Current Issue : January - March Volume : 2017 Issue Number : 1 Articles : 5 Articles
A guidance problem for impact time and angle control applicable to cooperative attack is considered based on the sliding mode\ncontrol. In order to satisfy the impact angle constraint, a line-of-sight rate polynomial function is introduced with four tuning\nparameters. And the time-to-go derivative with respect to a downrange orientation is derived to minimize the impact time error.\nThen the slidingmode control surface with impact time and angle constraints is constructed using nonlinear engagement dynamics\nto provide an accurate solution. The proposed guidance law is easily extended to a nonmaneuvering target using the predicted\ninterception point. Numerical simulations are performed to verify the effectiveness of the proposed guidance law for different\nengagement scenarios....
A guidance law for attacking ground target based on motion camouflage strategy is proposed in this paper. According to the relative\nposition between missile and target, the dual second-order dynamics model is derived. The missile guidance condition is given\nby analyzing the characteristic of motion camouflage strategy. Then, the terminal guidance law is derived by using the relative\nmotion of missile and target and the guidance condition. In the process of derivation, the three-dimensional guidance law could\nbe designed in a two-dimensional plane and the difficulty of guidance law design is reduced. A two-dimensional guidance law for\nthree-dimensional space is derived by bringing the estimation for target maneuver. Finally, simulation for the proposed guidance\nlaw is taken and compared with pure proportional navigation. The simulation results demonstrate that the proposed guidance law\ncan be applied to air-to-ground missiles....
The work presented in this paper has two major aspects: (i) investigation of a simple,\nyet efficient model of the NREL (National Renewable Energy Laboratory) 5-MW reference wind\nturbine; (ii) nonlinear control system development through a real-time nonlinear receding horizon\ncontrol methodology with application to wind turbine control dynamics. In this paper, the results\nof our simple wind turbine model and a real-time nonlinear control system implementation are\nshown in comparison with conventional control methods. For this purpose, the wind turbine control\nproblem is converted into an optimization problem and is directly solved by the nonlinear backwards\nsweep Riccati method to generate the control protocol, which results in a non-iterative algorithm.\nOne main contribution of this paper is that we provide evidence through simulations, that such an\nadvanced control strategy can be used for real-time control of wind turbine dynamics. Examples are\nprovided to validate and demonstrate the effectiveness of the presented scheme....
Over the last decade, aircraft morphing technology has drawn a lot of attention in the\naerospace community, because it is likely to improve the aerodynamic performance and the versatility\nof aircraft at different flight regimes. With the fast paced advancements in this field, a parallel\nstream of research is studying different materials and designs to develop reliable morphing skins.\nA promising candidate for a viable morphing skin is the sliding skin, where two or more rigid\nsurfaces remain in contact and slide against each other during morphing. The overlapping between\neach two panels create a backward-facing step on the airfoil surface which has a critical effect on\nthe aerodynamics of the wing. This paper presents a numerical study of the effect of employing\na backward-facing step on the suction side of a National Advisory Committee for Aeronautics\n(NACA) 2412 airfoil at a high Reynolds number of 5.9 Ã?â?? 106. The effects of the step location on the\nlift coefficient, drag coefficient and critical angle of attack are studied to find a favorable location for\nthe step along the chord-wise direction. Results showed that employing a step on the suction side of\nthe NACA 2412 airfoil can adversely affect the aforementioned aerodynamic properties. A drop of\n21.1% in value of the lift coefficient and an increase of 120.8% in the drag coefficient were observed in\ncase of a step located at 25% of the chord length. However, these effects are mitigated by shifting the\nstep location towards the trailing edge. Introducing a step on the airfoil caused the airfoilââ?¬â?¢s thickness\nto change, which in turn has affected the transition point of the viscous boundary layer from laminar\nto turbulent. The location of the step, prior or post the transition point, has a noteworthy effect on the\npressure and shear stress distribution, and consequently on the values of the lift and drag coefficients....
The present study aimed at studying the transition of annular lift fan aircraft through\ncomputational fluid dynamics (CFD) simulations. The oscillations of lift and drag, the optimization\nfor the figure of merit, and the characteristics of drag, yawing, rolling and pitching moments in\ntransition are studied. The results show that a two-stage upper and lower fan lift system can generate\noscillations of lift and drag in transition, while a single-stage inner and outer fan lift system can\neliminate the oscillations. The characteristics of momentum drag of the single-stage fans in transition\nare similar to that of the two-stage fans, but with the peak of drag lowered from 0.63 to 0.4 of\nthe aircraft weight. The strategy to start transition from a negative angle of attack âË?â??21ââ??¦ further\nreduces the peak of drag to 0.29 of the weight. The strategy also reduces the peak of pitching torque,\nwhich needs upward extra thrusts of 0.39 of the weight to eliminate. The peak of rolling moment in\ntransition needs differential upward thrusts of 0.04 of the weight to eliminate. The requirements for\nextra thrusts in transition lead to a total thrustââ?¬â??weight ratio of 0.7, which makes the aircraft more\nefficient for high speed cruise flight (higher than 0.7 Ma)....
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