As a clean, abundant, and renewable source of energy with a strategic location in close proximity to global population regions, ocean wave energy shows major promise. Although much wave energy converter development has focused on large-scale power generation, there is also increasing interest in small-scale applications for powering the blue economy. In this thesis, the objective was to optimize the performance of small-sized, portable, oscillating-body wave energy converters (WECs). Two types of oscillating body WECs were studied: bottom hinged and two-body attenuator. For the bottom-hinged device, the goal was to show the feasibility of an oscillating surge WEC and desalination system using numerical modeling to estimate the system performance. For a 5-day test period, the model estimated 517 L of freshwater production with 711 ppm concentration and showed effective brine discharge, agreeing well with preliminary experimental results. The objective for the two-body attenuator was to develop a method of power maximization through resonance tuning and numerical simulation. Three different geometries of body cross sections were used for the study with four different drag coefficients for each geometry. Power generation was maximized by adjusting body dimensions to match the natural frequency with the wave frequency. Based on the time domain simulation results, there was not a significant difference in power between the geometries when variation in drag was not considered, but the elliptical geometry had the highest power when using approximate drag coefficients. Using the two degree-of-freedom (2DOF) model with approximate drag coefficients, the elliptical cross section had a max power of 27.1 W and 7.36% capture width ratio (CWR) for regular waves and a max power of 8.32 W and 2.26% CWR for irregular waves. Using the three degree-of-freedom (3DOF) model with approximate drag coefficients, the elliptical cross section had a max power of 22.5 W and 6.12% CWR for regular waves and 6.18 W and 1.68% CWR for irregular waves. A mooring stiffness study was performed with the 3DOF model, showing that mooring stiffness can be increased to increase relative motion and therefore increase power. / Master of Science / As a clean, abundant, and renewable source of energy with a strategic location in close proximity to global population centers, ocean wave energy shows major promise. Although much wave energy converter development has focused on large-scale power generation, there is also increasing interest in small-scale applications for powering the blue economy. There are many situations where large-scale wave energy converter (WEC) devices are not necessary or practical, but easily-portable, small-sized WECs are suitable, including navigation signs, illumination, sensors, survival kits, electronics charging, and portable desalination. In this thesis, the objective was to optimize the performance of small-sized, oscillating body wave energy converters. Oscillating body WECs function by converting a device's wave-driven oscillating motion into useful power. Two types of oscillating body WECs were studied: bottom hinged and two-body attenuator. For the bottom-hinged device, the goal was to show the feasibility of a WEC and desalination system using numerical modeling to estimate the system performance. Based on the model results, the system will produce desirable amounts of fresh water with suitably low concentration and be effective at discharging brine. The objective for the two-body attenuator was to develop a method of power maximization through resonance tuning and numerical simulation. Based on the two- and three-degree-of-freedom model results with approximate drag coefficients, the elliptical cross section had the largest power absorption out of three different geometries of body cross sections. A mooring stiffness study with the three-degree-of-freedom model showed that mooring stiffness can be increased to increase power absorption.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: A measurement device was developed to accurately determine the pneumatic power performance of an Oscillating Water Column (OWC) model in a wave flume. The analysis of the pneumatic power is significant due to the wave-topneumatic energy being the primary energy conversion process and where the most energy losses can be expected. The aim of the research study is to address the accurate pneumatic power measurement of unsteady and bidirectional airflow in OWC model experiments. The two fundamental measurements required for the pneumatic power measurement are the pressure difference over an orifice on the OWC model and the volumetric flow rate of air through the outlet. The designed, constructed and assembled measurement device comprised of a venturi flow meter, containing a hot-film anemometer, which could measure the pressure drop and the volumetric flow rate in one device. The assembled pneumatic power measurement device was calibrated in a vertical wind tunnel at steady state. The results from the calibration tests showed that the volumetric flow rate measurements from the pneumatic power measurement device was accurate to within 3 % of the wind tunnel’s readings. The pneumatic power measurement device was incorporated onto a constructed Perspex physical model of a simple OWC device. This assembled system was used as the test unit in the wave flume at Stellenbosch University (SUN). The results from the experimental tests underwent comparative analysis with three analytical OWC air-flow models which were simulated as three scenarios using Matlab Simulink. These results showed that the measurement device has the ability to measure the pneumatic power but there is difficulty in modelling the complex air-flow system of the OWC device. This results in varying levels of agreement between the experimental and simulated pneumatic power results. The research study has revealed that there is difficulty in designing an accurate device for a wide range of test parameters due to the variance in output values. The unsteady and bidirectional nature of the air flow is also difficult to accurately simulate using a one-dimensional analytical model. Recommendations for further investigation are for CFD systems to be used for the analysis of the air-flow in an OWC system and to be used to validate future pneumatic power measurement devices. / AFRIKAANSE OPSOMMING: ‘n Meetinstrument was ontwikkel om die pneumatiese kraglewering van ‘n model van die Ossillerende Water Kolom (OWK) golfenergie omsetter in ‘n golf tenk akkuraat te meet. Dit is belangrik om die omskakeling van golf na pneumatiese energie te analiseer siende dat die grootste energieverlies in dié proses plaasvind. Die doel van hierdie navorsingsprojek was om die akkurate pneumatiese kragmeting van variërende en twee-rigting vloei van lug in ‘n OWK model na te vors. Die twee fundamentele metings wat benodig word vir die pneumatiese kragbepaling is die drukverskil oor die vloei vernouing en die volumetriese vloeitempo van lug deur die uitlaat van die toetstoestel. Die spesiaal ontwerpte meettoestel wat gebruik is in die eksperiment het bestaan uit ‘n venturi vloeimeter wat ‘n verhitte-film anemometer bevat het wat die drukverandering en die volumetriese vloeitempo kan meet in ‘n enkele instrument. Die pneumatiese kragmeting was gekalibreer in ‘n vertikale windtonnel waarin ‘n konstante vloei tempo geïnduseer was. Die kalibrasieproses het bevestig dat die meettoestel metings lewer met ‘n fout van minder as 3 % wanneer dit vergelyk word met die bekende konstante vloei tempo soos bepaal in die windtonnel. ‘n Fisiese model van ‘n vereenvoudigde OWK golfenergie omsetter was ontwerp en gebou uit Perspex om as toetstoestel te gebruik vir die evaluering van die ontwerpte pneumatiese kraglewering meettoestel. Die toetse was uitgevoer in ‘n golftenk by die Universiteit Stellenbosch (SUN). The toetsresultate was vergelyk met drie ander OWK lugvloei modelle wat gesimuleer was deur om die analitiese modelle op te stel en te simuleer in Matlab Simulink. Die vergelyking van modellering resultate het gewys dat die meettoestel die vermoë het om pneumatiese krag te meet. Daar was wel komplikasies met die modellering van die komplekse lugvloei in die OWK toestel, die resultate het geen definitiewe ooreenstemming gewys tussen die eksperimentele en gesimuleerde pneumatiese krag resultate nie. Die navorsingsprojek het gewys dat daar komplikasies is om ‘n enkel toestel te ontwerp wat oor ‘n wye bereik kan meet weens die variasie van die verskillende parameters. Die variërende en twee-rigting lugvloei is ook moeilik om akkuraat te simuleer met ‘n een-dimensionele analitiese simulasie model. Aanbevelings vir verdere navorsing sluit in om die lugvloei in die OWK stelsel te modelleer en te analiseer in ‘n drie-dimensionele model om die lesings van ‘n pneumatiese krag meettoestel te bevestig.

The current generation of Glass Ionomer Cements (GICs) have many advantageous properties over other dental restorative materials but lack the compressive strength of these other materials. The aim of this project is to increase the compressive strength of conventional Glass Poly-Vinyl-Phosphonate cement by inclusion of reactive sub-micron filler particles. The setting characteristics, chemical reactivity and cement strength have been found using oscillating rheology, infrared spectrometry, nuclear magnetic spectrometry, transmission electron microscopy, potentiometer analysis, laser diffractometry and mechanical analysis. The addition of sub-micron filler particles in direct weight by weight replacement of aluminosilicate glass of a control material has increased the ultimate compressive strength of the new cement from 206MPa (control) to 250MPa after 365 days of aging. The strength of the new filler enhanced cements were comparable with the control material after 3 hours. The setting chemistry of the filler enhanced cements follows the same order as the control cement but at a decelerated rate. Theoretical modelling found that a large volume of sub-micron filler could fit into interstitial spacing in formed cement however the alteration of the aluminosilicate glass to polyelectrolyte ratio has been found to drastically alter the cement setting time. The use of cubic and polyhedral shaped filler particles as supposed to spherical particles may increase the cement strength further as greater packing densities are achieved. The formulation of a Glass Ionomer Cement with increased compressive strength may find use as a posterior restorative or as a better material for restoration of lesions and cavity liners.

Cette thèse traite de la solution numérique de deux types de problèmes stochastiques. Premièrement, nous nous intéressons aux EDS fortement oscillantes, c'est-à-dire, les systèmes composés de variables ergodiques évoluant rapidement par rapport aux autres. Nous proposons un algorithme basé sur des résultats d'homogénéisation. Il est défini par un schéma d'Euler appliqué aux variables lentes couplé avec un estimateur à pas décroissant pour approcher la limite ergodique des variables rapides. Nous prouvons la convergence forte de l'algorithme et montrons que son erreur normalisée satisfait un résultat du type théorème limite centrale généralisé. Nous proposons également une version extrapolée de l'algorithme ayant une meilleure complexité asymptotique en satisfaisant les mêmes propriétés que la version originale. Ensuite, nous étudions la solution des EDS de type McKean-Vlasov (EDSPR-MKV) associées à la solution de certains problèmes de contrôle sous un environnement formé d'un grand nombre de particules ayant des interactions du type champ-moyen. D'abord, nous présentons un nouvel algorithme, basé sur la méthode de cubature sur l'espace de Wiener, pour approcher faiblement la solution d'une EDS du type McKean-Vlasov. Il est déterministe et peut être paramétré pour atteindre tout ordre de convergence souhaité. Puis, en utilisant ce nouvel algorithme, nous construisons deux schémas pour résoudre les EDSPR-MKV découplées et nous montrons que ces schémas ont des convergences d'ordres un et deux. Enfin, nous considérons le problème de réduction de la complexité de la méthode présentée tout en respectant la vitesse de convergence énoncée. / This Ph.D. thesis deals with the numerical solution of two types of stochastic problems. First, we investigate the numeric solution to strongly oscillating SDEs, i.e. systems in which some ergodic state variables evolve quickly with respect to the remaining ones. We propose an algorithm that uses homogenization results and consists of an Euler scheme for the slow scale variables coupled with a decreasing step estimator for the ergodic averages of the fast variables. We prove the strong convergence of the algorithm as well as a generalized central limit theorem result for the normalized error distribution. In addition, we propose an extrapolated version applicable under stronger regularity assumptions and which satisfies the same properties of the original algorithm with lower asymptotic complexity. Then, we treat the problem of solving decoupled Forward Backward Stochastic Differential equations of McKean-Vlasov type (MKV-FBSDE) which appear in some stochastic control problems in an environment of a large number of particles with mean field interactions. As a first step, we propose a new algorithm, based on the cubature method on Wiener spaces, to weakly approach the solution of a McKean-Vlasov SDE. It is deterministic and can be parametrized to obtain any given order of convergence. Using this first forward approximation algorithm, we construct two procedures to solve the decoupled MKV-FBSDE and show that they converge with orders one and two under appropriate regularity conditions. Finally, we consider the problem of reducing the complexity of the presented method while preserving the presented convergence rates.

Afin de clarifier et caractériser les mécanismes fondamentaux de formation des réseaux étendus cellulaires et dendritiques en régime diffusif, des expériences de solidification dirigée permettant l’observation in situ en temps réel de l’interface solide-liquide d’un alliage transparent ont été réalisées dans l’instrument « DECLIC-DSI» à bord de la Station Spatiale Internationale. Des procédures spécifiques d'analyse d'images ont été développées pour caractériser les réseaux et extraire des données de référence à comparer aux modèles théoriques ou numériques. Les mécanismes d’évolution et de sélection de l'espacement primaire sont décrits et reliés à la courbure macroscopique de l'interface qui apparait comme un paramètre important de la dynamique de réseau. L’obtention de réseaux homogènes étendus nous a permis d'observer des instabilités secondaires du régime cellulaire pour la première fois dans des systèmes tridimensionnels: Oscillation et multiplet structure. Nos analyses mettent en évidence l'absence de cohérence globale de l’oscillation, exceptée dans des zones localement ordonnées dans lesquelles les oscillations de cellules voisines peuvent être synchronisées. Dans une autre gamme de paramètres de contrôle, la formation de multiplets -autre type d'instabilité secondaire- a été observée. La structure et la dynamique de ces multiplets est décrite. Enfin, des essais comparatifs ont été réalisés au sol, pour les mêmes paramètres de croissance, afin de clarifier l'influence de la convection. Les différences entre les expériences au sol et en microgravité, en particulier concernant l'espacement primaire, sont reliées à l'amplitude de la convection. / To clarify and characterize the fundamental physical mechanisms active in the formation of three-dimensional (3D) arrays of cells and dendrites, in situ monitoring of series of experiments on a transparent alloy was carried out under low gravity in the DECLIC-DSI on-board the International Space Station. Image analysis procedures have been developed to characterize the patterns and get benchmark data to compare with theoretical or numerical modelling. The mechanisms of primary spacing evolution and selection are described and related to the macroscopic interface curvature that appeared to be a critical parameter. The extended homogeneous patterns obtained in microgravity enabled us to observe secondary instabilities of the cellular pattern for the very first time in 3D patterns: cell oscillation and multiplet structure. Our analyses highlight the absence of global coherence of cell oscillations, except in locally ordered areas where synchronization of neighbor cells may happen. In another range of control parameters, another type of secondary instability has been identified that corresponds to multiplet formation; the structure and dynamics of those multiplets are also described. Finally, comparative experiments have been performed on ground with similar growth parameters to point out the influence of convection. The differences between ground and microgravity results, especially regarding the primary spacing, are related to fluid flow magnitude.

L’objectif du présent travail a été de concevoir et de fabriquer des dispositifs sur silicium pour convertir de l’énergie thermique en une énergie électrique en utilisant le changement de phase liquide-gaz dans le but de générer une variation subite de pression suivie d’une conversion d’énergie mécanique vers une énergie électrique à l’aide d’un piézoélectrique. La construction des dispositifs a dû rester simple, avec des matériaux courants et en respectant des limites dimensionnelles. Empreinte inférieure à un diamètre de 20 mm et une épaisseur en dessous des 2 mm.Les prototypes fabriqués sont composés de 3 plaques en silicium, contenant une chambre d’évaporation, une chambre de condensation et un canal réunissant les deux. Un transducteur piézoélectrique a été reporté sur la chambre de condensation et assure l’étanchéité ainsi que la génération d’énergie électrique.Le processus de conception inclut plusieurs étapes, dont la définition de la géométrie et du type de fluide de travail utilisé en tant qu’agent thermique. Le travail effectué a permis de sélectionner le type de piézoélectrique, sa taille ainsi que sa méthode d’intégration. Une étude a également été conduite pour déterminer la méthode optimale d’assemblage des plaques en silicium.La réalisation pratique des dispositifs a été orientée vers la sélection des meilleurs procédés technologiques pour la fabrication des structures. Toutes les expériences ont été conduites en salle blanche avec utilisation de l’oxydation humide, la photolithographie, la gravure KOH, ainsi que d’une technique d’assemblage des plaques silicium avec utilisation de la résine SU-8 comme couche intermédiaire. En plus, quelques outils spécifiques ont été conçus lors du présent travail, pour faciliter la fabrication des dispositifs, dont un système sous vide dédié à l’assemblage des plaques en silicium.Les dispositifs ont été testés afin d’établir leur mécanisme d’oscillation thermique ainsi que leurs propriétés électriques. L’influence tu taux de remplissage et de la température de surface chaude sur le signal en sortie ont également été étudiées. Le calcul de l’énergie générée a aussi été effectué. Dans la dernière partie de l’étude, des étapes d’optimisation pour les dispositifs développés dans le présent travail sont proposées. / The goal of the present work was to design and fabricate a fully silicon oscillating device that converts thermal energy into electricity, applying phenomena of liquid to gas phase-change and piezoelectricity. It should be characterized by simplicity of construction, small size, and ease of manufacture. The diameter should not exceed 2 cm, while the thickness should be within 2 mm.The device was composed of three Si wafers comprising evaporation and condensing chambers, and the channel connecting these two elements. A PZT-based transducer mounted on top of the structure was applied to ensure energy conversion.The design process included the establishment of the device geometry, the type of the working fluid enclosed inside the system, a type, size and assembly technique of a piezoelectric element, as well as a bonding method of several silicon elements of the device.The practical realization of the designed prototypes was aimed at selecting the most suitable technological processes for structure fabrication. All the experiments had been performed in a clean room environment and employed wet oxidation, photolithography, a well-known, easily available wet chemical etching in KOH solution, and a silicon bonding technique with the use of SU-8 photoresist as an intermediate layer. Additionally, during the practical work a few tools have been designed and developed to enhance the device fabrication, amongst which a vacuum pump dedicated to bond the three silicon wafers as structural elements of the prototypesThe fabricated prototypes were tested in terms of oscillation mechanism and electrical properties. The influence of the filling ratio and the hot temperature value on the generated signal was established. Additionally, the power range of the prototypes has been evaluated. In the last part of the study, optimization steps for the devices developed in the present work have been proposed.

Les roulements soumis à des mouvements oscillatoires et des charges élevées sont nécessaires pour le fonctionnement de nombreux mécanismes industriels (actionneurs, commandes d’avions, machines pour l’usinage, robots, chaînes d’assemblages, …). Ces roulements sont soumis à des pressions de contact locales extrêmement élevées avec des vitesses de roulement faibles qui ne permettent pas une lubrification adéquate des interfaces des premiers corps avec de l’huile. Les essais d’endurance sur les roulements ont permis la reconstitution des courbes de dégradation pendant la vie du roulement. Des analyses des surfaces, effectués à chaque phase de la vie du roulement ont permis aussi bien de suivre l’évolution de la topographie à l’interface entre les pistes et les éléments roulants. D’autre parte, des analyses numériques par éléments finis ont permis d’obtenir des informations sur les distributions des contraintes et des déformations. Le croisement des résultats expérimentaux et numériques a donc permis la reconstruction des mécanismes locaux d’accommodation. Dans le cas d’un roulement oscillant non graissé, les déplacements relatifs et les contraintes sont principalement accommodés aux interfaces des premiers corps en contact, ce qui accélère l’endommagement final du roulement. Dans le cas d’un roulement oscillant graissé, une partie des déplacements relatifs et contraintes est accommodée dans une sous couche qui se forme dans la peau des éléments roulants. Cette accommodation se manifeste par l’accumulation de déformations plastiques qui s’avèrent être aussi à l’origine de l’endommagement final du roulement. L’analyse des surfaces de contact des roulements oscillants graissés montre qu’il se forme, en présence de la graisse et très tôt dans la vie du roulement, une couche (troisième corps graisse/particule et TTS en surface de la piste) qui protège les surfaces en contact. D’autre part, une expertise de roulement ayant fonctionné sur un avion de de type A340 révèle une forte similarité entre ses faciès d’usure et ceux obtenus lors des essais d’endurance, et valide ainsi les mécanismes d’accommodation reconstitués. Enfin, des questions portant sur les effets de la quantité de graisse, du glissement des éléments roulants, et des pauses sur un essai donné sont aussi traitées. / Bearings subjected to oscillatory motions and high loads are necessary for the operation of several industrial mechanisms (actuators, aircraft controls, machining, robots, assembly lines, ...). These bearings are subjected to extremely high local contact pressures with low running speeds, which do not permit adequate lubrication of the interfaces of the first bodies with oil. Endurance tests perfomed on commercial bearings allowed at reconstructing the evolution of the degradation curves during the bearing life. Surface analyses carried out at each phase of the bearing life also allowed at following the evolution of the topography at the interface between the bearing raceways and the rolling elements. On the other hand, numerical analyses, by finite element method, have led to obtain information on the distributions of stresses and deformations. The dialogue between experimental and numerical results allowed the reconstruction of the local accomodation mechanisms. In the case of ungreased oscillating bearings, the relative displacements are mainly accommodated at the surfaces of the first bodies in contact, which accelerates the damage of the bearing. In the case of greased oscillating bearings, part of the relative displacements and stresses are accommodated at the subsurface of the rolling elements. This accommodation mechanism is manifested by the accumulation of plastic deformations which are at the origin of the final degradation of the bearing. The analysis of the contact surfaces of the raceways of the greased oscillating bearings shows as well that, in the presence of grease, a layer (third body mixture of grease and particles, and TTS on the track surface) protects the surfaces of the raceway and thus accommodates the other part of the displacements and stresses. On the other hand, the analysis of an airelon bearing, dismounted from an A340 type aircraft, revealed a strong similarity between its topographies and those obtained during the performed endurance tests, validateing the reconstructed accommodation mechanisms. Finally, questions about the effects of the amount of grease, sliding of the rolling elements, and pauses on a given test heve been discussed too.

A conversão da energia das ondas dos oceanos em energia elétrica é uma alternativa para o problema da falta de combustíveis fósseis. Uma das possibilidades de aproveitamento é através de dispositivos cujo princípio de funcionamento é o de Coluna de Água Oscilante (CAO). No presente trabalho o objetivo é, através da modelagem computacional e do emprego do Design Construtal, maximizar a potência hidropneumática de um dispositivo conversor de energia das ondas do mar do tipo CAO. São analisados diferentes eixos da restrição física, no formato elíptico, que representa a turbina, e duas formas geométricas na região de transição entre a câmara hidropneumática e a chaminé do dispositivo CAO: trapezoidal e semicircular. Considerando um domínio bidimensional, as restrições para estes problemas são: Área da restrição elíptica (AR), Área total do dispositivo (AT) e razão entre a área da restrição elíptica e a área total (ϕn). Os graus de liberdade analisados são: a razão entre os comprimentos dos eixos da restrição elíptica (d1/d2) para o caso da restrição física da turbina, o ângulo de inclinação da parede (α) para o caso com região de transição trapezoidal, o raio (r) e H2/l (razão entre altura e comprimento da chaminé de saída da câmara CAO) para o caso com região de transição semicircular. Para a solução numérica é empregado um código de dinâmica dos fluidos computacional, FLUENT®, baseado no Método de Volumes Finitos (MVF). O modelo multifásico Volume of Fluid (VOF) é aplicado no tratamento da interação água-ar. O domínio computacional é representado por um tanque de ondas com um dispositivo CAO acoplado. Os resultados obtidos indicam que, para o estudo da região de transição trapezoidal o desempenho do conversor tem aproximadamente o mesmo desempenho para todas as geometrias estudadas. A região de transição semicircular, apresenta resultados para os quais foi possível otimizar a potência hidropneumática. O estudo da turbina indica que foi possível determinar uma geometria capaz de converter a energia da onda incidente ao dispositivo, sem que ocorresse a obstrução do escoamento de ar na chaminé do dispositivo CAO. Assim, mostra-se a relação entre o método Design Construtal e o clima de ondas na definição das dimensões que maximizam a potência hidropneumática. / The conversion of ocean’s wave energy into electrical energy is an alternative for the scarcity of fossil fuels. One of the possibilities of energy use is through devices, whose operating principle is the Oscillating Water Column (OWC). In this work the aim is, through computer modeling and the Constructal Design, to maximize hydropneumatic power of a power converter device type OWC. Different axes of physical constraint with elliptical shape, representing the effect of the turbine , are analyzed. Two geometric shapes in the transition region between the hydropneumatic chamber and the chimney OWC device, trapezoidal and semicircular, are also analyzed. Considering a two-dimensional domain the restrictions for this problem are: Elliptical restriction area (AR), Total area device (AT) and the ratio between the area of the elliptical restraint and the total area (ϕn). The considered degrees of freedom are: the ratio between the lengths of the axes (d1/d2) of the elliptical restraint, for the turbine’s physical constraint case, the inclination angle (α) of the wall for the trapezoidal transition case, and the radius (r) and H2/l (ratio between height and length of output chimney CAO) for the semicircular transition region case. For the numerical solution, a commercial code of computational fluid dynamics, FLUENT®, which is based on the Finite Volume Method (FVM), is employed. The multiphase model Volume of Fluid (VOF) is applied in the treatment of water-air interaction. The computational domain is represented by a wave tank with a fixed OWC device. The obtained results indicate that, for the study of the trapezoidal transition region, the performance of converter don’t seems to be compensatory only by changing the geometry of the trapezoidal area. However, for the semicircular transition region, it was possible to optimize a hydropneumatic power. The study of turbine effect indicates a geometry capable of converting the energy of the incident wave to the device, without obstructing the air flow in the chimney of de OWC, showing the relationship between the Constructal Design method and the wave climate in the definition of the dimensions that maximize the hydropneumatic power.

We study several different models of extended bodies in gravitational fields. Firstly, we revisit the glider model of a dumbbell-like oscillating body. We develop an independent scheme to integrate the equations of motion. We study the radial fall of a Newtonian spring, calculate the position shifts of the spring and find the critical value of the spring constant which cannot overcome the tidal forces. We argue that the relativistic glider model is unphysical due to its behaviour in the critical regions. Secondly, we show that Dixon's theory of extended bodies predicts a geodesic motion of the centre of mass in maximally symmetric spacetimes. We prove that a system of test particles can be described by a conserved stress-energy tensor and we evaluate the position shifts of the glider model in the maximally symmetric spacetimes, showing its disagreement with Dixon's theory. We thus conclude again that the glider model must be rejected. And thirdly, we study a model of an extended body consisting of interacting particles, which is in accord with Dixon's theory. We calculate the position shifts for this model and show that the model does not predict any measurable swimming effect. Finally, we estimate the numerical error of the calculation by finding the position shifts of the model in maximally symmetric...

Although oscillating water column type wave energy devices are nearing the stage of commercial exploitation, there is still much to be learnt about many facets of their hydrodynamic performance. This research uses the commercially available FLUENT computational fluid dynamics flow solver to model a complete OWC system in a two dimensional numerical wave tank. A key feature of the numerical modelling is the focus on the influence of the front wall geometry and in particular the effect of the front wall aperture shape on the hydrodynamic conversion efficiency. In order to validate the numerical modelling, a 1:12.5 scale experimental model has been tested in a wave tank under regular wave conditions. The effects of the front lip shape on the hydrodynamic efficiency are investigated both numerically and experimentally and the results compared. The results obtained show that with careful consideration of key modelling parameters as well as ensuring sufficient data resolution, there is good agreement between the two methods. The results of the testing have also illustrated that simple changes to the front wall aperture shape can provide marked improvements in the efficiency of energy capture for OWC type devices.