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    Active Vibration Suppression of Laminated Composite Structures Integrated with Magnetorheological Fluid Segments under Random Excitation

    , M.Sc. Thesis Sharif University of Technology Fattahi Massoom, Zahra (Author) ; Zabihollah, Abolghasem (Supervisor)
    Abstract
    Magnetorheological (MR) materials indicate variations in their rheological properties when subjected to different magnetic fields. They have quick time response, in the order of milliseconds, and therefore are potentially applicable to structures and devices when a tunable system response is required. This study presents vibration analysis of laminated composite plate using MR fluid lumps under Random Excitation. A structural dynamic modeling approach is discussed and vibration characteristics of MR adaptive structures are predicted for different magnetic field levels. Linear Quadratic Regulator (LQR) controller is designed to achieve the vibration suppression of the laminated plate. The... 

    High-frequency random vibrations of a stiffened plate with a cutout using energy finite element and experimental methods

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 234, Issue 16 , 2020 , Pages 3297-3317 Nokhbatolfoghahai, A ; Navazi, H. M ; Haddadpour, H ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Abstract
    In this paper, by employing the energy finite element analysis, the high-frequency vibrations of a stiffened plate having a cutout, subjected to random vibrations, have been analyzed, and the obtained results have been validated by use of experimental methods. By using equations for joining of structures, energy finite element analysis computer codes were developed for the coupling of beam-plate elements. Finally, a plate containing a cutout and three stiffeners was fabricated and subjected to high-frequency random vibration tests. The results of the prepared codes were compared with the results of experiments. These comparisons indicated that at high frequencies, the energy finite element... 

    Random Vibration Analysis for Multi-Story Base Isolated Structures

    , M.Sc. Thesis Sharif University of Technology Mehdizadeh Nasrabadi, Mohammad (Author) ; Bakhshi, Ali (Supervisor)
    Abstract

    Earthquake motions are among random excitation loads. For that we used random vibration approach to estimate response of multi-degree of freedom base isolated structures under ground excitation. Some models including linear model ,nonlinear Bouc-Wen and BBW models are studied for modeling the superstructure .Several base isolation models including the laminated rubber bearing, high damping laminated rubber bearing ,resilient-friction base isolator with or without sliding upper plate and the Electricity de France system, are studied . El Centro 1940 and Mexico City 1985 earthquake which preserve the nonstationary evolutions of amplitude and frequency content of ground accelerations... 

    Dynamic response of tank trains to random track irregularities

    , Article Meccanica ; Volume 53, Issue 10 , 2018 , Pages 2687-2703 ; 00256455 (ISSN) Nokhbatolfoghahai, A ; Noorian, M. A ; Haddadpour, H ; Sharif University of Technology
    Springer Netherlands  2018
    Abstract
    This paper presents a dynamic analytical model for tank train vibrations. The train is considered as a system of 27 degrees of freedom consisting of lateral, roll, yaw, vertical, and pitch motions for the vehicle body and its two bogies and lateral, roll and vertical motions for the four wheel-sets. Liquid sloshing in the tank is modeled using an equivalent mechanical mass-spring model. Coupling between the vehicle system and the railway track is realized through the interaction forces between the train and the rail, where the vertical and lateral irregularity profiles of the track are regarded as stationary ergodic Gaussian random processes and simulated by polynomial functions. Random... 

    Analytical and Experimental Study of Isolation of Sensitive Equipments from Ambient Vibrations

    , M.Sc. Thesis Sharif University of Technology Mahvash Mohammadi, Akbar (Author) ; Bakhshi, Ali (Supervisor)
    Abstract
    In some activities, an almost free of any vibration environment is needed. Semi conductor production process and microelectronic microscopes are two examples in which a quiet environment is essential. The goal of this thesis is to attenuate ambient vibrations effectively and to prepare a suitable environment for two microelectronic microscopes. The designed system must be practical, economical and capable of being made in a short time interval. Considering mentioned properties a steel table with bolt connections supported on 4 air springs was built. To investigate dynamic properties, modal analysis was performed with the aid of finite element packages and experiments. To extract oscillations... 

    Finite Element Method and Analytical Approach Solutions for a Conical Axisymmetric Shell Structure Under Random Acoustic Loading

    , M.Sc. Thesis Sharif University of Technology Fallah, Mohsem (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    Abstract
    When vibration of the structure is unrecognized we call it random vibrations which their analysis is very important in space structures because these structures are exposed to acoustic forces or forces produced by turbulence of the atmosphere when a spacecraft is launched. Also in the aviation field, the random vibration analysis use to examine the response of the aircraft and missile structures to atmospheric turbulence and gust. In this research dominated equations of a truncated conical axisymmetric shell structure with linearized approximation of Love’s equations under uniform pressure is utilized. Considering displacements in the form of Frobenius series expansion the frequencies and... 

    Vibration Behavior of Laminated Composite Beam Incorporated with MR (Magnetorheological) Fluid under Random Excitation

    , Ph.D. Dissertation Sharif University of Technology Momeni, Saman (Author) ; Behzad, Mehdi (Supervisor) ; Zabihollah, Abolghassem (Co-Supervisor)
    Abstract
    Laminated composite beams are being widely used in engineering applications, including aerospace and automobile where the structures are highly subjected to non-deterministic random loadings, requiring a reliable technique to ensure the stability of structure during operation. A Novel N-layer model of layerwise theory (LWT) for laminated composite beams incorporated with magnetorheological fluid (MR-laminated beams) is developed. In addition, a finite element model of tapered laminated composite beams incorporated with magnetorheological fluid (MR-tapered beam) based on layerwise theory is developed. The dynamic response of the present model for uniform and tapered beams have been compared... 

    Attenuation of random vibration in plates

    , Article AES-ATEMA International Conference Series - Advances and Trends in Engineering Materials and their Applications, 1 September 2009 through 4 September 2009, Hamburg ; 2009 , Pages 57-63 ; 19243642 (ISSN) ; 9780978047962 (ISBN) Jolghazi, S ; Mehdigholi, H ; Behzad, M ; Sharif University of Technology
    Abstract
    This paper is a study on control of vibration of plate subjected to random vibration loading using magnetorheological (MR) dampers. Some key issues, i.e. model reduction, modeling of the MR dampers and their applications in vibration control of plates, are addressed in this work. MR dampers are semi-active devices that use MR fluids to produce a controllable damping with low power requirement. In this paper, first, a model reduction method for preparing a reduce order model (ROM) is presented. The method uses an optimal model truncation method which in it the ROM to be constructed such that it will provide the same frequency response characteristics as the original full model within the... 

    Experimental works on dynamic behavior of laminated composite beam incorporated with magneto-rheological fluid under random excitation

    , Article ACM International Conference Proceeding Series, 8 February 2017 through 12 February 2017 ; Volume Part F128050 , 2017 , Pages 156-161 ; 9781450352802 (ISBN) Momeni, S ; Zabihollah, A ; Behzad, M ; Sharif University of Technology
    Association for Computing Machinery  2017
    Abstract
    Laminated composite structures are widely being used in modern industries particularly robot arms, aerospace and wind turbine blades where the structures mainly exposed to harsh random vibration and in turn, leads to unpredicted failure. Adding Magneto-rheological (MR) fluids in such structures may significantly improve their dynamic response. In the present work, the vibration response of laminated composite beams filled with MR fluids (MR laminated beam) under random loading has been investigated using experimental as well as simulation approaches. Finite Element Model (FEM) has been utilized to simulate the vibration response under random loading. An in-house set-up has been designed to... 

    A new study in designing MTMDs in SDOF and MDOF systems based on the spectral analysis method

    , Article Earthquake and Structures ; Volume 19, Issue 4 , 2020 , Pages 243-259 Baigoly, M ; Shargh, F. H ; Rofooei, F. R ; Sharif University of Technology
    Techno-Press  2020
    Abstract
    This study aims to optimize, design, and predict the MTMDs performance in SDOF systems using spectral analysis, and then apply their results to MDOF structures. Given the importance of spectral analysis in the design of new engineering structures, achieving a method for designing TMDs based on this theory can be of great importance for structural designers. In this study, several convenient combinations of MTMDs in an SDOF system are first considered to minimize the maximum displacement. For calculating the frequency ratios of dampers, an innovative technique is adopted in which the values of different modal responses obtained from the spectral analysis are approached together. This... 

    Geometrically Nonlinear Random Vibration of Structures Using Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Dabouee Moshkabadi, Mehdi (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    Abstract
    Indeterminate behavior of some forces in the aerospace industry due to flight at high speeds, gust, combustion, etc., has led to the exposure of structures to dynamic loads with random behavior in the nonlinear manner. To analyze problems in which the loading is random or the system parameters are random, the only possible way is to describe the system response in statistical values.Since most modern structures have complex geometry and the number of degrees of freedom is very high, advanced numerical solution methods are used to obtain the system response. In this study, the geometric nonlinear vibrations of structures under random loading are investigated by the finite element... 

    Stochastic Analysis of Base-Isolated Structures Considering Soil-Structure Interaction

    , M.Sc. Thesis Sharif University of Technology Samimi, Soheil (Author) ; Bakhshi, Ali (Supervisor)
    Abstract
    The main purpose of this study is stochastic analysis of base-isolated structures considering soil-structure interaction. Due to stochastic nature of earthquake and existence of uncertainties in non-linear behavior of and properties of soil, it is better to calculate the responses of the structure via random vibrations approach. In this approach first of all, the differential equations of structure are obtained in deterministic vibration mode and then by the available theories, differential equations of covariance of the responses are obtained. Solving these equations leads to the finding of the standard deviations of the responses of the structure in each moment. In backward differential... 

    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
    2013
    Abstract
    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... 

    A finite element model for tapered laminated beams incorporated with magnetorheological fluid using a layerwise model under random excitations

    , Article Mechanics of Advanced Materials and Structures ; Apr , 2018 , Pages 1-8 ; 15376494 (ISSN) Momeni, S ; Zabihollah, A ; Behzad, M ; Sharif University of Technology
    Taylor and Francis Inc  2018
    Abstract
    Laminated composite beams with variable thickness are being widely used in many engineering applications. To enhance the dynamic behavior of structures subject to random loading, tapered laminated beams incorporated with magnetorheological (MR) fluids (MR-tapered beam) are proposed. A finite element model has been developed for random vibration analysis of MR-tapered beam based on layerwise displacement theory. The effects of thickness ratios of tapered beam, magnetic fields, statistical properties, correlation and autocorrelation on dynamic behaviors of structures have been investigated. The proposed structural element significantly enhances the dynamic response of MR-tapered beam under... 

    A finite element model for tapered laminated beams incorporated with magnetorheological fluid using a layerwise model under random excitations

    , Article Mechanics of Advanced Materials and Structures ; Volume 27, Issue 1 , 2020 , Pages 12-19 Momeni, S ; Zabihollah, A ; Behzad, M ; Sharif University of Technology
    Taylor and Francis Inc  2020
    Abstract
    Laminated composite beams with variable thickness are being widely used in many engineering applications. To enhance the dynamic behavior of structures subject to random loading, tapered laminated beams incorporated with magnetorheological (MR) fluids (MR-tapered beam) are proposed. A finite element model has been developed for random vibration analysis of MR-tapered beam based on layerwise displacement theory. The effects of thickness ratios of tapered beam, magnetic fields, statistical properties, correlation and autocorrelation on dynamic behaviors of structures have been investigated. The proposed structural element significantly enhances the dynamic response of MR-tapered beam under... 

    Response of a suspended cable to narrow-band random excitation with peaked P.S.D

    , Article Mathematical and Computer Modelling ; Volume 41, Issue 11-12 , 2005 , Pages 1203-1212 ; 08957177 (ISSN) Kargarnovin, M. H ; Mehri, B ; Younesian, D ; Sharif University of Technology
    2005
    Abstract
    The response of a suspended cables subjected to narrow-band random excitations with two types of peaked P.S.D. is formulated and analyzed. Banach fixed-point theorem is used for eigenfunction analysis of the differential-integral equations of motion for the first time in this paper. Fredholm approach also is used in the free vibration analysis of the suspended cable and then using Galerkin mode approximation method, power spectral density, and root mean square of the response are computed for two practical types of excitation. All of the calculated results converted to dimensionless quantities make their usage easier in vibration analysis of some practical cases such as vibration of moving... 

    Flutter analysis of a nonlinear airfoil using stochastic approach

    , Article Nonlinear Dynamics ; Volume 84, Issue 3 , 2016 , Pages 1735-1746 ; 0924090X (ISSN) Irani, S ; Sazesh, S ; Molazadeh, V. R ; Sharif University of Technology
    Springer Netherlands 
    Abstract
    In this paper, the dynamic instability of a nonlinear system has been studied using the stochastic vibration analysis and employing statistical properties of the system response. In this method neither the time domain analysis nor limit cycle oscillations were used. A two degrees-of-freedom airfoil subjected to an aerodynamic quasi-steady flow with a nonlinear torsional spring was considered as the case study. The spring nonlinearity was examined in hardening and softening states. A random force in the form of the white noise with Gaussian function was added to the aerodynamic lift force. The statistical linearization and random vibration analysis were applied to the nonlinear system to... 

    Intelligent active vibration control of constrained manipulaors in robotic deburring

    , Article 2009 International Conference on Industrial Mechatronics and Automation, ICIMA 2009, Chengdu, 15 May 2009 through 16 May 2009 ; 2009 , Pages 76-80 ; 9781424438181 (ISBN) Daniali, M. M ; Vossoughi, G ; Sharif University of Technology
    2009
    Abstract
    In this paper, active vibration control of constrained manipulators used in automated deburring process is addressed. In order to suppress the random vibration generated due to the interaction force between robot end-effector and workpiece, an adaptive critic-based neurofuzzy controller is developed. This controller can adapt itself with different burr size. The control signal is fed to a piezoelectric actuator, which is mounted beside the workpiece. The piezoelectric actuator moves the workpiece to compensate the vibration. According to the intelligent behavior and system independent structure, the proposed design can be used for any industrial manipulator in various automated finishing... 

    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
    2010
    Abstract
    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...