Search for: dynamic-response
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    Site-dependent strength reduction factors for soil-structure systems

    , Article Soil Dynamics and Earthquake Engineering ; Volume 27, Issue 2 , 2007 , Pages 99-110 ; 02677261 (ISSN) Ghannad, M. A ; Jahankhah, H ; Sharif University of Technology
    The effect of soil conditions on strength reduction factors (SRFs) is investigated. Both site effect and soil-structure interaction (SSI) effect are considered in the study with special emphasis on the latter effect. The structure is modeled as an elasto-plastic single degree of freedom (SDOF) system, whereas the underlying soil is considered as a homogeneous half-space. The half-space is also replaced by a simplified 3DOF system, based on the concept of Cone Models. The whole 4DOF model is then analyzed under a total of 54 strong motions recorded on different soil types. A parametric study is done for a wide range of non-dimensional parameters, which completely define the problem. It is... 

    First order perturbation solution for axial vibration of tension leg platforms

    , Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 414-423 ; 10263098 (ISSN) Golafshani, A. A ; Tabeshpour, M. R ; Seif, M. S ; Sharif University of Technology
    Sharif University of Technology  2007
    The dynamic response of the leg (tether) of a Tension Leg Platform (TLP), subjected to axial load at the top of the leg, is presented. The structural model is very simple, but several complicated factors, such as foundation effect, buoyancy and simulated ocean wave load, are considered. As an application, the effect of added mass fluctuation on the dynamic response of the leg subjected to such a load is presented. This effect is important in the fatigue life study of tethers. A first order perturbation method is used, in order to formulate and solve the problem. The differential equation is solved by means of non-harmonic Fourier expansion, in terms of eigenfunctions obtained from a... 

    Study of pore pressure variation during liquefaction using two constitutive models for sand

    , Article Soil Dynamics and Earthquake Engineering ; Volume 27, Issue 1 , 2007 , Pages 60-72 ; 02677261 (ISSN) Taiebat, M ; Shahir, H ; Pak, A ; Sharif University of Technology
    Numerical analyses of liquefiable sand are presented in this paper. Liquefaction phenomenon is an undrained response of saturated sandy soils when they are subjected to static or dynamic loads. A fully coupled dynamic computer code is developed to predict the liquefaction potential of a saturated sandy layer. Coupled dynamic field equations of extended Biot's theory with u-P formulation are used to determine the responses of pore fluid and soil skeleton. Generalized Newmark method is employed for integration in time. The soil behavior is modelled by two constitutive models; a critical state two-surface plasticity model, and a densification model. A class 'B' analysis of a centrifuge... 

    An analytical method in computational aeroelasticity based on Wagner function

    , Article 25th Congress of the International Council of the Aeronautical Sciences 2006, Hamburg, 3 September 2006 through 8 September 2006 ; Volume 3 , 2006 , Pages 1808-1814 Shams, Sh ; Haddadpour, H ; Sadr Lahidjani, M. H ; Kheiri, M ; Sharif University of Technology
    Curran Associates Inc  2006
    This paper presents an analytical method in computational aeroelasticity for an airfoil considering two degrees of freedom (heaving and pitching) based on the Wagner integral function. In the obtained aeroelastic equations of motion, there are some integral parts that give an integro-differential system of equations. Using appropriate approximation for the Wagner function, a new form of equations can be obtained by derivation from mentioned equations. These equations are in the form of ordinary differential equations. Using the obtained equations, the flutter speed is predicted for a given airfoil and the results are compared with the results of other investigators. Also, the dynamic... 

    On the nonlinear dynamics of a multi-scale hybrid nanocomposite disk

    , Article Engineering with Computers ; Volume 37, Issue 3 , 2021 , Pages 2369-2388 ; 01770667 (ISSN) Safarpour, M ; Ebrahimi, F ; Habibi, M ; Safarpour, H ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2021
    This is the first research on the nonlinear frequency analysis of a multi-scale hybrid nanocomposite (MHC) disk (MHCD) resting on an elastic foundation subjected to nonlinear temperature gradient and mechanical loading is investigated. The matrix material is reinforced with carbon nanotubes (CNTs) or carbon fibers (CF) at the nano- or macroscale, respectively. We present a modified Halpin–Tsai model to predict the effective properties of the MHCD. The displacement–strain of nonlinear vibration of multi-scale laminated disk via third-order shear deformation theory (TSDT) and using Von Karman nonlinear shell theory is obtained. Hamilton’s principle is employed to establish the governing... 

    Optimal tuner selection using Kalman lter for a real-time modular gas turbine model

    , Article Scientia Iranica ; Volume 27, Issue 2 , 2021 , Pages 806-818 ; 10263098 (ISSN) Sheikhbahaei, R ; Vossughi, G ; Alasty, A ; Sharif University of Technology
    Sharif University of Technology  2021
    In this study, a real-time exible modular modeling approach to simulating the dynamic behavior of gas turbine engines based on nonlinear thermodynamic and dynamic laws is addressed. The introduced model, which is developed in the Matlab-Simulink environment, is an object-oriented high-speed real-time computer model and is capable of simulating the dynamic behavior of a broad group of gas turbine engines due to its modular structure. Moreover, a Kalman lter-based model tuning procedure is applied to decrease the modeling errors. Modeling errors are de ned as the mismatch between simulation results and available experimental data. This tuning procedure is an underdetermined estimation problem,... 

    Nonlinear vibrations of an inclined beam subjected to a moving load

    , Article Journal of Physics: Conference Series, 8 September 2009 through 10 September 2009, Cambridge ; Volume 181, Issue 1 , 2009 ; 17426588 (ISSN) Mamandi, A ; Kargarnovin, M ; Younesian, D ; Sharif University of Technology
    In this paper, the nonlinear dynamic responses of an inclined pinned-pinned Euler-Bernoulli beam with a constant cross section and finite length subjected to a concentrated vertical force traveling with constant velocity is investigated by using the mode summation method. Frequency analysis of the PDE's governing equations of motion for steady-state response is studied by applying multiple scales method. The nonlinear dynamic deflections of the beam are obtained by solving two coupled nonlinear PDE's governing equations of planar motion for both longitudinal and transverse oscillations of the beam. The dynamic magnification factor and normalized time histories of mid-point of the beam are... 

    Dynamic analysis of electrostatically actuated nanobeam based on strain gradient theory

    , Article International Journal of Structural Stability and Dynamics ; Volume 15, Issue 4 , 2014 ; ISSN: 02194554 Miandoab, E. M ; Pishkenari, H. N ; Yousefi Koma, A ; Sharif University of Technology
    In this study, dynamic response of a micro- and nanobeams under electrostatic actuation is investigated using strain gradient theory. To solve the governing sixth-order partial differential equation, mode shapes and natural frequencies of beam using Euler–Bernoulli and strain gradient theories are derived and then compared with classical theory. Galerkin projection is utilized to convert the partial differential equation to ordinary differential equations representing the system mode shapes. Accuracy of proposed one degree of freedom model is verified by comparing the dynamic response of the electrostatically actuated micro-beam with analogue equation and differential quadrature methods.... 

    Inelastic displacement ratios for soil-structure systems allowed to uplift

    , Article Earthquake Engineering and Structural Dynamics ; Vol. 43, issue. 9 , July , 2014 , p. 1401-1421 ; ISSN: 00988847 Ghannad, M. A ; Jafarieh, A. H ; Sharif University of Technology
    The simultaneous effects of soil-structure interaction, foundation uplift and inelastic behavior of the superstructure on total displacement response of soil-structure systems are investigated. The superstructure is modeled as an equivalent single-degree-of-freedom system with bilinear behavior mounted on a rigid foundation resting on distributed tensionless Winkler springs and dampers. It is well known that the behavior of soil-structure systems can be well described using a limited number of nondimensional parameters. Here, by introducing two new parameters, the concept is extended to inelastic soil-structure systems in which the foundation is allowed to uplift. An extensive parametric... 

    Requirements for soil-specific correlation between shear wave velocity and liquefaction resistance of sands

    , Article Soil Dynamics and Earthquake Engineering ; Vol. 57, issue , 2014 , pp. 152-163 ; ISSN: 02677261 Ahmadi, M. M ; Akbari Paydar, N ; Sharif University of Technology
    The application of the simplified method for evaluating the liquefaction potential based on shear wave velocity measurements has increased substantially due to its advantages, especially for microzonation of liquefaction potential. In the simplified method, a curve is proposed to correlate the cyclic resistance ratio (CRR) with overburden stress-corrected shear wave velocity (Vs1). However, the uniqueness of this curve for all types of soils is questionable. The objective of this research is to study whether the correlation between CRR and Vs1 is unique or not. Besides, the necessity of developing the soil-specific correlations is also investigated. Based on laboratory test data, a new... 

    Assessment of offshore structures under extreme wave conditions by Modified Endurance Wave Analysis

    , Article Marine Structures ; Volume 39 , December , 2014 , Pages 50-69 ; ISSN: 09518339 Dastan Diznab, M. A ; Mohajernassab, S ; Seif, M. S ; Tabeshpour, M. R ; Mehdigholi, H ; Sharif University of Technology
    Recently, various approaches have been introduced to estimate the response of offshore structures in different sea states by stepwisely intensifying records. In this article, a more practical approach entitled Modified Endurance Wave Analysis (MEWA) considering the random and probabilistic nature of wave loading and utilizing optimal time duration is introduced. Generation procedure of this approach is described based on two practical wave theories: random and constrained new-wave. In addition, assessment of a simplified model representing a typical fixed offshore platform under extreme wave conditions in the Persian Gulf is performed making use of MEWA. A comparative analysis has been also... 

    A new power management control strategy for a MV microgrid with both synchronous generator and inverter-interfaced distributed energy resources

    , Article IEEE International Symposium on Industrial Electronics ; 1- 4 June , 2014 , pp. 2529-2534 ; ISBN: 978-147992399-1 Zangeneh, M ; Hamzeh, M ; Mokhtari, H ; Karimi, H ; Sharif University of Technology
    Control strategies of a microgrid which includes both synchronous generators and converter-based distribution generation (DG) units must be designed such that effective operation of the microgrid is achieved. The main objective of this paper is to develop a high performance control strategy for an islanded medium voltage (MV) microgrid consisting of inverter and non-inverter interfaced DG units. A new control method for the synchronous generator in an islanded microgrid is proposed based on a virtual droop scheme. The proposed strategy can effectively manage the real and reactive powers of the microgrid among the inverter and non-inverter based DG units. The steady state and dynamic... 

    An investigation on the dynamic response of the shaking table steel deck using finite element

    , Article 11th World Congress on Computational Mechanics, WCCM 2014, 5th European Conference on Computational Mechanics, ECCM 2014 and 6th European Conference on Computational Fluid Dynamics, ECFD 2014 ; 2014 , pp. 1330-1340 ; ISBN: 9788494284472 Moghaddam, H ; Farzanian, K ; Taheri, E ; Sharif University of Technology
    This paper presents the results of an analytical study on the dynamic characteristics of the Shaking Table facilities at Sharif University. This 3 degree of freedom shaking table is driven by 3 servo-control hydraulic actuators, and consists of a 12 ton, 4m×4m×0.6m steel deck. The main objective of this investigation is to identify the degree of flexibility of the deck, and its adverse effects in causing errors in the simulation of seismic effects on different structural specimens. Many frame specimens of different weights and configurations are subjected to seismic motions, and their responses are calculated using FE models. Some of these models were designed to account for eccentric... 

    Nonlinear seismic response of concrete gravity dams due to foundation fault movement

    , Article Scientia Iranica ; Vol. 21, issue. 5 , 2014 , pp. 1539-1548 ; ISSN: 10263098 Ghaemian, M ; Vafai, A. H ; Karimi, Z ; Sharif University of Technology
    Not only should dams be evaluated for seismic shaking, but their capability to survive potential fault displacement in their foundations should also be assessed. Safety reviews of existing dams suggest that geological-seismic evaluation of some dam sites has failed to recognize the existence of possibly active faults. In this study, the nonlinear seismic behavior of concrete gravity dams, due to relative fault dislocation occurring in foundations, has been investigated. Two types of fault movement, including normal-slip and reverse-slip, have been considered. These two types, combined with the location of fault lines, with respect to the toe, middle, and heel of the dam base, angle of fault,... 

    Considering wave passage effects in blind identification of long-span bridges

    , Article Conference Proceedings of the Society for Experimental Mechanics Series ; Volume 5 , 2013 , Pages 53-66 ; 21915644 (ISSN); 9781461465638 (ISBN) Ghahari, S. F ; Ghannad, M. A ; Norman, J ; Crewe, A ; Abazarsa, F ; Taciroglu, E ; Sharif University of Technology
    Long-span bridges usually experience different input excitations at their ground supports that emanate from differences in wave arrival times, and soil conditions, as well as loss of coherency in arriving waves. These spatial variations can drastically influence the dynamic response; hence, this phenomenon must be considered in any vibration-based identification method. There are numerous Multi-Input Multi-Output (MIMO) identification techniques that may be applied to data recorded at long-span bridges that experience spatial variations in their input motions. However, inertial soil-structure interaction effects severely reduce the accuracy of these techniques because the actual Foundation... 

    Forced vibration of delaminated timoshenko beams under the action of moving oscillatory mass

    , Article Shock and Vibration ; Volume 20, Issue 1 , 2013 , Pages 79-96 ; 10709622 (ISSN) Kargarnovin, M. H ; Ahmadian, M. T ; Jafari Talookolaei, R. A ; Sharif University of Technology
    This paper presents the dynamic response of a delaminated composite beam under the action of a moving oscillating mass. In this analysis the Poisson's effect is considered for the first time. Moreover, the effects of rotary inertia and shear deformation are incorporated. In our modeling linear springs are used between delaminated surfaces to simulate the dynamic interaction between sub-beams. To solve the governing differential equations of motion using modal expansion series, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes necessary for forced vibration analysis. The obtained results for the free and forced vibrations of beams are... 

    Semi-analytical solution for the free vibration analysis of generally laminated composite Timoshenko beams with single delamination

    , Article Composites Part B: Engineering ; Volume 45, Issue 1 , 2013 , Pages 587-600 ; 13598368 (ISSN) Kargarnovin, M. H ; Ahmadian, M. T ; Jafari Talookolaei, R. A ; Abedi, M ; Sharif University of Technology
    A rather new semi-analytical method towards investigating the free vibration analysis of generally laminated composite beam (LCB) with a delamination is presented. For the first time the combined effects of material couplings (bending-tension, bending-twist, and tension-twist couplings) with the effects of shear deformation, rotary inertia and Poisson's effect are taken into account. The semi-analytical solution for the natural frequencies and mode shapes are presented by incorporating the constraint conditions using the method of Lagrange multipliers. To verify the validity and the accuracy of the obtained results, they were compared with the results from other available references. Very... 

    Dynamic response of Timoshenko beam under moving mass

    , Article Scientia Iranica ; Volume 20, Issue 1 , 2013 , Pages 50-56 ; 10263098 (ISSN) Eftekhar Azam, S ; Mofid, M ; Khoraskani, R. A ; Sharif University of Technology
    In this article, the dynamic responses of a Timoshenko beam subjected to a moving mass, and a moving sprung mass are analyzed. By making recourse to Hamilton's principle, governing differential equations for beam vibration are derived. By using the modal superposition method, the partial differential equations of the system are transformed into a set of Ordinary Differential Equations (ODEs). The resulted set of ODEs is represented in state-space form, and solved by means of a numerical technique. The accuracy of the results has been ascertained through comparing the results of our approach with those available from previous studies; moreover, a reasonable agreement has been obtained. The... 

    Damage assessment of a concrete arch dam through nonlinear incremental dynamic analysis

    , Article Soil Dynamics and Earthquake Engineering ; Volume 44 , January , 2013 , Pages 127-137 ; 02677261 (ISSN) Alembagheri, M ; Ghaemian, M ; Sharif University of Technology
    Damage assessment of concrete arch dams is carried out through nonlinear Incremental Dynamic Analysis (IDA) of a typical arch dam. In this study the Morrow Point arch dam is subjected to a set of 12 three-component earthquakes each scaled to 12 increasing intensity levels. The dam-foundation interaction effects have been investigated by varying foundation's modulus of elasticity to be equal and half of dam concrete's modulus of elasticity. Damage propagation through the dam body is investigated and various IDA curves are created. The performance and various limit-states of the dam structure are examined based on the obtained results. Simple damage indices are proposed through comparison of... 

    On the dynamic response of a delaminated composite beam under the motion of an oscillating mass

    , Article Journal of Composite Materials ; Volume 46, Issue 22 , 2012 , Pages 2863-2877 ; 00219983 (ISSN) Jafari Talookolaei, R. A ; Kargarnovin, M. H ; Ahmadian, M. T ; Sharif University of Technology
    SAGE  2012
    The dynamic response of a delaminated composite beam under the motion of an oscillatory mass moving with a constant velocity has been studied. The delaminated composite beam is modeled as four interconnected sub-beams using the delamination limits as their boundaries. The constrained model is used to model the delamination region. The continuity and equilibrium conditions are forced to be satisfied between the adjoining beams. A set of derived governing differential equations along with those obtained by imposing boundary conditions are simultaneously solved in a closed form manner. The results for the response of the delaminated beam were compared with those of the intact beam. Furthermore,...