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AQM controller design for TCP networks based on a new control strategy
, Article Telecommunication Systems ; Volume 57, Issue 4 , December , 2013 , Pages 295-311 ; 10184864 (ISSN) ; Jahangir, A. H ; Ebrahimi, B ; Sharif University of Technology
Kluwer Academic Publishers
2013
Abstract
When the network suffers from congestion, the core or edge routers signal the incidence of congestion through the active queue management (AQM) to the sources. The time-varying nature of the network dynamics and the complex process of retuning the current AQM algorithms for different operating points necessitate the development of a new AQM algorithm. Since the non-minimum phase characteristics of the network dynamics restrict direct application of the proportional-integral-derivative (PID) controller, we propose a compensated PID controller based on a new control strategy addressing the phase-lag and restrictions caused by the delay. Based on the unstable internal dynamics caused by the...
Dynamic modeling and simulation of brushless doubly fed induction machine in consideration of core loss
, Article IECON Proceedings (Industrial Electronics Conference) ; 2012 , Pages 1753-1757 ; 9781467324212 (ISBN) ; Tahami, F ; The Institute of Electrical and Electronics Engineers (IEEE); IEEE Industrial Electronics Society (IES) ; Sharif University of Technology
2012
Abstract
Brushless doubly fed induction machine has recently attracted attention in variable speed generators and motor drives. In order to have a high performance control, a precise dynamic model is required. This paper aims at introducing a model of brushless doubly fed induction machine taking core loss into account. The details of model derivation are outlined and the torque relation is expressed in the general reference frame. The model is then used for simulation of the dynamic performance of the machine. The error introduced by neglecting core loss effect is also shown
Steady state analysis of brushless doubly fed induction machine taking core loss into account
, Article IECON Proceedings (Industrial Electronics Conference) ; 2012 , Pages 2030-2035 ; 9781467324212 (ISBN) ; Tahami, F ; Sharif University of Technology
2012
Abstract
Brushless doubly fed induction machines show promising results for wind power applications. Due to their poor rotor magnetic coupling and relatively high value of slip, core loss is an important factor which affects the steady state and dynamic performance. The core loss effect on performance of brushless doubly fed induction machines has not been extensively studied in the literature. In this paper, a steady state equivalent circuit taking core loss into account is introduced. Simple relationships are derived which show that the brushless doubly-fed induction machine is similar to the cascaded doubly-fed induction machine in terms of core loss. The energy conservation principle is applied...
An equivalent circuit model for brushless doubly fed induction machine considering core loss
, Article 2012 3rd Power Electronics and Drive Systems Technology, PEDSTC 2012, 15 February 2012 through 16 February 2012 ; February , 2012 , Pages 348-353 ; 9781467301114 (ISBN) ; Tahami, F ; Sharif University of Technology
2012
Abstract
Brushless doubly fed induction machines show promising results for wind power applications. Due to their poor rotor magnetic coupling and relatively high value of slip, core loss is an important factor which affects the steady state and dynamic performance. The core loss in brushless doubly fed induction machines has not been extensively studied in the literature. In this paper, a steady state equivalent circuit taking core loss into account is introduced. Simple relationships are derived which show that the brushless doubly-fed induction machine is similar to the cascaded doubly-fed induction machine in terms of core loss. The proposed equivalent circuit is simulated to derive the steady...
Nonlinear analysis of 2D flexible flapping wings
, Article Nonlinear Dynamics ; Volume 81, Issue 1-2 , July , 2015 , Pages 299-310 ; 0924090X (ISSN) ; Zohoor, H ; Yoon, Yong Jin ; Sharif University of Technology
Kluwer Academic Publishers
2015
Abstract
Natural flyers have flexible wings, which deform significantly under the combined inertial and aerodynamic forces. In this study, we focus on the role of chord wise flexibility in 2D pitch and plunge motions. We derive the exact nonlinear 2D equations of motion for a flexible flapping wing with flying support. In achieving the closed-form equations, we use the exact strain field concerning considerable elastic deformations. After numerically solving the novel equations, we validate them in simulations with highly deformable wings. By coupling the derived equations of motion with fluid flow, we study the aerodynamic performance of the geometrically nonlinear flexible flapping wing. Through...
Multi-objective optimization of lean and sweep angles for stator and rotor blades of an axial turbine
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 229, Issue 5 , June , 2015 , Pages 906-916 ; 09544100 (ISSN) ; Benisi, A. H ; Assempour, A ; Pourfarzaneh, H ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
The axial turbine is one of the most challenging components of gas turbines for industrial and aerospace applications. With the ever-increasing requirement for high-aerodynamic performance blades, three-dimensional aerodynamic shape optimization is of great importance. In this research, the rear part of a gas turbine consisting of a one-stage axial turbine is optimized numerically. A useful optimization algorithm is presented to improve the efficiency and/or pressure ratio of the axial turbine with two different objective functions. The three-dimensional blade-shape optimization is employed to study the effects of the turbine stator and rotor lean and sweep angles on the turbine performance....
Simulation of DBD plasma actuator effect on aerodynamic performance improvement using a modified phenomenological model
, Article Computers and Fluids ; Volume 140 , 2016 , Pages 371-384 ; 00457930 (ISSN) ; Omidi, J ; Chaharlang Kiani, K ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
An improved phenomenological model is presented for numerical simulation of a Dielectric Barrier Discharge (DBD) plasma actuator for separation control of high angle of attack flow over a wind turbine airfoil. Based on existing numerical models and experimental measurements, a new model is proposed for prediction of the length of a plasma extent which is more consistent with previous observations. The electrical and hydrodynamic solvers used in the present study are validated against published experimental data. Then the applicability of a DBD actuator, mounted on a DU 91-W2-250 airfoil is extensively analyzed for a wide range of operating voltages and frequencies. The analysis is completely...
A practical method for aerodynamic investigation of WIG
, Article Aircraft Engineering and Aerospace Technology ; Volume 88, Issue 1 , 2016 , Pages 73-81 ; 00022667 (ISSN) ; Tavakoli Dakhrabadi, M ; Sharif University of Technology
Emerald Group Publishing Ltd
2016
Abstract
Purpose - The purpose of this paper is to present a fast, economical and practical method for mathematical modeling of aerodynamic characteristics of rectangular wing in ground (WIG) effect. Design/methodology/approach - Reynolds averaged Navier-Stokes (RANS) equations were converted to Bernoulli equation by reasonable assumptions. Also, Helmbold's equation has been developed for calculation of the slope of wing lift coefficient in ground effect by defining equivalent aspect ratio (ARe). Comparison of present work results against the experimental results has shown good agreement. Findings - A practical mathematical modeling with lower computational time and higher accuracy was presented for...
Drag reduction by a multi-point optimised hybrid flow control method for two supercritical airfoils
, Article European Journal of Computational Mechanics ; Volume 25, Issue 5 , 2016 , Pages 359-387 ; 17797179 (ISSN) ; Mazaheri, K ; Sharif University of Technology
Taylor and Francis Ltd
Abstract
Shock control bump (SCB), suction and blowing are three flow control methods used to control the shock wave/boundary layer interaction to reduce the resulting wave drag in transonic flows. An SCB uses a small local surface deformation to reduce the shock wave strength, while the suction decreases the boundary layer thickness and the blowing delays the flow separation. Here, we will use a multi-point continuous adjoint optimisation scheme to find the optimum design of suction and blowing separately or together, or with the SCB, on two supercritical airfoils, i.e. RAE-5225 and RAE-2822, for a wide range of off-design transonic Mach numbers. The RANS flow equations are solved using the Roe’s...
Guest editorial special section on microgrids
, Article IEEE Transactions on Smart Grid ; Volume 3, Issue 4 , December , 2012 , Pages 1857-1859 ; 19493053 (ISSN) ; Iravani, R ; Aminifar, F ; Hatziargyriou, N ; Lehtonen, M ; Sharif University of Technology
Abstract
Despite the significant research efforts devoted to the microgrid and smart grid areas, numerous problems related to real world implementations still remain unsolved. The present special issue was announced with the objective of addressing and disseminating state-of-the-art R&D results on microgrids to bring together researchers from both academia and industry with the goal of fostering interactions among stakeholders. In response, 190 two-page extended abstracts were received and considered for the first round of reviews. Authors of about 60 selected abstracts were then invited to submit the full papers in the second round and out of them 27 high-quality manuscripts were ultimately approved...
Robust controller design for governing steam turbine power generators
, Article Proceedings - The 12th International Conference on Electrical Machines and Systems, ICEMS 2009, 15 November 2009 through 18 November 2009, Tokyo ; 2009 ; 9784886860675 (ISBN) ; Tahami, F ; Sharif University of Technology
Abstract
The turbine control system is one of the key control loops in the dynamic performance of steam power generation units. In this paper a multivariable PID controller is designed for the governing system of steam turbine power generators. The necessary and sufficient conditions for existence of a strong robust H ∞ dynamic compensator are established in terms of linear matrix inequality (LMI) approach. This controller is designed in succeeding to the existing proportional controller in a power plant. To reach to this goal, the complete dynamic model of an actual turbine-generator including the governor, turbine and generator, are derived. Simulation results show that proposed controller has good...
Application of the adjoint optimisation of shock control bump for ONERA-M6 wing
, Article European Journal of Computational Mechanics ; Volume 26, Issue 5-6 , 2017 , Pages 557-583 ; 17797179 (ISSN) ; Mazaheri, K ; Sharif University of Technology
Abstract
This article is devoted to the numerical investigation of the shock wave/boundary layer interaction (SWBLI) as the main factor influencing the aerodynamic performance of transonic bumped airfoils and wings. The numerical analysis is conducted for the ONERA-M6 wing through a shock control bump (SCB) shape optimisation process using the adjoint optimisation method. SWBLI is analyzed for both clean and bumped airfoils and wings, and it is shown how the modified wave structure originating from upstream of the SCB reduces the wave drag, by improving the boundary layer velocity profile downstream of the shock wave. The numerical simulation of the turbulent viscous flow and a gradient-based adjoint...
Experimental study of flow field on stepped airfoil at very low Reynolds number
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 231, Issue 9 , 2017 , Pages 1706-1717 ; 09544100 (ISSN) ; Ghassemi, H ; Ebrahimi, A ; Ghasemi, B ; Sharif University of Technology
Abstract
In this article, the flow field around NACA0024 airfoil with step at lower and upper surfaces is experimentally investigated. For this purpose, particle image velocimetry technique based on the instantaneous flow structures is used to investigate the flow field around the airfoil at different times. All the experimental measurements in current study are conducted at very low Reynolds number condition based on the chord of the airfoil (Re=2000) and at angles of attack at 0° and 5° where the flow around airfoils is separated. The differences between vortical structures, mean streamlines, sizes of the wake regions, and vortex shedding of the stepped airfoils compared to unmodified airfoil are...
Hydro-aerodynamic mathematical model and multi-objective optimization of wing-in-ground effect craft in take-off
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 232, Issue 4 , 2018 , Pages 421-433 ; 14750902 (ISSN) ; Seif, M. S ; Sharif University of Technology
SAGE Publications Ltd
2018
Abstract
Hydro-aerodynamic mathematical model and multi-objective optimization of a popular wing-in-ground effect craft are presented in this research using a hydro-aerodynamic practical method and the genetic algorithm. The primary components of the wing-in-ground effect craft configuration include a compound wing, catamaran hull form and a power-augmented ram platform. The hydro-aerodynamic practical method with low computational time and high accuracy is performed by coupling hydrodynamic and aerodynamic considerations using the potential flow theory in ground effect and the semi-empirical equations proposed for high-speed marine vehicles. The trade-off between hydrodynamic and aerodynamic...
Atmospheric icing effects of S816 airfoil on a 600 kW wind turbine's performance
, Article Scientia Iranica ; Volume 25, Issue 5B , 2018 , Pages 2693-2705 ; 10263098 (ISSN) ; Sharif University of Technology
Sharif University of Technology
2018
Abstract
This study investigates the aerodynamic loads and energy losses of a typical 600 kW wind turbine with S816 airfoil blade under two different icing conditions. Three sections at different radial positions were considered to estimate the icing effect along the blade. Ice accretion simulations in wet and dry regimes were carried out using the NASA LEWICE 3.2 computer program. The airflow simulations were performed with CFD method and SST k -ω turbulence model. The results of these simulations, including streamlines, surface pressure, skin friction, lift, and drag coefficients, were inspected for both clean and iced airfoils. In the case of wet iced airfoil, a separation bubble was created in...
Performance evaluation of custom power devices in process of motor bus transfer
, Article 2009 4th IEEE Conference on Industrial Electronics and Applications, ICIEA 2009, Xi'an, 25 May 2009 through 27 May 2009 ; 2009 , Pages 2279-2284 ; 9781424428007 (ISBN) ; Abedi, M ; Darabi, F ; Sharif University of Technology
2009
Abstract
Quality and continuity of electrical power to sensitive loads especially in power plants and industrial sectors is of great importance. For this reason, bus transfer is used. During the bus transfer interval, sensitive loads especially motors will be interrupted, and may encounter difficulties. So, it is used reactive power compensator and custom power devices to mitigate stress in motors and improve power quality indices. This paper presents the effect of reactive power compensator and custom power devices paralleling with motor in process of bus transfer which is done in two methods: EMTS and STS. Also, it is investigated dynamic performance of induction motor and spin-down curves in...
Optimization of multiple transmission layouts for minimal energy consumption of a battery electric vehicle
, Article Scientia Iranica ; Volume 26, Issue 4A , 2019 , Pages 2382-2393 ; 10263098 (ISSN) ; Foumani, M. S ; Delkhosh, M ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
Battery Electric Vehicles (BEVs) are a promising solution for reducing the impacts of passenger vehicles on the environment. However, their driving range is restricted due to the limitations of battery technologies. This range can be extended by adoption of multiple-speed transmissions. Most of the comparisons in the related studies are based on non-optimal designs or limited to modal driving cycles. Furthermore, the impact of Power-Split. Continuously Variable Transmission (PS-CVT) layout with type III power How on the power consumption of BEVs has never been examined. In this paper, single-, two-, and three-speed transmissions along with PS-C'VTs with type I and III power flows are...
Optimization of multiple transmission layouts for minimal energy consumption of a battery electric vehicle
, Article Scientia Iranica ; Volume 26, Issue 4A , 2019 , Pages 2382-2393 ; 10263098 (ISSN) ; Saadat Foumani , M ; Delkhosh, M ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
Battery Electric Vehicles (BEVs) are a promising solution for reducing the impacts of passenger vehicles on the environment. However, their driving range is restricted due to the limitations of battery technologies. This range can be extended by adoption of multiple-speed transmissions. Most of the comparisons in the related studies are based on non-optimal designs or limited to modal driving cycles. Furthermore, the impact of Power-Split. Continuously Variable Transmission (PS-CVT) layout with type III power How on the power consumption of BEVs has never been examined. In this paper, single-, two-, and three-speed transmissions along with PS-C'VTs with type I and III power flows are...
Dynamic performance enhancement of RC slabs by steel fibers vs. externally bonded GFRP sheets under impact loading
, Article Engineering Structures ; Volume 213 , 2020 ; Khaloo, A ; Sadraie, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Recently, to improve the dynamic behavior of Reinforced Concrete (RC) slabs under impact load, the methods of externally bonding Glass Fiber Reinforced Polymer (GFRP) sheets to slab and internally reinforcing concrete by steel fibers have been proposed. Nevertheless, it is required to investigate the comparison between these two methods on response of RC slabs under impact loads. In this study, the influence of volume fraction of steel fibers, the number of GFRP sheet layers (one or two) and the arrangement of GFRP sheets (covering the whole or parts of surface), are examined. Performance of fourteen 1000 × 1000 × 75 mm concrete slabs including one plain slab, one steel RC slab, three steel...
A predictive control strategy for the sheppard-taylor based PFC rectifier
, Article 2008 IEEE 2nd International Power and Energy Conference, PECon 2008, Johor Baharu, 1 December 2008 through 3 December 2008 ; January , 2008 , Pages 1156-1160 ; 9781424424054 (ISBN) ; Sahari, A. A ; Tahami, F ; Sharif University of Technology
2008
Abstract
This paper investigates a predictive control strategy for a single-phase PFC rectifier exploiting the Sheppard-Taylor converter. By using this converter, the detuning problem occurring in conventional PFC rectifiers, especially at low input voltages, is avoided. This paper addresses a predictive method for designing the current controller of the Sheppard-Taylor PFC converter. The control law is derived for an ideal circuit as well as a more accurate model of the converter including parasitic elements. Input voltage feed-forward compensation provides sinusoidal input current and a desired output voltage even if the input voltage is distorted. To investigate the dynamic performance of the PFC...