Abstract Pool boiling process is frequently encountered in a number of engineering applications. However, it is difficult to exactly predict the heat transfer coefficient. This is because the boiling phenomenon is rather complex and influenced by many factors, such as surface condition, heater size, geometry, material, arrangement of heated rods, and refrigerants, etc. The key boiling parameters (bubble dynamics data) such as bubble departure diameter, frequency and nucleation site density will be varied in such different heated surface resulting in the different effect of heat transfer. The present study is ain at providing the pool boiling data for plasma coating and helical wire wrapped enhanced tubes. Furthermore, more fundamental of the physical phenomenon can be obtained. This study was performed experimentally. R-134a and R-600a were used as refrigerants. The surface condition will be changed with plasma spray coating and helical wire wrapped. It is expected that the surface condition can affect the nucleate boiling heat transfer in certain degree. In addition, boiling visualization was also made to broaden our basic understanding of the bubble diameter and dynamics while growing. Thermal design data of a flooded type evaporator of high performance as well as more and further physical insight of the above-stated nucleate boiling heat transfer can be acquired. The results will hopefully be helpful not only for the academia but for the industry.

If a known distribution on a real line is given, it can be wrapped on the circumference of a unit circle. This research entails the study of a univariate skew-normal distribution where the skew-normal distribution is generalised for the case of bimodality. Both the skew-normal and exible generalised skew-normal distributions are wrapped onto a unit circle, consequently referred to as a wrapped skew-normal and a wrapped exible generalised skew-normal distribution respectively. For each of these distributions a simulation study is conducted, where the performance of maximum likelihood estimation is evaluated. Skew scale mixtures of normal distributions with the wrapped version of these distributions are proposed and graphical representations are provided. These distributions are also compared in an application to wind direction data. / Dissertation (MSc)--University of Pretoria, 2019. / Statistics / MSc / Unrestricted

Cette étude vise à développer des connaissances sur le comportement d’un réservoir d’hydrogène àhaute pression en composite bobiné (fibre de carbone et résine époxy) soumis à des chocs en service, c'est-àdireà étudier les endommagements générés ainsi que leur évolution et leurs conséquences en service. Dansun premier temps, une étude micrographique sur les réservoirs impactés à des niveaux d’énergiecaractéristiques des chocs habituels de manutention a été réalisée afin d’observer les configurationsd’endommagement induites. Par la suite, différentes techniques d’impact sont comparées pour sélectionnercelle permettant de reproduire ces endommagements représentatifs des chocs subis par les réservoirs sur deséprouvettes prélevées dans des cylindres bobinés. Ces échantillons sont testés en traction monotone afin dequantifier l’abattement des propriétés mécaniques induites par l’endommagement. Puis, une approche demodélisation de l’évolution des dommages d’impact a été développée. Dans un souci de ménager le caractèreopérationnel de l’approche, elle est construite à partir d’outils simples permettant de traduire l’effet de lafissuration matricielle, de la rupture des fibres et du délaminage. Pour décrire la ruine de la structure, uneapproche de type « analyse progressive de la rupture » a été utilisée. Une fois validé sur éprouvette, lemodèle est appliqué au comportement de réservoirs complets afin d’estimer la tolérance aux dommages et deprévoir la diminution de pression d’éclatement provoquée par les chocs. / This study aims to develop knowledge about the behavior of a wound composite high-pressurehydrogen tank subjected to impact in service, that is to say, to study the damage generated and their evolutionand their consequences in service. At first, a micrographic study of reservoirs impacted at energy levelscharacteristic of common in-service shocks is performed to observe damage induced configurations.Thereafter, various impact techniques are compared to select the one able to reproduce this representativedamage on specimens cut from wound composite cylinders. These samples are tested under monotonictension to quantify the reduction of the mechanical properties induced by damage. Then, a model for theevolution of impact damage is developed. In order to maintain the operational nature of the approach, it isbuilt from simple tools to capture the effect of matrix cracking, fiber breakage and delamination. To describethe collapse of the structure, a "progressive failure analysis" is used. Once validated on specimens, the modelis applied to the behavior of wound composite tanks to estimate damage tolerance and predict the burstpressure decrease caused by shocks.

Doctor of Philosophy / Department of Civil Engineering / Hayder Rasheed / The analysis of concrete columns using unconfined concrete models is a well established practice. On the other hand, prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear analysis. Modern codes and standards are introducing the need to perform extreme event analysis. There has been a number of studies that focused on the analysis and testing of concentric columns or cylinders. This case has the highest confinement utilization since the entire section is under confined compression. On the other hand, the augmentation of compressive strength and ductility due to full axial confinement is not applicable to pure bending and combined bending and axial load cases simply because the area of effective confined concrete in compression is reduced. The higher eccentricity causes smaller confined concrete region in compression yielding smaller increase in strength and ductility of concrete. Accordingly, the ultimate confined strength is gradually reduced from the fully confined value fcc (at zero eccentricity) to the unconfined value f’c (at infinite eccentricity) as a function of the compression area to total area ratio. The higher the eccentricity the smaller the confined concrete compression zone. This paradigm is used to implement adaptive eccentric model utilizing the well known Mander Model and Lam and Teng Model. Generalization of the moment of area approach is utilized based on proportional loading, finite layer procedure and the secant stiffness approach, in an iterative incremental numerical model to achieve equilibrium points of P- and M- response up to failure. This numerical analysis is adaptod to asses the confining effect in circular cross sectional columns confined with FRP and conventional lateral steel together; concrete filled steel tube (CFST) circular columns and rectangular columns confined with conventional lateral steel. This model is validated against experimental data found in literature. The comparison shows good correlation. Finally computer software is developed based on the non-linear numerical analysis. The software is equipped with an elegant graphics interface that assimilates input data, detail drawings, capacity diagrams and demand point mapping in a single sheet. Options for preliminary design, section and reinforcement selection are seamlessly integrated as well. The software generates 2D interaction diagrams for circular columns, 3D failure surface for rectangular columns and allows the user to determine the 2D interaction diagrams for any angle  between the x-axis and the resultant moment. Improvements to KDOT Bridge Design Manual using this software with reference to AASHTO LRFD are made. This study is limited to stub columns.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Recent studies have shown that considering proof test data in a Reliability Based Design Optimization (RBDO) environment can result in design improvement. Proof testing involves the physical testing of each and every component before it enters into service. Considering the proof test data as part of the RBDO process allows for improvement of the original design, such as weight savings, while preserving high reliability levels. Composite Over-Wrapped Pressure Vessels (COPV) is used as an example application of achieving weight savings while maintaining high reliability levels. COPVs are light structures used to store pressurized fluids in space shuttles, the international space station and other applications where they are maintained at high pressure for extended periods of time. Given that each and every COPV used in spacecraft is proof tested before entering service and any weight savings on a spacecraft results in significant cost savings, this thesis put forward an application of RBDO that accounts for proof test data in the design of a COPV. The method developed in this thesis shows that, while maintaining high levels of reliability, significant weight savings can be achieved by including proof test data in the design process. Also, the method enables a designer to have control over the magnitude of the proof test, making it possible to also design the proof test itself depending on the desired level of reliability for passing the proof test. The implementation of the method is discussed in detail. The evaluation of the reliability was based on the First Order Reliability Method (FORM) supported by Monte Carlo Simulation. Also, the method is implemented in a versatile way that allows the use of analytical as well as numerical (in the form of finite element) models. Results show that additional weight savings can be achieved by the inclusion of proof test data in the design process. / AFRIKAANSE OPSOMMING: Onlangse studies het getoon dat die gebruik van ontwerp spesifieke proeftoets data in betroubaarheids gebaseerde optimering (BGO) kan lei tot 'n verbeterde ontwerp. BGO behels vele aspekte in die ontwerpsgebied. Die toevoeging van proeftoets data in ontwerpsoptimering bring te weë; die toetsing van 'n ontwerp en onderdele voor gebruik, die aangepaste en verbeterde ontwerp en gewig-besparing met handhawing van hoë betroubaarsheidsvlakke. 'n Praktiese toepassing van die BGO tegniek behels die ontwerp van drukvatte met saamgestelde materiaal bewapening. Die drukvatontwerp is 'n ligte struktuur wat gebruik word in die berging van hoë druk vloeistowwe in bv. in ruimtetuie, in die internasionale ruimtestasie en in ander toepassings waar hoë druk oor 'n tydperk verlang word. Elke drukvat met saamgestelde materiaal bewapening wat in ruimtevaartstelsels gebruik word, word geproeftoets voor gebruik. In ruimte stelselontwerp lei massa besparing tot 'n toename in loonvrag. Die tesis beskryf 'n optimeringsmetode soos ontwikkel en gebaseer op 'n BGO tegniek. Die metode word toegepas in die ontwerp van drukvatte met saamgestelde materiaal bewapening. Die resultate toon dat die gebruik van proeftoets data in massa besparing optimering onderhewig soos aan hoë betroubaarheidsvlakke moontlik is. Verdermeer, die metode laat ook ontwerpers toe om die proeftoetsvlak aan te pas om sodoende by ander betroubaarheidsvlakke te toets. In die tesis word die ontwikkeling en gebruik van die optimeringsmetode uiteengelê. Die evaluering van betroubaarheidsvlakke is gebaseer op 'n eerste orde betroubaarheids-tegniek wat geverifieer word met talle Monte Carlo simulasie resultate. Die metode is ook so geskep dat beide analitiese sowel as eindige element modelle gebruik kan word. Ten slotte, word 'n toepassing getoon waar resultate wys dat die gebruik van die optimeringsmetode met die insluiting van proeftoets data wel massa besparing kan oplewer.

The guided wave technique is commonly used for rapidly long-range pipeline inspection without removing the insulation of pipes. The torsional mode T(0,1) of the guided waves is usually generated to detect the defects in pipelines, since it has the advantage of being non-dispersive across the whole frequency range. However, a large number of pipelines are carrying fluid, wrapped with the coating material, and supported with clamp for the necessary manufacturing process in refinery and petro-chemical industrials. When these works are employed on the pipeline, the propagating guided waves may vary with the contents of material and how well the material compact on the pipe. Some energy of the incident guided wave in the pipe wall may leak into inside of contents or outside of wrapped materials and reduce the wave propagation distance. The effect of the fluid-filled pipe, the wrapped pipe, and the clamp support mounted on the pipe for guided wave propagation is investigated by both simulative and experimental methods. The wave structure of the T(0,1) mode in the pipes is analyzed by using the DISPERSE software for various cases to evaluate its influence to the guided wave propagation on the pipe. The amplitudes of the reflected signals from various features on the pipe are also measured using pipe screening system for calculating the attenuation of guided waves due to the features. The trend for the results is in good agreement between the experiments andpredictions for all cases of researches in this dissertation. It is found that the low viscosity liquid deposited in the pipe, such as water, diesel oil, and lubricant, has no effect on the torsional mode; while the high viscous of the fuel oil deposited in the pipe attenuates the reflection signal heavily for the pipe carrying fluid. In addition, both the full-filled and half-filled contents in the pipe are also studied in this case. The effects of the half-filled are the same as the full-filled results obtained. For the pipe wrapped with the coated material, the adhesive strength of the coated material is strong, such as bitumen and polyethylene; the attenuation of the guided waves is high; and there is almost no effect for mineral wool coating. Furthermore, the traveling distance of the guided waves in the pipe is also evaluated for various cases of the coated materials. The results indicate that the higher attenuation of the guided waves for the coated material, the shorter of the traveling distance in the pipe. For the clamp support mounted on pipe, the attenuation of the guided waves for the clamp support with a rubber gasket in between the pipe and the clamp is heavier than the case of clamp support without the rubber gasket is. Furthermore, the higher torque setting on the clamp (with or without the rubber gasket), the higher amplitude of the reflected signal is measured for the guided wave propagation. The effect of the frequency excitation is additionally demonstrated in this dissertation. It is noted that the higher amplitude of the reflected signal, the lower frequency excitation; moreover, theresonant effect is observed in the case of the clamp support with rubber gasket during the torque setting in the experiments. Good agreement has been obtained between the experiments and theoretical calculations of this effect.

Increasing energy demands as well as the depletion of traditional energy sources has led to the need for the development and improvement of energy conversion and storage technologies. Concerns regarding climate change and environmental awareness has also created increased support for renewable energy and clean technology research. One technology of interest is the photocatalyst, which is a material that is able to use natural light irradiation to create electrical currents or drive useful chemical reactions. For this purpose, a strong photocatalytic material has the following properties: i) strong absorbance over a wide solar radiation spectrum; ii) high surface area for adsorbance of target species; iii) high electron efficiency characteristics such as high conductivity, long charge-carrier lifetimes, and direct pathways for electron transport; and iv) good chemical stability. All of these requirements serve to maximize the efficiency and overall output of the device, and are a means of overcoming the performance hurdle required for the commercialization of various energy conversion technologies. Unfortunately, current photocatalytic materials suffer from small absorbance windows and high recombination rates which greatly reduce the conversion efficiency of the catalyst. Titanium dioxide (TiO2), the most well-known and widely used photocatalyst, can only absorb light within the ultraviolet (UV) range – which accounts for only a small fraction of the entire solar spectrum. For this reason, the majority of recent research has been directed toward producing photocatalysts that are able to absorb light within the visible and infrared range in order to maximize the amount of light absorbed in the solar spectrum. Other research is also being conducted to increase electrical conductivity and charge-carrier separation to further increase conversion efficiency. It is hoped that these two major problems surrounding photocatalysis can be solved by using novel functional nanomaterials. Nanomaterials can be synthesized using three main techniques: crystal structuring, doping, and heterostructuring. By controlling the structure of the crystal, materials of different phase, morphology, and exposed crystal facets can be synthesized. These are important for controlling the electronic properties and surface reactivity of the photocatalyst. Doping is the act of introducing impurities into a material in order to modify its band structure and create a red shift in light absorption. Lastly, heterostructuring is a method used to combine different photocatalysts or introduce co-catalysts in order to widen the range of absorption, encourage charge separation, or both. Many novel photocatalytic materials have been synthesized using these techniques. However, the next-generation photocatalytic material has remained elusive due to the high cost of production and complexity of synthesis. This thesis proposes a novel photocatalytic material that can be used in photocatalyzed waste-water remediation. Graphene-wrapped hierarchical TiO2 nanoflowers (G-TiO2) are synthesized using a facile synthesis method. TiO2 is a material of particular interest due to its chemical and photo-corrosion stability, high redox potential, strong electronic properties, and relative non-toxicity. Hierarchical structures are highly desired because they are able to achieve both high surface area and high conductivities. Graphene hybridization is a popular method for creating composites with highly conductive networks and highly adsorptive surfaces. To the best of my knowledge, the hybridization of graphene on hierarchical TiO2 structures without pre-functionalization of TiO2 has not yet been demonstrated in literature. Therefore, it is proposed that the use of such a material would greatly simplify the synthesis process and enhance the overall photocatalytic performance of TiO2 over that of commercial TiO2 photocatalysts. In the first study, hierarchical TiO2 nanoflowers are synthesized using a solvothermal reaction. It is then shown that under UV irradiation, the hierarchical TiO2 material is able to outperform commercial TiO2 material in the photodegradation of methylene blue (MB). Further characterization shows that this improvement is explained by a higher electrical conductivity, and exists in spite of having a lower specific surface area compared to the commercial material. In the second study, G-TiO2 is synthesized by mixing hierarchical TiO2 nanoflowers with graphene oxide (GO) and reducing GO in a hydrothermal reaction. Photocatalytic tests show that this hybridization further improves the performance of the hierarchical TiO2. Further studies reveal that an optimal graphene loading of 5 wt% is desired in order to achieve the higher rate of MB decomposition, and greatly outperforms P25 in this task. Characterization shows that G-TiO2 composites have increased specific surface area and electrical conductivity compared to the hierarchical TiO2 nanoflower. It is believed that this work will provide a simple and efficient avenue for synthesizing graphene–TiO2 composites with greatly improved photocatalytic activity. This work may also find use in other photocatalytic applications such as chemical deconstruction and manufacturing, hydrogen production, solar cells, and solar enhanced fuel cells.

This report is a master thesis, written by an engineering physics and electrical engineering student at Luleå University of Technology.The desires of this project was to remove dislocations from wrapped phase maps using sparse reconstructive methods. Dislocations is an error that can appear in phase maps due to improper filtering or inadequate sampling. Dislocations makes it impossible to correctly unwrap the phasemap.The report contains a mathematical description of a sparse reconstructive method. The sparse reconstructive method is based on KSVDbox which was created by R. Rubinstein and is free for download and use. The KSVDbox is a MATLAB implementation of a dictionary learning algorithm called K-SVD with Orthogonal Matching Pursuit and a sparse reconstructive algorithm. A guide for adapting the toolbox for inpainting is included, with a couple of examples on natural images which supports the suggested adaptation. For experimental purposes a set of simulated wrapped phase maps with and without disloca-tions were created. These simulated phase maps are based on work by P. Picart. The MATLAB implementation that was used to generate these test images can be found in the appendix of this report such that they can easily be generated by anyone who has the interest to do so. Finally the report leads to an outline of five different experiments that was designed to test the KSVDbox for the processing of dislocations. Each one of these experiments uses a different dictionary. These experiments are due to inpainting with, 1. A dictionary based on Discrete Cosine Transform. 2. An adaptive dictionary, where the dictionary learning algorithm has been shown what thearea in the phase map that was damaged by dislocations should look like. 3. An adaptive dictionary, where the dictionary learning algorithm has been allowed to trainon the phase map that with damages. This is done such that areas with dislocations areignored. 4. An adaptive dictionary, where training is done on a separate image that has been designedto contain general phase patterns. 5. An adaptive dictionary, that results from concatenating the dictionaries used in experiment 3 and 4. The first three experiments are complimented with experiments done on a natural image for comparison purposes.The results show that sparse reconstructive methods, when using the scheme used in this work, is unsuitable for processing of dislocations in phase maps. This is most likely because the reconstructive method has difficulties in acquiring a high contrast reconstruction and there is nothing in the algorithm that causes the inpainting from any direction to match with the inpainting from other directions.

A scarcity of experimental studies covering the decomposition of dismembered body parts has created a gap in knowledge of the effect of dismemberment on the estimation of post-mortem interval (PMI) and their post-mortem history in a forensic context. The aim of this study was to record the decay of detached body parts in some depositional settings where they are likely to be disposed of: burial, wrapping and freezing. A series of controlled laboratory experiments was carried out using Sus scrofa body parts and pork belly, to understand how ambient temperature, soil moisture, and wrapping and freezing of body parts affected their decomposition. Rates of decay were subject to a higher temperature and soil moisture level in a burial microenvironment, with metabolic microbial activity confirming the results. Temperature was a predominant factor in the decay rates of wrapped body parts, with a raised ambient temperature causing even higher temperature in the wrapped microenvironment, resulting in accelerated decay rates. Freezing decelerated the decomposition of body parts, retarding microbial growth and activity and causing differential decomposition between body parts. Freezing demonstrated morphological changes in body parts specific to this microenvironment. Predominantly Gram-negative bacteria that may be associated with body microflora were involved in decomposition in all three microenvironments. Taphonomic, chemical and microbiological analyses carried out in this study have a potential for forensic application in the examination of dismembered remains that have been deposited in freezing and indoor settings. Further experiments are necessary to understand buried decomposition patterns in field conditions.

Sandproduktion ist eine große Herausforderung in vielen Tiefbohrungen. Um sie zu verhindern wurden verschiedene Methoden und Bauteilen entwickelt, die unter dem Begriff Sandkontrollmaßnahmen zusammengefasst werden. Zu diesen zählt der Einbau von Sandfiltern als Standalone Screens oder Teil eines Gravel Packs. Aufgrund der vielen Einflussfaktoren aus Geologie und Betriebsweise sind die Funktionsweise und das Versagen von Sandfiltern nach wie vor Gegenstand aktueller Forschung. Eine Möglichkeit zur Untersuchung von Sandfiltern ist die Durchführung von laborativen Experimenten. In dieser Arbeit wird die Entwicklung von zwei Versuchsanlagen vorgestellt. Die Anlagen werden genutzt, um einen neuentwickelten Wickeldrahtfilter zu untersuchen. Der Filter unterscheidet sich von bisherigen Designs durch eine Beschichtung auf der Außenseite, die, durch die Verwendung von Materialien mit großer Härte, für eine größere Erosionsbeständigkeit sorgen soll. Eine umfassende Literaturrecherche zu den Versagensmechanismen und dem Stand der Technik von laborativen Untersuchungen an Sandfiltern bilden die Grundlage für diese Arbeit. Darauf aufbauend werden theoretische Vorüberlegungen zum Erosions- und Sandkontrollverhalten von Sandfiltern dargestellt. Die Versuchsanlagen ermöglichen zum einen die Durchführung von Sand Retention Tests und zum anderen die gezielte Erosion von Filterproben mittels einer kontinuierlichen Durchströmung mit einer Suspension. Die Ergebnisse werden genutzt, um grundlegende Aussagen zum Erosions- und Sandkontrollverhalten abzuleiten. Zusätzlich wird der neu entwickelte, beschichtete Filter mit konventionellen Filtern verglichen. Aus den Ergebnissen werden Limitationen der laborativen Untersuchungen zum Sandkontrollverhalten und Auswertungsempfehlungen formuliert. Ein Unterschied im Sandkontrollverhalten zwischen beschichteten und unbeschichteten Filtern kann nicht festgestellt werden. Es wird gezeigt, dass interne Turbulenz in den Öffnungen eines Sandfilters ein wichtiger Einflussfaktor auf die Erosion mit feinen Partikeln ist. Sandfilter können an unterschiedlichen Stellen erodieren, die sich nicht alle direkt auf die Funktionalität auswirken. Der Vergleich der Ergebnisse deutet darauf hin, dass beschichtete Filter eine längere Standzeit unter erosiven Bedingungen haben, da sie an der Außenseite weniger erodieren als unbeschichtete Wickeldrahtfilter. Aufgrund der besonderen Eigenschaften der Beschichtung kommt es jedoch zu größerer interner Erosion. Die Diskussion der durchgeführten Versuche liefert zusammen mit den umfangreichen theoretischen Vorüberlegungen einen Beitrag zum Verständnis über das Versagen von Sandfiltern, insbesondere das Zusammenspiel von Erosion und Sandkontrolle. Die Untersuchungen an Proben des neuartigen, beschichteten Filters bilden den Grundstein für derzeit laufende Feldeinsätze von Prototypen.