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    Optimal Trajectory Planning for Aircraft Microgravity Atmospheric Maneuver

    , M.Sc. Thesis Sharif University of Technology Saki, Reza (Author) ; Pourtakdoust, Hossein (Supervisor)
    Abstract
    The purpose of the current study is to design an optimal trajectory and control for an aircraft to perform a microgravity maneuver automatically. This subject is by itself an important research topic that has not yet been attempted via optimal control formulation and modelling. Space stations are commonly utilized to conduct long-term microgravity research. Unfortunately utility of space stations to perform space based microgravity experiments is expensive and inaccessible for many researchers and scientific institutions. However, since many experiments requiring microgravity conditions can be performed in short time intervals, there is a possibility to meet their demand via optimal... 

    Optimal trajectory planning for flight through microburst wind shears

    , Article Aerospace Science and Technology ; Volume 15, Issue 7 , October , 2011 , Pages 567-576 ; 12709638 (ISSN) Pourtakdoust, S. H ; Kiani, M ; Hassanpour, A ; Sharif University of Technology
    2011
    Abstract
    Microburst wind shear is a potential hazard for aviation safety, especially in some crucial phases of flight like take-off and landing. Optimal trajectories could be useful for suitable retrieval of transport aircrafts encountering microburst. These types of trajectories are investigated in this paper for landing phase in two scenarios of escape and landing utilizing the most recent realistic analytical model of the microburst. In this regard, a set of complete six degrees of freedom aircraft's equations of motion is taken in a variation formulation of this problem. This approach is particularly useful for determination of optimal escape or approach trajectories constrained with respect to... 

    A computationally efficient algorithm to find time-optimal trajectory of redundantly actuated robots moving on a specified path

    , Article Robotica ; 2018 ; 02635747 (ISSN) Mansouri, S ; Sadigh, M. J ; Fazeli, M ; Sharif University of Technology
    Cambridge University Press  2018
    Abstract
    time-optimal problem for redundantly actuated robots moving on a specified path is a challenging problem. Although the problem is well explored and there are proposed solutions based on phase plane analysis, there are still several unresolved issues regarding calculation of solution curves. In this paper, we explore the characteristics of the maximum velocity curve and propose an efficient algorithm to establish the solution curve. Then we propose a straightforward method to calculate the maximum or minimum possible acceleration on the path based on the pattern of saturated actuators, which substantially reduces the computational cost. Two numerical examples are provided to illustrate the... 

    Conflict resolution maneuvers based on genetic algorithm modified webs

    , Article 2009 IEEE Aerospace Conference, Big Sky, MT, 7 March 2009 through 14 March 2009 ; 2009 ; 1095323X (ISSN); 9781424426225 (ISBN) Malaek, M. B ; Alaeddini, A ; Sharif University of Technology
    2009
    Abstract
    In this paper, the problem of designing optimal conflict-free maneuvers for planar multiple aircraft encounters is studied. The maneuvers propose suitable heading changes for aircraft in a cooperative manner. The new mathematical approach provides optimal trajectories to resolve a wide variety of conflicts, especially in the presence of high-altitude Clear Air Turbulence (CAT). The proposed approach effectively uses Genetic Algorithms (GA), together with modified webs, to quickly find conflict-resolving maneuvers. Different case studies show the method is fast enough to be used for real-time applications when resolving conflicts involving two aircraft. It is also efficient enough to resolve... 

    Optimal trajectory planning for brachiation robot on ladder with irregular branches

    , Article Proceedings of the ASME Design Engineering Technical Conference, 28 August 2011 through 31 August 2011 ; Volume 6, Issue PARTS A AND B , August , 2011 , Pages 1131-1137 ; 9780791854839 (ISBN) Meghdari, A ; Lavasani, S. M. H ; Mousavi, M. S. R ; Norouzi, M ; Sharif University of Technology
    2011
    Abstract
    This paper deals with control of the brachiation robot. The brachiation is a type of mobile robot that moves from branch to branch like a long-armed ape. Here, as a new innovation, Pontryagin's minimum principle is used to obtain the optimal trajectories for two different problems. The first problem is "Brachiation between fixed branches with different distance and height" and the second is "Brachiating and catching the moving target branch". Theoretical results show that the control effort in the proposed method is reduced by 25% in comparison with the "Target Dynamics" method which was proposed in prior articles for this robot. The obtained optimal trajectory also minimizes the brachiation... 

    An accurate guidance algorithm for implementation onboard satellite launch vehicles

    , Article Scientia Iranica ; Volume 17, Issue 2 D , JULY-DECEMBE , 2010 , Pages 175-188 ; 10263098 (ISSN) Mardani, M ; Mobed, M ; Sharif University of Technology
    2010
    Abstract
    An algorithm for guiding a launch vehicle carrying a small satellite to a sun synchronous LEO is presented. Before the launch, a nominal path and the corresponding nominal control law for the entire journey are computed. For each sampling instant during the guided flight, a linear equation approximately relating the differences between the actual and nominal values is considered, and a LeastSquares formula using data from on-line state measurements is applied to compute the actual control. The coefficient matrices of the Least-Squares formula can be determined by off-line computations. The method enjoys simplicity of implementation by onboard computers, as well as robust accuracy against... 

    Optimal-time quadcopter descent trajectories avoiding the vortex ring and autorotation states

    , Article Mechatronics ; Volume 68 , 2020 Talaeizadeh, A ; Antunes, D ; Nejat Pishkenari, H ; Alasty, A ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    It is well-known that helicopters descending fast may enter the so-called Vortex Ring State (VRS), a region in the velocity space where the blade's lift differs significantly from regular regions and high amplitude fluctuations are often present. These fluctuations may lead to instability and, therefore, this region is avoided, typically by increasing the horizontal speed. This paper researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel experiments. Moreover, we propose that the so-called Windmill-Brake State (WBS) or autorotation region should also be avoided for... 

    Coupled Attitude-orbit Dynamics and Control of Solar Sail by Moving the Center of Mass

    , M.Sc. Thesis Sharif University of Technology Montazeri Hedesh, Hamidreza (Author) ; Asadian, Nima (Supervisor)
    Abstract
    In this thesis, firstly we have developed a coupled dynamic for the orbit and attitude of a solar sail. Secondly, we found an optimal trajectory from the Earth to Mars and tried to control the system on the optimal trajectory by a control mechanis which moves the center of mass of the sail. The solar sail is considered to be rigid and Ideally reflective which means the sail reflects the full extent of the photons it receives. Adjusting the center of mass of the sail is done by changing the position of two sliding masses rode on two rails perpendicular to each other. Moving the center of mass of the sail brings about a change in the attitude of the sail which then causes a deflection in the... 

    Minimum time trajectory optimization of a tail-sitter aerial vehicle using nonlinear programming

    , Article 2012 International Conference onAdvanced Mechatronic Systems, ICAMechS 2012 ; 2012 , Pages 275-280 ; 9780955529382 (ISBN) Banazadeh, A ; Assadian, N ; Saghafi, F ; Sharif University of Technology
    2012
    Abstract
    Aerial tail-sitters have drawn many attentions in recent years. The main challenge of employing these vehicles is to ensure safe and efficient takeoff and landing. The aim of the current study is to develop a gradient-base optimization algorithm for a jet aerial tail-sitter in order to obtain minimum time trajectories in transition flight phases. The vehicle is supposed to utilize thrust vectoring system instead of conventional control surfaces that will pose minimal drawbacks in terms of low speed efficiency and complexity. The time-optimal trajectories are computed using the nonlinear dynamic equations of motion of the vehicle in order to make sure that the vehicle can follow the optimum... 

    Trajectory optimization for a high speed planing boat based on Gauss pseudospectral method

    , Article Proceedings - 2011 2nd International Conference on Control, Instrumentation and Automation, ICCIA 2011 ; 2012 , Pages 195-200 Salarieh, H ; Ghorbani, M. T ; Sharif University of Technology
    Abstract
    In this paper, the problem of Optimal Trajectory Planning for a high speed planing boat under nonlinear equality and inequality path constraints, is addressed. First, a nonlinear mathematical model of the craft's dynamic is constructed. To solve a trajectory optimization problem, we can utilize the indirect or direct methods. In the indirect methods, the maximum principle of Pontryagin is used to transform the optimal control problem into Euler-Lagrange equations, on the other hand, in the direct methods it is necessary to transcribe the optimal control problem into a nonlinear programming problem (NLP) by discretization of states and controls. The resulted NLP can be solved by... 

    Near-optimal terrain collision avoidance trajectories using elevation maps

    , Article IEEE Transactions on Aerospace and Electronic Systems ; Volume 47, Issue 4 , October , 2011 , Pages 2490-2501 ; 00189251 (ISSN) Malaek, S. M ; Abbasi, A ; Sharif University of Technology
    2011
    Abstract
    The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so-called "quad-tree forms". The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the "cost map," lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different... 

    Nonholonomic motion planning based on optimal control for flight phases of planar bipedal running

    , Article Electronics Letters ; Volume 47, Issue 20 , 2011 , Pages 1120-1122 ; 00135194 (ISSN) Sadati, N ; Akbari Hamed, K ; Dumont, G. A ; Graver, W. A ; Sharif University of Technology
    2011
    Abstract
    Presented is a novel approach for online trajectory modification of joint motions to transfer a free open kinematic chain, undergoing flight phase, from a specified initial configuration to a specified final configuration. Formally, it is assumed that a nominal trajectory, computed offline, can reorient the kinematic chain (reconfiguration problem) for a given angular momentum on a time interval. A modification algorithm of body joints, based on optimal control, is developed such that for different angular momentums and time intervals, the same reconfiguration problem can be solved online. This approach can be utilised for space robotics applications and online computation of planar running... 

    Constrained optimization of sensors trajectories for moving source localization using TDOA and FDOA measurements

    , Article International Conference on Robotics and Mechatronics, ICROM 2015, 7 October 2015 through 9 October 2015 ; 2015 , Pages 200-204 ; 9781467372343 (ISBN) Adelipour, S ; Hamdollahzadeh, M ; Behnia, F ; Sharif University of Technology
    2015
    Abstract
    This paper examines the problem of determining optimal sensors trajectories for localization of a moving radio source based on Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) measurements in situations in which sensors are constrained both in their movements and regions of operation. By considering the movement of the source and constrained movement of the sensors, a constraint problem is formed which is solved to determine optimal trajectories of the sensors for source tracking. The validity of the proposed algorithm is assessed by two different simulation scenarios and the results verify its proper operation with estimation error decreasing in consecutive steps... 

    A real-time algorithm for variable-objective motion planning over terrain and threats

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 229, Issue 6 , 2015 , Pages 1043-1056 ; 09544100 (ISSN) Karimi, J ; Pourtakdoust, S. H ; Sharif University of Technology
    SAGE Publications Ltd  2015
    Abstract
    A major issue required to enhance the autonomy level of unmanned vehicles is real-time motion planning. In this context, optimal trajectories need to be generated online considering the vehicle's dynamic potentials and constraints. However, autonomous air vehicles often need to plan and execute their missions with varying objectives that may even be dictated in flight. Therefore, the current study introduces and focuses on the new concept of variable-objective motion planning. In this regard, a new dynamic multi-objective heuristic optimization algorithm is developed for path and motion planning of autonomous air vehicles in presence of deterministic terrain obstacles as well as random... 

    Near-optimal trajectories to manage landing sequence in the vicinity of controlled aerodromes

    , Article Journal of Aircraft ; Volume 47, Issue 1 , 2010 , Pages 129-140 ; 00218669 (ISSN) Malaek, S. M ; Nabavi, S. Y ; Sharif University of Technology
    Abstract
    A comprehensive approach is proposed to manage landing sequences and their associated trajectories for an arbitrary number of aircraft in the vicinity of a controlled aerodrome. The current approach, similar to that of "first come, first served," could consider different types of priorities as well as emergencies. The approach is especially useful to combine unstructured free-flight trajectories with structured ones during the approach phase of the flight A comprehensive cost function considers the relative size of all aircraft together with their relative speeds and flight directions. This helps optimize the amount of fuel consumption while respecting separation minima. Resulting... 

    Nonlinear optimal control of planar musculoskeletal arm model with minimum muscles stress criterion

    , Article Journal of Computational and Nonlinear Dynamics ; Volume 12, Issue 1 , 2017 ; 15551415 (ISSN) Sharifi, M ; Salarieh, H ; Behzadipour, S ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2017
    Abstract
    In this paper, the optimal performance of a planar humanlike musculoskeletal arm is investigated during reaching movements employing an optimal control policy. The initial and final states (position and velocity) are the only known data of the response trajectory. Two biomechanical objective functions are taken into account to be minimized as the central nervous system (CNS) strategy: (1) a quadratic function of muscle stresses (or forces), (2) total time of movement plus a quadratic function of muscle stresses. A two-degress of freedom (DOF) nonlinear musculoskeletal arm model (for planar movements) with six muscle actuators and four state variables is used in order to evaluate the proposed... 

    Optimum synthesis of fuzzy logic controller for trajectory tracking by differential evolution

    , Article Scientia Iranica ; Volume 18, Issue 2 B , 2011 , Pages 261-267 ; 10263098 (ISSN) Nejat Pishkenari, H ; Mahboobi, S. H ; Alasty, A ; Sharif University of Technology
    Abstract
    Differential Evolution (DE) and Genetic Algorithms (GA) are population based search algorithms that come under the category of evolutionary optimization techniques. In the present study, these evolutionary methods have been utilized to conduct the optimum design of a fuzzy controller for mobile robot trajectory tracking. Comparison between their performances has also been conducted. In this paper, we will present a fuzzy controller to the problem of mobile robot path tracking for a CEDRA rescue robot. After designing the fuzzy tracking controller, the membership functions will be optimized by evolutionary algorithms in order to obtain more acceptable results  

    Optimal trajectory design to Halo orbits via pseudo-invariant manifolds using a nonlinear four body formulation

    , Article Acta Astronautica ; Volume 110 , 2015 , Pages 115-128 ; 00945765 (ISSN) Sayanjali, M ; Pourtakdoust, S. H ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    This paper investigates the problem of optimal transfer trajectory design towards the L2 centered Halo orbit of the Sun-Earth three body system, where the initial launch is to start from a low Earth parking orbit (LEO). The proposed optimal transfer trajectory consists of an active part with low-thrust propulsion and a passive coasting part with no thrust or fuel consumption. In this respect a pseudo-stable manifold (SM) is initially determined through backward time integration of the bicircular four body (BCFB) equations of motion, whose initial states are obtained via stable manifolds of the restricted three body problem (R3BP). The optimal transfer trajectories are extracted via a hybrid... 

    Optimization of kinematic redundancy and workspace analysis of a dual-arm cam-lock robot

    , Article Robotica ; Volume 34, Issue 1 , 2016 , Pages 23-42 ; 02635747 (ISSN) Rezaeian Jouybari, B ; Ghaemi Osgouie, K ; Meghdari, A ; Sharif University of Technology
    Cambridge University Press  2016
    Abstract
    In this paper, the problem of obtaining the optimal trajectory of a Dual-Arm Cam-Lock (DACL) robot is addressed. The DACL robot is a reconfigurable manipulator consisting of two cooperative arms, which may act separately. These may also be cam-locked in each other in some links and thus lose some degrees of freedom while gaining higher structural stiffness. This will also decrease their workspace volume. It is aimed to obtain the optimal configuration of the robot and the optimal joint trajectories to minimize the consumed energy for following a specific task space path. The Pontryagin's Minimum Principle is utilized with a shooting method to resolve kinematic redundancy. Numerical examples... 

    Multiobjective genetic optimization of Earth-Moon trajectories in the restricted four-body problem

    , Article Advances in Space Research ; Volume 45, Issue 3 , February , 2010 , Pages 398-409 ; 02731177 (ISSN) Assadian, N ; Pourtakdoust, S. H ; Sharif University of Technology
    2010
    Abstract
    In this paper, optimal trajectories of a spacecraft traveling from Earth to Moon using impulsive maneuvers (ΔV maneuvers) are investigated. The total flight time and the summation of impulsive maneuvers ΔV are the objective functions to be minimized. The main celestial bodies influencing the motion of the spacecraft in this journey are Sun, Earth and Moon. Therefore, a three-dimensional restricted four-body problem (R4BP) model is utilized to represent the motion of the spacecraft in the gravitational field of these celestial bodies. The total ΔV of the maneuvers is minimized by eliminating the ΔV required for capturing the spacecraft by Moon. In this regard, only a mid-course impulsive...