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.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. / Increasing global energy demand as well as air quality concerns have in recent years led to the search for alternative clean fuels to replace fossil fuels. One such alternative is the blending of petrol (gasoline) with ethanol, which has numerous advantages such as ethanol’s ability to act as oxygenate thus reducing the carbon monoxide emissions from the exhaust of internal combustion engines of vehicles. However, the hygroscopic nature of ethanol is a major concern in obtaining a perfectly homogenized petrol-ethanol fuel. This problem has led to the study of ways of homogenizing the petrol-ethanol mixtures. Therefore, this thesis aimed at enhancing the homogenization of petrol-ethanol mixture. Ethanol concentration in ethanol-water mixture plays a key role in enhancing the homogenization of the fuel, thus the bioethanol employed in this study was dehydrated with silica gel using ultrasonication-enhanced adsorption. Afterwards, the dehydrated ethanol was used in studying the homogenization of the fuel blend. Water removal from the bioethanol using ultrasonication-enhanced adsorption shows a 28% increase when compared to the water removal using magnetic-stirring-enhanced adsorption, During ultrasonication-enhanced adsorption, the estimated adsorption enthalpy was – 1 592.82 J/mol (exothermic) and the entropy was -5.44 J/ K mol, indicating a non-ordered loading of water molecules in the adsorption site. In addition, a modified pseudo second order kinetic model given by was proposed for the ultrasonication-enhanced adsorption process. Effect of temperature during ultrasonication-enhanced adsorption was found to be directly proportional to the amplitude and the pulse rate. However, increase in the amplitudes at lower pulse rates resulted in better cavitation, and hence better adsorption. Furthermore, during phase behavior of ethanol-petrol blend, volume fractions of ethanol and petrol were studied with respect to t the depth within the storage container to confirm homogenization of the blend and time of storage. The binodal curve of the ternary diagram shows an increase of homogeneous region indicating an improved interaction between water and petrol. Therefore, the interesting results regarding the homogenization of the fuel blends resulted from using ultrasonication-enhanced blending were very promising, and could be a platform upon which further research efforts could be built on. The concentration distribution in the reactor showed proof of cavitation formation since in both directions, the variation of concentration with both time and distance was found to be oscillatory. On comparing the profiles in both directions, the concentration gradient, diffusion flux, and energy and diffusion rates were found to be higher in the vertical direction compared to the horizontal direction. It was therefore concluded that ultrasonication creates cavitation in the mixture which enhances mass transfer and mixing of ethanol and petrol. The horizontal direction was found to be the diffusion rate limiting step which proposed that the blender should have a larger height to diameter ratio. It is however recommended that further studies be done on the rate-limiting step so as to have actual dimensions of the reactor. Testing of the blended fuel in internal combustion engine showed an optimal performance of this fuel at 60 % volume ethanol content with higher fuel power. The results of fuel consumption and emissions (such as CO2 and CO) trends confirm various reports in literature on the performance of ethanol/petrol blended fuel.

Tandis que l'emploi des techniques de renforcement des structures s'est largement généralisé et diversifié, les méthodes de calcul et de simulation du comportement de telles structures, par nature composites, exigent encore de nombreux développements, tant sur le plan théorique (recours aux techniques d'homogénéisation), que numérique. Ainsi, dans le domaine du génie civil, une modélisation qualifiée de multiphasique a été récemment proposée pour les ouvrages en sols renforcés par inclusions linéaires continues souples (terre armée, géotextiles, etc.) ou raides (inclusions "rigides", pieux, etc.).Ce présent travail a pour but de développer une méthode de calcul rapide et fiable, à travers cette modélisation multiphasique, pour le dimensionnement vis-à-vis de sollicitations dynamiques dans le cas où l'ouvrage est renforcé par un groupe de pieux ou d'inclusions rigides, en se restreignant au cas de l'élastodynamique, c'est à dire d'un comportement élastique linéaire des différents constituants du sol renforcé. Il consiste d'une part à analyser la propagation d"ondes sismiques au sein du massif renforcé et d'autre part à mettre en oeuvre un outil numérique basé sur la méthode des éléments finis pour déterminer les fonctions d'impédance d'un sol renforcé par un réseau régulière d'inclusions vertical. D'où les effets de l'interaction sol-inclusions, ainsi de flexion et de cisaillement des inclusions sont pris en compte. / The reinforcement of structures in becoming an increasingly used technique, although the simulation and design of such structures still require many developpements both in theory (use of homogenization techniques) and numeric. Thus, in the civil engineering domains, a qualified multiphase model has been recently proposed for soil reinforced by continuous linear inclusions flexible (reinforced earth structures, geotextiles, etc. ) or stiff (rigid inclusions, piles, etc.).The present work aims to develop a fast and reliable method of calculation, through such a multiphase model, for the design with dynamic load applied on reinforced soil by a group of piles or rigid inclusions, by restricting the elastodynamic case, that is a linear elastic behavior for both constituents. It consists firstly to analyze the propagation of seismic waves in the solid reinforced and secondly to implement a fem.-based numerical code for determining the impedance functions of a reinforced soil by a regular vertical network inclusions. In this model, the interacton soil-inclusions and also the shear and flexural effects of inclusions are both taken into account.

Em áreas que demandam componentes de alto desempenho como a indústria automotiva, aeronáutica e aeroespacial, a otimização do desempenho dinâmico de estruturas é buscada através de diferentes abordagens, como o projeto de materiais específicos à aplicação, ou otimização estrutural topológica. Em particular, o método de otimização estrutural evolucionária bidirecional BESO (Bi-directional Evolutionary Structural Optimization) tem sido utilizado no projeto simultâneo de estruturas hierárquicas, o que significa que o domínio estrutural consiste não somente na estrutura como também na topologia microestrutural dos materiais empregados. O objetivo desse trabalho consiste em aplicar a metodologia BESO na resolução de problemas multiescala bidimensionais visando à maximização da frequência fundamental de estruturas, assim como a minimização de sua resposta quando sujeitas a excitações forçadas numa determinada faixa de frequências. O método da homogeneização é introduzido e aplicado na integração entre as diferentes escalas do problema. Em especial, o modelo de interpolação material é generalizado para o uso de dois materiais no caso de otimização da resposta no domínio da frequência. A metodologia BESO foi aplicada a casos de otimização tomando como domínio estrutural somente a macroescala (projeto estrutural), somente a microescala (projeto material), assim como ambas as escalas concomitantemente (projeto multiescala). Para os casos estudados, a redistribuição de material na macroescala levou a resultados melhores em relação à otimização que modifica a microestrutura. Para a maximização da frequência fundamental, a otimização multiescala obteve os melhores resultados, já para a minimização da resposta em frequência, a otimização somente na macroescala se mostrou mais eficiente. / In areas which demand high performance components, such as automotive, aeronautics and aerospace, the design of application deppendent materials and structural topology optimization are two approaches used in order to optimize structures‟ dynamic behaviour. In particular, the Bi-directional Evolutionary Structural Optimization (BESO) method has been applied to the simultaneous project of hierarchical structures, meaning that the project‟s domain consists not only on the structure on the macroscale, but also on the representative volume element (RVE) associated with the microstructure of the employed materials. The objective of this work is to apply the BESO method in order to solve multiscale bidimensional problems, more specifically, topology optimization problems for fundamental frequency maximization and minimization of the response in the frequency domain under harmonic excitation. The homogenization method is introduced and used to integrate the macro and microscales considered. Furthermore, the material interpolation model in generalized for two material domains in the response minimization problem. The BESO method was applied to optimizations problems where the structural domain was eiher the macrostructure (structural project), microstructure (material project), or both scales simultaneously (multiscale project). In general, material distribution at the macroscale lead to better results in comparison to optimization at the microscale. For fundamental frequency maximization, the multiscale approach obtained better results, while for minimization of the frequency response the results were optimal when the structural domain was restricted to the macrostructure.

Neste trabalho foi estudada a influência da homogeneização a alta pressão na retenção de antocianinas e na inativação da atividade enzimática da peroxidase e polifenoloxidase presentes naturalmente na polpa de açaí. Este trabalho foi dividido em duas etapas. Na primeira, a polpa de açaí teve suas propriedades físicoquímicas e comportamento reológico determinados. Na segunda etapa, a polpa de açaí passou por um pré-tratamento de filtração e posteriormente, foi tratada por homogeneização a alta pressão, com pressões de (100, 200 e 300) MPa e temperaturas de entrada do produto de (20 e 30) °C. Amostras da polpa de açaí processada foram analisadas quanto às propriedades físico-químicas, composição centesimal, teor de antocianinas, atividade antioxidante, teor de fenólicos totais, atividade enzimática (peroxidase e polifenoloxidase) e análise de cor. Os dados experimentais reológicos das curvas com taxas de cisalhamento ascendente e decrescente foram bem ajustados ao modelo Herschel-Bulkley. Esses dados apresentaram uma curva de histerese em sentido anti-horário, denotando um comportamento anti-tixotrópico. A polpa de açaí, utilizada na segunda parte deste trabalho, apresentou teor de sólidos totais variando entre (11,44 e 14,63) %, teor de antocianinas monoméricas (Am) (2,20 e 2,54) mg/g extrato seco, atividade antioxidante (AA) (7,68 e 8,27) mol TE/g extrato seco; fenólicos totais (FT) (25,51 e 34,57) mg GAE/g extrato seco e atividade enzimática da peroxidase (POD) entre (1,02E-2 e 3,73E-2) U/s.oBrix.g extrato seco e da polifenoloxidase (PFO) (2,87E-2 e 7,59E-2) U/s.oBrix.g extrato seco. O tratamento de homogeneização a alta pressão preservou 97,5 % do teor de antocianinas monoméricas presentes na polpa de açaí tratada após filtração. A enzima PFO apresentou uma inativação máxima de 47 % para a polpa de açaí tratada a 300 MPa; a máxima inativação obtida para a POD foi de 43,7 %, para tratamento a 300 MPa e temperatura de entrada do produto de 20 °C. O tratamento de homogeneização a alta pressão é uma alternativa ao tratamento térmico por reter as antocianinas e reduzir a atividade enzimática da POD e PFO. / The effect of high pressure homogenization on the stability of anthocyanins and on the inactivation of enzymatic activity of peroxidase and polyphenoloxidase from açaí pulp was studied in this work. Experimental investigations were carried out in two steps. Firstly, açaí pulp had its physicochemical properties and rheological behavior determined. Secondly, açaí pulp was pretreated through filtration and processed through high pressure homogenization at pressures of (100, 200 and 300) MPa and inlet product temperatures of (20 and 30) °C. The processed açaí pulp had its composition and physicochemical properties determined: analyses such as anthocyanin content, antioxidant activity, content of phenolic compounds, enzymatic activity (peroxidase and polyphenoloxidase) and color analysis were carried out. The experimental rheological data for increasing and decreasing shear rates were well correlated by the Herschel-Bulkley model. These data showed a counterclockwise hysteretic loop that indicates an anti-thixotropic behavior. The açaí used in the second part of this work presented a total solid content ranging from (11.44 and 14.63) %, total monomeric anthocyanins (Am) (2.20 and 2.54) mg / g dry matter, antioxidant activity (AA) (7.68 and 8.27) mol TE / g dry matter, total phenolic content (FT) (25.51 and 34.57) mg GAE / g dry matter, enzymatic activity of peroxidase (POD) from (1.02 E-2 and 3.73 E-2) U/s.oBrix.g dry matter and enzymatic activity of polyphenoloxidase (PFO) from (2.87 E-2 and 7.59 E-2) U/s.oBrix.g dry matter. The use of high pressure homogenization allowed the recovery of 97.5% of monomeric anthocyanins present in filtered açaí pulp. The enzyme PFO underwent a maximum inactivation of 47% for açaí pulp treated at 300 MPa, regardless of inlet temperature of the product; the maximum inactivation achieved for POD was 43.7%, for the treatment at 300 MPa and inlet temperature of the product of 20 °C. The treatment of high pressure homogenization is an alternative to heat treatment because it retains the anthocyanins and inactivates the enzymatic activity of POD and PFO.

The better understanding of the behavior of emulsions and suspensions is important in many applications. In general, emulsions allow the delivery of insoluble agents to be uniformly distributed in a more efficient way. At the same time suspensions of rigid particles are used as “smart materialsâ€� as their properties can be changed by the interaction with a magnetic or electric field. In the first part of the talk we consider a periodic emulsion formed by two Newtonian fluids in which one fluid is dispersed under the form of droplets of arbitrary shape, in the presence of surface tension. We assume the droplets have fixed centers of mass and are only allowed to rotate. We are interested in the time-dependent, dilute case when the characteristic size of the droplets aε, of arbitrary shape, is much smaller than the period length ε. We obtain a Brinkman type of fluid flow for the critical size aε = O(ε3) as a replacement of the Stokes flow of the emulsion. Additionally, using Mosco convergence and semigroup theory we extend the convergence to the parabolic case. For the case when the droplets convect with the flow, it can be shown again using Mosco-convergence that, as the size of the droplets converges to zero faster than the distance between the droplets, the emulsion behaves in the limit like the continuous phase and no “strangeâ€� term appears. Moreover, we determine the rate of convergence of the velocity field for the emulsion to that of the velocity for the one fluid problem in both the H1 and L2 norms. Additionally, a second order approximation is determined in terms of the bulk and surface polarization tensors for the cases of uniform and non-uniform surface tension. The second part of the talk is devoted to the study of MR fluids. We consider a suspension of rigid magnetizable particles in a non-conducting, viscous fluid with an applied external magnetic field. Thus, we use the quasi-static Maxwell equations coupled with the Stokes equations to capture the magnetorheological effect. We upscale using two scale asymptotic expansions to obtain the effective equations consisting of a coupled nonlinear system in a connected phase domain as well as the new constitutive laws. The proposed model generalizes the model of Rosenweig by coupling the velocity of the fluid and the magnetic field intensity. Using the finite element method we compute the effective coefficients for the MR fluid. We analyze the resulting MR model for Poiseuille and Couette flows and compare with experimental data for validation.

This project presents the homogenization analysis for a static contact problem with slip dependent friction between an elastic body and a rigid foundation. The homogenization for the static eigenvalue problem associated to this model is studied. We prove that the eigenvalues are of order epsilon. We obtain the limit problem for the contact model. The analysis is carried out by using the Gamma-convergence theory.

Submitted by RODRIGO YOKOYAMA XAVIER null (rodyok@hotmail.com) on 2017-02-16T01:10:07Z No. of bitstreams: 1 Dissertação Mestrado - Rodrigo Yokoyama Xavier.pdf: 6767206 bytes, checksum: 36a0ac2db721a2114f623ea26fe9f582 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2017-02-22T17:27:06Z (GMT) No. of bitstreams: 1 xavier_ry_me_guara.pdf: 6767206 bytes, checksum: 36a0ac2db721a2114f623ea26fe9f582 (MD5) / Made available in DSpace on 2017-02-22T17:27:06Z (GMT). No. of bitstreams: 1 xavier_ry_me_guara.pdf: 6767206 bytes, checksum: 36a0ac2db721a2114f623ea26fe9f582 (MD5) Previous issue date: 2017-01-30 / O nível de qualidade de peças produzidas a partir de grandes lingotes está intimamente relacionado à qualidade dos lingotes em si. Dentre os diversos defeitos inerentes ao processo de solidificação, destacam-se as microssegregações de elementos de liga, que causam uma deterioração nas propriedades do produto final. Uma maneira de reduzir o dano causado pela microssegregação é através do Tratamento Térmico de Homogeneização, este por sua vez demanda elevados tempos de processo, elevando custos e tempos de fabricação. Uma das formas de reduzir os tempos de homogeneização, uma vez que este apresenta caráter difusional, é através da redução do espaçamento interdendrítico. Neste trabalho foi analisada a influência da deformação plástica como forma de reduzir o espaçamento entre dendritas no tratamento térmico de homogeneização. Para tal fim, utilizou-se um lingote fundido em aço ferramenta de composição química similar ao AISI A2. As amostras foram retiradas do núcleo do lingote no estado bruto de solidificação e sofreram deformações de 0,6 e 1,3 através do processo de laminação a quente, sendo temperadas em água na sequência. Após laminadas as amostras passaram por um tratamento térmico de homogeneização na temperatura de 1200°C por 8h ou 16h e foram novamente temperadas em água. As análises foram feitas através de Microscopia Óptica, Dureza Vickers, Difratometria de Raios-X e Microscopia Eletrônica de Varredura. Foi observado em todas as amostras a presença de microrechupes, e uma microestrutura composta predominantemente por dendritas oriundas da solidificação, identificadas pela fase martensítica, envoltas por uma matriz formada de austenita retida, contendo carbonetos e sulfetos. Com a deformação plástica foi possível quebrar a estrutura dendrítica a aproximar as regiões segregadas das não segregadas. O tratamento térmico por um tempo de 8h não foi suficiente para homogeneizar a microestrutura e reduzir as microssegregações, independentemente do estado de deformação das amostras. O tratamento térmico por 16h apresentou os melhores resultados em relação à homogeneidade química, sendo tanto melhor o resultado quanto maior a deformação imposta às amostras. / The quality of pieces produced from large ingots is closely related to the quality of ingots itself. Among the various defects inherent to the solidification process, there is the microsegregation of alloying elements, causing a deterioration in the properties of the final product. One way to reduce the damage caused by microsegregation is through the homogenization heat treatment, this in turn demands long time of process, increasing costs and lead-times for manufacture. One way to reduce the homogenization time, since it has a diffusive character, is by reducing the interdendritic spacing. In this study was analyzed the influence of plastic deformation as a mean to reduce the spacing between dendrites in the homogenization heat treatment. For this purpose it was used a cast ingot of chemical composition similar to the AISI A2 tool steel. Samples were cut from the ingot center in the as-cast state and suffered deformations of 0.6 and 1.3 through the hot rolling process and quenched in water in the sequence. After rolling the samples passed through a homogenization heat treatment at a temperature of 1200°C for 8h and 16h and again were quenched in water. Analyses were performed by Optical Microscopy, Vickers Hardness, X-Ray Diffractometry and Scanning Electron Microscopy. It was observed in all samples the presence of microcavities, and a microstructure consisting predominantly by solidifications dendrites identified by a martensitic phase, involved by a retained austenite matrix containing carbides and sulfides. The plastic deformation broke the dendritic structure, and approached the segregated regions to the non-segregated regions. The heat treatment for 8h was not sufficient to homogenize the microstructure and reduce the microsegregation, independently of the deformation state of the samples. The heat treatment for 16h presented the best results in relation to the chemical homogeneity, and the better the result as the greater the deformation imposed on the samples.

Ces travaux se placent dans le cadre de l'étude des propriétés mécaniques des architectures à renforcement tridimensionnel dans les structures composites. Nous proposons une approche permettant de caractériser les propriétés mécaniques de structures composites Interlock et en particulier de résoudre les problèmes liés à la création de ces géométries complexes et leur discrétisation.Une des difficultés des approches méso-macro réside dans la manière de reproduire de façon fidèle la géométrie de ces architectures aux formes très complexes et d'obtenir en particulier un Volume Elémentaire Représentatif (VER) duquel on peut déduire par calcul éléments finis les propriétés mécaniques par homogénéisation. Cette pluralité des formes engendre des difficultés de mise en œuvre essentiellement géométriques et des difficultés de maillage bien connues : interpénétration et contact des mèches, maillage de fines couches de résines aux interfaces, détermination en tout point de l'orientation des fibres. Nous proposons une approche qui consiste à créer un modèle géométrique des mèches limitant ou contrôlant les intersections et les contacts, à définir un VER périodique et à mailler ce VER en tétraèdres avec des maillages conformes aux interfaces. Une fois le modèle maillé obtenu et les conditions de périodicités définies, les propriétés mécaniques effectives sont obtenues par homogénéisation. Les calculs par éléments finis sont réalisés avec le logiciel ABAQUS. Les tissages complexes ont été traités automatiquement avec cette technique. Les résultats sont confrontés à ceux d’autres modélisations, issus de la littérature et de l’expérience. / The work proposed here is devoted to the prediction and the characterization of the mechanical behavior of interlock woven composite structures. We propose an approach to characterize the mechanical properties of interlock woven composite structures and particularly to solve the problems associated with the creation of these complex geometries and their discretization into a conform mesh. One of the difficulties of this meso-macro approach is to reproduce faithfully the geometry of these architectures with complex shapes and to obtain a Representative Volume Element (RVE). Once this complex step is achieved, the mechanical properties of the composite can be thereafter obtained by homogenization from a finite element analysis. The difficulties to generate a RVE of such structures are well known: interpenetration and contacts between yarns, meshing of thin resin layers at interfaces, determination of the orientation of the fibers at all points of the structure. We propose an approach which consists of creating a geometric model of the yarns limiting or controlling the intersections and the contacts, defining a periodic RVE, meshing this RVE by tetrahedral with compatible meshes at the interfaces. Once the model is meshed and the symmetry conditions are defined, the properties are obtained by homogenization. The finite element calculations are performed on the ABAQUS software. Complex weaves can be automatically processed with this technique. The results are compared whit other modeling from the literature and with experimental data.

Soils are critical to ecosystem function as they provide essential nutrients for primary producers, habitat and organic energy for decomposers, and storage of organic matter. Irrigation with reclaimed water is an increasingly popular water conservation strategy; yet its high salinity and nutrient content potentially affect soil properties. In this study, set in a residential neighborhood of Tampa (U.S.). I tested whether there are distinct lawn system management strategies characterized by systematic differences in reclaimed water usage and irrigation and fertilization practices. I then investigated whether soil biogeochemistry responds to lawn system management strategy. My results indicated that amendment strategy, which includes water source type, frequency of fertilization, and frequency of irrigation varies among residents of comparable neighborhoods. In this case, these three categories of management behaviors tend to co-occur. Analysis of irrigation water samples collected in this study showed significant differences between potable and reclaimed water. Mainly, reclaimed water had higher conductivity and phosphate content than potable water. When looking at the soil biogeochemical characteristics of the study area I found that there were significant differences in soil nutrients and microbial biomass across amendment strategy. Soils with a high amendment strategy (frequently irrigation with nutrient-rich reclaimed water, plus frequent fertilizer addition) showed higher conductivity and a higher microbial biomass than soils on lawns with a low amendment strategy (infrequent irrigation with dilute potable water, plus infrequent fertilizer addition). A positive correlation between soil conductivity and microbial biomass was observed. These findings suggest that high amendment strategy increases the input flux of some nutrients to the soils and acts as a nutrient resource for soil microorganisms. The differences between soil and microbial biomass amendment strategy support the idea that decisions made by individuals about which management intensity strategy to use do affect the spatial variability of the ecosystem. These results contribute to the hypothesis of urban ecological urbanization by looking at the vertical social interactions between municipalities and individual homeowners. These interactions might explain the observed spatial variability of ecological characteristics. The results of this research affect the way information about the advantages of using reclaim water is advertised, in particular to homeowners.