Sharif Digital Repository

The electro-elastic fields of nano-sized piezoelectric structures are considered based on the non-classical continuum theory. Nowadays because of increasing the application of piezoelectric materials in nano technology and exclusive properties of this kind of materials, they can use as the ingredients of electromechanical systems. Therefore, the determination of induced electro-mechanical fields is important. In this study the constitutive equations based on non-classical continuum theory and general anisotropy for the elastic, piezoelectric and dielectric tensors are considered, and the electromechanical fields are determined using the micromechanical method. Furthermore, the size effects... 

With the progress of engineering science, the development of underground spaces and buried tunnels has witnessed remarkable expansion. Considering the frequency of hazardous events such as earthquakes and unforeseen consequences arising from underground activities and geology in underground engineering, the determination of the Dynamic Stress Concentration Factor (DSCF) has been widely recognized as a crucial factor in the study and design of tunnels and underground structures. It is also extensively considered in evaluating their damage. The investigation of wave dispersion and determination of the stress concentration factor was first proposed by Sezawa (1927). In this study, the... 

Meshless Methods using kernel approximation like Reproducing Kernel Particle Method (RKPM) are methods for solving partial differential equations that require only nodal data and a description of the geometry without requiring element connectivity data and mesh producing. An innovative method of nonplanar material partitioning method (NMPM) with implementation of RKPM is employed to calculate the stress intensity factor (SIF) at the tip of an anticrack sited in an isotropic plate under a remote applied loading. Numerical examples in comparison with the exact closed form expressions show that accurate SIF for mode I can be obtained.

 

By considering the effect of surface/interface stresses, classical problems of the interaction between dislocations/disclinations and nanowires are addressed. In particular, two distinct problems are solved: the first one consists of an edge dislocation seated inside the shell of a core-shell nanowire and the second one investigates a wedge disclination (dipole) located inside the shell of a core-shell nanowire. The stress field of the nanowire, strain energy per unit length and the image forces acting on the defects are calculated and discussed in detail. Moreover, the results are compared with their classical counterparts. These results show that by considering the effect of... 

The environmental pollutions besides wasting the valuable materials as two main challenges in pyrometallurgical processes have brought up the tendency towards the hydrometallurgical processes. In the present study, the recovery of germanium from leaching residues of zinc plant has been investigated. Firstly, the required tests for concentrating the residues through washing of the zinc were designed by taguchi method, and optimum condition for maximum leaching of zinc accompanied by minimum desolution of germanium were obtained. The sulfuric acid concentration, time, termperature of reaction, solid to liquid ratio and rate of stirring are the parameters studied in this research. The obtained... 

For half a century, the problem of extracting the components of the nonlocal moduli tensor of anisotropic materials has been remained unsolved. In the present work, for the first time, the solution of this problem is proposed and the components of nonlocal moduli tensor are obtained for close-packed crystals, i.e. face center cubic or hexagonal closed packed. To this end, new distinct nonlocal kernel functions which have the characteristics of discrete atomistic Green’s functions in the stress space are obtained through consideration of the nonlocal dispersion relations. Each of dispersion relations are associated with certain directions and are combined with ab initio Density Functional... 

This research is concerned with the investigation of forced time–harmonic vertical vibration of a rigid disk embedded in a transversely isotropic full space medium. By properties of integral transform methods, the generalized mixed boundary–value problem is formulated as a set of dual integral equations, which in turn, are reduced to a Fredholm equation of the second kind. The obtained Fredholm integral equation is solved by well-known numerical methods. Selected results for the load distribution on the disk and complex compliance are presented for various ranges of frequency.

 

The following dissertation examines the interaction between the free surface of a homogenous transversely isotropic half-space and a rigid circular foundation. The whole system is under a vertical and an inclined point loads applied simultaneously on the foundation and at the specified depth of the medium, respectively. Determination of the Green’s functions for the proposed mixed boundary value problem is of interest. By employment of the boundary conditions, the governing equations are represented in terms of a dual integral equation which are subsequently solved analytically. Furthermore, the exact closed-form expressions of the tilt (rotation and settlement) of the loaded rigid foundation... 

In this thesis, pull-in of nano/micromirrors under effects of capillary, Casimir and van der Waals (vdW) forces is investigated based on two models. In the first model, only rotation of torsional beams of mirror is considered. In the second model, effect of bending of the torsional beams is also considered. The static behavior of the mirror under capillary, Casimir and vdW loading are also studied using these models. Results show that neglecting bending effect, can lead to considerable overestimation in predicting the pull-in limits of the nano/micromirrors under these forces. Results reveal that the static behavior of the nano/micromirrors under these forces highly depends on 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... 

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... 

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... 

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...