Search for: dynamic-response
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    Investigation of critical influential speed for moving mass problems on beams

    , Article Applied Mathematical Modelling ; Volume 33, Issue 10 , 2009 , Pages 3885-3895 ; 0307904X (ISSN) Dehestani, M ; Mofid, M ; Vafai, A ; Sharif University of Technology
    A traveling mass due to its mass inertia has significant effects on the dynamic response of the structures. According to recent developments in structural materials and constructional technologies, the structures are likely to be affected by sudden changes of masses and substructure elements, in which the inertia effect of a moving mass is not negligible. The transverse inertia effects have been a topic of interest in bridge dynamics, design of railway tracks, guide way systems and other engineering applications such as modern high-speed precision machinery process. In this study an analytical-numerical method is presented which can be used to determine the dynamic response of beams carrying... 

    Effects of motion and structural vibration–induced loadings on the coupled dynamic response of a mono-column tension-leg-platform floating wind turbine

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 234, Issue 2 , 2020 , Pages 426-445 Imani, H ; Abbaspour, M ; Tabeshpour, M. R ; Karimirad, M ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Floating wind turbines are subjected to highly dynamic and complicated environmental conditions leading to significant platform motions and structural vibrations during operation and survival conditions. These motions and vibrations alter the induced loading characteristics; and consequently, affect the dynamic behavior of the system. In order to better understand the influence of such motions and structural vibrations, herein elastic structural disturbance of tower, on the system behavior, the spectral and statistical characteristics of a floating wind turbine dynamic responses under operational and survival conditions are fully explored using a fully coupled... 

    Thermo-mechanical Modeling of Angular Contact Ball-Bearings in High Speed Machine Tool Spindles

    , M.Sc. Thesis Sharif University of Technology Zahedi, Ali (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Machining in its general concept forms the major part of manufacturing processes regarding time and cost. Therefore any progress in machining techniques would be well beneficial. High speed machining is one of the recent concepts in machining technology which has attracted much attention and effort. But high speed spindles as the main part of high speed machines, have been notorious for their lack of reliability and sudden failure which originates mostly from thermal problems. In order to ensure reliable operation of spindles it is necessary to predict thermo-mechanical behavior of machine-tool spindles. The major sources of heat in a spindle are angular contact ball bearings (the most... 

    Performance Evaluation of Tuned Liquid Column Damper (TLCD)on Dynamic Response Mitigation of Tension Leg Platform

    , M.Sc. Thesis Sharif University of Technology Nikmehr, Latif (Author) ; Tabeshpour, Mohammad Reza (Supervisor)
    In recent decades due to declining reserves of fossil fuels on land and in shallow water areas, exploration and exploitation of oil and gas from deeper seas and oceans are rapidly making progress and since there are huge volumes of oil and gas reserves in deep waters of the Caspian Sea bed, in order to fulfill the purpose of oil exploration and exploitation in all sectors of the Caspian Sea, it seems mandatory to study in the field of platforms required for use in this area. One of these platforms is Tension Leg Platform with mooring lines called tendons that directly connected to the seabed. High axial stiffness makes this type of mooring lines constrained the vertical degrees of freedom... 

    Stability and Dynamic Response of Tension Leg Platform in Damaged Condition (Tendon Removed)

    , M.Sc. Thesis Sharif University of Technology Mahmoodi, Mohammad Reza (Author) ; Tabeshpour, Mohammad Reza (Supervisor)
    The tension leg platform is one of the compliant structures which are generally utilized for deep water oil explorations. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to vertical degrees of freedom it is stiff and resembles a fixed structure and is not allowed to float freely. A sudden disconnection of a tendon causes a change of stiffness and unbalance of forces and moments of the total system. The objective of this study is experimental and numerical investigation on behavior of ISSC TLP. Experiments were performed in the National... 

    Vibration Based Health Monitoring for Damage Detection of Composite Laminates

    , M.Sc. Thesis Sharif University of Technology Ghaffari, Hamid Reza (Author) ; Zabihollah, Abolghasem (Supervisor)
    Development of composite materials is one of the boldest technological advances of the last half of the twentieth century. This is due to their specific characteristics mostly considerably high strength-to-weight ratio, compared to metals and their highly customizing properties for different applications which make them a suitable material to be used in variety of domain from aerospace and automobiles to medical and sport equipments. Multi-stable asymmetrical laminates and non-uniform thickness laminated composite beams are being used as structural elements in a wide range of advanced engineering applications. Multi-stable asymmetrical laminates can be snapped between two or more geometries... 

    Dynamic Analysis of Floating Offshore Wind Turbines

    , M.Sc. Thesis Sharif University of Technology Imani, Hassan (Author) ; Abbaspour Tehrani Fard, Madjid (Supervisor)
    Use of wind energy is always one of the aims of man during the times. He used this energy for wheat grinding and sometimes for marine transportations. During recent decades, technology development forced human to harness this energy and use that for electricity production by employing onshore wind turbines. However, the modern engineering employed different arms of engineering such as marine engineering, civil engineering, mechanical engineering and electrical engineering for designing and installation of offshore wind turbines. But, huge water depths in offshore regions make the fixed leg turbines to be unacceptable solution. So, the floating wind turbines with mooring lines which attach... 

    Development of Inverse Vibration Technique for Damage Detection of Offshore Jacket-type Platforms

    , Ph.D. Dissertation Sharif University of Technology Haeri, Mohammad Hassan (Author) ; Golafshani, Ali akbar (Supervisor) ; Mohtasham Dolatshahi, Kiarash (Supervisor)
    In this dissertation a new approach is introduced for damage detection in offshore jacket platforms. The procedure uses the measured ambient vibration responses and the corresponding readable natural frequencies and mode shapes of the structural systems. Since offshore platforms are composed of heavy topsides supported by jacket structures, participation of the first mode is dominant in each direction in the response of the structure under field excitations. Moreover, ambient vibrations such as wave loads and boat impacts only excite the first modes of the structure. Therefore, it is difficult to find higher modes and the pertinent frequencies by use of accelerometers data. The introduced... 

    Low-velocity Impact Response of FML Beams with Considering Plasticity of Metal

    , M.Sc. Thesis Sharif University of Technology Rashedi, Hossein (Author) ; Koochakzadeh, Mohammad Ali (Supervisor)
    In this thesis an analytical model is applied to the dynamic response of fiber-metal laminate beams subjected to low-velocity impact. By using quasi-static consider-tions, a static model is developed using first order shear deformation beam theory and minimum total potential energy. In the next step, this static model is applied to the one degree of freedom non-linear spring-mass system for developing a model to predict dynamic response of low-velocity impact with the inclusion of material plasticity. By new explicit and simple expression, load-deflection curve, velocity-deflection curve, force-time history and deflection-time history can be derived. By using this analytical approach... 

    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... 

    Dynamic green function for response of timoshenko beam with arbitrary boundary conditions

    , Article Mechanics Based Design of Structures and Machines ; Volume 42, Issue 1 , 2 January , 2014 , Pages 97-110 ; ISSN: 15397734 Ghannadiasl, A ; Mofid, M ; Sharif University of Technology
    This paper presents the dynamic response of uniform Timoshenko beams with arbitrary boundary conditions using Dynamic Green Function. An exact and direct modeling technique is stated to model beam structures with arbitrary boundary conditions subjected to the external load that is an arbitrary function of time t and coordinate x and the concentrated moving load. This technique is based on the Dynamic Green Function. The effect of different boundary conditions, load, and other parameters is assessed. Finally, some numerical examples are shown to illustrate the efficiency and simplicity of the new formulation based on the Dynamic Green Function  

    Nonlinear dynamic analysis of a timoshenko beam resting on a viscoelastic foundation and traveled by a moving mass

    , Article Shock and Vibration ; Vol. 2014 , 2014 ; ISSN: 10709622 Mamandi, A ; Kargarnovin, M. H ; Sharif University of Technology
    The dynamic response of a Timoshenko beam with immovable ends resting on a nonlinear viscoelastic foundation and subjected to motion of a traveling mass moving with a constant velocity is studied. Primarily, the beam's nonlinear governing coupled PDEs of motion for the lateral and longitudinal displacements as well as the beam's cross-sectional rotation are derived using Hamilton's principle. On deriving these nonlinear coupled PDEs the stretching effect of the beam's neutral axis due to the beam's fixed end conditions in conjunction with the von-Karman strain-displacement relations is considered. To obtain the dynamic responses of the beam under the act of a moving mass, derived nonlinear... 

    Dynamic analysis of a rigid circular foundation on a transversely isotropic half-space under a buried inclined time-harmonic load

    , Article Soil Dynamics and Earthquake Engineering ; Vol. 63, issue , 2014 , pp. 184-192 Eskandari, M ; Ahmadi, S. F ; Khazaeli, S ; Sharif University of Technology
    The dynamic analysis of a surface rigid foundation in smooth contact with a transversely isotropic half-space under a buried inclined time-harmonic load is addressed. By virtue of the superposition technique, appropriate Green[U+05F3]s functions, and employing further mathematical techniques, solution of the mixed-boundary-value problem is expressed in terms of two well-known Fredholm integral equations. Two limiting cases of the problem corresponding to the static loading and isotropic medium are considered and the available results in the literature are fully recovered. For the static case, the results pertinent to both frictionless and bonded contacts are obtained and compared. With the... 

    Speed control of servo drives with a flexible couplings using fractional order state feedback

    , Article PEDSTC 2014 - 5th Annual International Power Electronics, Drive Systems and Technologies Conference ; 2014 , p. 25-30 Tahami, F ; Moghadam, B. E ; Sharif University of Technology
    Using elastic couplings in servo motor drives may lead to torsional oscillations which are usually extinguished by reducing the bandwidth of the control system as a countermeasure. A high performance servo drive however needs fast dynamic characteristics. The conventional controllers, such as PI controllers, may not be able to improve the dynamic response while keeping the system stable. Fractional order modeling offers a good framework for flexible structures such as two mass servo drives. In this paper, the dynamic response and stability of two-mass servo drive is improved using a fractional order controller. The fractional order controller allows increasing the phase margin of the system... 

    Nonlinear dynamic analysis of an axially loaded rotating Timoshenko beam with extensional condition included subjected to general type of force moving along the beam length

    , Article JVC/Journal of Vibration and Control ; Volume 19, Issue 16 , 2013 , Pages 2448-2458 ; 10775463 (ISSN) Mamandi, A ; Kargarnovin, M. H ; Sharif University of Technology
    In this paper the non-planar nonlinear dynamic responses of an axially loaded rotating Timoshenko beam subjected to a three-directional force traveling with a constant velocity is studied. On deriving the nonlinear coupled partial differential equations (PDEs) of motion the stretching effect of the beam's neutral axis due to the pinned-pinned ends' condition in conjunction with the von Karman strain-displacement relation are considered. The beam's nonlinear governing coupled PDEs of motion for the bending rotations of warped cross-section, longitudinal and lateral displacements are derived using Hamilton's principle. To obtain the dynamic responses of the beam, derived PDEs of motion are... 

    Analytical solution for the dynamic analysis of a delaminated composite beam traversed by a moving constant force

    , Article JVC/Journal of Vibration and Control ; Volume 19, Issue 10 , March , 2013 , Pages 1524-1537 ; 10775463 (ISSN) Kargarnovin, M. H ; Ahmadian, M. T ; Jafari Talookolaei, R. A ; Sharif University of Technology
    A closed form solution is presented in this paper to study the dynamics of a composite beam with a single delamination under the action of a moving constant force. The delaminated beam is divided into four interconnected beams using the delamination limits as their boundaries. Governing motion equations are derived in which the differential stretching and the bending-extension coupling are considered. The method of modal analysis is adopted to derive analytically the dynamic response of each beam. The obtained results for the free vibrations of delaminated beam are verified against reported similar results in the literature. Moreover, the maximum dynamic response of such a beam is compared... 

    Vibration analysis of delaminated Timoshenko beams under the motion of a constant amplitude point force traveling with uniform velocity

    , Article International Journal of Mechanical Sciences ; Volume 70 , 2013 , Pages 39-49 ; 00207403 (ISSN) Kargarnovin, M. H ; Jafari Talookolaei, R. A ; Ahmadian, M. T ; Sharif University of Technology
    A composite beam with single delamination traveled by a constant amplitude moving force is modeled accounting for the Poisson's effect, shear deformation and rotary inertia. The mechanical behavior between the delaminated surfaces is modeled using a piecewise-linear spring foundation. The governing differential equations of motion for such system are derived. Primarily, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes of such beam. Then, the Ritz method is employed to derive the dynamic response of the beam due to the moving force. The obtained results for the free and forced vibrations of beams are verified against reported similar... 

    Optimisation of anti-resonance vehicle configuration for vibration Attenuation of railway bridges

    , Article International Journal of Vehicle Structures and Systems ; Volume 5, Issue 2 , 2013 , Pages 63-67 ; 09753060 (ISSN) Vesali, F ; Kolagar, M ; Rezvani, M. A ; Sharif University of Technology
    MechAero Found. for Techn. Res. and Educ. Excellence  2013
    Movements of the wheel loads and their sequential entry onto the bridges are known as the two root causes for the vibrations of the railway bridges. It is possible to reduce the levels of the unwanted bridge deck oscillations by introducing one or more size adjusted wagon(s) in the train configuration. The added wagon(s) are of different size(s) compared with the other cars in the train configuration. This can disturb the periodicity in the wheel loading. Consequently, it can interfere with the resonance phenomena and prevent the bridge from excessive vibrations. The purpose of this research is to calculate proper sizes for the anti-resonance rail vehicles. Such vehicles need to fulfil the... 

    On the dynamic response of a half-space subjected to a moving mass

    , Article Mathematics and Mechanics of Solids ; Volume 17, Issue 4 , 2012 , Pages 393-412 ; 10812865 (ISSN) Dehestani, M ; Vafai, A ; Mofid, M ; Ahmadi, G ; Sharif University of Technology
    The dynamic response of a homogeneous, isotropic elastic half-space under a moving time-varying inertial load with subsonic speed is investigated. The surface of the half-space, which is under the action of the moving load, is a thin frictionless layer. In order to study the influences of the inertia of loads, the problem was first solved for a moving load and, then, the procedure was extended to include the inertial effects. The Navier equations of motion for the two-dimensional half-space were transformed to a system of wave-type partial differential equations using the Stokes-Helmholtz resolution. A new moving coordinate system was used and a modified system of equation was derived. The... 

    Dynamic control of beams acted by multiple moving masses in resonance state using piezo-ceramic actuators

    , Article Proceedings of SPIE - The International Society for Optical Engineering ; 2012 ; 0277786X (ISSN) ; 9780819489982 (ISBN) Mofid, M ; Eftekhar Azam, S ; Afghani Khorasghan, R ; Sharif University of Technology
    In this article the constitutive equation of an Euler-Bernoulli beam, excited by multiple moving masses is considered. A set of multiple piezo-ceramic actuators is used to harness the dynamic response of the beam. In this regard the beam response is suppressed by utilizing a linear control algorithm with a time varying gain matrix and displacement-velocity feedback. The efficiency of the results is investigated through the numerical analysis of an example problem