Sharif Digital Repository

The use of braced frames has become more popular in seismic design of buildings because of the simplicity in design and construction. The first event that occurs in the earthquake for a concentrically brace frame (CBF), is the buckling of the strut. The inelastic behavior of CBF systems is dominated by brace buckling, yielding and the post buckling behavior. The Inelastic performance of the brace is nonsymmetrical, because of the difference in the tensile and compressive strength of the brace and the deterioration in the resistance after buckling. so we have too complexity in modeling the inelastic performance of brace members. Also the subject of the near fault ground motion and design of... 

A major concern in directional well drilling is the transport mechanism of cuttings by drilling fluid. This thesis describes the effect of angular velocity and postbuckled vibrations of drillstring on cuttings transport in a directional well drilling. The analysis proceeds in two stages. First, a finite element model is used to predict the dynamic behavior of postbuckled drillstring inside a directional well. Second, a coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) approach to simulate the cuttings transport considering the dynamic collision process. In the combined computational fluid dynamics and discrete element method (CFD-DEM), the fluid phase is treated... 

The thesis addresses the buckling and post-buckling analysis of an elastic conical shell under non-uniform axial loading using finite element method. Non-uniform axial load is applied to one end of the truncated cone in the form of two equal-length loaded zones, diametrically opposite to each other. Material used in this thesis is isotropic with linear elasticity. The results are presented for different boundary condition. The results show that the buckling strength obtained by nonlinear analysis may be upto 40% less than the buckling strength obtained by linear analysis. The effects of boundary conditions and geometry on the results has been investigated  

In recent years, the world has seen a great progress in micro electro-mechanical systems (MEMS). Small size, low weight, high accuracy and low energy consumption have made these devices applicable in a variety of usages. In MEMS devices, mechanical components are used for specific purposes among which one of the most widely used are micro plates. Microplates are used in the structure of many devices such as microswitchs and atomic force microscopes. Therefore, studying of static and dynamic behavior of microplates is important. As the object gets smaller (to the scale of micro and nano meters), the classic theory of mechanics of continuous media cannot predict the behavior due to its... 

In the present study, the energy absorption mechanism is presented that used in two-dimensional microstructures. By studying the angular geometric parameters and the narrow ratio of the tilted members, we can use the property of the geometry of the structure to be bistable. In this way, there can be two stable geometries with different energies, which enters energy into the structure, such as the phase transformation to the second geometry that has more energy. By changing the geometric parameters, the deformed state can be stable or unstable. Because of the complex geometries that exist in this mechanism, additive production methods are more effective than geometric ratios or sharp points... 

The aim of this project is buckling and post-buckling analysis of laminated composite circular cylindrical shells under external pressure on the basis of different shell theories. Based on Donnell, Love, and Sanders nonlinear shell theories within the first-order shear deformation model and von Karman geometric nonlinearity, the potential energy of composite circular cylindrical shells under external pressure with simply supported edges is extracted and by minimizing of the total potential energy and implementing the Ritz method, buckling pressure, the nonlinear post-buckling analysis and the curves of static equilibrium paths are presented. Furthermore, the effect of the external energy due...