Sharif Digital Repository

In the current work, the two- and three-dimensional electro-elastic fields of periodically as well as arbitrarily distributed interacting quantum wires (QWRs) and interacting quantum dots (QDs) of arbitrary shapes within a piezoelectric matrix are studied analytically. The lattice mismatch between the QWR/QD and the barrier is accounted through prescribing an initial misfit strain field within the QWR/QD. The distinction between the electro-mechanical properties of the QWR/QD and those of the barrier is treated by introducing a novel electro-mechanical equivalent inclusion method in Fourier space (FEMEIM). Moreover, the theory can readily treat cases where the QWRs/QDs are multi-phase or... 

DNA molecule is one of the most important macromolecules in cell, which carries genetic information for life. DNA is often in confined geometries, such as, packaging in cell and DNA-protein interactions. While DNA is nearly a stiff polymer, its elastic behaviour plays a crucial role on its functionalities.Therefore, investigating the elastic and mechanical properties of DNA is really important.The elastic behaviour of a long and free DNA can be predicted very accurately by ”worm-like chain“ (WLC) model. In WLC model, DNA is assumed as a elastic rod with harmonic potential of local bending and twist.Many structural properties of DNA have been ignored in this model. But in recent years, by... 

The properties of metamaterials can be tailored through modification of their microstructures geometry. In this regard, a vast range of metamaterials have been designed. Auxetic metamaterials are a novel class of materials exhibiting the interesting characteristic of negative Poisson’s ratio. Theoretically, auxetic metamaterials have improved mechanical properties such as shear modulus and fracture toughness. The design and modeling of auxetic metamaterials is not completed yet. In order to exploit the interesting properties of auxetic metamaterials, their potential applications have been investigated in medical, sports, automobile and defense industries, so far. In the present work, the... 

In this study, static and dynamic buckling of laminated composite beams resting on an elastic foundation under thermal and mechanical load is studied. Beam is resting on an elastic foundation with hardening/softening term. Nonlinear governing equations are obtained based on the energy method and are solved via the multi-term Galerkin method and the Newton-Raphson numerical method. Critical dynamic load is estimated by the Hoff Simitses criterion. The results are validated with the results of available articles in this field. In the following, the effects of different parameters of the problem on the results are examined. Results reveal that for a sufficiently stiff softening elastic... 

Considering the role of fluid storage tanks within or after an earthquake and the irreparable damages of such structures that arise from the flammable or toxic nature of the fluids stored in them, it is very important to ensure stability and durability of the tanks under seismic loading. One of the most important damages to storage tanks within the past earthquakes has been lack of stability of their shells taking place in the form of a local bulge of wall, known as “elephant foot buckling’. This phenomenon is a subsequent of high levels of hoop tension, which is a result of containing liquid pressure, along with axial load of surrounding walls. Recent studies reveal that there is no... 

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 fluid structure interaction (FSI) problems are widely encountered in many industrial applications in mechanical, aerospace, biomedical, marine, and wind engineering. The main contributions of this research are focused on simulating flow with moving or deforming boundaries including FSI problems with large movement or deformations. In this regard, a hybrid finite-element-volume (FEV) method was used in an arbitrary Lagrangian-Eulerian (ALE) framework. In this research, a new layer-by-layer mesh movement strategy was developed to perform the unstructured grid movement more robustly. This strategy converts the complex data structure of an unstructured grid to a simple quasi-structured data... 

Applying of seismic waves and analysing of its reflections is of effective ways in exploration of the internal structur of the Earth. In this method the Earth is considered as a elastic body that seismic waves are propagated in it. In this thesis the how of creation and propagation of seismic waves is modeld at first and then the inverse problem, exploration of the internal structure of the Earth from observed data, is considered  

In this thesis, we consider a system containing fluid equations, structure equations, and equations of these two materials’ common interface in three dimensions and on the regular domains. We suppose that the solid which is described by the Lamé system of linear elasticity, moves inside an incompressible viscous fluid in three dimensions, and the fluid obeys the incompressible Navier-Stokes equations in a time-dependent domain. At the fluid–solid interface, natural conditions are imposed, continuity of the velocities and of the Cauchy stress forces. The fluid and the solid are coupled through these conditions. By this interaction, the fluid deforms the boundary of the solid which in turn... 

In this paper, the elastic response of a surface-stiffened transversely isotropic half-space subjected to a surface normal load is addressed. The half-space is reinforced by a Kirchhoff thin plate bonded to its surface. Two different boundary conditions are considered across the plate-half-space interface: (i) the classic approach in which the plate in-plane deformation is neglected by writing the interfacial boundary conditions across the plate mid-plane, and (ii) the refined approach that considers the in-plane deformation of plate due to bending by writing the boundary conditions across the bottom face of plate. By virtue of appropriate displacement potentials, the complete set of elastic... 

Numerical methods in fracture and crack propagation problems usually involve high computational costs. Adaptive finite element method is one of the techniques which can be used to simulate the crack propagation with an acceptable accuracy. In this thesis, various constitutive models are implemented for simulation of fracture, including the linear elastic fracture mechanics, cohesive zone model and continuum damage mechanics. The fracture mechanical evaluation is performed on a general integral technique for non-planar curved cracks in LEFM. In the second model, a bilinear cohesive zone model is applied to implement the traction-separation law. The Lemaitre damage model is employed and the... 

The first project ,paid to review and analysis types of crack and agents Also, was referred methods to control them in rail industry .
The wheel of Alestom train and UIC60 rail were simulated and stress analysis by software FEM (ANSYS and ABAQUS) , and effect of various parameters such as applied forces , train wheel diameter , contact position and rail inclination on stress values was studied . For comparision of results has been used analytic Hertz theory .
By using experimental data on the subsurface crack , those cracks were created in the wheel . For load on the modeling wheel and rail, ,assuming contact on the wheel rolling point , were used vertical load of wagon weight ( with... 

Twophase medias are one of the most complicated medias in engineering and because of its importance, its been considered by a lot of researchers ever since. Varaioty of the problems in these medias, has ended in lots of methods for studing them. The primariative efforts in modeling deformable pouros medias was done by Terzaghi and others have improved the primary consepts and have suggested different methods. One of the most common and applicable methods in these medias is u-p formulation. This form is applicable in low frequencies (such as earthquakes) with great accuracy. In this thises, this form is used as primery formulation. Because deformation in multiphase problems can be large, in... 

In many problems, the traditional elasticity cannot predict phenomenon such as nano-scale defects, surface effects, and stress concentration correctly. For example, analysis near the crack tip, dislocation and inhomogeneity shows inconsistent results because in this case values of stress go to infinity. Therefore for solving these kinds of problems, higher order continuum theories were introduced. The appearance of additional constants in the equations of motion can represent the atomic nature of materials. Furthermore, they can be utilized for determining properties of materials vibration with high frequency, granular materials, and polymers.First strain gradient theory introduced by... 

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 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... 

This thesis investigates the dynamic response of a viscoelastic plate resting on a viscoelastic Winkler foundation subjected to the excitation of a moving mass. Through application of the Laplace transform, the governing equation of the problem is derived for a general viscoelastic material. Thereafter, an analytical-numerical method is proposed in order to determine the dynamic response of the viscoelastic plate. The method is based on transforming the governing partial differential equation into a new solvable system of linear ordinary differential equations. To that extent, the proposed solution proves to be applicable to plates made of any viscoelastic material and with various boundary... 

Nowadays the combination of mechanical and electronic systems in small scales is gaining attention. Micro electro-mechanical systems are widely used in various industries such as car manufacturing and electronic chips. In these devices, the most important and useful mechanical structures are beams and plates. Therefore, investigating the mechanical properties of these structures in very small scales (micro and nano) is of great importance. Decreasing the size to these scales leads to the dependence of the behavior of these structures to size. Accordingly, some theories for prediction of these behaviors have been presented, one of which is the strain gradient theory. This theory is used in... 

Nowadays, by adding a small amount of a desired nanomaterial to a matrix having certain properties one may design a multifunctional nanocomposites with a remarkably improved macroscopic properties of interest. The capability of conventional continuum theories in treating the problems of embedded ultra-small inhomogeneity with any of its dimensions comparable to the characteristic lengths of the involved constituent phases is questioned, mainly, on the grounds of the accuracy and the size effect. In this work, effort is firstly directed at the prediction of the macroscopic shear modulus of composites consisting of nano-/micro-size fibers of elliptic cross-sections via couple stress theory, a... 

In the recent years, there has been great interest in exploring methods for assembly and manipulation at the micro/nanoscale to build miniaturized systems, devices, structures, and machines. This thesis aims at two-dimensional manipulation of nanoparticle using Atomic Force Microscope (AFM) probe. The nanoprobe is used to push the spherical micro/nanoparticle. Continuum based modeling and simulation of the manipulation task is presented. The proposed nanomanipulation model consists of all effective phenomena in nanoscale. Nanoscale interaction forces, elastic deformation in contact areas, and friction forces in tip/nanoparticle/substrate system are considered. The utilized friction models...