O objetivo principal deste trabalho é o desenvolvimento de controladores robustos baseados no princípio do modelo interno, em referenciais síncrono e estacionário, para aplicação ao estágio de saída de uma fonte ininterrupta de energia (UPS) a fim de minimizar a distorção na tensão de saída causada pela conexão de cargas não lineares balanceadas e desbalanceadas. A formulação em referencial estacionário (abc) é realizada através da aplicação de controladores com múltiplos modos ressonantes, a fim de se estabelecer erro nulo ao seguimento de referência senoidal e rejeição de distúrbios na tensão de saída devido às correntes com elevado conteúdo harmônico drenadas pelas cargas. Além disso, o controle é formulado em referencial síncrono (dq0) utilizando controladores Proporcional-Integral (PI) convencionais muito difundidos na maioria das aplicações comerciais de UPS. O projeto de ambos controladores é realizado utilizando uma metodologia de controle robusto com realimentação de estados, onde os parâmetros dos controladores são determinados através da resolução de um problema de otimização convexa sujeito a um conjunto de restrições na forma de desigualdades matriciais lineares (LMI). Uma análise comparativa de desempenho é realizada entre controladores com um modo ressonante (sintonizado na fundamental) e o PI em dq0, pois apresentam estruturas funcionalmente equivalentes sob a ótica do princípio do modelo interno aplicada a seus respectivos referenciais. Além do mais, demonstra-se a melhoria no desempenho com o uso dos controladores múltiplo ressonantes em referencial estacionário onde escolhe-se as frequências de ressonância de cada modo de maneira a suprimir os efeitos de harmônicas específicas na tensão de saída da UPS. A análise comparativa entre os controladores propostos é realizada através de simulações numéricas, utilizando os procedimentos de ensaio dinâmico e estático e as exigências estabelecidas pela norma internacional IEC 62040-3. / The main objective of this work is the development of robust controllers based on the internalmodel principle, in synchronous and stationary frames, applied to the output stage of an uninterruptible power supply (UPS), in order to minimize the output voltage distortion caused by the connection of balanced and unbalanced nonlinear loads. The formulation in stationary abc-frame is accomplished through the aplication of a multiple resonant controller, so that, it is possible to achieve zero-error tracking of the sinusoidal reference and disturbances rejection on the output voltage due to the high amount of harmonic currents drained by the loads. Moreover, a controller in synchronous reference frame (dq0 axis) is formulated through the application of conventional Proportional-Integral (PI) controllers which are widely used in comercial UPS applications. The design of both controllers is formulated using a state-feedback robust controlmethod, in which the controller parameters are determined by solving a convex optimization problem subject to a set of LMI constraints. A comparative analysis on the performance of the single-mode resonant controller (tuned at the fundamental frequency) and the PI controller is performed, because these controllers are functionally equivalent in the sense of the internal model principle applied to their respective frames. Furthermore, the improvement in performance is demostrated with the use of multiple resonant controllers in stationary abc-frame where the resonance frequencies are chosen to suppress the effects of a specific harmonic in the UPS output voltage. The comparative analysis of the proposed controllers is performed through numerical simulations, making use of the dynamical and steady-state test methods and performance requirements defined by the IEC 62040-3 international stardard.

This thesis was aimed developing a fundamental understanding of the boundary layer response to arbitrary motion. In this context arbitrary motion was defined as the unsteady translation and rotation of an object. Research objectives were developed from the gaps in knowledge as defined during the literature survey. The objectives were divided into three main activities; mathematical formulations for non-inertial bulk flow and boundary layer equations, implementation of said formulations in a numerical solver and simulations for various applications in arbitrary motion. Mathematical formulations were developed for the bulk flow and boundary layer equations in arbitrary motion. It was shown that the conservation of momentum and energy equations remains invariant in the non-inertial forms. The conservations of momentum equation can at most have six fictitious terms for unsteady arbitrary motion. The origin of the terms were found to be from transformation of the material derivative to the non-inertial frame. All fictitious terms were found to be present in the boundary layer equations, none could be eliminated during an order of magnitude analysis. The vector form of the non-inertial equations were implemented in a novel OpenFOAM solver. The non-inertial solver requires prescribed motion input and operate on a stationary mesh. Validation of the solver was done using analytical solutions of a steady, laminar flat plate and rotating disk respectively. Numerical simulation were done for laminar flow on a translating plate, rotating disk and rotating cone in axial flow. A test matrix was executed to investigated various cases of acceleration and deceleration over a range of 70 g to 700 000g. The boundary layer profiles, boundary layer parameters and skin friction coefficients were reported. Three types of boundary layer responses to arbitrary motion were defined. Response Type I is viscous dominant and mimics the steady state velocity profile. In Response Type II certain regions of the boundary layer are dominated by viscosity and others by momentum. Response Type III is dominated by momentum. In acceleration the near-wall velocity gradient increases with increasing acceleration. In deceleration separation occurs at a result of momentum changes in the flow. The mechanism that causes these responses have been identified using the developed boundary layer equations. In acceleration the relative frame fictitious terms become a momentum source which results in an increase in velocity gradient at the wall. In deceleration the relative frame fictitious terms become a momentum sink that induced an adverse pressure gradient and subsequently laminar separation. / Hierdie tesis is gerig op die ontwikkeling van 'n fundamentele begrip aangaande die grenslaag reaksie op arbitrêre beweging. In hierdie konteks word arbitrêre beweging gedefinieer as die ongestadigde translasie en rotasie van 'n voorwerp. Navorsingsdoelwitte is ontwikkel uit die gapings soos omskryf in die literatuuroorsig. Die doelwitte is verdeel in drie hoof aktiwiteite; wiskundige formulerings vir ongestadigde vloei en grenslaag vergelykings, implementering van hierdie formulerings in 'n numeriese kode en simulasies vir verskeie gevalle van arbitrêre beweging. Wiskundige formulerings is ontwikkel vir die vloei en grenslaag vergelykings in arbitrêre beweging. Daar is bewys dat die behoud van massa en energie vergelykings onveranderd in die nie-inertiële vorms bly. Die behoud van momentum vergelyking kan hoogstens ses fiktiewe terme vir ongestadigde, arbitrêre beweging hê. Die oorsprong van die terme is vanuit die transformasie van die ongestadigde en adveksie terme (aan die linker kant van die momentum vergelyking) na die nie-inertiële raam. Alle fiktiewe terme is teenwoordig in die grenslaag vergelykings. Die vektor vorm van die nie-inertiële vergelykings is in 'n nuwe OpenFOAM oplosser geïmplementeer. Die nie-inertiële oplosser vereis voorgeskrewe beweging insette en werk op 'n stilstaande rooster. Die oplosser is getoets teen analitiese oplossings van 'n gestadigde, laminêre plaat plaat en 'n roterende skyf, onderskeidelik. Numeriese simulasies is gedoen vir laminêre vloei op 'n translerende plaat, roterende skyf en roterende konus in aksiale vloei. 'n Toets matriks is gebruik om ondersoek in te stel na gevalle van versnelling en vertraging oor 'n verskeidenheid van 70 g tot 700 000 g. Die grenslaag profiele, grenslaag parameters en oppervlak wrywingskoëffisiënte is aangemeld nie. Drie tipes grenslaag reaksies op arbitrêre beweging is gedefinieer. Reaksie Tipe I is viskeus dominant en boots die bestendige snelheidsprofiel na. In reaksie Tipe II sekere dele van die grenslaag is oorheers deur viskositeit en ander deur momentum. Reaksie Tipe III word in totaliteit oorheers deur momentum. In versnelling die snelheid helling teen die objek neem toe met toenemende versnelling. In vertraging is 'n negatiewe snelheidsprofiel waargeneem as gevolg van momentum veranderinge in die vloei. Die meganisme wat hierdie reaksies veroorsaak is geïdentifiseer deur die grenslaag vergelykings. In versnelling word die fiktiewe terme 'n bron van momentum. Dit lei tot 'n toename in snelheid helling op die objek. In vertraging word die fiktiewe terme 'n momentum gebruiker wat 'n negatiewe drukgradiënt veroorsaak en gevolglik laminêre vloei wegbreking veroorsaak. / Thesis (PhD)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

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<p>Successful navigation requires an accurate mental spatial representation of the environment that can be updated during movement. Experiments with animals and humans have demonstrated the existence of two forms of spatial representation: egocentric (observer-centered) and allocentric (environment-centered). Unfortunately, specifically how humans use these two systems is not well understood. The current dissertation was focused on providing evidence differentiating human use of egocentric and allocentric spatial reference frames, specifically examining the characteristics and contributions from body-based sources. Two empirical chapters are presented that include experiments involving two common spatial tasks. In Chapter 2, updating of feature relations within a room-sized environment was examined by having observers provide directional judgments to learned features with respect to an imagined orientation that was either congruent or incongruent with their physical orientation. The information available for updating the physical orientation was manipulated across experiments. Performance differences between congruent and incongruent conditions demonstrated the reliance on egocentric representations for updating, and differentiated body- and knowledge-based components of the egocentric updating process. The specificity of the body-based component was examined in Chapter 3 by having observers detect changes made to a tabletop spatial scene following a viewpoint shift resulting from their movement, scene rotation or both. The relation between the extent of observer movement and the magnitude of the experienced viewpoint shift was manipulated. Change detection performance was best when the extent of observer movement most closely matched the viewpoint shift, and declined as the match declined. Thus, body-based cues contributed specific information for updating self-to-feature relations that facilitated scene recognition. Throughout the course of the research program it has become clear that humans rely on egocentric representations to complete these tasks, and sensory and motor modalities involved in self-motion are integrated for updating spatial relations of novel environments.</p> / Doctor of Philosophy (PhD)

This work has been motivated by the desire to enhance our knowledge about specific cognitive requirements of navigation in multiple reference frames environments and to understand the roles of the hippocampus and posterior parietal cortex in this behavior. The main conclusions of this thesis are: (a) We have developed a novel behavioral test called the Enemy Avoidance Task. The initial set of experiments has shown that laboratory rats are able to plan their movement with respect to a to-be-avoided moving object. Behavioral performance in the task may be quantitatively evaluated. (b) The aforementioned ability is crucially dependent on the functional integrity of the dorsal hippocampus. To the contrary, functional inactivation of the dorsal hippocampi by local infusion of tetrodotoxin did not cause any impairment in the ability of the animal to estimate its distance from a non-moving object. The finding suggests a specific role of the hippocampus in dynamic cognitive processes required for flexible navigation strategies such as continuous updating of information about the position of a moving stimulus. These results are at odds with the two major theories of hippocampal function (Cognitive map theory and Declarative memory theory) and therefore suggest that revision of the theories is necessary. (c)...

As nomads, humanity constantly moved and relocated for hundred thousands of years. Thereby, individuals or small groups of people had to navigate over very long distances in order to survive. As a result, successful spatial navigation was one of the key cognitive abilities, which ensured our survival. Although navigation has nowadays become less life-threatening, exploring our environment and efficiently navigating between places are still very important aspects in our everyday life. However, in order to be able to navigate efficiently, our brain has to perform a series of spatial cognitive operations. This dissertation is structured into three sections, which explore these cognitive operations from three different perspectives. In the first section I will elaborate about the role of reference frames in human spatial navigation. Specifically, in an online navigation study (study one) I will show that humans have distinct but stable reference frame proclivities. Furthermore, this study demonstrates the existence of a spatial strategy, in which the preference to use a particular reference frame is dependent on the axis of rotation (horizontal vs. vertical). In a follow-up study (study two) I will then analyze the factors underlying performance differences in navigation, as well as individual preferences using one or another spatial strategy. Interestingly, the results suggest that performance measures (reaction time and error rate) are influenced mostly by the factors gender and age. However, even more importantly, I will show that the prevalent factor, which influences the choice for an individual navigation strategy, is the cultural background of the participant. This underlines the importance of socio-economic aspects in human spatial navigation. In the second part of this thesis I will then discuss aspects of learning and memorizing spatial information. In this respect, the alignment study (study three) will show that humans are able to recall object-to-object relations (e.g. how to get from A to B) in a very brief time, indicating that such information is directly stored in memory. This supports an embodied (action-oriented) perspective of human spatial cognition. Following this approach, in the feelSpace study (study four) I will then investigate the long-term training effects with a sensory augmentation device. Most importantly, the respective results will demonstrate substantial changes in the subjective perception of space, in sleep stage architecture, and in neural oscillations during sleep. In the third and last section I will describe the importance of multimodal processes in spatial cognitive operations. Most importantly, in the platform study (study five) I will combine the topics of sensory augmentation and Bayesian cue combination. The results of this study show that untrained adult participants alternate rather than integrate between augmented and native sensory information. Interestingly, this alternation is based on a subjective evaluation of cue reliability. In summary, this thesis will present relevant and new findings for better understanding spatial strategy formation, learning and representing spatial relations in memory, and multimodal cue combination. An important and overarching aspect of this thesis is the characterization of individual differences in the context of human spatial navigation. Specifically, my research revealed individual differences in three areas: First, in utilizing egocentric or allocentric reference frames for spatial updating, second in individualized qualitative changes of space perception during long-term sensory augmentation, and third, in preferences to use native or augmented information in a cue combination task. Most importantly, I will provide a better definition and understanding of these individual differences, by combining qualitative and quantitative measures and using latest technologies such as online data recordings and interactive experimental setups. In fact, in the real world, humans are very active beings who follow individualized spatial cognitive strategies. Studying such interactive and individualized behavior will ultimately lead to more coherent and meaningful insights within the human sciences.

<p>ITU - T and the Moving Picture Expert Group (MPEG) have jointly, under the name of Joint Video Team (JVT), developed a new video coding standard. The standard is called H.264 and is also known as Advanced Video Coding (AVC) or MPEG-4 part 10. Comparisons shows that H.264 greatly outperforms MPEG-2, currently used in DVD and digital TV. H.264 halves the bit rate with equal image quality. The great rate - distortion performance means nevertheless a high computational complexity. Especially on the encoder side.</p><p>Handling of audio and video, e.g. compressing and filtering, is quite complex and requires high performance hardware and software. A video encoder consists of a number of modules that find the best coding parameters. For each macroblock several $modes$ are evaluated in order to achieve optimal coding. The reference implementation of H.264 uses a brute force search for this mode selection which is extremely computational constraining. In order to perform video encoding with satisfactory speed there is an obvious need for reducing the amount of modes that are evaluated.</p><p>This thesis proposes an algorithm which reduces the number of modes and reference frames that are evaluated. The algorithm can be regulated in order to fulfill the demand on quality versus speed. Six times faster encoding can be obtained without loosing perceptual image quality. By allowing some quality degradation the encoding becomes up to 20 times faster.</p>

ITU - T and the Moving Picture Expert Group (MPEG) have jointly, under the name of Joint Video Team (JVT), developed a new video coding standard. The standard is called H.264 and is also known as Advanced Video Coding (AVC) or MPEG-4 part 10. Comparisons shows that H.264 greatly outperforms MPEG-2, currently used in DVD and digital TV. H.264 halves the bit rate with equal image quality. The great rate - distortion performance means nevertheless a high computational complexity. Especially on the encoder side. Handling of audio and video, e.g. compressing and filtering, is quite complex and requires high performance hardware and software. A video encoder consists of a number of modules that find the best coding parameters. For each macroblock several $modes$ are evaluated in order to achieve optimal coding. The reference implementation of H.264 uses a brute force search for this mode selection which is extremely computational constraining. In order to perform video encoding with satisfactory speed there is an obvious need for reducing the amount of modes that are evaluated. This thesis proposes an algorithm which reduces the number of modes and reference frames that are evaluated. The algorithm can be regulated in order to fulfill the demand on quality versus speed. Six times faster encoding can be obtained without loosing perceptual image quality. By allowing some quality degradation the encoding becomes up to 20 times faster.

Cette thèse consiste à explorer une nouvelle approche pour la simulation d'objets flexibles par la mécanique des milieux continus, dans le cadre d'applications graphiques interactives telles que le jeu vidéo ou l'entraînement aux gestes chirurgicaux. Elle s'inscrit en continuité d'un stage de M2-R sur ce même sujet. Il est important de pouvoir régler simplement un compromis entre précision et temps de calcul suivant la nature de l'application. Les approches actuelles de simulation utilisent principalement la méthode des éléments finis. Celle-ci repose sur un maillage volumique des objets qu'il est souvent difficile d'adapter dynamiquement aux besoins de l'application. La nouveauté introduite par cette thèse est d'utiliser des repères déformables comme primitives cinématiques, avec des champs de déplacements inspirés des méthodes de 'skinning' utilisées en informatique graphique. Le but est d'éviter ainsi les difficultés liées au maillage volumique, ainsi que de faciliter le raffinement et la simplification adaptatives par simple ajout ou suppression de repère déformable là où c'est souhaitable. Ce travail est financé par le projet européen 'Passport for Virtual Surgery', dont le but est de créer automatiquement des modèles physiques pour l'entraînement aux gestes de chirurgie hépatique, à partir de données médicales et anatomiques personnalisées. Dans ce contexte, Guillaume, en collaboration avec d'autres membres du projet, mettra en place les outils nécessaires pour construire la scène physique à partir d'images médicales segmentées et de connaissances anatomiques génériques. Le foie sera dans un premier temps représenté par des modèles physiques précédemment développés à EVASION et étendus aux opérations de découpe. Par la suite, il y appliquera son nouveau modèle mécanique basé sur des repères déformables. The aim of this thesis is to develop a new approach for the simulation of flexible objects based on the continous middle method, related with interactive graphics applications such as video games or training in surgery. It is a continuity of the M2 research internship on the same topic. It is important to simply settle a compromise between accuracy and time computing according to the application. Current simulation approaches mainly use the finite element method, which is based on a volumetric mesh of the simulated objects. It is often difficult to dynamically adapt the needs to the application. The novelty of this thesis is to use deformable reference frames as kinematic primitives, with displacement fields based on 'skinning' methods used in computer graphics. The aim is to avoid the difficulties associated with volumetric mesh, and make the refinement and the adaptive simplification easier by adding or deleting deformable reference frames if necessary. This work is funded by the European project 'Passport for Virtual Surgery', which aims to automatically create models for physical training in gestures of liver surgery, from medical and anatomical custom data. In this context, Guillaume, in collaboration with other members of the project, will develop the tools necessary to build the physical scene from segmented medical images and generic anatomical knowledge. The liver will initially be represented by physical models previously developed in the EVASION team and then extended to cutting operations. Thereafter, Guillaume will apply his new mechanical model based on deformable reference frames. / Physically based deformable models have become ubiquitous in computer graphics. It allow to synthetize real behaviors, based on the physical laws from continuum mechanics. In this thesis, we focus on interactive simulations such as to video games or surgical simulators. The majority of the existing works focused up to here on the animation of objects made of homogeneous materials. Nevertheless, plenty of real objects, for instance like the biological structures, consist of multiple imbricated materials. Their decomposition in homogeneous zones requires a high-resolution spatial discretization to solve the variations of the material properties, which requires prohibitive computation time. In this context, we present new real time simulation techniques for deformable objects which can be cut. First of all, we present a real time method for cutting deformable objects in which, contrary to the previous methods, the object deforms on the cutting tool contact and cuts occur only when the pressure reaches a certain level. The independence of the physical, collision and visual models makes the topological changes easier. The GPU computing and local modifications enable fast execution. Then, a dynamic meshless method is described, which uses reference frames as control nodes instead of using points, with a displacement field formulation similar to skinning. It allows to easily tune the weights and benefits from the rigor of physical methods as the finite elements. The introduction of integration points, reducing the samples number by a least squares approximation, speeds up the spatial integrations. Other pre-computations are proposed in order to speed up the simulation time. Finally, new anisotropic shape functions are defined to encode the variations of material properties thanks to the introduction of the compliance distance. These complex shape functions uncouple the material resolution of the displacement functions ones. It allow an extremely sparse nodes sampling. The use of the compliance distance allows an automatic nodes distribution with regard to the material properties.

This thesis deals with inertial navigation systems issues. It describes basics of reference frames, coordinate systems and matrix calculations for AHRS. There are also basic information about inertial sensors, inertial measurements units and its mistakes. One of the purposes of this paper could be explanation of inertial navigation systems terms. The main object of this thesis is to explore the influence of using multiple sensors of same type to enhance measurements of AHRS systems.