The problem of damage accumulation in laminated composite materials hasreceived much attention due to their widespread application in the aerospace, automotive,civil, and sports industries. In the aerospace industry, composites are usedto make light weight and efficient structural components. In the Boeing 787, forexample, more than 50% of the structure is made of composite materials. Althoughthere have been significant developments in analyzing cross-ply laminates, none ofthe present approaches provides reasonable predictions for multidirectional laminatesin which intralaminar cracks may form in multiple orientations. Nevertheless, theprediction of damage accumulation and its effect on structural performance is a verydifficult problem due to complexity of the cracking processes.This study presents a synergistic damage mechanics (SDM) methodology to analyzedamage behavior in multidirectional composite laminates with intralaminarcracks in plies of multiple orientations. SDM combines the strengths of micro-damagemechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to these cracks. The micromechanics is performed on a representativeunit cell using a three-dimensional finite element analysis to calculate thecrack opening displacement accounting for the influence of the surrounding plies, theso-called constraint effect. This information is then incorporated in the CDM formulationdealing with laminates containing cracks in different ply orientations through a `constraint parameter'. Following CDM, a separate damage mode is defined for eachtype of crack and the expressions for engineering moduli of the damaged laminateare then derived in terms of crack density and the constraint parameter. The SDMmethodology is implemented for [0m/±θn/0m/2]s laminates containing cracks in ±θplies. It is then extended to [0m/±θn/90r]s and [0m/90r/±θn]s laminates with cracksadditionally in the 90°-plies. The predictions agree well with published experimentaldata as well as independent FE computations. Limited parametric studies areperformed to show usability of SDM for more general laminates.To predict the initiation and growth of intralaminar cracks, an energy basedmodel is proposed in which these cracks initiate and multiply when the work requiredto form new set of cracks exceeds a laminate dependent critical energy release rate.The approach requires determination of average crack opening and sliding displacementsat varying crack spacing. This task is performed through a suitable 3-D FEanalysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized,where the critical energy release rates in normal and shear modes are determinedby fitting the damage model with the experimental data for a reference laminate.The predictions from the model for [0/± θ4/01/2]s and [0/90/ ± 45]s laminates showremarkable agreement with the experimental results.The methodology and the results covered in this dissertation will be of interest tomechanics of materials researchers as well as to engineers in industry where compositematerials for structural applications are of interest.

­^¤å´£­n¡G The objective of this thesis is to simultaneously achieve two- dimensional control of transverse flux linear switched-reluctance machine (LSRM). Based on a theoretical matrix decomposition scheme, the overall structure of the control and drive systems can be constructed, and the associated man/machine interface can be designed. A fuzzy inference scheme has been selected to control the machine motion, while an orthogonal scheme has been developed to control the machine lift force. By realizing the control algorithm through digital signal processor (DSP), results show that the LSRM will be quite applicable for the desired operations of magnetic levitated vehicle.

The objective of this thesis is to present the algorithm of achieving speed and lift force controls of transverse flux linear switched-reluctance machine (LSRM) simultaneously. A high-speed digital signal processor based (DSP-based) switching controller will be implemented, and the desired speed control objective is realized by using a fuzzy control scheme. On the other hand, by using an indirect field-oriented control scheme, the LSRM reluctance forces, which are magnetically decoupled and position dependent, can be projected onto sets of stationary axes that are aligned with the motor fixed secondary poles. Hence by controlling flux on the specific stationary axis, the machine lift force can be properly controlled. Finally, adequate duty cycle distribution will be discussed and examined to asynchronously supply the required speed and lift force control objectives simultaneously.

This work addresses the issue of transverse combustion instabilities in annular gas turbine combustor geometries. While modern low-emissions combustion strategies have made great strides in reducing the production of toxic emissions in aircraft engines and power generation gas turbines, combustion instability remains one of the foremost technical challenges in the development of next generation combustor technology. To that end, this work investigates the response of a swirling flow and swirl-stabilized flame to a transverse acoustic field is using a variety of high-speed laser techniques, especially high-speed particle image velocimetry (PIV) for detailed velocity measurements of this highly unsteady flow phenomenon. A description of the velocity-coupled transverse instability mechanism is explained with companion measurements describing each of the velocity disturbance pathways. Dependence on acoustic frequency, amplitude, and field symmetry is discussed. Significant emphasis is placed on the response of a swirling flow field to a transverse acoustic field. Details of the dynamics of the vortex breakdown bubble and the shear layers are explained using a wide variety of measurements for both non-reacting and reacting flow cases. This thesis concludes with an overview of the impact of this work and suggestions for future research in this area.

<p>The Vasa ship is not adequately supported. Measurements of the hull show that the ship deforms and rotate towards the port side. In addition, damages on the hull at support areas have been observed. The damages are due to high compressive loads. At damaged zones the support has been removed and the loads are thus transferred to adjacent support stanchions. In order to design an improved support, knowledge of the mechanical behaviour of the material is needed. In particular, radial modulus, strength and deformation mechanisms are of interest. In the present study, the mechanical behaviour of recent oak and oak from Vasa is studied. Furthermore, effects of PEG content, degradation and moisture on the properties of Vasa oak are investigated.</p><p>Oak is characterized by a very abrupt change from earlywood to latewood, where the latewood is much denser than earlywood. Also present in oak are large rays in the radial direction of the wood.</p><p>Small specimens were tested in compression using Digital Speckle Photography (DSP) in order to obtain strain fields of the whole specimen surface. This technique also provided data on failure mechanisms. Dynamic mechanical thermal analysis (DMTA) was performed to establish differences in moisture softening.</p><p>In radial compression, modulus and strength of Vasa oak are reduced by 50% compared with recent oak. A significant change of failure mechanism is observed for Vasa oak. In recent oak, failure in radial compression is by continuous folds of rays in the earlywood followed by continued plastic collapse of the earlywood layer. In Vasa oak rays show a more brittle fracture in each earlywood region. DMTA results indicate no effect on moisture softening of Vasa oak from presence of PEG although more work is needed to confirm this. Moisture adsorption for PEG-extracted Vasa oak is not significantly higher than for recent oak below 60% RH, suggesting that the extent of degradation of Vasa oak is limited. Vasa oak containing PEG is much more hygroscopic than PEG-extracted Vasa oak already at 50%. This difference is increasing with increasing relative humidity.</p>

Cette thèse est consacrée à l'étude des propriétés ergodiques du feuilletage horosphérique d'une variété géométriquement finie à courbure négative $M$. Un de nos principaux résultats est la classification des mesures transverses quasi-invariantes dont la dérivée de Radon-Nikodym est un cocycle höldérien fixé, associé à une mesure de Gibbs. À un tel cocycle, nous associons certaines moyennes sur les horosphères et montrons qu'elles s'équidistribuent vers la mesure de Gibbs correspondante lorsque $M$ est compacte ou convexe-cocompacte. Lorsqu'elle n'est ni compacte ni convexe-cocompacte, nous limitons l'étude aux moyennes associées à la mesure d'entropie maximale. Nous montrons qu'elles forment une suite tendue, ce qui, dans le cas des surfaces, nous permet d'obtenir leur équidistribution vers cette mesure d'entropie maximale. En corollaire, nous obtenons l'équidistribution des orbites du flot horocyclique d'une surface hyperbolique géométriquement finie mais de volume infini.

Avec le nombre croissant de services accessibles par l'utilisateur sur un terminal mobile, les caractéristiques multi-standards et la reconfigurabilité des chaînes radio-fréquences amènent des contraintes de conception de plus en plus importantes sur les composants RF, en particulier sur les filtres. La solution que nous proposons dans ce travail consiste à répartir la fonction de filtrage sur l'ensemble de l'émetteur RF. Ainsi, tout en gardant sa fonctionnalité première, chaque composant (filtre, duplexeur, amplificateur, antenne...) apporte une fonction de filtrage supplémentaire et/ou complémentaire qui permet, une fois intégré dans l'ensemble de la chaîne, de répondre aux gabarits imposés par les différents standards. Ce mémoire présente une première étude sur ce sujet. Il met en évidence la faisabilité du concept de filtrage réparti, avec la présentation de quelques architectures multi-fonctions : amplificateur-filtrant, diviseur de puissance filtrant, antenne filtrante...

D'origine biologique, le bois présente des propriétés fortement variables rendant sa caractérisation parfois complexe. Une meilleure connaissance du comportement rhéologique et en particulier des propriétés viscoélastiques du bois est nécessaire au développement ainsi qu'à l'amélioration des processus de transformation et de fabrication de matériaux à base de bois utilisant ces propriétés.<br />Ainsi, l'objectif majeur de cette thèse est de caractériser le comportement différé du bois vert dans des conditions thermiques et hydriques contrôlées. Un dispositif expérimental parfaitement adapté aux spécificités du bois, et en particulier à son anisotropie et son hygroscopie, a été développé. Cet appareil, appelé WAVET (Environmental Vibration Analyser for Wood) assure la détermination des propriétés viscoélastiques du bois par des essais harmoniques en flexion simple encastrement pour des fréquences comprises entre 5.10-3 Hz et 10 Hz. Dimensionné pour fonctionner jusqu'à des pressions de l'ordre de 5 bars, il permet d'effectuer des essais en milieu anhydre ou saturé pour des températures variant de 0°C à 140°C. <br />Les résultats expérimentaux collectés à l'aide de cet appareil sur diverses essences tempérées permettent de mettre en évidence l'influence de nombreux paramètres sur les propriétés rhéologiques et notamment au niveau de la température de ramollissement, à savoir l'essence, la direction matérielle, le type de bois (normal/réaction), ou encore la structure anatomique et macromoléculaire. <br />L'étude de la dégradation thermique du bois saturé en eau dévoile des modifications biochimiques importantes au sein de ce biopolymère. Il apparaît clairement que les propriétés de rigidité et d'amortissement du bois traité thermiquement en milieu aqueux évoluent en fonction de la sévérité du traitement et de la structure native des macromolécules constitutives.

Nanoparticle assemblies are of current interest as they are used in a wide variety of industrial and biomedical applications. This work presents two studies aimed at understanding the magnetization dynamics and interparticle interactions in nanoparticle assemblies and various types of ferrofluids. First, we studied the influence of varying strengths of dipolar interaction on the static and dynamic magnetic properties of surfactant-coated monodispersed manganese-zinc ferrite nanoparticles using reversible transverse susceptibility. We tracked the evolution of the anisotropy peaks with varying magnetic field, temperature, and interaction strength. The anisotropy peaks of weakly interacting particles appears as non-symmetric peaks and at lower fields in a unipolar transverse susceptibility scan. On the other hand, a strongly interacting particle system exhibits symmetric anisotropy peaks situated at higher field values. In the second study, we successfully synthesized stable ferrofluids out of high quality Fe 3O4 and CoFe2O4 nanoparticles. Such ferrofluids are excellent systems for the investigation of physics of relaxation phenomena in magnetic nanoparticles. Motivated by the need to understand their peculiar magnetic response, a comparative study on Fe 3O4 - and CoFe 2O4 -based ferrofluids was performed. We investigated cases in which particle blocking and carrier fluid freezing temperatures were close and far apart from each other. Our experimental results reveal the true origin of the glass-like relaxation peaks that have been widely observed in ferrofluids by many groups but remained largely unexplained. Contrary to the speculation of previous literature, we argue that the formation of the magnetic anomaly is due not only to the particle blocking but also to its correlation with the the carrier fluid freezing effects. It is also shown that the nature of these peaks is strongly affected by varying particle size and carrier fluid medium. Quantitative fits of the frequency dependent AC susceptibility to the Vogel-Fulcher scaling law clearly indicate that the blocking of magnetic nanoparticles in the frozen state significantly affects the interparticle dipole-dipole interaction, causing characteristic spin-glass-like dynamics. A clear correlation between the blocking and freezing temperatures emerges from our studies for the first time.

Dispersion has been shown to degrade miscibility in miscible displacements by lowering the concentration of the injected solute at the displacement fronts. Dispersion can also improve oil recovery by increasing sweep efficiency. Either way, dispersion is an important factor in understanding miscible displacement performance. Conventionally, dispersion is measured in the laboratory by fitting the solution of one-dimensional convection-dispersion equation (CDE) to the effluent concentration from a core flood. However dispersion is anisotropic and mixing occurs in both longitudinal and transverse directions. This dissertation uses the analytical solution of the two-dimensional CDE to simultaneously determine longitudinal and transverse dispersion. The two-dimensional analytical solution for an instantaneous finite volume source is used to investigate anisotropic mixing in miscible displacements. We conclude that transverse mixing becomes significant with large a concentration gradient in the transverse direction and significant local variation in flow directions owing to heterogeneity. We also utilized simulation models similar to Blackwell's (1962) experiments to determine transverse dispersion. This model coupled with the analytical solution for two-dimensional CDE for continuous injection source is used to determine longitudinal and transverse dispersivity for the flow medium. The validated model is used to investigate the effect of heterogeneity and other first contact miscible (FCM) scaling groups on dispersion. We derive the dimensionless scaling groups that affect FCM displacements and determine their impact on dispersion. Experimental design is used to determine the impact and interactions of significant scaling groups and generate a response surface function for dispersion based on the scaling groups. The level of heterogeneity is found to most significantly impact longitudinal dispersion, while transverse dispersion is most significantly impacted by the dispersion number. Finally, a mathematical procedure is developed to use the estimated dispersivities to determine a-priori the maximum grid-block size to maintain an equivalent level of dispersion between fine-scale and upscaled coarse models. Non-uniform coarsening schemes is recommended and validated for reservoir models with sets of different permeability distributions. Comparable sweep and recovery are observed when the procedure was extended to multi-contact miscible (MCM) displacements. / text