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nonlinear-resonance
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Application of Variational Method in Analysis of Flow in an Ideal Stratified Fluid System
, Ph.D. Dissertation Sharif University of Technology ; Jamali, Mirmosadegh (Supervisor)
Abstract
Using Variational Method, two important hydrodynamic phenomena, “internal gravity waves” and “gravity currents”, are modelled theoretically in this research. Variational method as a robust technique for modelling complicated problems related to fluid mechanics gives us the ability of finding closed-form formula for predicting the behavior of the flow in an ideal fluid system. In the first part of this research, focusing on the nonlinear resonant interaction between surface and internal waves, we model the evolution of interfacial waves on the interface of a two-layer fluid system. This phenomenon play an important role in the mixture of the fluid and cascade of energy in the environment....
Interaction of Surface and Interfacial Waves Over Fluid Mud Bed
, Ph.D. Dissertation Sharif University of Technology ; Jamali, Mirmosadegh (Supervisor)
Abstract
Motivated by the role of interfacial instabilities in sediment resuspension, this paper provides quantitative measurements of the long-time behavior of the interfacial waves and the changes in vertical density during motion of a surface wave over a muddy bed. After an initial fluidization process, a 3D quasi-standing interfacial wave was observed at the interface as a result of a resonant wave interaction with the surface wave. In the process, the quasi-standing wave started growing exponentially at a rate of 0.052-0.081 1/s and then reached a maximum amplitude (kexpb=0.77-0.83). The interfacial wave then took a downward trend in the transition stage and approached a steady state...
Characterization of a nonlinear MEMS-based piezoelectric resonator for wideband micro power generation
, Article Applied Mathematical Modelling ; Volume 41 , 2017 , Pages 121-142 ; 0307904X (ISSN) ; Ahmadian, M. T ; Sharif University of Technology
Elsevier Inc
2017
Abstract
Micro-scale piezoelectric unimorph beams with attached proof masses are the most prevalent structures in MEMS-based energy harvesters considering micro fabrication and natural frequency limitations. In doubly clamped beams a nonlinear stiffness is observed as a result of midplane stretching effect which leads to amplitude-stiffened Duffing resonance. In this study, a nonlinear model of a doubly clamped piezoelectric micro power generator, taking into account geometric nonlinearities including stretching and large curvatures, is investigated. The governing nonlinear coupled electromechanical partial differential equations of motion are determined by exploiting Hamilton's principle. A...
Ultrasound dosimetery using microbubbles
, Article IFMBE Proceedings, 20 June 2011 through 23 June 2011 ; Volume 35 IFMBE , June , 2011 , Pages 359-362 ; 16800737 (ISSN) ; 9783642217289 (ISBN) ; Zahedi, E ; Tavakkoli, J ; Sharif University of Technology
2011
Abstract
In this paper, a new technique based on nonlinear resonance of microbubbles is investigated in order to estimate the amplitude of an ultrasound wave pressure field. First, the existing theoretical model is reviewed. Then, an experimental setup consisting of a bubble generator and transmitting/receiving ultrasound transducers operating in the 1 MHz frequency range is described. The effect of background noise is also taken into account. Results show that the second harmonic oscillations are detectable, paving the way to develop a quantitative method for in vivo calibration of ultrasound waves
Nonlinear Analysis of an Electrostatically Actuated Microbeam Considering Coupled Vibrations Due to Rotation
, Ph.D. Dissertation Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor) ; Firoozbakhsh, Keikhosrow (Supervisor)
Abstract
This research is concerned with the study of the static, dynamic, vibration and instability of an electrostatically actuated microbeam gyroscope considering geometric nonlinearities and electrostatic fringing fields. A vibrating microbeam gyroscope consists of a beam with a rigid (proof) mass attached to it and undergoes coupled flexural-flexural vibrations coupled with base rotation. The primary oscillation is generated in drive direction of the microbeam gyroscope by a pair of DC and AC voltages on the mass. The secondary oscillation occurring in the sense direction is induced by the Coriolis coupling caused by the input angular rate of the beam along its axis. In this case gyroscope acts...