Sharif Digital Repository

In this thesis, a deformation measure is introduced which leads to a class of strain measures in the Lagrangian and Eulerian descriptions. In order to develop a constitutive equation, a second-order constitutive relation based on these strain measures is considered for modeling the mechanical behavior of solids at finite deformation. For this purpose and performance evaluation of the proposed strains, a Hookean-type constitutive equation is considered and the uniaxial loading as well as simple shear and pure shear tests are examined and the results are compared with the test data. Also, in order to characterize the mechanical behavior of elastic continua, constitutive equations through a... 

In the present study, we analyzed the mechanical behavior of micro rotating disk based on the most general form of strain gradient elasticity. According to the fact that micro rotating disks have an important role in MEMS, it is necessary to present an exact analysis of their mechanical behavior. It is noticed experimentally that materials behave stronger in deformation as they get smaller. The classical continuum theory is not capable to predict such behavior; therefore, it is essential to use one of the non-classical continuum theories to analyze the material in micro scales, which can capture this phenomenon. In this work, the strain gradient theory is utilized to derive the governing... 

Determination of the elastic fields associated with a spherical multiply-coated inhomogeneous inclusion is a problem of great interest among researchers. In this work a set consisting of N+1 concentric spherical domains is considered. Each domain is either isotropic or spherically isotropic and is functionally graded (FG) in the radial direction. The outermost spherical surface is subjected to nonuniform loading and the constituent phases are subjected to some prescribed nonuniform body force and eigenstrain fields. When the outermost domain is an unbounded medium with zero eigenstrain and body force fields then an N-phase multi-inhomogeneous inclusion problem is realized for which the... 

In this study we investigated the stress effects on the fractured block in formation and its impact on flow through the matrix. At first the effect of various stresses on reduction of sample's pore volume and thereby reduction the permeability have been studied. The equations used to describe the elasticity relations in saturated matrix block is provided by Bayot theory. In this theory, the system of related equations to stress and strain changes have been developed in matrix. We have used finite element method in COMSOL software to solve the equation system created by elasticity relations in formation. After solving the equations, volume and volumetric strain changes which are caused by the... 

The use of metal matrix composite materials (MMC) in aerospace structures and engine parts has become more frequent recently. These materials are composed of metal matrices reinforced by hard discontinuous ceramic fibers, usually oriented longitudinally within the matrix, and due to the stability of the mechanical properties, including the hardness and the strength at high working temperatures, have found various applications.Stress transfer from the matrix to the fiber is known as the most important mechanism governing the deformation and the fracture response of such MMCs. The stress transfer characteristic of fiber reinforced composite materials under various mechanical and thermal... 

This thesis aims to introduce a numerical method for investigating the appropriate arrangement of visco-pseudo-elastic dampers applicable to shell and plate structures under large deformation. These passive dampers are considered as viscoelastic layers and discrete shape memory alloy (SMA) wires in which this combination improves their overall efficiency and reduces their drawbacks. Also, the main advantages of these dampers are discussed during some illustrative problems. The current finite element formulation is based on an incremental updated Lagrangian (UL) approach along with the Newmark's integration technique. In the layerwise shell element, the Mindlin-Reissner theory is adopted in... 

Previous studies indicate that increasing cement compressive strength can’t prevent loss of zonal isolation and casing collapse in worse case during well operations or formation loading. Since standard cements with high compressive strength can’t solve these problems, so application of elastic cements with low Young’s modulus and high Poisson’s ratio becomes important. These cements sustain generated stresses during well operations and prevent creation of point loads when formation creep occurs. For this purpose, a new additive was designed in order to improve the cement elasticity and tensile strength. It is a nanoparticle and named EX-RIPI (by Research Institute of Petroleum Industry,... 

Breast cancer is considered as the most common type of cancer in women worldwide and mammography is currently utilized as the principal method for screening the breast cancer. Breast Magnetic resonance imaging (MRI) can be used as a complementary imaging technique besides mammography. MRI technique involves scanning a patient before and repeatedly after the injection of the contrast agent (DCE-BMRI). This examination often takes 7-10 minutes and any movement of the patient’s breasts due to breath, heartbeat or deliberate movement, made in this relatively long acquisition period, leads to a distortion in images called motion artifact. This problem makes the quantitative analysis of the images... 

Under conventional seismic design strategies, civil engineering structures are designed to undergo inelastic deformation to dissipate earthquake energy, leading to residual displacements and nonlinear deformations in the structure. As a result, there is an essential need for structural health monitoring methods to detect and process these nonlinear behaviors. In this dissertation, a model-free Hysteresis Loop Analysis (HLA) method is developed to identify damage and monitor the structure's performance online, under the earthquake excitations in both severe linear and nonlinear scenarios. The structural models used to validate this method includes three types of one-story, five-story, and... 

Inadequate nutrition is perhaps the most important problem facing the poor. Being hungry lowers productivity and decreases individuals’ income. All of these factors conspire to help the poor stay poor. Raising the income of the poor is one solution for this problem if the elasticity of calorie and macronutrients with respect to income is greater than zero. This study employs both nonparametric and parametric methods to obtain the elasticity of per capita calorie and macronutrients with respect to household per capita expenditure. The case presented is for urban areas of Islamic republic of Iran, 2008-2016. Under each estimation strategy we employ, we find a strongly significant and positive... 

In the past few years mobile usage is increasing in Iran. Since mobile industry is growing and new innovations are presented, the competition between operators is rising. Although this competition has a great influence on the mobile demand for each operator, lack of the data of the all operators made us to use the data of one of the operators to investigate the demand. Based on the subscriber’s data of Hamrahe-Aval company, it has been introduced an estimation of a demand system for customers of this company by using AIDS model in this essay. This model includes three groups of services: sending short messages, calling to mobile numbers and calling to fixed numbers.
This study has two... 

In this work, we want to gain and analyze the dynamic equations of an open four bar mechanism with two flexible links and three flexible hinges. In continue, one of the applications of a 3-RRR mechanism has been mentioned and dynamic equations and angles behavior have been analyzed. The effect of hinge stiffnesses and their sequence has been investigated by using Hamilton principle. In addition, The behavior of the mechanism with flexible links has compared to the mechanism with non-flexible. At last, the results have been validated by ADAMS software.

 

In this thesis, We consider a model of a fluid–structure interaction defined on a bounded domain Ω ⊆ R2, that describes a body of elasticity interacting with a fluid. Ω is a bounded simply connected domain, consisting of two open sub-domains Ωs and Ωf .Ωf is the exterior domain with non-overlapping boundaries Γf and Γs, so that ∂Ωs = Γs. Ωs is an interior domain with boundary Γs.Ωs is occupied by an elastic body while Ωf is filled with a fluid.The interaction between the elastic body and the fluid takes place at the interface Γs.The dynamics of the fluid is described by the Navier–Stokes equation and the dynamics of the elastic body is described by an elasto-dynamic system of wave equations.... 

The success of matrix acid production operations and its proper efficiency is one of the main challenges for oil and gas companies. The heterogeneity of the reservoir formation (especially the permeability difference) in the area around the well due to the presence of different reservoir layers results in the non-uniform distribution of acid among them and adds acidizing challenges. In order to improve production conditions, stimulation fluid transfer to the low permeability layer, which is the main target of acidizing. In this study, a new generation of chemical diverter, called Viscoelastic Surfactant, has been used. These materials have two components of elastic and viscous behavior, and... 

Due to the inelasticity of the ground and geometric expansion, seismic waves are reduced by moving away from the center of wave propagation, which is called the attenuation of seismic waves. Therefore, the ground motions that occur at the site of the structures are different from the ground motions that are emitted from the source. The upcoming study investigates the attenuation of seismic waves in the geographical area of Iran based on the accelerogram data of Iran. Considering the consecutive occurrence of moderate to large earthquakes in Iran, the development of Iran's accelerography network, and the need to update the attenuation relationships by considering the parameters effective in... 

In this study, flexural vibration of a functionally graded nanotube under an initial stress is investigated. The small scale effect is taken into consideration based on Eringen’s nonlocal elasticity theory. The material properties are assumed to vary exponentially along the depth direction. The complete effect of the initial stress is taken into account in the problem formulation. The governing equations of motion are derived by using the Hamilton’s principle on the basis of the nonlocal Timoshenko beam theory. An analytical solution of the governing equations, for free vibration of a simply-supported nanotube is presented. Numerical results are presented to investigate the effect of the... 

To answer how large the welfare gains from international trade are, this thesis uses two main ideas: linkages and complementarity. A problem along the production chain can sharply reduce output under complementarity. In such a circumstance, international trade and importing in the sectors which are the weak links of the production chain, help solve this problem. Using a general equilibrium model, it is shown that, the complementarity of the intermediate goods assumption results in much higher welfare gains from international trade compared to similar international trade models which assume the substitutability of the intermediate goods  

Many regulations around the world use the Newmark method, directly or indirectly, in the design spectrum. Research on the Newmark design spectrum shows that this spectrum sometimes significantly differs from the earthquakes response spectra that have occurred; therefore, it is necessary to develop and introduce new design spectra by modifying the Newmark method to be more compatible with reality. The developed design spectra in seismic regulations around the world are directly affected by the records involved in their development. Thus, the appropriate design spectrum should be prepared based on the seismic characteristics of the faults of each country. Evaluation of the Iranian Seismic... 

Nowadays, robots are become more common in many important applications, such as academic and industrial issues. One of the most important robots are Multi-Arm manipulators which are used in many application such as moving objects, coloring, automatic welding and etc. Working with this kind of robots needs some vital attentions like planning their moving path. It is Because of the large number of obstacles that they face with in the path. Therefore, not only robots are not allowed to collision with themselves, but also they must not touch the obstacles. In the other words, they need Path planning. Generally, the equations of these robots are nonlinear. Therefore, computers and numerical... 

Abstract In this study, by using panel instrumental variable quantile regression method (IVQP) and household budget data during the years 2011-2018, income elasticity of Housing energy has been estimated at different levels of energy expenditure. This method helps to study the whole energy expenditure distribution instead of focusing on the average effects. The study results show that income elasticity has a downward trend with increasing energy consumption quantiles. In other words, households with higher consumption have less income elasticity, so that the income elasticity is estimated for 10, 90 percentage, 0.47, and 0.32 quantiles, respectively. Also, in another part of the research,...