Publication Date: 2015
Acta Astronautica (00945765)114pp. 174-183
Abstract Optimum design of an upper-stage with bipropellant propulsion system consists of optimization of three major subsystems including thruster, feeding subsystem, and propellant tanks. Optimization of such a complex system involved in optimization of many disciplines including structure, heat transfer, aerothermodynamics, guidance and control, trajectory and propulsion. Hard coupling of the disciplines increase the optimization processing times. Multidisciplinary design optimization algorithm can derive the optimum configuration but more elapsed time is needed for single-level methods such as all at once (AAO) and lower feasibility occurred in multi-level methods such as collaborative optimization (CO). In this paper, a new multidisciplinary design optimization framework is proposed for such coupled disciplines with concentrating on the propulsion system. The proposed framework uses Combined Single-level and Bi-level Optimizations (CSBO) frameworks to minimize numbers of design variables and system constraints when feasibility is increased. For this goal, modeling of every discipline is introduced and the design algorithm validated by redesigning of two real bipropellant thrusters. Three MDO frameworks are applied for our problem including AAO, CO and CSBO. Comparisons between the results show that CSBO can find the optimum solution in shorter elapsed time with lower F-count. Therefore, CSBO is more efficient for complex systems with coupled disciplines. © 2015 IAA.
Publication Date: 2018
Ocean Engineering (00298018)147pp. 517-530
Optimal design of an Autonomous Underwater Vehicle (AUV) consists of various subsystems and disciplines such as guidance and control, payload, hydrodynamics, power and propulsion, sizing, structure, trajectory and performance. The designed vehicle is also employed in an operational environment with tactical parameters such as distance to target, uncertainty in estimation of target position and target velocity. Multidisciplinary Design Optimization (MDO) is the best way for finding both optimum and feasible designs. In this paper, a new optimization design framework is proposed in which Multidisciplinary Feasible (MDF) as MDO framework and Particle Swarm Optimization (PSO) as optimizer were combined together for optimal and feasible conceptual design of an AUV. Initially, we found an optimal system design by using MDF-PSO methodology in engineering space for any single tactical situation (locally tactical parameters). Then the optimal off-design AUVs in tactical subspaces were found by minimizing the difference between the locally optimized objective function and sub-optimal objective function. In this framework, we have shown that not only is the tactical situation affected by AUV design parameters, but an optimal AUV for each tactical regions are also found. © 2017 Elsevier Ltd
Publication Date: 2016
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (09544100)230(6)pp. 1103-1113
This paper presents continuous curvature paths for unmanned vehicles such as robots and unmanned aerial vehicles. The importance of these paths is that both upper-bounded curvature and upper-bounded curvature derivatives are included in the path. The approach is based on replacement of the Dubins line with the quintic PH Bezier curves by computing a shape parameter by considering the kinematic constraints of the path. Since these paths are Dubins-based paths, their lengths are close to the minimum length. The effectiveness and sub-optimality of the proposed paths are demonstrated through fully nonlinear simulation. © 2015 Institution of Mechanical Engineers.
Publication Date: 2017
Journal of Aerospace Technology and Management (21759146)9(1)pp. 71-82
The optimum design of a solid propulsion system consists of optimization of various disciplines including structure, aerothermodynamics, heat transfer, and grain geometry. In this paper, an efficient model of every discipline has been developed, and a suitable framework is introduced for these hard-coupled disciplines. Hybrid optimization algorithm is used to find the global optimum point including genetic algorithm and sequential quadratic programing. To show the performance of the proposed algorithm, the required correction factor values have been carefully derived using comparison between more than 10 real solid propulsion systems and the proposed algorithm results. According to the results, the derived correction factors are close to 1, with scattering level better than 0.97. In addition, it is shown that the proposed algorithm (errors < 8%) is more accurate in comparison with the conventional approach (errors < 17%). Then, for a case study, multidisciplinary analysis has been done based on 3 general objectives including dry mass, total mass, and specific impulse. It means that the optimum specific impulse is not the maximum value and the optimum dry mass is not the minimum value. Finally, the proposed algorithm can be used to directly derive the optimum configuration for every mission requirement. © 2017, Journal of Aerospace Technology and Management. All rights reserved.
Publication Date: 2013
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.
Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment (14750902)233(3)pp. 918-936
The design process of an autonomous underwater vehicle requires mathematical model of subsystems or disciplines such as guidance and control, payload, hydrodynamic, propulsion, structure, trajectory and performance and their interactions. In early phases of design, an autonomous underwater vehicle is often encountered with a high degree of uncertainty in the design variables and parameters of system. These uncertainties present challenges to the design process and have a direct effect on the autonomous underwater vehicle performance. Multidisciplinary design optimization is an approach to find both optimum and feasible design, and robust design is an approach to make the system performance insensitive to variations of design variables and parameters. It is significant to integrate the robust design and the multidisciplinary design optimization for designing complex engineering systems in optimal, feasible and robust senses. In this article, we present an improved multidisciplinary design optimization methodology for conceptual design of an autonomous underwater vehicle in both engineering and tactic aspects under uncertainty. In this methodology, uncertain multidisciplinary feasible is introduced as uncertain multidisciplinary design optimization framework. The results of this research illustrate that the new proposed robust multidisciplinary design optimization framework can carefully set a robust design for an autonomous underwater vehicle with coupled uncertain disciplines. © IMechE 2018.
Publication Date: 2017
International Journal Of Technology (20869614)8(3)pp. 376-386
In this study, a method was developed for tuning moments of inertia for a free-flying dynamically similar/scaled model of an aircraft. For this method, the simulated annealing optimization algorithm was used to obtain similar mass-inertial properties of the model and the full-scale aircraft utilizing ballast weights. For a scaled model of a Su-27 fighter, the ballast arrangement were designed and weights were determined to achieve the required center of gravity position and the moments of inertia based on the similitude requirements. A computer code was developed, and the task of tuning inertia properties was performed. The results showed that the proposed optimization approach was successfully used to determine a feasible ballast weight and position. Moreover, the ballast weight reduced from 8.66 kg to 4.86 kg using the proposed technique, and the inertia characteristics' non-similarity was minimized. © 2017 IJTech.
This paper deals with mobile robot navigation in an unknown environment. The proposed algorithm is inspired from artificial potential field (APF) and rotational force method. In the proposed algorithm, the robot's velocity vector is simply determined by relative position vector of robot with respect to target and obstacles. This algorithm is applicable to both stationary and dynamic environments with one or more obstacles and guarantees that the robot can safely track the moving target even in the conditions of local minima or goal not reachable with obstacle nearby. In order to make the simulation more practical, it is applied to wheeled mobile robot. Simulation results show the effectiveness of the proposed approach. © 2014 IEEE.
Publication Date: 2009
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.
Publication Date: 2011
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.
Publication Date: 2015
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025pp. 432-437
Sensitivity analyses in the turning circle and zigzag maneuvers, as two main standard ones, are proposed here as a preliminary step to motion control design for an Autonomous Underwater Vehicle (AUV). The most effective parameters of the AUV are then adopted to be estimated by some adaptation mechanisms. Adaptive sliding mode control is developed to ensure the robust stability and performance, without a priori knowledge about the bound of perturbations. A simulation study is also presented to demonstrate the effectiveness of the method. © 2015 IEEE.
Publication Date: 2023
Journal of Navigation (03734633)76(6)pp. 709-730
This paper proposes a switched model to improve the estimation of Euler angles and decrease the inertial navigation system (INS) error, when the centrifugal acceleration occurs. Depending on the situation, one of the subsystems of the proposed switched model is activated for the estimation procedure. During global positioning system (GPS) outages, an extended Kalman filter (EKF) operates in the prediction mode and corrects the INS information, based on the system error model. Compared with previous works, the main advantages of the proposed switched-based adaptive EKF (SAEKF) method are (i) elimination of INS error, during the centrifugal acceleration, and (ii) high accuracy in estimating the attitude and positioning, particularly during GPS outages. To validate the efficiency of the proposed method in various trajectories, an experimental flight test is performed and discussed, involving a microelectromechanical (MEMS)-based INS. The comparative study shows that the proposed method considerably improves the accuracy in various scenarios. © The Author(s), 2024. Published by Cambridge University Press on behalf of The Royal Institute of Navigation.
Simulation is one of the best methods for education and understanding events and used in many fields of science, for example: space researches. For this reason, creating of a frictionless environment that can simulate the operations of satellites will be very usable and appropriate. Spherical air bearings, that we call them TESTBEDs in this paper, are one of the most common devices used in satellite attitude dynamics simulation, because they provide three degrees of freedom rotational motion. They are employed to develop, improve and carry out operational tests of sensors, actuators and attitude control algorithms in experimental framework. An explanation about system engineering tool for testbed design that used by our team in Space Research Lab will be presented in this paper. This systems engineering tool utilizes a testbed-based approach to efficiently track information regarding the mass, cost, operation and volume of simulator subsystems. This subsystem information is derived through a variety of means, including analytical relationships, iterative solvers, and databases of components appropriate for satellite simulators. Finally, a description of 3-DoF satellite simulator and it's subsystems (manufactured in Space Research Lab) by means of this system engineering tool will be demonstrated as a sample for validating results. © 2010 by ASME.
Publication Date: 2021
Journal of Navigation (03734633)74(4)pp. 801-821
This paper describes a camera simulation framework for validating machine vision algorithms under general airborne camera imperfections. Lens distortion, image delay, rolling shutter, motion blur, interlacing, vignetting, image noise, and light level are modelled. This is the first simulation that considers all temporal distortions jointly, along with static lens distortions in an online manner. Several innovations are proposed including a motion tracking system allowing the camera to follow the flight log with eligible derivatives. A reverse pipeline, relating each pixel in the output image to pixels in the ideal input image, is developed. It is shown that the inverse lens distortion model and the inverse temporal distortion models are decoupled in this way. A short-time pixel displacement model is proposed to solve for temporal distortions (i.e. delay, rolling shutter, motion blur, and interlacing). Evaluation is done by several means including regenerating an airborne dataset, regenerating the camera path on a calibration pattern, and evaluating the ability of the time displacement model to predict other frames. Qualitative evaluations are also made. Copyright © The Royal Institute of Navigation 2021.
Publication Date: 2022
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (09544100)236(7)pp. 1295-1303
For more than a decade, the multi-state constraint Kalman filter is used for visual-inertial navigation. Its advantages are the light-weight calculations, consistency, and similarity to the current mature GPS/INS Kalman filters. For using it in an airborne platform, an important deficiency exists. It diverges while the object stops moving. In this work, this deficiency is accounted for, by changing the state augmentation and measurement update policy from a time-based to horizontal travel-based scheme, and by reusing the oldest tracked point over and over. Besides the computational savings, it works infinitely with no extra errors in full-stops and with minor error build up in very low speeds. © IMechE 2022.
Publication Date: 2022
Journal of Sound and Vibration (10958568)535
In this article, a novel multi-objective modified fractional-order nonsingular terminal sliding mode (MFONTSM) controller is designed for the flexible spacecraft attitude control and passive vibration suppression, assuming the control torque saturation in the system dynamics. Then, by considering the effects of flexible components on the appendages modal equation as an external disturbance, an active FONTSM controller is designed separately to suppress any residual vibrations using piezoelectric actuators. The practical fixed-time stability of the closed-loop system is analyzed and proved using the Lyapunov theorem. Finally, the proposed controllers’ performance has been tested in the presence of uncertainties, external disturbances, and the absence of the damping matrix to study the proposed method's effectiveness. It was observed that the proposed passive and active control strategies were able to achieve fast attitude stabilization while providing substantial vibration suppression under uncertainty and disturbance even in the absence of any damping terms in the system. © 2022 Elsevier Ltd
Publication Date: 2010
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.
Publication Date: 2016
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025pp. 90-95
To improve the tracking control performance, in the presence of parametric uncertainties, for an autonomous underwater vehicle (AUV), the sensitive parameters are first identified, using the direct sensitivity analysis method. Then, an adaptive second order sliding mode controller is proposed to ensure the robust stability and performance, without any a priori knowledge on the upper bound of perturbations. To this end, a proportional integral derivative (PID) structure is adopted, as the sliding surface. The unknown sensitive parameters are estimated by some adaptive mechanisms. On the other hand, the second order sliding mode control (2-SMC) is developed to neutralize the effects of unstructured uncertainties and disturbances. The closed loop stability is shown, using the Lyapunov stability theorem, and verified by various numerical simulations. © 2016 IEEE.
Publication Date: 2018
Journal of Sound and Vibration (10958568)422pp. 300-317
The robust attitude and vibration control of a flexible spacecraft trying to perform accurate maneuvers in spite of various sources of uncertainty is addressed here. Difficulties for achieving precise and stable pointing arise from noisy onboard sensors, parameters indeterminacy, outer disturbances as well as un-modeled or hidden dynamics interactions. Based on high-order sliding-mode methods, the non-minimum phase nature of the problem is dealt with through output redefinition. An adaptive super-twisting algorithm (ASTA) is incorporated with its observer counterpart on the system under consideration to get reliable attitude and vibration control in the presence of sensor noise and momentum coupling. The closed-loop efficiency is verified through simulations under various indeterminate situations and got compared to other methods. © 2018 Elsevier Ltd
Publication Date: 2019
Aerospace Science and Technology (12709638)84pp. 361-374
In this paper, to control the six degree-of-freedom non-linear unmanned aerial vehicle, two strategies are implemented using adaptive super-twisting sliding mode control approach. The first one is a single-channel controller that is designed on the basis of decoupled equations of motion. The other one is a three-channel controller that is designed based on the coupling equations of motion along with an adaptive super-twisting observer. The stability of the closed loop system of the controller-observer is proven. The comparison between the single-channel controller and the three-channel could lead us to select between a little lower efficiency and less complexity versus efficiency and more complexity. To examine the performance and robustness of these two control loops, their performances are analyzed in the presence of combined uncertainties, including aerodynamics, mass, inertial moment, sensor, and actuator disturbances and parametric uncertainties in the stage separation phase. The explosive bolt separation mechanism is assumed to perform the stage separation, and its forces, moments and disturbances are modeled as needed. Finally, the responses are compared with the classic PID controller. © 2018 Elsevier Masson SAS
Publication Date: 2012
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.
Publication Date: 2024
Journal of Food Process Engineering (01458876)47(4)
A hybrid model is developed and evaluated to simulate the heat and mass transfer in the crystallization unit of a sugar factory. While the mass transfer is modeled by using the kinetic growth rate model, the heat transfer is simulated by applying the energy balance to the model. Here, the overall convection heat transfer coefficient of the crystallizer's heat exchanger is considered as a temperature-dependent function. As this makes the governing equations more realistic, it can help to increase the model accuracy. Additionally, a thorough examination of key practical equations and principles governing the sugar crystallization process is presented. A regression learner method is applied to extract the pattern of the overall heat transfer coefficient. According to our results, the regression learning model successfully predicts the heat transfer coefficient with an average 7% deviation from experimental results. For the hybrid model, an average deviation of about 10% is observed. The crystallizer's behavior is somehow linear, indicating a constant growth rate of sugar crystals. Furthermore, the heat transfer in the crystallizer is improved by increasing the working temperatures. Practical applications: The method and obtained results of this work could be used in the following practical purposes: to find the optimum working temperatures of crystallizers used in sugar industry and to predict total working time of batch crystallizers versus working parameters. © 2024 Wiley Periodicals LLC.
Publication Date: 2008
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.
Publication Date: 2023
ISA Transactions (00190578)138pp. 705-719
In this paper, the attitude of a spacecraft simulator is controlled in the presence of nonlinearities, uncertainties and constraints of the system. An optimization-based controller is developed in the closed form based on predicting the nonlinear responses of spacecraft system. For practical requirements of the spacecraft actuated by the reaction wheels (RWs), the control method considers the actuator limitation in the torques applied to RWs and the restriction in the angular momentum of the wheels due to the limited rotational speed of motors. In this way, the momentum constraint is equated with the torque constraint by a prediction-based transformation. Then, the constrained optimal control law is calculated by solving an equivalent optimization formulation. The constrained stability is analyzed by the Lyapunov second method and the bound of system response is obtained in terms of the prediction time. In the results, at first, the performance of the unconstrained version of the proposed controller, which leads to the feedback linearization like controller, is evaluated in the presence of uncertainties through computer simulations. Finally, the constrained version is simulated and experimentally implemented as hardware in the loop on the spacecraft simulator. The obtained comparative results indicate a good performance for the constrained controller in realistic conditions. © 2023 ISA
Publication Date: 2024
Arabian Journal for Science and Engineering (21914281)49(2)pp. 1697-1712
In this paper, an optimal nonlinear attitude controller is designed and implemented as hardware in the loop for a spacecraft simulator under various failures of reaction wheels. The proposed controller is developed in the closed form based on predicting the nonlinear continuous responses of spacecraft simulator. The special case of the controller when all uncertainties are ignored leads to feedback linearization. However, the stability of the controller in the presence of parametric uncertainties and unmodeled dynamics of the platform is analyzed, and the effect of the prediction time on the boundedness of system responses is presented. A redundant reaction wheel is located in the platform to compensate for failures of three main reaction wheels. How to distribute torque between healthy wheels under different types of failure including stuck and oscillatory failures is addressed and experimentally implemented. The laboratory results that are consistent with computer simulations show the accuracy and validity of the designed controller. It is seen that the spacecraft attitude converges in a limited time in the presence of system uncertainties and actuator failures. © King Fahd University of Petroleum & Minerals 2023.
Publication Date: 2017
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025pp. 101-106
In this paper the attitude control of a spacecraft simulator using Reaction Wheels (RW) as the actuators is investigated. The simulator attitude is controlled considering the saturation of RWs angular momentum and its angular rate. The main goal of the current study is to bring the RW s to the rest at the end of the maneuver without using extra actuators. A modified feedback linearization is applied to control the attitude of the system. To this end, the Euler angles of the simulator are considered as the output and the RWs angular momentums are assumed as the internal state variables. The internal dynamics stability is proved by rewriting the dynamics of the system in normal form. The stability of the proposed controller is analyzed using Lyapunov stability approach. The proposed algorithm is finally evaluated numerically and experimentally on an attitude spacecraft simulator. © 2017 IEEE.
Publication Date: 2019
Control Engineering Practice (09670661)84pp. 72-81
In this paper the attitude control of a spacecraft simulator using Reaction Wheels (RW) as the actuators is investigated. The main goal of the current study is to bring the RWs to the rest at the end of the maneuver without angular velocity measurement. A modified feedback linearization controller is applied by considering the Euler angles of the simulator as the output and the RWs angular momentums as the internal state variables. The stability of the proposed controller and the internal dynamics is analyzed using Lyapunov theory. Two modified sliding mode observers are designed to estimate the angular velocities of the spacecraft attitude control subsystem simulator. The proposed observers do not use the control input and the detailed knowledge of the model and thus it can be implemented easily. The global stability of the system is proved. The proposed controller and observers are finally evaluated numerically and experimentally on an attitude spacecraft simulator. © 2018 Elsevier Ltd
