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    Optimal stair climbing pattern generation for humanoids using virtual slope and distributed mass model

    , Article Journal of Intelligent and Robotic Systems: Theory and Applications ; Volume 94, Issue 1 , 2019 , Pages 43-59 ; 09210296 (ISSN) Shahrokhshahi, A ; Yousefi Koma, A ; Khadiv, M ; Mansouri, S ; Mohtasebi, S. S ; Sharif University of Technology
    Springer Netherlands  2019
    Abstract
    This study addresses optimal walking pattern generation for SURENA III humanoid robot in a stair-climbing scenario. To this end, the kinematic configuration of the 31-DOF humanoid robot is studied. Integrating the detailed dynamic properties of the robot, a comprehensive and precise dynamic model is developed for its lower-limb. In order to generate the optimal walking pattern for the considered humanoid robot, trajectories for feet and pelvis are first designed, and then joint angles are derived by means of inverse kinematics. Such a complete model provides the designer with the necessary tools to optimize the trajectory generation. Using two different types of objective functions, namely... 

    Pipe dampers as passive devices for seismic control of isolated bridges

    , Article Structural Control and Health Monitoring ; Volume 24, Issue 2 , 2017 ; 15452255 (ISSN) Mahjoubi, S ; Maleki, S ; Sharif University of Technology
    John Wiley and Sons Ltd  2017
    Abstract
    During an earthquake, pounding of bridge superstructure into abutments is potentially destructive to structural elements and may cause unseating failure and collapse. By using energy dissipative devices such as passive dampers, the harmful pounding force may be prevented. One of the most economical passive dampers for structural applications is the pipe damper, recently introduced by the authors. In this paper, computer models of a two-span 60-m long conventional overpass bridge are equipped with different lengths of two types of pipe dampers, namely the dual-pipe (DPD) and infilled-pipe (IPD) dampers. A simplified lumped-mass model for the bridge considering soil stiffness is proposed and... 

    Dynamics of the nanoneedle probe in trolling mode AFM

    , Article Nanotechnology ; Volume 26, Issue 20 , April , 2015 ; 09574484 (ISSN) Abdi, A ; Pishkenari, H. N ; Keramati, R ; Minary Jolandan, M ; Sharif University of Technology
    Institute of Physics Publishing  2015
    Abstract
    Atomic force microscopy (AFM), as an indispensable tool for nanoscale characterization, presents major drawbacks for operation in a liquid environment arising from the large hydrodynamic drag on the vibrating cantilever. The newly introduced 'Trolling mode' (TR-mode) AFM resolves this complication by using a specialized nanoneedle cantilever that keeps the cantilever outside of the liquid. Herein, a mechanical model with a lumped mass was developed to capture the dynamics of such a cantilever with a nanoneedle tip. This new developed model was applied to investigate the effects of the needle-liquid interface on the performance of the AFM, including the imaging capability in liquid  

    Permeability impairment study due to asphaltene deposition: experimental and modeling approach

    , Article Transport in Porous Media ; Volume 91, Issue 3 , February , 2012 , Pages 999-1012 ; 01693913 (ISSN) Bolouri, S. H ; Ghoodjani, E ; Sharif University of Technology
    2012
    Abstract
    This fact is well known that during any scenario of production, asphaltene deposition in porous media has a substantial effect on oil flow. But a clear understanding of asphaltene deposition mechanisms can help to minimize asphaltenic problem in oil-bearing formations. In this study, the experimental results of three dynamic CO 2 miscible injection tests were investigated. Regarding the effects of adsorption, mechanical entrapment, and sweeping mechanisms on permeability behavior, a mathematical mass and permeability variation model were developed. According to the experimental results asphaltene deposition causes a 70% loss of sand stone initial permeability while the loss is significantly... 

    Dynamic modeling of stick-slip motion in a legged, piezoelectric driven microrobot

    , Article International Journal of Advanced Robotic Systems ; Volume 7, Issue 3 , September , 2010 , Pages 201-208 ; 17298806 (ISSN) Kamali Eigoli, A ; Vossoughi, G. R ; Sharif University of Technology
    2010
    Abstract
    The motion of a stick-slip microrobot propelled by its piezoelectric unimorph legs is mathematically modeled. Using a continuously distributed mass model for the robot's body, the working equation of the mechanism is derived based on the assumption of linear Euler-Bernoulli beam theory and linear piezoelectric behavior. Moreover, the required condition for generating net motion is calculated in terms of physical characteristics of the microrobot. It is demonstrated that the higher the friction constant, then a lower average speed is obtained. Also, it is shown that a microrobot with heavier legs can move in a rougher environment. Regardless of the mass proportion between robot's main body... 

    Offline Optimization of a Four Dimensional TF/TA Problem Considering Engine Dynamics

    , M.Sc. Thesis Sharif University of Technology Gharib Otaghsaraee, Salman (Author) ; Nobahari, Hadi (Supervisor) ; Banazadeh, Afshin (Supervisor)
    Abstract
    In this thesis, the problem of offline trajectory optimization of a flying vehicle has been solved. Terrain following/ terrain avoidance has been considered as a guiadanec strategy of vehicle. The point-mass model in three dimensional space for flight simulation and the transfer functions for modeling of vehicle dynamics has been used. One of the constraints of this problem is related to engine’s dynamic behavior, which is not considered in the privious works. So in this thesis at first, a turbofan engine has been modeled and it’s static and dynamic model has been obtained. Then, the effect of engine’s dynamic model in the trajectory optimization has been investigated. The results show that... 

    Application of Endurance Time Method in Nonlinear Dynamic analysis of Elevated Tanks

    , M.Sc. Thesis Sharif University of Technology Rahmati, Mohammad (Author) ; Esmaeil Pourestekanchi, Homayoon (Supervisor)
    Abstract
    Endurance Time (ET) is a fairly comprehensive analytical method based on time history analysis applied for evaluating structural systems excited by dynamic loading of earthquake. In such evaluation assessment measure is based on endurance time of structure versus applied accelerogram function and parameters such as stiffness, lateral resistance, period of vibration and dynamic characteristics are not used directly. In this research nonlinear dynamic analysis of elevated steel tanks with laterally braced framed tower under the loading of earthquake records and ET accelerograms was studied and effectivity of ET method in analyzing such elevated tanks was verified. Due to complication of... 

    Effects of higher oscillation modes on TM-AFM measurements

    , Article Ultramicroscopy ; Volume 111, Issue 2 , 2011 , Pages 107-116 ; 03043991 (ISSN) Pishkenari, H. N ; Meghdari, A ; Sharif University of Technology
    Abstract
    The finite element method and molecular dynamics simulations are used for modeling the AFM microcantilever dynamics and the tip-sample interaction forces, respectively. Molecular dynamics simulations are conducted to calculate the tip-sample force data as a function of tip height at different lateral positions of the tip with respect to the sample. The results demonstrate that in the presence of nonlinear interaction forces, higher eigenmodes of the microcantilever are excited and play a significant role in the tip and sample elastic deformations. Using comparisons between the results of FEM and lumped models, how some aspects of the system behavior can be hidden when the point-mass model is...