Sharif Digital Repository

In this thesis, the nonlinear vibrations of the circular plate is examined using multiple scale methods and experimental tests. At first step, the nonlinear equations governing the problem are written using von Karman's assumption. In the next step, to solve nonlinear equations and calculate natural frequency, the problem is solved using multiple scale method and frequency charts are extracted as a function of the amplitude of vibration. . The design of the setup has been done in such a way that it is possible to simulate the boundary conditions. In the first phase, experimental tests was performed on a 0.3 mm thick aluminum sheet, which did not produce the desired results due to the... 

In this work, the dynamic competition between firms providing internet services is studied. The framework is Markov equilibrium whereby structural parameters are obtained using two-step estimations, allowing for analyzing the situation in case of subsidies for service upgrade. The results show that such subsidy has little effect on the number of firms while increasing the number of fast firms  

Vibration is one of the most important factors in design, operation and lifetime of drill strings. There for, investigation of vibrations in drill string, like every other rotary machine, is very important. The main goal of this research is developing a nonlinear model for a drill string system dynamics in an inclined well. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping, on the stability and vibration of a drill string are studied. Dynamic equation of the model is developed considering axial displacement and lateral bending geometric nonlinear coupling. The effect of drilling mud flow is modeled using Paidoussis formulations. Equation of motion... 

The present study is work on fabrication and characterization of a chitosan/ gelatin/ Mg substituted hydroxyapatite nano composite scaffold for bone tissue engineering. At the first step pure and Mg-substituted hydroxyapatite (HA) (Ca10-xMgx(PO4) 6OH2) nano-hexagonal rods with 14–45 nmdiameter.for this, calcium nitrate, magnesium phosphate hydrate and potassium dihydrogenphosphate were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg+2) especially from 0 to 8% (molar ratio) were incorporated as substituted into the calcium sol solution. Deionized water was used as a diluting media for HA sol preparation and ammonia was used to adjust the pH= 9.... 

The most popular system for quantification of the facial behaviors and expressions is the Facial Action Coding System (FACS). FACS provides a description of all possible and visually detectable facial variations in terms of 33 Action Units (AUs). The activation of each AU leads to a slight variation in the facial appearance, and any facial expression can be modeled by a single AU or a combination of AUs. Definition of AUs is such that they are sparse in multiple domains. The goal of this dissertation is utilizing these sparsity properties to develop an effective algorithm for automatic intensity estimation of AUs. One of the sparsity domains of AUs is the spatial domain that means the... 

MPD technique manages drilling pressure to keep bottom hole Pressure balanced in the well. The objective to this studs, is to approximate the well pressure to formation pressure to prevent entry of fluid into the well. MPD is a new method drilling in which, driller controls the annulus pressure in order prevent drilling problems. the circulating fluids system employed by MPD technology is more akin to that of a pressure vessel. In this thesis, using in laboratory-made machine, reacts with sudden changes in pressure at the bottom hole in the shortest possible time. Basically, this system is a system where well bore pressure management is obtained by adjusting the pressures along the well bore... 

Fractured reservoirs constitute a major portion of world’s petroleum reservoirs. Gravity drainage is the controlling production mechanism in these reservoirs. Thus, investigation of performance and oil production in fractured models has been the subject of many researches. Despite the considerable number of experimental and modeling studies in this area, the method of scale-up in single or multi block models is not broadly investigated. This work is divided into two experimental and modeling sections. For the experimental study, free fall gravity drainage experiments in synthetic single or multi block porous media were performed in order to investigate effects of different parameters... 

Today, one of the main concerns of steelmakers is the production of clean steel and the removal of non-metallic impurities in the melt. And in the present project, which is the production of clean steel with the minimum amount of oxygen content, firstly, the studies of clean steels and impurities in steel, the quantity, quality and gender of the impurities and also the methods of reducing them until Achieving clean steel is also considered to deoxygenate the steel and reduce the amount of oxygen to the minimum amount. Of course, it should be noted that the type of inclusions investigated in this study will be aluminum inclusions and the results will be analyzed according to the presence of... 

Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

In this study, free vibration analysis of moderately thick rectangular FG plates with general boundary conditions is investigated. Governing equations of motion are obtained based on the Mindlin plate theory. A semi analytical solution is presented for the governing equations using extended Kantorovich method (EKM). Results are compared and validated with available results in the literature. Effects of different parameters such as boundary conditions, material and geometrical parameters on natural frequencies of the FG plates are investigated  

Water injection is one of the main methods of enhanced oil recovery that its success depends on exact study of main effective parameters. Saturation functions including relative permeability function and capillary pressure function are one of the effective parameters on the success of water injection projects. In many reservoirs there is wide heterogeneity and various layering that have different absolute permeability. These features result in uncertainty to measurement of curves of saturation function. Experimental studies on this field are carried out on the composite cores that show heterogeneity and layering media of reservoir. By Scaling up the saturation functions from single cores to... 

Road construction and maintenance constitute a significant part of country-wide infrastructure development budget each year. This indicates the importance of planning and design of individual road alignment in reducing the development cost. This study presents a meta-heuristic algorithm based on the concept of electromagnetism, which explores and finds a good route between two given points within a three-dimensional (3-D) context. It defines the region in a continuous 3-D surface, identifies initial routes, which are directed and shaped toward better positions by the help of local and global search. The final good solution is fine-tuned to produce a better alignment. The behaviour of the... 

The goal of this thesis is modeling and simulation of aircraft landing motion in order to evaluate the performance of an optimal anti-skid brake system (ABS) for the main landing gears with friction effects. In this process, the aircraft 6DOF perturbed equations of motion augmented with pertinent friction and brake forces and moments have been utilized. Subsequently, the problem is formulated within the framework of an optimal LQR that has allowed for generation of control brake commands as well as aircraft landing performance at different landing conditions with and without the proposed ABS. The results demonstrate the proposed ABS has been effective in providing admissible landing... 

Due to the increase in the number of people interested in learning new languages, in recent years, multiple systems have been developed to teach new languages to those who are interested. These systems are called Computer Assisted Language Learning (CALL). However, the most credible CALL systems, like Duolingo, do not support Persian. So the of this study is to design and implement one of the technical parts of CALL systems, the Computer Assisted Pronunciation Training(CAPT), which is the part responsible for evaluating the learners' input voice's pronunciation and generating appropriate score and feedback.In this study, good pronunciation means correct expression of words, correct... 

Spin-Transfer Torque Magnetic RAM (STT-MRAM) is the most promising nonvolatile memory to replace SRAM technology in the Last-Level Cache (LLC) due to its benefits such as high density, near-zero cell leakage, and immunity to soft errors.However, due to its high retention failure and read disturbance rates in the downscaled technologies and the low data access rate in the LLC and the high number of read accesses, retention failure and read disturbance have become the main reliability challenges for STT-MRAM cache memory. The existing approaches to overcome these challenges impose significant area and performance overhead or adversely affect the other types of failures. In this thesis, we... 

It is the main idea of present thesis to provide a micromechanical method as a general treatment for several fundamental problems of the piezoelectric inhomogeneities. For initial demonstration of pertinent methodology, a single piezoelectric inhomogeneity of ellipsoidal geometry, under non-uniform far-field loading is considered. Accordingly, it is taken equivalent to elastic and dielectric inclusion problems connected by proper eigenstrain-electric field. This approach is named the electro-mechanical equivalent inclusion method (EMEIM) and requires that the electroelastic fields of the inhomogeneity to be equal to fields of the equivalent inclusions. Afterwards, the complex problem of... 

Traditional continuum theory of elasticity becomes remarkably inaccurate in the vicinity of singularities, and when the size eect is of concern. For example in the study of ultra-small objects and ultra-thin lms, near defects, near point of application of a concentrated load and as such, the classical solutions are not reliable. This work focuses on determination of the elastic elds of an edge dislocation near the grain boundary of two perfectly bonded nano-size crystals. It is proposed to study this problem in the context of surface/interface elasticity, and incorporate the eect of the grain boundary on the elastic elds. In contrast to the surface/interface elasticity theory, traditional... 

Most of the heavy oil reservoirs contain discontinuous shaly structures which affect fluid flow through porous media as well as oil recovery efficiency during EOR processes. However, selecting the best EOR technique which maximizes the oil recovery remains a topic of debate in the literature. In addition the effect of shale geometrical characteristics including: spacing from wells, discontinuity, orientation, number of shale streaks, shale's spacing and length on oil recovery factor are not well understood. In this work experiments have been performed on one-quarter five-spot glass micromodels. These models have been developed by a new method using laser technology. Generally, this research... 

The  usual  continuum  theories  are  inadequate  in  predicting  the  mechanical  behavior of solids in presence of small defects and stress concentrators; it is well known that such continuum methods are unable to detect the change of the size of  the  inhomogeneities  and  defects.   For  these  reasons  various  augmented  continuum theories and strain gradient theories have been proposed in the literature. The major difficulty in implication of these theories lies in the lack of information  about  the  additional  material  constants.  For  fcc  metals,  for  calculation of the associated characteristic lengths which arise in first strain gradient  theory,  an ... 

It is well known that the classical continuum theory does not consider size effect in predicting material’s behavior, however at the micro and nano scales, this effect is not negligible and the classical theory has deficiencies at these scales. To take into account the size effect, higher order continuum theories introduce new material constants into the formulation. One famous version of these theories is couple stress which is applied in this research. This theory considers size effect of inhomogeneity by employing Characteristic length of materials. Quasi-static couple stress and classical dynamic approaches do not include explicitly the size of the material unit cell in the formulation...