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Total 141 records

    Fractional order control of thermal systems: achievability of frequency-domain requirements

    , Article Nonlinear Dynamics ; Volume 80, Issue 4 , 2015 , Pages 1773-1783 ; 0924090X (ISSN) Badri, V ; Tavazoei, M. S ; Sharif University of Technology
    Abstract
    Fractional order models have been widely used in modeling and identification of thermal systems. General model in this category is considered as the model of thermal systems in this paper, and a fractional order controller is proposed for controlling such systems. The proposed controller is a generalization for the traditional PI controllers. The parameters of this controller can be obtained by using a recently introduced tuning method which can simultaneously ensure the following three requirements: desired phase margin, desired gain crossover frequency, and flatness of the phase Bode plot at this frequency. In this paper, it is found whether simultaneously achieving the mentioned... 

    Frequency domain identification of a tapered beam embedded by piezoelectric layer

    , Article 2016 International Conference on Advanced Mechatronic Systems, ICAMechS 2016, 30 November 2016 through 3 December 2016 ; 2017 , Pages 312-317 ; 23250682 (ISSN); 9781509053469 (ISBN) Banazadeh, A ; Ahranjani, F. F ; Kamankesh, Z ; Sharif University of Technology
    IEEE Computer Society  2017
    Abstract
    This study is conducted aiming to identify the dynamics of a tapered beam, embedded by piezoelectric layer. Narrowing the tip of the beam equipped with piezoelectric patches leads to optimize the output power after excitation by the frequency sweep input. An accelerometer is installed on the beam base, which measures the acceleration that is applied to the system. Piezoelectric sensors also measure the generated voltage. The experimental test data is handled through CIFER software, using Fourier transform and Bode plot in the frequency domain, to obtain appropriate transfer functions. MATLAB is used for nonlinear simulation and validation of discrete transfer functions by a set of data that... 

    Acoustic modeling from frequency-domain representations of speech

    , Article Proceedings of the Annual Conference of the International Speech Communication Association, INTERSPEECH, 2 September 2018 through 6 September 2018 ; Volume 2018-September , 2018 , Pages 1596-1600 ; 2308457X (ISSN) Ghahremani, P ; Hadian, H ; Lv, H ; Povey, D ; Khudanpur, S ; Sharif University of Technology
    International Speech Communication Association  2018
    Abstract
    In recent years, different studies have proposed new methods for DNN-based feature extraction and joint acoustic model training and feature learning from raw waveform for large vocabulary speech recognition. However, conventional pre-processed methods such as MFCC and PLP are still preferred in the state-of-the-art speech recognition systems as they are perceived to be more robust. Besides, the raw waveform methods - most of which are based on the time-domain signal - do not significantly outperform the conventional methods. In this paper, we propose a frequency-domain feature-learning layer which can allow acoustic model training directly from the waveform. The main distinctions from... 

    On a generalized fractional-order LTI compensator: Exact formulas for compensation at two different frequencies

    , Article JVC/Journal of Vibration and Control ; Volume 22, Issue 19 , 2016 , Pages 4074-4086 ; 10775463 (ISSN) Sayyaf, N ; Tavazoei, M. S ; Sharif University of Technology
    SAGE Publications Inc 
    Abstract
    Nowadays, design and tuning of controllers with predefined structures are among the most popular topics in control system theory. During the last decade, many studies have focused on designing fixed-structure fractional-order compensators. This paper presents a generalized version of fractional-order compensators to achieve the required magnitudes and phases at two given frequencies (for example, to achieve desired phase and gain margins with adjustable cross frequencies). In this generalization, at first some basic analysis of the phase behaviour of this introduced type of fractional-order compensators is presented. Also, exact formulas are found for designing this family of compensators in... 

    Desirably adjusting gain margin, phase margin, and corresponding crossover frequencies based on frequency data

    , Article IEEE Transactions on Industrial Informatics ; Volume 13, Issue 5 , 2017 , Pages 2311-2321 ; 15513203 (ISSN) Sayyaf, N ; Tavazoei, M. S ; Sharif University of Technology
    Abstract
    This paper presents an analytical method to tune a fixed-structure fractional-order compensator for satisfying desired phase and gain margins with adjustable crossover frequencies. The proposed method is based on the measured frequency data of the plant. Since no analytical model for the plant is needed in the compensator tuning procedure, the resulted compensator does not depend on the order and complexity of the plant. Also, sufficient conditions for the existence of a compensator with no zero and pole in the right half-plane for satisfying the aforementioned objectives are analytically derived. Furthermore, different hardware-in-the-loop experimental results are presented to show the... 

    Applications of Hough Transform in Frequency Domain for Radar Systems

    , M.Sc. Thesis Sharif University of Technology Hadavi, Mahdi (Author) ; Nayebi, Mohammad Mehdi (Supervisor)
    Abstract
    Hough transform is frequently used in radar applications. The structure of using this transformation in radars is so that it has been used only in Range radars which transmit short pulses and their primary goal is to make better estimation of the range of the targets. In this work, we introduce the ways in which we can use the Hough transform in Doppler radars which transmit long pulses and their primary goal is to make better estimation of target doppler. We must use Hough transform in time-doppler domain for this class of radars including continuous-wave radars. To prepare this time-doppler domain image some time-frequency transform must be applied to the radar received signal and a part... 

    Fractional order control of thermal systems: achievability of frequency-domain requirements

    , Article Nonlinear Dynamics ; Volume 80, Issue 4 , June , 2014 , Pages 1773-1783 ; ISSN: 0924090X Badri, V ; Tavazoei, M. S ; Sharif University of Technology
    Abstract
    Fractional order models have been widely used in modeling and identification of thermal systems. General model in this category is considered as the model of thermal systems in this paper, and a fractional order controller is proposed for controlling such systems. The proposed controller is a generalization for the traditional PI controllers. The parameters of this controller can be obtained by using a recently introduced tuning method which can simultaneously ensure the following three requirements: desired phase margin, desired gain crossover frequency, and flatness of the phase Bode plot at this frequency. In this paper, it is found whether simultaneously achieving the mentioned... 

    A comparison between modal damping ratios identified by NExT-ERA and frequency domain impact test

    , Article Journal of Computational and Applied Research in Mechanical Engineering ; Volume 8, Issue 1 , 2018 , Pages 15-24 ; 22287922 (ISSN) Nouri, A ; Hajirezayi, S ; Sharif University of Technology
    Shahid Rajaee Teacher Tarining University (SRTTU)  2018
    Abstract
    In this research, the modal parameters of a beam in free-free condition are extracted by performing different experiments in the laboratory. For this purpose, two different techniques are employed. The first methodology is considered as a time domain method in Operational Modal Analysis. The other one is frequency domain impact hammer test which is categorized as an Experimental Modal Analysis method and can be regarded as the most common method in modal analysis. Checking the results obtained by the two methods, one can notice a distinct inconsistency in modal damping ratios extracted by each method. However, based on recent publications on the subject, it can be inferred that the time... 

    Unreliability of frequency-domain approximation in recognising chaos in fractional-order systems

    , Article IET Signal Processing ; Volume 1, Issue 4 , December , 2007 , Pages 171-181 ; 17519675 (ISSN) Tavazoei, M. S ; Haeri, M ; Sharif University of Technology
    2007
    Abstract
    The effects of using frequency-domain approximation in numerical simulation of fractional-order systems are analytically studied. The main aim in the study is to determine the number, location and stability property of the equilibriums in a fractional-order system and its frequency-based approximating counterpart. The comparison shows that the original fractional-order system and its frequency-based approximation may differ from each other in some or all issues considered in the study. Unfortunately, these differences can lead to wrong consequences in some special cases such as detecting chaos in the fractional-order systems. It is shown that using the frequency-domain approximation methods... 

    Determination of complex modes in photonic crystal waveguides using the phase variation in characteristic coefficients

    , Article Optics Letters ; Volume 37, Issue 15 , 2012 , Pages 3078-3080 ; 01469592 (ISSN) Hosseinnia, A. H ; Khavasi, A ; Sarrafi, P ; Mehrany, K ; Sharif University of Technology
    OSA Pub  2012
    Abstract
    An efficient frequency-domain method, the phase variation monitoring (PVM) method, is proposed to determine the electromagnetic eigenmodes in two-dimensional photonic crystal waveguides. The proposed method is based on monitoring the reflection and transmission coefficients of incident plane waves. It is successfully applied to an illustrative line-defect photonic crystal waveguide and proved to be capable of calculating the in-plane leakage through the finite-size photonic crystal surrounding the line-defect. Calculation of the leakage loss is not only important for proper understanding of wave propagation within the defect but also for its significant role in applications of photonic... 

    A frequency domain proof for the equivalence of the maximally flat FIR fractional delay filter and the Lagrange interpolator

    , Article Digital Signal Processing: A Review Journal ; Volume 21, Issue 1 , 2011 , Pages 13-16 ; 10512004 (ISSN) Jahani Yekta, M. M ; Sharif University of Technology
    Abstract
    One of the most important properties of the maximally flat (MF) FIR fractional delay (FD) filter is its equivalence with the Lagrange interpolator for uniformly sampled signals. In this article, to provide the required background for the reader, we first propose a straightforward algebraic proof for this equivalence. This proof is given by simply demonstrating that the system of linear equations governing the maximally flatness property of this filter is the same as the one from which the coefficients of the Lagrange interpolator are computed. We then present the main contribution of the paper, which is a frequency domain proof for the same equivalence. In contrast with its classic... 

    Asymptotic swarm stability of fractional-order swarm systems in the presence of uniform time-delays

    , Article International Journal of Control ; Nov , 2015 , Pages 1-10 ; 00207179 (ISSN) Soorki, M. N ; Tavazoei, M. S ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    In this paper, asymptotic swarm stability of fractional-order swarm systems in the presence of uniform time-delays is studied. By using a frequency domain approach, the necessary and sufficient condition on the values of time-delay is derived to guarantee the asymptotic swarm stability under a directed/undirected interaction graph. Numerical examples are given to confirm the obtained analytical results  

    Asymptotic swarm stability of fractional-order swarm systems in the presence of uniform time-delays

    , Article International Journal of Control ; Volume 90, Issue 6 , 2017 , Pages 1182-1191 ; 00207179 (ISSN) Naderi Soorki, M ; Tavazoei, M. S ; Sharif University of Technology
    Taylor and Francis Ltd  2017
    Abstract
    In this paper, asymptotic swarm stability of fractional-order swarm systems in the presence of uniform time-delays is studied. By using a frequency domain approach, the necessary and sufficient condition on the values of time-delay is derived to guarantee the asymptotic swarm stability under a directed/undirected interaction graph. Numerical examples are given to confirm the obtained analytical results. © 2015 Informa UK Limited, trading as Taylor & Francis Group  

    Improved-resolution millimeter-wave imaging through structured illumination

    , Article Applied Optics ; Volume 56, Issue 15 , 2017 , Pages 4454-4465 ; 1559128X (ISSN) Shayei, A ; Kavehvash, Z ; Shabany, M ; Sharif University of Technology
    Abstract
    A resolution-improved active millimeter-wave (MMW) imaging structure, based on the theory of structured illumination, is proposed in this paper. The structured illumination is a well-defined concept for surpassing the diffraction limit in optical microscopy, where imposing grating patterns on the targeted object could help in moving the object frequency spectrum along the desired direction in the spatial frequency domain. This frequency shift helps in passing different parts of the object's frequency spectrum through the diffraction filter. The combination of resultant images provides a framework to pass a wider frequency band of the object, thereby achieving super-resolution. This idea has... 

    Optimum design of double ridge horn antennas with general cross-section

    , Article IET Microwaves, Antennas and Propagation ; Volume 13, Issue 5 , 2019 , Pages 546-553 ; 17518725 (ISSN) Oraizi, H ; Amini, A ; Shakoori, A ; Karimimehr, M ; Sharif University of Technology
    Institution of Engineering and Technology  2019
    Abstract
    In this study, an analytical method is proposed for design of double-ridged horn (DRH) antenna, which is based on impedance matching of the structure by the method of least squares (MLSs). New basis functions are used for the MLS to obtain optimum impedance functions for the realisation of maximum matching. The resultant reflection coefficients are compared with available methods. The proposed optimum synthesis method is applicable to the arbitrarily tapered DRH antenna with a general cross-section. As two applications, the proposed method is used for the design of linear and non-linear flares of DRH antennas with rectangular and elliptical cross-sections for operation in the frequency band... 

    Performing building vibration assessments by acoustic measurements

    , Article Building Acoustics ; Volume 27, Issue 1 , December , 2020 , Pages 21-33 Isavand, J ; Peplow, A ; Kasaei, A ; Sharif University of Technology
    SAGE Publications Inc  2020
    Abstract
    This article presents an innovative application of the frequency domain decomposition method based on an acoustic and vibration response. Frequency domain decomposition method has been frequently used for operational modal analysis testing in the last decade to identify modal parameters for in-situ case studies. For these studies, the outputs of the vibration response through accelerometers have been employed in the analysis. In this article, the frequency domain decomposition method is employed, for the first time, to analyze both acoustic and vibration response of the building which is a novel application in building vibration response. As a case study, a cylindrical shaped seven-story... 

    Limitations of frequency domain approximation for detecting chaos in fractional order systems

    , Article Nonlinear Analysis, Theory, Methods and Applications ; Volume 69, Issue 4 , 15 August , 2008 , Pages 1299-1320 ; 0362546X (ISSN) Tavazoei, M. S ; Haeri, M ; Sharif University of Technology
    2008
    Abstract
    In this paper, we analytically study the influences of using frequency domain approximation in numerical simulations of fractional order systems. The number and location of equilibria, and also the stability of these points, are compared between the original system and its frequency based approximated counterpart. It is shown that the original system and its approximation are not necessarily equivalent according to the number, location and stability of the fixed points. This problem can cause erroneous results in special cases. For instance, to prove the existence of chaos in fractional order systems, numerical simulations have been largely based on frequency domain approximations, but in... 

    Stability preservation analysis for frequency-based methods in numerical simulation of fractional order systems

    , Article SIAM Journal on Numerical Analysis ; Volume 47, Issue 1 , 2008 , Pages 321-338 ; 00361429 (ISSN) Tavazoei, M. S ; Haeri, M ; Bolouki, S ; Siami, M ; Sharif University of Technology
    2008
    Abstract
    In this paper, the frequency domain-based numerical methods for simulation of fractional order systems are studied in the sense of stability preservation. First, the stability boundary curve is exactly determined for those methods. Then, this boundary is analyzed and compared with an accurate (ideal) boundary in different frequency ranges. Also, the critical regions in which the stability does not preserve are determined. Finally, the analytical achievements are confirmed via some numerical illustrations. © 2008 Society for Industrial and Applied Mathematics  

    A necessary condition for double scroll attractor existence in fractional-order systems

    , Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 367, Issue 1-2 , 2007 , Pages 102-113 ; 03759601 (ISSN) Tavazoei, M. S ; Haeri, M ; Sharif University of Technology
    Elsevier  2007
    Abstract
    In this Letter, based on the stability theorem in fractional differential equations, a necessary condition is given to check existence of double scroll attractor in a fractional-order system. Numerical simulations are presented to evaluate accuracy of this condition in fractional-order Chen and Lü systems. Also, we show that using frequency domain approximation in the numerical simulations of fractional systems may result in wrong consequences. For example, this approximation can numerically demonstrate chaos in the non-chaotic fractional-order systems. Unfortunately, this mistake has occurred in the recent literature that found the lowest-order chaotic systems among fractional-order... 

    Development of SD-HACNEM neutron noise simulator based on high order nodal expansion method for rectangular geometry

    , Article Annals of Nuclear Energy ; Volume 162 , 2021 ; 03064549 (ISSN) Kolali, A ; Vosoughi, J ; Vosoughi, N ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    In this study, the SD-HACNEM (Sharif Dynamic - High order Average Current Nodal Expansion Method) neutron noise simulator in two energy groups using a second-order flux expansion method for two-dimensional rectangular X Y-geometry has been developed. In the first step, the calculations were performed for the steady state and results of ACNEM (Average Current Nodal Expansion Method) and HACNEM (High order Average Current Nodal Expansion Method) were examined and compared. To solve the problem, the power iteration algorithm has been used to calculate the distribution of neutron flux and neutron multiplication factor by considering the coarse-mesh (each fuel assembly one node). To validate the...