Sharif Digital Repository

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... 

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  

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... 

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... 

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... 

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...