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frequency-domain-analysis
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Total 94 records
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...
Multiple partial discharge sources separation using a method based on laplacian score and correlation coefficient techniques
, Article Electric Power Systems Research ; Volume 210 , 2022 ; 03787796 (ISSN) ; Vakilian, M ; Firuzi, K ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Partial discharge (PD) activity can be destructive to the transformer insulation, and ultimately may result in total breakdown of the insulation. Partial discharge sources identification in a power transformer enables the operator to evaluate the transformer insulation condition during its lifetime. In order to identify the PD source; in the case of presence of multiple sources; the first step is to capture the PD signals and to extract their specific features. In this contribution, the frequency domain analysis, the time domain analysis and the wavelet transform are employed for feature extraction purpose. In practice, there might be plenty of features, and in each scenario, only some of...
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...
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,...
Method of lines framework for analysis of arbitrary-shaped spatial periodic structures: a generalized formalism
, Article 2022 Workshop on Recent Advances in Photonics, WRAP 2022, 4 March 2022 through 6 March 2022 ; 2022 ; 9781665407021 (ISBN) ; Fathi, D ; Khavasi, A ; Rumpf, R. C ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
Method of lines (MoL) is numerically described for analysis of spatial periodic structures based on discrete finite difference hybridization of each transverse plane of multilayer structure. The results show rigorous simulation of the three-dimensional (3D) arbitrary-shaped space grating with the best convergence and high stability for highly conductive metallic layers. We propose our method to be considered for analysis of stacked rotated grating (SRG). Also, we propose time-varying MOL using implementation of the multi-frequency finite difference frequency domain (FDFD) method upon our presented method, so that one can simulate spatiotemporal structures in the hybridization framework...
A shooting approach to the scaled boundary finite element equations of elastodynamics in the frequency domain
, Article Computer Methods in Applied Mechanics and Engineering ; Volume 387 , 2021 ; 00457825 (ISSN) ; Sotoudeh, P ; Ghaemian, M ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Dealing with numerical analysis of problems, especially ones with semi-infinite boundaries, scaled boundary finite element method has emerged as one of the efficient tools for the task. Combining the exactness of strong forms with the flexibility of weak formulations makes the method an improvement to its predecessors. Problem with the method arises when the analytical solution of the semi-discretized system is not available, which is the case for numerous problems. In the most recent attempt to solve the issue, a shooting method was proposed for elastostatic problems. Generality of the method removes any concerns regarding the type of governing equations since it no longer needs any...
Analysis of frequency-dependent network equivalents in dynamic harmonic domain
, Article Electric Power Systems Research ; Volume 193 , 2021 ; 03787796 (ISSN) ; Hajipour, E ; Vakilian, M ; Rouzbehi, K ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Rational function-based models have proved to be very efficient for accurate frequency-dependent modeling of power system components. These models are able to characterize the components terminal behaviours (analysing the admittance matrix) for nodal analysis. This provides a fast convergence and inherent stability to the solution routine of the model. This work presents a general framework for interfacing the dynamic phasor method to the rational models. That would be promising for the electromagnetic transient analysis (under harmonic distortion), in the frequency domain. Therefore, Y-element rational pole-residue models (employing the vector fitting method) are developed. Moreover, the...
Development of SD-HACNEM neutron noise simulator based on high order nodal expansion method for rectangular geometry
, Article Annals of Nuclear Energy ; Volume 162 , 2021 ; 03064549 (ISSN) ; Vosoughi, J ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
In this study, the SD-HACNEM (Sharif Dynamic - High order Average Current Nodal Expansion Method) neutron noise simulator in two energy groups using a second-order flux expansion method for two-dimensional rectangular X Y-geometry has been developed. In the first step, the calculations were performed for the steady state and results of ACNEM (Average Current Nodal Expansion Method) and HACNEM (High order Average Current Nodal Expansion Method) were examined and compared. To solve the problem, the power iteration algorithm has been used to calculate the distribution of neutron flux and neutron multiplication factor by considering the coarse-mesh (each fuel assembly one node). To validate the...
Efficient scale estimation methods using lightweight deep convolutional neural networks for visual tracking
, Article Neural Computing and Applications ; 2021 ; 09410643 (ISSN) ; Ghanei Yakhdan, H ; Kasaei, S ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
In recent years, visual tracking methods that are based on discriminative correlation filters (DCFs) have been very promising. However, most of these methods suffer from a lack of robust scale estimation skills. Although a wide range of recent DCF-based methods exploit the features that are extracted from deep convolutional neural networks (CNNs) in their translation model, the scale of the visual target is still estimated by hand-crafted features. Whereas the exploitation of CNNs imposes a high computational burden, this paper exploits pre-trained lightweight CNNs models to propose two efficient scale estimation methods, which not only improve the visual tracking performance but also...
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...
Development of ultrasensitive biomimetic auditory hair cells based on piezoresistive hydrogel nanocomposites
, Article ACS Applied Materials and Interfaces ; Volume 13, Issue 37 , 2021 , Pages 44904-44915 ; 19448244 (ISSN) ; Moradi, H ; Pastras, C. J ; Abolpour Moshizi, S ; Wu, S ; Asadnia, M ; Sharif University of Technology
American Chemical Society
2021
Abstract
With an ageing population, hearing disorders are predicted to rise considerably in the following decades. Thus, developing a new class of artificial auditory system has been highlighted as one of the most exciting research topics for biomedical applications. Herein, a design of a biocompatible piezoresistive-based artificial hair cell sensor is presented consisting of a highly flexible and conductive polyvinyl alcohol (PVA) nanocomposite with vertical graphene nanosheets (VGNs). The bilayer hydrogel sensor demonstrates excellent performance to mimic biological hair cells, responding to acoustic stimuli in the audible range between 60 Hz to 20 kHz. The sensor output demonstrates stable...
Development of ultrasensitive biomimetic auditory hair cells based on piezoresistive hydrogel nanocomposites
, Article ACS Applied Materials and Interfaces ; Volume 13, Issue 37 , 2021 , Pages 44904-44915 ; 19448244 (ISSN) ; Moradi, H ; Pastras, C. J ; Abolpour Moshizi, S ; Wu, S ; Asadnia, M ; Sharif University of Technology
American Chemical Society
2021
Abstract
With an ageing population, hearing disorders are predicted to rise considerably in the following decades. Thus, developing a new class of artificial auditory system has been highlighted as one of the most exciting research topics for biomedical applications. Herein, a design of a biocompatible piezoresistive-based artificial hair cell sensor is presented consisting of a highly flexible and conductive polyvinyl alcohol (PVA) nanocomposite with vertical graphene nanosheets (VGNs). The bilayer hydrogel sensor demonstrates excellent performance to mimic biological hair cells, responding to acoustic stimuli in the audible range between 60 Hz to 20 kHz. The sensor output demonstrates stable...
Nonlinear pitch angle control of an onshore wind turbine by considering the aerodynamic nonlinearities and deriving an aeroelastic model
, Article Energy Systems ; 2021 ; 18683967 (ISSN) ; Moradi, H ; Tse, K. T ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
In this paper, the control problem of a wind turbine in region 3 (where the wind velocity is between the rated wind velocity and cut out wind velocity) has been investigated by considering the aerodynamic nonlinear behavior of the wind-structure interaction. The model has been developed by using the blade element momentum (BEM) theory to obtain the aerodynamic torque and aerodynamic loads in edgewise and flapwise directions. For validation, the aerodynamic behavior of the onshore NREL 5 MW turbine has been compared with the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) aeroelastic code in terms of the power coefficient. Wind speed is modelled as a three-dimensional profile with...
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...
Performing building vibration assessments by acoustic measurements
, Article Building Acoustics ; Volume 27, Issue 1 , December , 2020 , Pages 21-33 ; Peplow, A ; Kasaei, A ; Sharif University of Technology
SAGE Publications Inc
2020
Abstract
This article presents an innovative application of the frequency domain decomposition method based on an acoustic and vibration response. Frequency domain decomposition method has been frequently used for operational modal analysis testing in the last decade to identify modal parameters for in-situ case studies. For these studies, the outputs of the vibration response through accelerometers have been employed in the analysis. In this article, the frequency domain decomposition method is employed, for the first time, to analyze both acoustic and vibration response of the building which is a novel application in building vibration response. As a case study, a cylindrical shaped seven-story...
Frequency data-based procedure to adjust gain and phase margins and guarantee the uniqueness of crossover frequencies
, Article IEEE Transactions on Industrial Electronics ; Volume 67, Issue 3 , 2020 , Pages 2176-2185 ; Tavazoei, M. S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2020
Abstract
Analytical data-driven tuning procedures with the aim of adjusting the values of frequency-domain specifications, e.g., gain margin, phase margin, and corresponding crossover frequencies, are among the most popular control techniques in industrial control. But, the multiplicity of crossover frequencies, as an Achilles' heel in these procedures, may cause that the obtained control system does not meet the intended frequency-domain objectives. Motivated by this fact, this paper improves a newly proposed data-driven tuning procedure for arbitrarily setting the values of gain and phase margins and crossover frequencies, in the viewpoint of guaranteeing the uniqueness of crossover frequencies....
Beamforming, null-steering, and simultaneous spatial and frequency domain filtering in integrated phased array systems
, Article AEU - International Journal of Electronics and Communications ; Volume 110 , 2019 ; 14348411 (ISSN) ; Atarodi, S. M ; Sharif University of Technology
Elsevier GmbH
2019
Abstract
In the case that phased array systems are not capable of attenuating interferences, Radio Frequency (RF) front-ends and Analog Digital Converters (ADCs) with a large dynamic range are required to avoid saturation of the receiver. This leads to a higher power consumption. In this paper, employing N-path circuits in Mixer-First receivers, a novel method is introduced in which spatial and frequency blockers are eliminated right before entering the system on the antennas input. In fact using this technique, adjustable spatial notch filter and band-pass frequency filter are implemented to suppress spatial and frequency interferences. The proposed method enhances the robustness and effectiveness...
Combining pole placement and online empirical mode decomposition methods to adaptive active control of structural vibration
, Article Journal of Vibration and Acoustics, Transactions of the ASME ; Volume 141, Issue 4 , 2019 ; 10489002 (ISSN) ; Hosseini Kordkheili, S. A ; Navazi, H. M ; Bahai, H ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2019
Abstract
Using a combination of the pole placement and online empirical mode decomposition (EMD) methods, a new algorithm is proposed for adaptive active control of structural vibration. The EMD method is a time-frequency domain analysis method that can be used for nonstationary and nonlinear problems. Combining the EMD method and Hilbert transform, which is called Hilbert-Huang transform, achieves a method that can be implemented to extract instantaneous properties of signals such as structural response dominant instantaneous frequencies. In the proposed algorithm, these estimated instantaneous properties are utilized to improve the pole-placement method as an adaptive active control technique. The...
Enhanced stabilization diagram for automated modal parameter identification based on power spectral density transmissibility functions
, Article Structural Control and Health Monitoring ; Volume 26, Issue 7 , 2019 ; 15452255 (ISSN) ; Khodaygan, S ; Sharif University of Technology
John Wiley and Sons Ltd
2019
Abstract
Operational modal analysis based on power spectral density transmissibility (PSDT) functions is a useful tool to identify the modal parameters with low sensitivity to excitations. For pole extraction from the PSDT function, a proper parametric identification method such as the polyreference least squares complex frequency-domain method or poly-Max method can be used. Then, the poles are selected from a stabilization diagram (SD) with overestimating the system model order. Therefore, spurious modes can be identified that must be distinguished and removed from the system poles. To reach this aim, many techniques have been proposed and applied. In this paper, a new algorithm is proposed to...
A method for selection of structural theories for low to high frequency vibration analyses
, Article European Journal of Mechanics, A/Solids ; Volume 75 , 2019 , Pages 27-40 ; 09977538 (ISSN) ; Haddadpour, H ; Abadi, M. T ; Navazi, H. M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Energy methods such as Energy Flow and Statistical Energy Analyses have been popularly used to predict the medium to high frequency vibro-acoustic response of several structures. In these energy methods, usually the common simple structural theories are used for simplicity. Since, the effects of shear deformation and rotary inertia at high frequency regions are unavoidable, it is necessary to determine the validity of these theories in each frequency domain. This paper aims to propose a method for defining a criteria to select a proper structural theory based on the order of shear deformation and rotary inertia to be used in vibration analyses. Several common as well as higher-order beam...