Sharif Digital Repository

This paper presents a unified solution to buckling analysis of rectangular symmetrically laminated composite plates with elastically restrained edges. The plates are subjected to biaxial compression and boundary conditions are simulated by employing uniform distribution of linear and rotational springs at all edges. The buckling loads and corresponding mode shapes are obtained based on classical lamination theory and using the Ritz method with simple polynomials as deflection function without any auxiliary functions. The verifications of current study are carried out with available combinations of classic boundary conditions in the literature. Through parametric study with wide range of... 

In this study the axisymmetric and asymmetric problem of interaction between a transversely isotropic half-space and various rst order shear deformation plate theories including Mindlin, Reissner and Vasil'ev are addressed. In order to improve the accuracy of solution, the surface boundary conditions of the half-space are modied.Moreover, the results compared with the exact solution and the most appropriate result is identied. The displacement Green's functions are obtained for both cases, modied and unmodied boundary conditions which can be expressed in a closed form and a numerically evaluated part. The latter is calculated exploiting Built-in numerical interrelation function of... 

Vibration of a stationary structure excited by another structure moving on the surface of the stationary Structure is very common in engineering, such as vibration of bridges or railway track under travelling vehicles. In the simplest case, the moving structure maybe modeled as a constant load or a mass or an oscillator, in this case the moving mass is attached to the structure either by a spring or by a mass-spring assembly.The model of a moving mass brings some improvements to the model of the moving load where there is no inertia effect. However, the relative displacement between the moving structures and the beam cannot be considered in the moving mass model. A more appropriate model in... 

Reproducing kernel particle method (RKPM) is a meshfree method for solving various differential equations. RKPM is based on pure mathematics; therefore, it is in the center of attention of many scientists. One major problem in RKPM is satisfying the essential boundary conditions (EBCs) involving the derivative of the field function. This problem is considered herein and its solution is proposed. To this end, two actions should be undertaken. First, the concept of Hermitian interpolation is employed to add the derivative term to the reproducing equation of RKPM and a new meshless method called gradient RKPM (GRKPM) is introduced. Second, the corrected collocation method is modified so... 

In this study, the performance of different boundary conditions in dynamic analysis of embankment dams, with consideration of dam-foundation interaction, is compared. All of models are in 2D space. The behavior of dam and the foundation are assumed to be linear elastic. Dam is built of compacted clay, whereas three types of soil are considered for foundation: loose, Medium and dense sand. Direct method is used for dam-foundation interaction analysis. We used Finite Element Method (FEM) using 8-node, quadrilateral and isoparametric elements to analyse the models. The incitement is horizontal displacement with different frequencies that is applied to lower boundary of foundation. In addition,... 

Dissipative particle dynamics (DPD) is an emerging mesoscopic computational method in which the interparticle forces arise because of coarse-graining at the molecular level. In the asymptotic limit of large length scales, the governing equations of continuum are reproduced, as demonstrated in this work. This method of simulation has the capability of simulating larger order of time and space in compare with dynamic molecular method. One of the important applications of DPD is simulating the dilute polymer solution. In this project, we developed a general code to simulate dilute polymer behavior which consists of polymeric forces and different types of usual DPD boundary conditions. This code... 

In the first chapter of this thesis we consider the simplest problem of calculus of variation with mixed boundary conditions and we obtain the Euler-Lagrange equation. We will see that the work here is very similar to the work for Dirichlet boundary conditions. In chapter two we investigate the sufficient condition for the existence of solution. Here we will see the work is really different from the work for Dirichlet condition. In fact this result is published in a credible journal. The main work of this thesis will begin in chapter three and will end in chapter five. In these chapters we will investigate a necessary condition for existence of solution for a calculus of variation problem... 

The In this thesis, we focus are attention on elliptic boundry value problems in domain with nonsmooth boundaries and problems with mixed boundry conditions. Indeed most of the available mathematical theories about elliptic boundry value problems deal with domains with very smooth boundaries;few of them deal with mixed boundry conditions.However, the majority of the elliptic boundry value problems which arise in practice are naturally posed in domains whose geometry is simlpe but not smooth. These domains are very often three-dimensional polyhedra. For the purpose of solving them numerically these problems are usually reduced to two-dimensional domains. Thus the domains are plane polygons... 

The role of a mathematical model is to explain a set of experiments, and to make predictions. In setting up a mathematical model of a biological process, by a set of differential equations, it is very important to determine the numerical value of the parameters. For biological processes are typically valid only within a limited range of parameters. In the last decades, various cancer models have been developed in which the evolution of the densities of cells (abnormal, normal, or dead) and the concentrations of biochemical species are described in terms of differential equations. Some of these models use only ordinary differential equations (ODEs), ignoring the spatial effects of tumor... 

We investigate heat transfer between parallel plates separated by liquid argon using three-dimensional molecular dynamics (MD) simulations incorporating with 6-12 Lennard-Jones potential between molecule pairs. We use thermal walls constructed from the oscillating molecules, which are connected to their original positions using linear spring forces. Channel walls are maintained at specific temperatures using a recently developed interactive thermal wall model. This approach is much more effective than the one which uses a fixed lattice wall modeling to simulate the heat transfer between wall and fluid. Heat flux and temperature distribution in nanochannels are calculated for channel height... 

The investigation of the behavior of structures subjected to various kinds of loadings is of considerable importance. In this research, an attempt was made to analyze behavior of beams that a load is moving on them.Most of the existing relevant works in this field are dealt with examination of elastic beams with constant section, while in most cases beams with variable sections are used in order to have the optimum structure and appropriate stress distribution and to maximize strength to weight or cost ratio. While construct analysis is very advantageous, it is very difficult due to the complexities arising from the variable sections. But this design is so advantageous that it dominates... 

In recent years, application of porous media is highlighted among researchers due to their wider use in micro-scale problems, such as in gas reservoirs, micro-filtering, and heat exchangers. In such applications, accurate description of flow behavior, using governing equations based on continuum assumption, is not valid, since mean free path has the same order as the characteristic length of the problem. In such cases, imposing appropriate slip condition on the fluid-solid interface of porous media (in pore-scale level), based on kinetics theory, is an appropriate approach. For this purpose, pore-scale simulation of flow inside porous media in slippery and transient regimes is carried out... 

Taghizadeh Manzari, M. (In this work, a modified Smoothed Particle Hydrodynamics (SPH) method, with a new moving solid boundary treatment approach, is utilized to simulate the particulateflow problems. The renormalized first and second derivative schemes which lead tothe consistency of the method, are also used along with a modification to the continuityequation which prevents the spurious pressure oscillations. The proposed methodis validated by solving benchmark problems of solid body motion in channel flows.There is a good agreement between the obtained results and those reported in theliterature. The convergence of solutions for different domain discretizations is alsoassessed. In order... 

In this paper, a one-dimensional and two-dimensional numerical approach is used to study the effect of various parameters such as micro combustor height, mass flow rate and external convection heat transfer coefficient on the temperature and species mass fraction profiles. A premixed mixture of H2-Air with a multi-step chemistry (9 species and 19 reactions) is used. The transient gas phase energy and species conservation equations result in an Advection-Diffusion-Reaction system (A-D-R) that leads to two stiff systems of PDEs, which can not be solved by conventional Computational Fluid Dynamics (CFD) methods. In the present work, Strang splitting method, which is suitable for nonlinear stiff... 

Many human inventions are inspired by nature, such as fish swimming, bird/insect flight, etc. A basic consideration for the design of swimming machines is the design of propulsors. A creative design of propulsors can be inspired by fish locomotion. The term locomotion means that thrust is generated by undulation of fish body. Thus, there is no need to have an external propulsor. We need to understand how thrust is obtained by fish locomotion. In this study, sub-carangiform motion, which is a well known locomotion and which is practiced by most fish, is simulated numerically using Lattice Boltzmann method (LBM). To simulate the geometry of fishlike body, the profile of a flexible airfoil... 

In the present study, the preconditioned incompressible Navier‐Stokes equations with the artificial compressibility (AC) method formulated in the generalized curvilinear coordinates are numerically solved by using a high‐order compact finite‐difference scheme for accurately and efficiently computing the incompressible flows. A fourth‐order compact finite‐difference scheme is utilized to discretize the spatial derivative terms of the resulting system of equations and the time integration is carried out based on the dual time‐stepping method. The capability of the proposed solution methodology for computing the steady and unsteady incompressible viscous flows in a wide range of Reynolds... 

In recent decades the use of FRP materials for strengthening structures has been developed extensively, thanks to their high strength, sufficient stiffness, high durablity, and ease of use. A great deal of research has been conducted on strengthening reinforced concrete beams and columns with FRP composites. By contrast, not many researches are performed on slabs, especially two-way slabs. In these few researches, the loading and boundary conditions are limited to simplest ones. Therefore, in this thesis, the focus of attention is on strengthening reinforced concrete slabs under various loads and boundary conditions using FRP composites.
In this thesis, first, FRP composites and their... 

In this work, a new methodology for modeling the whole lung using porous media is presented. Dealing with the details of the proposed method establishes the need for some tools. Proposed method combines data extraction from lung images to identify large airways, porosity and porous region boundaries. Combining some sequential images, change in properties with time could be obtained. To obtain behavior of this porous media with respect to flow, a method based on the classification of bifurcations and gas exchange areas and pore scale modeling of these classes is proposed. All these require a specifically designed numerical tool. Development of this tool is the subject of the next parts of... 

In this thesis the scattering analysis of periodic rough surfaces is studied using the Spectral Finite Difference Time Domain (SFDTD) method. This method takes advantages of both wideband frequency response and stability criterion for all incident angles compared to other methods in solving the periodic problems. In the SFDTD method a wave with Constant Transverse Wavenumber (CTW) is used as the incident wave. As a result, the problem of time delay in periodic boundary is solved and Periodic Boundary Condition (PBC) can be implemented in time domain directly. Periodic rough surfaces are important part of electromagnetic propagation surfaces. Therefore analysis of scattering from these... 

In recent years, there have been a tremendous research performed in the field of sestems containing small scales. However, besides all advantages of such systems, microfluidic systems have extraordinary difficulties and pumping liquid drops as part of some of these systems has been very important issue. An approach related to flow control is use of surface acoustic waves (SAW), which is known as acoustofluidic device. So far, most researches have only qualitatively investigated acoustic flux phenomenon. On the other hand, computational research is ongoing more emphasizing on accuracy, optimization, and obtaining more detailed physical understanding of SAW applications. Investigation of the...