چكيده به لاتين
According to the advances in micro/nanosctructures’ industry, it has been observed that micro/nanoelectromechanics systems are vastly being used in fabricating devices as such, mass sensors, pressure sensors, chemical sensors to measure the materials’ molar concentration, actuators and resonators in miniature scale. Among the main properties of these devices, these are the slight weight, small dimensions, ultra-sensitivity and -reliability, higher strength, and also low manufacturing costs. This thesis aims to analyze the nonlinear and chaotic dynamics behavior of capacitive nanobeams considering the influence of intermolecular interactions. The small-scale effect and surface energy effect are included in the model based on consistent couple-stress theory and Gurtin-Murdoch surface elasticity theory, respectively. The governing equations are derived using Hamilton’s principle with the assumption of Euler-Bernoulli beam theory. In order to discretize the motion’s equations into a set of nonlinear ODEs, Galerkin’s decomposition method is implemented. In this paper, the chaotic vibrations of a nanoelectromechanical system incorporating size and surface effects based on non-classical theories, together with the influence of dispersion interatomic forces has been investigated, for the first time. The NEMS devices with double-sided electrostatic actuations tend to chaotic motion since a Homoclinic orbit is developed in the system dynamics for a certain values of system parameters. In this case, in the presence of all nanosized structure effects, bifurcation analysis has been carried out in order to capture some stable and unstable ranges of the electrostatic load parameters containing DC and AC voltage amplitudes and excitation frequency. Poincare portraits are utilized to demonstrate the system dynamics in discrete state-space. Fast Fourier Transformation (FFT) has been performed to validate the obtained results from bifurcation analysis. Furthermore, for the case of one-sided electrostatic actuation, the periodic steady-state behavior of the system have been analytically analyzed via employing perturbation techniques such as multiple scales time method. The influences of size-dependency, surface energy effect, and intermolecular forces on the softening and hardening behaviors of the NEMS device have been studied in the neighbor of the primary and superharmonic resonances. As numerical simulation, shooting method has been schemed to verify the results obtained from perturbation method. The results reported in this thesis can be used in designing and controlling novel nano/microelectromechanical systems.
