Department of Aerospace Engineering
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Our goal at the Department of aerospace engineering is to nurture competent, creative, and dedicated graduates who can play a significant role in scientific, industrial, and social fields. Our academic programs emphasize the latest scientific resources, applied research, and continuous interaction with the industry, preparing students for both professional careers and further academic pursuits.
Articles
WSEAS Transactions on Systems (11092777)5(12)pp. 2875-2880
Although direct and indirect methods have been widely applied to trajectory optimization problems, optimization results for these methods are sensitive to initial solutions in some cases. For the purpose of finding an appropriate initial solution of rendezvous problem to calculus-of-variations-based trajectory optimization, a numerical trajectory optimization method using a real-coded genetic algorithm is considered. The genetic algorithms are not hampered by ill-behaved gradients and are relatively insensitive to problems with a small radius of convergence. Those have been successfully applied to numerical optimization problems. The use of calculus of variations within the genetic algorithm optimization routine increases the precision of the final solution to levels uncommon for a genetic algorithm alone.
Proceedings of the IASTED International Conference on Modelling, Identification, and Control, MIC (22935126)pp. 247-252
In this paper, a 3-axis motion simulator, as a three degreeof-freedom test stand for aircraft instrument testing and calibrating within a Hardware-In-The-Loop Environment, is studied for control analyses. A mathematical model of the simulator mechanical structure is derived and then linearized using Taylor series expansion around the instantaneous equilibrium point which is the aircraft timedependant Euler angles and their rates. Also, the aircraft, earth and atmosphere are modeled in Matlab using Aerosim blocksets. A linear quadratic regulator (LQR) control law is developed to track the attitude, angular rates and angular acceleration of the Navion aircraft in a complicated maneuver. The control law is shown to be efficient in the presence of atmospheric turbulence, and robust to unknown bounded disturbances. The accuracy and correctness of the proposed control system is verified by the simulation.
Transactions of the Japan Society for Aeronautical and Space Sciences (05493811)50(170)pp. 225-230
An explicit guidance law is developed for a reentry vehicle. Motion is constrained to a three-dimensional Bezier curve. Acceleration commands are derived by solving an inverse problem related to Bezier parameters. A comparison with pure proportional navigation shows the same accuracy, but a higher capability for optimal trajectory to some degree. Other advantages such as trajectory representation with minimum parameters, applicability to any reentry vehicle configuration and any control scheme, and Time-to-Go independency make this guidance approach more favorable. © 2008 The Japan Society for Aeronautical and Space Sciences.
This paper presents the conceptual design of a sun-synchronous LEO Earth Observation microsatellite incorporated with Multidisciplinary Design Optimization (MDO) approach. The objective is to develop a structured system level for the design process including mission design parameters such as required Revisit Time (RT), and accessible Ground Sampling Distance (GSD). In order to apply MDO with the design process a sizing tool has been developed based on both mission and system design-estimating relationships. In addition, the conceptual design data and concepts of the microsatellites with the similar mission have been used to achieve a reliable sizing tool. The objective is to minimize the total mass of the satellite. A Genetic Algorithm (GA) is coupled with the developed sizing tool to obtain optimized design parameters for the microsatellite. © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Aerospace Science and Technology (12709638)12(3)pp. 241-247
An explicit guidance law that maximizes terminal velocity is developed for a reentry vehicle to a fixed target. Motion is constrained to an optimal, three-dimensional Bezier curve. Acceleration commands are derived by solving an inverse problem related to Bezier parameters. An optimal Bezier curve is determined by solving a real-coded genetic algorithm. For online trajectory generation, optimal trajectory is approximated by fixing the second control point of the Bezier curve. The approximated trajectory is compared with the pure proportional navigation, genetic algorithm and direct transcription's solutions. The near optimal terminal velocity solution compares very well with these solutions. The approach robustness is examined by Monte Carlo simulation. © 2007 Elsevier Masson SAS. All rights reserved.
Inverse Problems in Science and Engineering (17415985)16(2)pp. 187-198
An explicit guidance law that maximizes terminal velocity is developed for a re-entry vehicle to a fixed target. Motion is constrained to an optimal, 3D Bezier curve. Acceleration commands are derived by solving an inverse problem related to Bezier parameters. An optimal Bezier curve is determined by solving a real-coded genetic algorithm. For online trajectory generation, optimal trajectory is approximated by fixing the second control point of the Bezier curve. The near optimal trajectory is compared with the genetic solution and with a form of proportional navigation. The near optimal terminal velocity solution compares very well with the genetic solution and is superior to the proportional navigation one. The approach robustness is examined by Monte Carlo simulation.
Analytica Chimica Acta (18734324)(2)
A simple dispersive liquid-liquid microextraction methodology based on the application of 1-hexylpyridinium hexafluorophosphate [HPy][PF6] ionic liquid (IL) as an extractant solvent was proposed for the preconcentration of trace levels of zinc as a prior step to determination by flame atomic absorption spectrometry (FAAS). Zinc was complexed with 8-hydroxyquinoline (oxine) and extracted into ionic liquid. Some effective factors that influence the microextraction efficiency such as pH, oxine concentration, amount of IL, ionic strength, temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and the enhancement factor were 0.22 μg L-1 and 71, respectively. The relative standard deviation (RSD) for six replicate determinations of 13 μg L-1 Zn was 1.92%. In order to validate the developed method, a certified reference material (NIST SRM 1549) was analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the trace determination of zinc in water and milk samples. © 2009 Elsevier B.V. All rights reserved.
In this paper, the problem of attitude control of a 1D nonlinear flexible spacecraft is investigated. Two nonlinear controllers are presented. The first controller is based on dynamic inversion, while the second one is composed of dynamic inversion and μ-synthesis controllers. The extension of dynamic inversion approach to flexible spacecraft is impeded by the non-minimum phase characteristics when the panel tip position is taken as the output of the system. To overcome this problem, the controllers are designed by utilizing the modified output re-definition approach. It is assumed that only one torque on the hub is used. Actuator saturation is considered in the design of controllers. The performances of the proposed controllers are compared in terms of nominal performance, robustness to uncertainties, vibration suppression of panel, sensitivity to measurement noise, environment disturbance and nonlinearity in large maneuvers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a nonlinear model of the spacecraft are performed. Simulation results show the ability of the proposed controller in tracking the attitude trajectory and damping panel vibration. It is also verified that the perturbations, environment disturbance and measurement errors have only slight effects on the tracking and damping responses. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Scientia Iranica (23453605)17(2 A)pp. 81-88
Double Concave Friction Pendulum (DCFP) bearing is a new generation of friction isolator that contains two separate concave sliding surfaces with different properties. Accommodating enhanced performance, compared to the Friction Pendulum System (FPS), is one of the most important benefits of DCFP. Herein, the seismic behavior of structures isolated by DCFP bearings is compared with the response of the same buildings using the FPS bearing. Accordingly, a series of nonlinear dynamic analyses are carried out under ensembles of ground motions at three different hazard levels (SLE, DBE and MCE). Moreover, the adaptive behavior of DCFP and its advantages in protecting secondary systems is investigated. The probability of exceedance curves of peak roof acceleration, peak inter-story drift and peak isolator displacement is compared for two types of isolation system. The result supports the advantages of DCFP isolation systems. © Sharif University of Technology.
In this research, we combined ionic liquid-based dispersive liquid-liquid micro-extraction (IL-based DLLME) with stopped-flow spectrofluorometry (SFS) to evaluate the concentration of aluminum in different real samples at trace level. 1-Hexylpyridinium hexafluorophosphate [Hpy][PF6] ionic liquid and 8-hydroxyquinoline (oxine), which forms a highly fluorescent complex with Al3+, were chosen as the extraction solvent and chelating agent, respectively. The hydrophobic Al-oxine complex was extracted into the [Hpy][PF6] and separated from the aqueous phase. Then, the concentration of the enriched aluminum in the sediment phase was determined by SFS. Some effective parameters that influence the SFS signals and the micro-extraction efficiency, such as the suction and sending time, the concentration of the chelating agent, pH, the amount of the ionic liquid, the type of disperser solvent and diluting agent, ionic strength, extraction time, equilibration temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and enrichment factor were 0.05 μg L-1 and 100, respectively. The relative standard deviation (RSD) for six replicate determinations of 6 μg L-1 Al was 1.7%. The calibration graph using the pre-concentration system was linear in the range of 0.06-15 μg L-1 with a correlation coefficient of 0.9989. The developed method was validated by the analysis of certified reference materials and applied successfully to the determination of aluminum in several water, fruit juice and food samples. © 2010 Elsevier B.V. All rights reserved.
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