Current Issue : July - September Volume : 2014 Issue Number : 3 Articles : 5 Articles
An adaptive modified two-stage linear Kalman filtering algorithm is utilized to identify the loss of control effectiveness and the\nmagnitude of low degree of stuck faults in a closed-loop nonlinear B747 aircraft. Control effectiveness factors and stuck magnitudes\nare used to quantify faults entering control systems through actuators. Pseudorandomexcitation inputs are used to help distinguish\npartial loss and stuck faults. The partial loss and stuck faults in the stabilizer are isolated and identified successfully....
The presented research validates the capability of a loosely coupled computational fluid dynamics (CFD) and comprehensive\nrotorcraft analysis (CRA) code to calculate the flowfield around a rotor and test standmounted inside a wind tunnel.TheCFD/CRA\npredictions for the Full-Scale UH-60A Airloads Rotor inside the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-\nFoot Wind Tunnel at NASA Ames Research Center are compared with the latest measured airloads and performance data. The\nstudied conditions include a speed sweep at constant lift up to an advance ratio of 0.4 and a thrust sweep at constant speed up to\nand including stall. For the speed sweep, wind tunnel modeling becomes important at advance ratios greater than 0.37 and test\nstandmodeling becomes increasingly important as the advance ratio increases. For the thrust sweep, both the wind tunnel and test\nstand modeling become important as the rotor approaches stall. Despite the beneficial effects of modeling the wind tunnel and test\nstand, the new models do not completely resolve the current airload discrepancies between prediction and experiment....
Increasing the computational efficiency of attitude estimation is a critical problem related to modern spacecraft, especially for\nthose with limited computing resources. In this paper, a computationally efficient nonlinear attitude estimation strategy based\non the vector observations is proposed.The Rodrigues parameter is chosen as the local error attitude parameter, to maintain the\nnormalization constraint for the quaternion in the global estimator. The proposed attitude estimator is performed in four stages.\nFirst, the local attitude estimation error system is described by a polytopic linear model. Then the local error attitude estimator\nis designed with constant coefficients based on the robust H2 filtering algorithm. Subsequently, the attitude predictions and the\nlocal error attitude estimations are calculated by a gyro based model and the local error attitude estimator. Finally, the attitude\nestimations are updated by the predicted attitude with the local error attitude estimations. Since the local error attitude estimator is\nwith constant coefficients, it does not need to calculate thematrix inversion for the filter gain matrix or update the Jacobianmatrixes\nonline to obtain the local error attitude estimations. As a result, the computational complexity of the proposed attitude estimator\nreduces significantly. Simulation results demonstrate the efficiency of the proposed attitude estimation strategy....
The More Electrical Aircraft concept requires electronic devices able to efficiently and safely convert electrical power between\ndifferent voltage levels. Theentire realization of a bidirectional DC/DC converter, fromdesign to validation phase, is here discussed\nin detail. First, a boost full bridge electrical structure is selected, adopting a Parallel Input Parallel Output (PIPO) interleaving\ntechnique and an optimal turns ratio selection for the transformers in order to reduce both weight and size of the equipment. Next,\nmodulation schemes in both step-down and step-up modes are discussed. Successively ad hoc PI regulators for both operative\nmodes are presented. A key idea of the paper is that the converter behavior must be related not only to the control strategy but also\nto a global supervision logic able to safely conduct the converter operations and to react from external stimuli.Thus, a finite state\nmachine (FSM) approach is employed. An innovative strategy called buffermode is presented, defined as an intelligent combination\nof buck and boost modes. Extensive simulations and experimental results are shown, in order to confirm the effectiveness of the\nproposed approach....
The application and workflow of Computational Fluid Dynamics (CFD)/Computational Structure Dynamics (CSD) on solving the\nstatic aeroelastic problem of a slender rocket are introduced. To predict static aeroelastic behavior accurately, two-way coupling\nand inertia relief methods are used to calculate the static deformations and aerodynamic characteristics of the deformed rocket.\nThe aerodynamic coefficients of rigid rocket are computed firstly and compared with the experimental data, which verified the\naccuracy of CFD output.The results of the analysis for elastic rocket in the nonspinning and spinning states are compared with the\nrigid ones. The results highlight that the rocket deformation aspects are decided by the normal force distribution along the rocket\nlength. Rocket deformation becomes larger with increasing the flight angle of attack. Drag and lift force coefficients decrease and\npitching moment coefficients increase due to rocket deformations, center of pressure location forwards, and stability of the rockets\ndecreases. Accordingly, the flight trajectory may be affected by the change of these aerodynamic coefficients and stability....
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