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.
Kermanshahi, F.,
Mortazavi, M.,
Mohagheghi, M.,
Sajedi, M.S.,
Ziazi, R.M.,
Sadati, S.,
Pourzand, H.,
Goudarzi, N. IEEE Aerospace Conference Proceedings (1095323X)
In this paper, a full applicable procedure for design, optimization and manufacturing of an operational unmanned helicopter with deep and detailed research basis is presented. 12The proposed process deals with challenging aspects of manufacturing of the mentioned type of aircraft such as cost, weight, operation ability, reliability, mission justification, stability, performance, etc. To show the applicability of the proposed procedure, a realization of the process in production of an operational unmanned helicopter named as Parvan is described in this paper. Indeed, Parvan is a Remotely Piloted Helicopter (RPH) with 9 kilograms takeoff weight, and main rotor diameter of 1.54 meters which can lift up a 2 kilograms payload and fly in 120 kilometer radius of action for about 1.5 hours. ©2010 IEEE.
Aircraft Engineering and Aerospace Technology (17488842)82(2)pp. 107-115
Purpose - The purpose of this paper is to propose an efficient algorithm for trajectory planning of unmanned aerial vehicles (UAVs) in 2D spaces. This paper has been motivated by the challenge to develop a fast trajectory planning algorithm for autonomous UAVs through mid-course waypoints (WPs). It is assumed that there is no prior knowledge of these WPs, and their configuration is computed as in-flight procedure. Design/methodology/approach - Since the off-line techniques cannot be applied, it is required to apply an online trajectory planning algorithm. For this reason, based on the optimal control and the geometry, each segment of trajectory is designed with respect to a local frame. The algorithm is implemented as a real-time manner in terms of the down-range variable. Findings - The proposed algorithm tries to find not only a feasible trajectory (the constraint includes the maximum heading angle rate) but also an optimal trajectory (the objective locally is to minimize the length of the path). This online trajectory planning algorithm gradually produces a smooth 2D trajectory aiming at reaching the mid-course WPs and the final target so that they are smoothly connected with each other. The mid-course WPs are described through the given down-range, cross-range, and heading angle. Originality/value - Based on geometrical principles, this algorithm is capable of re-planning the trajectory as in-flight manner, and the computational burden approaches the online capabilities for UAVs with high velocity. © 2010 Emerald Group Publishing Limited.
In this paper, the problem of automated attitude control of a 3D nonlinear flexible spacecraft is investigated. Two nonlinear controller designs are presented. These controllers are composed of feedback linearization and μ-synthesis controllers. The first controller is based on classic feedback linearization, while the second one is robust feedback linearization. The robust feedback linearization method gives a linearizing control law that transforms the nonlinear system into a linear system based on operating condition. It is assumed that only three torques in three directions on the hub are 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 performance. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Aircraft Engineering and Aerospace Technology (17488842)82(3)pp. 194-203
Purpose - The purpose of this paper is the optimal design of a reentry vehicle configuration tominimize the mission costwhich is equal tominimize the heat absorbed (thermal protection system mass) and structural mass and to maximize the drag coefficient (trajectory errors and minimum final velocity). Design/methodology/approach - There are two optimization approaches for solving this problem: multiobjective optimization (lead to Pareto optimal solutions); and single-objective optimization (lead to one optimal solution). Single-objective genetic algorithms (GA) and multiobjective Genetic Algorithms (MOGA) are employed for optimization. In second approach, if there are n objectives (n + 1) GA run is needed to find nearest point (optimum point), which leads to increase the time processing. Thus, a modified GA called single run GA (SRGA) is presented as third approach to avoid increasing design time. It means if there are n objectives, just one GA run is enough. Findings - Two multi module function - Ackley and bump function - are selected for examination the third approach. Results of MOGA, GA and SRGA are presented which show SRGA approach can find the nearest point in much shorter time with acceptable accuracy. Originality/value - GA, MOGA and SRGA approaches are applied to multidisciplinary design optimization of a reentry vehicle configuration and results show the efficiency of SRGA in complex design optimization problem. © Emerald Group Publishing Limited.
Scientia Iranica (23453605)17(3 B)pp. 217-228
In this paper, the problem of attitude control of a ID non-linear flexible spacecraft is investigated. Three controllers are presented. The first is a non-linear dynamic inversion, the second is a linear μ-synthesis and the third is a composition of dynamic inversion and a μ-synthesis controller. It is assumed only one reaction wheel 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 panels, sensitivity to measurement noise, environment disturbance and non-linearity in large maneuvers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a non-linear 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. © Sharif University of Technology, June 2010.
In this paper, the problem of attitude control of a 3D nonlinear flexible spacecraft is investigated. Two nonlinear controllers are presented. The first controller is based on dynamic inversion, while the second approach is composed of dynamic inversion and μ-synthesis schemes. 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 three torques in three directions on the hub are used. In particular, the assumption that all sate variables are measurable is not realistic; hence sliding mode observers is used to estimate states. Actuator saturation is also considered in the design of controllers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a nonlinear model of the spacecraft are performed. 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. Simulation results confirm the ability of the proposed controller in tracking the attitude trajectory while damping the panel vibration. It is also verified that the perturbations, environment disturbances and measurement errors have only slight effects on the tracking and damping performances. © 2010 AACC.
Journal of Aircraft (00218669)47(4)pp. 1391-1398
This paper proposes an efficient algorithm with a novel procedure for trajectory planning of unmanned aerial vehicles in three-dimensional space. This work has been motivated by a challenge to develop a fast trajectory planning algorithm for autonomous unmanned aerial vehicles through the midcourse waypoints. The waypoints that are defined as a preflight or in-flight procedure are described in a five-dimensional configuration: the position in three dimensions plus desired crossing heading and flight-path angles. For achieving the waypoints, the Dubins path is extended to three-dimensional applications by using the geometrical concepts. In addition, the trajectory planning algorithm is represented as a set of ordinary differential equations called optimal-constrained-trajectory kinematics by applying the differential geometry concepts. Optimal-constrained-trajectory kinematic is a closed-loop guidance law that generates the guidance commands based on the waypoint configuration and minimum turning radius and is solved in a real-time manner. The proposed algorithm includes an operational framework that leads to gradually generating the smooth three-dimensional trajectory, aimed at reaching the midcourse targets and final target so that they are smoothly connected to each other. Finally, the simulation results show the capability of the algorithm in dynamic trajectory planning in low computational burden. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
IEEE Transactions on Aerospace and Electronic Systems (00189251)47(4)pp. 2423-2434
In this paper, the problem of attitude control of a 3D nonlinear flexible spacecraft is investigated. Two nonlinear controllers are presented. The first controller is based on dynamic inversion, while the second approach is composed of dynamic inversion and μ-synthesis schemes. The extension of dynamic inversion approach to flexible spacecraft is impeded by the nonminimum 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 redefinition approach. It is assumed that only three torques in three directions on the hub are used. Actuator saturation is also considered in the design of controllers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a nonlinear model of the spacecraft are performed. 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. Simulation results confirm the ability of the proposed controller in tracking the attitude trajectory while damping the panel vibration. It is also verified that the perturbations, environment disturbances, and measurement errors have only slight effects on the tracking and damping performances. © 2011 IEEE.
Applied Soft Computing (15684946)11(1)pp. 365-372
In this paper, an efficient strategy is proposed to design the altitude hold mode autopilot for a UAV which is non-minimum phase, and its model includes both parametric uncertainties and unmodeled nonlinear dynamics. This work has been motivated by the challenge of developing and implementing an autopilot that is robust with respect to these uncertainties. By combination of classic controller as the principal section of the autopilot and the fuzzy logic controller to increase the robustness in a single loop scheme, it is tried to exploit both methods advantages. The multi-objective genetic algorithm is used to mechanize the optimal determination of fuzzy logic controller parameters based on an efficient cost function that comprises undershoot, overshoot, rise time, settling time, steady state error and stability. Simulation results show that the proposed strategy performances are desirable in terms of the time response characteristics for both phugoid mode and short period mode, the robustness, and the adaptation of itself with respect to the large commands. © 2010 Elsevier B.V. All rights reserved.
JVC/Journal of Vibration and Control (10775463)17(13)pp. 1938-1951
In this paper, the problem of attitude control of a flexible spacecraft is investigated. Three controllers are presented. The first controller is based on dynamic inversion, while the second is based on the μ-synthesis method and the third approach is composed of dynamic inversion and μ-synthesis schemes. It is assumed that only one torque on the hub is used. Actuator saturation is also considered in the design of controllers. To evaluate the performance of the proposed controllers, an extensive number of simulations on the model of the spacecraft are performed. The performances of the proposed controllers are compared in terms of nominal performance, robustness to uncertainties, suppression of panel vibration, sensitivity to measurement noise, environment disturbance, and nonlinearity in large maneuvers. Simulation results confirm the ability of the proposed controller in tracking the attitude trajectory while damping the panel vibration. It is also verified that the perturbations, environment disturbances, and measurement errors have only slight effects on the tracking and damping performances. It is notable that the composite method (dynamic inversion and μ-synthesis) is not new; however, this application is new. © The Author(s) 2010 Reprints and permissions.
Abdolmohammad-Zadeh, Hossein,
Rezvani Z.,
Sadeghi, G.,
Zorufi E. Analytica Chimica Acta (18734324)(2)
The nickel-aluminum layered double hydroxide (Ni-Al LDH) was synthesized by a simple co-precipitation method with controlled pH and followed by hydrothermal treatment. The obtained nano-structured inorganic material was employed, for the first time, as a new solid-phase extraction (SPE) sorbent for the extraction and pre-concentration of trace levels of fluoride ions from aqueous solutions. An indirect method was used for monitoring of extracted fluoride ions. The method is based on the quenching effect of extracted fluoride ions upon the fluorescence intensity of Al-oxine complex via the forming of AlF63-, which was determined spectrofluorometrically at λem=510nm with excitation at λex=404nm. The effect of several parameters such as type of interlayer anion in Ni-Al LDH structure, pH, sample flow rate, elution conditions, amount of nano-sorbent, sample volume and co-existing ions on the extraction efficiency of the analyte were investigated. The results showed that fluoride ions could be retained on the Ni-Al (NO3-) LDH at pH 6.0 and stripped by 1.2mL of 3.0molL-1 NaOH. In the optimum experimental conditions, the limit of detection (3s) and enrichment factor were 9.0ngmL-1 and 50, respectively. The optimized method was successfully applied to the determination of fluoride concentration in various water samples. The results obtained from the proposed method were successfully compared with those provided by standard SPADNS method. © 2010 Elsevier B.V.
The purpose of this research is the optimal design of a reentry capsule configuration to minimize the mission cost which is usually modeled by minimizing reentry module mass (thermal protection system mass, propellant mass and structural mass). Multidisciplinary design optimization (MDO) is an important approach for the conceptual design of reentry capsule, because they are characterized by various disciplines that interact with one another. In this paper Trajectory, Aerodynamics, Structure, Thermal Protection System (TPS) and Deorbit Propulsion disciplines are modeled to optimize bi-conic configuration parameters. All At Once (AAO) frame work is developed and Genetic Algorithm (GA) is used to multidisciplinary conceptual design optimization of reentry mission with nonlinear constrains. © 2011 IEEE.
A simple solid phase extraction system based on the applying the nickel-aluminum layered double hydroxide (Ni-Al LDH) as a nano-sorbent was developed for the speciation analysis of chromium and manganese by flame atomic absorption spectrometry (FAAS). The method is based on the fact that Cr(VI) and Mn(VII) oxyanions could be adsorbed on the Ni-Al(NO3-) LDH and/or exchanged with LDH interlayer NO3- ions at pH 6.0, whereas Cr(III) and Mn(II) cations pass through the LDH-packed column without retention. The determinations of total Cr and Mn, and hence indirectly Cr(III) and Mn(II), involve the pre-oxidations of Cr(III) and Mn(II) to Cr(VI) and Mn(VII) with H2O2 and acidic solution of KIO4, respectively. Several important factors affecting the retention efficiency were investigated and optimized. In the optimum experimental conditions, the limits of detection (3Sb/m) for Cr(VI) and Mn(VII) were 0.51 and 0.47 ng mL-1, and the relative standard deviations were 2.5 and 3.2% (C = 30.0 ng mL-1, n = 6), respectively. The presented method was validated by the analysis of a certified reference material, and applied to the speciation of Cr and Mn in drinking waters, surface waters and industrial wastewater effluents. © 2012 Elsevier B.V. All rights reserved.
Applied Mechanics and Materials (discontinued) (16627482)225pp. 323-328
A new methodology has been proposed to design a dynamically similar/scaled model (DSM) of aircraft. This method uses the simulated annealing (SA) optimization algorithm to get the maximum similarity between model and full-scale aircraft with help of systems movement and using minimum ballast weight. For the 1/2 model of an unmanned aerial vehicle (UAV), internal arrangement is designed to achieve the desired model center of gravity position and moments of inertia. A computer code is developed, and model suitable arrangement is obtained. Results show that the proposed optimization approach to design of DSM was successfully used to find adequate model systems arrangement and minimizing ballast weight to access more capacities for dataacquisition systems or fuels. In this problem, ballast weight reduced about 0.6 kgf for a 55 kgf model, in addition of simplicity of DSM design for various configuration and flight regimes. © (2012) Trans Tech Publications, Switzerland.
Applied Mechanics and Materials (discontinued) (16627482)110pp. 2504-2512
Environmental simulation has an essential contribution in attitude determination and control verification tests of satellites. Specifically, real-time modeling of space environment can provide more precise and adapted simulation of real world in order to enable satellite attitude determination system by online outputs of sensors. Design and manufacturing of a moving mechanism which simulates the motion of real Sun relative to the satellite is proposed in this paper. Indeed, an artificial Sun carried by the mechanism will sensitize Sun Sensors mounted on a 3DOF model of satellite and finally the outputs of sensors are used to determine the attitude of the model satellite. The procedure of designing and manufacturing such a mechanism is described as follows. Firstly, the motion of Sun relative to the satellite on a specific orbit was ascertained. Next, considering the constraints such as laboratory space and its equipments, an appropriate mechanism was designed conceptually to satisfy the requirements. Then, the detailed characteristics of the mechanism were determined in the preliminary design phase and approved in the detailed design phase of the project. Finally, in order to verify the designed mechanism, a scaled down prototype was fabricated. Developmental tests on the prototype proved the ability of the model to simulate the Sun motion relative to the satellite properly. © (2012) Trans Tech Publications, Switzerland.
Journal of Aerospace Engineering (08931321)25(1)pp. 1-9
In this paper, the authors tried to design the altitude hold mode autopilot for unmanned aerial vehicles. This case presents an interesting challenge attributable to the nonminimum phase characteristic, nonlinearities, and uncertainties of the altitude to elevator relationship. A fuzzy logic autopilot in a single-loop scheme is proposed for the design of this autopilot. The multiobjective genetic algorithm is used to mechanize the optimal determination of fuzzy logic autopilot parameters on the basis of an efficient cost function that comprises undershoot, overshoot, rise time, settling time, steady state error, and stability. Simulation results show that the proposed strategy not only has a simple structure, but also has desirable performances in time response characteristics, robustness (against the unmodeled nonlinear terms and parametric uncertainties), and the adaptation of itself than the large commands. © 2012 American Society of Civil Engineers.
Asian Journal of Control (19346093)14(2)pp. 553-563
In this paper, the problem of attitude control of a three dimension nonlinear flexible spacecraft is investigated. Two nonlinear controllers are presented. The first controller is based on dynamic inversion, while the second approach is composed of dynamic inversion and μ-synthesis schemes. It is assumed that only three torques in three directions on the hub are used. Actuator saturation is also considered in the design of controllers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a nonlinear model of the spacecraft are performed. The performances of the proposed controllers are compared in terms of nominal performance, robustness to uncertainties, vibration suppression of panel, sensitivity to measurement noise, environmental disturbance and nonlinearity in large maneuvers. Simulation results confirm the ability of the proposed controller in tracking the attitude trajectory while suppressing the panel vibration. It is also verified that the perturbations, environment disturbances and measurement errors have only slight effects on the tracking and suppression performances. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.
Mathematical Problems In Engineering (1024123X)2013
This paper presents a new concept for atmospheric reentry online optimal guidance and control using a method called MARE G&C that exploits the different time scale featured by reentry dynamics. The new technique reaches a quasi-analytical solution and simplified computations, even considering both lift-to-drag ratio and aerodynamic roll as control variables; in addition, the paper offers a solution for the challenging path constraints issue, getting inspiration from the inverse problem methodology. The final resulting algorithm seems suitable for onboard predictive guidance, a new need for future space missions. © 2013 Davood Abbasi and Mahdi Mortazavi.
Archive of Applied Mechanics (14320681)83(9)pp. 1257-1272
An analytical transfer matrix method is presented to determine the effect of intermediate flexible constraints on the dynamic behavior of a multi-span beam subject to a moving mass. By using the Timoshenko beam theory on separate beams and applying the compatibility requirements on each constraint point, the relationships between every two adjacent spans can be obtained. By using a transfer matrix method, eigensolutions of the entire system can be determined. The forced responses can then be calculated by the modal expansion theory using the determined eigenfunctions. Some numerical results are presented to show the effects of intermediate constraints and locations on the dynamic response of the multi-span beams. It will be seen that the general formulation developed here can cover a large array of problems such as cracked or intermediately constrained beams. © 2013 Springer-Verlag Berlin Heidelberg.
Journal of Intelligent and Fuzzy Systems (18758967)24(3)pp. 499-509
The fuzzy sliding mode control based on the multi-objective genetic algorithm is proposed to design the altitude autopilot of a UAV. This case presents an interesting challenge due to non-minimum phase characteristic, nonlinearities and uncertainties of the altitude to elevator relation. The response of this autopilot is investigated through various criteria such as time response characteristics, robustness with respect to parametric uncertainties, and robustness with respect to unmodeled dynamics. The parametric robustness is investigated with reduction in significant longitudinal stability coefficients. Also, a nonlinear model in presence of the coupling terms is used to investigate the robustness with respect to unmodeled dynamics. In spite of a designed classic autopilot, it is shown by simulation that combining of the sliding mode control robustness and the fuzzy logic control independence of system model can guarantee the acceptable robust performance and stability with respect to unmodeled dynamics and parametric uncertainty, while the number of FSMC rules is smaller than that for the conventional fuzzy logic control. © 2013 - IOS Press and the authors. All rights reserved.
