Search for: dynamic-response
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    Assessing dynamic response of multispan viscoelastic thin beams under a moving mass via generalized moving least square method

    , Article Acta Mechanica Sinica/Lixue Xuebao ; Volume 26, Issue 5 , October , 2010 , Pages 721-733 ; 05677718 (ISSN) Kiani, K ; Nikkhoo, A ; Mehri, B ; Sharif University of Technology
    Dynamic response of multispan viscoelastic thin beams subjected to a moving mass is studied by an efficient numerical method in some detail. To this end, the unknown parameters of the problem are discretized in spatial domain using generalized moving least square method (GMLSM) and then, discrete equations of motion based on Lagrange's equation are obtained. Maximum deflection and bending moments are considered as the important design parameters. The design parameter spectra in terms of mass weight and velocity of the moving mass are presented for multispan viscoelastic beams as well as various values of relaxation rate and beam span number. A reasonable good agreement is achieved between... 

    Longitudinal and transverse vibration of a single-walled carbon nanotube subjected to a moving nanoparticle accounting for both nonlocal and inertial effects

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 42, Issue 9 , 2010 , Pages 2391-2401 ; 13869477 (ISSN) Kiani, K ; Sharif University of Technology
    Single-walled carbon nanotubes (SWCNTs) can be promising delivery nanodevices for a diverse range of applications, however, little is known about their dynamical interactions with moving nanoscale particles. In this paper, dynamic response of a SWCNT subjected to a moving nanoparticle is examined in the framework of the nonlocal continuum theory of Eringen. The inertial effects of the moving nanoparticle and the existing friction between the nanoparticle surface and the inner surface of the SWCNT are incorporated in the formulation of the problem. The equivalent continuum structure associated with the SWCNT is considered and modeled using nonlocal Rayleigh beam theory under simply supported... 

    Shaking table test on small-scale retrofitted model of Sefid-rud concrete buttress dam

    , Article Earthquake Engineering and Structural Dynamics ; Volume 39, Issue 1 , 2010 , Pages 109-118 ; 00988847 (ISSN) Ghaemmaghami, A. R ; Ghaemian, M ; Sharif University of Technology
    Sefid-rud concrete buttress dam with a height of 106m was damaged during the devastating 1990 Manjil earthquake. The dam was repaired and strengthened using epoxy grouting of cracks and the installation of post-tensioned anchors. In a previous study, nonlinear seismic response of the highest monolith with empty reservoir was investigated experimentally through model testing. A geometric-scaled model of 1:30 was tested on a shaking table to study dynamic cracking of the model. As a result of the similarity between model and prototype cracking pattern, the model was retrofitted according to prototype retrofitting plan after the Manjil earthquake and re-tested on shaking table to estimate the... 

    Response of the beams on random Pasternak foundations subjected to harmonic moving loads

    , Article Journal of Mechanical Science and Technology ; Volume 23, Issue 11 , 2010 , Pages 3013-3023 ; 1738494X (ISSN) Younesian, D ; Kargarnovin, M. H ; Sharif University of Technology
    Dynamic response of infinite beams supported by random viscoelastic Pasternak foundation subjected to harmonic moving loads is studied. Vertical stiffness in the support is assumed to follow a stochastic homogeneous field consisting of a small random variation around a deterministic mean value. By employing the first order perturbation theory and calculating appropriate Green's functions, the variance of the deflection and bending moment are obtained analytically in integral forms. To simulate the induced uncertainty, two practical cases of cosine and exponential covariance are utilized. A frequency analysis is performed and influences of the correlation length of the stiffness variation on... 

    A filtering technique for three-phase power systems

    , Article IEEE Transactions on Instrumentation and Measurement ; Volume 58, Issue 2 , 2009 , Pages 389-396 ; 00189456 (ISSN) Karimi Ghartemani, M ; Karimi, H ; Bakhshai, A. R ; Sharif University of Technology
    A novel filter for use in three-phase power systems is introduced. When the input to the filter is a balanced three-phase set of signals, the filter suppresses noise and distortions and extracts a smooth three-phase fundamental component. When the input signal to the filter is unbalanced, it extracts the fundamental positive-sequence component of the input signal. The filter also estimates the magnitude, phase angle, and frequency of the signal and adaptively follows the variations in all these three variables. The characteristics of the filter, including its mathematical equations, stability analysis, steady state, and dynamic responses, are discussed in this paper. The filter highly... 

    Micro resonator nonlinear dynamics considering intrinsic properties

    , Article Scientia Iranica ; Volume 16, Issue 2 B , 2009 , Pages 121-129 ; 10263098 (ISSN) Sayyaadi, H ; Tadayon, M. A ; Eftekharian, A. A ; Sharif University of Technology
    One of the most important phenomena to affect the motion behaviour of Micro Resonators is their thermal dependency. This has recently received the attention of researchers widely. A thermal phenomenon has two main effects, the first is damping, due to internal friction, and the second is softening, due to Young's modulus-temperature relationship. In this research work, some theoretical and experimental reported results are used to make a proper model, including thermal phenomena. Two Lorentzian functions are used to describe the restoring and damping forces caused by thermal phenomena. In order to emphasize the thermal effects, a nonlinear model of the MEMS, considering capacitor... 

    Numerical investigation of the effects of soil densification on the reduction of liquefaction-induced settlement of shallow foundations

    , Article Scientia Iranica ; Volume 16, Issue 4 A , 2009 , Pages 331-339 ; 10263098 (ISSN) Shahir, H ; Pak, A ; Sharif University of Technology
    The liquefaction phenomenon is usually accompanied by a large amount of settlement. Based on the observations made in past earthquakes, ground improvement by densification is one of the most useful approaches to reduce the liquefaction-induced settlement. Currently, there is no analytical solution for evaluation of the amount of settlement and tilting of footings that are constructed on densified ground surrounded by liquefiable soil. A number of factors, such as underlying soil properties, dimensions of the footing and earthquake loading characteristics, cause the problem to become complicated. In this paper, the dynamic response of shallow foundations on both liquefiable and... 

    Dynamic performance of concrete slabs reinforced with steel and GFRP bars under impact loading

    , Article Engineering Structures ; Volume 191 , 2019 , Pages 62-81 ; 01410296 (ISSN) Sadraie, H ; Khaloo, A ; Soltani, H ; Sharif University of Technology
    Elsevier Ltd  2019
    Reinforced concrete slabs are common structural elements that could be exposed to impact loading. Although use of reinforced concrete slabs and utilization of Fiber Reinforced Polymer (FRP) as alternative to traditional steel reinforcement slabs are growing, but the influence of various parameters on their response under impact loads is not properly evaluated. This study investigated the effect of rebar's material, amount and arrangement of reinforcements, concrete strength and slab thickness on dynamic behavior of reinforced concrete slabs using both laboratory experiments and numerical simulations. Performance of fifteen 1000 × 1000 mm concrete slabs, including two 75 mm thick plain slabs,... 

    A semi-active SMA-MRF structural stability element for seismic control in marine structures

    , Article Applied Ocean Research ; Volume 100 , 2020 Zareie, S ; Zabihollah, A ; Sharif University of Technology
    Elsevier Ltd  2020
    The stability and integrity of structures under indeterminant external loadings, particularly earthquakes, is a vital issue for the design and safe operation of marine and offshore structures. Over the past decades, many structural control systems, such as viscous-based systems, have been developed and embedded in marine and offshore structures, particularly oil platforms to maintain the stability and mitigate the seismic hazards. Rapid improvement in intelligent materials, including shape memory alloys (SMAs) and Magnetorheological fluid (MRF), have led to the design and development of efficient structural control elements. The present work aims to establish a framework for the structural... 

    Analysis and design of predictive control strategy for sheppard-taylor based PFC rectifier

    , Article 2008 IEEE International Symposium on Industrial Electronics, ISIE 2008, Cambridge, 30 June 2008 through 2 July 2008 ; 2008 , Pages 397-402 ; 1424416655 (ISBN); 9781424416653 (ISBN) Abedi, M. R ; Tahami, F ; Sharif University of Technology
    In this paper CCM/CVM operation and modeling of the Sheppard-Taylor topology is reviewed and a predictive control strategy is applied for a Sheppard-Taylor-based power factor correction (PFC) rectifier. Compared to conventional boost or buck - boost PFC's, this topology allows a better current tracking at the AC side, with a relatively reduced voltage at the DC side. Consequently, the high frequency AC filters required by the buck PECs are avoided, and the voltage stresses on the boost switches are significantly reduced. Furthermore In predictive control strategy the duty cycle required to achieve unity power factor in a half line period can be calculated in advance. The main advantage of... 

    Thermo-mechanical modeling of high speed spindles

    , Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 282-293 ; 10263098 (ISSN) Zahedi, A ; Movahhedy, M. R ; Sharif University of Technology
    Prediction of the thermo-mechanical behavior of machine-tool spindles is essential in the reliable operation of high speed machine tools. In particular, the performance of these high speed spindles is dependent on their thermal behavior. The main source of heat generation in the spindle is the friction torque in angular contact ball bearings. This paper presents an effort to develop a comprehensive model of high speed spindles that includes viable models for the mechanical and thermal behavior of its major components, i.e., bearings, shaft and housing. Spindle housing and shaft are treated as six-degree-of-freedom Timoshenko beam elements. Bearings are modeled as two-node elements with five... 

    Nonlinear dynamic analysis of an inclined Timoshenko beam subjected to a moving mass/force with beam's weight included

    , Article Shock and Vibration ; Volume 18, Issue 6 , 2011 , Pages 875-891 ; 10709622 (ISSN) Mamandi, A ; Kargarnovin, M. H ; Sharif University of Technology
    In this study, the nonlinear vibrations analysis of an inclined pinned-pinned self-weight Timoshenko beam made of linear, homogenous and isotropic material with a constant cross section and finite length subjected to a traveling mass/force with constant velocity is investigated. The nonlinear coupled partial differential equations of motion for the rotation of warped cross section, longitudinal and transverse displacements are derived using the Hamilton's principle. These nonlinear coupled PDEs are solved by applying the Galerkin's method to obtain dynamic responses of the beam. The dynamic magnification factor and normalized time histories of mid-point of the beam are obtained for various... 

    Coordinated control approaches for low-voltage ride-through enhancement in wind turbines with doubly fed induction generators

    , Article IEEE Transactions on Energy Conversion ; Volume 25, Issue 3 , 2010 , Pages 873-883 ; 08858969 (ISSN) Rahimi, M ; Parniani, M ; Sharif University of Technology
    This paper deals with the coordinated control of rotor- and grid-side converters in wind turbines with doubly fed induction generators (DFIGs) to improve the low-voltage ride-through capability. The rotor-side converter control and additional equipment, called stator damping resistor, are used to limit the rotor inrush current and to reduce the oscillations and settling time of DFIG transient response during the voltage dip. Also, the grid-side converter is controlled to limit the dc-link overvoltage during the voltage drop. It is found that the dynamics of the grid-side converter and dc-link voltage exhibit nonminimum phase behavior, and thus there is an inherent limitation on the... 

    Dynamic analysis of laminated composite plates traversed by a moving mass based on a first-order theory

    , Article Composite Structures ; Volume 92, Issue 8 , 2010 , Pages 1865-1876 ; 02638223 (ISSN) Ghafoori, E ; Asghari, M ; Sharif University of Technology
    The dynamic response of angle-ply laminated composite plates traversed by a moving mass or a moving force is investigated. For this purpose, a finite element method based on the first-order shear deformation theory is used. Stationary and adaptive mesh techniques have been applied as two different meshing schemes. The adaptive mesh strategy is then used to avoid off-nodal position of moving mass. In this manner, the finite element mesh is continuously adapted to follow and comply with the path of moving mass. A Newmark direct integration method is employed to solve the equations of motion. Parametric study is directed to find out how different parameters like mass of the moving object as... 

    Estimates of average inelastic deformation demands for regular steel frames by the Endurance Time method

    , Article Scientia Iranica ; Volume 16, Issue 5 A , 2009 , Pages 388-402 ; 10263098 (ISSN) Riahi, H. T ; Estekanchi, H. E ; Vafai, A ; Sharif University of Technology
    The Endurance Time (ET) method is a new dynamic pushover procedure in which structures are subjected to gradually intensifying acceleration functions and their performance is assessed based on the length of the time interval that they can satisfy required performance objectives. In this paper, the accuracy of the Endurance Time method in estimating average deformation demands of low and medium rise steel frames using ETASOf series of ET acceleration functions has been investigated. The precision of the ET method in predicting the response of steel frames in nonlinear analysis is investigated by considering a simple set of moment-resisting frames. An elastic-perfectly-plastic material model...