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    PID controller design for micro gas turbines using experimental frequency-response data and a linear identification technique

    , Article International Journal of Advanced Mechatronic Systems ; Volume 5, Issue 6 , 2013 , Pages 353-364 ; 17568412 (ISSN) Banazadeh, A ; Gol, H. A ; Ramazani, H ; Sharif University of Technology
    E-flow Inderscience  2013
    This paper discusses the identification process of engine dynamics and presents derived transfer function models including; thrust, shaft speed, compressor exit pressure and turbine exit temperature in relation to the fuel flow. Model identification approach, presented in this paper, is the first to consider frequency-sweep signals to excite dynamics, as well as to utilise windowing and smoothing techniques to reduce random errors in the spectral estimates. Here, frequency sweep provides a fairly uniform spectral excitation and chirp-z transform warrants the exact determination of the frequency responses that are robust to the uncertainties. The identified models are also validated with the... 

    Position convergence of informed agents in flocking problem with general linear dynamic agents

    , Article IET Control Theory and Applications ; Volume 9, Issue 3 , February , 2015 , Pages 392-398 ; 17518644 (ISSN) Yazdani, S ; Haeri, M ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    In most existing works on the flocking problem, results were obtained for the case where a double integrator dynamic is used to describe motion of agents and virtual leader. These results, however, may not be generalised to agents with general linear dynamic. In this study, it is shown that in the flocking of agents with a linear dynamic, the velocity convergence of agents does not generally lead to the position convergence of informed agents and the position convergence is possible only for a specified group of linear dynamics. In this study, a control protocol is proposed to flock agents with specified linear dynamics and guarantee the velocity convergence of all agents as well as average... 

    Complexity and variability of the center of pressure time series during quiet standing in patients with knee osteoarthritis

    , Article Clinical Biomechanics ; Volume 32 , 2016 , Pages 280-285 ; 02680033 (ISSN) Negahban, H ; Sanjari, M. A ; Karimi, M ; Parnian Pour, M ; Sharif University of Technology
    Elsevier Ltd 
    Background While several studies have investigated the traditional linear measures in patients with knee osteoarthritis, no study has yet reported the non-linear structure of postural sway in these patients. Methods We used two non-linear methods, recurrence quantification analysis (percent of determinism-%DET) and central tendency measure, to respectively investigate differences in the complexity and variability of sway dynamics between two groups of knee osteoarthritis patients (n = 27) and healthy controls (n = 27) under different conditions of postural and cognitive tasks. The experimental conditions included standing on (1) rigid surface with open eyes; (2) rigid surface with closed... 

    Seismic Response of “Karroon III” DAM to Non-Uniform Ground Motions

    , M.Sc. Thesis Sharif University of Technology Pouya, Mohammad Reza (Author) ; Ghaemian, Mohsen (Supervisor)
    Usually in analysis of arch dams, applied seismic motions on dam-foundation interface are assumed to be uniform. This is while that recorded motions show non-uniform accelerations in dam-foundation interface. Analyzing of the dam under this non-uniform accelerations we can find the importance of this assumption in analysis of arch dams. Two earthquakes were excited “KAROON III” dam at 20.11.2007 and 21.11.2007. The respective motions were recorded by the array of accelerometers that has been installed on the dam. The recorded motions, indicated non-uniformity of excitations in accelerometers were installed near the dam-foundation interface. Therefore this data provided an opportunity to... 

    Application of endurance time method in nonlinear seismic analysis of steel frames

    , Article Procedia Engineering ; Volume 14 , 2011 , Pages 3237-3244 ; 18777058 (ISSN) Riahi, H. T ; Estekanchi, H. E ; Seyedain Boroujeni, S ; Sharif University of Technology
    In Endurance Time (ET) method gradually intensifying acceleration functions are created in a manner that the linear and nonlinear response spectra of them, while being proportional to average of real earthquakes spectra, intensifies in a uniform manner with time. These functions are used as input functions for nonlinear time history analysis of structures and performance of structures is assessed based on the maximum time duration that they can meet the specified performance objectives. In this paper, application of the ET method in nonlinear seismic analysis of structures has been investigated. Numerical procedures and optimization techniques that are used for the production of acceleration... 

    Flocking of multi-agent systems with multiple second-order uncoupled linear dynamics and virtual leader

    , Article IET Control Theory and Applications ; Volume 10, Issue 8 , 2016 , Pages 853-860 ; 17518644 (ISSN) Yazdani, S ; Haeri, M ; Sharif University of Technology
    Institution of Engineering and Technology  2016
    In this study, flocking of multi-agent systems with virtual leader and linear dynamics is investigated. It is assumed that the dynamics of agents in each dimension is represented by a general second-order linear model. The proposed control protocol is composed of two terms, one for feed backing each agent's states and one for cooperative control. At first, the flocking problem of multi-agent systems with identical agents is discussed and then the proposed protocol is generalised to flock heterogeneous multi-agent systems. Under the proposed algorithm, the velocity convergence of whole group to a velocity of virtual leader is guaranteed while the connectivity of network is preserved and... 

    Adaptive nonlinear observer design using feedforward neural networks

    , Article Scientia Iranica ; Volume 12, Issue 2 , 2005 , Pages 141-150 ; 10263098 (ISSN) Dehghan Nayeri, M. R ; Alasty, A ; Sharif University of Technology
    Sharif University of Technology  2005
    This paper concerns the design of a neural state observer for nonlinear dynamic systems with noisy measurement channels and in the presence of small model errors. The proposed observer consists of three feedforward neural parts, two of which are MLP universal approximators, which are being trained off-line and the last one being a Linearly Parameterized Neural Network (LPNN), which is being updated on-line. The off-line trained parts are able to generate state estimations instantly and almost accurately, if there are not catastrophic errors in the mathematical model used. The contribution of the on-line adapting part is to compensate the remainder estimation error due to uncertain parameters... 

    Design of Arch Dams with Axial and Biaxial Strength of Concrete Based on Permissible Safety Factor

    , M.Sc. Thesis Sharif University of Technology Fakhri, Mahdi (Author) ; Ghaemian, Mohsen (Supervisor)
    The dams as one of the most costly and most fundamental infrastructure that human steps to make their, always paid special attention to people in different historical periods. According to the high cost of this structure, optimum design is so important. On other hand stability of structure as main aspects of the design that in the absence of it is threatening the lives of many people in downstream. Therefor the engineers consider two important aspect when they want to design a dam. The first step in designing is determinate the external loads. A designer not only must recognize this loads but also by using the material that he consume in the body of dams reach to a safety structure in During... 

    Determination of Parameters Affecting the Linear Seismic Evaluation of Gravity Dams Using Nonlinear Analysis

    , M.Sc. Thesis Sharif University of Technology Monazzam, Arash (Author) ; Ghaemian, Mohsen (Supervisor)
    Gravity dams are solid concrete structures that maintain their stability against design loads from the geometric shape and the mass and strength of the concrete. Because of their critical role in supplying portable and agricultural water and problems which would happen if they broke, it is required to consider their stability and keep them in safe conditions. They should be able to continue their function after a disaster such as earthquake. But most of them are aged dams with some have been built near faults. Indeed, there are some concerns regarding the performance of these dams under the effect of seismic loads. This research deals with performance evaluation of concerete gravity . The... 

    Performance Evaluation of Concrete Gravity Dam Using Crest Displacement by Nonlinear Analysis

    , M.Sc. Thesis Sharif University of Technology Enayati, Hamed (Author) ; Ghaemian, Mohsen (Supervisor)
    Concrete gravity dams are one of the most important infrastructures therefore their performance under seismic load is an important issue of concern for dam owners. It is necessary that these infrastructures to be able to continue their function after a disaster such as earthquake, as any damage can cause huge cost. For analysis of dams linear and nonlinear analyses are used. Because even operating loads will create cracks in the body of the dam, dam behavior can not always be considered linear. It is remarkable that these surface cracks can join together under seismic loads and this question the safety of dams. It is important to note that nonlinear analysis of concrete gravity dams is... 

    Increasing Robustness and Performance of the Ins-Dvl Underwater Navigation by Using Model-Aided Navigation

    , Ph.D. Dissertation Sharif University of Technology Karmozdi, Ali (Author) ; Salarieh, Hassan (Supervisor) ; Alasty, Aria (Supervisor) ; Hashemi, Mojtaba (Co-Supervisor)
    Dopller velocity log (DVL) is an important underwater navigation sensor. But in the INS-DVL integrated navigation systems, positional error grows unlimitedly over time. Also, the losing bottom lock (LBL) phenomenon is possible in DVL for various reasons such as AUV severe angular changes. So INS-DVL systems are not robust against environmental disturbances resulting in LBL. In this research, mode-aided navigation is used to improve the INS-DVL navigation system. Model-aided navigation is divided into two categories: using kinematic constraints and using kinetic model. Both approaches are used in this research to improve navigation performance and robustness. Initially, the existing kinematic... 

    Construction of Pt nanoparticle-decorated graphene nanosheets and carbon nanospheres nanocomposite-modified electrodes: Application to ultrasensitive electrochemical determination of cefepime

    , Article RSC Advances ; Volume 4, Issue 15 , 2014 , Pages 7786-7794 ; ISSN: 20462069 Shahrokhian, S ; Hosseini Nassab, N ; Ghalkhani, M ; Sharif University of Technology
    A novel ultrasensitive modified electrode was fabricated with a graphene nanosheets and carbon nanospheres (GNS-CNS)-based nanocomposite film as a powerful platform. Pt nanoparticles (PtNPs) were simply electrodeposited onto the GNS-CNS-coated glassy carbon electrode creating a PtNPs/GNS-CNS hybrid nanocomposite modified electrode. Scanning electron microscopy, energy dispersive X-ray spectroscopy and linear sweep voltammetry (LSV) techniques were used for the characterization of the prepared modified electrode. The results of investigation of electrochemical response characteristics of cefepime (CP) revealed a considerable improvement in the oxidation peak current of CP on PtNPs/GNS-CNS/GCE... 

    An investigation on the effects of gas pressure drop in heat exchangers on dynamics of a free piston stirling engine

    , Article International Journal of Engineering, Transactions B: Applications ; Volume 30, Issue 2 , 2017 , Pages 1243-1252 ; 1728144X (ISSN) Zare, S ; Tavakolpour Saleh, A. R ; Aghajanzadeh, O ; Sharif University of Technology
    Materials and Energy Research Center  2017
    This paper is devoted to study the effects of pressure drop in heat exchangers on the dynamics of a free piston Stirling engine. First, the dynamic equations governing the pistons as well as the gas pressure equations for hot and cold spaces of the engine are extracted. Then, by substituting the obtained pressure equations into the dynamic relationships the final nonlinear dynamic equations governing the free piston Stirling engine are acquired. Next, effects of the gas pressure drop in heat exchangers on maximum strokes of the pistons and their velocities and accelerations are investigated. Furthermore, influences of pressure drop increase in the heat exchangers on maximum and minimum gas... 

    Prediction of nonlinear dynamic coefficients of tilting-pad journal bearings with pad perturbation

    , Article Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology ; 2021 ; 13506501 (ISSN) Hojjati, M ; Farzanmehr, Y ; Mohammad Navazi, H ; Haddadpour, H ; Sharif University of Technology
    SAGE Publications Ltd  2021
    In this paper, a modified partial derivative method is developed to predict the linear and nonlinear dynamic coefficients of tilting-pad journal bearings with journal and pad perturbation. To this end, Reynolds equation and its boundary conditions along with equilibrium equations of the pad are used. Finite difference, partial derivative method, and perturbation technique have been employed simultaneously for solving these equations. The accuracy of the results is investigated by comparing the linear dynamic coefficients of three types of tilting-pad journal bearings with those published the literature. It is shown that the nonlinear dynamic coefficients depend on Sommerfeld number,... 

    Nonlinear vibrations of an inclined beam subjected to a moving load

    , Article Journal of Physics: Conference Series, 8 September 2009 through 10 September 2009, Cambridge ; Volume 181, Issue 1 , 2009 ; 17426588 (ISSN) Mamandi, A ; Kargarnovin, M ; Younesian, D ; Sharif University of Technology
    In this paper, the nonlinear dynamic responses of an inclined pinned-pinned Euler-Bernoulli beam with a constant cross section and finite length subjected to a concentrated vertical force traveling with constant velocity is investigated by using the mode summation method. Frequency analysis of the PDE's governing equations of motion for steady-state response is studied by applying multiple scales method. The nonlinear dynamic deflections of the beam are obtained by solving two coupled nonlinear PDE's governing equations of planar motion for both longitudinal and transverse oscillations of the beam. The dynamic magnification factor and normalized time histories of mid-point of the beam are... 

    Adaptive impedance control of UAVs interacting with environment using a robot manipulator

    , Article 2014 2nd RSI/ISM International Conference on Robotics and Mechatronics, ICRoM 2014 ; Oct , 2014 , p. 636-641 Sayyaadi, H ; Sharifi, M ; Sharif University of Technology
    In this paper, a nonlinear adaptive impedance controller is proposed for UAVs equipped with a robot manipulator that interacts with environment. In this adaptive controller, by considering the nonlinear dynamics model of the UAV plus the robot manipulator in Cartesian coordinates, all of model parameters are considered to be completely uncertain and their estimation is updated using an adaptation law. The objective of the proposed adaptive controller is the control of manipulator's end-effector impedance in Cartesian coordinates to have a stable physical interaction. The adjustable Cartesian impedance is a desired dynamical relationship between the end-effector motion in Cartesian... 

    Construction of a modified carbon paste electrode based on TiO2 nanoparticles for the determination of gallic acid

    , Article Journal of Solid State Electrochemistry ; Volume 17, Issue 1 , 2013 , Pages 157-165 ; 14328488 (ISSN) Tashkhourian, J ; Nami Ana, S. F ; Hashemnia, S ; Hormozi Nezhad, M. R ; Sharif University of Technology
    A modified carbon paste electrode was prepared by incorporating the TiO2 nanoparticles in the carbon paste matrix. The electrochemical behavior of gallic acid (GA) is investigated on the surface of the electrode using cyclic voltammetry and differential pulse voltammetry. The surface morphology of the prepared electrode was characterized using the scanning electron microscopy. The results indicate that the electrochemical response of GA is improved significantly at the modified electrode compared with the unmodified electrode. Furthermore, the capabilities of electron transfer on these two electrodes were also investigated by electrochemical impedance spectroscopy. Under the optimized... 

    The dynamic pull-in instability and snap-through behavior of initially curved microbeams

    , Article Mechanics of Advanced Materials and Structures ; Volume 19, Issue 6 , Jul , 2012 , Pages 485-491 ; 15376494 (ISSN) Zand, M. M ; Sharif University of Technology
    T&F  2012
    In this study, dynamic pull-in instability and snap-through buckling of initially curved microbeams are investigated. The microbeams are actuated by suddenly applied electrostatic force. A finite element model is developed to discretize the governing equations, and Newmark time discretization is employed to solve the discretized equations. The static pull-in behavior is investigated to validate the model. The results of the finite element model are compared with finite difference solutions and their convergence is examined. In addition, the influence of different parameters on dynamic pull-in instability and snap-through buckling is explored  

    Estimating seismic demand parameters using the endurance time method

    , Article Journal of Zhejiang University: Science A ; Volume 12, Issue 8 , 2011 , Pages 616-626 ; 1673565X (ISSN) Madarshahian, R ; Estekanchi, H ; Mahvashmohammadi, A ; Sharif University of Technology
    The endurance time (ET) method is a time history based dynamic analysis in which structures are subjected to gradually intensifying excitations and their performances are judged based on their responses at various excitation levels. Using this method, the computational effort required for estimating probable seismic demand parameters can be reduced by an order of magnitude. Calculation of the maximum displacement or target displacement is a basic requirement for estimating performance based on structural design. The purpose of this paper is to compare the results of the nonlinear ET method with the nonlinear static pushover (NSP) method of FEMA 356 by evaluating performances and target... 

    Nonlinear robust adaptive Cartesian impedance control of UAVs equipped with a robot manipulator

    , Article Advanced Robotics ; Volume 29, Issue 3 , Feb , 2015 , Pages 171-186 ; 01691864 (ISSN) Sharifi, M ; Sayyaadi, H ; Sharif University of Technology
    Robotics Society of Japan  2015
    In this paper, a new nonlinear robust adaptive impedance controller is addressed for Unmanned Aerial Vehicles (UAVs) equipped with a robot manipulator that physically interacts with environment. A UAV equipped with a robot manipulator is a novel system that can perform different tasks instead of human being in dangerous and/or inaccessible environments. The objective of the proposed robust adaptive controller is control of the UAV and its robotic manipulators end-effector impedance in Cartesian space in order to have a stable physical interaction with environment. The proposed controller is robust against parametric uncertainties in the nonlinear dynamics model of the UAV and the robot...