Le contrôle de la température d'un milieu thermique reste d'une grande importance en raison du coût économique qu'il peut engendrer. Ainsi, un moyen efficace de réduire les coûts de chauffage/refroidissement est de fournir un bon système de contrôle qui limite l'énergie nécessaire pour exécuter ces tâches. À cette fin, nous étudierons le contrôle d'une interface diffusive homogène finie utilisant le contrôleur CRONE de trois générations et contrôlons leurs comportements. La nouveauté de ce travail existe dans l'utilisation d'un contrôleur de commande fractionnaire (le contrôleur CRONE) appliqué à une unité d'ordre fractionnaire et l'utilisation d'un contrôleur complexe (la troisième génération) qui n'est pas si familier dans le domaine des contrôleurs. Les résultats montrent le comportement et la robustesse des contrôleurs CRONE de trois générations. / Controlling thermal medium’s temperature remains of a great importance, because of the economic cost that it may engender. Thus, one effective way to reduce heating/cooling cost is by providing a good control system that limits power needed to run these tasks. For this purpose, we will study the control of a finite homogeneous diffusive interface using the three generations CRONE controller and control their behaviors. The novelty of this work exists in the use of a fractional order controller (the CRONE controller) applied to a fractional order plant and the use of a complex controller (the third generation) which is not so familiar in the controllers domain. The results show the behavior and the robustness of the three generations CRONE controllers.

Most drill wear monitoring research found in the literature is based on conventional vibration technologies. However, these conventional approaches still have not attracted real interest from manufacturers for multiples of reasons: some of these techniques are not practical and use complicated Tool Condition Monitoring (TCM) systems with less value in industry. In addition, they are also prone to give spurious drill deterioration warnings in industrial environments. Therefore, drills are normally replaced at estimated preset intervals, sometimes long before they are worn or by expertise judgment. Two of the great problems in the implementation of these systems in drilling are: the poor signal-to-noise ratio and the lack of system-made sensors for drilling, as is prevalent in machining operations with straight edge cutters. In order to overcome the noise problems, many researchers recommend advanced and sophisticated signal processing while the work of Rehorn et al. (2005) advises the following possibilities to deal with the lack of commercial system-made sensors:  Some research should be directed towards developing some form of instrumented tool for drill operations.  Since the use of custom-made sensors is being ignored in drilling operations, effort should be focused on intelligent or innovative use of available sensor technology. It is expected that the latter could minimize implementation problems and allows an optimal drill utilization rate by means of modern and smart sensors. In addition to the accelerometer sensor commonly used in conventional methods, this work has considered two other sensor-based methods to monitor the drill wear indirectly. These methods entail the use of an instrumented drill with strain gauges to measure the torque and the use of an encoder to measure the Instantaneous Angular Speed (IAS). The signals from these sensors were analyzed using signal processing techniques such as, statistical parameters, Fast Fourier Transform (FFT), and a ii preliminary Time-Frequency (TF) analysis. A preliminary investigation has revealed that the use of a Regression Analysis (RA) based on a higher order polynomial function can very well follow and give prognosis of the development of the monitored parameters. The experimental investigation has revealed that all the above monitoring systems are sensitive to the deterioration of the drill condition. This work is however particularly concerned with the use of IAS on the spindle of the drill, compared to conventional monitoring systems for drill condition monitoring. This comparison reveals that the IAS approach can generate diagnostic information similar to vibration and torque measurements, without some of the instrumentation complications. This similitude seems to be logical, as it is well known that the increase of friction between the drill and workpiece due to wear increase the torque and consequently it should reduce or at least affect the spindle rotational speed. However, the use of a drill instrumented with a strain gauge is not practical, because of the inconvenience it causes on production machines. By contrast, the IAS could be measured quite easily by means of an encoder, a tachometer or some other smart rotational speed sensors. Thus, one could take advantage of advanced techniques in digital time interval analysis applied to a carrier signal from a multiple pulse per revolution encoder on the rotating shaft, to improve the analysis of chain pulses. As it will be shown in this dissertation, the encoder resolution does not sensibly affect the analysis. Therefore, one can easily replace encoders by any smart transducers that have become more popular in rotating machinery. Consequently, a non-contact transducer for example could effectively be used in on-line drill condition monitoring such as the use of lasers or time passage encoder-based systems. This work has gained from previous research performed in Tool Condition Monitoring TCM, and presents a sensor that is already available in the arsenal of sensors and could be an open door for a practical and reliable sensor in automated drilling. iii In conclusion, this dissertation strives to answer the following question: Which one of these methods could challenge the need from manufacturers by monitoring and diagnosing drill condition in a practical and reliable manner? Past research has sufficiently proved the weakness of conventional technologies in industry despite good results in the laboratory. In addition, delayed diagnosis due to time-consuming data processing is not beneficial for automated drilling, especially when the drill wears rapidly at the end of its life. No advanced signal processing is required for the proposed technique, as satisfactory results are obtained using common time domain signal processing methods. The recommended monitoring choice will definitely depend on the sensor that is practical and reliable in industry. / Dissertation (MEng)--University of Pretoria, 2012. / gm2013 / Mechanical and Aeronautical Engineering / MEng / Unrestricted

This thesis deals with a theoretical analysis and experimental verification of a new method for the refractive index of air measurement. This method uses a combination of laser and low-coherence interferometry. The experimental setup is based on the Michelson interferometer equipped with a double-spaced glass cell. The optical path difference between the inner and outer part of the cell that is proportional to air refractivity is estimated using two low-coherence interference signals. These signals are analysed in the frequency domain which results in the dependence of the phase change caused the by air on vacuum wavelength. This dependency is fitted by a theoretical function based on Edlén's equations in order to calculate the phase difference for laser wavelength. This value is then made more accurate utilising two laser interference signals and used for the air refractive index calculation. The new method was experimentally verified and compared to two different techniques. Moreover, the measurement uncertainty was evaluated.

L'objet de cette thèse est d'étudier les systèmes de cointégration fractionnaire de forme triangulaire mais également d'analyser l'apport de ces systèmes dans la modélisation des co-mouvements au sein des marchés financiers internationaux. La thèse s'articule autour de six chapitres équitablement répartis entre contributions économétriques et économiques. Concernant l'approche économétrique, un intérêt particulier est donné à l'estimation de ces systèmes en absence d'information sur les paramètres d'intérêts. Dans cette optique, plusieurs techniques d'estimation sont analysées et développées, essentiellement dans le domaine des fréquences car celui-ci permet un traitement semi-paramétrique des paramètres de nuisances. Les performances de ses estimateurs sont étudiés à travers des simulations mais également à travers l'étude des propriétés asymptotiques. Concernant l'approche économique, une première contribution exploite la cointégration fractionnaire pour révéler l'existence d'un système de taux de change entre certains pays Asiatiques. Une deuxième contribution porte sur l'analyse des interdépendances entre le marché du pétrole et divers taux de change au niveau de la volatilité. Une troisième contribution introduit un processus d'apprentissage adaptatif dans un modèle monétaire à plusieurs pays afin d'étudier sous quelles conditions un système de taux de change peut émerger. / The aim of the thesis is to study a triangular form of fractional cointegration systems and to investigate whether these systems allow to model the comovements in international financial markets. The thesis is organized around six chapters. Three of them are theory-oriented and the three others are empirics-oriented. Concerning the econometric approach, a particular interest is devoted to the estimation of these systems when all parameters of interest are unknown. To this extent, several estimation techniques are investigated and introduced, essentially in frequency domain as it allows a semi-parametric treatment of the nuisance parameters. Most of times, the performance of these estimators are studied by means of simulations but the asymptotic theory is also developed. Concerning the economic approach, a first contribution applies the fractional cointegration theory to reveal the existence of an exchange rate system between several Asian countries. A second contribution deals with the risk interdependences between the crude oil market and several exchange rates. A third contribution considers an adaptive learning mechanism in a multi-country monetary model to investigate the conditions under which an exchange rate system is likely to emerge.

The interaction of an HVDC converter with the connected power system is of complex nature. An accurate model of the converter is required to study these interactions. The use of analytical small-signal converter models provides useful insight and understanding of the interaction of the HVDC system and the connected system components. In this thesis analytical models of the HVDC converters are developed in the frequency-domain by calculating different transfer functions for small superimposed oscillations of voltage, current, and control signals. The objective is to study the dynamic proprieties of the combined AC-DC interaction and the interaction between different HVDC converters with small signal analysis. It is well known that the classical Bode/Nyquist/Nichols control theory provides a good tool for this purpose if transfer functions that thoroughly describe the 'plant' or the 'process' are available. Thus, there is a need for such a frequency-domain model. Experience and theoretical calculation have shown that voltage/power stability is a very important issue for an HVDC transmission link based on conventional line-commutated thyristor-controlled converters connected to an AC system with low short circuit capacity. The lower the short circuit capacity of the connected AC system as compared with the power rating of the HVDC converter, the more problems related to voltage/power stability are expected. Low-order harmonic resonance is another issue of concern when line-commutated HVDC converters are connected to a weak AC system. This resonance appears due to the presence of filters and shunt capacitors together with the AC network impedance. With a weak AC system connected to the HVDC converter, the system impedances interact through the converter and create resonances on both the AC- and DC-sides of the converter. In general, these resonance conditions may impose limitations on the design of the HVDC controllers. In order to improve the performance of the HVDC transmission system when it is connected to a weak AC system network, a reactive compensator with a voltage source converter has been closely connected to the inverter bus. In this thesis it is shown that the voltage source converter, with an appropriate control strategy, will behave like a rotating synchronous condenser and can be used in a similar way for the dynamic compensation of power transmission systems, providing voltage support and increasing the transient stability of the converter. / QC 20100708

The finite strip method (FSM) is a very efficient numerical method employed for performing the structural analysis of slender structures, such as cable-stayed bridges; the strip discretization of the model allows for the usage of a lower number of degrees of freedom, in comparison with the finite element method (FEM), while, as it will be discussed in the current research, the results obtained from both methods are in relatively good agreement. Moreover, to address the latest developments in the area of smart construction materials used for long-span bridges, the fiber reinforced polymer (FRP) composites were implemented for the bridge deck modeling, as part of a hybrid composite FRP cable-stayed bridge, and an extend laminate integrated finite strip method (LFSM) was applied for estimating the static structural performance of the hybrid composite FRP long-span cable-stayed bridge under several concentrated and uniformly distributed loadings. The free vibrations analysis was conducted for the Kap Shui Mun Cable-stayed Bridge model, and the natural frequencies were compared with the ones obtained from an FE model of the same bridge. One of the advantages of using the integrated finite strip method is that number of vibration modes, which can be included in the dynamic analysis when the effect of a sweeping sinus and a seismic loading are investigated when a conventional FE analysis would fail to converge. The outcomes of this research will set the stage for the hybrid long-span cable-stayed bridges modeling by the laminate integrated finite strip method (LFSM) which is more efficient and straightforward than the finite element analysis, for performing the static, free vibration, time domain, and frequency domain analyses.

Tato práce se zabývá analýzou power-bus struktur využitím metody založené na formulaci problému 2D hraniční integrální rovnicí ve frekvenční oblasti. Uvedená metoda byla implementována v Matlabu. Program umožňuje analyzovat obecné polygonální power-bus struktury s možností nastavení parametrů substrátu a libovolného počtu a umístění budících portů. Výstupem programu je frekvenční závislost rozložení elektrického pole mezi deskami struktury, vztahy mezi porty struktury vyjádřené např. impedanční maticí a vyzařovací diagram. Dále byla implementována možnost převodu výsledné impedanční matice do tzv. Touchstone formátu, pomocí něhož je možné modelovat analyzované struktury jako obecné N-porty (např. v ANSOFT Designeru), což umožňuje analýzu power-bus struktur s dalšími obvodovými prvky. Výsledky byly ověřeny pomocí existujících analytických vztahů pro jednoduché obdélníkové struktury, využitím komerčního simulačního programu a praktickým experimentem.

Metamaterials are typically described as materials with ’unusual’ wave propagation properties. Originally developed for electromagnetic waves, these materials have also spread into the field of acoustic wave guiding and cloaking, with the most relevant of these ’unusual’ properties, being the so called band-gap phenomenon. A band-gap signifies a frequency region where elastic waves cannot propagate through the material, which in principle, could be used to protect buildings from earthquakes. Based on this, two relevant concepts have been proposed in the field of seismic engineering, namely: metabarriers, and metamaterial-based foundations. This thesis deals with the development of the Metafoundation, a metamaterial-based foundation system for the seismic protection of fuel storage tanks against excessive base shear and pipeline rupture. Note that storage tanks have proven to be highly sensitive to earthquakes, can trigger sever economic and environmental consequences in case of failure and were therefore chosen as a superstructure for this study. Furthermore, when tanks are protected with traditional base isolation systems, the resulting horizontal displacements, during seismic action, may become excessively large and subsequently damage connected pipelines. A novel system to protect both, tank and pipeline, could significantly augment the overall safety of industrial plants. With the tank as the primary structure of interest in mind, the Metafoundation was conceived as a locally resonant metamaterial with a band gap encompassing the tanks critical eigenfrequency. The initial design comprised a continuous concrete matrix with embedded resonators and rubber inclusions, which was later reinvented to be a column based structure with steel springs for resonator suspension. After investigating the band-gap phenomenon, a parametric study of the system specifications showed that the horizontal stiffness of the overall foundation is crucial to its functionality, while the superstructure turned out to be non-negligible when tuning the resonators. Furthermore, storage tanks are commonly connected to pipeline system, which can be damaged by the interaction between tank and pipeline during seismic events. Due to the complex and nonlinear response of pipeline systems, the coupled tank-pipeline behaviour becomes increasingly difficult to represent through numerical models, which lead to the experimental study of a foundation-tank-pipeline setup. Under the aid of a hybrid simulation, only the pipeline needed to be represented via a physical substructure, while both tank and Metafoundation were modelled as numerical substrucutres and coupled to the pipeline. The results showed that the foundation can effectively reduce the stresses in the tank and, at the same time, limit the displacements imposed on the pipeline. Leading up on this, an optimization algorithm was developed in the frequency domain, under the consideration of superstructure and ground motion spectrum. The advantages of optimizing in the frequency domain were on the one hand the reduction of computational effort, and on the other hand the consideration of the stochastic nature of the earthquake. Based on this, two different performance indices, investigating interstory drifts and energy dissipation, revealed that neither superstructure nor ground motion can be disregarded when designing a metamaterial-based foundation. Moreover, a 4 m tall optimized foundation, designed to remain elastic when verified with a response spectrum analysis at a return period of 2475 years (according to NTC 2018), reduced the tanks base shear on average by 30%. These results indicated that the foundation was feasible and functional in terms of construction practices and dynamic response, yet unpractical from an economic point of view. In order to tackle the issue of reducing the uneconomic system size, a negative stiffness mechanism was invented and implemented into the foundation as a periodic structure. This mechanism, based on a local instability, amplified the metamaterial like properties and thereby enhanced the overall system performance. Note that due to the considered instability, the device exerted a nonlinear force-displacement relationship, which had the interesting effect of reducing the band-gap instead of increasing it. Furthermore, time history analyses demonstrated that with 50% of the maximum admissible negative stiffness, the foundation could be reduced to 1/3 of its original size, while maintaining its performance. Last but not least, a study on wire ropes as resonator suspension was conducted. Their nonlinear behaviour was approximated with the Bouc Wen model, subsequently linearized by means of stochastic techniques and finally optimized with the algorithm developed earlier. The conclusion was that wire ropes could be used as a more realistic suspension mechanism, while maintaining the high damping values required by the optimized foundation layouts. In sum, a metamaterial-based foundation system is developed and studied herein, with the main findings being: (i) a structure of this type is feasible under common construction practices; (ii) the shear stiffness of the system has a fundamental impact on its functionality; (iii) the superstructure cannot be neglected when studying metamaterial-based foundations; (iv) the complete coupled system can be tuned with an optimization algorithm based on calculations in the frequency domain; (v) an experimental study suggests that the system could be advantageous to connected pipelines; (vi) wire ropes may serve as resonator suspension; and (vii) a novel negative stiffness mechanism can effectively improve the system performance.

Ces travaux de recherche portent sur la problématique CEM (Compatibilité Electromagnétique) en électronique de puissance. Cette étude s'intéresse particulièrement à la modélisation HF (haute fréquence) des convertisseurs d'énergie dans le but d'étudier la propagation des perturbations conduites vers le réseau avec ou sans l’utilisation du RSIL (Réseau Stabilisateur d'Impédance de Ligne). Une première partie présente les outils de modélisation des sources de perturbation dans les convertisseurs statiques.La seconde partie est consacrée à la modélisation HF d'un système d'entraînement à vitesse variable. L'onduleur de tension triphasé est représenté par trois générateurs équivalents afin de reconstituer le découpage des tensions de sortie. Un modèle HF du câble blindé de 4 conducteurs tenant compte de la dissymétrie est ensuite proposé. Les résultats de simulation ont été validés par des relevés expérimentaux. La comparaison montre qu'il est possible de modéliser correctement le comportement HF du dispositif jusqu'à 20MHz.Une troisième partie porte sur la propagation des perturbations conduites vers le réseau sans RSIL. Il a fallu pour cela déterminer et modéliser l'impédance du réseau. L'influence du pont redresseur à diodes sur la propagation des perturbations de mode commun a ensuite été étudiée. Les résultats de simulation montrent que l'impact de ces perturbations sur la tension réseau est prépondérant lorsque le pont redresseur est à l'état bloqué. Les résultats expérimentaux ont permis de valider cette étude. Ce travail se termine par une étude préliminaire sur l'association de deux convertisseurs connectés localement à une même source d'énergie / These research works focus on EMC (Electromagnetic Compatibility) in power electronics systems. Specifically, the study focuses on HF (high frequency) modeling of the power converters in order to study the conducted emissions toward the power grids with or without the use of an LISN (Line Impedance Stabilisation Network). The first part presents the modeling tools of the electromagnetic emissions sources in power converters.The second part describes the HF modeling method of an adjustable speed drive (ASD) that will be used to estimate the conducted emissions. In a first part, a behavioural model of PWM inverter is proposed as an EMI noise source. Then, a model of the shielded 4-wire energy cable that taking into account of the dissymmetry structure is proposed and validated in the frequency domain for two different lengths. The comparison of measurement and simulation results of conducted emissions (with LISN) shows the good compromise between the simulation duration and accuracy of the results.A third part is dedicated to the propagation of conducted emissions toward the power grid without using a LISN. The first stage consists in proposing a model impedance of the network impedance. The influence of the bridge rectifier diodes on the propagation paths of common mode disturbances has been studied in the second step. The simulation results show that the impact of these disturbances on the network voltage is more important when the bridge rectifier is normally off-state. The experimental results have validated this study. This work concludes with a preliminary study on the association of two converters connected locally to a single energy source

Les progrès continus dans les techniques du stockage et de la collection des données permettent d'observer et d'enregistrer des processus d’une façon presque continue. Des exemples incluent des données climatiques, des valeurs de transactions financières, des modèles des niveaux de pollution, etc. Pour analyser ces processus, nous avons besoin des outils statistiques appropriés. Une technique très connue est l'analyse de données fonctionnelles (ADF).<p><p>L'objectif principal de ce projet de doctorat est d'analyser la dépendance temporelle de l’ADF. Cette dépendance se produit, par exemple, si les données sont constituées à partir d'un processus en temps continu qui a été découpé en segments, les jours par exemple. Nous sommes alors dans le cadre des séries temporelles fonctionnelles.<p><p>La première partie de la thèse concerne la régression linéaire fonctionnelle, une extension de la régression multivariée. Nous avons découvert une méthode, basé sur les données, pour choisir la dimension de l’estimateur. Contrairement aux résultats existants, cette méthode n’exige pas d'assomptions invérifiables. <p><p>Dans la deuxième partie, on analyse les modèles linéaires fonctionnels dynamiques (MLFD), afin d'étendre les modèles linéaires, déjà reconnu, dans un cadre de la dépendance temporelle. Nous obtenons des estimateurs et des tests statistiques par des méthodes d’analyse harmonique. Nous nous inspirons par des idées de Brillinger qui a étudié ces models dans un contexte d’espaces vectoriels. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished