In this work, numerical simulations of flow separation control are performed. The sep-aration control technique studied is called 'synthetic jet actuation'. The developed code employs a cell centered finite volume scheme which handles viscous, steady and unsteady compressible turbulent flows. The pulsating zero mass jet flow is simulated by imposing a harmonically varying transpiration boundary condition on the airfoil's surface. Turbulence is modeled with the algebraic model of Baldwin and Lomax. The application of synthetic jet actuators is based in their ability to energize the boundary layer, thereby providing signifcant increase in the lift coefficient. This has been corroborated experimentally and it is corroborated numerically in this research. The performed numerical simulation investigates the flow over a NACA0015 air-foil. For this flow Re = 9??105 and the reduced frequency and momentum coefficient are F+ = 1:1 and C?? = 0:04 respectively. The oscillatory injection takes place at 12.27% chord from the leading edge. A maximum increase in the mean lift coefficient of 93% is predicted by the code. A discrepancy of approximately 10% is observed with corresponding experimental data from the literature. The general trend is, how-ever, well captured. The discrepancy is attributed to the modeling of the injection boundary condition and to the turbulence model.A sensitivity analysis of the lift coefficient to different values of the oscillation parameters is performed. It is concluded that tangential injection, F + ?? O(1) and the utilized grid resolution around the site of injection are optimal. Streamline fields ob-tained for different angles of injection are analyzed. Flow separation and attachment as functions of the injection angle and of the velocity of injection can be observed. It is finally concluded that a reliable numerical tool has been developed which can be utilized as a support tool in the optimization of the synthetic jet operation and in the modeling of its operation.

Controlled cooling is an important part of steel production industry that affects the properties of the outcome steel. Many of the researches done in controlled cooling are experimental. Due to progress in the numerical techniques and high cost of experimental works in this field the numerical work seems more feasible. Heat transfer analysis is the necessary element of successful controlled cooling and ultimately achievement of novel properties in steel. Heat transfer on the surface of the plate normally contains different regimes such as film boiling, nucleate boiling, transition boiling and radiation heat transfer. This makes the analysis more complicated. In order to perform the heat transfer analysis often empirical correlations are being used. In these correlations the velocity and pressure within the fluid domain is involved. Therefore in order to obtain a better understanding of heat transfer process, study of hydrodynamics of the fluid becomes necessary. Circular jet due to its high efficiency has been used vastly in the industry. Although some experimental studies of round jet arrays have been done, yet the characteristics of a single jet with industrial geometric and flow parameters on the surface of a flat plate is not fully understood. Study of hydrodynamics of the jet impingement is the first step to achieve better understanding of heat transfer process. Finite element method as a popular numerical method has been used vastly to simulate different domains. Traditional approaches of finite element method, Lagrangian and Eulerian, each has its own benefits and drawbacks. Lagrangian approach has been used widely in solid domains and Eulerian approach has been widely used in fluid fields. Jet impingement problem, due to its unknown free surface and the change in the boundary, falls in the category of special problems and none of the traditional approaches is suitable for this application. The Arbitrary Lagrangian Eulerian (ALE) formulation has emerged as a technique that can alleviate many of the shortcomings of the traditional Lagrangian and Eulerian formulations in handling these types of problems. Using the ALE formulation the computational grid need not adhere to the material (Lagrangian) nor be fixed in space (Eulerian) but can be moved arbitrarily. Two distinct techniques are being used to implement the ALE formulation, namely the operator split approach and the fully coupled approach. This thesis presents a fully coupled ALE formulation for the simulation of flow field. ALE form of Navier-Stokes equations are derived from the basic principles of continuum mechanics and conservation laws in the fluid. These formulations are then converted in to ALE finite element equations for the fluid flow. The axi-symmetric form of these equations are then derived in order to be used for jet impingement application. In the ALE Formulation as the mesh or the computational grid can move independent of the material and space, an additional set of unknowns representing mesh movement appears in the equations. Prescribing a mesh motion scheme in order to define these unknowns is problem-dependent and has not been yet generalized for all applications. After investigating different methods, the Winslow method is chosen for jet impingement application. This method is based on adding a specific set of partial differential Equations(Laplace equations) to the existing equations in order to obtain enough equations for the unknowns. Then these set of PDEs are converted to finite element equations and derived in axi-symmetric form to be used in jet impingement application. These equations together with the field equations are then applied to jet impingement problem. Due to the number of equations and nonlinearity of the field equations the solution of the problem faces some challenges in terms of convergence characteristics and modeling strategies. Some suggestions are made to deal with these challenges and convergence problems. Finally the numerical treatment and results of analyzing hydrodynamics of the Jet Impingement is presented. The work in this thesis is confined to the numerical simulation of the jet impingement and the specifications of an industrial test setup only have been used in order to obtain the parameters of the numerical model.

The current thesis studies a model of two dimensional convection of an ideal gas in a rectangular domain having walls of finite thickness. The temperature outside of walls is considered constant. Heat exchange between walls and outside/inside air is computed using Newton's law of cooling. Heat transfer inside walls is modelled with the heat equation. The mathematical model inside enclosure involves Navier-Stokes equations coupled with equation of state for gas. The model is numerically studied using the method of large particles. One of the main goals of the current thesis was to develop a software in C# language for numerical solution of the above-described model. Physically meaningful results, including stream lines and distribution of parameters of gas and temperature inside solid walls were obtained.

Propagation of radiation in a waveguides is theoretically described by Maxwell&amp / #8217 / s equations. The gradient of refractive index and an influence on the waveguide by a superstrate requires a numerical solution of the differential equation. Iterative methods such as the Runge-Kutta approaches are used to calculate the effective refractive index in the waveguide depending on the superstrate&amp / #8217 / s and the waveguide&amp / #8217 / s local refractive indices. In this study,the refractive indices, and the model fields of the TE00 modes are calculated. The calculated fields of the 00 TE modes give information about the propagation of the light in the waveguide. Also, the precision of the Runge-Kutta aproaches has been tested. The advantages and disadvantages of the Runge-Kutta aproaches are discussed.

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The current thesis studies a model of two dimensional convection of an ideal gas in a rectangular domain having walls of finite thickness. The temperature outside of walls is considered constant. Heat exchange between walls and outside/inside air is computed using Newton's law of cooling. Heat transfer inside walls is modelled with the heat equation. The mathematical model inside enclosure involves Navier-Stokes equations coupled with equation of state for gas. The model is numerically studied using the method of large particles. One of the main goals of the current thesis was to develop a software in C# language for numerical solution of the above-described model. Physically meaningful results, including stream lines and distribution of parameters of gas and temperature inside solid walls were obtained.

This research is aimed to study the storage tank design parameters effects on the efficiency of the large solar hot water system. Detailed CFD simulation for the storage tank coupled with TRNSYS program simulation for the entire solar hot water system will be performed to study the system performance under various thermal stratification baffles design for the storage tank. The study is made for three representative cities of Taiwan by input their typical-meteorological-year data (TMY data). The results indicate the performance of a large solar hot water system can be significantly improved with proper designed thermal stratification baffles in the storage tank.

As part of a larger effort to understand the fundamental knowledge of polymer scratch behavior, this dissertation is focused on both experimental study and numerical analysis of scratch deformation of a broad range of polymers, with an emphasis on the mechanical understanding of how the scratch-induced damage is formed. An instrumented progressive load scratch method recommended by ASTM/ISO standards was adopted for the experimental work. The commercial finite element (FE) method package ABAQUS was employed as a numerical simulation tool to describe the stress-strain fields, and it analyzes the deformation mechanisms during the scratch process. A thorough parametric study has been performed to assess the influence of material parameters and surface properties, such as Young's modulus, yield strength, and friction coefficient, on the polymer scratch behavior. Upon investigation of the scratch behaviors of a broad range of polymer materials, various kinds of scratch damage features are identified and correlated with the mechanical characteristics of the polymers. A generalized scratch damage mechanism map for polymers is presented. Correlation between different material types and scratch damage mechanisms is made. It is found that both the material characteristics and the stress state exerted on the scratched surface are responsible for the observed scratch damage mechanisms. The phenomenological deduction of the scratch damage process based on the stick-slip mechanism is established. A more realistic material law for the scratch analysis is also provided. To evaluate the polymer resistance against scratch visibility quantitatively, an entirely new automated on-set scratch visibility determination methodology is developed based on typical visual characteristics of human eyes. Its application on the evaluation of mar and abrasion of polymer is also explored. This new methodology can quantify polymer scratch resistance consistently and reliably regardless of the sample surface characteristics and color.

A theoretical model and numerical simulation of a direct methanol fuel cell (DMFC) is developed to simulate the reaction mechanisms and the cell voltage under several different designing parameters and operational conditions. The results of a numerical simulation include the distributions of the proton current density, the concentration of methanol, the electrochemical reaction rates, the overpotential losses, and the pressures within proton exchange membrane layer, catalyst layer and diffusion layer. In addition, the influence of aforementioned operational conditions on methanol crossover in a direct methanol fuel cell is also investigated. Finally, the results of the model are compared to the results from the experimental work. The results show that increasing of temperature, pressure and anode catalyst loading can enhance the performance of a direct methanol fuel cell, and the concentration of methanol plays an important role in its performance. The optimal concentration of methanol for a direct methanol fuel cell is about 2M. Methanol crossover can be suppressed by decreasing methanol concentration and increasing thickness of polymer electrolyte membrane (PEM). However, under operating condition of high current density, thick PEM and low methanol concentration will cause large concentration overpotential and ohmic losses, respectively.

In this thesis, a numerical simulation model is applied to investigate the long-term shoreline changes behind detached breakwaters. The model includes three components, namely a wave model, a current model, and a shoreline change model. In the numerical simulations, various combinations of wave conditions and the placement of detached breakwater are chosen to explore the effect of detached breakwaters on the shoreline change. The results of calculation show that with incident wave angles within 0~45, wave height in the range of 0.5~1.5m, or the offshore distance to the detached breakwaters being 60~120m, the larger in any one of these three parameters is, the bigger the erosion distance onshore from the original shoreline and the extent of salient offshore are behind detached breakwaters. When incident angle of the wave increases, shoreline plan form becomes skewed, and the time required to arrive at equilibrium also increases, in addition to the position of the top of salient moves downcoast. Within the wave periods of 7~10 seconds tested, waves with large period are found to show slight decrease of the erosion distance onshore and the extent of salient offshore behind detached breakwaters. The plan form of the salient is not affected by wave period. However, the larger the wave period is, the sooner the long-tern shoreline will result. Moreover, for a detached breakwater constructed in the range of offshore distances within 1.0¡ÕS/B¡Õ2.0, variable offshore distances do not produce much difference in the erosion distance onshore and the extent of salient offshore behind detached breakwaters, and salient only will form. In the case of the S/B =< 0.8, a tombolo will result. Finally, the results of shoreline plan form from the numerical modeling are verified by the empirical parabolic bay shape equation of Hsu and Evans (1989), a small-scale hydraulic model, and two numerical models based on GENESIS and LITPACK. Overall, the result are in good agreement with these four different approaches, and therefore, the present model is suitable for practical engineering applications.