Sharif Digital Repository

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... 

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... 

Nowadays there are various means in the field of orbital mechanics used in different levels and their accuracy depends on the theory and complexity of the governing equations used in their development. Most of them just simulate the motion of an orbiting satellite while there exist some commercial products able to provide the user with the orbital performance specifications and almost none of them have a module to design an orbit, based on a required performance such as specific coverage / ground track, shadow/light duration, etc .... Although satisfying performance requirements and a set of orbital elements simultaneously only seems to be possible for some particular orbits, there is an... 

Various applications of speech processing systems are gaining more and more attention. Performances of these systems are dramatically affected in presence of background noise. Attempts toward improving quality of degraded speech have emerged into filed of speech enhancement which is one of the interesting topics in speech processing domain. In this thesis various single channel speech enhancement methods are studied briefly. Statistical methods as one of the most successful methods are studied more deeply. These methods are divided into two categories of short-term modeling of speech and long-term modeling. The aim of this thesis is to improve the performance of long-term methods of... 

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... 

Direct/inverse scattering of high frequency SH-waves by a circular micro-/nano-fiberembedded in an infinite elastic isotropic medium is addressed in the framework of couple stresstheory with micro inertia. The inadequacy of classical theory of elasticity in the problems dealingwith propagation of high frequency waves as well as the problems concerning the elastic fields inthe vicinity of micro-/nano-size defects in which the wavelengths and the size of the defects arecomparable to intrinsic length of the material is well-known. These dilemmas can be remedied byemploying the more accurate higher order continuum theories. So, in the context of couple stresstheory with micro inertia, the... 

One of the most important parts of vehicles and most of mechanical machines is power transmission system, especially the Gearbox used in them.In order to optimize the use of energy, especially fossil fuel, researchers are looking for new mechanisms to refine the operation of vehicles and other machines.One of the mechanisms which absorbed researcher’s attention during recent years is the Continuously Variable Transmission. By using these gearboxes which are replaced with older samples, we can have the continuous range of aspect ratio between two constant values. This important property causes the decrease of the use of fuel.In recent decades many manufacturers have used different kinds of... 

There are different classes of event-driven softwares. These softwares include Graphical user interface, web application or embedded software. In these kinds of softwares, each user's action while using application is known as "event". The application responds to the action through changing behaviour and then waiting for another event. Testing software is the best way for checking the quality assurance of event-driven softwares. However, there are some problems as cause of creating lots of event sequences in testing these kinds of softwares. Therefore, many solutions are introduced for these problems. The goal of this report, is presenting new testing procedure for event-driven web... 

After discovery of superconductivity in 1911 people try to find superconductors with higher Tc. High Tc superconductivity in cuprates and iron based superconductors was discovered in 1986 and 2008 respectively. However, there is not any unit theory for high Tc superconductivity in cuprates or iron based superconductors. Study of electronic and phonon structures of high Tc superconductor compounds can lead to find theory of high Tc superconductivity.
In this dissertation electronic structure of Ba1-xKxFe2As2, which belongs to class of 122 of iron based superconductor, under potassium doping x=0,0.5,1 has been studied. To this end ab-initio method and Density functional theory have been... 

Flight control system (FCS) design, analysis and modeling has an important role in aircraft design and development process. However, FCS analysis and studies are rarely focused at university levels and its know-how and technical issues are almost proprietary to various aircraft industries. One of the key goals of this thesis is to express, introduce and implement the processes that need to be followed for a sample longitudinal reversible FCS design (RFCS), where the modelling aspects are described for an existing aircraft. The latter is achieved using existing drawings, system and aerodynamic data of an existing aircraft utilizing commercial tools such as CATIA for initial design and ADAMS... 

The discovery of Iron-based superconductors with maximum transition temperature of 56 Kelvin and High critical magnetic field of the order of 50T at temperature 20K has created evolution in different fields of superconductivity including practical issues. BaFe2As2 family is one of the most important compounds of Iron-based superconductors and with different doping elements for instanse elements of the first column like Potassium inters superconducting state with critical temperature of 36K.
The purpose of this thesis is to localize the technology of making this compound in Iran which no project has been done in this field in the country before. In this thesis manufacturing, Optimization... 

Design and construction of an optical fiber sensor for liquid concentration detection are reported. This sensor operates based on light intensity modulation.Such modulation results from alteration of total internal reflection into partial reflection at the interface. It is well known that the extinction ratio is varied by changing the concentration.In this system,two optical fiber swere used, one transmitting the light source, another acting as the receiving fiber and a glass prism providing the total and partial reflections. The modulated intensity has been measured by using a receiving fiber. During the concentration measurements, when a liquid in a vessel touches the 45° faces of the...