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    A 1.5V 8-bit low-power self-calibrating high-speed folding ADC

    , Article 2005 PhD Research in Microelectronics and Electronics Conference, Lausanne, 25 July 2005 through 28 July 2005 ; Volume I , 2005 , Pages 33-36 ; 0780393457 (ISBN); 9780780393455 (ISBN) Movahedian, H ; Bakhtiar, M. S ; Sharif University of Technology
    An 8-bit High-speed folding/interpolating ADC is presented. Designed in 0.18μm CMOS technology, the ADC dissipates only 50mW from a single 1.5V supply. A novel technique based on using both N and P folding cells is used to widen the input range and a self-calibration technique based on using Trimmable MOSFETs is employed to improve the static and dynamic performance  

    Analysis of carrier dynamic effects in transistor lasers

    , Article Optical Engineering ; Volume 51, Issue 2 , December , 2012 ; 00913286 (ISSN) Horri, A ; Mirmoeini, S. Z ; Faez, R ; Sharif University of Technology
    We present an analytical model to analyze the influence of carrier dynamics on the static and dynamic responses of transistor laser (TL). Our analysis is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. We show that the details of the dc and small signal behavior of transistor lasers are strongly affected by the escape and capture times of carriers in quantum well (QW). Also, the effects of carrier recombination lifetime in the quantum well and base regions on the TL static and dynamic performances are investigated  

    The brushless doubly-fed machine vector model in the rotor flux oriented reference frame

    , Article 34th Annual Conference of the IEEE Industrial Electronics Society, IECON 2008, Orlando, FL, 10 November 2008 through 13 November 2008 ; January , 2008 , Pages 1415-1420 ; 9781424417667 (ISBN) Barati, F ; Oraee, H ; Abdi, E ; Shao, S ; Mc Mahon, R ; Sharif University of Technology
    IEEE Computer Society  2008
    The paper presents the vector model of the Brushless Doubly-Fed Machine (BDFM) in the rotor flux oriented reference frame. The rotor flux oriented reference frame is well known in the standard AC machines analysis and control. Similar benefits can be sought by employing this method for the BDFM The vector model is implemented in MATLAB/SIVIULINK to simulate the BDFM dynamic performance under different operating conditions. The predictions from the vector model are compared to those from the coupled circuit model in simulation. The results are shown for the cascade mode of operation. © 2008 IEEE  

    Investigation of core loss effect on steady-state characteristics of inverter fed brushless doubly fed machines

    , Article IEEE Transactions on Energy Conversion ; Volume 29, Issue 1 , March , 2014 , Pages 57-64 ; ISSN: 08858969 Hashemnia, M. N ; Tahami, F ; Oyarbide, E ; Sharif University of Technology
    Brushless doubly fed machine (BDFM) shows promising results for wind power and adjustable-speed drive applications. Due to poor rotor magnetic coupling and relatively high value of slip, core loss is an important factor which can affect the steady-state and dynamic performance of BDFM. Specifically, core loss plays a major role when evaluating the efficiency of the machine. By now, there is no comprehensive study on core loss effect on performance characteristics of BDFM in the literature. In this paper, based on the derived relations and applying transformation of parameters from one winding to another one, the steady-state equivalent circuit model of BDFM without core loss is modified in... 

    Large signal analysis of double quantum well transistor laser

    , Article Optical and Quantum Electronics ; Volume 45, Issue 5 , 2013 , Pages 389-399 ; 03068919 (ISSN) Horri, A ; Faez, R ; Sharif University of Technology
    In this paper, we present an analytical model for the large-signal analysis of the double quantum well (DQW) transistor laser. Our model is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. By using the presented model, effects of barrier width on DQW transistor laser static and dynamic performances are investigated. Also the static and dynamic responses of DQW transistor lasers are compared with single quantum well ones. Simulation results are in agreement with the numerical and experimental results reported by other researchers  

    Interaction of the dynamics of doubly fed wind generators with power system electromechanical oscillations

    , Article IET Renewable Power Generation ; Volume 7, Issue 2 , March , 2013 , Pages 89-97 ; 17521416 (ISSN) Jafarian, M ; Ranjbar, A. M ; Sharif University of Technology
    The interaction of the dynamics of doubly fed wind generators with the electromechanical mode of nearby synchronous generators (SGs) can affect the small signal stability of power systems with high penetration levels of wind power. In this study, a novel approach is developed to investigate these interactions and their impact on the damping of power system oscillations. In this approach it is not necessary to model the dynamic behaviour of system SGs and only the frequencies of system oscillations are important. This approach is based on the sensitivity of SGs electromechanical eigenvalue with respect to variations in the Jacobian matrix of power system. By applying this approach to a test... 

    The influence of vertical deflection of the supports in modeling squeeze film damping in torsional micromirrors

    , Article Microelectronics Journal ; Volume 43, Issue 8 , 2012 , Pages 530-536 ; 00262692 (ISSN) Moeenfard, H ; Taghi Ahmadian, M ; Sharif University of Technology
    Elsevier  2012
    The objective of this work is to create an analytical framework to study the problem of squeezed film damping in micromirrors considering the bending of the supporting torsion microbeams. Using mathematical and physical justifications, nonlinear Reynolds equation governing the behavior of the squeezed gas underneath the mirror is linearized. The resulting linearized equation is then nondimensionalized and analytically solved for two cases of the infinitesimal and finite tilting angle of the mirror. The obtained pressure distribution from the solution of the Reynolds equation is then utilized for finding the squeezed film damping force and torque applied to the mirror. The results show that... 

    Development of a semi-empirical method for hydro-aerodynamic performance evaluation of an AAMV, in take-off phase

    , Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 37, Issue 3 , May , 2015 , Pages 987-999 ; 16785878 (ISSN) Maali Amiri, M ; Tavakoli Dakhrabadi, M ; Seif, M. S ; Sharif University of Technology
    Springer Verlag  2015
    An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles accentuates a gap that can be usefully filled by a new vehicle concept, making use of both hydrodynamic and aerodynamic forces. A high speed marine vehicle equipped with aerodynamic surfaces (called an AAMV, ‘aerodynamically alleviated marine vehicle’) is one such concept. There are three major modes of motion in the operation of an AAMV including take-off, cruising and landing. However, during take-off, hydrodynamic and aerodynamic problems of an AAMV interact with each other in a coupled manner, which make the evaluation of this phase much more difficult. In this article, at first aerodynamic... 

    Comparison of dynamic and static performances of a quaternary distillation sequence

    , Article Industrial and Engineering Chemistry Research ; Volume 49, Issue 13 , June , 2010 , Pages 6135-6143 ; 08885885 (ISSN) Baghmisheh, G ; Shahrokhi, M ; Bozorgmehri, R ; Sharif University of Technology
    In this work, steady state and dynamic performances of quaternary distillation column sequences designed based on steady state and dynamic cost functions have been investigated. To quantify the dynamic performance, product losses due to disturbances have been considered in the objective function. In addition, variations of operating costs such as utilities have been considered in the objective function. To separate a quaternary mixture into four products, 22 configurations have been used. It has been observed that the feed composition, disturbance frequency and magnitude affect the dynamic behavior strongly. To decrease the optimization computational load, a scheme that provides a suboptimal... 

    Dynamic performance of different knee mechanisms with compliant joints

    , Article Scientia Iranica ; Volume 23, Issue 3 , 2016 , Pages 1055-1063 ; 10263098 (ISSN) Ghaemi, N ; Zohoor, H ; Ghaemi, H ; Sharif University of Technology
    Sharif University of Technology  2016
    Loss of lower extremities has been one of the main problems in human life. Although most of the available knee devices are aesthetically acceptable, there is a necessity for lighter and more compact mechanisms, especially for younger amputees. This problem can be solved by the combining compliant mechanism design with traditional mechanism design methods. In this study, one group of the prosthetics that is known as the compliant knee mechanisms" is evaluated. At first, the different knee mechanisms, such as fourand six-bar knee linkages are investigated to calculate the values of the control moments (actuator torque). Then, the suitable location (where the actuator torque is to be exerted)... 

    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... 

    Airborne turbines: The impact of scaling on system performance

    , Article ASME 2017 International Mechanical Engineering Congress and Exposition, IMECE 2017, 3 November 2017 through 9 November 2017 ; Volume 6 , 2017 ; 9780791858417 (ISBN) Mohafez, M. H ; Goudarzi, N ; ASME ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2017
    Tethered airborne wind energy systems are among emerging renewable energy technologies in recent years. These systems can harness greater power densities at higher altitudes with lower costs of installation and energy production in comparison with those from conventional ground-based energy harnessing technologies. A Buoyant Airborne Turbine (BAT) as a flying aerostat has a horizontal axis wind turbine within its shell and can elevate up to 600m. There are a number of pertinent parameters such as BAT configurations/component dimensions or its aerodynamic characteristics that impact the system total power performance. Identifying the optimum values of these parameters by conducting... 

    Stator-Flux-Oriented vector control for brushless doubly fed induction generator

    , Article IEEE Transactions on Industrial Electronics ; Volume 56, Issue 10 , 2009 , Pages 4220-4228 ; 02780046 (ISSN) Shao, S ; Abdi, E ; Barati, F ; McMahon, R ; Sharif University of Technology
    Brushless doubly fed induction generators (BDFIGs) show commercial promise for wind-power generation due to their lower capital and operational costs and higher reliability as compared with doubly fed induction generators. This paper presents a vector-control scheme for a BDFIG operating as a variable-speed generator. The proposed vector controller is developed on the power-winding stator-flux frame and can be used to control both the speed and the reactive power. The machine model and the control system are developed in MATLAB. The test results show that the proposed controller has good dynamic performance when changes in speed and reactive power are applied. © 2009 IEEE  

    Effect of active feather length on aerodynamic performance of airfoils at low reynolds number flow

    , Article AIAA AVIATION 2020 FORUM, 15 June 2020 through 19 June 2020 ; Volume 1 PartF , 2020 Esmaeili, A ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc, AIAA  2020
    To increase the flight endurance of a Micro air vehicle (MAVs), which operates at low Reynolds number flow, one way is to harvest energy during its flight. By inspiring from the nature when all the birds use their feathers to control and distribute their power along the flying time, a solution might be design of a piezoelectric plate as feathers, which scavenges energy directly from the fluid flow. Cantilevered beam with piezo-ceramic layer undergoing vortex-induced vibrations can convert the mechanical energy available from the ambient environment to a usable electrical power. Since a flow-driven piezoelectric composite beam takes a form of natural three-way coupling of the turbulent fluid... 

    Micro-plasma actuator mechanisms in interaction with fluid flow for wind energy applications: Physical parameters

    , Article Physics of Fluids ; Volume 32, Issue 7 , 2020 Omidi, J ; Mazaheri, K ; Sharif University of Technology
    American Institute of Physics Inc  2020
    Plasma actuator is a flow control device to improve the aerodynamic performance of wind turbine blades at low airspeeds. One of the most robust numerical models for simulation of plasma actuator interaction with the fluid flow is the electrostatic model. This model is improved recently and is extensively verified by the authors. Due to the high cost of performing experimental optimizations, the optimized geometrical dimensions and materials of a plasma actuator may be sought by this numerical model. The aim of the present study is the aerodynamic enhancement of a DU21 wind turbine blade airfoil in which the effect of geometric parameters and the dielectric material is examined separately.... 

    Applied flight dynamics modeling and stability analysis of a nonlinear time-periodic mono-wing aerial vehicle

    , Article Aerospace Science and Technology ; Volume 108 , 2021 ; 12709638 (ISSN) Farvardin Ahranjani, F ; Banazadeh, A ; Sharif University of Technology
    Elsevier Masson s.r.l  2021
    This paper presents fly-ability, trim-ability, stability, and control ability of a mono-wing aerial vehicle as an under-actuated multi-body system. A nonlinear mathematical model of this vehicle with translational and rotational movements is developed. Based on early simulations, a conceptual prototype of the mono-wing is initially designed and constructed. A comprehensive nonlinear simulation is then performed by modeling aerodynamic forces and moments using the Blade Element Momentum (BEM) theory. Modeling and simulation are validated against experimental data to satisfy research needs. Twenty-three efficient dynamic parameters of the mono-wing are studied in ninety-seven simulation... 

    Aerodynamic enhancement and improving the performance of a six-megawatt dowec wind turbine by micro-plasma actuator

    , Article International Journal of Mechanical Sciences ; Volume 195 , 2021 ; 00207403 (ISSN) Omidi, J ; Mazaheri, K ; Sharif University of Technology
    Elsevier Ltd  2021
    We have investigated the usage of a Dielectric Barrier Discharge (DBD) plasma actuator to improve the aerodynamic performance of an offshore 6 MW wind turbine. By controlling the aerodynamic load combined with pitch angles of 2, 5, and 10 degrees, we studied the plasma actuator effect on the overall harvested power. Actuators were installed in single and tandem configurations in different chord-wise locations to find the optimum design. The improved phenomenological model developed by authors was used in an analysis to simulate the interaction of the electrostatic field, the ionized particles and the fluid flow. A design software was used to estimate the harvested power of the real 3D blade.... 

    Evaluation of a cooling system integrated with different phase change materials and its effect on peak load shaving

    , Article International Journal of Energy Research ; Volume 45, Issue 7 , 2021 , Pages 10425-10449 ; 0363907X (ISSN) Riahi, A ; Kavian, S ; Jafari Mosleh, H ; Shafii, M. B ; Sharif University of Technology
    John Wiley and Sons Ltd  2021
    In this study, a vapor-compression cooling system utilizing different phase change materials (PCMs) has been studied whereby the electricity consumption peak load is shifted. More specifically, the dynamic performance of cooling systems with and without using PCM is evaluated for the hottest day of the year. The proposed system uses the cooling energy to freeze, or “discharge” the PCM during nighttime when the cooling load is minimally needed and uses the stored thermal energy during the peak load hours by melting, or “charging” the PCM. This leads to better performance during peak load hours when higher cooling loads are needed. Different PCMs including oleic acid, SP224A, CL, CaCl2·6H2O... 

    Stability Improvement and Protection of Grid-following Bidirectional Three-phase Voltage-sourced Converters under Unbalanced Grid Conditions

    , M.Sc. Thesis Sharif University of Technology Bahmani, Mehran (Author) ; Mokhtari, Hossein (Supervisor) ; Karimi, Houshang (Co-Supervisor)
    With the increasing expansion of modern DC loads and utilizing energy storage systems along with distributed renewable energy resources, grid-following bidirectional voltage-sourced converters (GFBVSCs) with fast dynamic performance are required. Due to the presence of single-phase loads and asymmetrical short circuit faults, unbalanced grid voltage conditions are available in the distribution system. Under unbalanced conditions, an oscillating component with a frequency of twice the grid angular frequency appears on the DC side. Removing double-frequency ripple in the DC link voltage without third harmonic current injection and reactive power injection to the grid based on the grid codes to... 

    A new multi-winding traction transformer equivalent circuit for short-circuit performance analysis

    , Article International Transactions on Electrical Energy Systems ; Vol. 24, issue. 2 , 2014 , pp. 186-202 ; ISSN: 20507038 Azizian, D ; Vakilian, M ; Faiz, J ; Sharif University of Technology
    Current and force calculations in different short-circuit conditions are required for short-circuit performance analysis of a multi-winding traction transformer which is one of the most important requirements in its design process. This paper extends the available low-frequency three-winding star equivalent circuits to develop a novel equivalent circuit for the four-winding traction transformers. The leakage inductances of the traction transformer are determined and employed to calculate the parameters of this developed star model. It is shown that the star equivalent circuit is a valid and appropriate model to simulate the steady-state and dynamic performance of the traction transformer...