Search for: spectral-analysis
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    Parameteric study of operability for a tourist submarine

    , Article 23rd International Conference on Offshore Mechanics and Arctic Engineering, Vancouver, BC, 20 June 2004 through 25 June 2004 ; Volume 3 , 2004 , Pages 635-641 Koulaei, R. T. P ; Rad, M ; Mousaviraad, S.M ; Sadathosseini, S. H ; Sharif University of Technology
    These days, tourist submarine industry has become of increasing interest and prosperity. A tourist submarine operating beneath a seaway suffers different undesired motions which may cause difficulty in operability for the vehicle and habitability of its passengers. From this point of view, this paper studies the hydrodynamic problem of submarine operability in waves. In this investigation strip theory has been used and effects of different parameters of sea state, sea direction, depth, speed and duration of operation have been considered. Results of presented case study indicate that speed effect is insignificant while the operating depth role seems more important  

    Locked and unlocked behaviour of mutually coupled microwave oscillators

    , Article IEE Proceedings: Microwaves, Antennas and Propagation, Stevenage, United Kingdom ; Volume 147, Issue 1 , 2000 , Pages 13-18 ; 13502417 (ISSN) Banai, A ; Farzaneh, F ; Sharif University of Technology
    IEE  2000
    The interinjection locking of microwave oscillators is investigated using differential equations governing the locking behaviour of two mutually coupled oscillators. The behaviour of the oscillators before and after locking is described, and the common oscillation frequencies, locking range and transient time constant are calculated. The spectra of the oscillators in the unlocked condition are also investigated, with particular attention to the spacing and amplitude variation of the spectral lines. Experimental results in connection with the theoretical investigations are also presented  

    Online Multi-step Ahead Prediction of Time-Varying Solar and Geomagnetic Activity Indices via Adaptive Neurofuzzy Modeling and Recursive Spectral Analysis

    , Article Solar Physics ; Volume 272, Issue 1 , 2011 , Pages 189-213 ; 00380938 (ISSN) Mirmomeni, M ; Lucas, C ; Araabi, B. N ; Moshiri, B ; Bidar, M. R ; Sharif University of Technology
    The time-varying Sun as the main source of space weather affects the Earth's magnetosphere by emitting hot magnetized plasma in the form of solar wind into interplanetary space. Solar and geomagnetic activity indices and their chaotic characteristics vary abruptly during solar and geomagnetic storms. This variation depicts the difficulties in modeling and long-term prediction of solar and geomagnetic storms. On the other hand, the combination of neurofuzzy models and spectral analysis has been a subject of interest due to their many practical applications in modeling and predicting complex phenomena. However, these approaches should be trained by algorithms that need to be carried out by an... 

    Estimating the depth of anesthesia using fuzzy soft computation applied to EEG features

    , Article Intelligent Data Analysis ; Volume 12, Issue 4 , 2008 , Pages 393-407 ; 1088467X (ISSN) Esmaeili, V ; Assareh, A ; Shamsollahi, M. B ; Moradi, M. H ; Arefian, N. M ; Sharif University of Technology
    IOS Press  2008
    Estimating the depth of anesthesia (DOA) is still a challenging area in anesthesia research. The objective of this study was to design a fuzzy rule based system which integrates electroencephalogram (EEG) features to quantitatively estimate the DOA. The proposed method is based on the analysis of single-channel EEG using frequency and time domain methods. A clinical study was conducted on 22 patients to construct subsets of reference data corresponding to four well-defined anesthetic states: awake, moderate anesthesia, surgical anesthesia and isoelectric. Statistical analysis of features was used to design input membership functions (MFs). The input space was partitioned with respect to the... 

    Spectral Analysis of Air Pollution in Tehran

    , M.Sc. Thesis Sharif University of Technology Zare Shahneh, Maryam (Author) ; Arhami, Mohammad (Supervisor)
    Tehran possesses various environmental crises due to excessive population growth, a huge increase of vehicles and heavy concentrated industries. One of the most important concern is air pollution. Spectral Analysis by discrete Fourier transform are described and applied to harmonic analysis of time series for detecting Present periodicities.
    The current work proposes an approach for the determine the contribution of different frequencies to the data variance using air quality measured data. In this research, we present a comprehensive review of methods for spectral analysis of nonuniformly sampled data. Because of The air quality data in Tehran have irregular sampling periods and... 

    Effects of Dynamics and Structure on Population-level Oscillations in Homogeneous Neuronal Networks

    , M.Sc. Thesis Sharif University of Technology Vatandoost kamali, Maryam (Author) ; Razvan, Mohammad Reza (Supervisor) ; Sharifi Tabar, Mohsen (Co-Advisor)
    Networks of neurons produce diverse patterns of oscillations, arising from the net-work’s global properties, the propensity of individual neurons to oscillate, or a mixture of the two. Here we describe noisy limit cycles and quasi-cycles, two related mech-anisms underlying emergent oscillations in neuronal networks whose individual com- ponents, stochastic spiking neurons, do not themselves oscillate. Both mechanisms are shown to produce gamma band oscillations atthepopulation level while individualneu-rons fire at a rate much lower than the population frequency. Spike trains in a network undergoing noisy limit cycles display a preferred period which is not found in the case... 

    Speech Recognition System Having Phoneme-Based Recognition

    , M.Sc. Thesis Sharif University of Technology Tabandeh Haghighi, Pouria (Author) ; Ghorshi, Mohammad (Supervisor) ; Mortazavi, Mohammad (Supervisor)
    This thesis describes a robust algorithm in speech recognition system based on phoneme recognition. Automatic speech recognition systems (ASR) can be divided into two main types: speaker-dependent continuous speech PC-based systems and speaker-independent continuous-speech server based systems. In speaker- independent systems, there is no need to have knowledge about the speaker(s) before using the system, on the other hand, in speaker dependent systems it is essential to have voice training by the speaker(s) supposed to work with the system. In this thesis, a speaker-independent continuous speech PC-based system has been chosen to work with. Acoustic-phonetic approach has been chosen among... 

    Investigation of Endurance Time Method in Seismic Analysis of Vertically Irregular Elastic Steel Frames

    , M.Sc. Thesis Sharif University of Technology Ahmadi, Mehdi (Author) ; Esmaeil Pourestekanchi, Homayun (Supervisor)
    Recent studies show that irregular structures have been damaged more than regular ones during earthquakes. This proves importance of seismic response determination of this type of structures. Today, Codes define irregularity in structures and restrict seismic analysis and design of these types of structures. The Endurance Time (ET) method is a time-history based dynamic pushover procedure for seismic analysis and design of structures that has been recently proposed in Sharif University. This thesis illustrates ET capability in analysis and design of vertically irregular frames. Irregular frames with three, seven and twelve story high were designed with two types of mass and stiffness... 

    Primordial Dipole Anisotropy on the Cosmic Microwave Background and Inflation Theory

    , M.Sc. Thesis Sharif University of Technology Jazayeri, Sadra (Author) ; Mansouri, Reza (Supervisor) ; Firouzjahi, Hassan (Supervisor)
    Cosmic Inflation, invented by Alan Guth in 1980’s, solves the shortcomings of the Standard Cosmology such as the flatness, the horizon and the monopoles problems and provides the seeds of large scale structure formation. The quantum fluctuations which are produced during inflationary epoch are redshifted and transferred from Microscopic scales to Macroscopic universe. We can observe this macroscopic fluctuations both on the CMB surface and on large scale structures. Data from WMAP and Planck missions(CMB space Telescopes) suitably confirms the general predictions of single field inflationary scenarios but still people search for finding primordial gravitational waves from the B-Mode signal... 

    Implementation of SPECAN Algorithm in the Synthetic Aperture Radars (SAR)

    , M.Sc. Thesis Sharif University of Technology Mohseni, Saied Reza (Author) ; Vosughi Vahdat, Bijan (Supervisor) ; Nayebi, Mohammad Mehdi (Co-Advisor)
    Environmental review, surveying land resources and the military mission requires high resolution imaging of large areas. in many cases, imaging should be performed during the night or in poor weather. Synthetic Aperture Radars (SAR)using long range propagation characteristics of radar signals and the complex information processing capability of modern digital electronics to provide high resolution image. The radar complements photographic and optical imaging capabilities because of them does not the time constraints, work and the weather. one of the most important methods for the extraction of synthetic aperture radar images by the method of imaging is the SPECAN algorithm. an important... 

    Toward naturalness in narrow-band speech compression

    , Article 2000 IEEE Internatinal Conference on Multimedia and Expo (ICME 2000), New York, NY, 30 July 2000 through 2 August 2000 ; Issue I/MONDAY , 2000 , Pages 440-443 Ghaemmaghami, S ; Sharif University of Technology
    This paper addresses a new mixed model for characterizing LPC excitation on a 3-band basis through analyzing harmonic structure of the residual signal. In addition, a sub-frame based analysis is developed for detecting both aperiodic pulses and noisy signals, which plays a major role in reduction of perceptual errors introduced by some certain consonants. Preliminary results show that near natural speech is achieved at 1050 bps, allocated to the excitation parameters, suggesting superiority of the proposed coding scheme to the MELP-2400 coding standard, in the sense of perceptual quality of reconstructed speech  

    Passive devices for wave induced vibration control in offshore steel jacket platforms

    , Article Scientia Iranica ; Volume 16, Issue 6 A , 2009 , Pages 443-456 ; 10263098 (ISSN) Golafshani, A. A ; Gholizad, A ; Sharif University of Technology
    Performances of tuned mass dampers and friction dampers to mitigate the wave induced vibrations in jacket type offshore platforms have been compared in this study. Due to the random nature of ocean waves, a full stochastic analysis method has been used to evaluate the response of the structures equipped with these devices. A stochastic linearization technique has been used to take the nonlinear behavior of friction dampers into account. The developed mathematical formulation has been applied to evaluate the response of realistic models, and to find out the optimal values for the adjustable parameters of friction dampers. The results have been verified in comparison with time domain nonlinear... 

    A new study in designing MTMDs in SDOF and MDOF systems based on the spectral analysis method

    , Article Earthquake and Structures ; Volume 19, Issue 4 , 2020 , Pages 243-259 Baigoly, M ; Shargh, F. H ; Rofooei, F. R ; Sharif University of Technology
    Techno-Press  2020
    This study aims to optimize, design, and predict the MTMDs performance in SDOF systems using spectral analysis, and then apply their results to MDOF structures. Given the importance of spectral analysis in the design of new engineering structures, achieving a method for designing TMDs based on this theory can be of great importance for structural designers. In this study, several convenient combinations of MTMDs in an SDOF system are first considered to minimize the maximum displacement. For calculating the frequency ratios of dampers, an innovative technique is adopted in which the values of different modal responses obtained from the spectral analysis are approached together. This... 

    Feasibility and Efficiency of Vibration Control Algorithms on Offshore Platforms

    , Ph.D. Dissertation Sharif University of Technology Gholizadeh, Amin (Author) ; Golafshani, Ali Akbar (Supervisor)
    Offshore platforms are of the economic life lines of oil rich countries. These infrastructures are located at severe environmental conditions, their construction and installation involves expense and these justify utilization of these structures with novel auxiliary vibration control device. Two passive vibration control systems have been evaluated in this study aiming to fatigue damage mitigation in offshore steel jacket platforms. Performances of tuned mass damper and friction damper to suppression of wave induced vibrations in fixed offshore platforms have been investigated in this study. Due to the random nature of ocean waves, a fully stochastic analysis method has been used to evaluate... 

    Vibration Control of Tension Leg Platfoem under Dynamic Loads

    , M.Sc. Thesis Sharif University of Technology Malayjerdi, Ebrahim (Author) ; Tabeshpour, Mohammad Reza (Supervisor)
    TLP is membership of compliant structures. In these platforms buoyancy is more than the weight and pretension compensates extra buoyancy. TLP is consisting of pontoons, columns and a deck. TLP is vertically moored with tendons and tendons extend from under the columns to sea bed. Marine structures vibrate due to applying environmental loads such as wind, waves, currents, earthquakes. Therefore vibration control of TLP is very important problem not only from motion aspect but also from design and fatigue point of view. In this thesis, passive vibration control of TLP with different TMDs are investigated. In first part, introduction of tension leg platforms, types of control mechanisms and... 

    An Exp. Study of the Effect of Sweep on the Wake of a 2-D Wing

    , M.Sc. Thesis Sharif University of Technology Yousefi, Ramin (Author) ; Soltani, Mohammad Reza (Supervisor)
    In this experimental study, a series of wind tunnel tests were performed to examine the wake flow profile over three swept wings with sweep angles of 23, 33 and 40 degrees with similar aspect ratio at various conditions. The airfoil of wing was a NACA 6-series airfoil designed to provide a laminar flow on the front half of the airfoil. The tests, made at a mid aerodynamic chord Reynolds number of 8×〖10〗^5, covered an angle of attack range of -2 to 10 degree. The wing tip vortex effects are eliminated by placing an End-plate on the wing tip.The tests were carried out at two main section of wing and two various position from behind of wing. A total pressure rake and transducers was used to... 

    Spectral Analysis of the Elastic Fields Associated With a Spherical Multi-Inhomogeneous Inclusion

    , M.Sc. Thesis Sharif University of Technology Khorshidi, Alireza (Author) ; Mohammadi Shoja, Hossein (Supervisor)
    Determination of the elastic fields associated with a spherical multiply-coated inhomogeneous inclusion is a problem of great interest among researchers. In this work a set consisting of N+1 concentric spherical domains is considered. Each domain is either isotropic or spherically isotropic and is functionally graded (FG) in the radial direction. The outermost spherical surface is subjected to nonuniform loading and the constituent phases are subjected to some prescribed nonuniform body force and eigenstrain fields. When the outermost domain is an unbounded medium with zero eigenstrain and body force fields then an N-phase multi-inhomogeneous inclusion problem is realized for which the... 

    Optimum Locations of Outrigger System for Earthquakes

    , M.Sc. Thesis Sharif University of Technology Sajjady, Reza (Author) ; Mofid, Masoud (Supervisor)
    Tall building development has been rapidly increasing world wide introducing new challenges that need to be met through engineering judgment. In modern tall buildings, lateral loads induced by wind or earthquake are often resisted by a system of coupled shear walls. But when the building increases in height, the stiffness of the structure becomes more important and introduction of outrigger beams between the shear walls and external columns is often used to provide sufficient lateral stiffness to the structure.In general, earthquake ground motion can occur anywhere in the world and the risk associated with tall buildings, especially under severe earthquakes,... 

    Studying the Behaviour of Split-Level Structures with Semi-Rigid Connections

    , M.Sc. Thesis Sharif University of Technology Khodayari, Abbas (Author) ; Khonsari, Vahid (Supervisor)
    Past earthquakes show that irregular structures have been more vulnerable than their regular counterparts. One of the common types of irregular buildings in urban areas is split-level ones. On the other hand, beam-to-column connections in steel structures are mostly of "semi-rigid" type. In this work, effects of different levels of rigidity of connections, 100%, 75%, 50% and 25%, on the behavior of a number of two-dimensional split-level steel structures, with 1.5 m difference in levels of floors, 2, 3, 5 and 6 bays, and 5, 10 and 15 stories, were studied. All frames were analyzed “with” and “without” considering the P-∆ phenomenon, with two methods, ‘equivalent static load,’ and ‘modal... 

    Investigating the Effects of Soft Stories on the Behavior of Steel Structures during Earthquakes

    , M.Sc. Thesis Sharif University of Technology Toghani, Mohammad Saeed (Author) ; Khonsari, Vahid (Supervisor)
    In this dissertation, a vast number of 2D steel IMFs (Intermediate Moment Frames) with various number of stories and bays, each having one soft storey, of various intensities (ordinary soft storey & extreme soft storey), were studied. The frames were loaded according to ASCE SEI-7-16 and were designed based on AISC-360-10. In order to make a storey softer than others, its height was increased with respect to those of other ones. The dynamic ‘nonlinear spectral analysis,’ and two different static approaches, namely those of ‘ASCE/SEI-7-90’ and ‘ASCE/SEI-7-16,’ were used to study the frames. Comparison of the results obtained from the three aforementioned methods, one dynamic and two static...