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frequency-domain-analysis
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Total 94 records
Design and Development of a Software for Analyzing Hydrodynamic Behavior of Spm System
, M.Sc. Thesis Sharif University of Technology ; Abbaspour, Madjid (Supervisor)
Abstract
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...
Analytical Design of Fixed-structure Fractional-order Controllers in Frequency Domain
, Ph.D. Dissertation Sharif University of Technology ; Tavazoei, Mohammad Saleh (Supervisor)
Abstract
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...
Achievable Delay Margin by Using PID Fractional-Order Controllers
, M.Sc. Thesis Sharif University of Technology ; Tavazoei, Mohammad Saleh (Supervisor)
Abstract
This paper concerns the delay margin achievable using fractional order Proportional_Integral_Derivative controllers for linear time- invariant systems subject to variable, unknown time delays. The basic issue under investigation addresses the question: What is the largest range of time delay so that there exists a single fractional order Proportional_Integral_Derivative controller to stabilize the delay plants within the entire range? Delay margin is a fundamental measure of robust stabilization against uncertain time delays and poses a fundamental, longstanding problem that remains open except in simple, isolated cases. In this research, we develop explicit expressions of the exact delay...
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 ; Bozorgmehry Boozarjomehry, Ramin (Supervisor)
Abstract
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...
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 ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
Abstract
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...
The Effects of PTO Characteristics on Performance of a Floating Point Absorber Wave Energy Converter
, M.Sc. Thesis Sharif University of Technology ; Behzad, Mahdi (Supervisor) ; Abazari, Abuzar (Supervisor)
Abstract
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 ; Sharif Bakhtiar, Mehrdad (Supervisor)
Abstract
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...
Waves in linear time-varying dielectric media
, Article 16th European Conference on Antennas and Propagation, EuCAP 2022, 27 March 2022 through 1 April 2022 ; 2022 ; 9788831299046 (ISBN) ; Mirmoosa, M. S ; Tretyakov, S. A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
In this paper, focusing on the frequency domain, we write the constitutive relation and the Helmholtz equation for linear, dispersive, and inhomogeneous time-varying media. Next, by assuming spatial homogeneity, we simplify the equations and explain how to calculate dispersion curves (the angular frequency with respect to the wave vector) for propagating waves. Furthermore, we show that under the simplifying assumption of instantaneous response, the developed general approach provides the same dispersion curves as reported earlier for the dispersion-less model of time-varying dielectric media. We believe that this study is important for investigations of wave phenomena in time-varying media,...
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) ; 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...
Topology optimization of wave barriers for mitigation of vertical component of seismic ground motions
, Article Journal of Earthquake Engineering ; 2017 , Pages 1-25 ; 13632469 (ISSN) ; Rezaie, A ; Rafiee Dehkharghani, R ; Sharif University of Technology
Abstract
Vertical vibration of structures due to strong near-field earthquakes could culminate in catastrophic consequences. In this article, the optimum patterns of two types of wave barriers with different geometry configurations, buried in the soil domain, are obtained in order to reduce the vertical acceleration of the top of a circular foundation placed on the soil surface. In order to look into the influence of various soil deposits, six soil deposits with diverse material properties and bedrock depths are examined. The topology optimization procedure for finding the optimum position of the wave barriers has been conducted using coupled finite element-genetic algorithm methodology. First, the...
Topology optimization of wave barriers for mitigation of vertical component of seismic ground motions
, Article Journal of Earthquake Engineering ; Volume 24, Issue 1 , 2020 , Pages 84-108 ; Rezaie, A ; Rafiee Dehkharghani, R ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
Vertical vibration of structures due to strong near-field earthquakes could culminate in catastrophic consequences. In this article, the optimum patterns of two types of wave barriers with different geometry configurations, buried in the soil domain, are obtained in order to reduce the vertical acceleration of the top of a circular foundation placed on the soil surface. In order to look into the influence of various soil deposits, six soil deposits with diverse material properties and bedrock depths are examined. The topology optimization procedure for finding the optimum position of the wave barriers has been conducted using coupled finite element-genetic algorithm methodology. First, the...
Time-domain ultrasound as prior information for frequency-domain compressive ultrasound for intravascular cell detection: A 2-cell numerical model
, Article Ultrasonics ; Volume 125 , 2022 ; 0041624X (ISSN) ; Nili, V. A ; Ejtehadi, M ; Savabi, R ; Kavehvash, Z ; Ahmadian, M. T ; Vahdat, B. V ; Sharif University of Technology
Elsevier B.V
2022
Abstract
This study proposes a new method for the detection of a weak scatterer among strong scatterers using prior-information ultrasound (US) imaging. A perfect application of this approach is in vivo cell detection in the bloodstream, where red blood cells (RBCs) serve as identifiable strong scatterers. In vivo cell detection can help diagnose cancer at its earliest stages, increasing the chances of survival for patients. This work combines time-domain US with frequency-domain compressive US imaging to detect a 20-μ MCF-7 circulating tumor cell (CTC) among a number of RBCs within a simulated venule inside the mouth. The 2D image reconstructed from the time-domain US is employed to simulate the...
Stockwell transform for epileptic seizure detection from EEG signals
, Article Biomedical Signal Processing and Control ; Volume 38 , 2017 , Pages 108-118 ; 17468094 (ISSN) ; Shayesteh, M. G ; Sharif University of Technology
Abstract
Epilepsy is the most common disorder of human brain. The goal of this paper is to present a new method for classification of epileptic phases based on the sub-bands of electroencephalogram (EEG) signals obtained from the Stockwell transform (ST). ST is a time-frequency analysis that not only covers the advantages of both short-time Fourier transform (FT) and wavelet transform (WT), but also overcomes their shortcomings. In the proposed method, at first, EEG signal is transformed into time-frequency domain using ST and all operations are performed in the new domain. Then, the amplitudes of ST in five sub-bands, namely delta (δ), theta (θ), alpha (α), beta (β), and gamma (γ), are computed. 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) ; 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
Speech enhancement using hidden Markov models in Mel-frequency domain
, Article Speech Communication ; Volume 55, Issue 2 , 2013 , Pages 205-220 ; 01676393 (ISSN) ; Sameti, H ; Sharif University of Technology
2013
Abstract
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...
Soil-buried wave barriers for vibration control of structures subjected to vertically incident shear waves
, Article Soil Dynamics and Earthquake Engineering ; Volume 109 , 2018 , Pages 312-323 ; 02677261 (ISSN) ; Rafiee dehkharghani, R ; Mohtasham dolatshahi, K ; Mirghaderi, R ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Traditionally, the effects of seismic forces on structures have been mitigated by installing supplemental energy dissipation systems. In this paper, a new approach is explored for the mitigation of earthquake-induced vibrations by obstructing the entrance of seismic energy to the structure through the insertion of some concrete wave barriers within the soil domain. To do so, genetic algorithm (GA) based adaptive optimization methodology is utilized that is capable of finding the efficient layout of the concrete barriers in a manipulated soil zone around the structure. The optimization methodology is coupled with finite element (FE) method for analyzing the complex wave propagation phenomenon...
Sensitivity analysis of simple methods in determination of offshore jacket structures levels stiffness
, Article Journal of Marine Science and Technology (Japan) ; 2021 ; 09484280 (ISSN) ; Ahmadi, A ; Sharif University of Technology
Springer Japan
2021
Abstract
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...
Sensitivity analysis of simple methods in determination of offshore jacket structures levels stiffness
, Article Journal of Marine Science and Technology (Japan) ; Volume 27, Issue 1 , 2022 , Pages 619-636 ; 09484280 (ISSN) ; Ahmadi, A ; Sharif University of Technology
Springer Japan
2022
Abstract
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...
Reduced common-mode voltage in Z-source inverters
, Article 8th Power Electronics, Drive Systems and Technologies Conference, PEDSTC 2017, 14 February 2017 through 16 February 2017 ; 2017 , Pages 413-418 ; 9781509057665 (ISBN) ; Zolghadri, M. R ; Yaghoubi, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2017
Abstract
Z-source family has been widespread in photovoltaic (PV) applications. In trasformerless grid-connected PV systems, the common mode voltage (CMV) time variations, cause the leakage current flow. This current flows through the stray capacitance of the PV panels. For a Z-Source Inverter (ZSI), the CMV would have higher high-frequency harmonics, due to the shoot through states within the switching cycles. In this paper, the CMV of a ZSI is analyzed and a simple method is proposed for the harmonic reduction of the CMV in the ZSI. The CMV reduction method is based on changing the switching states. The CMV in reduced method is compared to the CMV in the traditional ZSI in frequency domain by using...
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) ; Van Den Hof, P. M. J ; Jansen, J. D ; Rashtchian, D ; Sharif University of Technology
Society of Petroleum Engineers
2015
Abstract
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...