Search for: frequency-domain-analysis
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    Design and Development of a Software for Analyzing Hydrodynamic Behavior of Spm System

    , M.Sc. Thesis Sharif University of Technology Tahmasvand, Hossein (Author) ; Abbaspour, Madjid (Supervisor)
    In recent decades, SPM system has become a great method for transferring petroleum products to tankers and vice versa. SPM technology has shown his confidence and operation abilities. Sea waves are the most important phenomenon to be considered in the design of coastal and offshore structures. In this study dynamic motion of SPM floating structure is modeled under sea waves loading. Mooring lines connected to structure is modeled by using static stability equations and equivalent stiffness matrix is computed. First the SPM floating structure motion is modeled in 2 dimension (3 degree of freedom) using the boundary element method in frequency domain under regular sea waves loading and the... 

    Two Dimensional Elastic Wave Propagation Analysis in Functionally Graded Materials using Finite Element Method in both Time and Frequency Domain

    , M.Sc. Thesis Sharif University of Technology Taheri, Ali (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
    In this thesis the tow-dimensional wave propagation in a functionally graded elastic medium is considered. It is assumed that the stiffness and density of the medium vary continuously in one direction. This work presents analysis in both time and frequency domain. In time domain, a graded element is presented for static and dynamic analyses in FGMs. This element clearly simulates wave propagation in inhomogeneous materials. The most important property which an element must have to be reasonable in wave propagation analyses in FGMs is simulating reflection only from boundaries. In frequency domain a dynamic stiffness matrix is generated using stiffness and mass matrix used in time domain... 

    Analytical Design of Fixed-structure Fractional-order Controllers in Frequency Domain

    , Ph.D. Dissertation Sharif University of Technology Sayyaf, Negin (Author) ; Tavazoei, Mohammad Saleh (Supervisor)
    Due to the simplicity and generality, design of feedback control systems in the frequency domain is among the most prominent topics in the control systems engineering. The problem of compensation means properly adjusting the loop frequency response at critical frequencies. Considering the point that the traditional methods usually use trial and error procedures for compensation, analytical design of fixed-structure controllers for exactly adjusting such values has great importance. Benefitting from the capability of fractional-order dynamics, the compensation problem is studied from three aspects in this thesis. At first according to the importance of adjusting the system frequency response... 

    The Effects of PTO Characteristics on Performance of a Floating Point Absorber Wave Energy Converter

    , M.Sc. Thesis Sharif University of Technology Ramazani, Arman (Author) ; Behzad, Mahdi (Supervisor) ; Abazari, Abuzar (Supervisor)
    In recent years, the challenges of using fossil energy causes governments and researchers to focus on renewable energies. In this regard, one of the strategies for generating power is using wave energy converters. The aim of present study is modeling frequency and time domain analysis of the wave energy converter. the study focuses on the effect of Power-Take-Off system on the output power and efficiency under the Macoran sea waves. First, the concept of wave converters is explained and the commercialized ones are introduced. Then the related previous works are reviewed and the wave theories are briefly presented. In the following, a specified one-degree-of-freedom converter is modeled in... 

    A Novel Method for Analysis and Design of Class-E Power Amplifier with Design of a Power Amplifier Stage with a Tight Transmission Mask

    , M.Sc. Thesis Sharif University of Technology Babamir, Mehrdad (Author) ; Sharif Bakhtiar, Mehrdad (Supervisor)
    A new analytic method for class E power amplifiers in the frequency domain is presented. Closed form and fairly simple equations in terms of the circuit components for the output power at the carrier frequency and its harmonics as well as the power efficiency with its sensitivity to the load resistance and other circuit components are derived. This provides the facility to directly calculate the circuit components for the desired operation. Using the proposed model, equations to satisfy maximum power efficiency are derived. Also, a design guide based on a novel scaling method to facilitate the design procedures for the given constraints and conditions are presented. In the next step, a... 

    Development of an Intelligent Fault Diagnosing System for Diagnosis of Multiple Concurrent Asynchronous Faults for Tennessee Eastman Process

    , M.Sc. Thesis Sharif University of Technology Akbari, Reza (Author) ; Bozorgmehry Boozarjomehry, Ramin (Supervisor)
    Fault diagnosis in complex processes is very difficult due to their complexity and dimensionality, so it is of great importance. In previous works, concurrent fault diagnosing methods have not been able to diagnose faults with overlapping symptoms. On the other hand, there is no established and general method by which asynchronous concurrent faults with overlapping symptoms can be diagnosed. The purpose of this work is to come up with such a method in order to mitigate the shortcomings of the available methods which are not appropriate to be used for such a problem. In this problem, the main objective is to come up with course of events of faults according to their times occurrence. The... 

    Speech enhancement using hidden Markov models in Mel-frequency domain

    , Article Speech Communication ; Volume 55, Issue 2 , 2013 , Pages 205-220 ; 01676393 (ISSN) Veisi, H ; Sameti, H ; Sharif University of Technology
    Hidden Markov model (HMM)-based minimum mean square error speech enhancement method in Mel-frequency domain is focused on and a parallel cepstral and spectral (PCS) modeling is proposed. Both Mel-frequency spectral (MFS) and Mel-frequency cepstral (MFC) features are studied and experimented for speech enhancement. To estimate clean speech waveform from a noisy signal, an inversion from the Mel-frequency domain to the spectral domain is required which introduces distortion artifacts in the spectrum estimation and the filtering. To reduce the corrupting effects of the inversion, the PCS modeling is proposed. This method performs concurrent modeling in both cepstral and magnitude spectral... 

    A parallel cepstral and spectral modeling for HMM-based speech enhancement

    , Article 17th DSP 2011 International Conference on Digital Signal Processing, Proceedings, 6 July 2011 through 8 July 2011, Corfu ; 2011 ; 9781457702747 (ISBN) Veisi, H ; Sameti, H ; Sharif University of Technology
    An HMM-based speech enhancement in Mel-frequency domain is introduced and improved. It is shown that hidden Markov modeling in the Mel-frequency domain is beneficial due to its effective representation of the speech spectrum; however, speech enhancement in this domain requires an inversion from the Mel-frequency to the spectral domain which introduces distortion artifacts for spectrum estimation. To reduce the distortion effects of the inversion and employ the advantages of robustness modeling in the Mel-frequency domain, a parallel cepstral and spectral (PCS) modeling is proposed. In PCS, a concurrent modeling in both cepstral and spectral domains is performed. The performances of the... 

    A simplified method for phase noise calculation

    , Article Proceedings of the Custom Integrated Circuits Conference, 13 September 2009 through 16 September 2009 ; 2009 , Pages 535-538 ; 08865930 (ISSN) ; 9781424440726 (ISBN) Tohidian, M ; Fotowat Ahmady, A ; Kamarei, M ; Sharif University of Technology
    A new phase noise calculation method is proposed in which noise sources are modeled with single tone sources. It uses a nonlinear frequency-domain analysis to calculate total gain from noise sources to the output phase noise. This single tone (ST) simulation directly calculates noise frequency contributions and is much faster than Hajimiri's impulse sensitivity function (ISF) method. A quadrature VCO has been implemented in TSMC 0.18-μm CMOS and the predicted phase noise matches measurement. © 2009 IEEE  

    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
    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
    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  

    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
    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... 

    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
    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... 

    Nonlinear dynamic analysis of TLP surge motion using homotopy perturbation method

    , Article Ships and Offshore Structures ; Vol. 9, issue. 6 , May , 2014 , p. 569-577 Tabeshpour, M. R ; Shoghi, R ; Sharif University of Technology
    Tension leg platforms (TLPs) are well-known structures for oil exploitation in deep water. One of the current issues in compliant structures in the sea is variation in frequency and structural response due to a nonlinear parameter in the equation of motion. Variation of frequency is important in fatigue life study of tethers. A perturbation method is used in contrast to the traditional methods. This method does not require a small parameter for finding surge motion of TLP. In this paper, homotopy perturbation method (HPM) is used to solve a highly nonlinear differential equation of surge motion. Calculated responses by HPM are compared with those obtained from both linear and nonlinear... 

    Sensitivity analysis of simple methods in determination of offshore jacket structures levels stiffness

    , Article Journal of Marine Science and Technology (Japan) ; 2021 ; 09484280 (ISSN) Tabeshpour, M. R ; Ahmadi, A ; Sharif University of Technology
    Springer Japan  2021
    Dynamic analyses are necessary problems in offshore jacket structures design and assessment. These analyses have various applications in recognition of dynamic behavior, fatigue analysis, damage detection, etc. Natural frequencies and mode shapes, as inherent vibrational features of a structure, are key parameters in referred analyses. These parameters are mainly affected by mass and stiffness matrices and slightly by damping. Therefore, it is more important to estimate the stiffness matrix of a structure accurately, especially in stiff structures such as offshore jacket platforms. In many cases, the stiffness of levels is required. For example, it can be useful in the construction of an... 

    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
    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  

    New statistic to increase correctness in simulation factor screening using frequency domain method

    , Article Communications in Statistics - Theory and Methods ; Volume 41, Issue 12 , 2012 , Pages 2242-2255 ; 03610926 (ISSN) Sohi, Z. A ; Noorossana, R ; Akhavan Niaki, S. T ; Sharif University of Technology
    Simulation models often include a large number of input factors, many of them may be unimportant to the output; justifying the use of factor screening experiments to eliminate unimportant input factors from consideration in later stages of analysis. With a large number of factors, the challenge is designing experiments so that total number of runs and consequently the required time and cost decrease while achieving a satisfactory detection rate. This article employs frequency domain method (FDM) which is applicable in discrete-event simulation models to propose a new statistic defined as the ratio of estimated signal spectrum to maximum estimated noise spectrum. The proposed method not only... 

    Performance evaluation of asynchronous multi-carrier code division multiple access for next-generation long-reach fibre optic access networks

    , Article IET Optoelectronics ; Volume 9, Issue 6 , 2015 , Pages 325-332 ; 17518768 (ISSN) Shoreh, M. H ; Beyranvand, H ; Salehi, J. A ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    In this study, the authors evaluate the performance of asynchronous optical multi-carrier code division multiple access (MC-CDMA) for intensity modulated/direct detection systems to be used in next-generation optical access networks. The proposed system employs Gold sequence in frequency-domain to provide asynchronous resource sharing. In long-reach passive optical networks, fibre impairments degradation to the performance of ordinary optical CDMA can be avoided by frequency-domain digital compensation methods in the proposed MC-CDMA. In comparison with orthogonal frequency division multiple access, peak-to-average power ratio in the proposed MC-CDMA is reduced and asynchronous resource... 

    Localized identification of shear building with embedded foundation in frequency domain

    , Article Structural Design of Tall and Special Buildings ; Volume 17, Issue 2 , 2008 , Pages 245-256 ; 15417794 (ISSN) Sholeh, K ; Vafaie, A ; Kaveh, A ; Sharif University of Technology
    For studying the behavior of structure in an earthquake, it is advisable to model the structure as a multi-degrees of freedom system, consisting of numerous single-degree of freedom substructures and pay attention to soil-structure interaction. System identification is divided into two categories: namely time domain method and frequency domain approach. In this paper, a localized substructure identification of shear building considering the soil-structure interaction is presented using a frequency domain approach. In order to deal with noise-corrupted data, a spectral smoothing technique with Parzen's window reduction method is adapted. It is shown that better convergence and accuracy can be... 

    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
    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...