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boundary-conditions
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One Dimensional and Two Dimensional Numerical Investigation of Micro Scale Combustion
, M.Sc. Thesis Sharif University of Technology ; Saidi, Mohammad Said (Supervisor) ; Saidi, Mohammad Hasan (Supervisor) ; Shafii, Mohammad Behshad (Supervisor)
Abstract
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...
Scattering Analysis from Periodic Rough Surfaces Using Spectral-FDTD
, M.Sc. Thesis Sharif University of Technology ; Shishegar, Amir Ahmad (Supervisor)
Abstract
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...
Dynamic Response of a Finite Beam Subjected to a Moving Oscillator
, M.Sc. Thesis Sharif University of Technology ; Vafaei, Abolhassan (Supervisor)
Abstract
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...
Multi-scale Analysis of Dislocation Emission for Nano-crystalline Structures
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
Abstract
In this study, a new multi-scale hierarchical technique has been employed to investigate the role of edge dislocation on nano-plates with hex atomic structure in large deformation. Two multiscale hierarchical atomistic/molecular dynamics (MD)–finite element (FE) coupling methods are proposed to illustrate the influence of temperature on mechanical properties of Magnesium in large deformation. The atomic nonlinear elastic parameters are obtained via computing second-order derivative of Representative atom’s energy and RVE’s strain energy density with respect to deformation criterions (deformation gradient and Green strain tensor) to bridge between atomistic and continuum level, the...
Developing a Roadmap for Whole Lung Modeling and Some of the Required Software
, Ph.D. Dissertation Sharif University of Technology ; Saeedi, Mohammad Saeed (Supervisor)
Abstract
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...
Simulation of Self-Propulsive Phenomenon, Using Lattice Boltzmann Method
, M.Sc. Thesis Sharif University of Technology ; Tayyebi Rahni, Mohammad (Supervisor) ; Taghizadeh Manzari, Mehrdad (Supervisor)
Abstract
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...
Studying the Effect of Thermal Loading on Delamination Phenomenon of Composite Materials using Continuum Damage Mechanics
, M.Sc. Thesis Sharif University of Technology ; Abedian, Ali (Supervisor)
Abstract
Metal and inter-metallic matrix composites offer high performance materials suitable for many low weight applications which are of growing interest in high tech industries. However, to submit their entire potential applications, their complex mechanical behavior has to be understood. Nevertheless, one of the major setbacks of designing with these materials has been the delamination phenomenon. So far, this phenomenon has been considered from macro-mechanical point of view regarding laminates to be semi-isotropic or orthotropic; which indicates the importance of micro-mechanical research to be done. Furthermore, the fact that macroscopic response and failure mechanisms of these composites are...
Vibration of a Non-Ideal Simply Supported Euler Bernoulli FG Beam Excited by a Moving Oscillator on Viscoelastic Pasternak Foundation
, M.Sc. Thesis Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor)
Abstract
In this thesis, the influence of nonideal boundary conditions on the vibration of a functionally graded beam excited by a moving oscillator on Pasternak-type viscoelastic foundation has been investigated. The beam has simply-supported boundary conditions and is assumed that the right-hand-side boundary conditions allows for small deflection, moment and axial force. The beam property gradient is assumed to be in the thickness direction and varies according to the power law distribution. The Hamilton's principle is utilized to obtain the governing equations of motion under the assumptions of Euler-Bernoulli beam theory. The equations of motion of the beam are solved using an...
Dynamic Analysis of Timoshenko Beam with Nonuniform Cross Section and Kirchhoff Plate with Nonuniform Thickness Under Moving Mass
, M.Sc. Thesis Sharif University of Technology ; Mofid, Massoud (Supervisor)
Abstract
In this study dynamic response of Timoshenko beam and rectangular Kirchhoff plate under moving mass are investigated. Applying Hamilton’s principle, governing differential equations of beam and plate are derived considering the effect of moving mass. Afterward, a numerical-analytical solution based on eigen function expansion method for analyzing nonuniform beams and plates by means of beams’ and plates’ free vibration modes is presented and convergence of the solution is proved by proving that the governing differential equations of Timoshenko beam and Kirchhoff plates are self adjoint. Modal orthogonality circumstances are discussed due to their important role in eigen function expansion...
Euler-lagrange Equation for a Delay Variational Problem
, M.Sc. Thesis Sharif University of Technology ; Hesaraki, Mahmoud (Supervisor)
Abstract
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...
Buckling of Laminated Composite Plates with Elastically Restrained Boundary Conditions
, M.Sc. Thesis Sharif University of Technology ; Kochakzadeh, Mohammad Ali (Supervisor)
Abstract
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...
Dynamic Texture Segmentation in Video Sequences
, Ph.D. Dissertation Sharif University of Technology ; Manzuri Shalmani, Mohammad Taghi (Supervisor)
Abstract
Video segmentation means grouping of pixels of the video sequences into spatio-temporal regions which exhibit coherence in both appearance and motion. Due to complexity and spatio-temporal variations, dynamic texture segmentation is a one of the most challenging task in video processing. The problem of dynamic texture segmentation has received considerable attention due to the explosive growth of its applications in video analysis and surveillance systems. In this thesis, two novel approaches have been proposed. The first proposed method is based on generative Dynamic texture models (DTMs) which represent videos as a linear dynamical system. Since DTMs cannot be used for complex videos which...
Fluctuations in the order of System Size in the Avalanche-Size Distribution of Sandpiles Model
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
Since the concept of Self-Organized Criticality was introduced in terms of BTW Sandpiles model, its major features have been known as broad power law distributions without any tuning parameters. In some selforganized critical systems like brain and neural networks, some evidences and experiments show a periodic or non-power law distribution of avalanches in addition to the power-law distributions of avalanches. In this thesis we try to observe the same phenomenon in the well-known SOC models, namely the BTW and Manna sandpile models. We have considered small lattice sizes with periodic boundary conditions and a small amount of dissipation. Within such conditions we observe a periodic-like...
Cancer Models Based on Reaction-Diffusion Equations
, M.Sc. Thesis Sharif University of Technology ; Fotouhi, Morteza (Supervisor)
Abstract
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...
Comparison of Performance of Different Boundary Conditions in Numerical Analysis of Dam-Foundation Interaction
Under Dynamic Loads
,
M.Sc. Thesis
Sharif University of Technology
;
Pak, Ali
(Supervisor)
Abstract
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,...
Dynamic Behavior Beam and Plate on Foundation under Moving Mass
, Ph.D. Dissertation Sharif University of Technology ; Mofid, Massoud (Supervisor)
Abstract
The behavior of a beam under moving mass has been always interested in the dynamic of structures. In this study, the dynamic response of beam and plate with general boundary conditions under moving mass were investigated using the Dynamic Green Function. Since the majority of previous studies did not consider the Coriolis acceleration, therefore, this acceleration was used in the present study. Boundary conditions are modeled by the rotational and translational restraint. By moving close to the spring constants of the rotational and translational restraint to extreme values (zero and/or infinity), the boundary conditions can be attained for the desired combinations of end boundary conditions...
Interlaminar Stresses Analysis of Spherical Shell with Arbitrary Laminations and Boundary Conditions under Transverse Loads
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkheili, Ali (Supervisor)
Abstract
Today, composites are widely used in various industries, thus the study and analysis of properties and their behaviors are very important. In addition, the use of multi-layered composites in the aerospace industry is important. The composite-elastomer structures, specially their spherical shape, are widely used as flexible joint in aerospace industries, such as the thrust vector control system in solid-propellant rockets and the helicopter industry. In this study, an analytical approach is proposed for calculating the interlaminar stresses of laminated plates and spherical shells with arbitrary laminations and boundary conditions based on a threedimensional multi-term extended Kantorovich...
Simulation of Fluid-Solid Mixtures Using SPH Method
, M.Sc. Thesis Sharif University of Technology ; Taghizadeh Manzari, Mehrdad (Supervisor)
Abstract
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...
The Response of Transversely Isotropic Half-Space Stiened by a Surface Thick Plate
, M.Sc. Thesis Sharif University of Technology ; Eskandari, Morteza (Supervisor)
Abstract
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...
Pore-scale Simulation of Flow around a Micro-porous Square Cylinder, Using Hybrid LBM-FVM, Considering Slip Condition Inside Porous Media
, M.Sc. Thesis Sharif University of Technology ; Tayyebi Rahni, Mohammad (Supervisor)
Abstract
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...