ISRN Aerospace Engineering The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Attitude and Vibration Control of Flexible Spacecraft Using Singular Perturbation Approach Thu, 29 May 2014 13:09:11 +0000 This paper addresses a composite two-time-scale control system for simultaneous three-axis attitude maneuvering and elastic mode stabilization of flexible spacecraft. By choosing an appropriate time coordinates transformation system, the spacecraft dynamics can be divided into double time-scale subsystems using singular perturbation theory (SPT). Attitude and vibration control laws are successively designed by considering a time bandwidths separation between the oscillatory flexible parts motion describing a fast subsystem and rigid body attitude dynamics as a slow subsystem. A nonlinear quaternion feedback control, based on modified sliding mode (MSM), is chosen for attitude control design and a strain rate feedback (SRF) scheme is developed for suppression of vibrational modes. In the attitude control law, the modification to sliding manifold for slow subsystem ensures that the spacecraft follows the shortest possible path to the sliding manifold and highly reduces the switching action. Stability proof of the overall closed-loop system is given via Lyapunov analysis. The proposed design approach is demonstrated to combine excellent performance in the compensation of residual flexible vibrations for the fully nonlinear system under consideration, as well as computational simplicity. Morteza Shahravi and Milad Azimi Copyright © 2014 Morteza Shahravi and Milad Azimi. All rights reserved. Combination of Two Nonlinear Techniques Applied to a 3-DOF Helicopter Thu, 17 Apr 2014 13:06:49 +0000 A combination of two nonlinear control techniques, fractional order sliding mode and feedback linearization control methods, is applied to 3-DOF helicopter model. Increasing of the convergence rate is obtained by using proposed controller without increasing control effort. Because the proposed control law is robust against disturbance, so we only use the upper bound information of disturbance and estimation or measurement of the disturbance is not required. The performance of the proposed control scheme is compared with integer order sliding mode controller and results are justified by the simulation. P. Ahmadi, M. Golestani, S. Nasrollahi, and A. R. Vali Copyright © 2014 P. Ahmadi et al. All rights reserved. Enhancing the Supersonic Wind Tunnel Performance Based on Plenum Temperature Control Wed, 02 Apr 2014 00:00:00 +0000 The application of fuzzy logic controllers (FLCs) to the control of nonlinear processes, typically controlled by a human operator, is a topic of much study. In this paper, the design and application of a FLC is discussed to control the plenum chamber temperature for a blowdown supersonic wind tunnel (BSWT) with the aim of achieving the accurate and desired results. In this regard, first, a nonlinear mathematical model of special BSWT is developed in Matlab/Simulink software environment. Next, an artificially intelligent controller is designed using fuzzy logic approach. For this purpose, a proportional-derivative FLC (PD-FLC) system is developed in the Simulink toolbox to control the plenum stagnation temperature using a heater upstream of the plenum chamber. Finally, the system simulation results inside of the temperature and pressure controllers in comparison with the experimental run are presented. The results for Mach 2.5 blowdown run show the great performance of the Wind Tunnel Simulator Model and its temperature controller system. A. Nazarian Shahrbabaki, M. Bazazzadeh, A. Shahriari, and M. Dehghan Manshadi Copyright © 2014 A. Nazarian Shahrbabaki et al. All rights reserved. Satellite Attitude Control Using Analytical Solutions to Approximations of the Hamilton-Jacobi Equation Thu, 20 Feb 2014 05:59:29 +0000 The solution to the Hamilton-Jacobi equation associated with the nonlinear control problem is approximated using a Taylor series expansion. A recently developed analytical solution method is used for the second-, third-, and fourth-order terms. The proposed controller synthesis method is applied to the problem of satellite attitude control with attitude parameterization accomplished using the modified Rodrigues parameters and their associated shadow set. This leads to kinematical relations that are polynomial in the modified Rodrigues parameters and the angular velocity components. The proposed control method is compared with existing methods from the literature through numerical simulations. Disturbance rejection properties are compared by including the gravity-gradient and geomagnetic disturbance torques. Controller robustness is also compared by including unmodeled first- and second-order actuator dynamics, as well as actuation time delays in the simulation model. Moreover, the gap metric distance induced by the unmodeled actuator dynamics is calculated for the linearized system. The results indicated that a linear controller performs almost as well as those obtained using higher-order solutions for the Hamilton-Jacobi equation and the controller dynamics. Stefan LeBel and Christopher J. Damaren Copyright © 2014 Stefan LeBel and Christopher J. Damaren. All rights reserved. Condition Based Maintenance Optimization of an Aircraft Assembly Process Considering Multiple Objectives Tue, 11 Feb 2014 09:29:43 +0000 The Commercial Aircraft Cooperation of China (COMAC) ARJ21 fuselage’s final assembly process is used as a case study. The focus of this paper is on the condition based maintenance regime for the (semi-) automatic assembly machines and how they impact the throughput of the fuselage assembly process. The fuselage assembly process is modeled and analyzed by using agent based simulation in this paper. The agent approach allows complex process interactions of assembly, equipment, and maintenance to be captured and empirically studied. In this paper, the built network is modeled as the sequence of activities in each stage, which are parameterized by activity lead time and equipment used. A scatter search is used to find multiobjective optimal solutions for the CBM regime, where the maintenance related cost and production rate are the optimization objectives. In this paper, in order to ease computation intensity caused by running multiple simulations during the optimization and to simplify a multiobjective formulation, multiple Min-Max weightings are used to trace Pareto front. The empirical analysis reviews the trade-offs between the production rate and maintenance cost and how sensitive the design solution is to the uncertainties. J. Li, T. Sreenuch, and A. Tsourdos Copyright © 2014 J. Li et al. All rights reserved. Designing Stipulated Gains of Aircraft Stability and Control Augmentation Systems for Semiglobal Trajectories Tracking Thu, 30 Jan 2014 07:16:33 +0000 The main objective of the current investigation is to provide a simple procedure to select the controller gains for an aircraft with a largely wide complex flight envelope with different source of nonlinearities. The stability and control gains are optimally devised using genetic algorithm. Thus, the gains are tuned based on the information of a single designed mission. This mission is assigned to cover a wide range of the aircraft’s flight envelope. For more validation, the resultant controller gains were tested for many off-designed missions and different operating conditions such as mass and aerodynamic variations. The results show the capability of the proposed procedure to design a semiglobal robust stability and control augmentation system for a highly maneuverable aircraft such as F-16. Unlike the gain scheduling and other control design methodologies, the proposed technique provides a semi-global single set of gains for both aircraft stability and control augmentation systems. This reduces the implementation efforts. The proposed methodology is superior to the classical control method which rigorously requires the linearization of the nonlinear aircraft model of the investigated highly maneuverable aircraft and eliminating the sources of nonlinearities mentioned above. Mohamed Mostafa Y. B. Elshabasy, Yongki Yoon, and Ashraf Omran Copyright © 2014 Mohamed Mostafa Y. B. Elshabasy et al. All rights reserved. Approximate Solutions to Nonlinear Optimal Control Problems in Astrodynamics Tue, 01 Oct 2013 13:29:36 +0000 A method to solve nonlinear optimal control problems is proposed in this work. The method implements an approximating sequence of time-varying linear quadratic regulators that converge to the solution of the original, nonlinear problem. Each subproblem is solved by manipulating the state transition matrix of the state-costate dynamics. Hard, soft, and mixed boundary conditions are handled. The presented method is a modified version of an algorithm known as “approximating sequence of Riccati equations.” Sample problems in astrodynamics are treated to show the effectiveness of the method, whose limitations are also discussed. Francesco Topputo and Franco Bernelli-Zazzera Copyright © 2013 Francesco Topputo and Franco Bernelli-Zazzera. All rights reserved. Noncrystalline Binder Based Composite Propellant Tue, 24 Sep 2013 10:55:33 +0000 This study reports on propellants based on cross-linked HTPE binder plasticized with butyl nitroxyethylnitramine (BuNENA) as energetic material and HP 4000D as noncrystalline prepolymer. This binder was conducted with solid loading in the 85%. The results showed an improvement in processability, mechanical properties and burning rate. In addition, its propellant delivers (about 6 seconds) higher performance (specific impulse) than the best existing composite solid rocket propellant. Thermal analyses have performed by (DSC, TGA). The thermal curves have showed a low glass transition temperature () of propellant samples, and there was no sign of binder polymer crystallization at low temperatures (−50°C). Due to its high molecular weight and unsymmetrical or random molecule distributions, the polyether (HP 4000D) has been enhanced the mechanical properties of propellants binder polymer over a large range of temperatures [−50, 50°C]. The propellants described in this paper have presented high volumetric specific impulse (>500 s·gr·cc−1). These factors combined make BuNENA based composite propellant a potentially attractive alternative for a number of missions demanding composite solid propellants. Mohamed Abdullah, F. Gholamian, and A. R. Zarei Copyright © 2013 Mohamed Abdullah et al. All rights reserved. Nonlinear Control of a Satellite Electrical Power System Based on the Sliding Mode Control Mon, 16 Sep 2013 11:21:11 +0000 The power electronic interface between a satellite electrical power system (EPS) with a photovoltaic main source and battery storage as the secondary power source is modelled based on the state space averaging method. Subsequently, sliding mode controller is designed for maximum power point tracking of the PV array and load voltage regulation. Asymptotic stability is ensured as well. Simulation of the EPS is accomplished using MATLAB. The results show that the outputs of the EPS have good tracking response, low overshoot, short settling time, and zero steady-state error. The proposed controller is robust to environment changes and load variations. Afterwards, passivity based controller is provided to compare the results with those of sliding mode controller responses. This comparison demonstrates that the proposed system has better transient response, and unlike passivity based controller, the proposed controller does not require reference PV current for control law synthesis. Mohammad Rasool Mojallizadeh and Bahram Karimi Copyright © 2013 Mohammad Rasool Mojallizadeh and Bahram Karimi. All rights reserved. Cooperative Object Manipulation by a Space Robot with Flexible Appendages Wed, 11 Sep 2013 15:03:53 +0000 Modelling and control of rigid-flexible multibody systems is studied in this paper. As a specified application, a space robotic system with flexible appendages during a cooperative object manipulation task is considered. This robotic system necessitates delicate force exertion by several end-effectors to move an object along a desired path. During such maneuvers, flexible appendages like solar panels may get stimulated and vibrate. This vibrating motion will cause some oscillatory disturbing forces on the spacecraft, which in turn produces error in the motion of the end-effectors of the cooperative manipulating arms. In addition, vibration control of these flexible members to protect them from fracture is another challenging problem in an object manipulation task for the stated systems. Therefore, the multiple impedance control algorithm is extended to perform an object manipulation task by such complicated rigid-flexible multibody systems. This extension in the control algorithm considers the modification term which compensates the disturbing forces due to vibrating motion of flexible appendages. Finally, a space free-flying robotic system which contains two 2-DOF planar cooperative manipulators, appended with two highly flexible solar panels, is simulated. Obtained results reveal the merits of the developed model-based controller which will be discussed. P. Zarafshan and S. Ali A. Moosavian Copyright © 2013 P. Zarafshan and S. Ali A. Moosavian. All rights reserved. Novel Multipoint Relays Scheme Based on Hybrid Cost Function Thu, 22 Aug 2013 09:11:23 +0000 When evaluating the performance of QoS protocols, a number of factors have a major impact on the results. Notably, QoS is emphasized when mobile ad hoc networks (MANETs) are employed into aerospace fields. Some of these parameters are a particular manifestation of characteristics of the MANET environment, such as mobility. Indeed, our proposal is a novel multipoint relays scheme based on hybrid cost function taking into account QoS criteria and avoiding mobility effect of nodes, especially those selected as MPRs. A comprehensive simulation study was conducted to evaluate the performance of the proposed scheme. Performance results show that RQMPR outperforms existing MPR heuristic adopted in the ad hoc routing protocols OLSR and QOLSR, in terms of packet delivery and average end-to-end delay. Ali Ouacha, Bachir Bouamoud, Ahmed Habbani, and Jamal El Abbadi Copyright © 2013 Ali Ouacha et al. All rights reserved. A Numerical and Experimental Study of the Aerodynamics and Stability of a Horizontal Parachute Sun, 18 Aug 2013 08:45:44 +0000 The flow past a parachute with and without a vent hole at the top is studied both experimentally and numerically. The effects of Reynolds number and vent ratio on the flow behaviour as well as on the drag coefficient are examined. The experiments were carried out under free-flow conditions. In the numerical simulations, the flow was considered as unsteady and turbulent and was modelled using the standard - turbulence model. The experimental results reveal good agreement with the numerical ones. In both the experiments and numerical simulations, the Reynolds number was varied from 85539 to 357250 and the vent ratio was increased from zero to 20%. The results show that the drag coefficient decreases by increasing the Reynolds number for all the cases tested. In addition, it was found that at low and high Reynolds numbers, the parachutes, respectively, with 4% vent ratio and without vent are deemed more efficient. One important result of the present work is related to the effect of vent ratio on the stability of the parachute. Mazyar Dawoodian, Abdolrahman Dadvand, and Amir Hassanzadeh Copyright © 2013 Mazyar Dawoodian et al. All rights reserved. Lateral Control Implementation for an Unmanned Aerial Vehicle Tue, 11 Jun 2013 10:38:41 +0000 This paper presents practical aspects of guidance and control design for UAV and its flight test results. The paper focuses on the lateral-directional control and guidance aspects. An introduction to the mission and guidance problem is given first. Waypoints for straight and turning flight paths are defined. Computation of various flight path parameters is discussed, including formulae for real-time calculation of down-range (distance travelled along the desired track), cross-track deviation, and heading error of the vehicle; these are then used in the lateral guidance algorithm. The same section also describes how to make various mission-related decisions online during flight, such as when to start turning and when a waypoint is achieved. The lateral guidance law is then presented, followed by the design of a robust multivariable controller for roll control and stability augmentation. The controller uses the ailerons and rudder for control of roll angle and stabilization of yaw rate of the vehicle. The reference roll angle is generated by the nonlinear guidance law. The sensors available on-board the vehicle do not measure yaw rate; hence, a practical method of its estimation is proposed. The entire guidance and control scheme is implemented on the flight control computer of the actual aerial vehicle and taken to flight. Flight test results for different mission profiles are presented and discussed. R. Samar, M. Zamurad Shah, and M. Nzar Copyright © 2013 R. Samar et al. All rights reserved. Experimental Evaluation of the Density Ratio Effects on the Cooling Performance of a Combined Slot/Effusion Combustor Cooling System Thu, 30 May 2013 15:45:57 +0000 The purpose of this study is to investigate the effects of coolant-to-mainstream density ratio on a real engine cooling scheme of a combustor liner composed of a slot injection and an effusion array with a central dilution hole. Measurements of heat transfer coefficient and adiabatic effectiveness were performed by means of steady-state thermochromic liquid crystals technique; experimental results were used to estimate, through a 1D thermal procedure, the Net Heat Flux Reduction and the overall effectiveness in realistic engine working conditions. To reproduce a representative value of combustor coolant-to-mainstream density ratio, tests were carried out feeding the cooling system with carbon dioxide, while air was used in the main channel; to highlight the effects of density ratio, tests were replicated using air both as coolant and as mainstream and results were compared. Experiments were carried out imposing values of effusion blowing and velocity ratios within a range of typical modern engine working conditions. Results point out the influence of density ratio on film cooling performance, suggesting that velocity ratio is the driving parameter for the heat transfer phenomena; on the other hand, the adiabatic effectiveness is less sensitive to the cooling flow parameters, especially at the higher blowing/velocity ratios. Antonio Andreini, Gianluca Caciolli, Bruno Facchini, and Lorenzo Tarchi Copyright © 2013 Antonio Andreini et al. All rights reserved. A Model Matching STR Controller for High Performance Aircraft Mon, 20 May 2013 11:34:12 +0000 This paper presents a development, as well as an investigation of a Model Matching Controller (MMC) design based on the Self-Tuning Regulator (STR) framework for high performance aircraft with direct application to an F-16 aircraft flight control system. In combination with the Recursive Least Squares (RLS) identification, the MMC is developed and investigated for effectiveness on a detailed model of the aircraft. The popular robust Quantitative Feedback Theory (QFT) controller is also outlined and used to represent a baseline controller, for performance comparison during four simulated test flight maneuvers. In each of the four maneuvers, the proposed MMC provided consistently stable and satisfactory performance, including the challenging pull-up and pushover maneuvers. The baseline stationary controller has been found to become unstable in two of the four maneuvers tested. It also performs satisfactorily-to-arguably poorly in the remaining two as compared to the MMC. Simulation results presented in this investigation support a clear argument that the proposed MMC provides superior performance in the realm of automatic flight control. Adel A. Ghandakly and Jason A. Reed Copyright © 2013 Adel A. Ghandakly and Jason A. Reed. All rights reserved. Wake Measurements behind an Oscillating Airfoil in Dynamic Stall Conditions Mon, 22 Apr 2013 10:06:23 +0000 The unsteady flow field in the wake of an NACA 23012 pitching airfoil was investigated by means of triple hot-wire probe measurements. Wind tunnel tests were carried out both in the light and deep dynamic stall regimes. The analysis of the wake velocity fields was supported by the measurements of unsteady flow fields and airloads. In particular, particle image velocimetry surveys were carried out on the airfoil upper surface, while the lift and pitching moments were evaluated integrating surface pressure measurements. In the light dynamic stall condition, the wake velocity profiles show a similar behaviour in upstroke and in downstroke motions as, in this condition, the flow on the airfoil upper surface is attached for almost the whole pitching cycle and the airloads show a small amount of hysteresis. The deep dynamic stall measurements in downstroke show a large extent of the wake and a high value of the turbulent kinetic energy due to the passage of strong vortical structures, typical of this dynamic stall regime. The comprehensive experimental database can be considered a reference for the development and validation of numerical tools for such peculiar flow conditions. A. Zanotti, G. Gibertini, D. Grassi, and D. Spreafico Copyright © 2013 A. Zanotti et al. All rights reserved.