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    Viscous damping effect on the aeroelastic stability of subsonic wings: Introduction of the U–K method

    , Article Journal of Fluids and Structures ; Volume 73 , 2017 , Pages 1-15 ; 08899746 (ISSN) Beheshtinia, F ; Dehghani Firouz Abadi, R ; Rahmanian, M ; Sharif University of Technology
    This study aims at introduction of a novel method for evaluating the effect of viscous damping on the aeroelastic stability boundaries. The K-method is well-known for being one of the fastest methods in determining the instability conditions (i.e. critical speed and its corresponding frequency). However, formulation of the K-method is developed for aeroelastic systems without viscous damping and solution is valid where the introduced artificial damping is zero. Taking into account the framework of the K-method in general, this study has tried to remove the major shortcoming of the K-method, i.e. investigation of the effect of viscous damping on the aeroelastic stability boundaries. The... 

    Determining Response Quantities in Yielding Structures with Viscous Damping

    , M.Sc. Thesis Sharif University of Technology Rahmatabadi, Payman (Author) ; Khaloo, Alireza (Supervisor)
    In recent decades, considerable attention has been paid to application of passive energy dissipation systems in design of new buildings as well as in seismic rehabilitation of existing ones. The increased application of these devices in structures will depend on the availability of simplified methods for their analysis and design. In this study, considering high viscously damped single-degree-of-freedom systems, an equivalent linear system with new effective parameters is introduced which has capability to predict maximum displacement and maximum inertia force of the structure simultaneously. Effective mass and effective damping ratio as pair of effective parameters instead of the effective... 

    Experimental and numerical evaluation of proposed precast concrete connections

    , Article Structural Concrete ; Volume 17, Issue 6 , 2016 , Pages 959-971 ; 14644177 (ISSN) Yekrangnia, M ; Taheri, A ; Zahrai, S. M ; Sharif University of Technology
    In this article, the cyclic performance of an innovative precast beam-to-column connection is evaluated experimentally and numerically. Two full-scale beam-column cross-shape interior connection specimens named PF-1 and PF-2 are tested. By adding extra nuts to the connecting bolts, specimen PF-2 behaves in a more shear-dominant pattern and shows less pinching. Comparison of performance of these specimens with the numerical monolithic model in terms of stiffness, strength, ductility and energy dissipation capacity indicates the proposed system can provide conditions close to the monolithic connection. However, to reduce the pinching drawback, a minor modification was made leading to... 

    Nonlinear vibration analysis of directional drill string considering effect of drilling mud and weight on bit

    , Article Journal of Vibroengineering ; Volume 18, Issue 2 , 2016 , Pages 1280-1287 ; 13928716 (ISSN) Taheran, F ; Monfared, V ; Daneshmand, S ; Abedi, E ; Sharif University of Technology
    Vibromechanika  2016
    In this paper a nonlinear dynamic model for drill string in inclined well drilling is developed. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping on stability and vibration of the drill string are studied. Findings indicate the nonlinear effects are significant on the results. The effects of drilling mud flow rate and weight on bit on the natural frequencies and time responses are evaluated. Enhancement of drilling mud flow rate results in decreasing of natural frequencies and vibrational amplitude, while increasing the weight on bit, leads to decrease of the natural frequencies and increase the vibrational amplitude. © JVE INTERNATIONAL LTD