Search for: power-spectral-density
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    A structural model updating method using incomplete power spectral density function and modal data

    , Article Structural Engineering and Mechanics ; Volume 68, Issue 1 , 2018 , Pages 39-51 ; 12254568 (ISSN) Esfandiari, A ; Ghareh Chaei, M ; Rofooei, F. R ; Sharif University of Technology
    Techno Press  2018
    In this study, a frequency domain model updating method is presented using power spectral density (PSD) data. It uses the sensitivity of PSD function with respect to the unknown structural parameters through a decomposed form of transfer function. The stiffness parameters are captured with high accuracy through solving the sensitivity equations utilizing the least square approach. Using numerically noise polluted data, the model updating results of a truss model prove robustness of the method against measurement and mass modelling errors. Results prove the capabilities of the method for parameter estimation using highly noise polluted data of low ranges of excitation frequency. Copyright ©... 

    Non-fixed scatterers and their effects on MIMO multicarrier fading communication channels

    , Article 50th Annual IEEE Global Telecommunications Conference, GLOBECOM 2007, Washington, DC, 26 November 2007 through 30 November 2007 ; December , 2007 , Pages 3765-3769 ; 1424410436 (ISBN); 9781424410439 (ISBN) Saligheh Rad, H ; Gazor, S ; Shariatpanahi, P ; Sharif University of Technology
    There are two types of scatterers in a multipath propagation environment: fixed and non-fixed scatterers. Fixed scatterers like buildings, mountains and tree stems do not move, while non-fixed (moving) scatterers like cars, people and tree leaves move from their initial positions. In addition to different movements of the mobile station (MS) that cause different kinds of Doppler fading, movements of non-fixed scatterers are also anticipated to generate other kinds of fading/correlation. This fading changes depend on the type of the propagation environment and the type of movements of local surrounding scatterers. In this paper we characterize these effects in terms of temporal correlations.... 

    Comprehensive study on the results of tension leg platform responses in random sea

    , Article Journal of Zhejiang University: Science ; Volume 7, Issue 8 , 2006 , Pages 1305-1317 ; 10093095 (ISSN) Tabeshpour, M. R ; Golafshani, A. A ; Seif, M. S ; Sharif University of Technology
    Compliant offshore structures are used for oil exploitation in deep water. Tension leg platform (TLP) is a suitable type for very deep water. The nonlinear dynamic response of TLP under random sea wave load is necessary for determining the maximum deformations and stresses. Accurate and reliable responses are needed for optimum design and control of the structure. In this paper nonlinear dynamic analysis of TLP is carried out in both time and frequency domains. The time history of random wave is generated based on Pierson-Moskowitz spectrum and acts on the structure in arbitrary direction. The hydrodynamic forces are calculated using the modified Morison equation according to Airy's linear... 

    Ride comfort of high-speed trains travelling over railway bridges

    , Article Vehicle System Dynamics ; Volume 43, Issue 3 , 2005 , Pages 173-197 ; 00423114 (ISSN) Kargarnovin, M. H ; Younesian, D ; Thompson, D ; Jones, C ; Sharif University of Technology
    Taylor and Francis Ltd  2005
    The ride comfort of high-speed trains passing over railway bridges is studied in this paper. A parametric study is carried out using a time domain model. The effects of some design parameters are investigated such as damping and stiffness of the suspension system and also ballast stiffness. The influence of the track irregularity and train speed on two comfort indicators, namely Sperling's comfort index and the maximum acceleration level are also studied. Two types of railway bridges, a simple girder and an elastically supported bridge are considered. Timoshenko beam theory is used for modelling the rail and bridge and two layers of parallel damped springs in conjunction with a layer of mass... 

    Frequency response analysis for dynamic model identification and control of a ducted fan aerial vehicle in hover

    , Article Applied Mechanics and Materials, Neptun-Olimp ; Volume 332 , 2013 , Pages 56-61 ; 16609336 (ISSN) ; 9783037857335 (ISBN) Effati, M ; Banazadeh, A ; Sharif University of Technology
    System Identification is a key technology for the development and integration of modern engineering systems including unconventional flying vehicles. These systems are highly parametric with complex dynamics and nonlinearities. Ducted fans are special class of these vehicles that can take off vertically, hover and cruise at very low speed. In this paper, an exact equivalent linear system is found from the non-linear dynamic model of a ducted fan by use of frequency response identification. Here, power spectral density analysis is performed, using CIFER software, to evaluate the input-output responses in hover and to derive the transfer functions based on the coherence criterion. Then,... 

    An appropriate procedure for detection of journal-bearing fault using power spectral density, K-nearest neighbor and support vector machine

    , Article International Journal on Smart Sensing and Intelligent Systems ; Volume 5, Issue 3 , 2012 , Pages 685-700 ; 11785608 (ISSN) Moosavian, A ; Ahmadi, H ; Tabatabaeefar, A ; Sakhaei, B ; Sharif University of Technology
    Journal-bearings play a significant role in industrial applications and the necessity of condition monitoring with nondestructive tests is increasing. This paper deals a proper fault detection technique based on power spectral density (PSD) of vibration signals in combination with K-Nearest Neighbor and Support Vector Machine (SVM). The frequency domain vibration signals of an internal combustion engine with three journal-bearing conditions were gained, corresponding to, (i) normal, (ii) corrosion and (iii) excessive wear. The features of the PSD values of vibration signals were extracted using statistical and vibration parameters. The extracted features were used as inputs to the KNN and... 

    Discriminating early stage AD patients from healthy controls using synchronization analysis of EEG

    , Article 2011 6th International Conference on Digital Information Management, ICDIM 2011 ; 2011 , Pages 282-287 ; 9781457715389 (ISBN) Jalili, M ; Sharif University of Technology
    In this paper we study how the meso-scale and micro-scale electroencephalography (EEG) synchronization measures can be used for discriminating patients suffering from Alzheimer's disease (AD) from normal control subjects. To this end, two synchronization measures, namely power spectral density and multivariate phase synchronization, are considered and the topography of the changes in patients vs. Controls is shown. The AD patients showed increased power spectral density in the frontal area in theta band and widespread decrease in the higher frequency bands. It was also characterized with decreased multivariate phase synchronization in the left fronto-temporal and medial regions, which was... 

    Identification of dynamic properties of dams using system identification techniques and real earthquake excitations

    , Article 9th US National and 10th Canadian Conference on Earthquake Engineering 2010, Including Papers from the 4th International Tsunami Symposium, Toronto, ON, 25 July 2010 through 29 July 2010 ; Volume 9 , 2010 , Pages 6985-6996 ; 9781617388446 (ISBN) Bakhshi, A ; Meshkat, A ; Sharif University of Technology
    Investigation of the dynamic characteristics of an existing structure system based on field tests is of practical significance, since it can be employed in the field of examining construction quality, validating or improving analytical finite element structural models, or conducting damage assessment. The main purpose of this study is to investigate the dynamic characteristics of dams using the seismic response data. Whereas, in the process of frequency domain identification of dam properties, frequency response function (FRF) plays the most important role, evaluating the corresponding parameters with better accuracy has always been desirable. Therefore, a comparison was made between some... 

    EEG based biometrics using emotional stimulation data

    , Article 5th IEEE Region 10 Humanitarian Technology Conference, R10-HTC 2017, 21 December 2017 through 23 December 2017 ; Volume 2018-January , February , 2018 , Pages 246-249 ; 9781538621752 (ISBN) Khalil, R ; Arasteh, A ; Sarkar, A. K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    EEG based biometrics using linear Support Vector Machine (SVM) is proposed in this paper. Human identification using electroencephalographic signal was done in this research. Reliability of most of the biometrics systems is not up to the mark because of the possibility of being faked or duplicated. Here, the brain signatures were used as a possible biometric identifier. A Database for Emotion Analysis using Physiological Signals containing 40 trials from each participant was used. International 10-20 system of EEG electrode placement was employed and data from Cz electrode was taken for this research. Some researches showed nice performance with few subjects. Here, 20 subjects were used from... 

    A Fast Soft Decision Algorithm for Cooperative Spectrum Sensing

    , Article IEEE Transactions on Circuits and Systems II: Express Briefs ; Volume 68, Issue 1 , 2021 , Pages 241-245 ; 15497747 (ISSN) Golvaei, M ; Fakharzadeh, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Hidden Primary User problem caused by fading and shadowing severely affects the detection rate of the cognitive radio systems with a single spectrum sensor. Cooperative Spectrum Sensing has been introduced to tackle this problem by using the spatial diversity of spectrum sensors. It is shown that the use of soft decision algorithms in fusion center has a better performance than hard decision algorithms. The problem of soft decision based on sensor measurements perfectly matches the Machine Learning paradigm. In this brief, a novel fast soft decision algorithm is proposed based on Machine Learning theory for wideband Cooperative Spectrum Sensing, which finds a decision boundary to classify... 

    Designing a SSVEP based Brain-Computer Interface to Control the Keyboard

    , M.Sc. Thesis Sharif University of Technology Basere, Naser (Author) ; Shamsollahi, Mohammad Bagher (Supervisor)
    Brain Computer Interface (BCI) is a communication system between human brain’s activity and his environment such as prosthetic hand and wheelchair and other controlling devices.In this thesis we will introduce a new and easy spelling system by using Brain Computer Interface (BCI) based on Steady State Evoke Potential (SSVEP). This system is used for spelling the numbers of telephone keyboard by four flickers and clock shape. This system allows the user to spell numbers by gazing at one of four flickers (Clockwise rotation, Counter Clockwise rotation, Accept and Backspace), Clockwise is used to rotate clock hand toward right, Counter Clockwise to rotate clock hand toward left, Accept is used... 

    Multivariate Synchronization Analysis of Brain Electroencephalography Signals: A Review of Two Methods

    , Article Cognitive Computation ; Volume 7, Issue 1 , February , 2013 , Pages 3-10 ; 18669956 (ISSN) Jalili, M ; Sharif University of Technology
    Springer New York LLC  2013
    Temporal synchronization of neuronal activity plays an important role in various brain functions such as binding, cognition, information processing, and computation. Patients suffering from disorders such as Alzheimer’s disease or schizophrenia show abnormality in the synchronization patterns. Electroencephalography (EEG) is a cheap, non-invasive, and easy-to-use method with fine temporal resolution. Modern multichannel EEG data are increasingly being used in brain studies. Traditional approaches for identifying synchronous activity in EEG are through univariate techniques such as power spectral density or bivariate techniques such as coherence. In this paper, we review two methods for... 

    An investigation of the surface morphology of nanostructured nickel thin films prepared by electrodeposition

    , Article International Journal of Surface Science and Engineering ; Volume 10, Issue 5 , 2016 , Pages 444-455 ; 1749785X (ISSN) Torabi, M ; Dolati, A ; Sharif University of Technology
    Inderscience Enterprises Ltd 
    Nickel nanostructure thin films were electrodeposited on copper plates to investigate the fractal study. Scharifker's equations were derived for instantaneous and progressive nucleation and 3D growth of hemispherical centres under diffusion-controlled condition to calculate in situ change of fractal dimension of surface. It was assumed that the layer could be formed completely when fractal dimension of surface inclined to 2. Moreover, the fractal analysis of atomic force microscopy (AFM) images has confirmed the presumed model. Also, the power values of power spectral density (PSD) of the AFM images were determined using fast Fourier transform (FFT) algorithms. The PSD plots are approximated... 

    Nonlinear FM waveform design to reduction of sidelobe level in autocorrelation function

    , Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 1973-1977 ; 9781509059638 (ISBN) Ghavamirad, R ; Babashah, H ; Sebt, M. A ; Sharif University of Technology
    This paper will design non-linear frequency modulation (NLFM) signal for Chebyshev, Kaiser, Taylor, and raised-cosine power spectral densities (PSDs). Then, the variation of peak sidelobe level with regard to mainlobe width for these four different window functions are analyzed. It has been demonstrated that reduction of sidelobe level in NLFM signal can lead to increase in mainlobe width of autocorrelation function. Furthermore, the results of power spectral density obtained from the simulation and the desired PSD are compared. Finally, error percentage between simulated PSD and desired PSD for different peak sidelobe level are illustrated. The stationary phase concept is the possible... 

    Modal parameter identification of rotary systems based on power spectral density transmissibility functions

    , Article 2018 SAE World Congress Experience, WCX 2018, 10 April 2018 through 12 April 2018 ; Volume 2018-April , 2018 ; 01487191 (ISSN) Khodaygan, S ; Sharif University of Technology
    SAE International  2018
    Operational modal analysis based on power spectral density transmissibility functions (PSDT) is a powerful tool to identify the modal parameters with low sensitivity to excitations. The rotor systems may have the asymmetric damping or stiffness matrices which can lead to increase the difficulties of the identification procedure. In this paper, a new method is proposed to identify the modal parameters of the asymmetric rotary systems by the operational modal analysis based on the power spectral density transmissibility functions. For pole extraction from the PSDT function, a proper parametric identification method such as the Poly-reference Least Squares Complex Frequency-domain method... 

    On the positive definiteness of polarity coincidence correlation coefficient matrix

    , Article IEEE Signal Processing Letters ; Volume 15 , January , 2008 , Pages 73-76 ; 10709908 (ISSN) Haddadi, F ; Nayebi, M. M ; Aref, M. R ; Sharif University of Technology
    Polarity coincidence correlator (PCC), when used to estimate the covariance matrix on an element-by-element basis, may not yield a positive semi-definite (PSD) estimate. Devlin et al. (Devlin, 1975) claimed that element-wise PCC is not guaranteed to be PSD in dimensions p > 3 for real signals. However, no justification or proof was available on this issue. In this letter, it is proved that for real signals with p ≤ 3 and for complex signals with p ≤ 2, a PSD estimate is guaranteed. Counterexamples are presented for higher dimensions which yield invalid covariance estimates. © 2007 IEEE  

    A novel multi-access scheme for UWB-PPM communication systems

    , Article European Transactions on Telecommunications ; Volume 18, Issue 4 , 2007 , Pages 389-401 ; 1124318X (ISSN) Khani, H ; Azmi, P ; Sharif University of Technology
    In this paper, it is shown that some spikes exist in power spectral density (PSD) of ultra-wideband-time-hopping-pulse-position-modulation (UWB-TH-PPM) transmitted signal. Analytical and numerical simulation results show that these spikes severely degrade UWB-TH-PPM system bit-error-rate performance and must be properly removed. This paper proposes a novel multi-access scheme that uses both direct-sequence (DS) and time-hopping (TH) multi-access schemes to remove these harmful spikes. Analytical and numerical simulation results show that the proposed scheme removes the spikes from the PSD of the UWB-TH-PPM transmitted signal and yields better performance. In this paper, the performance of... 

    Probabilistic voltage harmonic analysis of direct torque controlled induction motor drives

    , Article IEEE Transactions on Power Electronics ; Volume 21, Issue 4 , 2006 , Pages 1041-1052 ; 08858993 (ISSN) Kaboli, S ; Vahdati Khajeh, E ; Zolghadri, M. R ; Sharif University of Technology
    In high frequency motor-drives such as direct torque controlled (DTC) induction motor drives, the motor harmonic loss, and electromagnetic interference are largely affected by the spectrum of the motor input voltage. Nonlinear elements in the control loop of DTC drive make harmonic analysis of the drive very complex compared to classical pulsewidth modulated controlled drives. In this paper, a probabilistic method to study the harmonic contents of voltage in DTC of induction motors is presented. The DTC voltage chain is simulated with a random process. Then, the autocorrelation function of voltage vectors is calculated and its power spectrum density is obtained. The effect of flux and torque... 

    Response of a suspended cable to narrow-band random excitation with peaked P.S.D

    , Article Mathematical and Computer Modelling ; Volume 41, Issue 11-12 , 2005 , Pages 1203-1212 ; 08957177 (ISSN) Kargarnovin, M. H ; Mehri, B ; Younesian, D ; Sharif University of Technology
    The response of a suspended cables subjected to narrow-band random excitations with two types of peaked P.S.D. is formulated and analyzed. Banach fixed-point theorem is used for eigenfunction analysis of the differential-integral equations of motion for the first time in this paper. Fredholm approach also is used in the free vibration analysis of the suspended cable and then using Galerkin mode approximation method, power spectral density, and root mean square of the response are computed for two practical types of excitation. All of the calculated results converted to dimensionless quantities make their usage easier in vibration analysis of some practical cases such as vibration of moving... 

    Identification of Vibrational Characteristic of System under Colored Excitation base on the Transmissibility Functions

    , M.Sc. Thesis Sharif University of Technology Afshar, Mehrnoosh (Author) ; Behzad, Mehdi (Supervisor)
    Operational modal analysis (OMA) techniques are proper methods to identify the modal parameters of the structures such as natural frequencies, damping ratios and mode shapes based on the system responses. First research in this area are stared from civil engineering. Difference between civil structure and industrial machines are in the type of excitation.in most industries such as aerospace or mechanical, colored or harmonic forces due to rotary machines, excited the system. Under this condition, traditional methods in OMA are not capable any more. Many works has been done to modify traditional methods. Most of these work limited to situations that forces are harmonic and harmonic...