Search for: frequency-domain-analysis
0.007 seconds
Total 88 records

    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... 

    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... 

    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
    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... 

    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... 

    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 discrete model for response estimation of soil-structure systems with embedded foundations

    , Article Earthquake Engineering and Engineering Vibration ; Volume 10, Issue 2 , June , 2011 , Pages 263-276 ; 16713664 (ISSN) Khodabakhshi, P ; Jahankhah, H ; Ghannad, M. A ; Sharif University of Technology
    The need for simplified physical models representing frequency dependent soil impedances has been the motivation behind many researches throughout history. Generally, such models are generated to capture impedance functions in a wide range of excitation frequencies, which leads to relatively complex models. That is while there is just a limited range of frequencies that really influence the response of the structure. Here, a new methodology based on the response-matching concept is proposed, which can lead to the development of simpler discrete models. The idea is then used to upgrade an existing simple model of surface foundations to the case of embedded foundations. The applicability of... 

    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
    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
    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  

    Design and Implementation of Time and Frequency Synchronization in LTE

    , Article IEEE Transactions on Very Large Scale Integration (VLSI) Systems ; Volume 23, Issue 12 , January , 2015 , Pages 2970-2982 ; 10638210 (ISSN) Golnari, A ; Shabany, M ; Nezamalhosseini, A ; Gulak, G ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    A novel architecture for efficient time and frequency synchronization, applied to the long-term evolution (LTE) standard, is proposed. For symbol timing, we propose applying a symbol-folding method on top of the sign-bit reduction technique, leading to a novel algorithm for the cyclic prefix-type recognition in LTE. Following the symbol timing, the fractional carrier frequency offset is estimated and compensated using an adaptive gain loop, which allows for a high-accuracy compensation in a short interval. In the frequency domain, for cell search, we propose a sign-bit reduction technique on top of the matched filter method for the primary synchronization signal detection. In addition, we... 

    Ground-based moving target imaging in a circular strip-map synthetic aperture radar

    , Article Proceedings of the 2015 IEEE 5th Asia-Pacific Conference on Synthetic Aperture Radar, APSAR 2015, 1 September 2015 through 4 September 2015 ; 2015 , Pages 835-840 ; 9781467372961 (ISBN) Samareh Hashemi, S. R ; Bayat, S ; Nayebi, M. M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    In this paper a novel algorithm for detection, parameter estimation, and image formation of a moving target in ground-based circular strip-map synthetic aperture radar (GBCSAR) is proposed. Because multiple similar scans of the scene with short revisit time are possible, moving target detection is performed by clutter cancellation. Despite of the frequency-domain or multi-antenna clutter cancellation methods, this system has the capability of removing the clutter completely regardless of the target speed or the signal to clutter ratio (SCR). Estimation of target parameters and range-cell migration correction (RCMC) is based on comparing two consecutive target images. Finally the azimuth... 

    Identification of free conducting particles in transformer oils using PD signals

    , Article Proceedings of the IEEE International Conference on Properties and Applications of Dielectric Materials, 19 July 2015 through 22 July 2015 ; Volume 2015-October , July , 2015 , Pages 724-727 ; 9781479989034 (ISBN) Firuzi, K ; Parvin, V ; Vakilian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Transformers are known as one of the most important equipment in power system transmission and distribution network. Safety of transformer insulation is determined mainly by its insulating oil dielectric strength. A major concern which threaten the withstand strength of a liquid insulation is the presence of particle contamination. One of the best methods to detect any abnormality and insulation weakness inside the transformer insulation is based on partial discharge (PD) measurement. Here, to identify the presence of conducting particles inside the transformer insulating oil, the general routine used for PD recognition is employed. This process involves the following steps: current signal... 

    Denoising of ictal EEG data using semi-blind source separation methods based on time-frequency priors

    , Article IEEE Journal of Biomedical and Health Informatics ; Volume 19, Issue 3 , July , 2015 , Pages 839-847 ; 21682194 (ISSN) Hajipour Sardouie, S ; Shamsollahi, M. B ; Albera, L ; Merlet, I ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Removing muscle activity from ictal ElectroEncephaloGram (EEG) data is an essential preprocessing step in diagnosis and study of epileptic disorders. Indeed, at the very beginning of seizures, ictal EEG has a low amplitude and its morphology in the time domain is quite similar to muscular activity. Contrary to the time domain, ictal signals have specific characteristics in the time-frequency domain. In this paper, we use the time-frequency signature of ictal discharges as a priori information on the sources of interest. To extract the time-frequency signature of ictal sources, we use the Canonical Correlation Analysis (CCA) method. Then, we propose two time-frequency based semi-blind source... 

    Calculation and analysis of thermal-hydraulics fluctuations in pressurized water reactors

    , Article Annals of Nuclear Energy ; Volume 76 , 2015 , Pages 75-84 ; 03064549 (ISSN) Malmir, H ; Vosoughi, N ; Sharif University of Technology
    Elsevier Ltd  2015
    Analysis of thermal-hydraulics fluctuations in pressurized water reactors (e.g., local and global temperature or density fluctuations, as well as primary and charging pumps fluctuations) has various applications in calculation or measurement of the core dynamical parameters (temperature or density reactivity coefficients) in addition to thermal-hydraulics surveillance and diagnostics. In this paper, the thermal-hydraulics fluctuations in PWRs are investigated. At first, the single-phase thermal-hydraulics noise equations (in the frequency domain) are originally derived, without any simplifying assumptions. The fluctuations of all the coolant parameters, as well as the radial distribution of... 

    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... 

    Pressure-transient analysis of bottomhole pressure and rate measurements by use of system-identification techniques

    , Article SPE Journal ; Volume 20, Issue 5 , October , 2015 , Pages 1005-1027 ; 1086055X (ISSN) Mansoori, M ; Van Den Hof, P. M. J ; Jansen, J. D ; Rashtchian, D ; Sharif University of Technology
    Society of Petroleum Engineers  2015
    This study presents a novel perspective on pressure-transient analysis (PTA) of downhole-pressure and flow-rate data by use of system-identification (SI) techniques as widely used in advanced process engineering. Key features of the paper are that it considers the classic PTA process from a system-theoretical perspective; derives the causal structure of the flow dynamics; proposes a method to deal with continuously varying pressure and flow-rate signals contaminated with correlated noise, which estimates physical reservoir parameters through a systematic matching procedure in the frequency domain; and can cope with arbitrary (i.e., not necessarily piecewise constant) flow-rate signals. To... 

    Experimental investigation of the leadingedge roughness on the boundary layer of a plunging airfoil

    , Article 27th Congress of the International Council of the Aeronautical Sciences 2010, ICAS 2010, 19 September 2010 through 24 September 2010, Nice ; Volume 2 , 2010 , Pages 1582-1588 ; 9781617820496 (ISBN) Rasi Marzabadi, F ; Soltani, M. R ; Masdari, M ; Sharif University of Technology
    Extensive experimental investigation was conducted to study the effect of leading-edge roughness on the state of the boundary layer of a wind turbine blade section. The application of surface grit roughness simulates surface irregularities that occur on the wind turbine blades. The measurements were done using multiple hot-film sensors and surface pressure transducers in both static and plunging oscillation of the airfoil. Frequency domain analysis was used to determine the state of the unsteady boundary layer  

    Generalization of order distribution concept use in the fractional order system identification

    , Article Signal Processing ; Volume 90, Issue 7 , July , 2010 , Pages 2243-2252 ; 01651684 (ISSN) Nazarian, P ; Haeri, M ; Sharif University of Technology
    In this paper, the order distribution concept in the frequency domain identification has been extended to include fractional order systems having poles and zeros simultaneously. The existing nonlinear optimization problem appeared when both poles and zeros, is are changed to a quadratic problem that can be solved using least squares algorithms. To collect the required data, system is excited by a multi sine input signal with appropriately selected frequencies. Then a nonparametric identification in frequency domain is accomplished to calculate the empirical transfer function estimate (ETFE). This estimate is then used to implement the frequency domain identification on all defined members of... 

    Identifiability of fractional order systems using input output frequency contents

    , Article ISA Transactions ; Volume 49, Issue 2 , Apr , 2010 , Pages 207-214 ; 00190578 (ISSN) Nazarian, P ; Haeri, M ; Tavazoei, M. S ; Sharif University of Technology
    In this paper, issues related to the identifiability of a fractional order system having its input and output frequency contents are discussed. The effects of the commensurate order α in the identifiability of the model structure and model parameters are analytically studied. It is shown that both identifiabilities (model structure and model parameters) are reduced remarkably for smaller values of α. This phenomenon is observed even though the input signals are rich enough and system belongs to the model set. Our understanding is that the problem arises since differences among different members of the model set fall beyond the practically recognizable precision range. The issue is more... 

    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 
    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... 

    Development and qualification of a thermal-hydraulic nodalization for modeling station blackout accident in PSB-VVER test facility

    , Article Nuclear Engineering and Design ; Volume 303 , 2016 , Pages 109-121 ; 00295493 (ISSN) Saghafi, M ; Ghofrani, M. B ; D'Auria, F ; Sharif University of Technology
    Elsevier Ltd  2016
    This paper deals with the development of a qualified thermal-hydraulic nodalization for modeling Station Black-Out (SBO) accident in PSB-VVER Integral Test Facility (ITF). This study has been performed in the framework of a research project, aiming to develop an appropriate accident management support tool for Bushehr nuclear power plant. In this regard, a nodalization has been developed for thermal-hydraulic modeling of the PSB-VVER ITF by MELCOR integrated code. The nodalization is qualitatively and quantitatively qualified at both steady-state and transient levels. The accuracy of the MELCOR predictions is quantified in the transient level using the Fast Fourier Transform Base Method...