The move from fossil fuels is getting more relevant throughout the globe, mainly for it getting more costly to emit CO$_2$. The steel industry is one of the biggest contributor of the CO$_2$ emissions, and is therefore very motivated to reduce their emissions. One way to reduce the emissions is to go from coal to bio-char as a reducing agent. BEST(Bio-energy and sustainable technologies) is a research institute in Austria, and have been tasked to do research on bio-char and what problems that may occur with changing from coal to bio-char. One problem with bio-char is that it is prone to self ignition. This project aims is to develop a numerical model that can simulate self heating within bio-char stockpiles. The tool will be for a one-dimensional case using Cartesian coordinates. The calculations are based on the SIMPLE algorithm for Navier-Stokes equations, which is widely used within CFD calculations. This tool has been used to do sensitivity analysis for multiple variables and parameter studies for kinetic parameters related to the oxidation that occurs when bio-char is exposed to oxygen. Results show that oxygen concentration is the limiting factor to how much heat is released within the bag during simulations. Results also show that the accurate descriptions of reaction schemes and their rate expressions is very important to get results that is in line with real world scenarios.

To accommodate an increasing number of tourists visiting Bequia, the second largest island of Saint-Vincent and the Grenadines, the local government constructed an airport, through a major coastline land-reclamation project. However, due to the prevailing ocean current patterns in the area, an inlet created on the east side of the new airport is prone to trapping significant amounts of ocean-borne debris. This litter accumulation creates a health risk to local fishermen who clean their daily catch using water from the inlet. It is proposed to install a rubble-mound groyne structure on the eastward side of the new inlet to address this problem. The utilisation of a coastline groyne in this case is somewhat unorthodox, as the latter is normally employed to mitigate against coastal erosion. The goal of this study is to optimise the groyne design with the assistance of a 3D numerical model. The ‘Delft3D’ open-source model (WAVE and FLOW modules) was selected to examine the effects of different orientations and lengths of the proposed groyne on the movements of floating debris. Included in the initial phase of the study was a field investigation to collect certain data which were necessary for model calibration and validation. This involves the use of an Acoustic Doppler Current Profiler (ADCP) to measure local shore bathymetry and also current velocities over a range of tidal cycles.

Master Thesis, Department of Mechanical Engineering / A comprehensive analytical model of an indirect internal reforming type tubular Solid Oxide Fuel Cell (IIR-T-SOFC) has been developed. Two-dimensional axisymmetric multicomponent gas flow fields and quasi-three-dimensional electric potential/current fields in the tubular cell are simultaneously treated in the model with consideration of the involved phenomena such as internal reforming, electrochemical reactions and radiative heat transfer. By using this model, the characteristics of the operating state of an IIR-T-SOFC were numerically examined. As a result, it was shown how the thermal field and power generation characteristics of the cell were affected by the gas inlet temperature, air flow rate, steam-methane ratio, reforming catalyst distribution and thickness of the electrodes. In particular, the optimized catalyst distribution greatly reduced both the maximum temperature and temperature gradients of the cell with little negative impact on the power generation performance of the cell. / 京都大学 / 0048 / 修士 / 修士(工学) / Kyoto University / TFtmp

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This thesis presents a three-dimensional groundwater modeling of Wekia springshed in central Florida using a numerical model, WASH123D. Springs have historically played an important role in Florida's history. The Wekiva River is a spring-fed system associated with about 19 springs connected to the Floridan aquifer. With increased urbanization and population growth in this region, there has been an increased strain on the water levels of Floridan aquifer which is a major source of potable water. Maintaining groundwater recharge to the aquifer is a key factor of the viability of the regional water supply as well as Wekiva ecosystem. Hence, the first-principle, physics-based watershed model WASH123D has been applied to conduct the study of Wekiva "springshed", which is the recharge area and watershed contributing groundwater and surface water to the spring. In this work, the hydrogeologic conditions of the Wekiva springshed are discussed followed by the modeling details such as mathematical background, domain discretization and initial and boundary conditions considered. Finally, the results from the model are discussed. The Wekiva WASH123D model was run to evaluate the average, steady state 1995 hydrological conditions. The distribution of simulated Floridan aquifer system groundwater levels using WASH123D shows very good agreement with the field observations at corresponding locations.

Rivers are considered as one of the most important surface water resources on the earth. During the time, most of the rivers on the earth experienced evolution and changes. River bends and confluences are one of the common cases in most rivers. There is a significant impact of the flow on the cross-sectional profile of river bends and confluences. Secondary currents are one of the important features that characterize flow in river bends and confluences. In such currents, fluid particles follow a helical path instead of moving nearly parallel to the axis of the channel. The local imbalance between the vertically varying centrifugal force and the cross-stream pressure gradient results in generating the secondary flow and raising a typical motion of the helical flow. Several studies, including experimental or mathematical, have been conducted to examine flow characteristics in curved open channels, river meanders, or confluences. In this research, the influence of secondary currents is studied on the elevation of water surface and the hydraulic structures in channel bends and confluences by employing a 3D OpenFOAM numerical model. The research implements a 3D OpenFOAM numerical model to simulate the horizontal distribution of the flow. In addition, the progress in unraveling and understanding the bend and confluent dynamics is discussed. The finite volume method in OpenFOAM software is used to simulate and examine the behavior of the secondary current. Thereafter, a comparison between the experimental data and a numerical model is conducted. Two sets of experimental data are used as the dataset for these two experiments are complete and validated; the data provided by Rozovskii (1961) for a sharply curved channel, and the dataset provided by Shumate (1998) for a confluent channel. Two solvers in OpenFOAM software were selected to solve the problem regarding the experiment: InterFoam and PisoFoam. InterFoam is a transient solver for incompressible flow that is used with open channel flow with Free Surface Model. PisoFoam is a transient solver for incompressible flow that is used with closed channel flow and Rigid-Lid Model. Various turbulence models (i.e., Standard k-ε, Realizable k-ε) are applied in the numerical model to assess the accuracy of turbulence models in predicting the behavior of the flow. The accuracies of various turbulence models are examined and discussed.

<p>The local corrosion of refractories at the slag/gas interface is a serious problem that limits the life of the refractories.Although, there have been several studies focused on understanding the Marangoni effect on the refractory dissolution process, there is little quantifiable analysis available. The aim of this study is to establish a better fundamental understanding of refractory dissolution mechanisms, and develop appropriate models for predicting the extent and rate of slag-line dissolution.</p> <p>In the first part of this research, experimental studies using a high temperature dip technique were performed: MgO refractory in SiO₂-CaO-FeO_x-MgO slag and Al₂O₃- SiO₂-CaO-FeO_x-MgO. The experiments were conducted at varies temperature. There was significant evidence of a spinel phase formed at the slag/refractory interface for slags containing 20wt.% Al₂O₃. This existence of the spinel seems to have retarded the dissolution of the refractory. The decrease in erosion rate in the presence of spinel is in proportion to the decrease in the equilibrium MgO concentration at the slag/solid interface. The activation energy is calculated from the relationship of effective mass transfer coefficient vs. temperature and found in the range of mass transfer activation energy.</p> <p>The second part of this search is developing a numerical model to predict the slag-line dissolution. An effective algorithm for analysis of unsteady Marangoni convection in refractory slag line dissolution has been developed. The results show that the Marangoni effect plays a very important role in slag-line erosion at this condition; both the moving boundary condition and curved surface condition have significant effects on the slag-line erosion rate. The comparison of experimental and numerical results shows that the model can predict the refractory maximum corrosion distance caused by Marangoni flow at the slag line. However, the eroded material volume was predicted within 20~30% deviation</p> / Doctor of Philosophy (PhD)

The electronic band structure of a semiconductor is an essential property to determine most of its optical characteristics. The complexity of the energy band structure calculations makes analytical calculations impossible. Any calculation leading to electronic band structures has to utilize numerical methods. In this thesis, two solvers were developed to calculate the energy band structure of 1D Kronig-Penney lattice, 30 diamond lattice-structure and silicon lattice. In this thesis, many of the important methods of calculating the energy band structures were discussed. Through comparisons among different methods, we have determined that Self-Consistent Pseudopotential Method, SCPM, is the most suitable method for calculating the energy band structures when self-sufficiency and accuracy are of special importance. The SCPM is an iterative method which was utilized in this thesis by using efficient numerical methods. Instead of using conventional numerical methods such as Finite Difference Method or Finite Element Method which cause inefficiency, this thesis calculates the energy band structure by utilizing Orthogonal Plane-Wave expansion of the potentials. The 1D electronic band structure solver was developed as a foundation for the implementation of the 30 electronic band structure solver. It uses a minimal number of Fourier coefficients to calculate the energy band structure of the 1D Lattices without compromising accuracy. The 30 electronic band structure solver development needs multiple changes and modifications to the 1D solver. As the 30 solver is essentially made using the 10 solver platform, it is also efficient and needs a minimal number of Fourier coefficients for accurate results. The 30 solver can be used for either Nearly Free Electron Method, NFEM, or SCPM calculations. The NFEM calculations were done on the diamond lattice structure. The results were shown to be the same as the benchmarks of [28, 80]. The silicon lattice energy band structure was also calculated with the 30 solver using SCPM with LOA. The results were in the same range as the four sets of data gathered from three benchmarks [58, 81, 82], showing good agreement. Based on the two comparisons made for the 30 solver, it was shown that it is a reliable and efficient program to calculate energy band structures of the 30 lattices. / Thesis / Master of Applied Science (MASc)

Yes / In this study, the evolution process of the swallow-tailed flip bucket water nappe entering into the plunge pool is simulated by using the standard 𝑘-𝜀 turbulence model and the volume of fluid method. The effects of the upstream opening width ratio and downstream bucket angle on the flow pattern, the unit discharge distribution and the impact pressure distribution are studied. Based on the numerical results, the inner and outer jet trajectories are proposed by using the data. Results show that the longitudinal stretching length decreases with the increase of the upstream opening width ratio, and increases with the increase of the downstream bucket angle. The water nappe enters the plunge pool in a long strip shape. Thus, the unit discharge distribution of water nappe entry is consistent with the pressure distribution at the plunge pool bottom. The upstream opening width ratio and downstream bucket angle should be chosen as their intermediate values in order to have a uniform discharge distribution and to reduce the pressure peak at the plunge pool floor, which is effectively to avoid instability and destruction of plunge pool floor. / National Science Fund for Distinguished Young Scholars (No. 51625901) and National Nature Science Foundation of China (No: 51579165).

The importance of precise values for the parameters used in heat and mass transfer models has been demonstrated by many research studies. Thermal conductivity values used in previous models are usually empirical and fluctuate. Theoretical analysis and estimations of wood thermal conductivities in the radial and tangential directions were conducted with the geometric models built up from the macro- and micro-structure observations. Theoretically, thermal conductivity in the radial direction is about 1.5 to 2.5 times of the tangential direction for softwood species with moisture content (MC) below Fiber Saturation Point (FSP). When MC is over the FSP, tangential radial thermal conductivity both increase dramatically and are linear function of MC. The two thermal conductivity values are close with a ratio of near one estimated by the model for MC above the FPS. In hardwood species, radial thermal conductivity estimated by the model is 1.5 times of the tangential thermal conductivity. Validation tests for model estimations of thermal conductivities in the radial and tangential directions for three wood species showed the reliability of the geometric models developed in this project. Correlations between the wood thermal conductivity and structure parameters, such as latewood percentage and cell wall percentage, were examined. Linear relationships for the thermal conductivity and average temperature in wood were established in both radial and tangential directions of three wood species. A two-dimensional transient heat conduction model was developed utilizing thermal conductivity values derived from geometric models. The anisotropic material property affect on heat transport in radial and tangential directions was discussed using an assumed situation. The simulation run showed slightly faster heat flow in the radial direction than in the tangential direction due to higher thermal conductivity in the radial direction. Validation tests on practical wood blocks showed the 2D model with the use of theoretical thermal conductivity values can predict good temperature distribution in wood during the heating process. However, in the practical wood samples with curved rings on the cross section, no significant difference was found in the two transverse directions. Mathematica software was introduced in this study for the intense and complicated math calculations and model programming. Mathematica was found to be a powerful technique for solving sophisticated math problems. It had abundant and flexible plotting options for providing optimized presentations for the results. These advantages make Mathematica popular for engineering modeling research. / Ph. D.