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Stability Improvement and Protection of Grid-following Bidirectional Three-phase Voltage-sourced Converters under Unbalanced Grid Conditions
, M.Sc. Thesis Sharif University of Technology ; Mokhtari, Hossein (Supervisor) ; Karimi, Houshang (Co-Supervisor)
Abstract
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...
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) ; Tavakolpour Saleh, A. R ; Aghajanzadeh, O ; Sharif University of Technology
Materials and Energy Research Center
2017
Abstract
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...
Optimal passive vibration control of Timoshenko beams with arbitrary boundary conditions traversed by moving loads
, Article Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics ; Volume 222, Issue 2 , 2008 , Pages 179-188 ; 14644193 (ISSN) ; Kargarnovin, M. H ; Esmailzadeh, E ; Sharif University of Technology
2008
Abstract
Passive control of vibration of beams subjected to moving loads is studied in which, an optimal tuned mass damper (TMD) system is utilized to suppress the undesirable beam vibration. Timoshenko beam theory is applied to the beam model having three types of boundary conditions, namely, hinged-hinged, hinged-clamped, and the clamped-clamped ends, and the governing equations of motion are solved using the Galerkin method. For every set of boundary conditions, a minimax problem is solved using the sequential quadratic programming method and the optimum values of the frequency and damping ratios for the TMD system are obtained. To show the effectiveness of the designed TMD system, simulations of...
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...
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...
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) ; Abdi, E ; Barati, F ; McMahon, R ; Sharif University of Technology
2009
Abstract
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
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...
Aerodynamic performance of a dragonfly-inspired tandem wing system for a biomimetic Micro air vehicle
, Article Frontiers in Bioengineering and Biotechnology ; Volume 10 , 2022 ; 22964185 (ISSN) ; Montazer, E ; Ward, T. A ; Nik Ghazali, N. N ; Anjum Badruddin, I ; Sharif University of Technology
Frontiers Media S.A
2022
Abstract
The flying agility demonstrated by dragonflies is accomplished by means of complex aerodynamic forces produced by flapping their four wings arranged in a tandem configuration. The current study presents a novel tandem flapping wing mechanism for a biomimetic air vehicle that was designed and manufactured to experimentally investigate the aerodynamic forces. By optimizing the configuration and using spatial network analysis, it is shown that the designed structure can flap the wings in a linear up–down stroke motion and is capable of maintaining good consistency and aerodynamic performance. Such a mechanism could be used in a future biomimetic micro air vehicle (BMAV) design. The mechanism...
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) ; Kavian, S ; Jafari Mosleh, H ; Shafii, M. B ; Sharif University of Technology
John Wiley and Sons Ltd
2021
Abstract
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...
Performance analysis and transient simulation of a vapor compression cooling system integrated with phase change material as thermal energy storage for electric peak load shaving
, Article Journal of Energy Storage ; Volume 35 , 2021 ; 2352152X (ISSN) ; Jafari Mosleh, H ; Kavian, S ; Shafii, M. B ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
A vapor-compression cooling system utilizing PCM is studied whereby the electricity consumption peak load is shifted. More specifically, the dynamic performance of the cooling system with and without PCM is evaluated and is presented with details on the hottest day of the year in Tehran, Iran. 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 cooling energy during the peak load hours by melting or “charging” the PCM. This leads to better performance during the peak load hours when higher cooling loads are required. Oleic acid was chosen as PCM. The simulation was performed in EES...
Micro-plasma actuator mechanisms in interaction with fluid flow for wind energy applications: Physical parameters
, Article Physics of Fluids ; Volume 32, Issue 7 , 2020 ; Mazaheri, K ; Sharif University of Technology
American Institute of Physics Inc
2020
Abstract
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....
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) ; Mazaheri, K ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
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....
Micro-plasma actuator mechanisms in interaction with fluid flow for wind energy applications: operational parameters
, Article Engineering with Computers ; 2022 ; 01770667 (ISSN) ; Mazaheri, K ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
Plasma actuator is a flow control device which may be used to improve the performance of wind turbine blades at low airspeeds. One of the most robust numerical models to simulate the interaction of the plasma actuator with the fluid flow is the electrostatic model. This model is improved by the authors. Due to the high cost of performing experimental optimization, the optimization of plasma actuators may be investigated by this numerical model. To optimize the aerodynamic performance of a Delft University (DU) wind turbine airfoil in a full stall condition, we used the operational parameters (voltage, frequency and the waveform) applied to the plasma actuator as the main design variables. We...
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...
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...
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...
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) ; Bakhtiar, M. S ; Sharif University of Technology
2005
Abstract
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
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) ; Goudarzi, N ; ASME ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2017
Abstract
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...
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) ; Taghi Ahmadian, M ; Sharif University of Technology
Elsevier
2012
Abstract
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...
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...