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Aerospace Science and Technology - Volume:11 Issue: 1, Winter and Spring 2017

Journal of Aerospace Science and Technology
Volume:11 Issue: 1, Winter and Spring 2017

  • تاریخ انتشار: 1395/01/20
  • تعداد عناوین: 6
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  • S.Hamid Jalali -Naini *, Sh. Ahmadi Darani Page 1
    In this paper, the preferred region of design parameters for quasi-normalized equations of single-axis attitude control of rigid spacecraft using pulse-width pulse-frequency modulator (PWPFM) is presented for rest-to-rest maneuvers. Using the quasi-normalized equations for attitude control reduces the system parameters, that is, the moment of inertia, the filter gain, and the maximum torque of modulator are merged to other parameters and the total number of parameters is reduced. Therefore, the computational burden is decreased and moreover, the results are usable for grouped parameters, regardless of the value of each parameter separately. The optimization is carried out by grid search method with the performance index of fuel consumption or number of thruster firings for a range of inputs. Finally, the suggested upper and lower bounds of parameters are obtained based on the optimization results.
    Keywords: Spacecraft Attitude Control, Pulse, Width Pulse, Frequency Modulator, Quasi, Normalization, Optimization
  • H. Shahverdi *, A. S. Nobari, H. Bahrami Torabi Page 9
    The aim of this paper is to provide an aeroelastic computational tool which determines the induced wing loads during flapping flight. For this purpose, a Finite Element (FE) code based on a four-node plate bending element formulation is developed to simulate the aeroelastic behavior of flapping wings in low incompressible flow. A quasi-steady aerodynamic model is incorporated into the aeroelastic model for predicting the aerodynamic loads. In order for the validation of the present tool, the modal and dynamic response analyses of a rotating flat plate under pure flapping motion are firstly examined and the effect of dynamic stiffness on the plate response, due to the presence of shortening terms in the equations of motion, is also investigated. Finally, the aeroelastic analysis of an insect-like wing under a specified motion is carried out and the induced loads including shear force and bending moment at the wing root are determined. The obtained results signify the contribution of wing structural elasticity to the induced loads.
    Keywords: Aerodynamic, Aeroelastic, Flapping wing, Finite element, Dynamic stiffness
  • S.A. Hosseini Kordkheili *, A. Merati Page 21
    Thermal buckling behavior of truncated conical liner reinforced by laminated composite is investigated in the presence of a general initial imperfection. For this purpose, the method of virtual work and first-order strain-deformation shell theory are employed to extract equilibrium equations. To this end, a finite element code is developed using the 3D 8-node shell element with six degrees of freedom as an analysis tool. Also, the variation of thickness in conical composite shell is considered. Several problems withc-c, s-s, c-f boundary conditions are solved using code to highlight the effect of imperfection size and position. In this way, the most effective imperfection at each boundary condition is determined.
    Keywords: Thermal buckling, Composite shell, Finite element method, Local imperfection, Truncated conical liner
  • M. Malekzadeh * Page 35
    In this article, the issue of attitude control and active vibration suppression of a nonlinear flexible spacecraft is assessed through piezoelectric patches as actuator and sensors. Two controller loops are applied: the inner loop, to make the panel vibration damped through piezoelectric patches; and the outer loop, to perform spacecraft maneuver using the reaction wheel acting on the hub. An optimal controller is designed in the inner loop and two robust controllers are designed as the outer loop, which are used interchangeably. One is a high-ordersliding mode controller using super twisting algorithm and the other is a nonsingular terminal sliding mode controller. With respect to the non-minimum phase properties of the system, if the panel deflection is defined as the output, the output redefinition approach is introduced.The performances of the proposed controllers are compared in terms of tracking attitude trajectory, panel vibration suppression, robustness towards uncertainties, sensor noise, disturbances and nonlinearity in large maneuvers.
    Keywords: Active control, Flexible Spacecraft, piezoelectric patches, super twisting algorithm, nonsingular terminal sliding mode, output redefinition approach
  • A. R. Jahangirian *, M. Ebrahimi Page 47
    An efficient method for scattering Genetic Algorithm (GA) individuals in the design space is proposed to accelerate airfoil shape optimization. The method used here is based on the variation of the mutation rate for each gene of the chromosomes by taking feedback from the current population. An adaptive method for airfoil shape parameterization is also applied and its impact on the optimum design and convergence of the optimization process isinvestigated. In order to demonstrate the efficiency of the proposed method, a geometric inverse design using Genetic Algorithm is carried out and the capability of the method for producing airfoil shapes is assessed. The performance of the method is further evaluated by an aerodynamic shape optimization. Results indicate the merits of the method in increasing the maximum objective value about7percent as well as decreasing the total computational time up to28 percent.
    Keywords: Genetic Algorithm, Shape Optimization, Adaptive Mutation, Computational Fluid Dynamics
  • I. Mohammadzaman *, H. Dehghani Firouzabadi Page 61
    In this paper, a robust autopilot is proposed using stable interpolation based on Youla parameterization. The most important condition of stable interpolation between local controllers is the preservation of stability so that each local controller can ensure stability for an open neighborhood around a nominal point. The proposed design used fixed-order robust controller with parameter-dependent central polynomial for each vertex of the polytope to decrease the conservation of each local controller. A stability-preserving gain-scheduled controller was designed using a newly proposed algorithm in the flight envelop for a parameter varying model. The results of simulation confirm the efficiency of the proposed method.
    Keywords: Robust autopilot, stability preserving interpolation, fixed, order controller, parameter, dependent central polynomial