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response-function
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Frequency-domain stable state-space system identification
, Article Transactions of the Institute of Measurement and Control ; Volume 26, Issue 4 , 2004 , Pages 261-272 ; 01423312 (ISSN) ; Sadati, N ; Ranjbar, A. M ; Sharif University of Technology
Arnold
2004
Abstract
Due to possible distortion contained in frequency-domain data, system identification methods based on data-matching alone do not guarantee stable models. This is a model of a linear system from its frequency response data. It is an improvement and an extension of previous work. The method first identifies a matrix-fraction description of the transfer function matrix of the system from data. Then, through forming a multivariable observable or controllable canonical form, the method separates and replaces the unstable subsystem by a stable subsystem having approximately the same frequency response. Finally, it calculates the Markov parameters of the resulting model and obtains a state-space...
Receptance coupling for end mills
, Article International Journal of Machine Tools and Manufacture ; Volume 43, Issue 9 , 2003 , Pages 889-896 ; 08906955 (ISSN) ; Altintas, Y ; Movahhedy, M ; Sharif University of Technology
2003
Abstract
Identification of chatter free cutting conditions, the chatter stability lobes, requires a measurement of the frequency response function (FRF) of each tool mounted on the spindle. This paper presents a method of assembling known dynamics of the spindle-tool holder with an analytically modeled end mill using the receptance coupling technique. The classical receptance technique is enhanced by proposing a method of identifying the end mill-spindle/tool holder joint dynamics, which include both translational and rotational degrees of freedom. The method requires measurement of FRFs with impact tests applied on the spindle-tool holder assembly and blank calibration cylinders attached to the...
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) ; Ghareh Chaei, M ; Rofooei, F. R ; Sharif University of Technology
Techno Press
2018
Abstract
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 ©...
Spin and charge fluctuations in a one-dimensional lattice with long-range interactions
, Article Physica B: Condensed Matter ; Volume 571 , 2019 , Pages 204-209 ; 09214526 (ISSN) ; Davoudi, B ; Sharif University of Technology
Elsevier B.V
2019
Abstract
We study the competition between spin and charge fluctuations of the extended Hubbard model with on-site and dipole-dipole interactions in a one-dimensional lattice. Using the extended two-particle self consistent (ETPSC) method, we find the corresponding expressions for spin and charge response functions. In this approach, the irreducible spin and charge vertices are a function of inter-particle distance (r) and wave-number (q). This theory allows us to determine the crossover temperatures and the dominant instability as a function of U and V. The phase diagrams are obtained for several effective particle densities: n = 0.5, n = 1 and n = 4/3. Each phase diagram (U − V − T space)...
Structural damage detection using principal component analysis of frequency response function data
, Article Structural Control and Health Monitoring ; Volume 27, Issue 7 , 2020 ; Nabiyan, M. S ; Rahimzadeh Rofooei, F ; Sharif University of Technology
John Wiley and Sons Ltd
2020
Abstract
In this paper, a new sensitivity-based model updating method is presented based on the changes of principal components (PCs) of frequency response function (FRF). Structural damage estimation, identification of damage location and severity, is conducted by an innovative sensitivity relation. The sensitivity relation is derived by incorporating PC analysis (PCA) data obtained from the incomplete measured structural responses in a mathematical formulation and is then solved by the least square method. In order to demonstrate the performance of the proposed method, it is applied to a truss and a frame model. The results prove the ability of the method as a robust damage detection algorithm in...
Damage detection of offshore jacket structures using frequency domain selective measurements
, Article Journal of Marine Science and Application ; Volume 12, Issue 2 , June , 2013 , Pages 193-199 ; 16719433 (ISSN) ; Golafshani, A. A ; Ghodrati, E ; Sharif University of Technology
2013
Abstract
The development of damage detection techniques for offshore jacket structures is vital to prevent catastrophic events. This paper applies a frequency response based method for the purpose of structural healthCgreater detection efficiency. In addition, the performance of the proposed method was evaluated in relation to multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform, and the results proved to be satisfactory utilizing the proposed methodology
Prediction of spindle dynamics in milling by sub-structure coupling
, Article International Journal of Machine Tools and Manufacture ; Volume 46, Issue 3-4 , 2006 , Pages 243-251 ; 08906955 (ISSN) ; Gerami, J. M ; Sharif University of Technology
2006
Abstract
The Stability of machining process depends on the dynamics of the machine tool, among other things. However, the dynamics of the machine tool changes when the tool is changed. To avoid the need for repeating the measurements, sub-structuring analysis may be used to couple the tool and spindle frequency response functions. A major difficulty in this approach is the determination of joint stiffness and damping between the two sub-structures. In particular, the measurement of rotational responses (RDOFs) at joints is a difficult task. In this research, a simple joint model that accounts for RDOFs is proposed. It is shown that this model avoids RDOF measurement while taking into account the...
The Impact of Unconditional Cash Subsidies on the Iranian Households Cigarette Consumption by Using Dose-Response Function
, M.Sc. Thesis Sharif University of Technology ; Keshavarz Haddad, Gholamreza (Supervisor)
Abstract
This study aims to estimate impact of the energy subsidy reform on household’s cigarette consumption in urban and rural areas in 2010-2012. According to the household size,income generated from receiving cash subsidies is different across families. So to measure the household’s response to different levels of subsidies on consumers spending, the doseresponse function is used. Our main contribution is estimation and calculation of cigarette spending reaction to the unconditional cash transfer by dose of the subsidy that they received, while the previous works in this literature have used the well know binary variable of being on the exposure of program. In terms of being on the exposure of...
Study of Optical and Transport Properties of Sr2RuO4 Superconductor
, M.Sc. Thesis Sharif University of Technology ; Kargarian, Mehdi (Supervisor)
Abstract
The nature of the Cooper pairing in the paradigmatic unconventional superconductor Sr2RuO4 is an outstanding puzzle in condensed matter physics. Despite the tremendous efforts made in the past twenty-seven years, neither the pairing symmetry nor the underlying pairing mechanism in this material has been understood with clear consensus. This is largely due to the lack of a superconducting order that is capable of interpreting in a coherent manner the numerous essential experimental observations. At this stage, it may be desirable to reexamine our existing theoretical descriptions of superconducting Sr2RuO4.This thesis focuses on the experiments that have been carried out so far on Sr2RuO4 and...
Nonlinear optical response in gapped graphene
, Article Journal of Physics Condensed Matter ; Volume 24, Issue 20 , 2012 ; 09538984 (ISSN) ; Sharif University of Technology
2012
Abstract
We present a formulation for the nonlinear optical response in gapped graphene, where the low-energy single-particle spectrum is modeled by massive Dirac theory. As a representative example of the formulation presented here, we obtain a closed form formula for the third harmonic generation in gapped graphene. It turns out that the covariant form of the low-energy theory gives rise to peculiar logarithmic singularities in the nonlinear optical spectra. The universal functional dependence of the response function on dimensionless quantities indicates that the optical nonlinearity can be largely enhanced by tuning the gap to smaller values
System identification techniques of smart structures with piezoelements
, Article 17th IASTED International Conference on Modelling and Simulation, Montreal, QC, 24 May 2006 through 26 May 2006 ; Volume 2006 , 2006 , Pages 534-539 ; 10218181 (ISSN) ; 0889865949 (ISBN); 9780889865945 (ISBN) ; Yousefi Koma, A ; Khanmirza, E ; Sharif University of Technology
2006
Abstract
Analytical and numerical system identification (system ID) techniques of smart structures with piezoelements are introduced and compared in this paper. Simplicity and low cost of numerical system ID methods developed here make them beneficial in control design and implementation as well as in optimization of location and size of actuators and sensors of the smart structure. The accuracy of these techniques is then verified using analytical system ID, which derives the dynamic model of the structure from differential equations. In the first numerical system ID technique, Finite Element Method (FEM) is employed to model the dynamic system and to obtain the Frequency Response Function (FRF)....
Robust control of smart beam with pizoelectric actuators
, Article Eight IASTED International Conference on Control and Applications, Montreal, QC, 24 May 2006 through 26 May 2006 ; Volume 2006 , 2006 , Pages 41-47 ; 0889865531 (ISBN); 9780889865532 (ISBN) ; Yousefi Koma, A ; Akbari, S ; Zadeh, B. T ; Sharif University of Technology
2006
Abstract
In this paper, a robust control system is developed for a flexible beam with piezoelectric actuators (called Smart Beam). The active control system of smart beam satisfied desired properties for all admissible measurement and plant noises, disturbances and model uncertainties. Thus it is the best candidate for sensitive industrial, medical and etc. robot arms and bases a new concept in the use of smart structures in robotics. The Frequency Response Function (FRF) of the smart beam was obtained from a Finite Element (FE) model. The corresponding transfer function was derived from the □ synthesis and several control schemes were then designed to suppress the vibration. Results showed the...
Properties of charge and magnetic impurities in a spin-polarized electron gas: A semiclassical approach
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 28, Issue 3 , 2005 , Pages 313-322 ; 13869477 (ISSN) ; Esfarjani, K ; Sharif University of Technology
2005
Abstract
Analytical studies on the effect of charge and magnetic impurities in a spin-polarized electron gas (SPEG) are carried out using a Thomas-Fermi semiclassical approximation (TFSA). The susceptibility matrix of an SPEG is calculated within the TFSA framework. Charge, spin and mixed charge-spin screening lengths are defined and calculated for the bulk metals (Fe, Co and Ni). It is found that these screening lengths do not strongly depend on temperature in metallic samples. Based on the Ruderman-Kittel-Kasuya-Yoshida (RKKY) model, the magnetic response function is then used to calculate the dependence of the exchange coupling between two ferromagnetic layers. It is seen that the exchange...
Modelling plastic scintillator response to gamma rays using light transport incorporated FLUKA code
, Article Applied Radiation and Isotopes ; Volume 70, Issue 5 , May , 2012 , Pages 864-867 ; 09698043 (ISSN) ; Etaati, G. R ; Ghal Eh, N ; Safari, M. J ; Afarideh, H ; Asadi, E ; Sharif University of Technology
2012
Abstract
The response function of NE102 plastic scintillator to gamma rays has been simulated using a joint FLUKA+PHOTRACK Monte Carlo code. The multi-purpose particle transport code, FLUKA, has been responsible for gamma transport whilst the light transport code, PHOTRACK, has simulated the transport of scintillation photons through scintillator and lightguide. The simulation results of plastic scintillator with/without light guides of different surface coverings have been successfully verified with experiments
Identification of composite-metal bolted structures with nonlinear contact effect
, Article Computers, Materials and Continua ; Volume 70, Issue 2 , 2022 , Pages 3383-3397 ; 15462218 (ISSN) ; Mahariq, I ; Pourghasem, M ; Mulki, H ; Jarad, F ; Sharif University of Technology
Tech Science Press
2022
Abstract
The middle layer model has been used in recent years to better describe the connection behavior in composite structures. The influencing parameters including low pre-screw and high preload have the main effects on nonlinear behavior of the connection as well as the amplitude of the excitation force applied to the structure. Therefore, in this study, the effects of connection behavior on the general structure in two sections of increasing damping and reducing the stiffness of the structures that lead to non-linear phenomena have been investigated. Due to the fact that in composite structure we are faced to the limitation of increasing screw preload which tend to structural damage, so the...
Vibration analysis of Setar for extracting the frequency response function (FRF)
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 15 , 2010 , Pages 485-490 ; 9780791843888 (ISBN) ; Arzanpour, S ; Alghassi, H ; Behzad, M ; Sharif University of Technology
Abstract
Extraction of the frequency response of a musical instrument is the first step to analyze its vibration characteristic. This research introduces the results of several experiments implemented on Setar, a Persian long-necked lute. Setar has a wooden, reflective sound-box which is highly coupled with its surrounding air. High level of damping in addition to the composite properties in Setar, consequences dissimilar frequency domain vibration patterns. At lower frequencies, the response exhibits very distinct modal behavior, while in higher frequencies an overall effect of close modes is demonstrated. In this paper different approaches are utilized to handle both frequency regimes; and their...
Dynamic stability of a Hexaglide machine tool for milling processes
, Article International Journal of Advanced Manufacturing Technology ; Volume 86, Issue 5-8 , 2016 , Pages 1753-1762 ; 02683768 (ISSN) ; Movahhedy, M. R ; Zohoor, H ; Alasty, A ; Sharif University of Technology
Springer-Verlag London Ltd
Abstract
One of the major issues related to parallel kinematic machine tools (PKMs) is their structural dependency on their configuration. In this paper, the machine configuration effect on its stability is investigated for the case of a Hexaglide machine tool. An FEM model of the Hexaglide machine tool is developed. The frequency response function (FRF) at the tool tip is obtained by a modal analysis. The numerical results are validated through comparison with those of an experimental modal test. The pose dependency of the PKM stability over its workspace is investigated. It is shown that the machine stability over the workspace is dependent on the spindle/tool/holder system characteristic. For...
Exact solution for frequency response of sandwich microbeams with functionally graded cores
, Article JVC/Journal of Vibration and Control ; Volume 25, Issue 19-20 , 2019 , Pages 2641-2655 ; 10775463 (ISSN) ; Fallah, F ; Sharif University of Technology
SAGE Publications Inc
2019
Abstract
Based on the Euler–Bernoulli beam model and the modified strain gradient theory, the size-dependent forced vibration of sandwich microbeams with a functionally graded (FG) core is presented. The equation of motion and the corresponding classical and nonclassical boundary conditions are derived using the Hamilton’s principle. An exact solution of the governing equation is developed for sandwich beams with various boundary conditions and subjected to an arbitrarily distributed harmonic transverse load. Finally, parametric studies are presented to investigate the effects of geometric ratios, length scale parameters, power index, boundary conditions, layup, and thickness of the FG layer on the...
Free vibrations of functionally graded material cylindrical shell closed with two spherical caps
, Article Ships and Offshore Structures ; 2021 ; 17445302 (ISSN) ; Kiani, Y ; Bagheri, N ; Eslami, M. R ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
Free vibration response of a cylindrical shell closed with two hemispherical caps at the ends (hermit capsule) is analysed in this research. It is assumed that the system of joined shell is made from functionally graded materials (FGM). Properties of the shells are assumed to be graded through the thickness. Cylindrical and hemispherical shells are unified in thickness. To capture the effects of through-the-thickness shear deformations and rotary inertias, first order theory of shells is used. Donnell type of kinematic assumptions are adopted to establish the general equations of motion and the associated boundary and continuity conditions with the aid of Hamilton's principle. The resulting...
Structural and dynamical fingerprints of the anomalous dielectric properties of water under confinement
, Article Physical Review Materials ; Volume 5, Issue 2 , 2021 ; 24759953 (ISSN) ; Esfandiar, A ; Hassanali, A ; Ejtehadi, M. R ; Sharif University of Technology
American Physical Society
2021
Abstract
There is a long-standing question about the molecular configuration of interfacial water molecules in the proximity of solid surfaces, particularly carbon atoms, which plays a crucial role in electrochemistry and biology. In this study, the dielectric, structural, and dynamical properties of confined water placed between two parallel graphene walls at different interdistances from the angstrom scale to a few tens of nanometer have been investigated using molecular dynamics. For the dielectric properties of water, we show that the dielectric constant of the perpendicular component of water drastically decreases under sub-2-nm spatial confinement. The dielectric constant data obtained through...