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    Stability Analysis and Imrovement in DC Grids Using Active Method

    , Ph.D. Dissertation Sharif University of Technology Asbafkan, Ali (Author) ; Mokhtari, Hossein (Supervisor)
    This dissertation is concened with the stability analysis and improvement in active power distribution grids. In active power grids, voltage stability challenges may occur due to the dynamic interactions among power electronic converters. In this research, power electronic converters are modeled in canonical form to investigate the effect of control loops on their impedance characteristics. The concept of dynamic interaction is explained from the impedance pint of view, which is the base of the stability criteria and imopedance coordinatioan. The concept of passivity is also explained and combined with the dynamic interaction to detect unstable modes from the DC bus impedance (Zbus)... 

    A Framework for Seismic Risk Assessment of Electrical Substation Equipment with Reliability and Endurance Time Methods

    , M.Sc. Thesis Sharif University of Technology Ghahremani Baghmisheh, Amir (Author) ; Esmaeil Purestekanchi, Homayoon (Supervisor)
    Influences of dynmic interaction between substation equipment on responses and fragility are studied. Proposing a framework for seismic risk analysis of substation equipment using reliability and endurance time methods is another aim of this project. Risk, in this contex, means the probability of exceeding monetary loss. Three dimensional models of four vulnerable types of equipment including surge arrester, current transformer, circuit breaker and disconnect switch are developed and verified. Six different systems of equipment connected through rigid bus bars comprising of two, three and four equipment are considered. Fragility curves are developed for equipment in both unconnected and... 

    Effects of Pile Soil Structure Interaction on the Seismic Response of a 6 Story Building

    , M.Sc. Thesis Sharif University of Technology Aminikhah, Ahmad (Author) ; Ahmadi, Mohammad Mahdi (Supervisor)
    Numerous structures which are involved in seismic soil-pile-structure interaction have been damaged، failure in piles or even collapsed that can’t predict. Because of difficult modeling in soil، pile، structure interaction prediction the response of structure is impossible. In this study with using the finite element Abaqus software tries to understand the effect of soil pile structure interaction in structure response. By using the time history of Elcentro، structure with different boundary conditions were analyzed and the response of them were compared. Models have different boundary condition such as fixed base، pile groups and pile raft. Also in this study the effect of mat in... 

    Fragility and Risk Analysis of Electrical Substation Equipment Using Reliability and Endurance Time Methods

    , M.Sc. Thesis Sharif University of Technology Delaviz Bonab, Arman (Author) ; Esmail Pourestekanchi, Homayoon (Supervisor)
    Electrical substations and its vital components such as switchgears, have experienced severe damage during recent earthquakes, followed by widespread blackouts around the world. To improve the seismic resiliency of power grids and use probabilistic decision-making frameworks, comprehensive fragility data for the different equipment is needed. The purpose of this study is to assess the vulnerability of equipment in substations and to develop fragility curves for this equipment. For this purpose, four main equipment of switchgear, namely circuit breaker, disconnect switch, current transformer and surge arrester, have been modeled in three dimensions and verified. After examining the different... 

    The impact of wind farms with doubly fed induction generators on power system electromechanical oscillations

    , Article Renewable Energy ; Volume 50 , 2013 , Pages 780-785 ; 09601481 (ISSN) Jafarian, M ; Ranjbar, A. M ; Sharif University of Technology
    Introduction of large amounts of new wind generation can affect the small signal stability of power systems with three mechanisms: displacing synchronous generators (SGs); reducing SGs power generation; and the dynamics of wind farms (WFs) interacting with the electromechanical mode of SGs. In this paper a novel approach is developed to investigate the impact of the latter mechanism on existing power systems oscillations. In this approach, the dynamic behavior of grid connected WFs is studied independent of the dynamic behavior of system SGs. This approach helps to identify the conditions in which the dynamics of WFs may interact with the electromechanical mode of SGs. Also it helps to... 

    An inextensible membrane at the interface of a transversely isotropic bi-material full-space

    , Article International Journal of Engineering Science ; Volume 91 , June , 2015 , Pages 34-48 ; 00207225 (ISSN) Kalantari, M ; Khojasteh, A ; Mohammadnezhad, H ; Rahimian, M ; Pak, R. Y. S ; Sharif University of Technology
    Elsevier Ltd  2015
    A theoretical formulation is presented for the determination of the dynamic interaction of a horizontally loaded inextensible circular membrane embedded at the interface of a transversely isotropic bi-material full-space, using cylindrical co-ordinate system and applying Hankel integral transforms in the radial direction and Fourier series, the problem will be changed to a system of four separate integral equations, which, in turn, are reduced to a pair of Fredholm equations of the second kind that are amenable to numerical treatments. The impedance functions have been evaluated in dynamic case, which can be directly used in soil-structure-interaction and engineering problems. It is shown... 

    Unbalance-induced rub between rotor and compliant-segmented stator

    , Article Journal of Sound and Vibration ; Volume 429 , 2018 , Pages 96-129 ; 0022460X (ISSN) Behzad, M ; Alvandi, M ; Sharif University of Technology
    Academic Press  2018
    Today, turbomachinery designers are trying to attain zero clearances for optimizing performance and efficiency of machine by designing advanced compliant-segmented seals. This trend involves secondary issues such as rotor-to-stator contact interaction which is to be treated with more technical knowledge in rotordynamic design and condition monitoring programs. The aim of this paper is to gain insight into dynamic interaction between a flexible rotor and a set of compliant arc-shaped segments as stator system. Specifically, the unbalanced-induced forward rubbing response is investigated in tight clearance condition during resonance-passing situations. A Jeffcott rotor modeling is used for... 

    Enhanced local viscosity around colloidal nanoparticles probed by equilibrium molecular dynamics simulations

    , Article Journal of Chemical Physics ; Volume 155, Issue 17 , 2021 ; 00219606 (ISSN) Rabani, R ; Saidi, M. H ; Joly, L ; Merabia, S ; Rajabpour, A ; Sharif University of Technology
    American Institute of Physics Inc  2021
    Nanofluids - dispersions of nanometer-sized particles in a liquid medium - have been proposed for a wide variety of thermal management applications. It is known that a solid-like nanolayer of liquid of typical thicknesses of 0.5-1 nm surrounding the colloidal nanoparticles can act as a thermal bridge between the nanoparticle and the bulk liquid. Yet, its effect on the nanofluid viscosity has not been elucidated so far. In this article, we compute the local viscosity of the nanolayer using equilibrium molecular dynamics based on the Green-Kubo formula. We first assess the validity of the method to predict the viscosity locally. We apply this methodology to the calculation of the local... 

    Neural-network-based observer for real-time tipover estimation

    , Article Mechatronics ; Volume 15, Issue 8 , 2005 , Pages 989-1004 ; 09574158 (ISSN) Meghdari, A ; Naderi, D ; Alam, M. R ; Sharif University of Technology
    Tipover issue is an important problem in autonomous mobile manipulators. This issue is becoming more important in new generation of mobile robots where their size and weight are reduced, and they are designed to work on uneven terrains with higher speeds. Estimating the distance from the tipover stability margin would enhance the capability of the mobile manipulators in correcting their motion. For a valid estimation of the tipover margin one must take into account the full dynamic interaction between the vehicle and its manipulator. In mobile manipulators with several degrees of freedom a huge amount of time is needed to solve equations of motion while real-time tipover control needs a fast... 

    Forced vibration of delaminated timoshenko beams under the action of moving oscillatory mass

    , Article Shock and Vibration ; Volume 20, Issue 1 , 2013 , Pages 79-96 ; 10709622 (ISSN) Kargarnovin, M. H ; Ahmadian, M. T ; Jafari Talookolaei, R. A ; Sharif University of Technology
    This paper presents the dynamic response of a delaminated composite beam under the action of a moving oscillating mass. In this analysis the Poisson's effect is considered for the first time. Moreover, the effects of rotary inertia and shear deformation are incorporated. In our modeling linear springs are used between delaminated surfaces to simulate the dynamic interaction between sub-beams. To solve the governing differential equations of motion using modal expansion series, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes necessary for forced vibration analysis. The obtained results for the free and forced vibrations of beams are... 

    Effects of rigid bus conductors on seismic fragility of electrical substation equipment

    , Article Soil Dynamics and Earthquake Engineering ; Volume 125 , 2019 ; 02677261 (ISSN) Baghmisheh, A. G ; Estekanchi, H. E ; Sharif University of Technology
    Elsevier Ltd  2019
    The present paper studies the impact of dynamic interaction between high-voltage substation equipment on the response and vulnerability of substation equipment. The 3D numerical model is developed for four types of vulnerable equipment in the both unconnected and connected conditions. The bus slider-rigid bus assembly is utilized to establish the connection between the equipment. The incremental dynamic analysis is carried out in the developed systems to produce the fragility function for each equipment. Also, the Monte Carlo approach is employed to evaluate the accuracy of the generated functions. It is concluded that the incorporation of connection parts in the model can significantly... 

    Longitudinal and transverse vibration of a single-walled carbon nanotube subjected to a moving nanoparticle accounting for both nonlocal and inertial effects

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 42, Issue 9 , 2010 , Pages 2391-2401 ; 13869477 (ISSN) Kiani, K ; Sharif University of Technology
    Single-walled carbon nanotubes (SWCNTs) can be promising delivery nanodevices for a diverse range of applications, however, little is known about their dynamical interactions with moving nanoscale particles. In this paper, dynamic response of a SWCNT subjected to a moving nanoparticle is examined in the framework of the nonlocal continuum theory of Eringen. The inertial effects of the moving nanoparticle and the existing friction between the nanoparticle surface and the inner surface of the SWCNT are incorporated in the formulation of the problem. The equivalent continuum structure associated with the SWCNT is considered and modeled using nonlocal Rayleigh beam theory under simply supported... 

    Enhancement of the tipover stability of mobile manipulators with non-holonomic constraints using an adaptive neuro-fuzzy-based controller

    , Article Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering ; Volume 223, Issue 2 , 2009 , Pages 201-213 ; 09596518 (ISSN) Ghaffari, A ; Meghdari, A ; Naderi, D ; Eslami, S ; Sharif University of Technology
    The stability issue of mobile manipulators, particularly when the end-effector and the vehicle have to follow a predefined trajectory (for some special duties like painting a plane or carrying a light load), is a crucial subject and needs special attention. In this paper, by utilizing the manipulator compensation motions, the instantaneous proper configuration for a redundant mobile robot is determined. A fast methodology taking into account the dynamic interaction between the manipulator and the vehicle is proposed for enhancing the tipover stability (i.e. stability against overturning) of the mobile manipulator by employing the soft computing approach including a genetic algorithm, neural...