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    H∞ control of a flexible transmission system

    , Article Proceedings of the Thirty-Sixth Southeastern Symposium on System Theory (SSST04), Atlanta, GA., 14 March 2004 through 16 March 2004 ; Volume 36 , 2004 , Pages 536-540 Amirifar, R ; Sadati, N ; Sharif University of Technology
    An application of a continuous-time H∞ control to a flexible transmission system is presented. This approach has been proposed in order to assure high control performance in the presence of large load variation on the system. In this approach, the loading variations are considered as the multiplicative perturbation of the nominal plant. The desired specifications are enforced in the H∞ problem as the constraints on weighting functions. After an initial design procedure, the parameters of weighting functions, in order to obtain the desired performances, are tuned and then the final weighting functions are derived. The simulation results for three different loadings are given and compared  

    Comparing the stability regions for fractional-order PI controllers and their integer-order approximations

    , Article Proceedings of the IEEE Conference on Decision and Control, 15 December 2010 through 17 December 2010, Atlanta, GA ; 2010 , Pages 720-725 ; 01912216 (ISSN) ; 9781424477456 (ISBN) Rahimian, M. A ; Tavazoei, M. S ; Sharif University of Technology
    This paper proposes a scheme for computing the stable regions from which the parameters of a fractional-order PI controller can be selected. In particular, we extend a previously investigated method for plotting the stability regions of PIλ controllers to their integer-order approximations. Next we compare the two stability regions and derive their overlapping sections, which is referred to as the implementable stability region. In order for the final closed-loop system to be stable, the designer must choose the controller parameters from the overlapping section of the two stability regions. The devised scheme we believe can facilitate the design procedure for fractional-order PI... 

    Partial integrity of unstable LTI systems

    , Article 24th Mediterranean Conference on Control and Automation, 21 June 2016 through 24 June 2016 ; 2016 , Pages 1302-1306 ; 9781467383455 (ISBN) Eslami, M ; Nobakhti, A ; Babazadeh, M ; MCA ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    This paper considers the Integral Stabilizability (IS) and partial integrity of Linear Time Invariant (LTI) systems with an unstable sub-system. The main contribution of the paper is to show that if the unstable sub-system can be stabilized by means of output feedback, then one obtains an integrity condition which is actually equivalent to that of open-loop stable systems, with two additional assumptions. This means the condition may be evaluated solely on the basis of plant information and does not rely on the knowledge of the values of the controller parameters  

    Design of a gain-scheduling anti-swing controller for tower cranes using fuzzy clustering techniques

    , Article CIMCA 2006: International Conference on Computational Intelligence for Modelling, Control and Automation, Jointly with IAWTIC 2006: International Conference on Intelligent Agents Web Technologies and International Commerce, Sydney, NSW, 28 November 2006 through 1 December 2006 ; 2006 ; 0769527310 (ISBN); 9780769527314 (ISBN) Sadati, N ; Hooshmand, A ; Sharif University of Technology
    IEEE Computer Society  2006
    The main objective of this paper is to design a fast,non-expensive and practical controller for towercranes. The controllers are designed to transfer theloads from point to point, as fast as possible, and at thesame time the load swing is kept small during thetransfer process. Moreover, variations of the systemparameters such as cable length are taken intoconsideration. It is shown how the state feedbackcontrollers along with the gain scheduling could beused for a time varying linear model with varyingparameters. For this reason, linear controllers aredesigned for a number of operating points, where theirparameters are interpolated for conditions in between.In this way, a globally nonlinear... 

    A fault-tolerant and robust controller using model predictive path integral control for free-flying space robots

    , Article Frontiers in Robotics and AI ; Volume 9 , 2022 ; 22969144 (ISSN) Raisi, M ; Noohian, A ; Fallah, S ; Sharif University of Technology
    Frontiers Media S.A  2022
    The use of manipulators in space missions has become popular, as their applications can be extended to various space missions such as on-orbit servicing, assembly, and debris removal. Due to space reachability limitations, such robots must accomplish their tasks in space autonomously and under severe operating conditions such as the occurrence of faults or uncertainties. For robots and manipulators used in space missions, this paper provides a unique, robust control technique based on Model Predictive Path Integral Control (MPPI). The proposed algorithm, named Planner-Estimator MPPI (PE-MPPI), comprises a planner and an estimator. The planner controls a system, while the estimator modifies... 

    Decision Matrix for Time-Critical Optimal Trajectories for Air-Launch of Small Satellites

    , M.Sc. Thesis Sharif University of Technology Farzam Nik, Ehsan (Author) ; Malaek, Mohammad Bagher (Supervisor)
    One of the satellite time-critical launch methods is air-launch, which is considered in this research thoroughly. The Large number of important parameters of this method makes the system highly complex. In such complex systems, usual methods of design and development will not be effective. Moreover, based on systemic approaches, interfaces between different elements of a complex system have significant effects on the performance of the whole system. One of the methods for analysis of such systems is “Design Structure Matrix” or DSM. This method is based on system engineering principles and has confirmed capabilities in analysis of highly coupled systems.
    In this research, the air launch... 

    Roughening transition and universality of single step growth models in (2+1)-dimensions

    , Article New Journal of Physics ; Volume 19, Issue 6 , 2017 ; 13672630 (ISSN) Dashti Naserabadi, H ; Saberi, A. A ; Rouhani, S ; Sharif University of Technology
    We study (2+1)-dimensional single step model for crystal growth including both deposition and evaporation processes parametrized by a single control parameter p. Using extensive numerical simulations with a relatively high statistics, we estimate various interface exponents such as roughness, growth and dynamic exponents as well as various geometric and distribution exponents of height clusters and their boundaries (or iso-height lines) as function of p. We find that, in contrary to the general belief, there exists a critical value at which the model undergoes a roughening transition from a rough phase with in the Kardar-Parisi-Zhang universality to a smooth phase with , asymptotically in... 

    Decomposition and robust non-fragile stabilisation of singular time-delay systems

    , Article IET Control Theory and Applications ; Volume 12, Issue 13 , 2018 , Pages 1882-1888 ; 17518644 (ISSN) Zahedi, F ; Haeri, M ; Sharif University of Technology
    This study presents a new approach to decompose singular time-delay systems (STDSs) in a way that they can be transformable to normal time-delay systems (TDSs) with a lower order. Necessary and sufficient conditions are provided to determine which STDSs can be transformed to TDSs. Also, a stabilisation method is provided to stabilise the system, while the time delay in the system can belong to several distinct intervals or even everywhere. The proposed method is non-fragile towards controller parameters. This method also reveals one of the many applicable situations of the proposed decomposition. The effectiveness of the proposed method is illustrated through some examples. © 2018 The... 

    Comparing the performance of reference trajectory management and controller reconfiguration in attitude fault tolerant control

    , Article 2017 Asia Conference on Mechanical and Aerospace Engineering, ACMAE 2017, 29 December 2017 through 31 December 2017 ; Volume 151 , 2018 ; 2261236X (ISSN) Moradi, R ; Alikhani, A ; Jegarkandi, M. F ; Sharif University of Technology
    EDP Sciences  2018
    Reference trajectory management is a method to modify reference trajectories for the faulty system. The modified reference trajectories define new maneuvers for the system to retain its pre-fault dynamic performance. Controller reconfiguration is another method to handle faults in the system, for instance by adjusting the controller parameters (coefficients). Both of these two methods have been considered in the literature and are proven to be capable of handling various faults. However, the comparison of these two methods has not been considered sufficiently. In this paper, a controller reconfiguration mechanism and a reference trajectory management are proposed for the spacecraft attitude... 

    Chaos control via a simple fractional-order controller

    , Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 372, Issue 6 , 2008 , Pages 798-807 ; 03759601 (ISSN) Tavazoei, M. S ; Haeri, M ; Sharif University of Technology
    Elsevier  2008
    In this Letter, we propose a fractional-order controller to stabilize the unstable fixed points of an unstable open-loop system. Also, we show that this controller has strong ability to eliminate chaotic oscillations or reduce them to regular oscillations in the chaotic systems. This controller has simple structure and is designed very easily. To determine the control parameters, one needs only a little knowledge about the plant and therefore, the proposed controller is a suitable choice in the control of uncertain chaotic systems. © 2007 Elsevier B.V. All rights reserved  

    Surface acoustic waves as control actuator for drop removal from solid surface

    , Article Fluid Dynamics Research ; Volume 53, Issue 4 , 2021 ; 01695983 (ISSN) Noori, M. S ; Taleghani, A. S ; Rahni, M. T ; Sharif University of Technology
    IOP Publishing Ltd  2021
    Several types of research are performed on flow control and this fact highlights the importance of this topic. Over the last two decades, actuators based on acoustic waves have attracted much attention and have been used in widespread applications from mixing to pumping. This paper reveals the effects of some control parameters such as wave amplitude and wave frequency on the dynamical behavior of a sessile drop in order to change the flow characteristics. For this purpose, the removal of water from surfaces and drop movement against gravity are considered. Flow dynamics is simulated using lattice Boltzmann method. The results show that the drop can be removed from the surface in a short... 

    PI design based on DMC strategy

    , Article Transactions of the Institute of Measurement & Control ; Volume 27, Issue 1 , 2005 , Pages 21-36 ; 01423312 (ISSN) Haeri, M ; Sharif University of Technology
    Proportional and integral (PI) control parameters are determined by approximating a dynamic matrix control (DMC). Since accuracy of the approximation depends on DMC parameters in a complicated manner, a combination of direct and indirect optimization methods are employed in this paper. Quadratic programming (QP) is used to determine PI parameters, and a simple grid method is used to find optimal DMC parameters. A tuning formula for the PI controller based on a curve-fitting technique, is suggested. Computer simulations are performed to compare performance of the new PI design method with those achievable using some existing PI controllers. © 2005, Sage Publications. All rights reserved  

    Fabrication of AZ91/ SiCp Composite In Semi-Solid State By Using Electromagnetic Stirring, Microstructures And Mechanical Properties

    , M.Sc. Thesis Sharif University of Technology Ghaderi, Mohammad (Author) ; Aashuri, Hossein (Supervisor)
    In this study AZ91 alloy reinforced by SiC particles processed by semi-solid casting was produced by using electromagnetic stirrer. In order to prevent ignition and oxidation of the melted AZ91 alloy 1 Wt.% of calcium was added to the melt. In order to surface oxidation of SiC particles, they were heat treated in 1100 ᵒC for 2 hours before adding to the melt. Different methods of adding SiC particles to the melt were investigated. Particle distribution in the matrix was studied qualitatively and quantitatively using microscopic images and image analysis, respectively. It is shown that higher amount of reinforcement particle need to be added to the melt in multi-steps. Frequency versus... 

    Improving integral square error performance with implementable fractional-order PI controllers

    , Article Optimal Control Applications and Methods ; Vol. 35, Issue. 3 , May/June , 2014 , pp. 303-323 Rahimian, M. A ; Tavazoei, M. S ; Sharif University of Technology
    In this paper, an algebraic rule for tuning the integer realizations of fractional-order PI controllers is developed, with an integral square error performance index, which outperforms that of an optimal ordinary PI controller. To this end, the PIλ control structure is used in conjunction with a third-order integer approximating filter to provide a three parameter fixed-structure extension of the ordinary PI controller. Next, the extra degree of freedom in setting the order of integration λ is leveraged to introduce a steepest descent direction in the extended controller parameter space. It is then stated that shifting the parameters of an ordinary PI controller along the proposed descent... 

    Continuous ant colony filter applied to online estimation and compensation of ground effect in automatic landing of quadrotor

    , Article Engineering Applications of Artificial Intelligence ; Vol. 32, issue , June , 2014 , p. 100-111 Nobahari, H ; Sharifi, A. R ; Sharif University of Technology
    The automatic landing of a quadrotor is often associated with model uncertainties, measurement noises, and ground effect phenomenon. To mitigate these challenges, the accurate estimation of states especially the height above the ground, and its rate of change is vital. Moreover, the error of ground effect model can also be estimated and compensated during landing. In this paper, the recently developed continuous ant colony filter is implemented for integrated estimation of states and parameters. The estimated states are used in height control loop. To investigate the closed loop performance of the filter, two control strategies, a classical proportional-integral-derivative controller and a... 

    Non-fragile control and synchronization of a new fractional order chaotic system

    , Article Applied Mathematics and Computation ; Volume 222 , 2013 , Pages 712-721 ; 00963003 (ISSN) Asheghan, M. M ; Delshad, S. S ; Hamidi Beheshti, M. T ; Tavazoei, M. S ; Sharif University of Technology
    In this paper, we address global non-fragile control and synchronization of a new fractional order chaotic system. First we inspect the chaotic behavior of the fractional order system under study and also find the lowest order (2.49) for the introduced dynamics to remain chaotic. Then, a necessary and sufficient condition which can be easily extended to other fractional-order systems is proposed in terms of Linear Matrix Inequality (LMI) to check whether the candidate state feedback controller with parameter uncertainty can guarantee zero convergence of error or not. In addition, the proposed method provides a global zero attraction of error that guarantees stability around all existing... 

    Non-fragile tuning of fractional-order PD controllers for IPD-modelled processes

    , Article IFAC Proceedings Volumes (IFAC-PapersOnline) ; 2013 , Pages 361-366 ; 14746670 (ISSN) ; 9783902823274 (ISBN) Bahavarnia, M ; Tavazoei, M. S ; Mesbahi, A ; Sharif University of Technology
    This paper deals with introducing non-fragile algebraic tuning rules for fractional-order PD controllers where they are used in controlling processes modeled in Integral Plus Delay (IPD) forms. These tuning rules are obtained based on a recently introduced approach, named as the centroid approach, which results in non-fragile tuning methods. Based on this approach, the centroids of two-dimensional admissible regions or the center of gravity of three-dimensional admissible regions in controller parameter space give non-fragile options for choosing controller parameters. © 2013 IFAC  

    Object-oriented design for system identification and its application in chemical engineering industries

    , Article International Journal of Modelling and Simulation ; Volume 33, Issue 1 , 2013 , Pages 33-39 ; 02286203 (ISSN) Masoumi, S ; Boozarjomehry, R. B ; Sharif University of Technology
    Application of advanced process control methods in a chemical plant requires a model which represents the transient behaviour of the plant. However, only a few plant-wide identification methods have been proposed for chemical processes. In this paper, an objectoriented process identifier (OPI) framework has been introduced for plant-wide identification to show how using object-oriented design can provide a general plant-wide modelling framework for various systems including chemical processes. The interactions between units are considered in plant-wide identification methods. As a result, the obtained models can predict the system behaviour in new operating conditions better than those... 

    Inverse dynamics control of needle in prostate brachytherapy

    , Article 2012 IEEE International Conference on Industrial Technology, ICIT 2012, Proceedings ; 2012 , Pages 510-515 ; 9781467303422 (ISBN) Maghsoudi, A ; Jahed, M ; Sharif University of Technology
    IEEE  2012
    Needle insertion into the soft tissue has been the subject of many studies during the last decade, while needle control has become a crucial training tool, evaluating surgeon's skills in such critical incision. This study considers a model-based dynamics equation for the needle movement through the soft tissue. In the proposed model, the force distribution along the needle shaft is estimated through the use of tissue deformation data and tissue model. A novel algorithm for the needle control simulation is also proposed based on the developed dynamics equation of the needle movement. To point out the role of mechanical properties of the soft tissue, an inverse dynamics control method is used... 

    Welding current and arc voltage control in a GMAW process using ARMarkov based MPC

    , Article Control Engineering Practice ; Volume 19, Issue 12 , December , 2011 , Pages 1408-1422 ; 09670661 (ISSN) Mousavi Anzehaee, M ; Haeri, M ; Sharif University of Technology
    A predictive functional controller based on ARMarkov model structure has been designed to control welding current and arc voltage in a GMAW process. The closed loop system performance is investigated through computer simulations and is compared by those achieved from implementing two commonly used controllers i.e. PI and feedback linearization based PID. The local stability of the closed loop system is analyzed in the presence of uncertainties in the linearized model of the process as well as the control parameters. Finally it is shown that the proposed controller performs like a PI controller along with a pre-filter compensator