Sharif Digital Repository

In a classical finite element approach, interfaces are tracked and meshed. This mesh strategy introduces mesh distortions and difficulties to mesh the possibly complex interface shape. The Partition of Unity Method (PUM) alleviates these difficulties by allowing the discontinuities to be mesh-independent. This thesis concentrates on the blending elements in the eXtended Finite Element Method (XFEM).
The XFEM method enables local enrichments of approximation spaces. The standard finite elements are used in the major part of the domain and enriched elements are employed where special solution properties such as discontinuities and singularities shall be captured. In the extended finite... 

There are various physical phenomena involving discontinuities and interfaces. The finite element method (FEM) has become the most popular and influential analytical tool for solving these physical phenomena. In the analysis of progressive failures because of discontinuities and interfaces, the mesh adaptive refinement in diverse stages of process is of great importance and, at each stage the mesh conforming to the shape of the interfaces is not inconsiderable. Consequently, the requirement of mesh adaption may necessitate high expenses of time and capacity. In contrast, the extended finite element method (XFEM) has been developed to efficiently perform modeling of problems including... 

Sodium Hydroxide production industry is among the largest chemical industries that annually produces 66 million tons worldwide. NaOH which is produced through electrochemical cells needs to be further enriched. The use of membrane technology as a substitute for conventional processes has been a point of interest. Thin film composite membrane is among favorable membrane because of its ability to be customized layer by layer individually. In this thesis, for the purpose of making an optimized membrane for NaOH enrichment, we studied the preparation conditions and witnessed that by increasing MPD from 1.5 %wt. to 4.5%wt. The flux experiences a minimum at 3.5%wt, which is the maximum for... 

When a crack is subjected to a compression field, it will close and its edges will get into contact with each other. Depending on the direction and magnitude of the loads and also the coefficient of friction, ‘stick’ or ‘slip’ situationsbetween the edges will occur. This type of crack is known as ‘frictional crack.’ In this project, first these cracks are studied analytically and the order of singularity is derived using asymptotic analysis and also the analytical fields are determined for both ‘isotropic’ and ‘orthotropic’ materials. Then, numerical simulations are carried out using extended finite element method which is considered as the most powerful means for analyzing the problems... 

In various industries, for energy production, fossil fuels are burned. Oxygen needed for combustion, taken directly from the ambient air; So that the inert gas is about 80%. The presence of this inert gas, mainly nitrogen, reduce combustion efficiency and increase the use of combustible material. In this project with the help of membrane technology, was used to remove the amount of nitrogen in the air so that the incoming air into the combustion chamber is enriched with oxygen. For this purpose, several gas separation membrane was applied and evaluated. Then, according to the oxygen enrichment, fuel efficiency and the amount of savings, increasing chamber temperature, reduction manufacturing...