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In this thesis a new image-based texturing method has been developed. This new method allows users to synthesize tiled textures that can be mapped to any quadrilateral mesh without discontinuity or singularity. An interface has been developed that allows user control over out put textures. Three methods have been included in the interface to create a periodic looking texture for 3D models and two methods have been developed to create wallpaper images (repeating textures on a 2D surface). Using these texturing methods, texturing problems are simplified, and more time can be spent solving artistic problems.

In this thesis a new image-based texturing method has been developed. This new method allows users to synthesize tiled textures that can be mapped to any quadrilateral mesh without discontinuity or singularity. An interface has been developed that allows user control over out put textures. Three methods have been included in the interface to create a periodic looking texture for 3D models and two methods have been developed to create wallpaper images (repeating textures on a 2D surface). Using these texturing methods, texturing problems are simplified, and more time can be spent solving artistic problems.

In this thesis work, our main motivation is to create computer aided art work which can eventually transform into a sculpting tool. The work was inspired after Taubin’s work on constructing Hamiltonian triangle strips on quadrilateral meshes. We present an algorithm that can divide a closed 2-manifold surface into exactly two regions, bounded from each other by a single continuous curve. We show that this kind of surface division is possible only if the mesh approximation of a given object is a two colorable quadrilateral mesh. For such a quadrilateral mesh, appropriate texturing of the faces of the mesh using a pair of Truchet tiles will give us a Duotone Surface. Catmull-Clark subdivision can convert any given mesh with arbitrary sided polygons into a two colorable quadrilateral mesh. Using such vertex insertion schemes, we modify the mesh and classify the vertices of the new mesh into two sets. By appropriately texturing each face of the mesh such that the color of the vertices of the face match with the colored regions of the corresponding Truchet tile, we can get a continuous curve that splits the surface of the mesh into two regions. Now, coloring the thus obtained two regions with two different colors gives us a Duotone Surface.

By defined structuring of sliding surfaces at dynamic contact seals friction and leakage can be reduced. Compared to macro-structures, micro-structures have the advantage of a quasi-homogeneous influence on the fluid behavior in the sealing gap. The development of suitable microstructures based on prototypes, whose properties are studied on the test bench, is very expensive and time-consuming due to the challenging manufacturing process and measuring technologies, which are necessary to investigate the complex rheological behavior within the sealing gap. A simulation-based development of microstructured sealing surfaces offers a cost- and time-saving alternative. This paper presents a method for simulative design and optimization of microstructured sealing surfaces at the example of a microstructured mechanical face seal.

O trabalho investiga a influencia dos parametros de processo: relacao D/Y e numero dos discos do agregado de texturizacao nas propriedades de frisagem dos filamentos de poliester texturizados por falsa torcao. Sao realizados ensaios numa texturizadeira industrial simulando diferentes niveis dos fatores D/Y e numero de discos.Analises estatisticas sao apresentadas e comprovam a influencia dos fatores nas caracteristicas de frisagem com nivel de confianca de 5%. Verifica-se que a combinacao de D/Y elevado com numero de discos elevado aumenta os valores dos parametros de frisagem do fio texturizado. / The work investigates the influence of process parameters: the factor D / Y and the aggregate number of disks in the texturing properties crimping of textured polyester filaments for false twist. Tests were performed in an industrial texturing machine simulating different levels of factors D / Y and number of discs. Results of statical analyses are presented and show the influence of factors on the characteristics of crimping with a confidence level of 5%. It is found that the combination of D / Y with a high number of discs increases the high values of the parameters of the crimp textured yarn.

O trabalho investiga a influencia dos parametros de processo: relacao D/Y e numero dos discos do agregado de texturizacao nas propriedades de frisagem dos filamentos de poliester texturizados por falsa torcao. Sao realizados ensaios numa texturizadeira industrial simulando diferentes niveis dos fatores D/Y e numero de discos.Analises estatisticas sao apresentadas e comprovam a influencia dos fatores nas caracteristicas de frisagem com nivel de confianca de 5%. Verifica-se que a combinacao de D/Y elevado com numero de discos elevado aumenta os valores dos parametros de frisagem do fio texturizado. / The work investigates the influence of process parameters: the factor D / Y and the aggregate number of disks in the texturing properties crimping of textured polyester filaments for false twist. Tests were performed in an industrial texturing machine simulating different levels of factors D / Y and number of discs. Results of statical analyses are presented and show the influence of factors on the characteristics of crimping with a confidence level of 5%. It is found that the combination of D / Y with a high number of discs increases the high values of the parameters of the crimp textured yarn.

By defined structuring of sliding surfaces at dynamic contact seals friction and leakage can be reduced. Compared to macro-structures, micro-structures have the advantage of a quasi-homogeneous influence on the fluid behavior in the sealing gap. The development of suitable microstructures based on prototypes, whose properties are studied on the test bench, is very expensive and time-consuming due to the challenging manufacturing process and measuring technologies, which are necessary to investigate the complex rheological behavior within the sealing gap. A simulation-based development of microstructured sealing surfaces offers a cost- and time-saving alternative. This paper presents a method for simulative design and optimization of microstructured sealing surfaces at the example of a microstructured mechanical face seal.

Virtual reality (VR) applications are becoming increasingly popular and are being used in various applications. VR applications can be used to simulate large real-world landscapes in a computer program for various purposes such as entertainment, education or business. Typically, 3-dimensional (3D) and VR applications use environments that are made up of meshes of relatively small size. As the size of the meshes increase, the applications start experiencing lagging and run-time memory errors. Therefore, it is inefficient to upload large-sized meshes into a VR application directly. Manually modelling an accurate real-world environment can also be a complicated task, due to the large size and complex nature of the landscapes. In this research, a method to automatically convert 3D point-clouds of any size and complexity into a format that can be efficiently rendered in a VR application is proposed. Apart from reducing the cost on performance, the solution also reduces the risks of virtual reality induced motion sickness. The pipeline of the system incorporates three main steps: a surface reconstruction step, a texturing step and a segmentation step. The surface reconstruction step is necessary to convert the 3D point-clouds into 3D triangulated meshes. Texturing is required to add a realistic feel to the appearance of themeshes. Segmentation is used to split large-sized meshes into smaller components that can be rendered individually without overflowing the memory. A novel mesh segmentation algorithm, the Triangle Pool Algorithm (TPA) is designed to segment the mesh into smaller parts. To avoid using the complex geometric and surface features of natural scenes, the TPA algorithm uses the colour attribute of the natural scenes for segmentation. The TPA algorithm manages to produce comparable results to those of state-of-the-art 3D segmentation algorithms when segmenting regular 3D objects and also manages to outperform the state-of-the-art algorithms when segmenting meshes of real-world natural landscapes. The VR application is designed using the Unreal and Unity 3D engines. Its principle of operation involves rendering regions closer to the user using highly-detailed multiple mesh segments, whilst regions further away from the user are comprised of a lower detailed mesh. The rest of the segments that are not rendered at a particular time, are stored in external storage. The principle of operation manages to free up memory and also to reduce the amount of computational power required to render highly-detailed meshes. / Dissertation (MEng)--University of Pretoria, 2020. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

High temperature thermal energy harvesting has attracted much attention recently. In order to achieve stable operation at high temperatures there is emerging need to develop efficient and oxidation-resistant materials. Most of the well-known materials with high dimensionless figure of merit (ZT) values such as Bi2Te3, PbTe, skutterudites, and half-Heusler alloys, are not thermally stable at temperatures approaching 500°C or higher, due to the presence of volatile elements. Oxide thermoelectric materials are considered to be potential candidates for high temperature applications due to their robust thermal and chemical stability in oxidizing atmosphere along with the reduced toxicity, relatively simpler fabrication, and cost. In this dissertation, nanoscale texturing and interface engineering were utilized for enhancing the thermoelectric performance of oxide polycrystalline Ca3Co4O9 materials, which were synthesized using conventional sintering and spark plasma sintering (SPS) techniques. In order to tailor the electrical and thermal properties, Lu and Ga co-doping was investigated in Ca3Co4O9 system. The effect of co-doping at Ca and Co sites on the thermoelectric properties was quantified and the anisotropic behavior was investigated. Because of the effective scattering of phonons by doping-induced defects, lower thermal conductivity and higher ZT were achieved. The layered structure of Ca3Co4O9 has strong anisotropy in the transport properties. For this reason, the thermoelectric measurements were conducted for the samples along both vertical and horizontal directions. The ZT value along the vertical direction was found to be 3 to 4 times higher than that along the horizontal direction. Metallic inclusions along with ionic doping were also utilized in order to enhance the ZT of Ca3Co4O9. The texturing occurring in the nanostructured Ca3Co4O9 through ion doping and Ag inclusions was studied using microscopy and diffraction analysis. Multi-length scale inclusions and heavier ion doping in Ca3Co4O9 resulted in higher electrical conductivity and reduced thermal conductivity. The maximum ZT of 0.25 at 670°C was found in the spark plasma sintered Ca2.95Ag0.05Co4O9 sample. In literature, limited number of studies have been conducted on understanding the anisotropic thermoelectric performance of Ca3Co4O9, which often results in erroneous estimation of ZT. This study addresses this limitation and provides systematic evaluation of the anisotropic response with respect to platelet microstructure. Textured Ca3Co4O9/Ag nanocomposites were fabricated using spark plasma sintering (SPS) technique and utilized for understanding the role of microstructure towards anisotropic thermoelectric properties. The thermoelectric response was measured along both vertical and horizontal direction with respect to the SPS pressure axis. In order to achieve enhanced degree of texturing and increase electrical conductivity along ab planes, a two-step SPS method was developed. Ag nanoinclusions was found to increase the overall electrical conductivity and the thermoelectric power factor because of improved electrical connections among the grains. Through two-step SPS method, 28% improvement in the average ZT values below 400°C and 10% improvement above 400°C in Ca3Co4O9/Ag nanocomposites was achieved. Lastly, this dissertation provides significant progress towards understanding the effect of synthesis method on thermoelectric properties and evolution of textured microstructure. The anisotropy resulting from the crystal structure and microstructural features is systematically quantified. Results reported in this study will assist the continued progress in developing Ca3Co4O9 materials for practical thermoelectric applications. / PHD / Among the wide range of renewable energy sources, wasted thermal energy has attracted worldwide interest as it is freely available from most of the industrial and natural processes. Among various choices for converting thermal energy into electricity, thermoelectric devices are attractive as they are solid state, noiseless, no moving parts, and can be easily integrated with most of the heat sources. Thus, there has been significant efforts to develop high efficiency thermoelectric energy harvesting devices. However, currently available thermoelectric materials are not thermally stable in oxidizing environments because of heavy metals’ evaporation and reactivity. In order to overcome this limitation of thermoelectric materials, in this dissertation, the focus is on developing calcium cobalt oxide (Ca₃Co₄O₉) materials through innovation in the processing, composition design, and modulation of the thermal transport mechanism by exploiting the anisotropy. Ca₃Co₄O₉ is promising candidate for high temperature thermoelectric applications due to its thermal and chemical stability in oxidizing atmosphere, reduced toxicity, easy fabrication, and low cost. Its main disadvantages are the high thermal conductivity and low electrical conductivity. In order to tailor the electrical and thermal properties, Lu and Ga co-doped Ca₃Co₄O₉ were synthesized and characterized. The thermoelectric measurements were conducted along both vertical and horizontal directions with respect to pressure axis during spark plasma sintering. Layered structure of Ca₃Co₄O₉ induces strong anisotropy in the transport properties which indicates that textured microstructure will result in better properties. Texturing and interface engineering were employed to control the grain orientation and thereby improve the electrical and thermal properties. In textured and nanostructured Ca₃Co₄O₉, Ag inclusions along with ionic doping was utilized to enhance the thermoelectric performance. In literature, the importance of the anisotropy in Ca₃Co₄O₉ has been less emphasized, which has restricted accurate thermoelectric evaluation of this material for practical application. In order to address this issue, first textured Ca₃Co₄O₉/Ag nanocomposites were fabricated using spark plasma sintering (SPS) techniques and next detailed investigation was conducted on correlation between microstructure and anisotropic thermoelectric properties. The power factor of the Ca₃Co₄O₉/Ag nanocomposites at high temperatures was almost 50% enhanced, as compared to the pure Ca₃Co₄O₉, which resulted in 50% improvement in ZT both horizontal and vertical directions. The samples with texturing along the vertical direction were used to perform the long-term durability test and almost same value of resistivity was maintained after a long-term heating. Two-step SPS method was developed to improve the in-plane electrical conductivity. Through this newly proposed synthesis process, 28% improvement in the average ZT values below 400°C and 10% improvement above 400°C was obtained in Ca₃Co₄O₉/Ag nanocomposites. Using a wide range of composition and synthesis process, the anisotropy and microstructural effects clarified in this study provides promising pathway towards enhance the thermoelectric performance of Ca₃Co₄O₉ materials.