ارتعاشات ناخطي و مدل سازي الكترومكانيكي ميكروتيرها و نانو لوله هاي سيال بر

چكيده انگليسي :

Nonlinear Vibration and Electromechanical Modeling of Microbeams and Nanotubes Conveying Fluid Mahmood Ali Asgari Mahmood aliasgari@gmail com 23th January 2013 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisors Hamid Reza Mirdamad hrmirdamadi@cc iut ac ir Mostafa Ghayour ghayour@cc iut ac ir Abstract In this project an aeroelastic model for electrostatically actuated microbeams subjected to external airflow is investigated The effect of flow velocity on the static and dynamic pull in instability phenomena is surveyed The airflow passes between a microbeam and a ground rigid plate Both doubly clamped and cantilever micro beams are analyzed The first order fringing field effect is included for modeling electrostatic force Moreover membrane stretching of microbeam generated by immovable boundary conditions is accounted to improve accuracy Navier Stokes equation is utilized for deriving fluid structure interaction FSI equation The results indicate that contrary to the singly clamped microbeam by considering dynamic pressure of external flow a doubly clamped microbeam would become unstable sooner and pull in instability could occur for lower voltages However this effect for the doubly clamped microbeam could be ignored except for very high velocities In addition we could observe a significant retardation in pull in instability for a cantilever microbeam in the range of pre flutter velocities By including the gyroscopic terms for this microbeam we could see a significant rise and fall effect for the post flutter and pre flutter velocities respectively Moreover in the field of nanosystems we introduce carbon nanotubes CNT as a material that has a significant potential for application in the FSI fields Therefore natural frequency and nonlinear response of CNT conveying fluid based on coupling of nonlocal theory and von Karman s stretching are obtained Homotopy analysis method HAM is used for solving nonlinear differential equation of system and convergence region of approach presented Effects of mid plane stretching nonlocal parameter and their coupling in the model are investigated It is concluded that stretching effect is significant only for higher amplitude initial excitations and lower beam aspect ratios Moreover by including the slip boundary condition the effect of nano size flow is revealed for the nonlinear vibration model We conclude that small size effects of nano tube and nano flow have impressed critical velocity of fluid significantly specially for gas fluid Analytical results obtained from HAM solution show a satisfactory agreement with numerical solutions such as Runge Kutta Having an analytical approach we have been able to investigate the unbounded growth of amplitude of vibrations for flow velocities near the critical velocity For the rest of this survey an electromechanical model is proposed for CNTs conveying fluid and by this way the effect of applied voltage on the natural frequencies and divergence instability is investigated The Van der Waals force between the outer surface of nanotube and substrates is also included in the modeling Two methods of actuation are considered for electrostatic actuation as the single side and double side actuation We conclude that both of these methods reduce the stability of nanotube and critical flow velocities Therefore a combined method is proposed as the third method of actuation by exerting some controls based on the transverse displacement and velocity of the midpoint of nanotube The effects of considering these controls on the stability and limitation of the vibration amplitude of nanotube are revealed by determining the nonlinear dynamic response of the nanotube obtained from numerical solutions Keyword carbon nanotube CNT homotopy analysis method HAM slip boundary condition fluid structure interaction FSI microelectromechanical systems MEMS nanoelectromechanical systems NEMS

عسگري، محمودعلي

ارتعاشات ناخطي و مدل سازي الكترومكانيكي ميكروتيرها و نانو لوله هاي سيال بر

نانو لوله ي كربني , روش تحليلي هوموتوپي , شرط مرزي لغزشي , اندركنش سيال - سازه , نانو سيستم هاي الكترومكانيكي , ميكروسيستم هاي الكترومكانيكي