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In this thesis we investigate acoustic metamaterials and how they can influence incident sound waves. Specifically we are interested in the mathematical technique of transformation acoustics and how several simple examples of metamaterials, devised via transformation acoustics, can be realised physically. We present a simple methodology for optimising microstructure consisting of rods with elliptical cross sections arranged on a rectangular array in order to best fit the material properties required by a desired transformation. We present in detail three such examples: a one dimensional scaling, the beam shifter, and a right angle bend. We apply the one dimensional scaling to a quarter wavelength resonator, theoretically predicting that we are able to lower the active frequency of the resonator without increasing its physical length. This result is then confirmed experimentally. We provide further experimental evidence of the broad band nature of the microstructure and suggest how it could be applied as a one dimensional acoustic cloak. Finally we present numerical simulations of acoustic propagation through microstructure chosen to realise a beam shifter and right angle bend. These are devices associated with more complicated two dimensional transformations that may prove useful in the field of noise control and redirection.

Microalgae surpass the lipid productivity of terrestrial plants by several folds. However, due to the high moisture content and rigidity of algal cell walls, extraction of lipids from algae is still a significant technological challenge. In this research, an attempt was made to develop an algal lipid separation process which is energy efficient and effective. Algal related research requires a unique set of knowledge in areas of algae culturing, measuring cell concentration, harvesting, cell rupturing and lipid quantification. The first section of this thesis focuses on the state of the art as well as knowledge gained during preliminary studies. The second section of this thesis focuses on selecting a suitable measurement technique for quantification of algal cell disruption induced by homogenization. The selected method, hemocytometry was used to measure the degree of algal cell disruption induced by homogenization. In the third section, various homogenization treatments were evaluated for determining the fraction of cells disrupted during the homogenization. Finally, lipid extraction efficiency of homogenized algae was evaluated using different extraction solvents under different homogenization conditions. Preliminary research concluded that using cell counting is the most suitable technique to measure the effect of high pressure homogenization on concentrated microalgae. It was observed that higher pressure and increased number of passes increase the degree of cell disruption. Concentrated, non stressed samples show best response to homogenization. Out of the three solvents used for solvent extraction, chloroform gave a higher extraction yield at low intensity homogenizations. However at harsher homogenization levels the advantage of chloroform was not significant. Lipid extraction efficiency increases with increased levels of homogenization. However, a significant increase in lipid yields was not detected beyond 20 000 psi and 2 passes of homogenization treatment.

Reliable temperature time series are necessary to quantify how our world is changing. Unfortunately many non-climatic artefacts, known as inhomogeneities, affect these time series. When looking at real world data it is often not possible to distinguish between these non-climatic artefacts and true climatic variations that are naturally found in our world. Therefore, trying to remove the non-climatic artefacts with complete confidence is problematic, but leaving them in could lead to misinterpretation of climate variations. In creating realistic, homogeneous, synthetic, daily temperature series the truth can be known about the data completely. Known, created inhomogeneity structures can be added to these series, allowing the distinguishing between true and artificial artefacts. The application of homogenisation algorithms to these created inhomogeneous data allows the assessment of algorithm performance, as their returned contributions are being compared to a known standard or benchmark, the clean data. In this work a Generalised Additive Model (GAM) was used to create synthetic, clean, daily temperature series. Daily data pose new challenges compared to monthly or annual data owing to their increased variability and quantity. This is the first intercomparison study to assess homogenisation algorithm performance on temperature data at the daily level. The inhomogeneity structures added to the clean data were created by perturbing the inputs to the GAM, which created seasonally varying inhomogeneities, and by adding constant offsets, which created constant inhomogeneities. Four different regions in the United States were modelled, these four regions are climatically diverse which allowed for the exploration of the impact of this on homogenisation algorithm performance. Four different data scenarios, incorporating three different inhomogeneity structures, were added and evaluations also investigated how these impacted algorithm performance. Eight homogenisation algorithms were contributed to this study and their performance was assessed according to both their ability to detect change points and their ability to return series that were closer to the clean data than they were on release. These evaluations sought to aid the improvement of these algorithms and enable a quantification of the uncertainty remaining in daily temperature data even after homogenisation has taken place. Evaluations were also made of the benchmarks as it was important that benchmark weaknesses were taken into account. It was found that more climatologically diverse regions were harder to model and less climatologically diverse regions were easier to homogenise. Station density in a network and the presence of artificial trend inhomogeneities did not impact algorithm performance as much as changes in autocorrelations did, and the latter area was an area that most algorithms could improve on. This work feeds into the larger project of the International Surface Temperature Initiative which is working on a wider scale and with monthly instead of daily data.

Flexible pipes are essential components in the subsea oil and gas industry, where they are used to convey fluids under conditions of extreme external pressure and (often) axial load, while retaining low bending stiffness. This is made possible by their complex internal structure, consisting of unbonded components that are, to a certain extent, free to move internally relative to each other. Due to the product's high value and high cost of testing facilities, much e ort has been invested in the development of analytical and numerical models for simulating flexible pipe behaviour, which includes bulk response to various loading actions, calculation of component stresses and use of this data for component fatigue calculations. In this work, it is proposed that the multi-scale methods currently in widespread use for the modelling of composite materials can be applied to the modelling of flexible pipe. This allows the large-scale dynamics of an installed pipe (often several kilometers in length) to be related to the behaviour of its internal components (with characteristic lengths in millimeters). To do this, a formal framework is developed for an extension of the computational homogenisation procedure that allows multiscale models to be constructed in which models at both the large and small scales are composed of different structural elements. Within this framework, a large-scale flexible pipe model is created, using a two-dimensional corotational beam formulation with a constitutive model representative of flexible pipe bulk behaviour, which was obtained by further development of a recently proposed formulation inspired by the analogy between the flexible pipe structural behaviour and that of plastic materials with non-associative flow rules. A three-dimensional corotational formulation is also developed. The model is shown to perform adequately for practical analyses. Next, a detailed finite element (FE) model of a flexible pipe was created, using shell finite elements, generalised periodic boundary conditions and an implicit solution method. This model is tested against two analytical flexible pipe models for several basic load cases. Finally, the two models are used to carry out a sequential multi-scale analysis, in which a set of simulations using the detailed FE model is carried out in order to find the most appropriate coefficients for the large-scale model.

Dans cette thèse, nous proposons de développer un outil de conception pour la mise en forme des bouteilles en PET par le procédé d'étirage-soufflage. Nous avons implémenté un logiciel de simulation numérique qui utilise une méthode meshless : la méthode des éléments naturels contraints (C-NEM). Pour alimenter le logiciel nous avons modélisé le comportement mécanique du PET par un modèle non linaire anisotrope. Pour modéliser le comportement du PET nous avons réalisé une série d’essais qui nous a permis de lier les propriétés macroscopiques à l'état de la microstructure Une fois la simulation d'étirage-soufflage effectuée, nous connaissons la géométrie de la bouteille ainsi que la description de sa microstructure : orientation et cristallinité. A partir du calcul précédent nous pouvons, à l'aide de la micromécanique linéaire, calculer la résistance de la bouteille finie à diverses sollicitations / In this thesis, we propose to develop a tool to design the stretch blow-molding process of PET bottles. We have implemented a software of numerical simulation which uses a meshless method : the constrained natural element method (C-NEM). In order to provide this software, we modeled the mechanical behaviour of PET by a non linaire anisotropic model. To model the behavior of PET we carried out a series of tests that allowed us to link the macroscopic properties to the state of the microstructure. Once the simulation of the stretch blow made, we know the geometry of the bottle and the description of its microstructure : orientation and crystallinity. From the previous calculation we can, using linear micromechanic, calculate the resistance of the bottle over to various loads

In this thesis we study elliptic PDEs and PDE systems with e-pcriodic coeffi- cients, for small E, using the theory of two-scale homogenisation. We study a class of PDEs of partially degenerating type: PDEs with coefficients that are not uniformly elliptic with respect to E, and become degenerate in the limit E -t O. We review a recently developed theory of homogenisation for a general class of partially degenerating PDEs via the theory of two-scale convergence, and study two such problems from physics. The first problem arises from the study of a linear elastic composite with periodically dispersed inclusions that are isotropic and (soft' in shear: the shear modulus is of order E2. By passing to the two- scale limit as E -t 0 we find the homogenised limit equations to be a genuinely two-scale system in terms of both the macroscopic variable x and the micro- scopic variable y. We discover that the corresponding two-scale limit solutions must satisfy the incompressibility condition in y and therefore the composite only undergoes microscopic deformations when a (microscopically rotational' force is applied. We analyse the corresponding limit spectral problem and find that, due to the y-incompressibility, the spectral problem is an uncoupled two-scale prob- lem in terms of x and y. This gives a simple representation of the two-scale limit spectrum. We prove the spectral compactness result that states: the spectrum of the original operator converges to the spectrum of the limit operator in the sense of Hausdorff. The second problem we study is the propagation of electro- magnetic waves down a photonic fibre with a periodic cross section. We seek solutions to Maxwell's equations, propagating down the waveguide with wave number k E2-close to some (critical' value. In this setting, Maxwell's equations are reformulated as a partially degenerating PDE system with z-periodic coeffi- cients. Using the theory of homogenisation we pass to the limit as E -t 0 to find a non-standard two-scale homogenised limit and prove that the spectral compact- ness result holds. We finally prove that there exist gaps in the limit spectrum for two particular examples: a one-dimensionally periodic 'multilayer ' photonic crystal and a two-dimensionally periodic two-phase photonic crystal with the in- clusion phase consisting of arbitrarily small circles. Therefore, we prove that these photonic fibres have photonic band gaps for certain k.

El objetivo de la tesis fue evaluar la aptitud tecnológica de la leche tratada por ultra alta presión homogenización (UHPH) como alternativa a la pasteurización en el tratamiento de higienización de la leche para la obtención de queso fresco. Dicho objetivo se llevó a cabo mediante (a) la determinación de las condiciones óptimas de presión y temperatura, estudiando los efectos de la UHPH en las propiedades de coagulación, (b) la identificación de cambios a nivel de las interacciones proteicas de la cuajada así como de la composición proteica de la membrana del glóbulo graso, (c) la evaluación de la aptitud quesera de la leche produciendo quesos frescos a escala piloto, (d) la determinación de la vida útil mediante el seguimiento de la evolución durante la conservación en refrigeración de la microbiota, composición y bioquímica de los quesos, (e) la evaluación de la textura, reología, microstructura y color de los quesos así como la aceptabilidad en su consumo mediante un análisis sensorial.La utilización de la UHPH con una sola etapa y presiones superiores a 200 MPa resultó en una mejora de las propiedades de coagulación. Las condiciones óptimas de tratamiento fueron establecidas como 300 MPa y 30 ºC. La UHPH favoreció las uniones vía calcio de las caseínas y las interacciones hidrofóbicas tanto de caseínas como de proteínas del suero en la cuajada, inhibiendo las interacciones vía puentes de hidrógeno. Al reducir significativamente el tamaño de los glóbulos grasos, la UHPH provocó la adsorción de proteínas de la leche a nivel de la membrana de los glóbulos grasos. La UHPH empeoró en cierta medida el corte de la cuajada produciéndose más finos de quesería por desmenuzado de los granos de cuaja e insuficiente cohesión de los granos. Los quesos frescos producidos con leche tratada por UHPH presentaron mayor vida útil (19 vs. 13 días). El crecimiento de lactococos fue potenciado durante los primeros días de la conservación. Por lo contrario, no se detectaron lactobacilos durante todo el período de almacenamiento. El crecimiento de levaduras y hongos fue parcialmente inhibido resultando en recuentos más bajos al final de la vida útil de los quesos. Durante el almacenamiento, los quesos producidos con leche tratada por UHPH presentaron menor desuerado que aquellos producidos con leches tratadas convencionalmente, resultando en contenidos más altos de humedad y sal. Aunque no se observaron diferencias en el contenido en grasa y proteínas, los quesos UHPH presentaron niveles más bajos de proteólisis y lipólisis. Así mismo, los perfiles en ácidos grasos libres fueron significativamente diferentes. La oxidación lipídica, detectada como el mayor inconveniente, resultó en un gran número de compuestos volátiles tales como aldehídos y cetonas cuya presencia explicó la aparición de flavores defectuosos detectados por algunos de los catadores. Finalmente, la UHPH resultó en quesos más firmes, menos deformables, con menor sensación acuosa en boca y más blancos. Estos cambios podrían atribuirse a los efectos de la UHPH en los glóbulos grasos. A excepción de la escasa sensación acuosa en boca, los catadores calificaron como mejores las características estructurales de los quesos frescos.En conclusión, los resultados obtenidos revelaron que la UHPH es una tecnología prometedora para el tratamiento de la leche de quesería ya que puede alargar la vida útil y mejorar algunas de las características tales como la textura y la microestructura de los quesos frescos. Al solventar los problemas de oxidación mediante la modificación de algunas piezas metálicas del equipo, se espera obtener quesos frescos con una calidad en el sabor similar o incluso superior a la de los quesos producidos con leche tratada convencionalmente. / Among the emerging technologies for minimal food-processing, ultra-high pressure homogenisation (UHPH) is a promising technology for liquid foods such as milk owing to the fact that (a) it is a continuous process, (b) it performs two separated processes at once, i.e., pasteurisation and homogenisation, (c) it can deal with volumes usual at pilot-scale with a view to go for larger volumes such as those at production-scale, (d) it can provoke high temperatures but at such a short time that heat effect can be minimised, and finally, (e) it requires the same equipments as a common homogeniser. UHPH, as a food technology alternative to conventional heat-treatments, is currently investigated in a wide range of liquid foods. Research not only aims at evaluating the effects on the liquid food itself but also on the capacity in obtaining manufactured products and the quality of the final products. The present thesis aimed at assessing the suitability of UHPH as an alternative to conventional processes for the manufacture of starter-free fresh cheeses through (a) determination of optimal pressure and temperature conditions for cheese production, by studying the effects of UHPH on the rennet coagulation properties, (b) identification of changes at the nature of protein interactions and the protein composition of the milk fat globule membrane (MFGM), in order to better understand the overall effect of UHPH on the coagulation and cheese-making properties of milk, (c) evaluation of the suitability of UHPH-treated milk for the manufacture of fresh cheeses, by producing starter-free fresh cheeses at a pilot-scale, (d) determination of the shelf life of produced cheeses, by following their microbiological, compositional and biochemical evolution during cold storage, (e) evaluation of the texture, rheology, microstructure and colour of produced cheeses, and their aptness for consumption through a sensory analysis.Rennet coagulation properties of milk were enhanced by single-stage UHPH over 200 MPa, and optimal UHPH conditions were set to 300 MPa and 30 ºC. UHPH increased calcium-bonding of caseins within curds, impaired hydrogen bonding and favoured hydrophobic interactions. Moreover, by greatly reducing milk fat globule size, UHPH provoked the adsorption of milk proteins onto the MFGM. UHPH impaired in some extent curd cutting due to crumbling, improper matting and poor grain cohesion. Cheeses from UHPH-treated milk showed longer microbiological shelf life (19 vs. 13 days). Lactococci growth was enhanced at an early stage of the storage period but lactobacilli were not detected. The growth of yeasts and moulds was partly inhibited resulting in lower counts at the end of their shelf life. During storage, UHPH cheeses expelled less whey than those from conventionally treated, resulting in higher moisture and salt contents. Although fat and protein contents on a dry basis were not affected, lower levels of proteolysis and lipolysis were observed. Moreover, free fatty acid profiles greatly differed. Oxidation was found to be the major drawback resulting in a great number of volatile compounds, e.g., aldehydes and ketones, which presence explained off-flavours detected by some panellists. Finally, UHPH treatment of milk resulted in firmer, less deformable, with lower water-mouth feeling, and whiter fresh cheeses. Such changes could be attributed to the effects on the fat globules. Except for the dry mouth-feeling, the sensory panel described the structural attributes of cheeses from UHPH-treated milk as their best characteristics.In conclusion, these results show that UHPH is a promising technology as treatment of milk for the manufacture of fresh cheese by increasing their shelf life and improving some of their characteristics such as texture and microstructure. By solving the oxidation problems through the modification of some metal pieces of the UHPH equipment, fresh cheeses with similar or even higher flavour quality are expected to be obtained with UHPH-treated milk than with conventionally treated milk.

Miniemulsion technology is attracting increasing interest for the preparation of nano-size particles. However, the barrier to industrialising miniemulsion-based products is the lack of an energy efficient and scalable homogenisation device. Current laboratory techniques consist of batch units, however trends are leaning towards developing continuous processes. The objective of the work presented here is to investigate the use of the rotor-stator (RS) and static mixers (SM) as homogenisation devices and ultimately develop a continuous emulsification/polymerisation process for the preparation of miniemulsions. Initially we investigated the RS as a homogenisation device and found that we were able to generate droplets ranging from 300 nm to 2 μm, at industrially pertinent solids content. Subsequently, we investigated the use of SM and compared their performance in terms of mean droplet size evolutions with the rotor-stator. We were able to generate droplets < 200 nm in size and polymerise them in a stable fashion. All the available emulsification devices were then compared in terms of power/energy consumption, droplet size distributions and shear rates. It was observed that with energy costs being of similar orders of magnitude, SM imposed less shear, produced relatively narrow distributions and were better adapted to scale-up, making them the optimal choice for miniemulsification. Energy savings were increased by reducing coalescence during the emulsification step by using in situ generated surfactants, ultimately reducing emulsification time. Neutralising a water-soluble base with an oil-soluble acid almost instantaneously generates in situ surfactants at the oil-water interface. The reduction in emulsification time was partially attributed to the elimination of the relatively slow adsorption step typical of preformed surfactants. These results were used to show that emulsifying in situ formulations at moderate flow rates in line with SMX mixers can substantially reduce emulsification time from 30 minutes, with preformed surfactants, to ~30 seconds. With such a rapid emulsification step, it was possible to test the feasibility of the continuous emulsification process followed by polymerisation in a tubular reactor. Comparing this process with a batch operation, similar results for the ratio of NP/ND and conversion were obtained, but the continuous process was accomplished in a single step. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-04-19 03:32:08.766

Les matériaux céramiques présentent généralement des propriétés mécaniques très intéressantes pour la réalisation de blindages. Ce sont des matériaux très durs et pourtant légers. Les plaques de blindages en céramique sont classiquement mises en forme par pressage à haute température de poudres, ce qui limite la taille et la forme des réalisations tout en impliquant un coût élevé. Une alternative pour produire ces pièces est le moulage d’un composite constitué de particules de céramiques dans une matrice époxy. Ce procédé permet de réduire le coût des pièces tout en autorisant des géométries plus complexes et des dimensions plus importantes.Le comportement mécanique de ce type de matériau dépend de multiples paramètres de conception : propriétés mécaniques des constituants (matrice polymère et particules céramiques), proportion volumique des deux phases, taille et distribution spatiale des particules ou encore l’adhésion entre les constituants. L’objectif de la thèse est d’évaluer l’influence de ces paramètres sur les propriétés d’usage du matériau. Pour ce faire, une analyse multi-échelle du matériau sous sollicitations quasi-statique et dynamique est réalisée.Plus précisément, les propriétés statiques et dynamiques du composite à renforts particulaires ont été déterminées pour différentes combinaisons de ces paramètres de conception. En particulier, le mécanisme de décohésion particule/matrice a été spécifiquement étudié. Les approches de Modèles de Zone Cohésive (CZM) et de Mécanique de la Rupture Finie (FFM) ont été utilisées pour modéliser ce phénomène et un fort effet de taille des particules a été observé. / Ceramics have extensively been used for ballistic protection in the last decades. The combination of their mechanical properties makes them very interesting for armouring. Indeed, they exhibit a high hardness, large compression strength, high stiffness and low density. Ceramic armouring plates are commonly manufactured through a sintering process, where ceramic powders are pressed at high temperatures. This manufacturing process tends to limit the size and shape of components and imparts high costs. On the other hand, moulding using a polymer matrix composite provides an alternative process for developing lower cost parts whilst accommodating increased complexity of geometry and size.However, the mechanical behaviour of such a material is not completely known and depends on multiple design parameters: the mechanical properties of the phases, their volume fraction, the size and spatial distributions of the particles, and the adhesion between the components. The objective of the thesis is to evaluate the influence of the main morphological parameters on the overall mechanical properties, emphasising the influence of the particle/matrix adhesion. To do so, both numerical and experimental multiscale analyses of the material under quasi-static and dynamic loadings were carried out.More precisely, static and dynamic properties of the particle-reinforced composite have been determined for different combinations of the design variables. In particular, attention has been dedicated to the particle/matrix decohesion mechanism. Cohesive zone models (CZM) and Finite Fracture Mechanics (FFM) approaches were used to model this phenomenon and a strong effect of the particle size on debonding was observed.