Sharif Digital Repository

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.... 

Shape memory alloys (SMAs) are smart materials with the ability to recover their original shape. Growing the industrial and laboratory applications of SMAs, the study of their mechanical behavior is extremely important. Recently, the shape memory alloys have been investigated by empirical and experimental methods. The results show that these materials also in nano scale keep up their particular properties to a critical size. Because of the size dependence of the material properties at the nano scale, the constitutive models based on classical continuum mechanics cannot describe phenomena observed in the nano scale. For a successful application of SMAs at nano scale, nonlocal theory can be... 

In many structures, crack creation is one of the most significant fracture mechanisms. To predict these fracture mechanisms accurate numerical modeling is necssary. Finite Element Method (FEM) is one of the substantial methods in analysis of numerical fracture problems in recent past decades. But, this method has difficulties in remeshing of elements in each step of calculation in fracture mechanics or large deformation analysis. Therefore, the theory was defined that, without using elements, just with setting of characteristics nodes in geometry of problem, the differential equations can be solved. These methods are called Meshfree or Meshless methods. RKPM is a new meshfree method for... 

In this paper, a hierarchical RVE-based continuum-atomistic multiscale framework is established on the basis of the nonlinear finite element method and molecular dynamics simulation in order to model the geometric and material nonlinearities of deformable solids. In this framework, the coarse scale material properties required for nonlinear finite element method are directly exploited via fine scale atomistic simulation of atomic RVEs designated for each coarse scale integration point and required boundary conditions for atomic RVE simulation are achieved from the coarse scale kinematical response. In order to ensure the kinematical and energetic consistency between the two scales, the... 

By studying change of ion concentrations in animal cells, researchers have reach to important information about cell cycles such as cell growth, muscle cell contraction and cell migration. Manner and amount of passage of ions through cell membrane are basic information that for studying the cell cycle is required. In this thesis, by using two methods, Forward-Reverse constant velocity Steered Molecular Dynamics (FR-cv-SMD) and classical Equilibrium Molecular Dynamics (EMD), diffusion coefficient and Potential of Mean Force (PMF) of sodium and potassium permeation through their protein channels are obtained. For verification the molecular dynamics (MD) methods, diffusion coefficient of K+... 

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... 

One of the extensively used, yet complex, structures in the industry is pre-twisted Micro/Nano beams. Studying their mechanical behavior helps to have a broader view of them. In this present study, explores and analyzes the behavior of a pre-twisted Micro/Nano beam with a quadrangular/rectangular cross-section using the strain gradient theory and modified couple stress theory. Using the calculus of variations and the Hamiltonian principle the elastodynamics governing partial differential equations of transverse deflection of the pre-twisted Micro/Nano beam with hinged-hinged boundary conditions are derived. Then the mechanical behavior of the pre-twisted Micro/Nano beam in static mode and... 

In the first part of this thesis, limitations on magnetic field distribution are studied. After that methods of creating high gradient magnetic field and limitations on it is discussed. In the second part, magnetic properties of materials and the effect of particle shape and size on these properties are studied. In this part a comprehensive analysis on demagnetizing field inside magnetic bodies is also conducted and its dependence on material susceptibility and shape is discussed. At the end of this part the effect of particle shape and size on its hysteresis loop is demonstrated theoretically, practically and by computer simulation. In order to ...