In this thesis the Counter Rotating vertical Axis Floating Tilting wind turbine (CRAFT) has been explored by creating a simulation model in the program Simulink. The CRAFT prototype is a new type of wind turbine under development by World Wide Wind and Uppsala University with the aim to produce a large scale floating vertical axis wind turbine (VAWT) with two cone shaped counter rotating turbines. The objective of this thesis is to study the required size of the secondary generator in the CRAFT. The generator is required in order to keep both of the turbines rotating with the same but opposite rotational speed, even when the turbines are experiencing different wind loads. Further areas that are investigated are if certain parameters have a specifically high impact on the need for the secondary generator.  The objective was reached by creating a model of the prototype and implementing control algorithms for both the secondary and main generator in order to control the rotational speed of the turbines. The behaviour of the CRAFT was then simulated with different wind loads and varying parameters such as the size of the main load, the size of the power output to the secondary generator and the wing length of the lower turbine. The simulations showed that it is possible to keep the rotational speed of the two turbines equal and opposite even during turbulent wind loads with the chosen control algorithm. The simulation also showed that if a small deviation in the turbine's rotational speed is allowed, a secondary generator of only 1 kW is needed instead of the currently used 5 kW generator. It was also shown that the elongating of the lower turbine wings had a small and positive effect on the energy output of the CRAFT.

<p dir="ltr">Improving launch vehicle and satellite propulsion system performance directly correlates to the delivery of more mass (or quantity) on orbit from launch vehicles, longer duration satellite missions, and longer ranges for missiles/interceptors. Alternative propulsion devices such as rotating detonation engines (RDEs) offer the potential for significant performance gains but their operability has only been demonstrated on “battle hardened” laboratory devices for rocket applications. The objective of this research was to demonstrate cooling and structural approaches that mature rotating detonation rocket engines (RDREs) to flight like maturation levels.</p><p dir="ltr">Multiple 1.6”/4.1 cm diameter RDE combustors were designed, fabricated, and tested. The RDE tested the most accumulated 309 seconds of hot fire testing and 118 starts/shutdowns. Long duration testing was completed to characterize heat flux and high cycle fatigue (HCF) loading. Large quantities of short duration tests were completed to evaluate thermal cycling impacts to the combustor structure and evaluate low cycle fatigue (LCF) loading. The hardware experienced 118 LCF loadings on the combustor cooling passages, equivalent to the amount of thermal cycle starts and shutdowns. An endurance test was completed at 60 seconds in duration, demonstrating operation well beyond thermal steady state. Additionally, ~3.7 million HCF loadings were placed on the combustor cooling passages, equivalent to the approximate amount of detonation wave passes present for all of the WC 2.0 testing.</p><p dir="ltr">Predicted operating pressures ranged from 5 to 15 atm. The highest-pressure conditions resulted in hot gas wall temperatures exceeding 1000°F on the outerbody of the combustor and injector face temperatures peaking at 350°F. Water calorimetry was used to compute heat fluxes, which were then compared to traditional rocket engine throat level heat fluxes calculated using Bartz equations under average operating conditions. The outerbody heat fluxes reached up to 3.7 kW/cm², while injector face heat fluxes reached a maximum of 1.6 kW/cm². When compared to Bartz throat level values, the outer-body heat fluxes varied from 0.9 to 1.6 times the throat level values, and injector heat fluxes ranged from 0.3 to 0.5 times the throat level values.</p><p dir="ltr">A combined thermal and pressure loading fatigue assessment was completed that took into consideration mean stresses and cumulative damage from the spectrum of loading events. Traditional rocket combustor life is typically limited by the thermal cycles that can be placed on the cooling channel hot wall. The fatigue analysis results highlight the reduction in available low cycle fatigue life as RDE's experience larger thermal loads when compared to traditional rocket combustors. Low cycle fatigue life will become especially challenging in higher chamber pressure combustors where thermal environments are more extreme, and the ability keep hot wall temperatures within acceptable levels is more challenging.</p><p dir="ltr">The study also highlights that the passing detonation wave provides a high cycle fatigue (HCF) failure mechanism that is not present in traditional rocket combustors. This failure mechanism is the result of the pressure pulse provided by the passing detonation wave causing a variable load on the hot wall. This variable load is applied at frequencies commonly in the 10's of kHz, resulting in large quantities of loading cycles when operated at rocket like durations (>60 sec). This HCF failure mechanism is most impactful at larger chamber pressures where the detonation pressure ratio causes peak pressures to be elevated, resulting in larger cyclic stresses and strains in the hot wall. The results indicate that high chamber pressure combustors may experience HCF life exceedances within seconds of operation.</p>

The ever increasing demand for a clean and renewable energy source has stimulated research for alternatives for the use of fossil fuels, which contribute significantly to global warming. The SO2 oxidation reaction was studied for production of hydrogen as a clean and renewable energy carrier. This reaction occurs at a lower standard electrode potential (0.158 V vs. SHE) than normal water electrolysis (1.23 V vs. SHE). This is a theoretical indication that the SO2 oxidation reaction has possible potential when compared to normal water electrolysis, since hydrogen production may occur at lower potentials and therefore lower cost. Rh was compared with Pt for the SO2 oxidation reaction since little research has been done on this catalyst and many studies exist in which Pt was used as catalyst. The oxygen reduction reaction and ethanol oxidation reaction were also included in this study to create a foundation for the catalysts studied, since the SO2 oxidation reaction is complicated by different adsorbed species that can form according to various mechanisms. The electrochemical techniques employed in this study to characterize the catalysts included cyclic voltammetry from which onset potentials and limiting current densities were determined, as well as from which some qualitative analysis was done. Linear polarization experiments were used during rotating disk electrode studies from which Levich and Koutecky-Levich analyses were done and the number of electrons transferred calculated and compared between the two catalysts. From the Koutecky-Levich analysis the kinetic current density was also obtained for use in Tafel analysis for further comparison between catalysts. It was found that Rh showed good behaviour for the oxygen reduction reaction when compared to Pt with similar onset potentials and limiting current densities. From Levich analysis it was concluded that both catalysts achieved diffusion limitation at high overpotentials. However, from the calculated number of electrons transferred it was evident that a difference in mechanism existed between catalysts and that the mechanism for both changed in the potential range studied, which is confirmed by the Tafel slopes. For the ethanol oxidation reaction it was shown that Rh exhibited very low catalytic activity in comparison with Pt. However, it was concluded from cyclic voltammetry and rotating disk electrode studies that more adsorbed species were present on the surface of Rh than on Pt. These results confirmed the possibility of using Rh as a co-catalyst together with Pt since it was shown from rotating disk electrode studies that low adsorption of ethanol and its oxidation products caused species to be transported away from the surface of the electrode during rotation. For the SO2 oxidation reaction it was found that Rh exhibited very poor catalytic activity together with being very susceptible to poisoning by adsorbed species. Pt showed very good behaviour, which corresponded well with what had been observed in literature. Levich analysis revealed that Pt did not exhibit diffusion limitation and Koutecky-Levich analysis revealed that a 2 electron reaction occurred on Pt, which corresponds with the SO2 oxidation reaction during which 2 electrons are transferred. It was, therefore, shown that Rh could exhibit good behaviour and act as a suitable catalyst in certain circumstances. However, for the SO2 oxidation reaction, which was the main focus of this study it was shown that Rh is not a suitable catalyst, either alone or as co-catalyst. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

The ever increasing demand for a clean and renewable energy source has stimulated research for alternatives for the use of fossil fuels, which contribute significantly to global warming. The SO2 oxidation reaction was studied for production of hydrogen as a clean and renewable energy carrier. This reaction occurs at a lower standard electrode potential (0.158 V vs. SHE) than normal water electrolysis (1.23 V vs. SHE). This is a theoretical indication that the SO2 oxidation reaction has possible potential when compared to normal water electrolysis, since hydrogen production may occur at lower potentials and therefore lower cost. Rh was compared with Pt for the SO2 oxidation reaction since little research has been done on this catalyst and many studies exist in which Pt was used as catalyst. The oxygen reduction reaction and ethanol oxidation reaction were also included in this study to create a foundation for the catalysts studied, since the SO2 oxidation reaction is complicated by different adsorbed species that can form according to various mechanisms. The electrochemical techniques employed in this study to characterize the catalysts included cyclic voltammetry from which onset potentials and limiting current densities were determined, as well as from which some qualitative analysis was done. Linear polarization experiments were used during rotating disk electrode studies from which Levich and Koutecky-Levich analyses were done and the number of electrons transferred calculated and compared between the two catalysts. From the Koutecky-Levich analysis the kinetic current density was also obtained for use in Tafel analysis for further comparison between catalysts. It was found that Rh showed good behaviour for the oxygen reduction reaction when compared to Pt with similar onset potentials and limiting current densities. From Levich analysis it was concluded that both catalysts achieved diffusion limitation at high overpotentials. However, from the calculated number of electrons transferred it was evident that a difference in mechanism existed between catalysts and that the mechanism for both changed in the potential range studied, which is confirmed by the Tafel slopes. For the ethanol oxidation reaction it was shown that Rh exhibited very low catalytic activity in comparison with Pt. However, it was concluded from cyclic voltammetry and rotating disk electrode studies that more adsorbed species were present on the surface of Rh than on Pt. These results confirmed the possibility of using Rh as a co-catalyst together with Pt since it was shown from rotating disk electrode studies that low adsorption of ethanol and its oxidation products caused species to be transported away from the surface of the electrode during rotation. For the SO2 oxidation reaction it was found that Rh exhibited very poor catalytic activity together with being very susceptible to poisoning by adsorbed species. Pt showed very good behaviour, which corresponded well with what had been observed in literature. Levich analysis revealed that Pt did not exhibit diffusion limitation and Koutecky-Levich analysis revealed that a 2 electron reaction occurred on Pt, which corresponds with the SO2 oxidation reaction during which 2 electrons are transferred. It was, therefore, shown that Rh could exhibit good behaviour and act as a suitable catalyst in certain circumstances. However, for the SO2 oxidation reaction, which was the main focus of this study it was shown that Rh is not a suitable catalyst, either alone or as co-catalyst. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Solutions of the magnetohydrodynamic (MHD) equations are very important for modelling laboratory, space and astrophysical plasmas, for example the solar and stellar coronae, as well as for modelling many of the dynamic processes that occur in these different plasma environments such as the fundamental process of magnetic reconnection. Our previous understanding of the behavior of plasmas and their associated dynamic processes has been developed through two-dimensional (2D) models. However, a more realistic model should be three-dimensional (3D), but finding 3D solutions of the MHD equations is, in general, a formidable task. Only very few analytical solutions are known and even calculating solutions with numerical methods is usually far from easy. In this thesis, 3D solutions which model magnetic reconnection and rigidly rotating magnetized coronae are presented. For magnetic reconnection, a 3D stationary MHD model is used. However, the complexity of the problem meant that so far no generic analytic solutions for reconnection in 3D exist and most work consists of numerical simulations. This has so far hampered progress in our understanding of magnetic reconnection. The model used here allows for analytic solutions at least up to a certain order of approximation and therefore gives some better insight in the significant differences between 2D and 3D reconnection. Three-dimensional numerical solutions are also obtained for this model. Rigidly rotating magnetized coronae, on the other hand, are modeled using a set of magnetohydrostatic (MHS) equations. A general theoretical framework for calculating 3D MHS solutions outside massive rigidly rotating central bodies is presented. Under certain assumptions, the MHS equations are reduced to a single linear partial differential equation referred to as the fundamental equation of the theory. As a first step, an illustrative case of a massive rigidly rotating magnetized cylinder is considered, which somehow allows for analytic solutions in a certain domain of validity. In general, the fundamental equation of the theory can only be solved numerically and hence numerical example solutions are presented. The theory is then extended to include a more realistic case of massive rigidly rotating spherical bodies. The resulting fundamental equation of the theory in this case is too complicated to allow for analytic solutions and hence only numerical solutions are obtained using similar numerical methods to the ones used in the cylindrical case.

A rotating diffusion cell (RDC) has been used to study the kinetics of extraction of the transition metals cobalt (II), nickel (II), copper (II) and zinc (II) from sulphate solutions into either of two extractants held in n-heptane; di-(2-ethylhexyl) phosphoric acid (D2EHPA) or di-(2- ethylhexyl) dithiophosphoric acid (D2EHDTPA). The metal concentration was 10 mM and the aqueous pH was held at 4.5. The extractant concentration was varied between 0.015 to 0.4 M. In the case of cobalt extraction by D2EHPA, the metal concentration and the pH were varied Different diluents and modifiers were also studied.The rate of extraction by D2EHDTPA was found to be faster than D2EHPA. A comprehensive mathematical model, based upon established two film theory, was developed and used to describe the above experimental results. The model was also used to predict values of the important parameters. ... These values compared well with those found by other authors but using quite different experimental techniques. OS4 In the case of cobalt extraction by D2EHPA, the more polar diluents lowered the initial rate. The overall model predicts such behaviour where the rate is also dependent on the partition coefficients of the extractant. Finally, the theory of the RDC allows the prediction of the diffusion layer thicknesses, this information together with the reaction zone thickness is used to explore the influences of diffusion and chemical reaction on the overall transfer process. The diffusion processes are calculated to be the most important of the two. This is especially so for the D2EHDTPA systems.

<p>The behavior of fibers suspended in a flow between two counter-rotating discs has been studied experimentally. This is inspired by the refining process in the papermaking process where cellulose fibers are ground between discs in order to change performance in the papermaking process and/or qualities of the final paper product.</p><p>To study the fiber behavior in a counter-rotating flow, an experimental set-up with two glass discs was built. A CCD-camera was used to capture images of the fibers in the flow. Image analysis based on the concept of steerable filters extracted the position and orientation of the fibers in the plane of the discs. Experiments were performed for gaps of 0.1-0.9 fiber lengths, and for equal absolute values of the angular velocities for the upper and lower disc. The aspect ratios of the fibers were 7, 14 and 28.</p><p>Depending on the angular velocity of the discs and the gap between them, the fibers were found to organize themselves in fiber trains. A fiber train is a set of fibers positioned one after another in the tangential direction with a close to constant fiber-to-fiber distance. In the fiber trains, each individual fiber is aligned in the radial direction (i.e. normal to the main direction of the train).</p><p>The experiments show that the number of fibers in a train increases as the gap between the discs decreases. Also, the distance between the fibers in a train decreases as the length of the train increases, and the results for short trains are in accordance with previous numerical results in two dimensions.Furthermore, the results of different aspect ratios imply that there are three-dimensional fiber end-effects that are important for the forming of fiber trains.</p>

Slow speed rotating machines are the mainstay of several industrial applications worldwide. They can be found in paper and steel mills, rotating biological contractors, wind turbines etc. Operational experience of such machinery has not only revealed the early design problems but has also presented opportunities for further significant improvements in the technology and economics of the machines. Slow speed rotating machinery maintenance, mostly related to bearings, shafts and gearbox problems, represents the cause of extended outages. Rotating machinery components such as gearboxes, shafts and bearings degrade slowly with operating time. Such a slow degradation process can be identified if a robust on-line monitoring and predictive maintenance technology is used to detect impending problems and allow repairs to be scheduled. To keep machines functioning at optimal levels, failure detection of such vital components is important as any mechanical degradation or wear, if is not impeded in time, will often progress to more serious damage affecting the operational performance of the machine. This requires far more costly repairs than simply replacing a part. Over the last few years there have been many developments in the use of Acoustic Emission (AE) technology and its analysis for monitoring the condition of rotating machinery whilst in operation, particularly on slow speed rotating machinery. Unlike conventional technologies such as thermography, oil analysis, strain measurements and vibration, AE has been introduced due to its increased sensitivity in detecting the earliest stages of loss of mechanical integrity. This programme of research involves laboratory tests for monitoring slow speed rotating machinery components (shafts and bearings) using AE technology. To implement this objective, two test rigs have been designed to assess the capability of AE as an effective tool for detection of incipient defects within low speed machine components (e.g. shafts and bearings). The focus of the experimental work will be on the initiation and growth of natural defects. Further, this research work investigates the source characterizations of AE signals associated with such bearings whilst in operation. It is also hoped that at the end of this research program, a reliable on-line monitoring scheme used for slow speed rotating machinery components can be developed.

Parmi les méthodes appliquées dans le cadre de la maintenance des installations industrielles, l'analyse vibratoire constitue une des plus répandues. En effet, les signatures vibratoires apparaissant sur une installation en cours de fonctionnement sont étroitement liées à leur comportement dynamique et à leur état fonctionnel. Ce travail a pour objectif de développer et expérimenter des techniques et outils de calculs numériques pour l'interprétation d'indicateurs d'état issus de mesures vibratoires sur une machine tournante. La validation est faite sur un ensemble motoréducteur à engrenages. Pour cela, nous avons développé deux outils d'analyse numérique : un premier permettant de déterminer les caractéristiques modales d'une structure complexe puis un second, développé sur la base des ondelettes, pour détecter les défauts naissants sur un motoréducteur. Les performances relatives des différents outils sont comparées au regard de ce qui se fait dans la littérature. Enfin, une étude expérimentale sur banc d'essais a été menée dans le but de tester la sensibilité et les limites de la méthode. Le mémoire est articulé comme suit : une première partie développe les principales techniques vibratoires actuelles avec leurs performances et limites. De la deuxième partie traitant les théories et méthodes d'analyse modale découle une troisième présentant des méthodes améliorées. Dans la quatrième partie, une étude expérimentale sur banc d'essais a été menée dans le but de tester la sensibilité de la méthode. Une approche par la décomposition en ondelettes des signaux a été notamment utilisée. Il est démontré que cette méthode a une application intéressante dans le domaine des analyses vibratoires de structures complexes / Vibrations analysis appears to be one of the most efficient methods among those that are actually used in the field of preventive and condition-based maintenance of industrial equipments. Indeed, vibration signs from a working machine depend tightly on its dynamical behaviour and health. This thesis consists on developing some new techniques and numerical calculation tools which help while interpreting indicators issued from vibrations measurements of rotating machinery. Validation has been done especially on case study of a complex bench constituted by motor with gear transmission. Technically, it aims on one part in determining modal characteristics of the whole system, and on another part in finding out a reliable method for rotating machinery defaults detecting. The first part resumes main present vibrating techniques. From the second part which treats theoretical modal analysis arises a developing improved methods third one. At this step, some numerical codes permitting treatment and quick interpretation of analysis results were drawn up. On the fourth part, an experimental study on a test bed was carried out with the aim of confronting theoretical, analytical and numerical results with real ones.An approach by wavelet decomposition of signals was particularly used here. It is shown that this method has got interesting application in the field of complex structures vibration analysis

Numerical simulations of atmospheric and oceanic flows are fundamentally limited by a lack of model resolution. This thesis describes the application of unstructured mesh finite element methods to geophysical fluid dynamics simulations. These methods permit the mesh resolution to be concentrated in regions of relatively increased dynamical importance. Dynamic mesh adaptivity can further be used to maintain an optimised mesh even as the flow develops. Hence unstructured dynamic mesh adaptive methods have the potential to enable efficient simulations of high Reynolds number flows in complex geometries. In this thesis, the thermally driven rotating annulus is used to test these numerical methods. This system is a classic laboratory scale analogue for large scale geophysical flows. The thermally driven rotating annulus has a long history of experimental and numerical research, and hence it is ideally suited for the validation of new numerical methods. For geophysical systems there is a leading order balance between the Coriolis and buoyancy accelerations and the pressure gradient acceleration: geostrophic and hydrostatic balance. It is essential that any numerical model for these systems is able to represent these balances accurately. In this thesis a balanced pressure decomposition method is described, whereby the pressure is decomposed into a ``balanced'' component associated with the Coriolis and buoyancy accelerations, and a ``residual'' component associated with other forcings and that enforces incompressibility. It is demonstrated that this method can be used to enable a more accurate representation of geostrophic and hydrostatic balance in finite element modelling. Furthermore, when applying dynamic mesh adaptivity, there is a further potential for imbalance injection by the mesh optimisation procedure. This issue is tested in the context of shallow-water ocean modelling. For the linearised system on an $f$-plane, and with a steady balance permitting numerical discretisation, an interpolant is formulated that guarantees that a steady and balanced state remains steady and in balance after interpolation onto an arbitrary target mesh. The application of unstructured dynamic mesh adaptive methods to the thermally driven rotating annulus is presented. Fixed structured mesh finite element simulations are conducted, and compared against a finite difference model and against experiment. Further dynamic mesh adaptive simulations are then conducted, and compared against the structured mesh simulations. These tests are used to identify weaknesses in the application of dynamic mesh adaptivity to geophysical systems. The simulations are extended to a more challenging system: the thermally driven rotating annulus at high Taylor number and with sloping base and lid topography. Analysis of the high Taylor number simulations reveals a direct energy transfer from the eddies to the mean flow, confirming the results of previous experimental work.