Sharif Digital Repository

The finite-size effect in gravitational microlensing provides a possibility to measure the variation of surface brightness of stars from centre to limb which is called limb darkening profile. Measuring limb darkening profile provides information about star atmosphere. It is also useful in other fields of astrophysics. In this thesis we develop a numerical method to recover limb darkening of source stars from single lens microlensing light curves with finite source effect in which the lens transits the source disk. We use the Finite Element Method (FEM) as an inversion tool for discretization and inversion of the finite source effect integral equation. This method makes no explicit assumption... 

Existing closed form solutions of contaminant transport problems are limited by the mathematically convenient assumption of uniform flow. These solutions cannot be applied for coastal aquifers where seawater intrusion induces a variable velocity field. The Fourier series method is adapted to obtain a semi-analytical solution for contaminant transport in confined coastal aquifer in which the saltwater wedge is in equilibrium with a freshwater discharge flow. The developed method can be applied for different scenarios of contamination. Two scenarios dealing with, respectively, contaminant leakage from a source at the aquifer top surface and aquifer contamination from the landward boundary are... 

The standard model of Cosmology (SM), based on Einstein’s theory of general relativity (GR), is the best model in describing the cosmic-scale observations. In galactic scales, however, galactic dynamics show a discrepancy between the observed luminous mass and the predicted value from the theory. Two approaches are suggested to eliminate this inconsistency: assuming the existence of dark matter within the context of GR, or modifying the theory of gravity in galactic scales, like MOND or MOG. In this thesis, we study the spherical collapse and the formation of shell galaxies in MOG, in comparison with SM. We introduce the action and the field equations of MOG and the equation of motion of a... 

Invariant manifolds are important objects in the theory of dynamical systems. The stable manifold theorem is a very important theorem about this concept which proves the existence of stable and unstable manifolds in a wide range of dynamical systems. The importance of invariant manifolds encourages us to view their pictures. It helps us to understand their bahavior. For this purpose, at first we need to approximate the invariant manifold we want to visualize. There are several algorithms designed to approximate invariant manifolds. Those algorithms approximate a set of points on an invariant manifold and then provide an approximation of the manifold by the calculated points. Visualizing an... 

Electromagnetic wave scattering from objects is one of the most important problems in applied electromagnetics. Usually the electromagnetic scattering characteristic from an object is analyzed with the assumption that the object is in free space. If the object is not near other objects or surfaces this is acceptable. However if the object is near other objects or surfaces then the interactions between the scattered wave from the object and surroundings can significantly alter the scattering characteristic from the object.In this thesis we have proposed a method for the analysis of electromagnetic scattering from an object in the presence of rough surfaces. This method is based on the... 

In recent years design and manufacturing of high speed marine vessels has been developed. to estimate and control dynamics of these vessels the dynamic equation is needed.The aim of this research is Determination of hydrodynamic and aerodynamic coefficients and longitudinal dynamic equation of a high speed catamaran wich is a kind of AAMV. There are three ways to determine these coefficients. Analytical method which is usually not applicable for industrial problems, Experimental method which is too expensive and numerical method which have two parts. The first is softwares that analyse the flow with assumption that the fluid is inviscid and second softwares which solve the full Navier-Stokes... 

A finite volume algorithm to assess hydrodynamic aspects of a rigid and up to three degrees of freedom marine structure in the context of transient two-phase flow o viscous incompressible fluids is presented. Different components of the algorithm are selected just after a complete review of all probable choices. Using a collocated arrangement to save data, a fractional step method is applied to satisfy Navier-Stokes and continuity equations, as an appropriate choice in transient flows. Also, a volume fraction transport equation is solved to capture large and complex deformations of the interface between two phases. So, an effective fluid is introduced by combining two immiscible phases in... 

This study considers blood flow in total cavopulmonary connection (TCPC) morphology, which is created in Fontan surgical procedure in patients with single ventricle heart disease. Ordinary process of TCPC operation reduces the pulmonary blood flow pulsatility; because of right ventricle being bypassed. This phenomenon causes a lot of side effects for patients. A cardiac surgeon has suggested that keeping main pulmonary artery (MPA) partially open, would increase pulmonary flow pulsations. MPA gets closed in ordinary TCPC operation. The purpose of current study is to verify the effects of keeping MPA partially open on pulmonary flow pulsations, by means of computational fluid dynamics (CFD).... 

Three dimensional analyses have been carried out for predicting the behavior of the jointed rock slope of the abutments of the bridge which is proposed to be constructed across the river Karun4 in Iran using 3DEC. The rock overall slope angle is approximately 60 to 70 degrees, composed of highly jointed rock mass and the joint spacing and orientation are varying at different locations. Since 3DEC is a three-dimensional numerical code, utilizes a Lagrangian calculation scheme to model large movements and deformations of a blocky system, allows for modeling of large movements and rotations, and including complete detachment of rigid or deformable discrete blocks has been utilized for the... 

Innovations in laser, microwaves, and similar technologies have significantly advanced thermal treatments for diseases or even injuries concerning skin tissue. For a thorough understanding in the underlying mechanisms of bioheat transfer behavior of skin,a1D unsteady non-dimensional hyperbolic model of heat transfer through this tissue with metabolic heat generation which is subject to specific boundary conditions, is solved numerically using the finite difference method. A thermal shock is generated at the base of the tissue, which moves forward with a finite speed. A Numerical solution for a simple one-layer skin tissue is obtained. Then, the effects of various parameters, time step,... 

The numerical solution of differential equations in high dimensions has always been a challenge and has been associated with various computational difficulties. These equations appear naturally in a variety of problems such as financial mathematics, control, and physics, and their optimal solution with high accuracy and speed can open new windows on new applications. Conventional methods such as Finite element and finite difference method in high dimensions lose their efficiency, which is a barrier to fast and accurate calculation of these equations. In this dissertation first, we review some theoretical and practical aspects of deep neural networks and then we try to examine the recent... 

The purpose of this study is to numerically investigate the Vortex-Induced Vibration (VIV) around the cylinder, which occurs in many engineering structures, including offshore structures, offshore risers, deep-sea pipelines, bridges, cables, and tall buildings. This phenomenon is non-linear and self-limitting and is the major cause of fatigue and failure in engineering structures. At the same time, it is possible to harvest Aquatic Clean Energy from Vortex-Induced Vibration. This research investigates the single degree of freedom and two degrees of freedom oscillator. The numerical model is validated using an experimental model in the Sharif University of Technology's advanced hydraulics... 

With the process of achieving a higher state of social development and technological advances, the need for higher and more strict safety standards has been increased. In this regard, it is of great importance to have an accurate understanding of the fire phenomena and its consequences. Among the adverse effects of fire, a significant percentage of the fire fatalities is related to the fire-induced buoyant gases (smoke) flow which can lead to suffocation. Therefore, it is necessary to know the physics of the fire phenomena well. In fire investigation methods, the numerical study is an appropriate choice, because of the lower executive cost (relative to the experimental study) and the wider... 

Wellbore instability is one of the serious problems during drilling. This can cause delay in drilling, increasing drilling costs and in some cases well abandonment. The present project investigates the effects of non- isothermal drilling and the difference in salt concentration between formation fluid and drilling fluid on the stability of wellbores drilled in the saturated porous shale formations subjected to an arbitrary stress field. This project also focuses on the analysis of wellbore stability in shale formations in which the thermal diffusivity is higher than fluid invasion and the mechanism of heat transfer is dominated by conduction. The governing equations used in this dissertation... 

The main effort of this thesis is to present a numerical method to simulate and implement a special type of controllers, called proportional-weighted integral (PWI) controllers. For this purpose, at first mathematical equations of the fractional order proportional-integral controllers have been investigated in the time domain, and then by generalization of these controllers, the PWI controllers are achieved. Next the discretization of these controllers are carried out and the performance of the controllers are simulated by means of this discretization and comparison between these controllers and the conventional PI controllers has been held. After that a method for estimation of these... 

The investigation of the behavior of structures subjected to various kinds of loadings is of considerable importance. In this research, an attempt was made to analyze behavior of beams that a load is moving on them.Most of the existing relevant works in this field are dealt with examination of elastic beams with constant section, while in most cases beams with variable sections are used in order to have the optimum structure and appropriate stress distribution and to maximize strength to weight or cost ratio. While construct analysis is very advantageous, it is very difficult due to the complexities arising from the variable sections. But this design is so advantageous that it dominates... 

Theoretical studies in the analysis of sheet metal failures are referred to obtain the Forming Limit Diagrams (FLDs). Since extracting the Forming Limit Diagrams experimentally is cost and time consuming, many researches have been accomplished for obtaining these diagrams theoretically. However, in many of these researches, the assumption of plane stress state has been used to obtain the FLD, which is not correct in some processes such as hydroforming because of high level of normal stress. In this study, determination of the forming limit diagram with existence of the normal stress is based on the Marciniak and Kuczynski model. Newton-Raphson method has been used to find the set of... 

The advent of nanopore-based sensors based on resitive pulse sensing gave rise to a remarkable breakthrough in the detection and characterization of nanoscale species. The sensors can detect the species’concentration, size, and charge using the resistive pulse characteristics. Some strong correlations have been reported between the resitive pulse characteristics and the particle’s geometrical and physical properties. These correlations are commonly used to obtain information about the particles in commercial devices and research setups. The correlations, however, do not consider the simultaneous effect of influential factors such as particle shape, charge, and off-axis translocation, which... 

Flame Response to acoustic excitation which plays an important role in combustion chamber stability state may be found through numerical simulation. A finite volume code of higher order accuracy developed for compressible flows was adopted. Species equations along with a single-step irreversible reaction model were added to this non-reacting program. Changes were also made to the energy equation. Premixed methane/air flame in tubes was studied and the same problem was solved with FLUENT software. It was found that whether the Lewis number is considered constant or temperature dependent has a strong effect on flame structure and shape and that using mean values for gas properties yields out... 

Heat pipe is a device with several applications in various industries such as electronics cooling, nuclear and renewable technologies. This apparatus transfers heat from a hot source to a cold one. Thermosyphon is a special type of heat pipe that transmits heat using gravitational forces. Although scholars have performed many experiments on thermosyphon, mostly they were about the thermal characteristics of thermosyphon and rarely the hydraulic specifications of thermosyphon have been investigated. But it is clear that these two specifications (thermal, hydraulic) relate to each other closely and detailed study about their interaction may bring out better results. In this thesis, initially a...