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Analysis of a fractional order Van der Pol-like oscillator via describing function method
, Article Nonlinear Dynamics ; Volume 61, Issue 1-2 , 2010 , Pages 265-274 ; 0924090X (ISSN) ; Haeri, M ; Tavazoei, M. S ; Sharif University of Technology
2010
Abstract
In this paper, the behavior of a fractional order Van der Pol-like oscillator is investigated using a describing function method. A parametric function for the boundary between oscillatory and nonoscillatory regions of this system is extracted. The analytical results are evaluated by numerical simulations which demonstrate sufficient reliability of the proposed analyzing method
Explicit approximate solution for finding the natural frequency of the motion of pendulum by using the HAM
, Article Applied Mathematical Sciences ; Volume 3, Issue 21-24 , 2009 , Pages 1023-1030 ; 1312885X (ISSN) ; Doosthoseini, A ; Doosthoseini, E ; Abachi, T ; Sharif University of Technology
Abstract
In this work, we use a powerful analytical method called homotopy analysis method (HAM) to derive the frequency of a nonlinear oscillating system. Unlike the perturbation method, the HAM does not require the addition of a small physically parameter to the differential equation. It is applicable to strongly and weakly nonlinear problems. Moreover, the HAM involves an auxiliary parameter, h, which renders the convergence parameter of series solutions Controllable, and increases the convergence, and increases the convergence significantly. This article depicts that the HAM is an efficient and powerful method for solving oscillating systems
An analytical approach in analysis of local oscillator near-the-carrier AM noise suppression in microwave balanced mixers
, Article IEEE Transactions on Microwave Theory and Techniques ; Volume 57, Issue 1 , 2009 , Pages 760-766 ; 00189480 (ISSN) ; Banai, A ; Farzaneh, F ; Sharif University of Technology
2009
Abstract
In this paper, a new formulation based on conversion matrix method is proposed to analyze "near-the-carrier local ocillator (LO) noise" down conversion to IF in microwave mixers. This method could be easily applied to analyze LO noise down conversion in any type of mixer. Practical results of this method have been compared with the envelope method and measurement results. It is shown that despite the conventional AM noise suppression in balanced mixers, the near-the-carrier LO noise suppression does not occur necessarily at the center frequency of hybrid in balanced mixers. AM noise suppression values are predicted precisely. © 2009 IEEE
A power-efficient LC quadrature VCO for RFID, zigbee and bluetooth standards
, Article Advances in Electrical and Computer Engineering ; Volume 9, Issue 3 , 2009 , Pages 34-38 ; 15827445 (ISSN) ; Atarodi, M ; Sharif University of Technology
2009
Abstract
A multi-band CMOS LC Quadrature Voltage Control Oscillator (QVCO) with minimum power consumption is developed to meet the phase noise and frequency band requirements of RFID, Zigbee and Bluetooth standards. To accomplish the multi-band receiving architecture at low power consumption, current switching technique with optimized cross-coupled transistor sizes has been used. A comprehensive analysis of small signal model for complementary architecture including transistor noise sources and their effects on output phase noise amount has been discussed. Using extracted small signal model, coupled and coupling transistor sizes for minimum power consumption and the least achievable phase noise have...
Innovations in non-linear oscillations of a pendent drop from a capillary tip during formation and detachment - an LBM simulation
, Article Journal of Applied Fluid Mechanics ; Volume 14, Issue 1 , 2020 , Pages 331-344 ; Taeibi Rahni, M ; Zareh, M ; Sharif University of Technology
Isfahan University of Technology
2020
Abstract
Individual drops are suitable tools to study the liquid-fluid interfacial properties. In this work, force-displacement equation and non-linear oscillations of a pendent drop are numerically investigated. The presented novel force-displacement function allows following the dynamics of a pendent drop and realizing its elastic behavior. The growth and detachment of drop, which is pending due to gravity from a capillary tip, is considered (assuming high density and high viscosity ratios and immiscible two-phase flows). Two-dimensional multi-relaxation time lattice Boltzmann method (MRT-LBM) was used to simulate growth, detachment, and oscillations of the drop using a conservative model for...
Experimental investigation of velocity profiles in the wake of an oscillating airfoil
, Article 2007 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007, San Diego, CA, 30 July 2007 through 2 August 2007 ; Volume 1 SYMPOSIA, Issue PART B , August , 2007 , Pages 1873-1882 ; 0791842886 (ISBN); 9780791842881 (ISBN) ; Mahmoudi, M ; Sharif University of Technology
2007
Abstract
A series of experiments were carried out to study the unsteady wakes behind an oscillating airfoil. The airfoil is a section of a wind turbine blade oscillating in pitch about the quarter chord axis at various reduced frequencies, oscillation amplitude and mean angles of attack. Real time velocity profiles were obtained using total and static pressure at 35 vertically aligned points behind the airfoil via two similar rakes. The rakes were located at a distance of 1.5 chord length behind the model. The results show great influence of oscillation amplitude and reduced frequency on the wake velocity profiles. Copyright © 2007 by ASME
Some sufficient conditions for the intersection with the vertical isocline in the Liénard plane
, Article Applied Mathematics Letters ; Volume 19, Issue 5 , 2006 , Pages 491-497 ; 08939659 (ISSN) ; Moradifam, A ; Sharif University of Technology
2006
Abstract
In this work we study the problem of whether all trajectories of the system ẋ=y-F(x) and ẏ=-g(x) cross the vertical isocline, which is very important for the existence of periodic solutions and oscillation theory. Sufficient conditions are given for all trajectories to cross the vertical isocline. © 2005 Elsevier Ltd. All rights reserved
Loss of lock-in in VIV due to spanwise variations of diameters
, Article Ocean Engineering ; Volume 220 , 2021 ; 00298018 (ISSN) ; De Langre, E ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Elongated cylindrical structures with non-uniform diameters, under cross-flow, are often encountered in marine engineering and energy harvesting devices. In this work, the vortex-induced vibrations of elastically supported circular tapered and wavy cylinders with different cross sections areas are studied numerically using a wake oscillator model. The effect of the tapering ratio on the amplitude of oscillation is particularly analyzed. For tapered cylinders it is found that the amplitude of oscillation under flow decreases strongly when a critical tapering is reached. This is consistent with experimental data. A similar effect is found in wavy cylinders. A third system, consisting of a...
Investigation of the locking bandwidth in linear and circular arrays of mutually coupled oscillators, intended for microwave power combining
, Article IEE Proceedings: Microwaves, Antennas and Propagation ; Volume 152, Issue 6 , 2005 , Pages 441-448 ; 13502417 (ISSN) ; Farzaneh, F ; Ayazian, S ; Sharif University of Technology
2005
Abstract
An array of N weakly coupled oscillators is investigated in two major configurations. The locking bandwidth for linear and circular arrays is assessed through an array coupling matrix, in a worst-case free-running frequency distribution of oscillators. The superior locking bandwidth for circular arrays is demonstrated
Force and moment measurements on a fighter model in heaving motion
, Article 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 10 January 2005 through 13 January 2005 ; 2005 , Pages 6197-6206 ; Soltani, M. R ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2005
Abstract
Extensive wind tunnel tests have been conducted to study the unsteady aerodynamic behavior of a standard dynamics model, SDM, oscillating in plunge mode. The unsteady aerodynamic behavior of various missile and aircraft configurations under pitching motion has been studied so far. However up to now, there is little or no result on the plunging behavior of an aircraft or missile as a whole and the present experiments can be considered as one of the first attempts to study the compressible flowfield over an aircraft undergoing plunging motion. The experiments involved measuring the normal force and pitching moment of the model oscillating in plunge at Mach numbers of 0.4, 0.6 and 1.5 and...
Temperature dependence of the amplifying parameters of a copper vapor laser
, Article Laser Physics ; Volume 14, Issue 8 , 2004 , Pages 1050-1053 ; 1054660X (ISSN) ; Sadighi Bonabi, R ; Parvin, P ; Zand, M ; Sharif University of Technology
2004
Abstract
A pair of copper vapor lasers in an oscillator-amplifier configuration were used to investigate the temperature dependence of the small-signal gain and saturation intensity and output power of the laser at the 510.6 and 578.2 nm transitions individually. An optimum working temperature of 1520°C was determined, and a maximum output power equivalent to 33 W/l was extracted
Flow analysis around a pitching airfoil
, Article Collection of Technical Papers - 22nd AIAA Applied Aerodynamics Conference, Providence, RI, 16 August 2004 through 19 August 2004 ; Volume 2 , 2004 , Pages 914-924 ; 10485953 (ISSN) ; Mani, M ; Soltani, M. R ; Boroomand, M ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2004
Abstract
A series of low-speed wind tunnel tests were performed to investigate the unsteady pressure distribution over an airfoil. Dynamic pitching motion was produced by oscillating the model over a range of reduced frequencies, k=0.022 - 0.066. In addition, steady data were acquired and examined to furnish as a baseline for analysis and comparison. The model was oscillated between 0-18° angle of attack. Surface static pressure was measured from x/c=5-80% for both upper and lower surfaces. The pressure coefficients in the low angle of attack range showed little overshoot when compared with the static values, while for the large angle of attack cases the differences were significant. For a constant...
Linear phase detection using two-phase latch
, Article Electronics Letters ; Volume 39, Issue 24 , 2003 , Pages 1695-1696 ; 00135194 (ISSN) ; Atarodi, M ; Sharif University of Technology
2003
Abstract
Modified two-phase latch and flip-flop are introduced to implement a linear phase-detector (LPD) for 1/N-rate clock recovery applications. This technique greatly simplifies the required circuitry of the LPD and makes it suitable for higher speed applications while consuming less power compared to the conventional techniques
Output power variations in two mutually coupled microwave oscillators and the effect of non-linear reactance on the locking bandwidth
, Article IEE Proceedings: Microwaves, Antennas and Propagation ; Volume 150, Issue 2 , 2003 , Pages 61-66 ; 13502417 (ISSN) ; Farzaneh, F ; Sharif University of Technology
2003
Abstract
The locking of two mutually coupled microwave oscillators is considered. The common frequency of oscillation is obtained both without and in the presence of a non-linear reactance. The effect of the non-linear reactance on the locking bandwidth is studied. It is shown analytically that, unlike the common injection locked oscillator case, the locking bandwidth can be either increased or decreased by the non-linearity. The variations in amplitude of oscillations is investigated. It is demonstrated that the total power delivered by the active devices decreases in interinjection locked oscillators
Pressure dependence of the small-signal gain and saturation intensity of a copper vapor laser
, Article Applied Optics ; Volume 42, Issue 6 , 2003 , Pages 1013-1018 ; 1559128X (ISSN) ; Sadighi, R ; Parvin, P ; Sharif University of Technology
2003
Abstract
The small-signal gain coefficient and the saturation intensity of a copper vapor laser have been measured for both 510.6- and 578.2-nm transitions through the implementation of a discharge driven oscillatoramplifier configuration. Pressure dependence of the gain and saturation property of the laser has been investigated. © 2003 Optical Society of America
Closed-Form oscillatory condition in electrical circuits containing two fractional order elements
, Article IEEE Transactions on Circuits and Systems II: Express Briefs ; Volume 69, Issue 6 , 2022 , Pages 2687-2691 ; 15497747 (ISSN) ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
Oscillatory condition in LTI dynamic systems is generally expressed as possessing purely imaginary solutions by their characteristic equations. Dealing with the class of fractional order systems, such a condition is equivalently restated as owing complex roots with specific arguments by a polynomial defined based on the system characteristic equation. The degree of this polynomial can be unboundedly high. Consequently, such statement for the oscillatory condition in fractional order systems, which is based on arguments of the roots of a polynomial with an unbounded degree, cannot be viewed as a closed-form expression. To tackle this challenge, this brief introduces an approach to obtain a...
Design and Implementation of a Voltage Controlled Oscillator For 77GHz Automotive Radar
, M.Sc. Thesis Sharif University of Technology ; Medi, Ali (Supervisor)
Abstract
Wideband mm-wave radars are gaining popularity in automotive applications due to their superiority in harsh weather conditions, high distance resolution, precise velocity measurement, and superior spatial resolution. The primary purpose of this thesis is to design and implement a voltage-controlled oscillator for 77GHz automotive radar applications.Phase noise -as one of the most crucial specifications in VCO design- Phase noise improvement techniques as well as harmonic engineering methods are delineated. Also, an Ocean-based code for ISF simulation is introduced and developed to obviate the need for additional signal processing software so that simulation speed increases...
Design and Implementation of a Low Phase Noise Oscillator using Oversized Cavity Resonator
, M.Sc. Thesis Sharif University of Technology ; Banai, Ali (Supervisor)
Abstract
The aim of doing this project is design and fabrication of a X band low phase noise oscillator Using oversized cavity resonator and transposed gain amplifier.One of the most important factors in reducing oscillators phase noise is the quality factor of its resonator and by increasing the quality factor, we can reduce the phase noise. So by doing this , in this project we want to increase the quality factor of the resonator part of the oscillator and design an oscillator in the X frequency band ( approximately 8 GHz ) .As we know the Q factor for waveguide cavity resonator is increased when we use them in the higher order modes and there is a great improvement in Q factor T when we use them...
Experimental and Numerical Investigation on the Hydrodynamic Properties of Heave Plates in Translational and Rotational Oscillations
, Ph.D. Dissertation Sharif University of Technology ; Behzad, Mehdi (Supervisor)
Abstract
Many offshore platforms as TLP, Semi-submersible and Spar are used for oil extraction and energy harvesting. One of the challenges of these structures is related to vibrations due to the environmental sea waves and wind loads. The optimal way for the response reduction of an offshore structure in heave direction is the installing of thin heave plate. The heave plate induces vortex shedding and pressure drop on fluid flow downstream. Diameter difference of heave plates in an array can improve the obtained damping and added mass for a given small spacing between plates, which has not been studied up to now. Hence, in the present thesis it was observed that converting of the uniform to...
Design of an X-Band Quadrature Voltage-Controlled Oscillator (QVCO) in 0.18µm CMOS Technology
, M.Sc. Thesis Sharif University of Technology ; Medi, Ali (Supervisor)
Abstract
Voltage Controlled Oscillator (VCO) is one of the essential blocks in communication transceivers. The important specifications of the VCOs like Phase Noise, always is a motivation for researchers in order to introduce novel approaches to conquer these challenges. By development of technology and appearance of new fabrication technologies, this issue take more attention that the past. Also the out of control parameters like process variation and temperature, affect that. So, according to the challenges ahead and the demand of transceiver systems for low phase noise and reasonable power consumption, solutions for overcome these challenges. Finally, a class-C VCO with the tuning range of 4.25-5...