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.

 

In practice, structures made of concrete are full of cracks. The strength of concrete is mainly determined by the tensile strength, which is about 10% of the compressive strength. As long as cracking in concrete is unavoidable, we have to try to minimize their detrimental effects. This objective can be achieved by resisting (or limiting) propagation of existing cracks. Because of this, reinforcement (mostly steel) is used to increase the carrying capacity of the material and to control the development of cracks. Concrete structures that fail, already shows a large number of large and small cracks before their maximum carrying capacity is reached. The failure of concrete can be characterized... 

In this thesis we review several arithmetical questions about the diophantine equation φ[x]=q where φ is a nondegenerate symmetric bilinear form on a finite dimensional vector space, φ[x] is the corresponding quadratic form and q is a nonzero element of the ground field. We obtain class number and mass formulae for the orthogonal group associated to φ in a number field utilizing the concept of quadratic forms, lattices and adelic language  

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... 

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... 

The purpose of this research is to monitor the health of structures using the updated finite element model, in which digital images are used to optimize the numerical model. Structural Health Monitoring (SHM) is always an important and significant issue that has attracted the attention of many researchers in recent years. In general, some researches have been conducted in this field using physical sensors that provide discrete data to the system for analysis. Using cameras to monitor the structure makes it possible to extract continuous and integrated data from the structure using digital images, which is a significant advantage compared to physical sensors.In this research, a steel... 

In this thesis, a coarse-grained multi-scale method for 2D crystallyn solids based-on finite element consepts has presented. In this method, both scales are atomic scale and similar to what we see in non-local QC method, the entire atomic structure will be intact. Accordingly, calculations of potential functions and forces in the domain will have the atomic accuracy. In the presented method to reduce the domain’s degrees of freedom, the classical finite-element meshing concept to mesh the elastic linear areas in the domain is used and the MD calculations will done on the mesh nodes. Therefore, degrees of freedom in the system will reduce and consequently, the computational cost will reduce.... 

The purpose of this study is to investigate the effect of radiation pressure on accretion disks. The radiation density causes the separation of electrons from ions which leads to the creation of an internal electric dipole. In this study Radiation density is calculated using the Eddington limit. Afterwards radiation pressure is calculated with the use of collisions between photons and electrons in the plasma. Collisions are assumed to happen only between photons and electrons, due to the larger cross section of electrons compared to protons. The mentioned assumption causes the creation of an electric dipole and with it an internal electric field. The separation of the charges is assumed to... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

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... 

In order to increase the network performance, to discover network security threats, to guarantee the quality of services, to simulate networks and develop new network protocols, network designers and operators need software tools to analyze the network traffic. The first step to do this analysis is network monitoring. This can be done by using various software and hardware tools.
In this research we developed a tool which analyzes the network traffic using appropriate statistical methods. The models which are analyzed in this application are: Poisson, Self-similar and Weibull. This application analyzes the network traffic based on this statistical models and calculates their parameters....