Les variateurs de vitesse sont constitués de convertisseurs statiques qui permettent de varier la vitesse de rotation des moteurs électriques triphasés. Cependant, ces convertisseurs sont à l'origine de perturbations électromagnétiques conduites de mode commun. L'objectif de ce travail porte sur la réduction ces perturbations conduites, par l’élaboration d’une nouvelle stratégie de commande basée sur la modulation de largeur d’impulsions (MLI). Cette commande est appliquée à un variateur de vitesse composé d’un redresseur MLI à absorption sinusoïdale. Un état de l’art des solutions d’atténuation des perturbations conduites a été réalisé ; à l’issu duquel, il en résulte que la MLI est une technique intéressante pour la réduction des perturbations de mode commun. Une stratégie de modulation basée sur la méthode de synchronisation des commutations entre redresseur et onduleur, nommée synchronisation totale, a été développée. Dans le but de mettre en avant l’impact de cette méthode sur le niveau des perturbations, une étude des phénomènes relatifs aux commutations des transistors de puissance est menée. Un modèle de représentation simplifié des commutations a permis l’évaluation des performances de la synchronisation totale sur la tension de en mode commun. Cette méthode a ensuite été validée expérimentalement au travers d’un prototype intégrant un algorithme d’application de la stratégie de modulation proposée. Les résultats obtenus ont permis de montrer les avantages de la méthode de synchronisation totale principalement dans la réduction des dimensions des filtres CEM utilisés pour la mise en conformité des variateurs de vitesse. / The adjustable speed drives (ASDs) use the static converters that allow varying the speed of the three phase electrical motors. However, these converters are the main source of the common mode conducted emissions. The objective of this research work focuses on the reduction of conducted emissions, through the development of a new control strategy based on pulse width modulation (PWM). This strategy is applied to an adjustable speed drives that is composed from an Active Front End (AFE). A state of art of the different solutions of the reduction of the conducted emissions has been achieved. This study shows that the control strategy (PWM) is a useful technique for reducing common mode interferences. A new PWM strategy allowing the synchronization of all the switching cell of the AFE and inverter has been developed and will be noted "full synchronization". In order to highlight the impact of this method on the conducted emissions, a study of phenomena related to the power transistors' switching is carried out. A simplified model of the switching allowed the evaluation of the performances of full synchronization method on the common mode voltage. This method was then validated experimentally on an ASD prototype using the developed control strategy algorithm. The obtained results show the advantages of the proposed full synchronization method, mainly in the reduction of the dimensions of the EMI filters for compliance with EMC standards.

A dissertation submitted in partial compliance with the requirements for a Master's Degree in Technology: Chiropractic, Technikon Natal, 1997. / The purpose of this investigation, was to determine what role cryotherapy plays in conjunction with manipulation headaches. / M

No description available.

The relationship between surface energy and precipitated graphite form in Fe-C alloys was examined in this thesis.Surface tension and contact angle data were obtained using the sessile drop technique. Carbon saturated, puron iron crucibles were melted on pyrolytic graphite, the effect of time, temperature (1500-1600°C) and additions of Ni, Mn, S or Ce being examined. The graphite form was established by metallographic examination. An average ƔLV of 1152 dynes/cm was determined for the Fe-C alloys (4.6% C) at approximately 1300°C, the average contact angle being 128°. No significant change occurred with additions of Ni ( 0.85%) and Mn ( 1.65%). Additions of S lowered the surface energy and increased the equilibrium contact angle. Ce additions had a similar effect although a direct comparison with the Fe-C alloys could not be made as different temperatures were used. However, the interfacial energy difference apparently increased with increasing Ce content, implying an adsorption of Ce to the graphite-melt interface. The change from the flake to the nodular form was accomplished in several transition stages, the interfacial energy differences being small, indicating a marked dependence on the solidification and growth conditions. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

This master’s research is a phenomenological inquiry into the pedagogical moment in teacher education. This phenomenon is explored through a conceptual lens that draws from the phenomenological pedagogical ideals that are intrinsic to the work of both Ted Aoki and Max van Manen. Following a comprehensive outline of the phenomenological methodology that guides this thesis, the pedagogical moment is described in terms of three phases: tension, opening and pulse. The phenomenon is further explored through several sub themes relating to the lifeworld existentials (time, body, space, relation to other). This research intertwines several phenomenological concepts (such as intentionality, embodiment, consciousness, pedagogy, and motion sensitive phenomenology), within the context of one “living” phenomenon as a way of shedding light on what it is like to experience a pedagogical moment from within the tensions of practicum teaching.

The problem of this study was to investigate the resilient effects of selected string tensions in various types of tennis rackets. The rackets selected were the Wilson T-2000, Head Professional, Head Master, Dunlop Fort, Dunlop Austral, and Yamaha Composite. Each racket was randomly strung and tested at 45, 52.5, and 60 pounds of string tension. The testing involved dropping a tennis ball 100 inches onto the racket face, which was stationary, and measuring the height of the ball bounce. The data collected from the rackets and string tensions were analyzed by the analysis of variance and the .05 level of confidence was used to determine significance. A significant difference occurred between the Head Professional and Wilson T-2000 and the Head Professional and Yamaha Composite. Significant differences occurred between all three string tensions.

The new Ashton Bridge is a concrete tied-arch structure with a cable-supported deck, which spans 110 metres below the arching ribs. The tie-beam members, connecting the arch ribs, each have six longitudinal tendons that have primarily straight profiles. The author set out to validate the structural behaviour of the tie-beams, after the post-tensioning construction stage. This objective was achieved by validating selected finite element model parameters with field conducted tests. The input parameter, which is the prestress loading onto the structure, was validated with tendon elongation measurements and tendon lift-off tests. The output parameter, which is the strain and displacement response of the structure, was verified by measuring the elastic deck shortening and the strain gauge readings. Lower tendon extensions were encountered during tensioning. This required calibration of the friction coefficients and model updating. Lift-off tests and deck shortening measurements provided and order size estimation of the structural behaviour, but was not adequate for model validation. The strain gauge readings showed a close correlation with the expected strain state of the structure and offered insight into the behaviour of the structure during post-tensioning. The methods described in this dissertation may be used for validating the structural behaviour of concrete bridges subject to post-tensioning. Suggestions for improving tendon lift-off tests and deck shortening measurements are also presented.

This work presents an all-Mach method for two-phase inviscid flow in the presence of surface tension. A modified version of the Hartens, Lax, Leer and Contact (HLLC) approximate Riemann solver based on Garrick et al. [1] is developed and combined with the popular Volume of Fluid (VoF) method: Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM). This novel combination yields a scheme with both HLLC shock capturing as well as accurate liquid-gas interface tracking characteristics. To ensure compatibility with VoF, the Monotone Upstream-centred Scheme for Conservation Laws (MUSCL) [2] is applied to non-conservative (primitive) variables, which yields both robustness and accuracy. Liquid-gas interface curvature is computed via both height functions [3, 4] and the convolution method [5]. This is in the interest of applicability to both cartesian and arbitrary meshes. The author emphasizes the use of VoF in the interest of surface tension modelling accuracy. The method is validated using a range of test-cases available in literature. The results show flow features that are in agreement with experimental and benchmark data. In particular, the use of the HLLC-VoF combination leads to a sharp volume fraction and energy field with improved accuracy (up to secondorder).

This thesis examines the use of diagonal tension (shear) testing to determine factors affecting shear strength of Interlocking Compressed Earth Block (ICEB) panels. This work expands on the current information available about strength properties of ICEB assemblies, which are dry-stacked, as opposed to having mortared beds. Variables such as block strength, grout strength and grouting pattern can influence the results of these types of tests and are examined in this investigation. To study variables affecting diagonal shear strength, 9 panels were tested, consisting of blocks produced by a manual block press. Strength testing was adopted from common ASTM standards to determine constituent material properties. A modified version of ASTM E519 test procedure is used to perform diagonal tension testing. Imaging analysis, using a high resolution camera, was run simultaneously during testing to capture displacement histories of select panels. It was determined that both block and grout strength significantly affect the shear strength of ICEB panels. Additionally, vertical grouting and block type also have a strong influence. Imaging analysis results confirm that the dominant failure mode in ICEB panels is bed joint sliding both pre and post peak load, with noticeable displacements at head joint locations on a few panels. Lastly, diagonal cracking along the block face was noticeable on several panels following peak load. Further testing remains to determine other factors affecting shear strength, namely, the application of normal pre-compression loads to the panel.

Ce travail de thèse s’inscrit dans le cadre du projet INTERREG Luminoptex et vise à réaliser des diodes organiques de redressement pour des applications de récupération d’énergie électromagnétique pour de l’éclairage ambiant autonome sur support textile. Des diodes à base de pentacène et de polymère P3HT ont été fabriquées selon deux configurations: verticale et coplanaire en utilisant aussi bien des procédés simples et peu couteux que des procédés de lithographie électronique. Les performances de ces diodes ont été améliorées par l’utilisation de monocouches auto assemblées SAM de PFBT (2,3,4,5-6 pentafluorobenzénethiol) qui permettent de réduire les barrières d’injection des porteurs de charges denviron 0.5eV. Dans le cas des diodes polymères, une couche d’injection à base de P3HT dopé au Triflate de cuivre a été étudiée et utilisée pour l’amélioration de l’injection. Des rapports de rectification élevés ont été obtenus ( 107) avec des tensions de fonctionnement très faibles (de 20 à 80mV). Les travaux de simulation ont montré par ailleurs, que ces diodes peuvent atteindre des fréquences de fonctionnement de l’ordre du GHz.Ces composants ont été ensuite réalisés sur substrat flexible de papier pour un transfert sur les surfaces textiles. / This thesis work is a part of the INTERREG Luminoptex project and aims to produce organic rectifier diodes for electromagnetic energy harvesting applications for autonomous ambient lighting on textile support. Pentacene oligomer and P3HT polymer diodes have been fabricated in two configurations: vertical and coplanar structures using soft technology and low cost processes or electron beam lithography technique. The performance of these diodes has been improved by the use of PFBT (2,3,4,5-6 pentafluorobenzenethiol) SAM self-assembled monolayers that reduce the injection barriers of charge carriers by about 0.5eV. In the case of polymer diodes, an injection layer based on P3HT doped with copper triflate was studied and used to improve the current injection. High rectification ratios were obtained ( up to 107) with very low operating voltages (from 20 to 80mV). Simulation study has also shown that these diodes can reach operating frequencies in the GHz range. These devices were then made on a flexible paper substrate for transfer to textile surfaces.