Sharif Digital Repository

Sandwich plates have been used in wide range of aerospace, civil, marine and petroleum applications due to their high stiffness-to-weight ratio and load-carrying capability. In most of practical applications in aerospace, marine and offshore industries, sandwich structures are surrounded by a fluid flow e.g. water and air which causes the significant effects on their design parameters namely natural frequency and buckling load. In the present study, Based on the Kirchhoff-Love theory within von Kármán’s geometric nonlinearity, the nonlinear vibration analysis of multilayered sandwich plates subjected to potential flow (inviscid and incompressible fluids) is presented. Rectangular sandwich... 

In this study, the linear dynamic response of an inclined FGM Timoshenko beam on linear viscoelastic foundation subjected to a traveling mass with constant and variable velocity is investigated. Timoshenko beam theory and von-karman strain-displacement relations are utilized to model the problem. the FGM beam is made of metal and ceramic and it is assumed that material properties of the beam vary continuously in the thickness direction according to the exponential law and the power-law form. The kelvin-voigt damping model is applied to model the internal damping of the FGM beam. The partial differential equations of motion for the bending rotation of cross-section, longitudinal and... 

In this thesis, we investigate interactions of a double-gyre in the North Atlantic and the earth’s Chandler wobble using a single-layer ocean model based on depth-averaged Navier-Stokes equations and multiple-scale spectral solutions to it. The overall transfers of energy and angular momentum from the double-gyre to the Chandler wobble are used to calibrate the turbulence parameters of the idealized ocean model and Smagorinsky eddy viscosity is used to estimate turbulent diffusion terms. Our model is tested against a multilayer quasi-geostrophic ocean model in turbulent regime, and base states used in parameter identification are obtained from mesoscale eddy resolving numerical simulations.... 

In the present study, the buckling of generally laminated truncated conical shells having thickness variation expressed by a linear function, subjected to axial compression with simply or clamped supports has been considered. To begin with, the fundamental relations for a conical shell with variable thickness have been derived applying thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy; non-linear terms of Donnell equations by the help of adjacent-equilibrium criterion are linearized. Governing equations are solved using power series method and are applicable for all combinations of classical boundary conditions. The results are validated with Galerkin... 

The turbulence in the atmosphere will limit the performance of astronomical telescopes on the ground thus a technique for solving this problem is needed that is Adaptive optics technique. We know Adaptive optics in its simplest definition as a process to improve the quality of image by means of deformation of the wave fronts to compensate the beam path anomalies. The main components of this system are the wave front sensor and deformable mirror. Deformable mirror is used in the system of this technique also plays an important role in the correction of anomalies of eye. Type of actuators that can be used for deformable mirror, pattern of them, and also the way of connecting the actuators to... 

Micro and nano electromechanical systems technology has experienced lots of progress in recent years. These systems are widely used in sensors and actuators due to their small size low weight and low energy consumption. Electrostatically actuation is one of the simplest and most prevalent methods of actuation and sensing in these systems. Electrostatically actuated micro and nanobeams are used in many devices such as micro and nano switches, resonators, signal filters, tunable capacitors, pressure and mass sensors, etc. Experimental results and measurements have shown that classical theories contain error in prediction of static and dynamic ... 

Microelectromechanical have wide application in mechanic, aerospace, medical, transport and information technology.
Due to large scale application and production, low costs and low energy consumption, these systems have been used in wide range of fields of engineering. Electrostatically actuated microbeams are extensively used as microelectromechanical systems (MEMS) such as microswitch and microresonator. The main component of electrically driven is microbeam. Microbeam acts as top surface of a capacitor with fixed bottom. The capacitance of capacitor changes due to the deflection of the microbeam. In this study static deflection of electrostatically actuated microbeam has been... 

In this thesis, a reduced model of a distributed one-dimensional Solid Oxide Fuel Cell (SOFC) system is presented. Consequently the reduced model is used to estimate the states of the exact model. The reduced model is derived using the exact solution of the distributed model and implementing the Karhunen-Loève-Galerkin procedure. To achieve an exact solution of the distributed model, method of lines is used. In the method of lines, accuracy of the solution depends on the number of grid points. To increase the accuracy, the number of grid points should be increased which will lead to a high order dynamic model. Such a model is not suitable for state estimation, optimization or control... 

In this dissertation, hybrid meshless method for electromagnetic wave scattering has been presented. The idea of the dissertation is the use of two robust meshless shape functions i.e. MLS and RPIM simultaneously to solve differential and integral equations from 3D scattering equations respectively. Finite element method (FEM) and method of moments (MoM) are used extremely for computing scattering problems. These methods are powerful and their results are accurate enough. One of their disadvantages is the need of mesh generation. Mesh generation in FEM is a time consuming process. Furthermore, in electromagnetic problems that involve geometrical, the use of an underlying mesh creates... 

High power, broadband amplifiers at microwave and millimeter wave frequencies are needed for military and civilian applications. High power, broadband, high linearity, low noise, high efficiency and graceful degradation on failure are among the most important features in amplifier design. Solid state and vacuum tube devices have many disadvantages. A promising solution has been spatial power combining technique. Spatial power combining is a method of coherently combining the power of many amplifying devices using free space as the power dividing/combining medium within a guided wave structure in contrast to traditional circuit based amplifiers. This thesis presents the design and fabrication... 

In this thesis we study sharp spatial and temporal mean-square regularity results for a class of semi-linear parabolic stochastic partial differential equations (SPDEs) driven by infinite dimensional fractional Brownian motion with the Hurst parameter greater than one-half. In addition, the mean-square numerical approximations of such problems are investigated, performed by the spectral Galerkin method in space and the linear implicit Euler method in time. We see that by using the obtained sharp regularity properties of the problems one can identify optimal mean-square convergence rates of the full discrete scheme. At the end, these theoretical findings are accompanied by several numerical... 

In this thesis we study Galerkin methods for semilinear stochastic partial differential equations (SPDEs) with multiplicative noise and Lipschitz continuous nonlinearities. The strong error of convergence for spatially semidiscrete approximations as well as a spatio-temporal discretization which is based on a linear implicit Euler–Maruyama method, are also investigated. We see that the obtained error estimates in both cases as well as the regularity results for the mild solution of the SPDE are optimal. The results hold for different Galerkin methods such as the standard finite element method or spectral Galerkin. At the end, these theoretical findings are accompanied by several numerical... 

In this thesis, we consider an implicit approximation scheme for the stochastic heat equation with additive and multiplicative space-time white noise. we use the spectral Galerkin method in space combined with the linear implicit Euler method in time to simulate weak approximation error