Дисертації з теми "Hysteresis modelling"

This thesis presents a model of fabric bending hysteresis. The hysteresis model is designed to reproduce the fabric bending measurements taken by the Kawabata Evaluation System (KES) and the model parameters can be derived directly from these property measurements. The advantage to using this technique is that it provides the ability to simulate a continuum of property curves. Results of the model and its components are compared and constrasted with experimental results for fabrics composed of different weaves and yarn types. An attempt to incorporate the bending model as part of a fabric drape simulation is also made.

The achievable accuracy of hygrothermal building component simulation is significantly dependent on the applied material functions. These functions are determined by the material modelling marking the connection between the basic storage and transport parameters which are obtained from basic measurements, and the storage and transport coefficients which are defined within the balance and flow equations. It is the aim of the present study to develop a flexible and widely applicable material model which is not restricted to the current level of the transport theory. Furthermore, limits and options of this model are to be validated by means of four building materials on the basis of special transient moisture profile measurements. The study’s starting point is a comprehensive investigation of both, the different existing modelling approaches and the available experimental methods to determine basic hygrothermal material parameters. On this basis, the material modelling is set into the context of the heat and moisture transport theory derived from thermodynamics. The involved limits and restrictions are highlighted and options as well as requirements for further developments are pointed out. The developments this study focuses on comprise three fields: experiments for basic property determination, material modelling, and experiments for material model validation. The set of basic material investigation methods has been extended by the drying experiment under defined conditions. The different influences on the drying as well as its application to hygrothermal material model calibration are pointed out and appraised. On this basis, a drying apparatus is designed, built and applied. Ultimately, standardisation criteria and the derivation of a single-value drying coefficient are evaluated. Appropriate extensions are indicated. Based on the bundle of tubes approach, an own material model is developed. It is coupled with a mechanistical approach accounting for serial and parallel structured moisture transport phenomena. The derived liquid water conductivity is adjusted by the help of measured conductivity data close to saturation as well as within the hygroscopic moisture range. Subsequently, two internal modelling parameters are calibrated which is done by numerical simulation of the water uptake and the drying experiment under consideration of the hysteresis of moisture storage. Facilitating its application to the obtained laboratory data, the material model has been implemented into a computer program. It is applied to the four building materials brick, lime-sand brick, aerated concrete and calcium silicate. The adjusted material functions are shown and discussed. In all four cases, the calibration provides an excellent agreement between measured and calculated material behaviour. As experimental basis of the material model validation, the instantaneous profile measurement technique (IPM) has been extended to be applied in Building Physics. Special equipment is developed and measurement procedures are designed. Different models to derive the water content from dielectric data obtained by Time Domain Reflectometry (TDR) measurements are evaluated and implemented. Ultimately, an extensive program of transient moisture profile measurements within the hygroscopic and the overhygroscopic moisture content range is conducted and evaluated. Within the frame of validation, the developments on the experimental as well as on the modelling fields are combined. The IPM experiments are recalculated on the basis of the measured initial and boundary conditions applying the adjusted and calibrated material functions. The comparison of measured and calculated data reveals the power of the developed material modelling just as the consequences of the simplifications made on the transport theory level. The distinct influences of the hysteresis of moisture storage consisting of effects depending on the process history and effects depending on the process dynamics, are proven. By the presented study, the material modelling has been decisively further developed, the set of basic measurement methods has been extended by a substantial experiment and the instantaneous profile measurement technique has been made applicable to Building Physics. Moreover, the influences of the process history and the process dynamics on the moisture transport and the resulting moisture profiles could be shown and proven. By that, not only a material model is now available which perfectly applies to the requirements of flexibility, applicability and extendability. The obtained data provides also a powerful basis for further research and development
Die Genauigkeit hygrothermischer Bauteilsimulation hängt maßgeblich von den verwendeten Materialfunktionen ab. Sie werden durch die Materialmodellierung bestimmt, welche die Verbindung zwischen den aus Basisexperimenten gewonnenen Speicher- und Transportparametern sowie den innerhalb der Bilanz- und Flussgleichungen definierten Speicher- und Transportkoeffizienten herstellt. Ziel der vorliegenden Arbeit ist zum einen die Entwicklung eines flexiblen, breit anwendbaren und gleichzeitig nicht auf den gegenwärtigen Stand der Transporttheorie beschränkten Materialmodells. Dessen Grenzen und Möglichkeiten sollen zum anderen auf der Grundlage spezieller instationärer Feuchteprofilmessungen anhand von vier Baustoffen untersucht und aufgezeigt werden. Ausgangspunkt der Arbeit ist eine ausführliche Beleuchtung sowohl der vorhandenen Modellansätze als auch der zur Verfügung stehenden experimentellen Methoden zur Bestimmung hygrothermischer Basisparameter. Auf dieser Grundlage wird die Materialmodellierung in den Kontext der aus der Thermodynamik abgeleiteten Wärmeund Feuchtetransporttheorie eingeordnet. Die damit verbundenen Grenzen und Einschränkungen werden hervorgehoben und Entwicklungsmöglichkeiten sowie weiterer Entwicklungsbedarf aufgezeigt. Dieser umfasst drei Bereiche: die Experimente zur Bestimmung von Basisparametern, die Materialmodellierung, sowie Experimente zur Modellvalidierung. Die Reihe der Basisexperimente wird um den Trocknungsversuch unter definierten Bedingungen erweitert. Die verschiedenen Einflüsse auf die Trocknung und deren Anwendung in der Kalibrierung hygrothermischer Materialmodellierung werden herausgestellt und bewertet. Darauf aufbauend wird eine Apparatur entworfen, gebaut und angewendet. Schließlich werden Kriterien zur Standardisierung und Ableitung eines Einzahlenkennwertes evaluiert. Sinnvolle Erweiterungen werden aufgezeigt. Es wird ein eigenes Materialmodell auf der Grundlage eines Porenbündelansatzes hergeleitet, welches mit einem mechanistischen Ansatz gekoppelt wird, der den Feuchtetransport in seriell und parallel strukturierte Bereiche untergliedert. Die abgeleitete Flüssigwasserleitfähigkeit wird anhand von Leitfähigkeitsmessdaten im nahe gesättigten sowie im hygroskopischen Feuchtebereich justiert. Zwei interne Modellparameter werden anschließend unter Berücksichtigung der Hysterese der Feuchtespeicherung anhand des Aufsaug- und des Trocknungsversuches kalibriert. Das Materialmodell ist zur Erleichterung der Anwendung in ein Computerprogramm zur Anpassung an die Labordaten implementiert worden. Das Programm wird auf die vier Baustoffe Ziegel, Kalksandstein, Porenbeton und Calciumsilikat angewendet. Die entsprechend angepassten Materialfunktionen werden gezeigt und diskutiert. Im Rahmen der Kalibrierung wird eine hervorragende Übereinstimmung zwischen gemessenem und berechnetem Materialverhalten erreicht. Zur Modellvalidierung wird die Augenblicksprofilmethode (IPM) für die bauphysikalische Anwendung erweitert. Spezielle Apparaturen werden entwickelt und Versuchsabläufe entworfen. Modelle zur Ableitung des Wassergehaltes aus mit Hilfe der Time Domain Reflectometry (TDR) gewonnenen Dielektrizitätsmessdaten werden evaluiert und implementiert. Schließlich wird ein umfangreiches Programm an Feuchteprofilmessungen im hygroskopischen und überhygroskopischen Feuchtebereich umgesetzt und ausgewertet. Im Rahmen der Validierung werden die Entwicklungen auf experimenteller sowie auf Modellierungsebene zusammengeführt. Die IPM Experimente werden anhand der gemessenen Anfangs- und Randbedingungen und auf der Grundlage der angepassten und kalibrierten Materialfunktionen nachgerechnet. Der Vergleich zwischen Messung und Rechnung offenbart die Stärke der entwickelten Materialmodellierung ebenso, wie den Einfluss der auf Ebene der Transporttheorie getroffenen Vereinfachungen. Ein deutlicher Einfluss der sich aus der Prozessgeschichte sowie der Prozessdynamik zusammensetzenden Hysterese der Feuchtespeicherung kann nachgewiesen werden. Mit der vorliegenden Arbeit ist somit nicht nur die Materialmodellierung entscheidend weiterentwickelt, die Reihe der einfachen Basisexperimente um einen wesentlichen Versuch erweitert und die Augenblicksprofilmethode für bauphysikalische Belange anwendbar gemacht worden, es wurden auch die Einflüsse der Prozessgeschichte, und erstmals auch der Prozessdynamik, auf den Feuchtetransport sowie die sich einstellenden Feuchteprofile deutlich aufgezeigt und nachgewiesen. Es ist demnach nicht nur ein Materialmodell, welches den gestellten Anforderungen an Flexibilität, breite Anwendbarkeit und Erweiterbarkeit genügt, entwickelt worden, es wird mit den gewonnenen Messdaten auch die Grundlage weiterer Forschung zur Verfügung gestellt

The achievable accuracy of hygrothermal building component simulation is significantly dependent on the applied material functions. These functions are determined by the material modelling marking the connection between the basic storage and transport parameters which are obtained from basic measurements, and the storage and transport coefficients which are defined within the balance and flow equations. It is the aim of the present study to develop a flexible and widely applicable material model which is not restricted to the current level of the transport theory. Furthermore, limits and options of this model are to be validated by means of four building materials on the basis of special transient moisture profile measurements. The study’s starting point is a comprehensive investigation of both, the different existing modelling approaches and the available experimental methods to determine basic hygrothermal material parameters. On this basis, the material modelling is set into the context of the heat and moisture transport theory derived from thermodynamics. The involved limits and restrictions are highlighted and options as well as requirements for further developments are pointed out. The developments this study focuses on comprise three fields: experiments for basic property determination, material modelling, and experiments for material model validation. The set of basic material investigation methods has been extended by the drying experiment under defined conditions. The different influences on the drying as well as its application to hygrothermal material model calibration are pointed out and appraised. On this basis, a drying apparatus is designed, built and applied. Ultimately, standardisation criteria and the derivation of a single-value drying coefficient are evaluated. Appropriate extensions are indicated. Based on the bundle of tubes approach, an own material model is developed. It is coupled with a mechanistical approach accounting for serial and parallel structured moisture transport phenomena. The derived liquid water conductivity is adjusted by the help of measured conductivity data close to saturation as well as within the hygroscopic moisture range. Subsequently, two internal modelling parameters are calibrated which is done by numerical simulation of the water uptake and the drying experiment under consideration of the hysteresis of moisture storage. Facilitating its application to the obtained laboratory data, the material model has been implemented into a computer program. It is applied to the four building materials brick, lime-sand brick, aerated concrete and calcium silicate. The adjusted material functions are shown and discussed. In all four cases, the calibration provides an excellent agreement between measured and calculated material behaviour. As experimental basis of the material model validation, the instantaneous profile measurement technique (IPM) has been extended to be applied in Building Physics. Special equipment is developed and measurement procedures are designed. Different models to derive the water content from dielectric data obtained by Time Domain Reflectometry (TDR) measurements are evaluated and implemented. Ultimately, an extensive program of transient moisture profile measurements within the hygroscopic and the overhygroscopic moisture content range is conducted and evaluated. Within the frame of validation, the developments on the experimental as well as on the modelling fields are combined. The IPM experiments are recalculated on the basis of the measured initial and boundary conditions applying the adjusted and calibrated material functions. The comparison of measured and calculated data reveals the power of the developed material modelling just as the consequences of the simplifications made on the transport theory level. The distinct influences of the hysteresis of moisture storage consisting of effects depending on the process history and effects depending on the process dynamics, are proven. By the presented study, the material modelling has been decisively further developed, the set of basic measurement methods has been extended by a substantial experiment and the instantaneous profile measurement technique has been made applicable to Building Physics. Moreover, the influences of the process history and the process dynamics on the moisture transport and the resulting moisture profiles could be shown and proven. By that, not only a material model is now available which perfectly applies to the requirements of flexibility, applicability and extendability. The obtained data provides also a powerful basis for further research and development.
Die Genauigkeit hygrothermischer Bauteilsimulation hängt maßgeblich von den verwendeten Materialfunktionen ab. Sie werden durch die Materialmodellierung bestimmt, welche die Verbindung zwischen den aus Basisexperimenten gewonnenen Speicher- und Transportparametern sowie den innerhalb der Bilanz- und Flussgleichungen definierten Speicher- und Transportkoeffizienten herstellt. Ziel der vorliegenden Arbeit ist zum einen die Entwicklung eines flexiblen, breit anwendbaren und gleichzeitig nicht auf den gegenwärtigen Stand der Transporttheorie beschränkten Materialmodells. Dessen Grenzen und Möglichkeiten sollen zum anderen auf der Grundlage spezieller instationärer Feuchteprofilmessungen anhand von vier Baustoffen untersucht und aufgezeigt werden. Ausgangspunkt der Arbeit ist eine ausführliche Beleuchtung sowohl der vorhandenen Modellansätze als auch der zur Verfügung stehenden experimentellen Methoden zur Bestimmung hygrothermischer Basisparameter. Auf dieser Grundlage wird die Materialmodellierung in den Kontext der aus der Thermodynamik abgeleiteten Wärmeund Feuchtetransporttheorie eingeordnet. Die damit verbundenen Grenzen und Einschränkungen werden hervorgehoben und Entwicklungsmöglichkeiten sowie weiterer Entwicklungsbedarf aufgezeigt. Dieser umfasst drei Bereiche: die Experimente zur Bestimmung von Basisparametern, die Materialmodellierung, sowie Experimente zur Modellvalidierung. Die Reihe der Basisexperimente wird um den Trocknungsversuch unter definierten Bedingungen erweitert. Die verschiedenen Einflüsse auf die Trocknung und deren Anwendung in der Kalibrierung hygrothermischer Materialmodellierung werden herausgestellt und bewertet. Darauf aufbauend wird eine Apparatur entworfen, gebaut und angewendet. Schließlich werden Kriterien zur Standardisierung und Ableitung eines Einzahlenkennwertes evaluiert. Sinnvolle Erweiterungen werden aufgezeigt. Es wird ein eigenes Materialmodell auf der Grundlage eines Porenbündelansatzes hergeleitet, welches mit einem mechanistischen Ansatz gekoppelt wird, der den Feuchtetransport in seriell und parallel strukturierte Bereiche untergliedert. Die abgeleitete Flüssigwasserleitfähigkeit wird anhand von Leitfähigkeitsmessdaten im nahe gesättigten sowie im hygroskopischen Feuchtebereich justiert. Zwei interne Modellparameter werden anschließend unter Berücksichtigung der Hysterese der Feuchtespeicherung anhand des Aufsaug- und des Trocknungsversuches kalibriert. Das Materialmodell ist zur Erleichterung der Anwendung in ein Computerprogramm zur Anpassung an die Labordaten implementiert worden. Das Programm wird auf die vier Baustoffe Ziegel, Kalksandstein, Porenbeton und Calciumsilikat angewendet. Die entsprechend angepassten Materialfunktionen werden gezeigt und diskutiert. Im Rahmen der Kalibrierung wird eine hervorragende Übereinstimmung zwischen gemessenem und berechnetem Materialverhalten erreicht. Zur Modellvalidierung wird die Augenblicksprofilmethode (IPM) für die bauphysikalische Anwendung erweitert. Spezielle Apparaturen werden entwickelt und Versuchsabläufe entworfen. Modelle zur Ableitung des Wassergehaltes aus mit Hilfe der Time Domain Reflectometry (TDR) gewonnenen Dielektrizitätsmessdaten werden evaluiert und implementiert. Schließlich wird ein umfangreiches Programm an Feuchteprofilmessungen im hygroskopischen und überhygroskopischen Feuchtebereich umgesetzt und ausgewertet. Im Rahmen der Validierung werden die Entwicklungen auf experimenteller sowie auf Modellierungsebene zusammengeführt. Die IPM Experimente werden anhand der gemessenen Anfangs- und Randbedingungen und auf der Grundlage der angepassten und kalibrierten Materialfunktionen nachgerechnet. Der Vergleich zwischen Messung und Rechnung offenbart die Stärke der entwickelten Materialmodellierung ebenso, wie den Einfluss der auf Ebene der Transporttheorie getroffenen Vereinfachungen. Ein deutlicher Einfluss der sich aus der Prozessgeschichte sowie der Prozessdynamik zusammensetzenden Hysterese der Feuchtespeicherung kann nachgewiesen werden. Mit der vorliegenden Arbeit ist somit nicht nur die Materialmodellierung entscheidend weiterentwickelt, die Reihe der einfachen Basisexperimente um einen wesentlichen Versuch erweitert und die Augenblicksprofilmethode für bauphysikalische Belange anwendbar gemacht worden, es wurden auch die Einflüsse der Prozessgeschichte, und erstmals auch der Prozessdynamik, auf den Feuchtetransport sowie die sich einstellenden Feuchteprofile deutlich aufgezeigt und nachgewiesen. Es ist demnach nicht nur ein Materialmodell, welches den gestellten Anforderungen an Flexibilität, breite Anwendbarkeit und Erweiterbarkeit genügt, entwickelt worden, es wird mit den gewonnenen Messdaten auch die Grundlage weiterer Forschung zur Verfügung gestellt.

This thesis highlights generic aspects of contact angle hysteresis and stick-slip motion,encountered in most practical wetting situations.First, we study the scaling relation between the heterogeneity strength and the amplitudeof the contact angle hysteresis it induces in the model configuration of a chemicallyheterogeneous microchannel. A key parameter which determines the qualitativefeatures is the heterogeneity wavelength. In particular, we identify a near-thresholdbehavior where the quadratic scaling between the heterogeneity amplitude and the resultinghysteresis, already known for a dilute system of wetting defects, is explainedby the closeness to the threshold, and a macroscopic limit without observable stick-slipwhere this scaling is linear.In the second part, we adapt the description to the configuration of a meniscusaround a wavy fibre. This adaptation brings the generic results of the first part in thereach of experiments. A comparison with experiments is achieved at the level of theindividual topography-induced jumps.In the third part, we expand the formulation to treat the quasi-steady interface shapecontact line dynamics and study how the the presence of stick-slip motion at the observableor unobservable scale modifies the scaling relation between the contact linevelocity and contact angle. We recover the known result that the scaling exponent dependson the nature of the externally controlled parameter, identify the causes of thisdependency in the corresponding static limits, and predict the disappearance of this dependencyabove a critical velocity which decreases with the heterogeneity wavelength.Finally, we show trough examples how the modelling framework which permitscapturing contact angle hysteresis and stick-slip motion in a minimalistic way can beadopted to treat configurations with a finite amount of contact points, or the 3D problemof a drop with a deformed contact line. We discuss the arising configuration-specificeffects, also in configurations of biomimetic interest.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

La durabilité des structures en béton armé ainsi que leur durée de vie sont étroitement liées à la mise en œuvre simultanée de nombreux phénomènes physiques et chimiques. Ceux-ci sont de diverses natures mais restent, en général, fonction des propriétés hydriques des matériaux étudiés. Ainsi, la prédiction des dégradations potentielles d'un matériau cimentaire requiert l'étude du transport de l'eau liquide et des phases gazeuses à travers ce dernier, considéré comme un milieu poreux. En milieu naturel, les structures subissent des variations périodiques de l'humidité relative extérieure (HR). Cependant, la plupart des modèles de transfert hydrique préexistants dans la littérature, s'intéresse uniquement au processus de séchage. Il existe peu de modèles décrivant à la fois l'humidification et le séchage du matériau (ces deux phénomènes se produisent dans le matériau en condition naturelle d'humidité relative (HR)). Tenir compte des phénomènes d'hystérésis dans les transferts hydriques réduit à nouveau le nombre de modèles à disposition. Ainsi, cette thèse s'attache à proposer une meilleure compréhension de l'état hydrique du béton en fonction des variations d'humidité relative extérieure, sur la base d'une nouvelle campagne expérimentale et de modélisations numériques. Un soin sera apporté afin de tenir compte dans les modèles numériques des effets d'hystérésis. Dans ce travail, nous détaillerons, tout d'abord, un modèle multi-phasiques complet. Un modèle simplifié est obtenu, sur la base de considérations théoriques et de vérifications expérimentales dans le cas où la perméabilité intrinsèque à l'eau liquide reste très inférieure à la perméabilité intrinsèque au gaz. Une étude comparative des modèles d'hystérésis couramment utilisés permet d'obtenir un jeu de modèles proposant les meilleures prédictions d'isothermes de sorption d'eau et de leurs hystérésis. Par la suite, le modèle de transport simplifié est couplé avec les modèles d'hystérésis sélectionnés afin de simuler les transferts hydriques dans des bétons soumis à des cycles d'humidification-séchage. La comparaison avec des données expérimentales révèle que la prise en compte de l'hystérésis de l'isotherme de sorption d'eau ne peut pas être négligé. De plus, il est montré que les prédictions obtenues avec des modèles d'hystérésis théoriques, sont les plus cohérentes avec les résultats expérimentaux, en particulier, pour des chemins secondaires d'hystérésis. Plusieurs scénarios (conditions environnementales, bétons différents) sont également simulés. Les résultats obtenus pointent à nouveau la nécessité de tenir compte de l'hystérésis lors de la modélisation des transferts hydriques à travers des matériaux cimentaires soumis à des variations d'humidité relative. La définition d'une profondeur pour laquelle le profil hydrique du béton est modifié par les variations périodiques d'humidité relative permet de mieux comprendre comment la modélisation de la pénétration des espèces ioniques est influencée par les cycles d'humidification-séchage. Par ailleurs, notre analyse révèle qu'il est pertinent de considérer l'effet de Knudsen pour la diffusion de la vapeur afin d'améliorer la prédiction de la diffusivité apparente
The durability of reinforced concrete structures and their service life are closely related to the simultaneous occurrence of many physical and chemical phenomena. These phenomena are diverse in nature, but in common they are dependent on the moisture properties of the material. Therefore, the prediction of the potential degradation of cementitious materials requires the study of the movement of liquid-water and gas-phase transport in the material which is considered as a porous medium. In natural environment, structures are always affected by periodic variations of external relative humidity (RH). However, most moisture transport models in the literature only focus on the drying process. There are few researches considering both drying and wetting, although these conditions represent natural RH variations. Even few studies take into account hysteresis in moisture transport. Thus, this work is devoted to better understand how the moisture behaviour within cementitious materials responds to the ambient RH changes through both experimental investigations and numerical modelling. In particular, hysteretic effects will be included in numerical modelling. In this thesis, we first recalled a complicate multi-phase continuum model. By theoretical analysis and experimental verification, a simplified model can be obtained for the case of that the intrinsic permeability to liquid-water is smaller than the intrinsic permeability to gas-phase. The review of commonly-used hysteresis models enabled to conclude a set of best models for the prediction of water vapour sorption isotherms and their hysteresis. After that, the simplified model was coupled with selected hysteresis models to simulate moisture transport under drying and wetting cycles. Compared with experimental data, numerical simulations revealed that modelling with hysteretic effects can provide much better results than non-hysteresis modelling. Among different hysteresis models, results showed that the use of the conceptual hysteresis model, which presents closed form scanning loops, can provide more accuracy predictions. Further simulations for different scenarios were also performed. All comparisons and investigations enhanced the necessity of considering hysteresis to model moisture transport for varying relative humidity at the boundary. The investigation of moisture penetration depth could provide a better understanding of how deep moisture as well as ions can move into the material. Furthermore, the analysis revealed that the consideration of Knudsen effects for diffusion of vapour can improve the prediction of the apparent diffusivity

DC currents that flow through the ground can be injected to the star windings of power transformers from their grounded neutral points and close their path with transmission lines. The geomagnetically induced currents (GICs) and AC/DC convertors of high voltage direct current (HVDC) systems are the sources of such DC currents. These currents may cause saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomenon results in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and misoperation of protective relays menaces the power network. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC. Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis. In this project until now, a new algorithm for digital measurement of the core materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Three dimensional finite element models of various core types of power transformers are created to study the effect on them due to DC magnetization. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a distributed reluctance network method has been outlined. In this thesis a method for solving such a network problem with coupling to an electrical circuit and taking hysteresis into account is suggested.

QC 20121121

In order to design a power transformer it is important to understand its internal electromagnetic behaviour. That can be obtained by measurements on physical transformers, analytical expressions and computer simulations. One benefit with simulations is that the transformer can be studied before it is built physically and that the consequences of changing dimensions and parameters easily can be assessed. In this thesis a time-domain transformer model is presented. The model includes core phenomena as magnetic static hysteresis, eddy current and excess losses. Moreover, the model comprises winding phenomena as eddy currents, capacitive effects and leakage flux. The core and windings are first modelled separately and then connected together in a composite transformer model. This results in a detailed transformer model. One important result of the thesis is the feasibility to simulate dynamic magnetization including the inhomogeneous field distribution due to eddy currents in the magnetic core material. This is achieved by using a Cauer circuit combined with models for static and dynamic magnetization. Thereby, all magnetic loss components in the material can be simulated accurately. This composite dynamic magnetization model is verified through experiments showing very good correspondence with measurements. Furthermore, the composite transformer model is verified through measurements. The model is shown to yield good correspondence with measurements in normal operation and non-normal operations like no-load, inrush current and DC-magnetization.
QC20100708

Box-girder bridges supported by single reinforced concrete (RC) columns are expected to sustain seismic shocks with minor structural damages in seismically active regions where transportation is substantially required for rescuing and evacuating tasks. Such viaducts are vulnerable to damage when they are subjected to strong ground motions and acceleration pulse records, especially when responding in a flexural mode or having relatively low core confinement. Using a nonlinear dynamic solver that applies the fibre element method, global and local damage curves are computed based on the dissipated energy under hysteretic curves and based on constitutive curves, respectively. The RC bridge with seismic isolation bearing is used as an alternative system to control the damage, and modelled using linkage elements between the substructure and super structure. It was found that seismic isolation can be controlled to dissipate partial seismic energy so that the RC column gains the least possible minor damage. Using a MatLab program, a fibre element nonlinear model was built using a simplified iterative process and simplified constitutive relations. The number of fibres and elements under the dynamic loading was found to be affecting the final results of the analysis. Using crack growth modelling based on fracture mechanics, the combined discrete element/finite element explicit-Elfen code was applied to investigate the crack growth in 3D dynamically loaded RC columns. Despite its excessive computational cost and time, this code provides reliable information about local damage in the RC column core. Earthquake records with the pulse acceleration phenomenon have a severe damage potential on the structure. The difference in damage intensities was detected by crack growth modelling for the same problem using different loading rates. Critically stressed zones can be investigated independently by using the relative response technique, in which responses from the numerically analysed structure are re-used as applied loads onto a small-scale crack model for the critical member. Two general conclusions can be obtained; bridges with single RC columns designed by the demand/capacity criterion could suffer severe damage and possible collapse when subjected to strong ground motions. Secondly; hysteresis-based methods provide a global damage evaluation based on strength and ductility only regardless of the damage growth inside the concrete core and the buckling of bars, which could lead to progressive collapse.

Finite element analysis (FEA) is a numerical analysis method which is used widely to obtain approximate solutions in many fields of engineering. With sophisticated computer hardware and software. FEA has recently become an effective tool in the design of rubber components.

Thesis (MEng)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: Rubber is the main component of the pneumatic tire. When rubber is put under cyclic loading, like when a tire is rolled, heat is generated and stored in the rubber, due to hysteresis. Heat stored in the tire is increased by factors like under-inflation, overloading, speeding and defects in the tire. The heat causes high temperatures in the tire due to the poor thermal conductivity of rubber. When the temperature in the rubber increases to 185 °C, pyrolysis and thermo-oxidation starts and can cause the tire to eventually explode. A numerical model of a rolling passenger vehicle tire was developed to calculate the temperature distribution inside the tire and analyse the effect of different operating conditions on the temperature. Operating conditions include loading, inflation pressure, rolling velocity and ambient temperature. The tire was modelled by a single rubber type, using the Mooney-Rivlin material model. The bead wire was modelled using an isotropic material model, while the body and steel cord plies were modelled as rebars. The cavity, used to inflate the tire, included the pressure increase due to the volume change, when the tire is loaded. The numerical model was validated using experimental data from tests done on an actual tire. These tests included deformation and contact stress analysis, as well as surface temperature measurements. Numerical results showed an increase in temperature when the load, rolling velocity and the ambient temperature were increased, as well as when the inflation pressure was decreased. The trends of the numerical data matched the trends of the experimental data. However, the values of the numerical model were not consistent with the experimental data due to material properties from literature being used to model the tire.
AFRIKAANSE OPSOMMING: Rubber is die hoofkomponent in die pneumatiese band. As rubber onder ’n sikliese las geplaas word, soos wanneer ’n band rol, word hitte gegenereer en in die rubber gestoor as gevolg van histerese. Die hitte wat in die band gestoor word, word verhoog deur faktore soos lae inflasiedruk, hoë las, hoë rol snelhede en gebreke in die band. Die hitte veroorsaak hoë temperature in die band weens die swak termiese geleiding van rubber. As die temperatuur in die band hoër as 185 °C raak, vind piroliese en termo-oksidasie plaas en die band kan uiteindelik ontplof. ’n Numeriese model van ’n passasiersmotorband is ontwikkel om die temperatuurverspreiding te bepaal, asook om die effek van verskillende werkstoestande op die temperatuur te analiseer. Die band is gemodelleer met een tipe rubber en die Mooney-Rivlin materiaal-model is gebruik om die rubber te beskryf. Die spanrand van die band is deur ’n isotropiese materiaalmodel gemodelleer, terwyl die hoof- en staalkoordlae as bewapening gemodelleer is. Die holte wat gebruik word om die band op te blaas, neem die druk toename as gevolg van die verandering in volume in ag wanneer die band belas word. Die numeriese model was bekragtig met eksperimentele data wat deur toetse op ’n werklike band onttrek is. Die toetse sluit die volgende in: vervormingen kontakspanninganalises, asook temperature wat op die oppervlak van die band gemeet is. Die numeriese resultate toon ’n toename in temperatuur wanneer die las, rolsnelheid en omgewingstemperatuur verhoog word, asook waneer die inflasiedruk verlaag word. Die numeriese model se tendense stem ooreen met die eksperimentele data, maar die waardes van die numeriese model is nie in ooreenstemmig met die eksperimentele data nie. Die verskil is as gevolg van die materiaaleienskappe wat uit die literatuur geneem is.

To sum up, the objective of the project was to construct a mathematical model that would sufficiently describe the behaviour of the complex hydraulic press system under analysis. Through the Simscape tool inside the Simulink environment, it was possible to select elementary blocks that expressed similar physical behaviour with respect to those corresponding elements comprising the real machine. The second goal of the project was to analyze different control designs, that could be implemented given the control variables at disposal, to minimize the filling error inside the piston chamber. Such error if present could cause instability in the vertical motion of the hydraulic cylinders, as well as deviation of pressure value inside the chamber from the optimal one, requested to achieve good performances in the tile formation process. The current open-loop behaviour has been shown to generate large filling errors during the pressing cycle, and such errors have been drastically reduced up to an order of $10$, by implementing the closed-loop control schemes presented. The first control scheme is based on a feedback measurement coming from an hydraulic volumetric flow rate sensor, and even though it showed good performances relative to the minimization of the filling error, it lacks in practicality, since such sensor is not available in the real setup. Therefore, a closed-loop control scheme based on the pressure measurement feedback, and an hysteresis controller, forcing the pressure signal to remain inside a bandwidth around the optimal value, has produced similar if not better results with respect to the more theoretical approach but with the advantage of practicality.

A hydraulic damper plays an important role in tuning the handling and comfort characteristicsof a vehicle. Tuning and selecting a damper based on subjective evaluation, by considering theopinions of various users, would be an inefficient method since the comfort requirements of usersvary a lot. Instead, mathematical models of damper and simulation of these models in variousoperating conditions are preferred to standardize the tuning procedure, quantify the comfortlevels and reduce cost of testing. This would require a model, which is good enough to capture thebehaviour of damper in various operating and extreme conditions.The Force-Velocity (FV) curve is one of the most widely used model of a damper. This curve isimplemented either as an equation or as a look-up table. It is a plot between the maximum forceat each peak velocity point. There are certain dynamic phenomena like hysteresis and dependencyon the displacement of damper, which cannot be captured with a FV curve model, but are requiredfor better understanding of the vehicle behaviour.This thesis was conducted in cooperation with Volvo Cars with an aim to improve the existingdamper model which is a Force-Velocity curve. This work focuses on developing a damper model,which is complex enough to capture the phenomena discussed above and simple enough to beimplemented in real time simulations. Also, the thesis aims to establish a standard method toparameterise the damper model and generate the Force-Velocity curve from the tests performedon the damper test rig. A test matrix which includes the standard tests for parameterising andthe extreme test cases for the validation of the developed model will be developed. The final focusis to implement the damper model in a multi body simulation (MBS) software.The master thesis starts with an introduction, where the background for the project is described and then the thesis goals are set. It is followed by a literature review in which fewadvanced damper models are discussed in brief. Then, a step-by-step process of developing thedamper model is discussed along with few more possible options. Later, the construction of a testmatrix is discussed in detail followed by the parameter identification process. Next, the validationof the developed damper model is discussed using the test data from Volvo Hällered ProvingGround (HPG). After validation, implementation of the model in VI CarRealTime and Adams Caralong with the results are presented. Finally the thesis is concluded and the recommendations forfuture work are made on further improving the model.
En hydraulisk stötdämpare spelar en viktig roll för att fordonets hantering och komfort. Attjustera och välja en stötdämpare baserat på subjektiv utvärdering, genom att beakta olika användares åsikter, skulle vara en ineffektiv metod eftersom användarnas komfortkrav varierarmycket. Istället föredras matematiska modeller av stötdämpare och simulering av dessa modellerunder olika driftsförhållanden för att standardisera inställningsförfarandet, kvantifiera komfortnivåerna och minska testkostnaden. Detta skulle kräva en modell som är tillräckligt bra för attfånga upp stötdämparens beteende under olika drifts- och extrema förhållanden.Force-Velocity (FV) -kurvan är en av de mest använda stötdämparmodellerna. Denna kurvaimplementeras antingen som en ekvation eller som en uppslagstabell. Det är ett diagram somredovisar den maximala kraften vid varje maxhastighetspunkt. Det finns vissa dynamiskafenomen som hysteres och beroende av stötdämparens förskjutning, som inte kan fångas med enFV-kurvmodell, men som krävs för att bättre förstå fordonets beteende.Denna avhandling genomfördes i samarbete med Volvo Cars i syfte att förbättra den befintligastötdämparmodellen som är en Force-Velocity-kurva. Detta arbete fokuserar på att utveckla enstötdämparmodell, som är tillräckligt komplex för att fånga upp de fenomen som diskuteratsovan och tillräckligt enkel för att implementeras i realtidssimuleringar. Avhandlingen syftarockså till att upprätta en standardmetod för att parametrisera spjällmodellen och generera ForceVelocity-kurvan från de test som utförts på stötdämpartestriggen. En testmatris som innehållerstandardtest för parametrisering och extrema testfall för validering av den utvecklade modellenkommer att utvecklas. Det sista fokuset är att implementera stötdämparmodellen i en multi-bodysimulation (MBS) programvara.Examensarbetet inleds med en introduktion, där bakgrunden för projektet beskrivs ochdärefter definieras målen med arbetet. Det följs av en litteraturöversikt där några avanceradestötdämparmodeller diskuteras i korthet. Därefter diskuteras en steg-för-steg-process för attutveckla stötdämparmodeller tillsammans med några fler möjliga alternativ. Senare diskuteraskonstruktionen av en testmatris i detalj följt av parameteridentifieringsprocessen. Därefterdiskuteras valideringen av den utvecklade stötdämparmodellen med hjälp av testdata från VolvoHällered Proving Ground (HPG). Efter validering presenteras implementeringen av modellen iVI CarRealTime och Adams Car tillsammans med resultaten. Slutligen avslutas rapporten medslutsatser från arbetet och rekommendationer för framtida arbete görs för att ytterligare förbättramodellen.

The work presented in this thesis is divided into two parts. The first part is the sorption of Ni and Eu to granitic materials, and cation exchange capacity measurements for powdered and intact samples. The second part is method development on autoradiography. In the first part, static batch sorption experiments were carried out to study the relative sorption properties of different granitic rocks and minerals. Experimental data were described using non-electrostatic correction models such as the Langmuir, Freundlich and Linear models. Sorption data obtained for sorption in a constant pH environment and variable metal concentration were used to test the Component Additive Model (CAM). Sorption test studies carried out using energy dispersive X-ray microanalysis were used to map the sorption of Eu on an intact sample. The results showed the CAM was applicable for Ni sorption to BG but that it was not applicable for Eu sorption to any of the granitic rocks studied. The sorption data fitted the CAM in the following order; BG (1) > GA (0.7) > RG (0.5) > GG (0.2), GrG (0.2) for Ni sorption and RG (0.7) > BG (0.4) > GA (0.2), GG (0.2), GrG (0.2) for Eu sorption to the different granitic rocks. Values in brackets represent the ratio of Rd-predicted/Rd-calculated. Results from the application of the CAM showed it was not possible to predict the Rd of the bulk sample from the component minerals. Desorption studies at constant pH were analysed by calculating the hysteresis H. The results showed that the higher the Rd the higher the hysteresis. Surface complexation using JChess Geochemical Code was used to obtain surface complexation parameters for the metal-solid complex for sorption in variable pH and constant metal concentration. Experimental data were described by the mass action law to obtained proton stoichiometry at which the sorption edge is defined. Results showed the presence of NaCl decreased the sorption of Ni, and increased the sorption of Eu. Sorption kinetics experiments in different carbonate complexing environments were carried out to study the effect of carbonate on Eu sorption capacity and rate of sorption. Data were fitted to first and second order kinetic models to investigate the sorption rates. Results showed the sorption to be fast initially before reaching a steady state after more than 200 hours of equilibration. Kinetic data confirmed the low sorption capacity observed for quartz. Data obtained for sorption in a mixed radionuclide system were modelled using the Linear model and the surface complexation model. The surface complexation constants are correlated to the Rd values obtained from the linear sorption isotherms. Modelling the results using Rdmix and Rdsing showed that sorption was suppressed in a mixed system, with no effect observed for sorption to feldspar in single and mixed systems. Cation exchange capacity (CEC) measurements were undertaken to deduce a correlation between the CEC of powdered rock samples and intact sample using rock beakers developed from the British Geological Survey by applying the Bascomb method in which the pH was buffered to pH 8.1. Normalising the results using the surface area showed that the CEC of the rock beakers was 6 orders of magnitude greater than that of the powdered sample. In the second part, a method for differentiating two or more radionuclides using storage phosphor imaging plates coupled with the Storm Scanner system was tested. Initial results showed that it is possible to differentiate one radionuclide from another in a mixed system using different levels of shielding.

The erosion and transport of fertile topsoil is a serious problem in the U.S., Australia, China and throughout Europe. It results in extensive environmental damage, reduces soil fertility and productivity, and causes significant environmental loss. It is as big a threat to the future sustainability of global populations as climate change, but receives far less attention. With both chemicals (fertilizers, pesticides, herbicides) and biological pathogens (bacteria, viruses) preferentially sorbing to silt and clay sized soil particles, estimating contaminant fluxes in eroded soil also requires predicting the transported soils particle size distribution. The Hairsine-Rose (HR) erosion model is considered in this thesis as it is one of the very few that is specifically designed to incorporate the effect of particle size distribution, and differentiates between non-cohesive previously eroded soil compared with cohesive un-eroded soil. This thesis develops a new extended erosion model that couples the HR approach with the one-dimensional St Venant equations, and an Exner bed evolution equation to allow for feedback effects from changes in the local bed slope on surface hydraulics and erosion rates to be included. The resulting system of 2I +3 (where I = number of particle size classes) nonlinear hyperbolic partial differential equations is then solved numerically using a Liska-Wendroff predictor corrector finite difference scheme. Approximate analytical solutions and series expansions are derived to overcome singularities in the numerical solutions arising from either boundary or initial conditions corresponding to a zero flow depth. Three separate practical applications of the extended HR model are then considered in this thesis, (i) flow through vegetative buffer strips, (ii) modelling discharge hysteresis loops and (iii) the growth of antidunes, transportational cyclic steps and travelling wave solutions. It is shown by comparison against published experimental flume data that predictions from the extended model are able to closely match measurements of deposited sediment distribution both upstream and within the vegetative buffer strip. The experiments were conducted with supercritical inflow to the flume which due to the increased drag from the vegetative strip, resulted in a hydraulic jump just upstream of the vegetation. As suspended sediment deposited at the jump, this resulted in the jump slowly migrating upstream. The numerical solutions were also able to predict the position and hydraulic jump and the flow depth throughout the flume, including within the vegetative strip, very well. In the second application, it is found that the extended HR model is the first one that can produce all known types of measured hysteresis loops in sediment discharge outlet data. Five main loop types occur (a) clockwise, (b) counter-clockwise, (c,d) figure 8 of both flow orientations and (e) single curve. It is clearly shown that complicated temporal rainfall patterns or bed geometry are not required to developed complicated hysteresis loops, but it is the spatial distribution of previously eroded sediment that remains for the start of a new erosion event, which primarily governs the form of the hysteresis loop. The role of the evolution of the sediment distribution in the deposited layer therefore controls loop shape and behavior. Erosion models that are based solely on suspended sediment are therefore unable to reproduce these hysteretic loops without a priori imposing a hysteretic relationship on the parameterisations of the erosion source terms. The rather surprising result that the loop shape is also dominated by the suspended concentration of the smallest particle size is shown and discussed. In the third application, a linear stability analysis shows that instabilities, antidunes, will grow and propagate upstream under supercritical flow conditions. Numerical simulations are carried out that confirm the stability analysis and show the development and movement of antidunes. For various initial parameter configurations a series of travelling antidunes, or transportational cyclic steps, separated by hydraulic jumps are shown to develop and evolve to a steady form and wave speed. Two different forms arise whereby (a) the deposited layer completely shields the underlying original cohesive soil so that the cohesive layer plays no role in the speed or shape of the wave profile or (b) the cohesive soil is exposed along the back of the wave such that both the non-cohesive and cohesive layers affect the wave profile. Under (a) the solutions are obtained up to an additive constant as the actual location of the boundary of the cohesive soil is not required, whereas for (b) this constant must be determined in order to find the location on the antidune from where the cohesive soil becomes accessible. For single size class soils the leading order travelling wave equations are fairly straightforward to obtain for both cases (a) and (b). However for multi-size class soils, this becomes much more demanding as up to 2I + 3 parameters must be found iteratively to define the solution as each size class has its own wave profile in suspension and in the antidune.

Geomagnetic disturbances that result from solar activities can affect technological systems such as power networks. They may cause DC currents in power networks and saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomena result in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and malfunction of protective relays menaces the power network stability. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon. Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC. Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis. In this project, a new algorithm for digital measurement of the magnetic materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Two and three dimensional finite element models of various core types of power transformers are created to study the effect of DC magnetization on transformers. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a novel topological based time step transformer model has been outlined. The model can employ a detailed magnetic circuit and consider nonlinearity, hysteresis and eddy current effects of power transformers. Furthermore, the proposed model can be used in the design process of transformers and even extend other application such as analysis of electrical machines. The numerical and experimental studies in this project lead to understanding the mechanism that a geomantic disturbance affects power transformers and networks. The revealed results conclude with proposals for mitigation strategies against these phenomena.

QC 20150210

Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network.

The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering.

The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent

The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error.

KEYWORDS:Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling.

In order to remain competitive in the marketplace, all motor vehicle manufacturers face difficult decisions with regard to balancing cost vs. feature. That is to say that the manufacturer must balance the cost of the product to the customer to remain competitive whilst offering appropriate technology and standard features required by that customer. All motor manufacturers are therefore under pressure to keep costs of nonfeature items to a minimum. One of the cost reductions items prevalent on most vehicles is the deletion of the structural member that attaches the rear bumper, known as the bumper beam (RBB), which is researched in this Thesis. This generates average vehicle savings of $20 and, as this is invisible to the customer, should enable the manufacturers to realise a significant saving or allow this revenue to be spent on additional feature without loss of vehicle function. However, in nearly all cases, deletion of the rear bumper beam has the effect of degrading the steering responses of the vehicle by 1 to 1½ rating points (out of 10), which is contrary to the premise of cost reductions; which is to ensure that vehicle function is unaffected. Initial analysis of vehicles with deleted rear bumper beams cannot show an objective measurable difference in any vehicle behaviours with or without the beam fitted, and hence CAE studies using ADAMS models cannot verify the effects of the bumper beam. It was necessary to employ unconventional modelling and testing methods such as rigid body, flexible body model techniques as well as experimental studies included driving robots and expert driver appraisals. The research demonstrated that vehicle modelling methods currently used, cannot establish or predict the complete vehicle ride and handling status. A total vehicle model approach should be used without separating the body CAE model and vehicle dynamics ADAMS model into separate entities. Furthermore, it was concluded that the determination to the effects of body hysteresis rather than pure stiffness is of crucial importance and that the steering attribute could be maintained with the deletion of the RBB analytically.

In order to remain competitive in the marketplace, all motor vehicle manufacturers face difficult decisions with regard to balancing cost vs. feature. That is to say that the manufacturer must balance the cost of the product to the customer to remain competitive whilst offering appropriate technology and standard features required by that customer. All motor manufacturers are therefore under pressure to keep costs of nonfeature items to a minimum. One of the cost reductions items prevalent on most vehicles is the deletion of the structural member that attaches the rear bumper, known as the bumper beam (RBB), which is researched in this Thesis. This generates average vehicle savings of $20 and, as this is invisible to the customer, should enable the manufacturers to realise a significant saving or allow this revenue to be spent on additional feature without loss of vehicle function. However, in nearly all cases, deletion of the rear bumper beam has the effect of degrading the steering responses of the vehicle by 1 to 1½ rating points (out of 10), which is contrary to the premise of cost reductions; which is to ensure that vehicle function is unaffected. Initial analysis of vehicles with deleted rear bumper beams cannot show an objective measurable difference in any vehicle behaviours with or without the beam fitted, and hence CAE studies using ADAMS models cannot verify the effects of the bumper beam. It was necessary to employ unconventional modelling and testing methods such as rigid body, flexible body model techniques as well as experimental studies included driving robots and expert driver appraisals. The research demonstrated that vehicle modelling methods currently used, cannot establish or predict the complete vehicle ride and handling status. A total vehicle model approach should be used without separating the body CAE model and vehicle dynamics ADAMS model into separate entities. Furthermore, it was concluded that the determination to the effects of body hysteresis rather than pure stiffness is of crucial importance and that the steering attribute could be maintained with the deletion of the RBB analytically.

Recent researches on the effects of environmental degradation on food security suggest that a better understanding of the relationship between agricultural intensification and pollutant transfer is urgently required to support the implementation of sustainable agricultural policies, globally. Poor understanding of the hydrological behaviour of clay-rich soils in intensively managed agricultural regions is highlighted as an important problem. The study therefore evaluated precipitation-soil water chemistry relationships, soil variability and concentration-discharge relationships at the farm-scale based on datasets from the North Wyke Farm Platform between 2011 and 2013. The three main hypothesis were that (1) precipitation and soil water chemistry are significantly related (2) significant relationships exists between the distribution of soil physiochemical characteristics and the managments of the fields, and that (3) hydrological behaviour of fields underlain by certain dominant soils in the study area are different from that of other fields. The basis of this work was to elucidate links between sources of pollutants and water quality, further understanding of the effect that management of the soil may have upon the quality of the water and improve understanding of the pathways of pollutants within intensively managed landscapes. Precipitation chemistry of the study area was chemically different from that of the other regions in the United Kingdom, and was influenced by contributions from sea salts and terrestrial dusts. The soil chemistry was rich in organic matter which contributed significantly (r2>0.60; p<0.05) to the distribution of total carbon and total nitrogen in the fields. Mean total carbon and nitrogen stocks ranged 32.4 - 54.1 t C ha-1, and 4 - 6.2 t Na ha-1, respectively in the entire farm platform while runoff coefficient at four selected fields (Pecketsford, Burrows, Middle and Higher Wyke Moor, and Longlands East) varied between 0.1 and 0.28 in January and November, 2013. The study rejected the first and third hypotheses, and concluded that the study area is largely influenced by contributions from the surface runoff mechanisms. The study also noted that sodium and chloride ions were dominant in the precipitation chemistry, and therefore suggests their further investigation as conservative tracers in the soil and runoff chemistry.

Bridge bearing is an essential component with the function of connecting the superstructure and substructure of the bridge, transmitting load and providing movability to the superstructure. Under dynamic conditions, the internal friction of bridge bearing dissipates the vibration energy and therefore reduces the dynamic response of the bridge. Meanwhile, bearing friction is considered to have possible contribution to some nonlinear dynamic behaviour of the bridge structure, which requires further investigation.However, bearing friction, in most cases, are ignored or considered roughly and implicitly as part of structural damping in current bridge designing codes and methods. Most previous research was also focusing on bearing friction’s effect under high-amplitude vibration conditions, such as earthquake or heavy wind load. Bearing friction’s effect under common low-amplitude vibration in SLS such as train-induced vibration and vehicle-induced vibration is less attended. Although the effect of such low-amplitude vibration is less significant to structural safety, it plays an essential role to the bridge’s traffic safety and comfort. Meanwhile, the cumulative effect of such vibration can significantly influence the life and durability of bridge bearings due to its high occurring frequency. Hence, a clearer understanding of bearing dynamic behaviour is required to improve the understanding of bridge and bearing dynamics.In this thesis, an advanced numerical tool is developed for dynamic analysis of bearing friction. A 3D pot bearing finite element that can be implemented in commercial FE software ABAQUS, is programmed based on the mathematical friction models developed in previous research and the Bouc-Wen hysteretic model. Numerical results that accord with the results of relevant friction tests are produced by the calibrated and validated bearing finite element, giving proof that the element is capable to reflect the dynamic friction response of bridge pot bearing in reality.The 3D shell numerical model of Banafjäl bridge located on the Bothnia Line in Norrland, Sweden, is built as a study case of bridge dynamic analysis in this thesis, with implementation of the newly developed bearing element. The feasibility of implementing the bearing element in bridge dynamic analysis is proven by the numerical results. The nonlinear influence of bearing friction on the dynamic response of bridge structure, especially the influence on structural damping properties, is discussed preliminarily. The analysis results show that with the consideration of bearing friction, the damping presents a clear amplitude-dependency, which accords the phenomenon reported in previous research.

Although a superconductor has zero resistivity when carrying a direct current, losses do occur when it is exposed to an alternating magnetic field and/or is carrying an alternating current. The magnitude of these so-called AC losses depends on the operating temperature, the amplitude and the direction of the magnetic field, the transport current, and the frequency. Therefore, the use of high-temperature superconductors, HTSs, in electric power components such as cables, transformers or reactors, requires knowledge of the AC losses.

This thesis deals with the development of AC loss models for HTSs, mainly for Bi-2223 tapes. In particular, the orientation of the applied magnetic field is taken into account in the modelling. The basis for the models is the results of experimental investigations.

The basic concepts of HTSs with special emphasis on the modelling of AC losses are presented. These can be broken down into several components. Their sources and natures are described. One of the components is the hysteretic loss and it is the dominating loss in AC applications at power frequencies. Therefore, the other loss components are neglected in the modelling.

Models are presented and the associated parameters are investigated with respect to their dependence of the magnetic field as well as the temperature. The AC losses for parallel and perpendicular magnetic field with respect to the wide side of the tape are calculated numerically. Moreover, a semi-empirical model for intermediate angels of the applied magnetic field is proposed. The comparisons show good agreement with experimental results.

Keywords: High-temperature superconductors, AC loss modelling, hysteresis, E-J characteristic.

Non-Aqueous Phase Liquids (NAPLs) include commonly occurring organic contaminants such as gasoline, diesel fuel and chlorinated solvents. When released to subsurface environments their spreading is a complex process of multi-component, multi-phase flow. This work has strived to develop new models and methods to describe the spreading of NAPLs in heterogeneous geological media. For two-phase systems, infiltration and immobilisation of NAPL in stochastically heterogeneous, water-saturated media were investigated. First, a methodology to continuously measure NAPL saturations in space and time in a two-dimensional experiment setup, using multiple-energy x-ray-attenuation techniques, was developed. Second, a set of experiments on NAPL infiltration in carefully designed structures of well-known stochastic heterogeneity were conducted. Three detailed data-sets were generated and the importance of heterogeneity for both flow and the immobilised NAPL architecture was demonstrated. Third, the laboratory experiments were modelled with a continuum- and Darcy’s-law-based multi-phase flow model. Different models for the capillary pressure (Pc) – fluid saturation (S) – relative permeability (kr) constitutive relations were compared and tested against experimental observations. A method to account for NAPL immobility in dead-end pore-spaces during drainage was introduced and the importance of accounting for hysteresis and NAPL entrapment in the constitutive relations was demonstrated. NAPL migration in three-phase, water-NAPL-air systems was also studied. Different constitutive relations used in modelling of three-phase flow were analysed and compared to existing laboratory data. To improve model performance, a new formulation for the saturation dependence of tortuosity was introduced and different scaling options for the Pc-S relations were investigated. Finally, a method to model the spreading of multi-constituent contaminants using a single-component multi-phase model was developed. With the method, the migration behaviour of individual constituents in a mixture, e.g. benzene in gasoline, could be studied, which was demonstrated in a modelling study of a gasoline spill in connection with a transport accident.
Flerfasföroreningar innefattar vanligt förekommande organiska vätskor som bensin, dieselolja och klorerade lösningsmedel. Spridningen av dessa föroreningar i mark är komplicerad och styrs av det samtidiga flödet av organisk vätska, vatten och markluft samt utbytet av komponenter (föroreningar) mellan de olika faserna. Detta arbete syftade till att utveckla nya metoder och modeller för att studera spridningen av flerfasföroreningar i mark: (i) En metodik utvecklades för att i laboratorium noggrant och kontinuerligt mäta hur en organisk vätska är rumsligt fördelad i en tvådimensionell experimentuppställning. Metoden baserades på röntgenutsläckning för olika energinivåer. (ii) Infiltration av organisk vätska i vattenmättade medier studerades för olika konfigurationer av geologisk heterogenitet. I experimentuppställningen packades olika sandmaterial noggrant för att konstruera en välkänd, stokastiskt heterogen struktur. Spridningsprocessen dokumenterades i tre detaljerade mätserier och heterogenitetens påverkan på flöde och kvarhållning av den organiska vätskan påvisades. (iii) Experimenten simulerades med en numerisk modell. Olika modeller prövades för att beskriva de grundläggande relationerna mellan kapillärtryck (Pc) vätskehalt (S) och relativ permeabilitet (kr) för detta tvåfassystem av vatten och organisk vätska. En relation infördes för att beskriva partiell orörlighet hos den organiska vätskan i porer vars halsar tillfälligt blockeras av vatten då mediet avvattnas. Vikten av att i de grundläggande relationerna ta hänsyn till hysteresis och kvarhållning av organisk fas visades. (iv) Olika Pc-S-kr relationer för trefassystem av vatten, organisk vätska och markluft testades mot befintliga experimentella data. En ny relation för hur slingrigheten (eng. tortuosity) beror av vätskehalten infördes i kr-S relationen och olika möjligheter för att skala Pc-S relationen analyserades. (v) En modelleringsmetodik utvecklades för att studera spridningen av flerkomponentsföroreningar. Med metoden kunde spridningsbeteendet hos enskilda, särskilt skadliga komponenter som t.ex. bensen särskiljas då ett bensinutsläpp i samband med en transportolycka simulerades.

In glacierised regions, suspended sediment fluxes are highly responsive to climate-driven environmental change and can provide important information regarding the relationships between glacier variations, climate and geomorphic change. As a result, understanding patterns of suspended sediment transport and their relationship with meltwater delivery is of critical importance. However, studies of glacial suspended sediment transport are often limited by interpreting patterns of suspended sediment transfer based on whole-season data, allowing precise patterns to become masked. This thesis aims to contribute to the understanding of suspended sediment transfer in glacierised basins through the investigation of patterns of suspended sediment delivery to the proglacial area of Storglaciären, a small polythermal valley glacier located in the Tarfala valley, Arctic Sweden. High temporal resolution discharge and suspended sediment concentration data were collected during two summer field campaigns at Storglaciären. Interpretations of suspended sediment transport data were made using diurnal hysteresis and sediment availability data, combined with suspended sediment shape and magnitude data classified by applying principal component and hierarchical cluster analyses. Analysis of the dominant discharge generating processes at Storglaciären was also conducted using principal component analysis, allowing patterns of discharge to be better understood. This was complemented by analysis of the structure and evolution of the glacier drainage system by linear reservoir modelling and flow recession analysis. The results suggest that patterns of discharge and suspended sediment transport at Storglaciären are complex, with distinct processes and magnitudes of transport evident at both proglacial outlet streams, Nordjåkk and Sydjåkk. These processes are intrinsically linked to meteorological variables, with both ablation-driven and precipitation-driven discharge exerting influence over patterns of suspended sediment transport in the proglacial area of Storglaciären.

Dans le contexte des futurs stockages des matières nucléaires en couches géologiques profondes, le transfert desélénium 79 des eaux de nappes vers la biosphère, par le biais de l'irrigation, est un des scenarii envisagés parl'ANDRA. Le sol servirait alors d'interface entre la géosphère et la biosphère.Le modèle actuellement utilisé pour évaluer la mobilité de nombreux éléments dans le sol repose sur une représentationsimple de leur distribution entre la quantité adsorbée sur le sol et la quantité restante en solution (modèleKd), considérée comme instantanée, réversible et linéaire avec la concentration de contamination. Ce modèleprésente des lacunes vis-à-vis du sélénium puisque ce dernier peut être présent sous différents états redoxqui contrôlent sa mobilité et dont les cinétiques de transformation entre ces états sont peu connues (Se(-II), Se(0),Se(IV) et Se(VI)).Dans le but d'améliorer les prédictions faites sur la mobilité du sélénium dans un sol, le séléniate (Se(VI)), qui estla forme la plus mobile, a été utilisé pour étudier ses interactions vis-à-vis de deux sols différents (sol B et sol R).Un modèle cinétique, alternatif au modèle Kd, a été développé pour décrire l'évolution des stocks de Se(VI) ensolution, en considérant une fraction de sélénium associée au sol de façon réversible (potentiellement mobile) etune fraction stabilisée sur le sol (fixée pseudo-irréversiblement). Ce modèle intègre des cinétiques de stabilisationbiotique et abiotique sur le sol, et une cinétique de réduction en solution.Afin d'acquérir les paramètres des modèles, des expériences en batchs et en réacteurs à flux ouvert avecl'utilisation de sacs à dialyse ont été réalisées. L'acquisition des paramètres a permis de confronter les modèlescinétiques et Kd dans différents scenarii réalistes de contamination (chronique ou séquentielle) d'un sol de surfacepar du 79Se(VI).De plus, les mécanismes de sorption du Se(VI) au sein des deux sols ont été évalués en batch avec l'ajout de compétiteursspécifiques vis-à-vis de certains sites pouvant sorber ce dernier (acides humiques et carbonates de calcium).Ceci a été complété avec l'étude de la sorption du Se(VI) sur des phases pures commerciales (silice, hydroxyded'aluminium, goethite, bentonite, carbonate de calcium et acides humiques) ou extraites d'un sol (substanceshumiques), pour différentes concentrations en Se(VI) (10-8, 10-6 et/ou 10-3 mol/L), de l'impact de l'ajout dephases pures réactives, dans les sols, sur la sorption du Se(VI).Il a été montré que le Se(VI) était sorbé sous la forme de complexes de sphères externes (CSE) au sein du sol Rpour des concentrations inférieures à 10-6 mol/L, tandis que dans le sol B, la majorité était sorbée sous la formesde complexes de sphère internes (CSI). La formation de CSE étant réversible et instantanée, l'utilisation du modèleKd était donc suffisante pour décrire la sorption du Se(VI) au sein du sol R, dans les expériences en réacteursà flux ouvert.A contrario, pour le sol B, il a été montré que le modèle Kd, contrairement au modèle cinétique, présentait deslacunes pour décrire la sorption pseudo-irréversible du Se(VI), engendrée par la formation de CSI.Il a été montré que les mécanismes biotiques étaient majoritaires au sein du sol B, en raison de l'apport de nutrimentspour les microorganismes, par l'utilisation de sacs à dialyse en cellulose régénérée. Cependant les mécanismesabiotiques ont aussi eu lieux au sein du sol B.14/256Les études sur les phases pures ont montré que seuls l'hydroxyde d'aluminium (pH 5,2 et 8) et la goethite (pH 5,2)pouvaient sorber le Se(VI) respectivement de manière pseudo-irréversible et réversible (pour [Se(VI)] < 10-6mol/L).Enfin, il a été montré que l'ajout de certaines phases pures (goethite et hydroxyde d'aluminium) au sein des deuxsols, pouvait entrainer une augmentation ou une diminution de la sorption du Se(VI) par rapport à celle attendue(additivité réactionnelle). Les interactions solide/solide directes et/ou indirectes, (la plus connue étant le coating)peuvent être à l'origine de la difficulté d'évaluation, de manière générique, de la sorption du Se(VI) au sein dusol, connaissant seulement sa composition élémentaire.

This work describes a possibility to use a shape memory alloy as a non-traditional actuator in a particular mechatronic system. The practical part of this work is dedicated to the experimental property verification of the chosen shape memory alloy and also to the design and realization of the new type of electrically controlled gabled valve that uses a shape memory alloy as an actuator. This valve is designed as a replacement of the traditional solution and is also integrated into McKibbens pneumatic muscle endcap. There are also results of practical functional verification of the designed gabled valve solution listed here, and the limited condition for its manufacturing and use is stated here. In the theoretical part of this work, firstly, the shape memory alloy and non-linear systems hysteresis type are discussed. Secondly a new particular solution is designed, which is based on a non-linear computational element, defined by goniometric cosine function. Finally, the properties of the designed solution are verified through the simulations and with the use of experimentally gained datas.

L'impact des émissions fugitives sur l'environnement est un enjeu capital pour les industries. Ainsi, de nombreuses réglementations et normes sont établies afin de prévenir des risques et limiter leurs impacts. L'une des sources majeures de ces émissions provient de la robinetterie industrielle. Dans ce domaine, l'un des systèmes les plus communs est le presse-garniture. Dans le secteur de l'Energie, l'étanchéité peut être garantie sur les éléments mobiles par un empilement de bagues en Graphite Expansé Matricé (GEM); matériau relativement souple, plébiscité pour ses caractéristiques et ayant une structure macroscopique particulière. Ces travaux de thèse s'intéressent à la compréhension du comportement mécanique complexe des solutions d'étanchéité de type GEM. L'objectif est de déterminer le comportement mécanique de ces garnitures afin de prédire leur étanchéité. Dans le but de caractériser ce comportement, diverses campagnes d'essais sont menées sur des joints en situation. Ainsi, sur la base d'un montage existant et d'un dispositif développé spécifiquement pour cette étude, la caractérisation de ce type de joints est effectuée via des essais de compression charge-décharge et cyclique. La base de données qui en résulte permet le développement d'un modèle numérique apte à décrire le comportement complexe de ces systèmes presse-garnitures. Ce modèle phénoménologique de type Hyperélasto-Hystérésis (HH) correspond à une loi additive en contrainte avec une contribution hyperélastique et une contribution hystérétique. La comparaison des réponses expérimentales et numériques du joint, dans le cadre de l'étude d'un seul joint mais également pour des empilements, est discutée
The impact of fugitive emissions leakage rate on the environment is an essential issue for industries. Therefore, many regulations and standards are created to prevent risks and to limit their impacts. One of these major sources of fugitive emissions comes from industrial valves. In the Valve Industrie, the tightness of stem are often ensured by stuffing box seal. In the energy sector, the tightness could be ensure with compression packing which is manufactured in exfoliated graphite; which is a relatively flexible material, endorsed for its characteristics and having a particular macroscopic structure. The aim of this study is to improve the knowledge of the complex mechanical behaviour of compression packing in exfoliated graphite. The aim is to determinate the mechanical behaviour of these packings in order to predict their tightness. To characterize this behaviour, various test campaigns are conducted on seals in situation. Thus, based on an existing apparatus and a device developed specifically for this study, the characterization of this kind of packing is performed through loading-unloading and cyclic compression tests. A numerical model which is able to describe a complexe mechanical behaviour of compression packing, is performed thanks to resulting database. This Hyperelasto-Hysteresis phenomenological model corresponds to an additive decomposition in stress with an hyperelastic contribution and an hysteretic contribution. The comparison of the experimental and numerical responses of the seal, as part of the study a single seal but also of a packing, is discussed

Le présent travail vise à étudier l’influence de la microstructure des éco-matériaux de construction alternatifs utilisés dans les parois des bâtiments, tels que le béton de polystyrène sur les transferts de chaleur et d’humidité. L’objectif de ces travaux de thèse est de prédire le comportement hygrothermique des bâtiments dans une optique d’amélioration de la durabilité et des performances énergétiques. Afin d’y parvenir, ceci nécessite une approche multi-échelle qui consiste d’abord à décrire minutieusement la microstructure des matériaux étudiés, puis à maîtriser les interactions entre les différentes phases les composant à l’échelle microscopique, dans le but de mieux appréhender leur comportement à l’échelle macroscopique. Par la suite, des simulations numériques des transferts couplés de chaleur et d’humidité seront menées, prenant en compte la microstructure et la morphologie réelles des matériaux à travers des volumes 3D reconstruits grâce à la micro-tomographie à rayons X. Pour mener à bien la modélisation, il a fallu caractériser le matériau au niveau microscopique. Plusieurs techniques d’imagerie ont été utilisées afin d’obtenir une description fine de la microstructure du béton de polystyrène et des différentes phases qui le composent. Le matériau a été scanné au micro-tomographe à rayons X pour obtenir les reconstructions 3D du volume réel, qui ont montré son hétérogénéité microstructurale complexe. Le matériau a également été observé au microscope électronique à balayage en vue d’évaluer l’interface entre les deux phases, qui ne montre pas de zone de transition. Une campagne de caractérisation macroscopique et expérimentale du béton de polystyrène a été réalisée. Elle inclut la détermination des propriétés physiques et hygrothermiques du matériau, ainsi que l’impact de son état hydrique et thermique sur ces mêmes propriétés. Le béton de polystyrène montre d’excellentes performances en ce qui concerne l’isolation thermique et le stockage de chaleur, mais une capacité de régulation d’humidité négligeable. Ensuite, des expérimentations ont été mises en place dans le but de mieux appréhender les transferts d’humidité dans le matériau soumis à différentes conditions climatiques. Des échantillons sont soumis à des sollicitations hydriques cycliques dans le but de mettre en exergue le phénomène d’hystérésis de sorption d’eau, et un suivi d’humidité relative à l’intérieur des échantillons sera assuré grâce aux instruments adaptés. Un modèle de transferts couplés de chaleur et d’humidité a été élaboré. Il prend en compte l’effet de l’hystérésis de sorption d’eau et inclut ainsi l’historique des états hydriques. Au niveau macroscopique, les résultats des simulations sont confrontés aux relevés expérimentaux et ont montré une bonne adéquation. A l’échelle microscopique, des simulations seront effectués sur les volumes réels reconstruits par tomographie afin de prendre en compte l’hétérogénéité de la microstructure du matériau multiphasique
The present work aims to study the influence of the sorption hysteresis phenomenon on heat and moisture transfer in building materials. In order to achieve this, we first describe the microstructure of materials, which will allow a better understanding of their behavior at the macroscopic scale. Subsequently, numerical simulations of the coupled heat and mass transfers will be conducted, taking into account the real microstructure of the materials using X-rays reconstructed 3D volumes. Several imaging techniques have been used to obtain a fine description of the microstructure of polystyrene concrete and its different phases. The 3D reconstructions of the actual volume were obtained using X-rays micro-tomography, which showed its complex microstructural heterogeneity. Afterwards, we carried out a campaign of macroscopic experimental characterization of the material. It included the determination of the physical and hygrothermal properties of the polystyrene concrete, as well as the impact of temperature and relative humidity on these same properties. Polystyrene concrete shows excellent performance in thermal insulation and heat storage. Later, experiments have been set up in order to better understand the moisture transfer in samples subjected to cyclic stresses, in order to highlight the sorption hysteresis effect. A model of coupled heat and moisture transfers has been developed, taking into account the effect of sorption hysteresis and thus including the hydric history of the material. The results of the numerical simulations were compared to the experimental ones and showed a good match. 3D simulations will be performed on the actual volumes reconstructed by tomography to take into account the heterogeneity of the material

Le coût, l'autonomie et la durée de vie sont les principaux aspects qui freine le public dans l'achat d'une voiture électrique. Tous ces aspects sont liés à la batterie qui ne permet de stocker qu'une quantité limitée d'énergie. Dans ces conditions, il est indispensable de maîtriser les pertes d'énergie de la chaîne de traction. La machine électrique étant le principal consommateur d'énergie, elle joue un rôle important dans l'efficacité énergétique globale. Dans ce contexte, comment réduire les pertes de la machine électrique pour la rendre plus efficace ? Pour répondre à cette question, l'objectif de ce travail est de modéliser (avec une précision suffisante) et réduire les pertes fer dans notre application machine électrique de traction afin de les maîtriser. On comblera ainsi le manque de confiance en les modèles de pertes fer que peut avoir le concepteur de machine du concepteur de machine en lui permettant de réaliser des optimisations fines jusque dans les dernières phases de développement. Dans la première partie de ce manuscrit, le lecteur découvrira alors une machine synchrone à rotor bobiné du point de vue du matériau magnétique doux. Les premières conclusions montrent qu'une modélisation fine est nécessaire pour bien prendre en compte les phénomènes générateurs de pertes. On s'intéresse également à la mesure des matériaux magnétiques doux afin de comprendre de manière générale et tangible les pertes dans le matériau. On prend également conscience de la toute première source d'incertitude des modèles, la mesure du matériau. Enfin, nous présentons les démarches couramment rencontrées dans la littérature pour la modélisation des pertes fer. Face aux limitations des modèles couramment rencontrés, le modèle LS (un modèle d'hystérésis scalaire qui décompose les pertes en une contribution statique et une contribution dynamique) est redéveloppé afin qu'il réponde encore mieux aux exigences de l'industrie automobile. Il est précis et facilement identifiable à partir de mesures faciles à réaliser. La contribution statique reprend le modèle de Preisach formulé à l'aide des fonctions d'Everett dont l'identification à partir des caractéristiques mesurées est directe. La contribution dynamique quant à elle est dorénavant identifiable à partir de caractérisations en induction sinusoïdales. La précision du modèle ainsi améliorée est ensuite validée sur 63 cas tests exigeants dont la forme de l'induction est à fort contenus harmoniques. Le modèle développé est ensuite couplé avec un modèle électromagnétique élément finis de la machine électrique et validé par l'expérience. Les mesures faites sur le matériau étant l'un des points faibles des modèles, une méthodologie permettant d'évaluer la pertinence de la plage des mesures est proposée. On dresse également un état de l'art de l'impact du process (découpage, empilement et assemblage des tôles) sur les pertes fer afin d'aider le concepteur à mettre en balance les impacts liés au process qui n'ont pu être modélisés. Enfin des méthodologies parmi lesquels, les méthodologies des plans d'expériences sont mises en place afin d'optimiser les cartographies de commandes en des temps de calcul raisonnables. On montre des gains allant jusqu'à 50% de réduction des pertes totales de la machine dans certaines zones de fonctionnement par rapport à une optimisation dont l'objectif serait de minimiser uniquement les pertes dans les conducteurs de la machine. Ces résultats montrent l'intérêt d'utiliser un modèle de pertes fer précis afin de réduire les pertes totales de la machine
Cost, range and lifetime are the main aspects that hold back the consumer to buy electric cars. These three aspects are all related to the battery which stores a limited amount of energy. Under such condition energy consumption is a major concern in electric cars. As the major electricity consumer, electrical machines play a key role for global energy savings. In this context how the electric machine can be made more energy efficient? To answer this question this thesis aim to model (accurately enough) and reduce the iron losses in traction electrical machine for electrical car. Indeed iron loss model suffer from a lack of confidence when it comes to fine optimization during the late phase of development. This thesis answers this question and takes into account the development criteria of the car industry and the constraints of the electric car. The first part of the thesis gives an overview of the application by taking a wounded rotor synchronous machine as a case study. The reader will discover the electrical machine with a soft magnetic material perspective. First, conclusion show that fine modelling of the electric machine is necessary to achieve desired accuracy. An overview on soft magnetic material behavior and measurements is then given. The reader will then acquire a broad feeling on soft magnetic material behavior and understands the first source of inaccuracy of the models (the measurements). Then, the typical models for predicting iron losses in magnetic materials are presented in a literature review. The second part of this study focus on iron loss modelling aspect. The loss surface model (a scalar hysteresis model made of a static and dynamic contribution) is used as the base of this modelling work. The static contribution is re-developed using Everett function formulation of the Preisach model is used to allow easy identification of the model directly from measurements. The identification of the dynamic contribution is re-worked to allow identification from sine-wave measurements (triangular wave measurement previously required). The model accuracy is improved and validated on 63 test cases with high harmonic distortion wave forms. The iron loss model is then coupled to finite element model of the electric machine and the limits of the model are investigated. One of the limits coming from measurement limitation, a methodology to evaluate the relevance of the measurement range is proposed. A literature review of the main impact of the process including cutting, stacking and assembling effects on electrical steel magnetic characteristics is intended to complement the modelling work to help the decision making of the designer on aspects that cannot be modeled. Finally methodologies playing with the modelling hypothesis and involving design of experiment and response surface are presented to reduce computational time and allow the optimization of the control of the machine. The optimizations carried out show total machine loss reduction up to 50% for some working point of the machine compared to an optimization dedicated to minimize only Joule's losses. This results show the interest of using a reliable iron loss model to reduce the total loss of the machine

This thesis deals with computer modeling of temperature hysteresis during phase change, namely complete and partial phase change. There is performed a review of methods for modeling temperature hysteresis based on the enthalpy method and the effective heat capacity method. In the case of complete phase change, there are several methods that use the effective heat capacity method, as well as the heat source method, which, on the contrary, is a certain analogy of the enthalpy method. The following are works dealing with modelling of partial phase change, the most interesting of which is due to the validation method of static hysteresis and the method designed by Bony and Citherlet. The second part of this thesis deals with the hysteresis behavior of the material with phase change, which is organic paraffin RT 27. The input data obtained by differential scanning calorimetry was converted to the dependence of the enthalpy on temperature. These curves was represented by piecewise linear function. In the case of partial phase transformations, a modeling method based on the methods proposed by Bonym and Citherlet was designed. An one-dimensional model enabling thermal simulation of the material was implemented in the MATLAB software environment. The results obtained with this simulation are finally compared with a model that does not consider thermal hysteresis.

Sous des températures et des pressions élevées constantes, les matériaux métalliques de structure subissent une dégradation mécanique par fluage qui entraîne des changements microstructuraux. Ces derniers, s'ils ne sont pas surveillés à temps, peuvent entraîner des incidents sérieux, notamment dans le domaine de la production d’énergie électrique (centrales électriques). Pour déterminer les changements microstructuraux, le matériau doit avoir une forme et une taille spécifiques pour que l'analyse des images obtenues par microscopie électronique à balayage, diffraction par rétrodiffusion d'électrons, etc. soit effectuée. Cette préparation destructive demande à extraire le matériau à tester du système, et à le modifier pour la mesure. Afin de surmonter ce problème, dans ce travail de thèse sont proposées trois techniques micro magnétiques non destructives, pour étudier l'évolution des signatures magnétiques par rapport aux niveaux de rupture auquel les matériaux sont exposés. Il est légitime de supposer que tous les changements microstructuraux qui se produisent dans le matériau vont se refléter dans les signatures magnétiques mesurées. Le matériau étudié ici est de l'acier à haute teneur en chrome très sensible au fluage et principalement utilisé dans les centrales thermiques. Certains paramètres magnétiques, tels que la coercivité, la réversibilité magnétique, sont dérivés et montrent de fortes corrélations avec la microstructure. De même, des techniques basées sur les courbes d'hystérésis et le bruit magnétique de Barkhausen sont également appliquées. Pour quantifier davantage les résultats obtenus à partir des signatures magnétiques des matériaux, le modèle de Jiles-Atherton a été adapté à la simulation des signaux de contrôle non destructif. A l’inverse, la possibilité de déterminer les paramètres du modèle à partir des seules mesures de contrôle non destructif est démontrée. Cela apporte des éléments complémentaires à l’interprétation physique des changements microstructurels. La technique de modélisation peut aider en outre à résoudre le problème de l'absence de normes dans les essais non destructifs, quel que soit le dispositif expérimental utilisé. Les paramètres sont enfin comparés pour révéler la sensibilité de chacun d’entre eux aux changements microstructuraux, et ce en fonction de chaque technique de contrôle non destructif utilisée
Under constant high temperatures and pressure, the material undergoes mechanical creep degradation which leads to microstructural changes. These microstructural changes if not monitored on time, can lead to some serious fatal accidents such as in power plants. To investigate these microstructural changes, the material has to be shaped in a certain specific shape and size to have the imaging analysis using Scanning electron microscopy, Electron backscatter diffract ion etc. which are destructive in nature and involve high equipment cost. In order to overcome this issue, this thesis work, incorporates three different non-destructive techniques, to study the evolution of magnetic signatures with respect to the level of rupture they are exposed to. It is legitimate to assume that all the microstructural changes that occur in the material can be reflected in the corresponding magnetic signatures measured. The material that has been studied here is high chromium creep degraded steel which is used in the thermal power plant. The magnetic signatures are evaluated in terms of microstructural information to draw the conclusions. Some magnetic parameters from the curves, such as coercivity, magnetic reversibility are derived which show strong correlations with the microstructure. Similarly, techniques based on Hysteresis curves, and magnetic Barkhausen Noise are also implemented. To further quantify the results obtained from the magnetic signatures of the materials, a model has been developed to derive model parameters in order to physically interpret the microstructural changes. The modelling technique will help in overcoming the issue of lack of standards in NDT, irrespective of the experimental set-up involved. The parameters are compared to reveal sensitivity based on the technique. Finally, conclusion has been drawn to check which parameters are correlated to microstructure for a particular NDT technique used

The eciency of electrical machines is of major concern due to their widespread usage and the globally increasing awareness of energy consumption issues. Iron losses have a signicant impact on the total and thus researchers and manufacturers of electrical machines are developing dierent strategies in order to reduce them. The iron losses are highly dependent on the magnetic material that is used and thus it is necessary to identify its relevant characteristics. In this work, the development of a control system for inducing a pure sinusoidal magnetic ux density in the magnetic material is described. This is necessary in order to perform characterisation of the magnetic material. The main diculty is the highly non-linear and hysteretic relationship between the magnetic eld strength and the magnetic ux density. In order to mitigate the eect of the hysteresis, a mathematical inverse model was used in the control system. To nd a suitable model, an extensive study of literature was performed and discussed in this work. The Preisach model and its dynamic extension was chosen as the most suitable approach. A detailed description of both theory and implementation details is provided in this work. Furthermore, the model is validated by comparing simulation against measurement data for two dierent materials. In the last part of this work, the inverse model is combined with a controller to form a feedback control system. Two dierent control schemes are investigated: a simpler PI controller and a more elaborate disturbance observer (DOB) based control scheme. The DOB is used to observe the hysteresis inversion error and the observation is used to correct for the error. The controller's ability to produce a pure sinusoidal magnetic ux density was assessed by simulations with dierent magnetic materials at varying frequencies.
Verkningsgraden for elmotorer ar av okande intresse pa grund av deras omfattande anvandning och vaxande oro for globala energiforbrukningsfragor. Jarnforluster har ett stort inytande i de totala forlusterna och ar darfor ett viktigt omrade for forskare och tillverkare av elektriska motorer. Jarnforlusterna beror till stor del av det magnetiska materialet som anvands i konstruktion av elmotorer och det ar darfor nodvandigt att identiera materialets egenskaper. I det har arbetet beskrivs utvecklingen av ett reglersystem for att inducera en ren sinusformat magnetisk odestathet i ett magnetiskt material. Detta ar nodvandigt for att kunna bestamma det magnetiska materialets egenskaper under kontrollerade forhallanden. Huvudsvarigheten ar det icke-linjara sambandet mellan magnetiska faltstyrkan och odest atheten. Sambandet formar en hysteres och for att eliminera dess inytande anvandes en matematisk invers model. For att hitta en lamplig model genomfordes en literaturstudie och Preisach modellen och dess dynamiska utokning valdes. I detta arbete nns en detaljerad beskrivning av bade teorin bakom modellen och dess implementering. Modellen utvarderades genom att jamfora matvarden med simulationsresultat for olika magnetiska material. I sista delen av detta arbete kombineras inversmodellen med ett reglerssystem for att kunna uppna en sinusformat odestathet i det magnetiska materialet. Tva olika regleralgoritmer utvarderas, en enklare PI-regulator och en regulator som inkluderar en sa kallat "Disturbance Observer" (DOB). DOB:n anvandes for att observera felet som uppstar vid invertering av hysteresen och for att korrigera felet. De bada regulatorernas formaga attaterskapa en ren sinusformat magnetisk odestathet testas genom att genomfora simulationer for olika magnetiska material vid varierande frekvenser.

The thesis deals with the development of a new hysteresis model and the design of observers for systems with non-monotonic nonlinearities and for a clas of two-degre-of-fredom Euler- Lagrange systems (2-DOF robot). Hysteresis modeling is useful to design new smart-materials based devices, as Nitinol stent of comon use nowadays in many surgical aplications, and to improve the control of hysteretic actuators. The new model, named generalized constructive model, is able reproduce a wider clas of hysteresis nonlinearities than some of the most known models as the Clasical Preisach, the Nonlinear Preisach and the Prandtl-Ishlinski (PI) models, describing a larger number of materials. The new model is developed by an algorithm that makes use of hysteresis minor lop chords, minor lops arisen from reversal branches up to n-order. This aproach that does not make use of analytic functions, adjusting their parameters fit experimental measurements, alows to relax the hysteresis properties of equal minor lops and equal vertical chords, required by the Clasical and the Nonlinear Preisach models, buthat do not hold for a number of smart materials. Four version of the model have ben described analyzed and new les constraining properties have ben introduced to state the representation theorems of the model. The price to be paid for such wider aplicability and precision are the greater experimental measurements that ned to be colected. By mean of numerical simulations acuracy new model is compared with respecto the Clasical, Nonlinear and PI models, showing higher precision, even in the case of the experimental hysteresis temperature versus electrical resistivity of the Nitinol wire shape memory aloy. Numerical solutions for the model implementation and a rate-dependent version, for hystereses that depend also by the input rate, are proposed. To complete first part of the thesis, an academic example of a two link planarobot, which motors have ben idealy substituted by shape memory aloy actuators, show the importance of the hysteresis modeling to control such actuators. The second part of the thesis deals with reduced order observer design for nonlinear systems. observer design is derived aplying the Imersion and Invariance (I&I) technique, recently introduced in literature. This technique alows to estimate a subset of the system variables overcoming isues arisen by high gain aproaches. The design requires solution of partial diferential equations (PDEs) joined to the estimation eror definition and dynamics. This technique, asumed that solutions PDEs are obtained, is more general and alow to cope with systems for which other clasic aproaches, as the ones based on the pasivity of the estimation eror system and circle criteria based, fail for conservativenes. Then, it has ben defined a global observer for a clas of systems with non-monotonic nonlinearities, and in particular for clas of Euler-Lagrange systems with tre like mechanical configurations (robots), achieving global convergence of thestimation eror. A separation principle for the later systems is proposed with computed torque and nonlinear PD-like terms controlaw by mean of Lyapunov-based tols. Numerical simulationshown the performances of the proposed observer and the output fedback design.

Le travail de thèse est consacré à l'étude numérique de nanoparticules (NPs) magnétiques core@shell Fe3O4@CoO présentant des propriétés d'échange bias (EB) en utilisant la méthode Monte Carlo (MC). En particulier, nous nous sommes concentrés sur l'étude de l'effet des réponses collectives (interactions inter-particules telles que les interactions dipolaires (ID)) sur les propriétés magnétiques de ces structures. Des résultats expérimentaux préliminaires, montrant l'existence d'une relation entre le décalage du cycle d'hystérésis et l'interaction entre NPs, ont motivé le travail numérique mené dans le cadre de cette thèse.La première partie de ce mémoire est une étude méthodologique visant à trouver les conditions optimales pour simuler les cycles d'hystérésis d'une façon correcte par MC.Les résultats révèlent une dépendance linéaire entre le champ coercitif Hc et la constante d'anisotropie effective pour des conditions non biaisées (algorithme libre, algorithme du cône, algorithme mixte). La deuxième partie est consacrée à l'étude, à l'échelle atomique, des nanostructures présentant l'EB dont nous avons reproduit les deux caractéristiques (un décalage du cycle d'hystérésis, une augmentation importante de Hc).Nous avons également proposé une méthode permettant l'évaluation de la valeur de l'anisotropie effective.En passant à l'échelle d'une assemblée de NPs, plusieurs modèles furent étudiés. Nous arrivons à interpréter les résultats expérimentaux selon le degré d'agrégation des NPs. Nous montrons que l'agrégation (interactions d'échanges entre les NPs) a un effet direct sur le champ d'échange bias, mais le rôle d'ID sur le champ d'échange mérite des études complémentaires
This thesis is dedicated to the numerical study by means of Monte Carlo (MC) simulations of core@shell Fe3O4@CoO magnetic nanoparticles (NPs) presenting exchange bias properties (EB). In particular, we focused our study on the effect of collective responses (inter-particle interactions as dipolar interactions (DI)) on the magnetic properties of these structures. Our numerical work is motivated by some preliminary experimental results showing the existence of a relationship between the hysteresis loop shift (exchange bias field) and the interaction between NPs. The first part of this thesis is a methodological study to figure out the optimal conditions to simulate hysteresis loops correctly by MC. The results reveal that the coercive field Hc is linearly related to the effective anisotropy constant for non-biased conditions (free algorithm, cone algorithm, mixed algorithm). The second part is dedicated to the study of exchange-biased nanostructures at the atomic scale. We have been able to reproduce both characteristics of EB (hysteresis loop shift, significant increase in Hc). A method allowing the evaluation of the effective anisotropy has been proposed. Considering an assembly of nanoparticles, several models are studied. The experimental results are interpreted according to the degree of aggregation of NPs. It was shown that the aggregation (exchange interactions between NPs) has a direct effect on the exchange bias field, but the role of the ID on the exchange field requires complimentary calculations to be clarified

Le present document est une contribution a l'etude experimentale, theorique et numerique du comportement thermomecanique d'un alliage a memoire de forme industriel niti. Le travail est constitue principalement de trois parties : validation des hypotheses de base utilisees dans les lois de comportement, realisation d'essais mecaniques pour caracteriser les comportements ferroelastique et superelastique du materiau, et modelisation tridimensionnelle appliquee au calcul de structures. L'objectif d'un tel travail est de fournir a l'ingenieur de bureau d'etudes un outil numerique capable de dimensionner des pieces de structures en alliages a memoire de forme. Les lois de comportement sont etablies a partir d'hypotheses physiques, en particulier concernant l'origine de l'hysteresis tant thermique que mecanique. Celles-ci sont validees a partir d'experiences realisees en cisaillement simple en ferroelasticite et en superelasticite, sur des polycristaux de niti, mais aussi sur des monocristaux de cuznal. De plus, les predictions quantitatives du modele sont alors satisfaisantes. Une campagne d'essais homogenes de caracterisation (traction, compression et cisaillement) est effectuee a differentes temperatures. Ces essais ont ete realises sur des toles ayant ete soumises au meme traitement thermomecanique prealable. Ils mettent en evidence la complexite des phenomenes physiques a modeliser : comportement fortement non lineaire a hysteresis, dependance des proprietes caracteristiques avec la temperature, dissymetrie de comportement entre traction et compression. Le schema constitutif sous sa forme tridimensionnelle est alors identifie a ces essais, et modelise correctement la majorite des comportements observes. Ce schema est implante dans un code de calculs elements finis ecrits en grandes transformations, qui utilise la notion de coordonnees materielles entrainees. Finalement, la demarche de modelisation est validee : les predictions des simulations numeriques sont comparees avec des experiences mettant en evidence des sollicitations heterogenes, soit de localisation observee lors de traction de tole, soit de flexion de poutre.

Le transizioni di fase si verificano in molti processi importanti in fisica, scienze naturali e ingegneria: quasi tutti i prodotti industriali prevedono la solidificazione. Fra gli esempi ci sono la fusione del metallo, la ricottura dell'acciaio, la crescita dei cristalli, la saldatura termica, il congelamento del suolo, il congelamento e lo scioglimento dell'acqua sulla superficie terrestre, la conservazione del cibo e altri. Tutti questi processi sono caratterizzati da due fenomeni fondamentali: diffusione del calore e scambio di calore latente di transizione di fase. In questa tesi, che si articola in quattro parti distinte, si trattano le transizioni di fase da diversi punti di vista. La prima parte, intitolata "Controllo e controllabilità delle EDP con isteresi con un'applicazione nella modellazione delle transizioni di fase", è un ponte tra la controllabilità delle EDP con isteresi e le transizioni di fase. Infatti, grazie allo speciale legame tra operatori di isteresi e transizioni di fase, i risultati di controllabilità che dimostriamo possono essere applicati al cosiddetto problema di Stefan con rilassamento. Questo è un esempio di un modello base di transizione di fase, poiché tiene semplicemente conto della diffusione del calore e dello scambio di calore latente. Nella seconda e nella terza parte vengono considerati modelli più complicati, che tengono conto anche degli aspetti meccanici del processo. Più precisamente nella seconda parte, intitolata "Un problema di mezzo poroso viscoelastoplastico con transizione di fase", si ricava e si studia un modello per la filtrazione in mezzi porosi che tiene conto degli effetti del congelamento e dello scioglimento dell'acqua nei pori. La terza parte, il cui titolo è "Fatica e transizione di fase in una trave elastoplastica oscillante", è dedicata alla derivazione e allo studio di un modello che descrive l'accumulo di fatica in una trave oscillante nell'ipotesi che il materiale possa recuperare parzialmente per effetto di fusione. Infine, nella quarta parte, intitolata "Regolarità per problemi variazionali in doppia fase", si affronta il problema della maggiore differenziabilità delle soluzioni del problema dell'ostacolo. In particolare si tratta del caso di condizioni di crescita non standard, che include i cosiddetti funzionali a doppia fase. Tali funzionali descrivono il comportamento di materiali fortemente anisotropi le cui proprietà di indurimento cambiano drasticamente con il punto, quindi mostrano la transizione di fase più drastica. Le tecniche qui impiegate sono diverse da quelle usate nel resto della tesi, poiché si basano sui metodi diretti appartenenti alla teoria della regolarità nel campo del Calcolo delle Variazioni.
Phase transitions occur in many relevant processes in physics, natural sciences, and engineering: almost every industrial product involves solidification at some stage. Examples include metal casting, steel annealing, crystal growth, thermal welding, freezing of soil, freezing and melting of the earth surface water, food conservation, and others. All of these processes are characterized by two basic phenomena: heat-diffusion and exchange of latent heat of phase transition. In this thesis, which consists of four distinct parts, we deal with phase transitions from different points of view. The first part, titled "Control and controllability of PDEs with hysteresis with an application in phase transition modeling", is a bridge between controllability of PDEs with hysteresis and phase transitions. Indeed, thanks to the special link between hysteresis operators and phase transitions, the controllability results that we prove can be applied to the so-called relaxed Stefan problem. This is an example of a basic model of phase transition, since it simply accounts for heat-diffusion and exchange of latent heat. More complicated models, which take into account also the mechanical aspects of the process, are considered in the second and in the third part. More precisely in the second part, titled "A viscoelastoplastic porous medium problem with phase transition", we derive and investigate a model for filtration in porous media which takes into account the effects of freezing and melting of water in the pores. The third part, whose title is "Fatigue and phase transition in an oscillating elastoplastic beam", is devoted to the derivation and the study of a model describing fatigue accumulation in an oscillating beam under the hypothesis that the material can partially recover by the effect of melting. Finally, in the fourth part, titled "Regularity for double-phase variational problems", we address the problem of the higher differentiability of solutions to the obstacle problem. In particular we deal with the case of non-standard growth conditions, which includes the so-called double-phase functionals. Such functionals describe the behavior of strongly anisotropic materials whose hardening properties drastically change with the point, hence they exhibit the most dramatic phase transition. The techniques here employed are different from those used in the rest of the thesis, since they rely on the direct methods pertaining to the regularity theory in the field of Calculus of Variations.

This Ph.D. dissertation is the result of a three-year research activity focused on structural and seismic engineering applied to innovative timber constructive systems. The main purpose is to give a contribution to international scientific research and current design practice about the seismic behaviour of timber shear-wall systems, which still represent an innovation in the construction industry and are being developed due to their favourable characteristics. An initial overview on the use of main timber structural systems in seismic-prone areas for low- and medium-rise buildings is provided, within the context of current European seismic code. The theme of the seismic design of timber shear-wall systems is discussed in the first part, giving close attention to linear and non-linear modelling criteria: various strategies are proposed and main characteristics are highlighted. Basic definitions and concepts proper of the seismic analysis of timber structures are provided. A particular attention is paid to the definition and application of the capacity design approach and the close link with the concept of behaviour factor is emphasized. Finally, the definition of behaviour factor, as product between an “intrinsic” capacity of the structure and a design over-strength value is proposed. This definition allows to characterize the structural systems with their proper dissipative capacity and to evaluate separately the safety reserve introduced by design. The second part analyses the structural behaviour of the cross-laminated timber (CLT) technology, which represents one of the most common timber structural systems. The concepts of ductility, dissipative capacity, regularity and irregularity applied to CLT system are provided. The seismic response and the dissipative capacity of this system are firstly evaluated via an experimentally based procedure. Then, the evaluation of its intrinsic dissipative capacity is determined via non-linear numerical modelling with the aim of studying the correlation with the construction variables. Results show that the construction design decisions affect the seismic response and dissipative capacity of buildings, as opposed to apply a single behaviour factor value to the whole CLT technology. A statistical analysis applied to numerical results allowed also to propose analytical formulations for the computation of the suitable behaviour factor value for regular buildings. Then, the same analyses carried out on in-elevation non-regular buildings returned a correction factor to account for the reduction in dissipative capacity due to irregularity. The application of the CLT technology to realize high-rise buildings is presented in the third part, analysing the behaviour of slender buildings with seismic resisting core and perimeter shear walls. The major limitations and drawbacks in realizing these structures in areas characterized by high seismic intensity and their implication in the design are reported. The final part presents three novel structural systems as alternative to more common technologies, as CLT or platform frame. These innovative systems are characterized mainly by a diffuse dissipative and deformation capacity when subjected to seismic loads, while in CLT system such capacity is concentrated in connection elements. This different response is studied via quasi-static tests and numerical simulations. In detail, two non-glued massive timber shear walls and a mixed steel-timber wall with an innovative bracing system are presented.
Questa tesi di dottorato è il risultato di tre anni di attività di ricerca in ambito ingegneristico strutturale applicato allo studio di sistemi costruttivi innovativi in legno. Il principale obiettivo è quello di fornire un contributo alla ricerca scientifica internazionale e ai metodi attuali di progettazione in merito alla risposta sismica di sistemi in legno a pareti sismo-resistenti, i quali rappresentano tutt’ora un’innovazione nel settore delle costruzioni e si stanno diffondendo grazie alle loro caratteristiche favorevoli. Una panoramica iniziale sull’utilizzo dei principali sistemi strutturali in legno in zone sismiche per la realizzazione di edifici bassi o di media altezza viene fornita e contestualizzata nella vigente normativa sismica europea. La prima parte della tesi affronta il tema della progettazione sismica di sistemi a pareti in legno, con particolare attenzione ai criteri di modellazione lineare e non lineare, proponendo diverse strategie ed evidenziandone le caratteristiche. In questa parte vengono forniti inoltre definizioni e concetti fondamentali propri dell’analisi sismica di strutture in legno. Un’attenzione particolare è riservata alla definizione e applicazione del “capacity design”, sottolineandone lo stretto legame con il concetto di fattore di struttura. Viene proposta infine una definizione del fattore di struttura come prodotto tra una parte intrinseca alla struttura e una sovraresistenza di progetto. Tale definizione permette di caratterizzare i sistemi strutturali con la propria capacità dissipativa e di valutare separatamente la riserva di sicurezza introdotta dalla progettazione. La seconda parte della tesi analizza il comportamento strutturale della tecnologia X-Lam (CLT), che rappresenta uno dei più comuni sistemi strutturali in legno. In questa parte vengono approfonditi i concetti di duttilità, capacità dissipativa, regolarità e irregolarità applicati al sistema X-Lam. La risposta sismica e la capacità dissipativa di questo sistema sono state preliminarmente valutate tramite una procedura analitico-sperimentale. Modelli numerici non-lineari hanno quindi permesso di valutarne la capacità dissipativa intrinseca in funzione delle variabili costruttive proprie del sistema. I risultati mostrano come le decisioni costruttive in fase di progettazione influenzino la risposta sismica dell’edificio; ciò è in contrasto all’applicazione di un unico valore del fattore di struttura per l’intera tecnologia X-Lam. Un’analisi statistica applicata a tali risultati numerici ha consentito di proporre formulazioni analitiche per il fattore di struttura per edifici regolari in funzione delle caratteristiche dell’edificio stesso. Infine, le stesse analisi condotte su edifici non regolari in altezza hanno fornito un coefficiente per tenere in conto della riduzione di capacità dissipativa a causa dell’irregolarità. Nella terza parte viene presentata un’applicazione della tecnologia X-Lam per costruire edifici alti, analizzando il comportamento di edifici snelli con nucleo sismo-resistente e pareti aggiuntive perimetrali. Vengono riportati inoltre le principali limitazioni e inconvenienti nel realizzare tali strutture in aree caratterizzate da elevata intensità sismica e le loro implicazioni nella progettazione. La parte finale descrive e analizza tre sistemi strutturali in legno innovativi, come alternative a tecnologie più comuni, quali X-Lam o platform-frame. Questi sistemi, soggetti ad azioni sismiche, sono caratterizzati da una capacità deformativa e dissipativa diffusa, al contrario del sistema X-Lam in cui tale capacità è concentrata principalmente negli elementi di connessione. Questa risposta differente è studiata attraverso test sperimentali quasi statici e simulazioni numeriche. In dettaglio, sono presentati e analizzati due sistemi a pareti massicce stratificate; realizzate senza l’uso di colla tra gli strati e una parete ibrida acciaio-legno con un sistema innovativo di controvento.

In this thesis two all-steel BRB have been designed, manufactured and tested, and both satisfy the testing protocols required by EU and US codes. They are composed of a steel slotted restraining unit which stabilizes the steel core. The first one, the Modular Buckling Restrained Brace (MBRB), is composed by several seriated modules which contain several dissipation units connected in parallel, which yield under shear forces. Although it has good hysteretic response and a high ductility, its core is heavy and expensive to manufacture. The second one,the Slotted Buckling Restraining Brace (SBRB), solves these two shortcomings. It yields under axial forces, like the conventional BRBs, but the usual solid core has been substituted by a perforated plate. The core is a one-piece element composed of two lateral bands, of a nearly uniform section and designed to yield, connected by stabilizing bridges, which behave elastic. The buckling prevention of the lateral bands is done by the restraining unit and the stabilizing bridges. Design expressions have been proposed to design both devices, and a numerical material model have been formulated and implemented in commercial finite element method software to numerically simulate the behavior of the braces, which will reduce the need of full scale tests for its design
En la present tesi, dos BVR totalment metàl·lics s’han dissenyat, fabricat i assajat, satisfent tots dos els requeriments dels protocols definits per les normes europees i americanes. Estan formats per un element de travat ranurat que estabilitza el nucli metàl·lic. El primer d’ells, el Braç de Vinclament Restringit Modular (BVRM), està format per diversos mòduls seriats que a la vegada contenen diverses unitats de dissipació, que plastifiquen sota esforços tallants, connectades en paral·lel. Tot i que té un bon comportament histerètic i una gran ductilitat, el nucli és pesat i difícil de fabricar. El segon braç, anomenat Braç de Vinclament Restringit Ranurat (BVRR), soluciona aquests inconvenients. Plastifica sota esforços axials, de la mateixa manera que els BVR convencionals, però el nucli massís és substituït per una platina perforada. Aquest nucli consisteix en un únic element composat per dos bandes laterals, dissenyades per a plastificar i amb una secció quasi constant, connectades per diversos ponts estabilitzadors que es mantenen sempre en el seu rang elàstic. Aquests ponts, juntament amb l’element de travat, impedeixen el vinclament de les bandes laterals. S’han proposat diverses expressions de disseny pels dos braços. S’ha formulat i implementat, en un programa d’elements finits comercial, un model de material per a simular numèricament el comportament dels braços, reduint així la dependència dels assajos a escala real durant el seu procés de disseny

Connections and fasteners play an essential role in the determination of strength and stability, ductility and robustness, i.e., the overall behaviour of timber structures. In particular, connections subjected to static loads are to be investigated in terms of strength and stiffness, whereas the ones designed to withstand cyclic (e.g., seismic) loads need also the definition of their complete hysteretic response. This Ph.D. dissertation focuses on the behaviour of modern connections being developed and employed in timber engineering. An initial overview on mechanical connections employed in timber structures and their evolution is reported in the introductive section of this thesis. Advantages as well as critical issues of traditional connections are the motivations for the evolution and the improvements brought by innovative connections. Two different applications of innovative timber connections are analysed and hereby discussed, each one facing different issues. The first one claims to give an insight into modern screws employed in Timber-concrete composite (TCC) structures, where the major objective is to achieve maximum strength and above all stiffness. The second is directly focused on the cyclic performance of modern connections employed in Cross Laminated Timber (CLT) structures where dissipative capacity and structural damping are of utmost importance. Consequently, the present manuscript is subdivided into two main parts. The first part deals with TCC joints realized with modern screws. The key-point to guarantee adequate mechanical performance to these composite structures is the use of connectors that demonstrate sufficient shear strength and stiffness at the interface between timber beam and concrete slab independently of the presence of an intermediate layer. Modern cylindrical connectors, such as self-tapping screws, are rising interest because they combine remarkable performance, when their withdrawal capacity is exploited, and quickness of execution especially in case of onsite installation. In this paper, a theoretical approach to calculate shear strength and stiffness of TCC joints made with inclined screws is discussed and compared to current design procedures. Furthermore, a report on short-term push-out tests of TCC joints realized with inclined self-tapping screws carried out varying fastener arrangement, diameter and concrete type is given. Consequently, a comparison between the results obtained with the theoretical method and experimental tests is reported and critically discussed in terms of both strength and stiffness. The last section of the first part present the design of an innovative connector that combines the use of self-tapping screws and a glass-fibre reinforced polymer (GFRP) element as components to realize structural TCC joints. FRP is being used in civil engineering since decades, but most of these applications utilize pre-impregnated thermosetting composites, the most common of which is carbon fibre-reinforced polymer (CFRP). On the contrary, injection moulded thermoplastic materials are relatively new and lack of history of their use in civil infrastructures. The aim is to develop a connection that solves typical installation issues of inclined screws and avoids stress concentration issues that may occur in the concrete layer. Numerical simulations, carried out to design this particular joint and exploiting a hybrid approach, are described in detail. Then, results from the experimental tests conducted to investigate the behaviour of the device subjected to shear loading conditions are compared with the analytical predictions valid for inclined screws previously described. The second part of this work focuses on the developing of an innovative earthquake-resistant connections employed for CLT structures. The seismic performance of CLT buildings is mainly related to the capability of joints to perform plastic work, since timber elements have limited capability to deform inelastically. Nowadays, the use of hold-down and angle bracket connections, which were originally developed for platform-frame constructions, has been extended also to CLT buildings. Nevertheless, the dissipative capacity of light-frame buildings is mainly diffused in nailing between frames and panels while, in CLT walls, the dissipative contribution is exclusively assured by ductile joints connecting the panels. The need of more reliable connections that provides well predictable and stable hysteretic behaviour, reduced pinching phenomenon (caused by the wood embedment) and strength degradation, justifies the continuous development of “innovative” connections. In this work, a newly developed connection element that overcomes the aforementioned issues and works for both tensile or shear loads is designed and assessed, and various significant aspects are discussed. Initially, the design procedure of the connection element and preliminary experimental tests that validates the numerical predictions are illustrated. Then, improved versions of the device are illustrated and their experimental results reported with particular attention in describing their hysteretic response and coupled shear-tension strength domain. In this work, an important role is also given to the application of the capacity design criteria applied at the joint level in order to guarantee the best exploitation of the connection’s dissipative capacity. Therefore, theoretical concepts, which describe the overstrength of traditional and innovative connections, confirmed by experimental tests of the brackets anchored to a CLT panel, are also given. In the last chapter is presented a numerical model that, following a macro-element approach, reproduces the actual cyclic response of the investigated device when subjected to combined shear-tension loads. Finally, the results of Non-Linear Dynamic Analyses of a case study CLT building realized which such model are reported and the seismic capacity of the case study building is evaluated. With these two examples, this thesis aims to give an original contribution in the evaluation of performance of innovative connection systems for timber structures, combining the use of theoretical, numerical and experimental models, and highlighting the emerging differences with respect to the use of traditional fasteners and connections.
Le connessioni e gli elementi di fissaggio svolgono un ruolo essenziale nella determinazione della resistenza, stabilità e solidità, ovvero nella risposta globale delle strutture del legno. In particolare, le connessioni soggette a carichi statici devono essere studiate in termini di resistenza e rigidezza, mentre quelle progettate per resistere a carichi ciclici (ad es. sismici), necessitano anche della completa definizione della loro risposta isteretica. Questa tesi si concentra sul comportamento dei collegamenti moderni sviluppati e impiegati nell'ingegneria del legno. Una prima panoramica sulle connessioni meccaniche impiegate nelle strutture del legno e la loro evoluzione è riportata nella sezione introduttiva di questa tesi. Vantaggi e criticità delle connessioni tradizionali sono le motivazioni dell’evoluzione e dei miglioramenti prodotti dalle connessioni innovative. Vengono analizzate e discusse due diverse applicazioni di connessioni per strutture in legno, ognuna delle quali espone aspetti e problematiche diverse. Il primo afferma di dare una panoramica delle moderne viti utilizzate nelle strutture composte legno-calcestruzzo (TCC), dove l'obiettivo principale è ottenere massima resistenza e ancor più rigidezza. Il secondo, è incentrato direttamente nell’analisi delle prestazioni cicliche delle connessioni moderne utilizzate nelle strutture in CrossLam (CLT) in cui la capacità dissipativa e lo smorzamento strutturale sono della massima importanza. Di conseguenza, il presente manoscritto è suddiviso in due parti principali. La prima parte riguarda le giunzioni legno-calcestruzzo realizzate con viti moderne. Il punto chiave per garantire prestazioni meccaniche adeguate a queste strutture composite è l'utilizzo di connettori caratterizzati da un'adeguata resistenza e rigidezza tra trave di legno e soletta di calcestruzzo, indipendentemente dalla presenza di uno strato intermedio. I connettori cilindrici moderni, come le viti autofilettanti, possiedono un crescente interesse perché combinano elevate prestazioni, se è sfruttata la loro elevata capacità ad estrazione, e rapidità di esecuzione. In questo lavoro viene proposto un approccio teorico semplificato per calcolare la resistenza al taglio e la rigidezza dei giunti TCC realizzati con viti inclinate e poi confrontato con le attuali procedure di progettazione. Inoltre, viene fornito un rapporto sulle prove di push-out a breve termine di giunti TCC realizzati con viti autofilettanti inclinate, effettuate con vari tipi di fissaggio, diametro e tipo di calcestruzzo. Di conseguenza, viene anche riportato un confronto tra i risultati ottenuti con il metodo teorico e le prove sperimentali e viene discusso criticamente in termini di forza e rigidezza. L'ultima sezione della prima parte comprende la progettazione di un connettore innovativo che combina l'utilizzo di viti autofilettanti e polimero termoplastico rinforzato con fibra di vetro (GFRP) per realizzare giunti TCC strutturali. Gli FRP vengono utilizzati nell’ingegneria civile da decenni, ma la maggior parte di queste applicazioni utilizza compositi termoindurenti pre-impregnati, il più comune dei quali è il polimero rinforzato in fibra di carbonio (CFRP). Al contrario, i materiali termoplastici sono relativamente nuovi e mancano di storia nell'utilizzo nell'infrastruttura civile. Le simulazioni numeriche, effettuate per progettare questo giunto, sono descritte in dettaglio. Quindi, i risultati delle prove sperimentali condotte per esaminare il comportamento del dispositivo sottoposto a condizioni di carico di taglio sono confrontati con le previsioni analitiche descritte. La seconda parte di questo lavoro si concentra sullo sviluppo di collegamenti innovativi impiegati per le strutture in CLT. La prestazione sismica degli edifici CLT è principalmente legata alla capacità dei collegamenti di plasticizzarsi, poiché gli elementi del legno hanno una capacità limitata di deformazione inelastica. Oggi, l'utilizzo di connessioni quali hold-down e angolari, originariamente sviluppati per costruzioni tipo platform-frame, è stato esteso anche agli edifici CLT. Tuttavia, la capacità di dissipazione degli edifici a telaio è diffusa soprattutto nella connessione telaio-pannello, mentre nelle strutture in CLT il contributo dissipativo è assicurato esclusivamente da connessioni duttili che collegano i pannelli. La necessità di una connessione più affidabile che fornisca un comportamento isteretico prevedibile ed affidabile, un fenomeno ridotto di “pinching” (causato dal rifollamento del legno) e una degrado di resistenza giustifica lo sviluppo continuo di connessioni "innovative". In questo lavoro è stato progettato e valutato un elemento di connessione che sormonti i problemi sopradescritti e che lavora sia per i carichi di trazione che per taglio, e ne vengono discussi gli aspetti più significativi. Inizialmente viene illustrata la procedura di progettazione dell'elemento di connessione e dei test sperimentali preliminari che convalidano le previsioni numeriche. Successivamente vengono descritte le fasi di progettazione e test di ulteriori versioni migliorate delle staffe dissipative e sono riportati i loro risultati sperimentali facendo particolare attenzione nel descrivere la loro risposta isteretica e il dominio di resistenza tensione-taglio. Un ruolo importante in questo lavoro è dato all'applicazione dei criteri di gerarchia delle resistenze (progettazione in capacità) a livello di connessione al fine di garantire il miglior sfruttamento della capacità dissipativa della connessione. Di conseguenza, vengono forniti concetti teorici che descrivono l’applicazione di tali concetti a connessioni tradizionali e innovative, e confermate da prove sperimentali delle staffe oggetto di studio ancorate a un pannello CLT. Infine, i risultati di simulazioni numeriche dettagliate e prove cicliche quasi-statiche sono state utilizzate per sviluppare un modello di macro-elemento implementato in un codice numerico che ha permesso di determinare le prestazioni sismiche di un edificio caso studio in CLT realizzato con tali connessioni. Con questi due esempi la presente tesi mira a definire un originale procedura di valutazione delle performance delle connessioni innovative per legno, combinando l'uso di modelli teorici, numerici ed analisi sperimentali e mettendone in evidenza le differenze emergenti rispetto all'impiego di sistemi di connessioni tradizionali.

Magnetic hysteresis modelling plays a crucial role in determining the electromagnetic properties of soft magnetic materials. A new approach to modelling is the use of recurrent neural networks, capable of time dependent, dynamic, sequential mapping. This research investigates the implementation and accuracy of this approach among other available hysteresis models.
thesis (MEng(ElectronicsEngineering))--University of South Australia, 2004.

This thesis is primarily concerned with the electrical characterization and modelling of perovskite solar cells. Perovskite cells are a new player in the photovoltaic arena with several intriguing properties. One of these is the presence of intrinsic mobile ions which make these semiconductors simultaneously ionic conductors at room temperature. The presence of mobile ions is significant in that it leads to a number of transient behaviours in optoelectronic measurements, including nominally simple current-voltage measurements where the phenomena are broadly labelled as aspects of ``I-V hysteresis''. The first two-thirds of this thesis describes our work on extended drift-diffusion models which incorporate the presence of mobile ions into the conventional equations of semiconductor physics. These allow us to uncover mechanistic explanations for a variety of transient behaviours which are broadly caused by coupling between electronic and ion dynamics. The first third (Chapter 2) deals with hysteresis in the form of rate-dependent I-V sweeps: a selection of unusual measurements of this type is presented including a temporary enhancement in open-circuit voltage following prolonged periods of negative bias, dramatically S-shaped current-voltage sweeps, decreased current extraction following positive biasing or ``inverted hysteresis'', and non-monotonic transient behaviours in the dark and the light. This initial study is supplemented with a more in-depth investigation of inverted hysteresis and its correlation with band-alignment. The second third (Chapter 3) delves deeper into electrical characterization with a first-principles study of electrical impedance spectroscopy. We focus on accounting for features in the measured capacitance spectrum (sufficient for a full account of the total impedance due to the Kramers-Kronig relations) of standard-structure (non-inverted) perovskite cells. Here our models make clear the necessity of distinguishing fundamental contributions to the measured capacitance due to charging, from those due to currents delayed by slow processes such as ion migration. With this distinction clearly established we provide a detailed account of all the major features observed in impedance measurements of these cells, including the exotic and previously puzzling appearance of giant photo-induced capacitance, loop features and negative capacitance. The final part of this thesis in Chapter 4 concerns the integration of perovskite cells into tandem arrangements with a partner such as the crystalline silicon cell. Of relevance to any thin-film solar cell, and to 4-terminal tandem cells in particular, is the specifications of its transparent conductor layers. We analyze transparent conductor requirements under different regimes of metallization (the addition of metallic bus-bars or fingers). Here a key parameter is the minimal achievable wire width, which dictates the necessary tradeoff between transparency and conductivity in the underlying transparent conductor. We identify \SI{30}{\micro \metre} as a critical width below which many emerging transparent conducting layers such as carbon nanotubes and graphene become competitive with state-of-the-art transparent conductive oxides such as ITO for a stand-alone perovskite cell. We also discuss a novel strategy for integrating perovskite and Si cells into a single monolithic structure without the need for a tunnel junction or recombination layer. This is identified as being possible due to the presence of interfacial sub-gap states which can facilitate high-conductivity ohmic contact between TiO$_2$ and p-type Si, and has significant advantages in terms of reducing optical losses and processing steps.

The electromagnetic machines like the dc, induction, synchronous motor/generator and the transformer have an energy flow framework that is similar. All these machines deal with electrical energy in the electrical domain that is interfaced with the magnetic domain. Except for the transformer, the other machines also have one more energy interface i.e. with the mechanical domain. In all these machines, the magnetic domain acts as the silent energy manager. The electrical and the mechanical domain energies will have to pass through the magnetic domain and appropriately get routed. In recognition of the commonality of this pattern of energy flow, this thesis proposes a generalised model of a multiphase electromagnetic device wherein the dc machine, induction machine, synchronous machine and the transformers are special cases of the proposed generalised model. This is derived using bond graphs that is based on the underlining principle of Energy Flow rooted in the concept of Conservation of Energy. A model is a set of mathematical equations representing a physical system. A model is as good as a modeller understanding of the physical system and the underlying approximation he makes while writing down the equations describing the models behaviour to the stimulus. A modelling language tool, which can cut down the approximations made by using the power of identified analogous characteristics across the physical domain, can help make a model more close to real life situation. Bond Graph is such a modelling language which is powerful enough to model the non-linear, multi-disciplinary, hybrid continuous-discrete phenomena encountered in a real life physical system. Bond graphs as a modelling tool was introduced by Professor H.Paynter at Massachusetts Institute of Technology in 1959. The Bond Graph methodology is based on consideration of energy flows between the ports of the components of an engineering system. Bond Graph methodology enables one to develop a graphical model that is consistent with the first principle of energy conservation without having the need to start with establishing and reformulating equations. The derivation of a mathematical model from the graphical description is automated by software tools. As a consequence, a modeller using this methodology can focus on modelling of the physical system. In the graphical representation of bond graph the vertices of a bond graph denote subsystems, system components or elements, while the edges, called power bonds, represent energy flows between them. The nodes of a bond graph have power ports where energy can enter or exit. Bond graph models are developed in a hierarchical top-down or bottom-up approach by using component models or elements from model libraries. An electromagnetic machine is a black box having an assemblage of windings in iron resulting in a combination of input/output ports on shaft and electrical terminals. Abstraction of an machine model by a modeller matching the vision of the observer above is an ideal goal. Bond graph methodology is an appropriate tool for trying to reach this goal as it is based on object oriented modelling techniques. There have been few attempts to model electric machine in bond graph earlier. A well established DC motor bond graph has been widely used in all bond graph literature. But AC rotating machine being a higher order nonlinear system poses a tougher challenge. Here too, there have been few attempts in modelling AC machines. It is observed that majority of AC machine bond graph models have been built up from their mathematical models. But as the bond graph modelling technique is based on the unifying theory of energy exchange, better insight into the system is achievable if the model is conceptualised from its physical structure. This thesis starts from the basic theory of energy port to conceptualise the generalised model from physical correspondence. In this thesis a Rotating Electrical Machine is studied as a physical system. The energy ports inside this physical system is identified. When a physical system receives the energy through its energy port in one energy cycle, it processes this energy in one of the three ways. The received energy is converted into useful work or it is dissipated or stored. The storage can further be classified into two ways, either as kinetic energy or as potential energy. For a rotating electric machine the input-output port for energy exchange are either in electrical or mechanical domain depending on the class of the machine. The magnetic domain across all class of electromagnetic device acts as the energy manager. In order to capture the features of the energy jumping across the air gap in a rotating electrical machine, wherein the magnetic fields from spatially distributed windings of the stator and rotor interplay, an Axis Rotator (AR) element -a mathematical commutator, is introduced in this thesis as a new bond graph element. In a multiphase device, the energy from the various phases and spatial axes are transferred through the axis rotator element. The Axis Rotator is a critical element which helps distinguish between the various classes of electromagnetic devices. The defining features of the Axis Rotator helps in deriving the various special electromagnetic devices (such as the dc machine, induction machine, synchronous machine and the transformer) from the generalised model. The Axis Rotator exists in the magnetic domain. It naturally inherits the characteristics of the magnetic domain. The Axis Rotator as a bond graph element is complex. In a specific case of 3φ Induction Motor an alternative bond graph model with all integral elements is developed. By one to one correspondence with the AR bond graph model, the inner component of ’AR’ can be identified. Another advantage of using this model is that saturable and non-saturable magnetic permeance can be separated out, a useful feature in the nonlinear model discussed next. One of the most distinguishing features of the magnetic domain is the existence of Magnetic Hysteresis. Magnetic Hysteresis is a well understood and studied subject. But this physical process is wilfully ignored by the modelling community at large. The main reason for this is the difficulty of modelling a nonlinear phenomena. The bond graph modelling naturally allows the inclusion of such non-idealities within its framework. This thesis proposes the generalised model along with the inclusion of magnetic non-linearities and non-idealities into the model of the system. This inherent strength of bond graph model flows from the fact that the models in bond graph are developed from the first principles of energy conversation and the mathematical equations are derived later from the evolved graph. The tools that are available for bond graph simulation are not adequate for power electronics systems. The existing tools do not address space vectors and frame transformations. As a consequence it is difficult to simulate the electromagnetic device models developed in this thesis. The need for a bond graph tool to address vectors and frame transformations, a common occurrence in electric machines dynamic model study was acutely felt. This necessitated a support for handling complex data class from the underlying mathematical engine of the software. MATLAB/Simulink is the commonly available mathematical tool which has a support for complex variables. Therefore during the course of this research work a new software tool box was developed which meets the need of electromagnetic machines in particular and other engineering domains in general. For developing the new bond graph simulation software, the language extender approach was chosen, as it combines the capabilities of existing popular mathematical engine with its tested graphical frontend and the flexibility of combining different modelling technique like bond graph, block diagram, equations etc. It also ensures portability as they are compiled by interpreted language compiler of the mathematical engine and are thus independent of the computer operating system. C-MEX S-function methodology was used to develop the software as it has access to lower level functions and methods of the underlying mathematical engine. This helps in speeding up the software execution time alongwith the flexibility in defining new complex elements like the Nonlinear Axis Rotator. In conclusion, this thesis makes the following contributions: (i) The Axis rotator concept to handle space vectors and frame transformations, (ii) generalised model of the electromagnetic device, (iii) introduction of the saturation and hysteresis non-linearity in the magnetic domain, (iv) development of the bond graph toolbox to handle vector and frame transformations.

The aim of the current study is to model (non-wetting) liquid flow in a packed bed under the influence of gas flow. It has been observed experimentally that non-wetting liquid flows in a packed bed in form of small droplets and rivulets falling through the void regions. Continuum models have not been successful in predicting liquid flow paths when the liquid is injected through a point source in the packed bed. In the current study, we present a discrete deterministic model for modeling the liquid flow in a packed bed, under the influence of gas flow. When a high velocity gas blast in injected into a dry packed bed, a cavity or a void is formed in front of the nozzle. The cavity size increases with increasing gas velocity and exhibits hystersis in size upon increasing and decreasing gas flow rate. The cavity size is very important in determining the gas penetration into the packed bed. A proper gas flow profile prediction is necessary for determining it’s effect on the liquid flow behavior. Attempts at modeling cavity sizes have mostly been confined to experimental studies and development of correlations. Different correlations show different dependence on operating as well as bed parameters and a fundamental understanding of the cavity formation and hystersis phenomena is missing. We adopt a combined Eulerean-Lagrangian approach to study the above mentioned phenomena mathematically. Gas is modeled as a continua and solid as discrete (soft sphere D.E.M. approach). Hystersis and cavity formation studies are carried out in a 2D-slot rectangular packed bed. A discrete deterministic liquid flow model (developed and validated under structured packing conditions using x-ray radiography flow visualization technique), is used to study the effect of presence of liquid on the dry bed void size, when liquid is injected in a packed bed through a point source. It is found that the gas pushes the liquid away from the nozzle side wall. Also, the cavity sizes during gas velocity decreasing case are found to be larger in size than the void size obtained during velocity increasing case for the same inlet gas flow rate. This difference is void size leads to more gas penetration into the bed and thus more liquid shift away from the nozzle side wall. Presence of liquid is found to affect the void size (compared to dry bed size) negligibly.

碩士
淡江大學
土木工程研究所
82
The purpose of this research is to establish a new damping model of soils for dynamical solution using the integration technique With the hysteretic type of damping ratio determined from the laboratory dynamic tests varying frequencies , a time dependent equivalent viscous coefficient can be obtained using the Fourier Integral . By doing so , the typical viscous coefficient ( or in a matrix form ) , representing energy absorbing ability of the soils and perhaps for the energy dissipation along the structure in more detailed form , can then be used in the analytical studies . Research work conducted herein is modeled with the behavior of axial loaded pile . Comparison are made with the use of traditional modelling. It is found that the prediction of the model is as good as that of the convention . Moreover , the proposed modification of frequency dependent soil damping eliminate the possible interference of numerical shortcoming at high frequencies .