hypersonic flow are investigated. The cylindrical panel is also\nsubjected to in-plane external loads and a linear temperature variation in the thickness direction. The temperature dependent\nmaterial properties of panel which are assumed to be changed through the thickness direction only can be determined by a simple\npower distribution in terms of the volume fractions. With Hamilton�s principle for an elastic body, a nonlinear dynamical model\nbased on Reddy�s first-order shear deformation shell theory and von Karman type geometric nonlinear relationship is derived in\nthe form of partial equations. A third-order piston theory is adopted to evaluate the hypersonic aerodynamic load. Here, Galerkin�s\nmethod is employed to discretize this continuous nonlinear dynamic system to ordinary differential governing equations involving\ntwo degrees of freedom. The chaotic and periodic response are studied by the direct numerical simulation method for influences of\ndifferentMach number and the value of in-plane load.The bifurcations, Poincare section, waveform, and phase plots are presented....
Energy efficiency plays important role in aeroelastic design of flying wing aircraft and may be attained by use of lightweight\nstructures as well as solar energy. NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft) is a newly developed\ncomputer program which uses a nonlinear composite beam theory that eliminates the difficulties in aeroelastic simulations of\nflexible high-aspect-ratio wings which undergoes large deformation, as well as the singularities due to finite rotations. NATASHA\nhas shown that proper engine placement could significantly increase the aeroelastic flight envelope which typically leads to more\nflexible and lighter aircraft. The areas of minimum kinetic energy for the lower frequency modes are in accordance with the zones\nwith maximum flutter speed and have the potential to save computational effort. Another aspect of energy efficiency for High\nAltitude, Long Endurance (HALE) drones stems from needing to minimize energy consumption because of limitations on the\nsource of energy, that is, solar power.NATASHA is capable of simulating the aeroelastic passive morphingmaneuver (i.e.,morphing\nwithout relying on actuators) and at as near zero energy cost as possible of the aircraft so as the solar panels installed on the wing\nare in maximum exposure to sun during different time of the day....
3D transonic flow over swept and unswept wings with an J-78 airfoil at spanwise sections is studied numerically at negative and\nvanishing angles of attack. Solutions of the unsteady Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume\nsolver on unstructured meshes. The numerical simulation shows that adverse Mach numbers, at which the lift coefficient is highly\nsensitive to small perturbations, are larger than those obtained earlier for 2D flow. Due to the larger Mach numbers, there is an\nonset of self-exciting oscillations of shock waves on the wings. The swept wing exhibits a higher sensitivity to variations of the\nMach number than the unswept one...
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