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    Free and forced random vibration analysis of sandwich plates with thick viscoelastic cores

    , Article JVC/Journal of Vibration and Control ; Volume 19, Issue 14 , 2013 , Pages 2223-2240 ; 10775463 (ISSN) Mahmoudkhani, S ; Haddadpour, H ; Navazi, H. M ; Sharif University of Technology
    Free vibrations and the transverse response of sandwich plates with viscoelastic cores under wide-band random excitation is studied with special attention to the so-called pumping, thickness-shear and stretching modes. The quadratic displacement field is adopted for all displacement components of the core to accurately capture the higher modes excited by the wide-band excitation. The Love-Kirchhoff plate theory is used for the face layers. The viscoelastic behavior of the core is modeled by the Golla-Hughes-McTavish method. An analytical solution using the normal mode method is provided for the simply supported boundary conditions by including a different family of modes. The effects of some... 

    Nonlinear dynamic analysis of atomic force microscopy under deterministic and random excitation

    , Article 2006 ASME International Mechanical Engineering Congress and Exposition, IMECE2006, Chicago, IL, 5 November 2006 through 10 November 2006 ; 2006 ; 1096665X (ISSN); 0791837904 (ISBN); 9780791837900 (ISBN) Pishkenari, H. N ; Behzad, M ; Meghdari, A ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2006
    This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as Averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for... 

    Experimental investigation on the micro-step control disturbance rejection under random excitations

    , Article DETC2005: ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Long Beach, CA, 24 September 2005 through 28 September 2005 ; Volume 1 B , 2005 , Pages 1747-1751 ; 0791847381 (ISBN) Ghafari, A. S ; Behzad, M ; Sharif University of Technology
    Effect of random signals with various powers, as current loads, on positioning and disturbance rejection problems on micro-step PID closed loop control system is addressed in this paper. Experimental results due to implementing different white noise power, speed, and a 0.3 N.m disturbance load torque show that, Random noise source changes current profile and affects the accuracy of positioning in tracking and disturbance rejection problems. Performance of the PID proposed controller under the implementation of random noise on phases of the HSM has been proved to be accurate enough even under disturbance torque acting on the system. Copyright © 2005 by ASME  

    Vibration Analysis of viscoelastic Sandwich Plates Under the Effects of Nonlinearities and Random Excitations

    , Ph.D. Dissertation Sharif University of Technology Mahmoudkhani, Saeed (Author) ; Haddadpour, Hassan (Supervisor)
    Different aspects of oscillatory behaviors of sandwich structures with viscoelastic cores are investigated in the present study in four parts. In the first part, an analytical study is conducted to determine the variation of linear frequencies and damping ratio of different families of modes with system parameters. The participation of different families of modes such as the so-called pumping or thickness-shear modes along with the overall bending modes in the transverse response of the structure to transverse wide-band excitation is also investigated in this part. The formulation of the problem is established by assuming quadratic variation of displacement components of the core through the... 

    Effects of structural configuration on vibration control of smart laminated beams under random excitations

    , Article Journal of Mechanical Science and Technology ; Volume 24, Issue 5 , 2010 , Pages 1119-1125 ; 1738494X (ISSN) Zabihollah, A ; Sharif University of Technology
    The influence of structural configuration on vibration responses of smart laminated beams under random loading is studied. The effect of laminate configurations and locations of sensors/actuators in the smart system is also investigated. The layer-wise approximation for displacement and electric potential is utilized to construct the finite element model. The closed-loop control response is determined through an optimal control algorithm based on the Linear Quadratic Regulator (LQR). The correlation coefficient between the input random force and the applied actuating voltage for various configurations is also computed. It is revealed that for softer configurations, the correlation... 

    Design of optimum vibration absorbers for a bus vehicle to suppress unwanted vibrations against harmonic and random road excitations

    , Article Scientia Iranica ; Volume 28, Issue 1 , 2021 , Pages 241-254 ; 10263098 (ISSN) Rezazadeh, A ; Moradi, H ; Sharif University of Technology
    Sharif University of Technology  2021
    Unwanted vibrations of vehicles are regarded as harmful threats to human health in biomechanical and psychophysical terms. Road roughness is considered as the main cause of unwanted vibrations of bus vehicles. Vertical seat vibrations were found via simulating a 10-Degree-Of-Freedom (10-DOF) model of an intercity bus vehicle under harmonic and random excitations caused by road roughness. To suppress undesirable vibrations, mass-spring-damper passive absorbers were proposed in a 13-Degree-Of- Freedom (13-DOF) model of the bus. Following the optimization of the characteristics of embedded passive absorbers under each seat and implementation of the designed absorbers, the vertical displacement... 

    Vibration control of beams on elastic foundation under a moving vehicle and random lateral excitations

    , Article Journal of Sound and Vibration ; Volume 331, Issue 6 , March , 2012 , Pages 1217-1232 ; 0022460X (ISSN) Zarfam, R ; Khaloo, A. R ; Sharif University of Technology
    The formulation of three-dimensional dynamic behavior of a Beam On Elastic Foundation (BOEF) under moving loads and a moving mass is considered. The weight of the vehicle is modeled as a moving point load, however the effect of the lateral excitation is considered by modeling: (case 1) a lateral moving load with random intensity for wind excitation and (case 2) a moving mass just in lateral direction of the beam for earthquake excitation. A Dirac-delta function is used to describe the position of the moving load and the moving mass along the beam. The beam foundations are considered as elastic Winkler-type in two perpendicular transverse directions. This model is proposed to investigate the...