Sharif Digital Repository

Tapering the beam along its length may lead to an increase in the voltage density of piezoelectric energy harvester. In this study, the energy harvester voltage with linear variable cross section is studied by developing an analytical method in both linear and nonlinear states. In linear mode, the results are compared with the experimental results. For the development of linear and nonlinear analytic relations, the Euler–Bernoulli beam and linear voltage variations in the thickness direction are used, and for the separation of variables, the mass normalized mode shapes has been used. The results of the linear analytical method are compared with the results of past research and experimental... 

The main purpose of this dissertation is to study thermoelastic behaviors in rotating disks subjected to thermal shock loads based on the generalized and classic theories of coupled thermoelasticity. To this end, this research has been carried out in two stages. In the first stage, thermoelasticity problems in an axisymmetric rotating disk with constant thickness made of a homogeneous isotropic material are analytically solved. In this stage, based on the classical and generalized coupled theories, and dynamic and quasi-static uncoupled theories, an analytical method based on the Fourier-Bessel transform is employed to obtain the thermoelastic solutions. Then, closed-form formulations are... 

Evolution of electrical devices and the need for wireless sensor and remote control has led to extensive research in field of energy harvesting. Regarding this approach, most studies devoted to use of piezoelectric effect in converting the dissipative vibration energy into usable electrical energy. Despite extensive progress made in this field of engineering, there were no significant growth in analytical solution and implementation of mathematical equations related to dynamic and electricity of piezoelectric harvester of beams with different geometries. The main focus of this thesis is solving constitutive and coupled electromechanical equations of piezoelectric harvester related to a... 

Typical thermoacoustic systems deal with the conversion of heat energy to sound energy and vice versa. Recent advances in the field of thermoacoustics have altered the working mechanism of many conventional heating and cooling devices. These systems have three highlighted advantages: first, they have simple structure, no moving parts, low cost of manufacture, and high reliability; second, by using inert gases as working fluid, they are environmentally friendly; and finally, heat driven thermoacoustic devices can be driven by low quality energy sources such as waste heat and solar energy.
The main focus of the present thesis is on the application of the thermoacoustic technology in the... 

Vibrations with high amplitudes in continuous systems and models with multiple degrees of freedom, in specific conditions, is concomitant with a phenomenon called internal resonance. In the presence of this phenomenon, energy is transferred from one directly excited mode to the other vibrating modes of the structure results in response of the structure to be combination of the excited modes. In that situation occurrence of the internal resonance may decrease the level of undesired vibrations of the structure. This behavior is of interest especially in sandwich structures with viscoelastic cores that are designated to improve the damping characteristics of the structure and the property may... 

In the present study, an analytical procedure has been presented to analyze a generic two-dimensional frictional multiple contact problem between two isotropic, homogeneous and elastically similar half planes, under the constant normal (including applied moments) and oscillatory tangential loading, with partial slip behavior. This procedure is based on the classical singular integral equations approach. By applying boundary conditions at nonsingular end points, new side conditions have been derived and titled “the consistency conditions” for multiple contacts. These conditions are necessary for determining the position of nonsingular end points, when the number of them exceeds the number of... 

The meaning and the nature of space and it’s essential properties seems to be one of the oldest problems which has been continuing to occupy human’s mind during centuries. It can be counted as a common ground between philosophy, mathematics, physics and even art. However this thesis concentrates on the philosophical and mathematical attitudes, neglecting the other aspects of the issue. Prima facie, it appears that the concept of space is essentially mingled with geometry, the science which seems to investigate the essentials of space. Taking it for granted, Kant regarded space, and so Euclidean geometry which dominates it, as an indispensible and necessary structure of the human’s mind.... 

Since speaking seems to be the foremost skill in language learning, the evaluation of speaking ability has become increasingly important in recent years. Moreover, research on rater effect in speaking performance assessment has provided evidence for a considerable degree of variability among raters. This study investigated the use of holistic vs. nalytic rating scales in rating Iranian EFL learners‟ speaking performance. Moreover, the current study explored the effects of gender and experience on raters‟ rating in rating Iranian EFL learners‟ speaking performance applying holistic vs. analytic rating scales. The effects of ater variables (gender and experience) on weighing components of... 

Groundwater resources in arid and semi-arid regions, which the most parts of them have not had enough surface water, is of great importance. Due to the paramount importance of these vital resources, many scholars have conducted various studies on groundwater contamination and, especially, on nitrate as the best indicator of groundwater contamination because of its ability to transport, its low absorption, and its durability in water. In this study, using qualitative methods, groundwater contamination of Mashhad aquifer was evaluated, and then in order to obtain better adjustment with urban areas, these methods were modified which resulted in better correlation with measured nitrat. Based on... 

Arcs and rings are used extensively in structures such as submarines and bridges due to their particular geometry. On the other hand, in multi-part rocket, due to the high temperature gradients, they form the fastening rings of functional materials (FGM). Considering the importance of this structural element, in this thesis, linear and nonlinear behavior (including bending and post-buckling) of rings made of functionally graded materials under different types of thermo-mechanical loading has been investigated. First, the governing equations are derived from the principle of minimum potential energy, based on the two theorems of Donnell and Love. Donnell's theory equations are solved... 

Forced convection in a parallel plate channel filled by porous medium, with walls held at constant heat flux is investigated. A criterion for employing a local Thermal Equilibrium assumption between solid matrix and fluid in a porous channel is developed. Darcy-Brinkman-Forchheimer momentum equation is solved by Homotopy perturbation method. The energy equation for solid and fluid phases employing Local Thermal Non Equilibrium (LTNE) assumption is solved for fully developed and thermally developing forced convection. The analysis leads to an expression for fluid and solid temperatures and also the local Nusselt number. The effect of pertinent parameters such as the Darcy number, the Inertia... 

The potential of phase change process in liquids at microscale has been a favorite for the scientists to fabricate this type of micropumps. To hold unidirectional flow in microchannels usually nozzle-diffuser arrangement is used. Due to the existence of difference in pressure drop in the nozzle and diffuser sections, one can see unidirectional flow through diffuser direction. The objective of this article is to analyze analytically the thermo-hydrodynamic behavior of the Isopropyl Alcohol (IPA) bubble of a phase change micropump. Considering the simultaneous effects of hydrodynamic and thermal characteristics of the bubble in the bubble generation chamber, and temperature-saturation... 

In tis study, 4 approaches were applied for estimating Minimum Miscibility Pressure (MMP). An oil sample from Norooz and Soroosh field has examined by means of association gas of foroozan field and Carbon Dioxide gas in experimental approach.the experimental method used for estimating MMP in Slim-tube. This kind method is applied in industry widely. The results indicate that the MMP of Carbon Dioxide and Norooz field oil is 3538 psi and with Soroosh field oil is 3650psi. the MMP of foroozan associated gas and Norooz field oil is 5643 psi and MMp with this gas and soroosh field oil not estimating  

Metagrating is a new concept for wavefront manipulation that, unlike phase gradient metasurfaces, does not suffer from low efficiency and also has a less complicated fabrication process. However, they have some drawbacks, which we are trying to resolve in this thesis. First, a compound metallic grating is proposed for anomalous reflection. We propose an analytical method for analyzing the electromagnetic response of this grating and show that the structure can have unprecedented near-to-unitary efficiency. Next, two-dimensional (2D) metagratings are proposed for diffraction pattern control. We first present an analytical method for diffraction analysis of 2D compound metallic grating. As a... 

The demand for electrical energy is increasing. The main source of energy at this moment is fossil fuels. High price, great amount of pollution, uneven distribution and global warming are major disadvantages of fossil fuels. Using renewable resources can tackle these issues. Hence, the demand for renewable energy are highly increased. The wind energy is one type of renewable energy. Increasing the wind power penetration impairs the functionality of power system and causes the environmental issues. In order to have a stable power system this effect should be investigated thoroughly. Due to the inherent uncertain characteristics of wind energy, it is desirable to determine the characteristics... 

The standard model of Cosmology (SM), based on Einstein’s theory of general relativity (GR), is the best model in describing the cosmic-scale observations. In galactic scales, however, galactic dynamics show a discrepancy between the observed luminous mass and the predicted value from the theory. Two approaches are suggested to eliminate this inconsistency: assuming the existence of dark matter within the context of GR, or modifying the theory of gravity in galactic scales, like MOND or MOG. In this thesis, we study the spherical collapse and the formation of shell galaxies in MOG, in comparison with SM. We introduce the action and the field equations of MOG and the equation of motion of a...