Search for: frequency-response
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    Criteria for response monotonicity preserving in approximation of fractional order systems

    , Article IEEE/CAA Journal of Automatica Sinica ; Volume 3, Issue 4 , 2016 , Pages 422-429 ; 23299266 (ISSN) Tavazoei, M. S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    In approximation of fractional order systems, a significant objective is to preserve the important properties of the original system. The monotonicity of time frequency responses is one of these properties whose preservation is of great importance in approximation process. Considering this importance, the issues of monotonicity preservation of the step response and monotonicity preservation of the magnitude-frequency response are independently investigated in this paper. In these investigations, some conditions on approximating filters of fractional operators are found to guarantee the preservation of step magnitude-frequency response monotonicity in approximation process. These conditions... 

    Application of nonlocal strain–stress gradient theory and GDQEM for thermo-vibration responses of a laminated composite nanoshell

    , Article Engineering with Computers ; 14 March , 2020 Moayedi, H ; Ebrahimi, F ; Habibi, M ; Safarpour, H ; Foong, L. K ; Sharif University of Technology
    Springer  2020
    In this article, thermal buckling and frequency analysis of a size-dependent laminated composite cylindrical nanoshell in thermal environment using nonlocal strain–stress gradient theory are presented. The thermodynamic equations of the laminated cylindrical nanoshell are based on first-order shear deformation theory, and generalized differential quadrature element method is implemented to solve these equations and obtain natural frequency and critical temperature of the presented model. The results show that by considering C–F boundary conditions and every even layers’ number, in lower value of length scale parameter, by increasing the length scale parameter, the frequency of the structure... 

    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 ©... 

    Structural damage detection using principal component analysis of frequency response function data

    , Article Structural Control and Health Monitoring ; Volume 27, Issue 7 , 2020 Esfandiari, A ; Nabiyan, M. S ; Rahimzadeh Rofooei, F ; Sharif University of Technology
    John Wiley and Sons Ltd  2020
    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... 

    Magnitude-frequency responses of fractional order systems: Properties and subsequent results

    , Article IET Control Theory and Applications ; Volume 10, Issue 18 , 2016 , Pages 2474-2481 ; 17518644 (ISSN) Tavazoei, M. S ; Sharif University of Technology
    Institution of Engineering and Technology  2016
    This study deals with the properties of magnitude-frequency responses in fractional order systems. Using Phragmén-Lindelöf theorem in complex analysis, it is shown that the supremum of the magnitude-frequency response of a fractional system with a commensurate order less than one cannot be greater than that of its integer order bounded-input, bounded-output stable counterpart. Further results are also obtained on magnitude-frequency response of stable/unstable fractional order systems. Moreover, it is found that the supremum (infimum) of the magnitude-scaling frequency of the family of fractional order systems having a fixed structure and different orders in the range (0, 2) is a piecewise... 

    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) Khanmirza, E ; Yousefi Koma, A ; Akbari, S ; Zadeh, B. T ; Sharif University of Technology
    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... 

    Effect of co Addition on Magnetic Properties of Nanocrystalline FINEMET Alloy

    , M.Sc. Thesis Sharif University of Technology TavaKoli, Zeinab (Author) ; Maddah Hosseini, Hamid Reza (Supervisor)
    In this work, the effect of chemical composition on structural, mechanical, electrical and magnetic properties of nanocrystalline Finemet-type alloys with the composition of Fe73.5Si13.5B9Nb3Cu1 , Fe77Si11B9Nb2.4Cu0.6 and (〖Fe_0.5 Co_0.5)〗_77 Si_11 B_9 Nb_2.4 Cu_(0.6 )was investigated. The samples were prepared by vacuum arc melting of high purity constitution in order to obtain a nanocrystalline structure. The amorphous ribbons were then annealed under vacuum with the same conditions of temperatures and time to compare their properties. The structural and thermal properties of the samples were analyzed using various techniques such as X-ray Diffraction (XRD) and Differential Scanning... 

    Dynamic Behavior and Stability Analysis of Rotor-Seal System

    , M.Sc. Thesis Sharif University of Technology Azarakhsh, Pooria (Author) ; Mohammmad Navazi, Hossein (Supervisor)

    Algebraic conditions for monotonicity of magnitude-frequency responses in all-pole fractional order systems

    , Article IET Control Theory and Applications ; Volume 8, Issue 12 , 2014 , Pages 1091-1095 ; ISSN: 17518644 Tavazoei, M. S ; Sharif University of Technology
    This study deals with the investigation of the magnitude-frequency responses of all-pole fractional order systems in the viewpoint of extrema existence in these responses. In this investigation, a sufficient algebraic condition, two necessary algebraic conditions, and a necessary and sufficient algebraic condition are obtained to guarantee the non-existence of extrema in the magnitude-frequency response of all-pole fractional order systems. Some examples are presented to show the effectiveness of the results of the paper  

    PID controller design for micro gas turbines using experimental frequency-response data and a linear identification technique

    , Article International Journal of Advanced Mechatronic Systems ; Volume 5, Issue 6 , 2013 , Pages 353-364 ; 17568412 (ISSN) Banazadeh, A ; Gol, H. A ; Ramazani, H ; Sharif University of Technology
    E-flow Inderscience  2013
    This paper discusses the identification process of engine dynamics and presents derived transfer function models including; thrust, shaft speed, compressor exit pressure and turbine exit temperature in relation to the fuel flow. Model identification approach, presented in this paper, is the first to consider frequency-sweep signals to excite dynamics, as well as to utilise windowing and smoothing techniques to reduce random errors in the spectral estimates. Here, frequency sweep provides a fairly uniform spectral excitation and chirp-z transform warrants the exact determination of the frequency responses that are robust to the uncertainties. The identified models are also validated with the... 

    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) Isapour, A ; Sadati, N ; Ranjbar, A. M ; Sharif University of Technology
    Arnold  2004
    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) Park, S. S ; Altintas, Y ; Movahhedy, M ; Sharif University of Technology
    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... 

    Dynamics of interface traps in bonded silicon wafers

    , Article Proceedings of SPIE - The International Society for Optical Engineering ; Volume 4580 , 2001 , Pages 391-398 ; 0277786X (ISSN) Khorasani, S ; Motieifar, A ; Rashidian, B ; Sharif University of Technology
    In this article, a time-domain non-linear model is proposed for quantum dynamics of interface traps. This model includes the effects of thermoionic emission, combined with the drift and tunneling currents. The model is simplified for the case of interface traps of the directly bonded Silicon wafers, and linearized. Therefore, an equivalent electrical circuit is obtained being composed of two resistive and capacitive branches. The theory predicts a close spacing between the corresponding zero and pole in the frequency response of the system, being justified by experiment on directly bonded n-type Silicon wafers. The low frequency response to a square-wave is quite in agreement with the... 

    Nano-resonator frequency response based on strain gradient theory

    , Article Journal of Physics D: Applied Physics ; Vol. 47, Issue. 36 , 2014 ; ISSN: 00223727 Miandoab, E. M ; Yousefi Koma, A ; Pishkenari, H. N ; Fathi, M ; Sharif University of Technology
    This paper aims to explore the dynamic behaviour of a nano-resonator under ac and dc excitation using strain gradient theory. To achieve this goal, the partial differential equation of nano-beam vibration is first converted to an ordinary differential equation by the Galerkin projection method and the lumped model is derived. Lumped parameters of the nano-resonator, such as linear and nonlinear springs and damper coefficients, are compared with those of classical theory and it is demonstrated that beams with smaller thickness display greater deviation from classical parameters. Stable and unstable equilibrium points based on classic and non-classical theories are also compared. The results... 

    Modeling, simulation and frequency-response identification of a quadrotor

    , Article Proceedings of the IASTED International Conference on Modelling, Identification and Control ; 2013 , Pages 476-483 ; 10258973 (ISSN) ; 9780889869431 (ISBN) Shadram, Z ; Bassam, S. S ; Sharif University of Technology
    Due to their agile manoeuvrability and simplicity of construction, quadrotor are employed in a variety of applications. Most of their expenses are due to complex control systems, since, to reduce these expenses, low cost control methods which are based on linear models should be used to achieve an autonomous flight. First, the process of accurate dynamic modeling of a sample quad rotor which is simulated by MATLAB SIMULINK is presented. Then, a frequency sweep input stimulates the virtual model in order to identify a linear model based on frequency response analysis. Consequently, the desired linear model is obtained in both hover and yaw mode of motion. However, pitch and roll mode were too... 

    Nonlinear vibration of beams under nonideal boundary conditions

    , Article Acta Mechanica ; Volume 218, Issue 3-4 , 2011 , Pages 259-267 ; 00015970 (ISSN) Kamali Eigoli, A ; Ahmadian, M. T ; Sharif University of Technology
    In this paper, we investigate the influence of nonideal boundary conditions on the nonlinear vibration of damped Euler-Bernoulli beams subjected to harmonic loads. These nonidealities allow for small deflections and/or moments at the supports of the beam. Using the iteration perturbation method, analytical expressions for the case of simply supported beams with immovable end conditions are provided. The results reveal that the first order of approximation obtained by the proposed method is more accurate than the perturbation solutions. Moreover, compared with the previous studies, some interesting phenomenon is predicted. We have shown that in some special combinations of the nonidealities... 

    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) Mansour, H ; Arzanpour, S ; Alghassi, H ; Behzad, M ; Sharif University of Technology
    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) Najafi, A ; Movahhedy, M. R ; Zohoor, H ; Alasty, A ; Sharif University of Technology
    Springer-Verlag London Ltd 
    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... 

    On the nonlinear dynamics of trolling-mode AFM: analytical solution using multiple time scales method

    , Article Journal of Sound and Vibration ; Volume 423 , 9 June , 2018 , Pages 263-286 ; 0022460X (ISSN) Sajjadi, M. R ; Nejat Pishkenari, H ; Vossoughi, G ; Sharif University of Technology
    Academic Press  2018
    Trolling mode atomic force microscopy (TR-AFM) has resolved many imaging problems by a considerable reduction of the liquid-resonator interaction forces in liquid environments. The present study develops a nonlinear model of the meniscus force exerted to the nanoneedle of TR-AFM and presents an analytical solution to the distributed-parameter model of TR-AFM resonator utilizing multiple time scales (MTS) method. Based on the developed analytical solution, the frequency-response curves of the resonator operation in air and liquid (for different penetration length of the nanoneedle) are obtained. The closed-form analytical solution and the frequency-response curves are validated by the... 

    Obtaining the Frequency Response of Voltage Transformers

    , M.Sc. Thesis Sharif University of Technology Moharrami Shahbekandi, Saeed (Author) ; Mokhtari, Hossein (Supervisor)
    In this thesis a new method to determine the accuracy of CVT in measuring harmonics has been proposed. Capacitive voltage transformers are known as an important tool in measuring the harmonics. However, the frequency response of CVT contains cut-off and pass characteristics, because of the resonances of the internal elements. One of the main problems is in determining the frequency response of HV voltage source capable of accurate change to apply to CVT. The proposed method reduces the voltage level of the HV source. Also, the source structure and the effect of the additional elements are described and the accuracy of the method has been evaluated by simulation and experimental results