Sharif Digital Repository

Innovations in laser, microwaves, and similar technologies have significantly advanced thermal treatments for diseases or even injuries concerning skin tissue. For a thorough understanding in the underlying mechanisms of bioheat transfer behavior of skin,a1D unsteady non-dimensional hyperbolic model of heat transfer through this tissue with metabolic heat generation which is subject to specific boundary conditions, is solved numerically using the finite difference method. A thermal shock is generated at the base of the tissue, which moves forward with a finite speed. A Numerical solution for a simple one-layer skin tissue is obtained. Then, the effects of various parameters, time step,... 

The main goal of this project is analysis, design and implementation of scanning near field optical system for detection of biological species. The activities fall in two main category. Theoretical and experimental. In theoretical part, after studying different models describing near field interaction, we have developed software for computationally analysis of nonlinear interaction of light with nanostructures, considering third order nonlinear susceptibility and dispersion behavior of permittivity for metallic nanostructures. The software implements three dimensional finite difference time domain (FDTD) method for analysis of interaction of electromagnetic wave with matter. In developed... 

Neutron noise equations, which are obtained by assuming small perturbations of macroscopic cross sections around a steady-state neutron field and by subsequently taking the Fourier transform in the frequency domain, have been usually solved by analytical techniques or by resorting to diffusion theory, but in this thesis, in order to increase of accuracy of neutron noise calculation, has been used transport approximation for neutron noise calculation and the Monte Carlo method has been used to solve transport equation of the neutron noise in the frequency domain. Since the transport equation of the neutron noise is a complex equation, a new Monte Carlo technique for treating complex-valued... 

In this research, a simple yet efficient two-dimensional model of proton exchange membrane fuel cell (PEMFC) is developed using stream function-vorticity formulation. The model accounts for the fluid flow and masstransport processes in cathode gas channel and gas diffuser layer. The governing equations are decoupled and solved usingtwo efficient approaches, Alternating Direction Implicit (ADI) and False Transient Method (FTM) in a modified geometry to simulate the fully-developed condition consistently. An in-house code was developed to perform a parametric study of fuel cell performance. The results show the variations of important parameters along the cathode channel such as velocity... 

High temperature gas cooled reactors (HTGR) are one of the most promising reactors in the new generation of world commercial reactors. They are divided into two main categories: Prismatic gas cooled reactors and pebble bed gas cooled reactors. These reactors have many advantages, such as inherent safety, high thermodynamic efficiency and the possibility of producing hydrogen. One of the most important challenges in developing these reactors is providing appropriate codes in design and simulating their performance. Two codes have been developed in this thesis. The first, THFAM, is a steady state thermal hydraulic code which helps in analyzing a fuel assembly. The second, named THCM is... 

In this thesis, localization of a postulated noise from limited neutron detectors sparsely distributed throughout the core of a typical VVER-1000 reactor is investigated. For this purpose, developing a 2-D neutron noise simulator for hexagonal geometries based on the 2-group diffusion approximation, the reactor dynamic transfer function is calculated. The box-scheme finite difference method is first developed for hexagonal geometries, to be used for spatial discretisation of both 2-D 2-group static and noise diffusion equations. Using the discretised static equations, a 2-D 2-group static simulator (HEXDIF-2) is developed which its results are benchmarked against the well-known CITATION... 

A prismatic high temperature gas-cooled reactor (HTGR), which is a graphite moderated, helium-cooled reactor, is a promising candidate for next generation nuclear power plant in that it enables applications, such as hydrogen production or process heat for petrochemical by supplying heat with core outlet temperatures as high as 1000°C. A Thermal Hydraulic Analysis Code (THAC) for gas-cooled reactors has been developed. THAC implicitly solves heat transfer equation of fuel, graphite block and helium. Three types of fuel pins were considered; solid fuel pin, fuel pins with inside holes and annular fuels with coolant flow from its inside and outside surfaces. THAC predicts axial and radial... 

In this study, the Shokov-BGK model of the Boltzmann equation is reformulated and generalized to consider the real gas effects. At first, the formulation is performed to consider an arbitrary specific heats ratio and the correct Prandtl number for polyatomic gases. Here, the resulting equations of the present formulation are numerically solved by applying the high-order finite-difference weighted essentially non-oscillatory (WENO) scheme. The present solution method is tested by computing the one-dimension Reiman problem with different specific heats ratios for a wide range of the Knudsen numbers. The results are compared with the available gas-kinetic results which show good agreement. It... 

One of the common and efficient methods in the construction of large-scale structures from composites is the Vacuum Assisted Resin Transfer Molding (VARTM) method, which is widely used in the automotive industry, wind turbine blades, warships and pleasure boats, etc. VARTM is one of the liquid molding methods in which one side of the closed mold is replaced with a vacuum bag and the resin flows into the mold only with the help of air pressure (pressure of one atmosphere). One of the main challenges in the vacuum resin molding process is to be aware of the physics governing the flow motion in the porous mold so that the dry spots formed in the mold can be located accordingly. On the other... 

The increasing need for more efficient and environmentally friendly microturbines necessitates the utilization of compact recuperators resulting in lower fuel consumption and emissions. The goal of this research is to determine the performance behavior of a primary surface recuperator to be incorporated in a 100 kW microturbine. Primary surface recuperator, known for relatively favorable characteristics in heat transfer, low weight, and high efficiency is considered as a candidate in aviation engines. In this research, a computational model for heat transfer and pressure losses is used for the design optimization of annular involute-profile cross wavy primary surface recuperators in... 

In the present study, the numerical simulation of 2D inviscid compressible cavitation flow is performed by using the compact finite-difference method. The problem formulation is based on the multiphase compressible Euler equations with the assumption of the homogeneous equilibrium model and the system of baseline differential equations is comprised of the continuity, momentum and energy equations for the vapor-liquid mixture. To complete the system of governing equations, the ideal gas relation is used for the vapor phase and the Tait relation is applied for the liquid phase, and therefore, the compressibility effects are considered for both the vapor and liquid phases. To analyze the flow... 

In this work, a high-order accurate gas kinetic scheme based on the compact finite-difference Boltzmann method (CFDBM) is developed and applied for simulating the compressible rarefied gas flows. Here, the Shakhov model of the Boltzmann equation is considered and the spatial derivative term in the resulting equation is discretized by using the fourth-order compact finite-difference method and the time integration is performed by using the third-order TVD Runge-Kutta method. A filtering procedure with three discontinuity-detecting sensors is applied and examined for the stabilization of the solution method especially for the problems involving the discontinuity regions such as the shock. The... 

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 the present study, the numerical simulation of the panel flutter in compressible inviscid flow is performed by the compact finite difference method. For this purpose, the 2D compressible Euler equations written in the arbitrary Lagrange-Eulerian form are considered and the resulting system of equations in the generalized curvilinear coordinates is solved by the fourth-order compact finite-difference method. An appropriate nonlinear filter is applied for the shock capturing and for the solution to be stable. The governing equation for the panel is also numerically solved by using the fourth-order compact finite difference method. The time integration in the flow domain is made by the... 

In this study, the viscous compressible flow is simulated over two-dimensional geometries by using the immersed boundary method and applying a high-order accurate numerical scheme. A fourth-order compact finite-difference scheme is used to accurately discretize the spatial derivative terms of the governing equations and the time integration is performed by the fourth-order Runge–Kutta scheme. To regularize the numerical solution and eliminate spurious modes due to unresolved scales, nonlinearities and inaccuracies in implementing boundary conditions, high-order low-pass compact filters are applied. A uniform Cartesian grid that is not coincident with the body surface is used and the boundary... 

In the present study, the numerical simulation of incompressible laminar and turbulent flows using a high-order finite difference lattice Boltzmann method is presented. To handle curved geometries with non uniform grids, the incompressible form of lattice Boltzmann equation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting equation are discretized using the fifth-order WENO scheme. The advantage of using the WENO-LBM developed is that it needs less number of grid points and remains stable even at high Reynolds number flows. For the temporal term, the fourth-order explicit Rung-Kutta scheme is adopted for laminar flow calculations and... 

In the present thesis, a high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied for an accurate and efficient numerical simulation of liquid-vapor two-phase flows. At first, the stability of the fourth-order CFDLBM is performed by using the von Neumann stability analysis for the D2Q7 and D2Q9 lattices. The stability analysis indicates that the CFDLBM proposed is stable and thus suitable for the simulation of high Reynolds number flows. The high-order CFDLBM is then developed and applied to accurately compute 2-D and 3-D incompressible flows in the Cartesian coordinates. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized... 

In the study, the simulation of two-dimensional cavitating flows is performed by applying a high-order accurate numerical method to the preconditioned, homogenous, multiphase Navier-Stokes equations. The baseline differential equations system is comprised of the mixture volume, mixture momentum and constituent volume fraction equations. A coordinate transformation is applied and the resulting system of governing equations in curvilinear coordinates is discretized using a fourth-order compact finite-difference scheme. The high-order accurate numerical scheme employing the suitable linear and nonlinear filters to account for density jumps across the cavity interface is shown to yield an... 

Two-dimensional incompressible flow analysis is one the most important applied issues in engineering and applied science field. Numerical solution of governing equations of flow requires exact computational grid generation.In complex geometries, generation of the grid which is coincident to the body is very difficult and time consuming. Immersed boundary method is an appropriate superseded method of body conformal grid generation in flow field numerical solution. In this method a grid which is not coincidentto bodyis generated and flow field properties are modified on points adjacent to the boundary of the object (Ghost Cell Method) to satisfy boundary conditions.
The purpose of this... 

In this study, fluid-solid interaction (FSI) is simulated computationally by using a high-order accurate numerical method. The two-dimensional incompressible viscous flows are considered in the fluid domain. The primary problem with solutions of the incompressible Navier–Stokes equations is the difficulty of coupling changes in the velocity field with changes in the pressure field while satisfying the continuity equation. Herein, the artificial compressibility method is used to overcome this difficulty. Preconditioning is implemented to reduce the stiffness of the system of equations to increase the convergence rate of the solution. Using preconditioning, physical solutions even at low...