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Nonlinear Vibration and Pull-in Analysis in Electrostatically Actuated Nano/Micromirrors
, Ph.D. Dissertation Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor)
Abstract
The important role of MEMS devices in optical systems has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical Systems (MOEMS), which mainly includes nano/micromirrors and torsional nano/microactuators. These devices have found variety of applications in optical switches, displays, micro scanning mirrors, optical cross-connects, interferometery, spectroscopy, aberration correction and biomedical imaging. In this project, the static and dynamic behavior of electrostatic nano/micromirrors under the effect of intermolecular surface forces and squeezed film damping are studied. The prior art published in the literature have mainly used pure torsion models. In a...
Numerical simulation of density current using two-phase flow
, Article 2006 2nd ASME Joint U.S.-European Fluids Engineering Summer Meeting, FEDSM 2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2006 , 2006 ; 0791837831 (ISBN); 9780791837832 (ISBN) ; Firoozabadi, B ; Sharif University of Technology
2006
Abstract
Due to shear layer at the interface of density current and ambient fluid, density current disturbs and entrains the surrounding fluid. Most existing analytical and numerical models for density current flows are based on the equations for single-phase flows. In this research, the density current has been modeled with two-phase flow model. The governing equations are continuity, x- momentum, and y- momentum equations for every fluid. The volume-of-fluid (VOF) interface tracking technique which uses a piecewise-linear interface calculation (PLIC) in each cell is used to determine the deformation of free surface in density current, numerically. Surface tension is implemented by the continuous...
Dynamics of a delaminated timoshenko beam subjected to a moving oscillatory mass
, Article Mechanics Based Design of Structures and Machines ; Volume 40, Issue 2 , Apr , 2012 , Pages 218-240 ; 15397734 (ISSN) ; Ahmadian, M. T ; Jafari-Talookolaei, R. A ; Sharif University of Technology
2012
Abstract
This paper presents dynamic response of a delaminated composite beam under the action of moving oscillatory mass. The Poisson's effect, shear deformation and rotary inertia have been considered in this analysis. We have used the constrained mode model to simulate the behavior between the delaminated surfaces. Based on this model, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes for the delaminated beam. Then, the forced response is determined by employing the modal series expansion technique. The obtained results for the free and forced vibrations of beams are verified against reported similar results in the literature. Moreover, the...
Control design and passivity analysis for scaled one-dimensional bilateral teleoperated nanomanipulation
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 10, Issue PART A , 2010 , Pages 279-285 ; 9780791843833 (ISBN) ; Vossoughi, G. R ; Ahmadian, M. T ; Tajaddodianfar, F ; Sharif University of Technology
Abstract
In this paper, a novel control approach for onedimensional bilateral teleoperated nanomanipulation system is proposed. While manipulating objects with a nanomanipulator, real time visual feedback is not available. So, force feedback is used to compensate for the lack of visual information. Since nanometer scale forces are dominated by surface forces instead of inertial forces as in macro world, scaling of nanoforces is one of the major issues of teleoperation system. The Hertz elastic contact model is used to model the interactions between the slave robot and the environment. The proposed approach uses the simple proportional derivative control, i.e., the master and slave robots are...
Hydrodynamics of fingering instability in the presence of a magnetic field
, Article Fluid Dynamics Research ; Volume 48, Issue 5 , 2016 ; 01695983 (ISSN) ; Ashouri, M ; Ebrahimi, B ; Sharif University of Technology
Institute of Physics Publishing
Abstract
The hydrodynamics of two immiscible fluids in a rectangular Hele-Shaw cell under the influence of a magnetic field is studied, both theoretically and numerically. A linear stability analysis is conducted to determine the effect of magnetic fields on the formation of viscous fingers. As a result, an analytical solution is found to calculate the growth rate of perturbations. For numerical simulation of the two-phase flow, the interfacial tension is treated as a body force using the continuum surface force model and the interface tracking is performed by the volume of fluid method. The variations of the width and growth rate of fingers in an unstable displacement versus Hartmann number, a...