Sharif Digital Repository

Alumina as an engineering ceramic has special characteristics such as hardness, high abrasive, fatigue and corrosion resistance but suffers from low toughness. One effective method in improving toughness is adding second phases such as tetragonal zirconia and carbon nanotubes.
In this research, alumina- zirconia nanopowders has been prepared by solution combustion method and carbon nanotubes was added to it by two different ways: 1) in situ synthesis of CNTs by CVD 2) dispersion of CNTs by heterocoagulation method. In the case of in situ synthesis of CNTs in AZ matrix, the synthesis temperature and flow ratio of N2/C2H2 gases was investigated and optimum conditions were 800̊C and 300/30,... 

Wireless Sensor Network (WSN) is a rapidly growing technology that is used to meet different requirements of a wide range of applications. Energy conservation is one of the main design challenges in WSNs due to limited energy resources. Routing plays a significant role for energy efficient communication in WSNs. Although there are many research studies that utilize energy efficient routing to conserve energy in WSNs, there are a few works that took advantage of machine learning techniques for saving energy through energy efficient routing.The main goal of this thesis is to indicate that machine learning is a functional approach to many problems in WSNs. To fulfill this goal we first... 

In respiratory system of live bodies, different mechanical phenomena such as air suction, diffusion and deposition of particles and transport of species between air and blood take place. Furthermore, the geometry of lung is a complex and multi scale geometry. In order to reduce these complexities, the acinus behavior is transformed to numerical functions which can be used as boundary conditions for simulating upper generations of the lung. Hence, in current study, the air flow suction of the lung is described as a function of the mechanical properties of the lung tissue. This task is fulfilled by modeling the flow for different Elastic moduli and taking fluid structure interaction into... 

After three decades of research, the concept of emotion as an aspect of initelligence in artificial systems, is still unclear. Most of emotion models in AI are aimed to simulate the emotional states of human in differenct levels of abstraction and functionality. Therefore, the concept of emotions in artificial systems is completely dependent on human being’s emotional states and can not be used as a general tool for improving the intellingence of artificial systems. In this thesis, we have tried to show that defining emotion in a more abstract level can expand the domain of its appications in AI. According to some existing theories about emotions, we modeled emotions as local semi-soloutions... 

Two methods for simulating material behavior of heart mitral valve leaflet tissue are developed in this thesis, in the finite element setting. First, a mixed pressure-displacement formulation is used to implement the constitutive material behavior with general 3D elements. Second, a shell is formulated that incorporates the 3D material behavior by use of a local plane stress iteration method. Both of these works are based on an existing invariant-based strain energy function that has been experimentally determined for the mitral valve leaflet tissue. Since this material is considered to be nearly incompressible, a mixed pressure-displacement (u/p) formulation is needed to apply the material... 

Hydraulic fracturing process as one of the most important ways to inhanse of production requires careful study and investigation and due to its importance has been studied for decades. The effect of this process on the production at oil and gas industry has many complexities and these complexities with the complex structure of natural gaps, would be multiplied. In this thesis effect of hydraulic fracturing operation on the production of natural fractures at naturaly fractured reservoirs from two aspects of hydraulic and geomechanics will be investigated. First we provide models for fractures network by using UDEC software after that investigate the effect of hydraulic farcture on the natural... 

One of the key issues in the operations of on orbit servicing to unmanned satellites is to provide a safe and reliable docking process. In this thesis, the dynamic behavior of a flexible probe in the central docking mechanism of unmanned satellites is investigated. For this purpose, first a dynamic analysis software has been applied to build a three dimensional model with the assumption of flexible clamped beam as a shock absorber, finally, the impact phenomone is simulated. therefore, in addition to solving a three-dimensional problem and studying the impact phenomenon between chaser and target satellite, it is possible to consider the parameters such as the type of connection between the... 

In this thesis, we investigate the theoretical and experimental vibrations of a cylindrical shell with an electrorheological core. Magnetorheological and electrorheological fluids are the most suitable materials used in smart structures and have various applications in the automotive, aerospace, civil engineering, medical engineering and robotics industries. We use starch particles and silicone oil to make electrorheological fluid. Then we make a sandwich beam with an ER core and extract the modal parameters of the structure using the modal test. Using the ASTM standard, we estimate the shear modulus of the fabricated ER fluid. In the following, based on the equations developed for the...