Dissertations / Theses: 'Flexible fibres'

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Daieff, Marine. "Deformation and shape of flexible, microscale helices in viscous flows." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC189/document.

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Les interactions fluide-structure sont d'un grand intérêt en ingénierie et pour des applications industrielles et médicales. Comprendre les interactions entre des particules aux formes complexes et des écoulements peut mener à de nouveaux projets pour l'administration ciblée de médicaments, pour des micro capteurs de débit et à une meilleure compréhension du comportement des micro-organismes. Dans cette thèse, nous étudions l'interaction fluide-structure de particules chirales de taille microscopique à bas nombres de Reynolds. Les particules sont rigides et confinées dans une géométrie 2D ou flexibles avec une forme hélicoïdale. Combiner des techniques de microfabrication, comme des méthodes d'assemblage multi-échelles et la microfluidique, permet d'avoir un excellent contrôle à la fois sur les propriétés géométriques et mécaniques des fibres et aussi sur les caractéristiques de l'écoulement comme ses propriétés Newtoniennes et non Newtoniennes, sa vitesse et sa géométrie. Dans un premier temps, nous avons étudié des fibres rigides, 2D et asymétriques, i.e. des fibres en L. Les confinements latéral et transversal ont été étudiés tout comme la forme de la fibre. Lorsque la particule est transportée dans un écoulement visqueux, elle tourne jusqu'à atteindre une orientation d'équilibre. Dans cette orientation particulière, la fibre se décale vers les murs latéraux du canal. Une étude complète des trajectoires de la fibre a été réalisée et des comparaisons avec des particules symétriques ont été faites. Ce sujet de recherche pourrait aider à concevoir des dispositifs pour trier des particules à des fins médicales. Dans un second temps, nous avons étudié des fibres hélicoïdales flexibles de taille micrométrique. La dynamique de formation de l'hélice a été analysée. Les hélices se forment à partir de rubans droits 2D qui, de façon spontanée, s'enroulent quand ils sont libérés dans l'eau. La forme hélicoïdale est obtenue seulement quelques minutes après la libération des rubans mais l'hélice continue à rétrécir pendant plusieurs heures jusqu'à ce qu'elle atteigne une courbure préférentielle. Deux temps caractéristiques sont identifiés dans cette dynamique de formation. Un modèle a été développé pour comprendre le complexe équilibre entre les forces élastiques, de tension de surface et visqueuses aux temps courts. Après avoir analysé plusieurs hypothèses, comme l'impact d'une couche sacrificielle, une possible modification du module du matériau et la présence de fluage, l'évolution du rayon de l'hélice aux temps longs s'explique probablement par du fluage. La dynamique d'extension et de relaxation de la fibre flexible a aussi été étudiée dans des fluides Newtonien et non Newtonien. L'étude dans des solutions de polymères est pertinente et intéressante car la taille des micro hélices est comparable à celle des flagelles des micro-organismes et à celle de chaînes de polymères de grande masse moléculaire. Il s'agit donc d'un problème mutli-échelles complexe car la viscosité locale au niveau du ruban pourrait être différente de la viscosité globale de l'écoulement
Fluid-structure interactions are of wide interest in engineering, industrial and medical applications. Understanding the interactions between complex shaped particles and flows might lead to new designs for targeted delivery, microflow sensors and to a better understanding of the behavior of microorganisms. In this thesis, we study the fluid-structure interaction of microscale chiral particles at low Reynolds numbers. The particles are rigid and confined in a 2D geometry or flexible with a helical shape. The combination of microfabrication techniques, such as multiscale assembly methods and microfluidics, enables to have a perfect control on both the geometrical and mechanical properties of the fibers and the flow features such as Newtonian or non Newtonian properties, the flow velocity and the flow geometry. First we studied asymmetric 2D rigid fibers, i.e. L-shaped fibers. Both lateral and transversal confinements have been investigated, as well as the shape of the fiber. When the particle is transported in viscous flows, it rotates until reaching an equilibrium orientation. In this specific orientation, the fiber drifts towards the lateral walls of the channel. A full investigation on the trajectories of the fiber has been performed and comparisons with symmetric particles have been done. Such research may help design devices to sort particles for medical purposes. Secondly we studied flexible microscale helical fibers. The dynamics of the helix formation has been investigated. The helices are formed from straight 2D ribbons, which spontaneously coil when released in water. The helical shape is reached only several minutes after the release but the helix keeps shrinking during several hours until reaching a preferred curvature. Two different timescales are identified in this formation dynamics. A model has been developed to understand the complex balance between elastic, surface tension and viscous forces at short times. After investigating several assumptions such as the impact of a sacrificial layer, a possible change in the modulus of the material and a creep behavior, the evolution of the radius at long times is most likely explained by creep. The extension and relaxation dynamics of the flexible fiber has also been studied in Newtonian and non Newtonian fluids. The study in polymer solutions is relevant and interesting because the size of the microhelix is comparable to the flagella of microorganisms and to the chains of high molecular weight polymers. Complex multiscale problems are then involved as the local viscosity at the scale of the ribbon might differ from the global viscosity at the scale of the flow

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Harris, Samantha Mary. "Dynamics of semi-flexible fibres in viscous flow." Thesis, University of Leeds, 2007. http://etheses.whiterose.ac.uk/53/.

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The dynamics of semi-flexible fibres in shear flow and the effect of flexibility on the swimming speed of helical flagella are investigated. High aspect ratio particles such as carbon and glass fibres are often added as fillers to processed polymers. Although these materials have high rigidity, the large aspect ratiomakes the fibres liable to bending during flow. Other high aspect ratio fibres that behave as semi-flexible fibres include carbon nano-tubes, paper fibres and semi-flexible polymers such as the muscle protein f-actin. Most theoretical studies assume that fibres are either rigid or completely flexible, but in this thesis fibres with a finite bending modulus are considered. A semi-flexible fibre is modelled as a chain of shorter rods linked together. A bending torque is included at the joints between the rods to account for the rigidity. In shear flow the simulation reproduces the C and S turns observed in experiments on semi-flexible fibres. The results for finite aspect ratio fibres predict changes to the period of rotation and drift between Jeffery orbits. The direction of drift for a flexible fibre depends on both the intial orientation and the fibre’s flexiblity. We also present a linear analysis of how small distortions to a straight semi-flexible fibre grow when the flow places the fibre under compression. These results are in agreement with our full simulations and the growth rates of the distortions to a straight fibre allow us to predict the most unstable mode at a particular flow rate. To allow for intrinsically bent or helical equilibrium shapes a second simulation method is developed that includes a twisting torque at the joints between the rods as well as a bending torque. Using this simulation we measure the period of rotation and orbit drift of permanently deformed fibres in shear flow and show that due to the asymmetry of a helix, shear induced rotation results in translation and orbit drift for both rigid and semi-flexible fibres. Bacteria such as Vibrio alginolyticus and Escherichia coli swim by rotating one or more helical flagella. Vibrio alginolyticus has only one flagella and changes direction by altering its sense of rotation. Experimental observations of Vibrio alginolyticus have found that backwards swimming is 50% faster than forwards swimming speed however, previous numerical simulation results have shown only a 4% difference for flagella of the same dimensions. We use our simulation to consider how flexiblity affects the swimming speed of helical flagella and show that for a constant angular velocity, difference between forwards and backwards swimming speed ranges between 0-23%depending on the exact stiffness chosen. We explain the differences in swimming speeds of semi-flexible fibres by investigating the shape changes which occur and comparing them to the results for swimming speeds of rigid flagella of varying dimensions.

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Joung, Clint Gwarngsoo. "Direct simulation studies of suspended particles and fibre-filled suspensions." Thesis, The University of Sydney, 2003. http://hdl.handle.net/2123/554.

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A new Direct Simulation ﬁbre model was developed which allowed ﬂexibility in the ﬁbre during the simulation of ﬁbre suspension ﬂow.This new model was called the 'Chain-of-Spheres' model.It was hypothesised that particle shape and deformation could signiﬁcantly aﬀect particle dynamics,and also suspension bulk properties such as viscosity.Data collected from the simulation showed that ﬂexible ﬁbres in shear ﬂow resulted in an order of 7 −10% bulk relative viscosity increase over the 'rigid' ﬁbre result.Results also established the existence of a relationship between bulk viscosity and particle stiﬀness. In comparison with experimental results,other more conventional rigid ﬁbre based methods appeared to underpredict relative viscosity.The ﬂexible ﬁbre method thus markedly improved the ability to estimate relative viscosity.The curved rigid ﬁbre suspension also exhibited increased viscosity of the order twice that of the equivalent straight rigid ﬁbre suspension.With such sensitivity to ﬁbre shape,this result has some important implications for the quality of ﬁbre inclusions used.For consistent viscosity,the shape quality of the ﬁbres was shown to be important. The 'Chain of Spheres' simulation was substantially extended to create a new simulation method with the ability to model the dynamics of arbitrarily shaped particles in the Newtonian ﬂow ﬁeld.This new '3D Particle' simulation method accounted for the inertial force on the particles,and also allowed particles to be embedded in complex ﬂow ﬁelds.This method was used to reproduce known dynamics for common particle shapes,and then to predict the unknown dynamics of various other particle shapes in shear ﬂow. In later sections, the simulation demonstrated inertia-induced particle migration in the non-linear shear gradient Couette cylinder ﬂow,and was used to predict the ﬁbre orientation within a diverging channel ﬂow.The performance of the method was veriﬁed against known experimental measurements,observations and theoretical and numerical results where available.The comparisons revealed that the current method reproduced single particle dynamics with great ﬁdelity. The broad aim of this research was to better understand the microstructural dynamics within the ﬁbre-ﬁlled suspension and from it,derive useful engineering information on the bulk ﬂow of these ﬂuids.This thesis represents a move forward to meet this broad aim.It is hoped that future researchers may beneﬁt from the new approaches and algorithms developed here.

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Joung, Clint Gwarngsoo. "Direct simulation studies of suspended particles and fibre-filled suspensions." University of Sydney. Chemical Engineering, 2003. http://hdl.handle.net/2123/554.

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A new Direct Simulation ﬁbre model was developed which allowed ﬂexibility in the ﬁbre during the simulation of ﬁbre suspension ﬂow.This new model was called the �Chain-of-Spheres �model.It was hypothesised that particle shape and deformation could signi ﬁcantly a ﬀect partic e dynamics,and also suspension bulk properties such as viscosity.Data collected from the simulation showed that ﬂexible ﬁbres in shear ﬂow resulted in an order of 7 −10% bulk relative viscosity increase over the �rigid �ﬁbre result.Results also es- tablished the existence of a relationship between bulk viscosity and particle sti ﬀness.In comparison with experimental results,other more conventional rigid ﬁbre based methods appeared to underpredict relative viscosity.The ﬂexible ﬁbre method thus markedly improved the ability to estimate relative viscosity.The curved rigid ﬁbre suspension also exhibited increased viscosity of the order twice that of the equivalent straight rigid ﬁbre suspension.With such sensitivity to ﬁbre shape,this result has some important implications for the quality of ﬁbre inclusions used.For consistent viscosity,the shape quality of the ﬁbres was shown to be important. The �Chain of Spheres �simulation was substantially extended to create a new simulation method with the ability to model the dynamics of arbitrarily shaped particles in the Newtonian ﬂow ﬁeld.This new �3D Particle �simulation method accounted for the inertial force on the particles,and also allowed particles to be embedded in complex ﬂow ﬁelds.This method was used to reproduce known dynamics for common particle shapes,and then to predict the unknown dynamics of various other particle shapes in shear ﬂow. In later sections, the simulation demonstrated inertia-induced particle migration inthe non-linear shear gradient Couette cylinder ﬂow,and was used to predict the ﬁbre orientation within a diverging channel ﬂow.The performance of the method was veriﬁed against known experimental measurements,observations and theoretical and numerical results where available.The comparisons revealed that the current method reproduced single particle dynamics with great ﬁdelity. The broad aim of this research was to better understand the microstruc- tural dynamics within the ﬁbre-ﬁlled suspension and from it,derive useful engineering information on the bulk ﬂow of these ﬂuids.This thesis represents a move forward to meet this broad aim.It is hoped that future researchers may bene ﬁt from the new approaches and algorithms developed here.

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Thompson, Ian. "Use of steel fibres to reinforce cement bound roadbase." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366364.

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Vakil, Ali. "Three-dimensional flow through forming fabrics and the motion of flexible fibres in flow." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/19328.

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This dissertation addresses the 3D flow through forming fabrics. In the first part of this thesis, the single phase 3D flow through certain specific fabrics was modeled. In practice, the Reynolds number of the fabric flow, based on paper-side filament diameter, is around 100. Consequently, it is not too surprising that the permeability of the fabrics was found to vary approximately as Re ⁻⁰˙⁴, which is intermediate between the expected low Re (Re⁻¹) and high Re (Re⁰) limits. The resistance of a multilayer fabric was found to be nearly equal to the sum of the resistance of each layer considered in isolation. The effect of filament-scale and weave-scale flow non-uniformity on the fiber distribution in the finished paper was considered. For one specific fabric, there was 3 times more chance for short fibers to accumulate initially over openings than blockages of the fabric. Jet-to-wire speed ratio was found to have an insignificant effect on permeability results, but a marked effect on the Machine Direction shear stress in the vicinity of the paper-side filaments. In an attempt to model sheet formation, numerical simulations of the motion of a single fiber in the flow field of a cylinder was carried out as a canonical test case of the fiber/filament interaction system. Seven dimensionless groups govern the problem. A range of dimensionless groups were found for which the fiber hung up on the cylinder, whereas for other values of the dimensionless groups the fiber slid over the cylinder. In general, longer and more flexible fibers had a greater likelihood to be caught by the filament. Yawed finite aspect ratio cylinders at moderate Reynolds numbers are approximate representations of fibers in the flow field of forming fabrics. No analytical solution or any experimental data are reported in the literature to predict the drag and lift force on such particles in such flows. Computational Fluid Dynamics (CFD) simulations were conducted to find the drag and lift coefficients of inclined finite circular cylinders at Reynolds numbers in the range 1-40. The simulations showed that the Independence Principle was highly inaccurate for low inclination angles.

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Zhang, Xi. "Polymer composites incorporating engineered electrospun fibres : flexible design and novel properties for biomedical applications." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/30904.

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Due to their unique structure and flexible choice of materials, electrospun degradable and biocompatible polymer fibres are considered to be extremely suitable for biomedical applications such as tissue engineering and drug delivery, either on their own or integrated within composites. Conventional electrospun fibre composites are typically based on non-woven mats and therefore limited to simple-curved geometries (films, membranes, etc.). For aqueous composites such as hydrogels, the hydrophobicity of the materials sometimes prohibits fibres to be easily integrated or distributed in these composites. In this thesis, a review on the topic is firstly presented in Chapter 2, introducing and discussing engineering of electrospun fibre as well as their biomedical applications. In Chapter 3, electrospun polylactide (PLA) fibres reinforced poly(trimethylene carbonate) (PTMC) composites are prepared. The composites are loaded with both continuous and short PLA fibres, achieving significant mechanical enhancement and offering opportunities to produce composites conveniently using liquid formulations. Chapter 4 presents the development of shape memory polymer composites based on a combination of PLA fibres and a PTMC matrix. By loading different amounts of short fibres with different aspect ratios or by using plasticisers, the shape memory behaviour is modulated; and composites of more complex geometries are produced. In Chapter 5, PTMC-PLA fibre composites are made into drug release system. Dexamethasone-loaded PLA fibres are integrated into a PTMC matrix, showing sustained drug release and stimulating stem cell osteogenic differentiation. This concept gives promise to loading various drugs into photo-crosslinked structures without denaturation. In Chapter 6, electrospun PLA fibres are functionalized by amphiphilic block copolymer polylactide-block-poly[2-(dimethylamino)ethyl methacrylate] (PLA-b-PDMAEMA) for the development of carboxymethylcellulose composites hydrogels. Functionalization of PLA fibres not only allows for easy integration and dispersion into the hydrogel, but also enhances the interfacial bonding between fibre and hydrogel. In the last chapter (Chapter 7), some conclusions are drawn and future works are discussed.

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Chegenizadeh, Amin. "Experimental approach to investigate reinforced clay." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/2288.

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Soil reinforcement with discrete flexible fibres has always been an issue for further research. In Geotechnical engineering field, the research on sandy soil has considerably been more than the clayey one. The main reason for this lack can be expressed as the complexity of clayey material due to their cohesion and interaction between clay and reinforcement.The present research aims to show possibility of discrete fibre usage in clay. For this purpose, selection of material has been conducted with special care to make the project outcome applicable to industry projects. The fibre which was used for this research prepared by BASF Company in Western Australia and currently is used in fibre reinforced concrete for infrastructure projects. Kaolin has been used as soil part and provided by Prestige Company.Experimental approach was applied to investigate the effect of different parameters on composite soil strength. These tests cover the variety range of soil mechanics tests from compaction tests to triaxial compression tests. The results from all the tests were presented in the thesis.A theoretical model was also developed for clayey material for the first time with the use of modified cam clay model to predict the behaviour of samples precisely. This model is based on the rule of mixture and considers the effect of soil and fibre separately. The model was validated with the results from CD triaxial test.

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Ducourthial, Guillaume. "Développement d'un endomicroscope multiphotonique compact et flexible pour l'imagerie in vivo haute résolution de tissus biologiques non marqués." Thesis, Limoges, 2014. http://www.theses.fr/2014LIMO0004/document.

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La microscopie multiphotonique est un outil essentiel d’investigation en biologie cellulaire et tissulaire. Son extension à l’endoscopie est l’objet d’intenses efforts de recherche pour des applications en neurosciences (imagerie cérébrale du petit animal) ou en clinique (diagnostic précoce, aide à la biopsie). Ce manuscrit porte sur le développement d’un endomicroscope multiphotonique présentant des performances inédites. Ce dispositif est alimenté par un oscillateur titane-saphir standard. Vient ensuite un module de pré-compensation des distorsions linéaires et non linéaires se produisant dans la fibre endoscopique. Ce module permet d’obtenir des impulsions compressées de 39 fs à la sortie d’une fibre microstructurée air-silice innovante à double gaine de 5 mètres de long qui est optimisée pour l’excitation multiphotonique (cœur central de 3,4 µm à maintien de polarisation) et la collection du signal produit par les cibles biologiques. A l’extrémité de la fibre, on trouve une sonde endoscopique, de 2,2 mm de diamètre pour 37 mm de long, composée d’un micro-scanner à fibre optique et d’un micro-objectif achromatique de distance de travail supérieure à 400 µm. La résolution spatiale de l’appareil vaut 0,83 µm et l’acquisition se fait en simultané sur deux canaux spectraux à 8 images/s. L’appareil a permis l’enregistrement d’images in vivo sans marquage des tubules et de la capsule rénale, respectivement par fluorescence à deux photons des flavines et par génération de second harmonique du collagène, avec 30 mW sur les tissus et jusqu’à 300 µm sous la surface de l’organe
Multiphoton microscopy is an essential investigative tool in cell and tissue biology. Its extension to endoscopy is the subject of intensive research for applications in neuroscience (brain imaging of small animals) or clinical (early diagnosis, help for biopsy). This manuscript focuses on the development of an endomicroscope with multiphoton unprecedented performance. This device is powered by a standard titanium-sapphire oscillator. Then comes a pre-compensation module of linear and nonlinear distortions occurring in the endoscopic fiber. This module provides compressed pulses of 39 fs at the direct output of 5 meters long innovative double-clad air-silica microstructured fiber which is optimized for multiphoton excitation (polarization maintaining central core of 3.4 µm) and the collection of the signal produced by biological targets. At the end of the fiber, there is an endoscopic probe, 2.2 mm in diameter and 37 mm long, composed of a micro fiber scanning system and an achromatic micro-objective with a working distance greater than 400 µm. The spatial resolution of the device is 0.83 µm and the acquisition is done simultaneously on two spectral channels at 8 frames/s. The device has recorded in vivo images without label of the tubules and the renal capsule, respectively by two-photon excitation fluorescence of flavins and second harmonic generation of collagen, with 30 mW on the tissues and 300 µm below the surface of the organ

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Nauman, Saad. "Geometrical modelling and characterization of 3D warp interlock composites and their on-line structural health monitoring using flexible textile sensors." Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10010/document.

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Ce mémoire de thèse de doctorat est structuré en deux parties. Dans la 1ère partie, une nouvelle approche traitant la caractérisation géométrique et mécanique est décrite. La modélisation géométrique de tissu 3D interlock est corrélée avec les paramètres de tissage afin de mieux prendre en compte ces paramètres. Le tissage de tissu 3D interlock est décrit en détail. Par la suite, une étude a été menée pour mieux comprendre les changements qui se produisent dans une mèche de carbone lorsque cette dernière est intégrée dans un renfort. Un coefficient de transfert des propriétés mécaniques a été proposé permettant une meilleure compréhension de l’influence des paramètres structuraux sur les propriétés d’un composite. Dans la 2eme partie du mémoire, un système de mesure in situ pour les composites a été développé. Ce système comporte un capteur souple et un module de traitement de données et d’amplification des signaux. Le capteur fibreux développé durant nos recherches a été inséré pendant le tissage comme un fil de trame. Le système a été testé sur une plaque en composite, contenant les renforts en 3D interlock, en traction. Le capteur suit fidèlement les déformations de la plaque composite jusqu’à la rupture
This thesis is divided in two parts. In the first part a geometrical modelling approach has been developed in tandem with weaving parameters. The reinforcements were woven on a modified conventional loom to study the geometry of these structures. Their weaving has been described in detail. The weaving parameters have been correlated to the modelling approach. The meso structural modelling approach is capable of predicting essential reinforcement geometrical characteristics at meso structural level without being too complicated. Furthermore, mechanical characterization of 3D interlock reinforcements has been carried out in such a way that a track of mechanical properties during the complete production cycle has been maintained. A novel parameter called strength transfer coefficient was proposed which allows better understanding of the influence of structural parameters on the final properties of the composite. In the second part of the thesis an online structural health monitoring system which is composed of a textile based sensor and signal amplification and treatment module, has been developed. This system is capable of detecting structural deformations in the composite as the sensor is integrated during the manufacturing of the reinforcement and can follow its deformation pattern when composite is subjected to tensile loading in a real time

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Arora, Neha. "Contribution to the concept of micro factory : design of a flexible electromagnetic conveyor system." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2347.

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L’objectif de la thèse est de réaliser un système de convoyage flexible permettant de déplacer des micro-objets. Ce système pourra être amené à être intégré dans une micro-usine ce qui nécessite une forte reconfigurabilité et une faible consommation d’énergie. Ces deux critères ont donc été considérés lors de la conception du système de convoyage. Ce dernier est basé sur un actionneur planaire électromagnétique, développé au sein du laboratoire Roberval, et sur une surface intelligente composée de 5 × 5 cellules élémentaires permettant chacune de déplacer la partie mobile dans les deux directions du plan et des rotations autour de l'axe perpendiculaire au plan. Un modèle analytique de l’actionneur a été développé afin de calculer les efforts électromagnétiques ainsi que le déplacement de la partie mobile. Ce modèle a été utilisé lors de la phase de conception du système de convoyage. Un prototype expérimental a ensuite été fabriqué et testé ce qui a permis de valider le principe de fonctionnement proposé. Des tests expérimentaux ont montré la possibilité de réaliser des déplacements de grande étendue dans les deux directions du plan. De multiples tests expérimentaux (pilotage en boucle ouverte, caractérisation des performances telles que rectitude de déplacement, répétabilité de positionnement, charge déplaçable, …) a été réalisée afin de qualifier les performances du système de convoyage. Les points sur la réalisation : - Une modélisation statique sous RADIA a été développée afin de concevoir la surface intelligente notamment la zone de transition entre deux cellules voisines. Une modélisation dynamique réalisée sous MATLAB a permis de simuler le comportement d’un moteur en boucle ouverte et en boucle fermée. - Un prototype de surface intelligente, composé d’un circuit imprimé multicouches (4 couches) de dimensions 130 mm x 130 mm, a été conçu sous EAGLE software. L’influence de la distance entre les deux premières couches a été étudiée à l’aide des modèles développés afin d'assurer un déplacement uniforme dans les deux directions. - Un test expérimental avec LABVIEW interface d'une cellule élémentaire de la surface intelligente avec une partie mobile composée de deux moteurs magnétiques orthogonaux a été réalisé et a permis de valider le fonctionnement du système de convoyage dans les deux directions du plan. - Une autre série de tests avec LABVIEW interface a été réalisée afin de valider expérimentalement le déplacement de la partie mobile avec la surface intelligente au niveau des zones de transition entre les cellules élémentaires. Ces tests expérimentaux ont montré des déplacements de grande étendue dans les deux directions du plan et de rotation autour de l'axe perpendiculaire au plan. Des déplacements de grande étendue et des rotations de la partie mobile ont été mesurés à l’aide d’une méthode de traitement d'image réalisée sous MATLAB. - Parallèlement, on a étudié un capteur à déplacement optique à haute résolution qui peut être intégré dans le convoyeur. Un algorithme robuste pour le traitement du signal de capteur à fibres optiques à haute résolution pour mesurer de déplacement est développé. Dans cet algorithme, la position optimale de la partie mobile est déterminée pour obtenir un basculement sans arrêt entre les sondes et l'algorithme est implémenté sous MATLAB et validée par la mise en œuvre des signaux expérimentaux. Ces travaux de thèse ont été publiés dans une revue internationale (Computers in Industry (COMIND)) et présentés dans des congrès internationaux (IEEE Sensors, REM Mechatronics, AIM, IWMF) pendant les années 2011 à 2016
The aim of the thesis is to provide a flexible conveyor system for moving micro-objects. The system may need to be integrated into a micro-factory which requires high reconfigurability and low power consumption. These two criteria have been considered in the design of the conveyor system. The conveyor is based on a planar electromagnetic actuator developed in the Laboratoire Roberval of the UTC, and on smart surface composed of 5 x 5 unit cells; each ceii moves th movable part in the two directions of the plane. An analytical model of the actuator has been developed in order to calculate the electromagnetic forces and the displacement of the mobile part. This modei has been used during the design phase of the conveying system. An experimental prototype is then manufactured and tested which has validated the proposed principle of operation. Experimental tests have shown the ability to perform wide area displacement in both directions of the plane. Numerous experimental tests (control in open loop and closed loop performance characterization as straightness of movement, position repeatability, coupled- decoupled analysis...) have been done to qualify the performance of the conveyor system. Experiments for rotations about the axis perpendicular to the olane have also been performed successfully. Work synthesis: - Static modeling under RADIA was developed in order to design the conveyor surface especially for the transitio zone between two neighboring cells. A dynamic modeling under MATLAB allowed to simulate the behavior of single axis motor in open loop and closed loop control. - A conveyor surface prototype, consisting of a multilayer printed circuit board (4 layers) of dimensions 130 mm x 130 mm, was designed under EAGLE software. The influence of the distance between the first two layers was studied using the developed models to ensure uniform displacement in both the directions. - The experimental tests (with LABVIEW interface) of an elementary cell of the intelligent surface with a moving part composed of two orthogonal magnetic motors has been carried out that allowed to validate the operation of the conveying system in both directions of the plane. - Another series of tests with LABVIEW interface were carried out in order to validate experimentally the displacement of the mobile part with the smart surface at the transition zones between the elementary cells. - These experimental tests showed displacements of great extent in the two directions of the plane and of rotation about the axis perpendicular to the plane. - Long displacements and rotations of the moving part were measured using image processing algorithm developed in MATLAB. - At the same time, a high resolution fiber optic displacement sensor was studied that can be integrated into the conveyor surface locally for the precise positioning. A robust signal processing algorithm for high resolution displacement measurement was developed. In this algorithm, - The optimum position of the movable part is determined in order to obtain a continuous switching betwee the two fiber optic probes ; - The usable parts of the signals obtained from two probes were then filtered to measure the displacement using interpolation method ; The algorithm is implemented under MATLAB and validated by the implementation of the experimental signals. The work have been published in an international journal (Computers in Industry (COMIND)) and presented at international congresses (IEEE Sensors, REM Mechatronics, AIM, IWMF) during the years 2011 to 2016

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Lubin, Jérôme. "Vers le déploiement d'un réseau de capteurs enfouis dans des multi-plis carbone-epoxy pour l'instrumentation in-situ de structures composites pour l'avionique." Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2199/.

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Les matériaux composites à base de fibre carbone suscitent un intérêt grandissant dans l'industrie en général et avionique en particulier. Très appréciés pour leur résistance exceptionnelle aux efforts de traction ils présentent également un poids bien plus faible que les métaux y compris l'aluminium. Cela permet d'envisager la construction d'aéronefs d'une très grande solidité tout en réduisant significativement leur consommation en carburant. Cependant les composites carbone sont relativement fragiles sous des efforts en flexion ou compression. Leur durée de vie est peu connue et dépend fortement de la géométrie des pièces qui sont souvent surdimensionnées par sécurité. Afin de prévenir d'éventuels accidents et conserver des pièces légères il est indispensable d'évaluer leur état de santé. L'objectif de cette thèse est la conception d'une solution d'instrumentation à base de capteurs miniaturisés en technologie silicium sensibles aux vibrations mécaniques et capables de détecter l'apparition d'un défaut dans la structure. Nous développé un procédé de fabrication simple et robuste pour des capteurs dont l'élément sensible est une jonction PN de type Zéner implémentée dans du polysilicium. Nous avons démontré dans un premier temps une sensibilité aux vibrations mécaniques. La capacité de ces capteurs à faire du suivi de réticulation en autoclave a également été démontrée. La phase suivante a concerné l'étude d'un procédé de packaging souple robuste et modulable pour la mise en réseau des capteurs. Enfin la dernière étape concerne l'étude d'un circuit électronique permettant la lecture du signal et la réduction du bruit de fond
Manufacturers are using more and more carbon fibers composite materials in their structures. The aviation industry in particular is very interested by these new materials. Carbon fibers are capable of sustaining greater axial strain than their metallic equivalents and are lighter. Their properties allow for the design of more robust and lightweight aircrafts which would in turn bring about lots of benefits: longer lifespan, less fuel consumption, etc. For the time being, aircraft components in carbon composites are oversized for security reasons. Carbon fiber composites are not as good at withstanding torsion and flexion as they are at withstanding axial strain. The lifetimes of the components are not well known and investigation results are not easily transferable from one design to another. In order to ensure operational safety while keeping parts lightweight, health monitoring becomes indispensable. The goal of this PhD thesis is to propose a monitoring solution based on small sensors using silicon technology. These sensors are sensitive to mechanical vibrations and can be used to detect the appearance of faults in the structure. We developed a process which is simple yet robust for manufacturing sensors. The sensitive element is a polysilicon Zener PN. First we demonstrate that the sensors are sensitive to mechanical vibrations. Then we demonstrate the usage of our sensors in monitoring the annealing step in autoclave for carbon fiber polymer pieces. Next step consists in the study of a strong and flexible packaging that can be used with any shape of piece. Finally, we studied the electronic circuits able to read the signal and reduce the background noise

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13

Rezak, Sheila. "Analysis of flexible fiber suspensions using the Lattice Boltzmann method." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24798.

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Thesis (Ph.D.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Co-Chair: Aidun, K. Cyrus; Committee Co-Chair: Ghiaasiaan, Mostafa; Committee Member: Deng, Yulin; Committee Member: Empie, Jeff; Committee Member: Patterson, Tim.

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14

Ybañez, y. Valeros Numer. "The crack bridging behavior of flexible fibers." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11817.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1995.
Includes bibliographical references (leaves 162-165).
by Numer Ybañez y Valeros.
M.S.

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15

Shehata, Hussein A. H. "HVAC systems using flexible fibre impeller fans." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297764.

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16

Sagnol, Loba. "Experimental and analytical study of the reinforcement of pavements by glass fibre grids." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAD042.

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Cette thèse traite de l’effet des grilles en fibre de verre, utilisées pour renforcer les structures routières, sur la liaison entre deux couches d’enrobés bitumineux, la durée de vie en fatigue et le module de rigidité des ´éprouvettes cylindriques renforcées, ainsi que sur les déflexions mesurées sur une section de route renforcée in situ. Des essais de cisaillement (LEUTNER) ainsi que de module et de fatigue (ITT) ont été conduit sur des éprouvettes renforcées et non renforcées en utilisant différentes grilles, différentes émulsion ainsi que différentes quantités d’émulsion. Pour ces essais, une surface de test a été construite in-situ, de laquelle les ´éprouvettes ont ´été extraites. Une section de route in-situ a ´également été construite, renforcée avec 3 différentes grilles et avec deux sections de références. Les déflexions de la chaussée ont été déterminées avant et après les travaux. Une modélisation de la structure a été faites basée sur les résultats des mesures de déflexion
This PhD-study evaluates the impact of glass fibre grids, used to reinforced asphalt structures, on the bonding between two asphalt layers, the fatigue life and the stiffness modulus of reinforced cylindrical specimens as well as on the deflections measured on a reinforced in-situ road section. Shear tests (LEUTNER) as well as modulus-tests and fatigue-tests (ITT) were conducted on reinforced and unreinforced specimens, using different grids, different emulsions and different emulsion quantities. For this tests, an outdoor test-surface was constructed, from which the specimens were extracted. A in-situ road test section was also constructed, reinforced with 3 different grids and having two reference sections. The deflections of the road were determined before and after the construction works. A modelisation of the structure, based on the deflection measurements, was made

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17

Hofmann, John. "Extension of the Method of Ellipses to Determining the Orientation of Long, Semi-flexible Fibers in Model 2- and 3-dimensional Geometries." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23921.

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The use of fiber-reinforced polymer composites formed via injection molding is of increasing interest due to their superior mechanical properties as compared to those of the polymer matrix alone. These mechanical properties, however, are strongly dependent on the fiber length and orientation distributions within a molded part. As such, there is a need to understand and model the orientation evolution of chopped fibers in flow in order to accurately simulate the final fiber orientation distribution within injection molded parts. As a result of this, accurate and reliable experimental measurement of fiber orientation is needed. Within this research, the application and validity of the Method of Ellipses for determining the orientation of long, semi-flexible glass fibers within injection molded composites has been investigated. A fiber suspension with an average length of approximately 3.9 mm was the focus of this study and assumed to be representative of commercial distributions. A novel method to quantify fiber curvature was developed and utilized to show that flexibility in center-gated disc and the end-gated plaque samples was minimal on average for the selected fiber length distribution. Thus, it was determined that the Method of Ellipses was applicable when utilized to obtain reliable orientation data for the selected long glass fiber suspension and within the chosen geometries that exhibit 1-, 2-, and 3-dimensional velocity fields. However, a modified image analysis width was found to be necessary in regions of highly aligned fibers, due to the increase in ellipse size and the need to reduce the number of partial objects and thus minimize error. This allowed for a direct comparison of the experimental orientation behavior of short and long glass fibers within the center-gated disc and the end-gated plaque, as well as the effect of the orientation distributions on the global modulus of the part.
Ph. D.

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18

Marheineke, Nicole [Verfasser]. "Turbulent Fibers : On the Motion of Long, Flexible Fibers in Turbulent Flows / Nicole Marheineke." Aachen : Shaker, 2005. http://d-nb.info/1186577657/34.

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19

Lu, Chi Ph D. Massachusetts Institute of Technology. "Flexible fibers for optoelectronic probing of spinal cord circuits." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111328.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 117-128).
The majority of the neural engineering efforts in the past decade have focused on brain interfaces. The searching of tools for recording and modulation of neural activity in the spinal cord limits fundamental understanding of neural dynamics in this organ. Spinal cord poses a challenge to probe design due to its fibrous structure, repeated deformation, low elastic modulus, and sensitivity to implantation procedures. This work addresses the elastic modulus mismatch between spinal cord tissue and synthetic devices by designing flexible multifunctional neural probes capable of conforming to the spinal cord geometry and mechanical properties, while providing functions for optical stimulation and neural recording. In this thesis, fiber drawing techniques are applied to produce flexible and stretchable probes. The utility of the devices for recording and optical stimulation is demonstrated in the spinal cord of transgenic mice expressing the light sensitive protein channelrhodopsin 2 (ChR2). Furthermore, it is shown that the optical stimulation of the spinal cord with the polymer fiber probes induces on-demand limb movements. Finally, the modest dimensions and high flexibility of the devices permitting chronic implantation into the mouse spinal cord with minimal damage to the neural tissue are demonstrated. The findings of this thesis are anticipated to aid the studies of the spinal cord circuits and pave way to new directions in flexible fiber-based optoelectronic devices.
by Chi Lu.
Ph. D.

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20

Billaud, Antonin. "Power-scaling of wavelength-flexible two-micron fibre sources." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/425928/.

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In this thesis we explore thulium doped silica fibre based sources, focusing on laser and amplified spontaneous emission behaviours. We analyse new ways of improving fibre cavity performances by first demonstrating a novel way of manufacturing doped fibres showing high pump absorption whilst retaining ease of use for cleaving and splicing. This new process offers a trade-off between circular and non-circular fibre geometries by maintaining advantages of both configurations. An implementation process on fibre drawing towers is detailed for future large scale production of highly circular active fibres with high mode scrambling, resulting in high pump absorption comparable, and potentially higher, to octagonal fibre. We then introduce a new way of improving fibre tip movement insensitivity in free-space feedback arms by utilising corner-cubes as reflective elements, with results showing transverse fibre tip movement of more than a millimetre in specific configurations whilst maintaining high feedback efficiency. Output power variation of less than 35% was demonstrated over a translation window of ±1.2mm in some cases. Exploiting the movement insensitive properties offered by a corner-cube, a tunable ring laser based on fibre tip movement and a Fabry-Perot etalon is demonstrated. Up to 5nm of quasi-continuous fine tuning is proven with a theoretical accuracy of 8pm/μm fibre tip movement and a linewidth lower than 1.5GHz is demonstrated. Potential for rapid wavelength scanning and for much broader tuning over a window of few tens of nm is proposed with further modifications of the experimental setup to allow wider fibre tip movement without feedback losses appearing. Focus is then centred on the broad tuning capabilities on thulium doped silica fibres and a CW laser source allowing tuning over more than 130nm in the 2μm band is described. Tuning is achieved by the use of a digital micro-mirror device (DMD) coupled with a diffraction grating, allowing further spectral shaping. Up to 8.5W of output power is displayed, pump power limited, with capabilities for multi-wavelength emission and spectral power density shaping by adjustment of the micro-mirror matrix reflective pattern. Modification of the system was explained in order to achieve different requirements, either by improving tuning range, accuracy or minimal line width. Utilising the fast dynamics of a doped fibre cavity, a cavity is built around an acousto-optic modulator to frustrate lasing in order to create a feedback tolerant pulsed amplified spontaneous emission (ASE) source. This source was designed to allow generation of a pulsed wavelength-controllable ASE via the use of a DMD coupled with a diffraction grating. A core-pumped setup is demonstrated, reaching tuning from 1860 to 1950nm and a cladding-pumped architecture is built for longer wavelengths generation to improve compatibility with amplifier stages. This source displayed tuning performances from 1940 to 2020nm with peak power of up to 1.5kW and pulses shorter than 100ns. Multi-waveband behaviour is demonstrated and output bandwidth is controlled through the DMD. A cladding-pumped amplification stage is described and amplification of the ASE output by 15dB, reaching up to 72W, pump limited, was demonstrated corresponding to peak powers of more than 5kW. Prospects for pumping of a ZGP OPO cavity with an ASE are discussed, detailing the potential benefits of utilising a bandwidth-adjustable ASE source for mid-infrared generation.

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21

Algarra, Nicolas Pierre. "Pénétration d'une fibre flexible dans un milieu granulaire dense." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066500/document.

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Nous étudions de manière expérimentale un cas d’interaction fluide/structure entre une fibre élastique et un milieu granulaire dense proche du jamming. Dans notre dispositif expérimental horinzontal, un milieu granulaire bidimensionnel, aléatoire et dense est en interaction avec une fibre élastique encastrée. L'extrémité encastrée de cette fibre est en translation par rapport aux grains tandis que son extrémité libre fait initialement face au flux de grains dans une géométrie de pénétration, avant de se défléchir par interaction avec les grains. Les paramètres de contrôle de notre système sont la compacité du milieu granulaire, la longueur et la rigidité de la fibre. Notre dispositif nous permet de mesurer la déformée de la fibre, les efforts que les grains exercent sur la fibre, notamment la force de traînée et de suivre les réorganisation du milieu granulaire. Sous certaines conditions expérimentales, nous avons observé que ce système présente plusieurs régimes d'évolution. A faible et à forte déflexions de la fibre, le système connaît une évolution stochastique, liée à la nature aléatoire du milieu granulaire : respectivement de petites fluctuations de la fibre autour de sa position d'équilibre et des événements brusques de balayage de la fibre en flexion associés à des avalanches granulaires. La transition entre ces deux régimes est associée à une brisure de symétrie qui affecte tant la fibre que le milieu granulaire. Dans une première partie, nous étudions comment la déflexion de la fibre est influencée par les paramètres de contrôle, en particulier par l'écart au jamming. Dans une seconde partie, nous montrons qu'une asymétrie de densité se développe dans le milieu granulaire lorsque la fibre est suffisamment défléchie. Dans une troisième partie, nous tentons de comprendre l'évolution des forces mesurées à l'aide de simulations numériques de l'Elastica sur une poutre sous chargement. Enfin, nous proposons un modèle de compaction des grains par la fibre qui est en bon accord avec l'évolution expérimentale du système. Une application de cette thèse est la compréhension des mécanismes de pénétration d'une racine ou d'une tige dans un sol granulaire
We study experimentally a fluid/structure interaction between an elastic fiber and a dense granular medium near the jamming transition. In our horizontal setup, a bidimensionnal and dense random packing is interacting with a clamped elastic fiber. The clamped end of the fiber is in translation relative to the the grains while the free end faces initially the grain flux in a penetration geometry before being deflected by grain/fiber interactions. The control parameters of our system are the packing fraction of the medium, the length and the rigidity of the fiber. Our setup allows us to measure the deflected shape of the fiber, the forces exerted by the grains on the fiber (including the drag force) and to follow the reorganizations of the granular medium. Under some experimental conditions, we observed that this system exhibits several regimes of evolution. For low and large fiber deflections, the system evolves stochastically as a consequence of the random nature of the granular medium : respectively small fluctuations of the fiber around its equilibrium position and sudden events of unlozding of the fiber in flexion associated to granular avalanches. The transition between those two regimes is associated with a symmetry breaking that affects the granular medium as well as the fiber. In a first part, we study how the fiber deflection is influenced by the control parameters, particularly by the distance to jamming. In a second part, we show that a packing fraction asymmetry appears in the granular medium when the fiber is deflected enough. In a third part, we try to understand the evolution of the measured forces using numerical simulations of the Elastica on a constrained beam. Finally, we propose a model of compaction of the grains by the fiber that is in a good aggreement with the experimental evolution of the system. An application of this thesis is the understanding of the mechanisms involved in the penetration of a root or a beam in a granular soil

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Allende, Sofia. "Dynamique et statistiques de particules allongées et flexibles dans des écoulements turbulents." Thesis, Université Côte d'Azur, 2021. https://tel.archives-ouvertes.fr/tel-03284996.

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Cette thèse analyse la dynamique de petits objets complexes immergés dans des environnements turbulents. Les champs turbulents peuvent être vus comme des champs aléatoires très fluctuants, dont les statistiques sont en général fortement non-Gaussiennes et se caractérisent par la présence de fluctuations très violentes. En pratique, la turbulence est le mécanisme dominant régissant le transport et le mélange de matière. Dans leurs détails, les propriétés statistiques du transport turbulent dépendent de la nature des particules considérées. Ici, nous nous concentrons sur le transport de petites particules complexes, qui sont caractérisées par une interaction non triviale entre leur masse, leur forme et leur rhéologie. Notre objectif est d’acquérir une compréhension physique de la façon dont les fluctuations turbulentes prescrivent la dynamique de ces particules complexes, et se manifestent au travers à la fois des phénomènes collectifs comme la concentration préférentielle, ou des phénomènes individuels allants de la déformation de particules jusqu’à leur fragmentation. Ces manifestations physiques de la turbulence ont des conséquences tant au niveau industriel que du développement durable. Par exemple, le transport atmosphérique de cendres volcaniques a des conséquences dans le secteur aéronautique commercial, ainsi que la floraison de méduses ou de phytoplancton dans les océans a des conséquences à la fois sur la maintenance des circuits de refroidissement des centrales thermiques, et sur la thermodynamique de la Terre.Nos recherches s'appuient sur des simulations numériques massives et systématiques basées sur l'intégration directe des équations de Navier-Stokes incompressibles, ce pour générer une turbulence isotrope homogène à très haut nombre de Reynolds. À partir de ces simulations, nous analysons les statistiques de différents types de particules tels que des sphéroïdes inertiels ou des fibres flexibles. Pour les sphéroïdes, nos travaux montrent que les dynamiques translationnelles et rotationnelles sont essentiellement découplées. Alors que le mouvement de translation se rattache à celui d’une sphère avec une masse effective, la dynamique de l'orientation présente des caractéristiques plus complexes. Cette complexité se reflète dans les statistiques du taux de rotation et dans les propriétés de concentration. Ainsi, la dynamique de rotation n'est pas universelle et dépend de la forme spécifique des particules.Pour les fibres nous constatons que leur dynamique est, la plupart du temps, qualitativement très semblable à celle d’une tige rigide. En des occasions très rares et intermittentes les fibres flambent violemment, et ces événements se corrèlent aux fortes compressions locales exercées par le fluide turbulent. En outre, les statistiques de l'orientation des fibres diffèrent sensiblement des statistiques de tiges parfaitement rigides, même en dehors de ces événements de flambages. Ces déviations peuvent être comprises comme des « anomalies d'alignement » causées par la flexibilité. Notre observation principale est le fait que le couplage entre les fibres et la turbulence peut se modéliser en termes de différents processus d’activation, qui rendent compte à la fois des statistiques du flambage et des anomalies de l'alignement. Nous étudions enfin la fragmentation des fibres dues à la turbulence. À cette fin, nous implémentons dans nos codes numériques deux mécanismes de rupture : flexion et tension. Nous esquissons un cadre stochastique de tels événements catastrophiques, qui justifie l'usage d'équations cinétiques du type Smoluchowski pour la description statistique de la fragmentation en temps long, et ce malgré la présence des corrélations temporelles non triviales dans les fluctuations turbulentes Lagrangiennes. Cette description ouvre des perspectives pour mieux quantifier la fragmentation des matériaux fragiles dans les codes utilisés pour la prévention des risques dans des cadres industriels
This thesis analyses the dynamics of small complex objects immersed in a turbulent environment. Turbulent flows are akin to apparent random fields, that usually display very non-Gaussian and fluctuating statistics, and which are known to enhance the mixing and the transport of the objects that they carry. Here, we focus on the transport of small complex particles, which are characterized by a non-trivial interplay between their mass, their shape and their rheology. Our aim is to gain a physical understanding on how turbulent fluctuations prescribe the dynamics of such complex particles, and lead to various physical phenomena, including preferential concentration, their deformation or catastrophic events such as their fragmentation. Studying such phenomena is relevant for both industrial and sustainability issues. For instance, while volcanic ash has direct impacts for the commercial flight industry, the blooming of diverse types of species such as jellyfishes or phytoplankton has consequences both for the maintenance of power plants and for the thermodynamics of our planet.Our approach relies on a systematic use of massive numerical simulations of the Navier-Stokes equations to generate homogeneous isotropic turbulence at high Reynolds number, and analyze in details the statistics of various types of particles such as inertial spheroids and flexible fibers. For small inertial spheroids, our numerical work shows that the translational and the rotational motion are essentially decoupled. While the translational motion can be described by the motion of a sphere with a suitably defined effective mass, the rotational dynamics displays more intricate features. This reflects in the statistics of the rotation rate and in the concentration properties. Conversely to translational motion, the rotational dynamics is therefore non-universal and depends on the specific shape of the spheroids.For small inertialess fibers, which constitute a paradigmatic example of flexible elongated particles, we find that the dynamics is most of the time closely resembling that of a stiff rod. Yet, in very rare and intermittent episodes, the fibers experience violent buckling events, which correlate to strong local compressions exerted by the local turbulent flow. Besides, detailed statistical investigations reveal that flexibility also produces misalignments of the fibers, e.g. deviations in the statistics of the orientation compared to the dynamics of a completely stiff rod. Our most salient observation is that the coupling between such flexible fibers and the turbulence can be phenomenologically modeled in terms of various activation processes, both for the buckling rate and for the misalignments statistics.We finally investigate scenarios for turbulent fragmentation of brittle fibers. To that end, we implement in our numerics two mechanisms leading to the fibers breaking in smaller pieces, either because of tensile failure or because of flexural failure. We sketch a stochastic description of such violent events that paves the way to better parametrization of turbulent-induced fragmentation of brittle material in industrial codes

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23

Kennedy, I. "Vibration transmissibility characteristics of fibre and steel reinforced flexible pipes." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378334.

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24

Abdulgader, Mohamed E. Essa. "Development of Flexible Fibre Biofilm Reactors for Treatment of Milk Processing Wastewater." Thesis, Griffith University, 2011. http://hdl.handle.net/10072/366653.

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Food processing industries use considerable amounts of fresh water for their industrial purposes. These industries generate large quantities of high strength organic wastewaters which are usually biodegradable and amenable to biological treatment systems. Numbers of biological methods are still in use for the treatment of food processing wastewaters, either anaerobic or aerobic systems. In this research, the performance using newly developed laboratory scale sequencing batch flexible fibre biofilm reactor (SB-FFBR), single stage flexible fibre biofilm reactor (SS-FFBR) and newly developed multiple stage flexible fibre biofilm reactors (MS-FFBR) for treatment of milk processing wastewater were experimentally investigated.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
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Pelegrino, Eloá Cristina Figueirinha. "Avaliação do desempenho de um reator biológico anaeróbio com leito constituído de fibras flexíveis aplicado ao tratamento de esgoto." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18138/tde-04042017-163911/.

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Nas últimas décadas diversos tipos de meio suporte têm sido propostos para a melhoria da eficiência e/ou aumento da compacidade de reatores biológicos tratando esgoto sanitário. No presente trabalho de doutorado são apresentados os resultados obtidos com a aplicação de um novo tipo de reator biológico anaeróbio de fluxo ascendente com leito de fibras flexíveis aplicado ao tratamento de esgoto sintético. Sua concepção foi motivada pelas dificuldades verificadas em alguns tipos de reatores de leito expandido, os quais ao longo do tempo de operação podem perder suas características hidrodinâmicas iniciais, devido ao acúmulo de biomassa, passando a apresentar expansão não homogênea do leito. A proposta de uso da fibra de nylon como meio suporte se deveu a sua capacidade de atuar como leito flexível - quando fixo em apenas uma de suas extremidades - que, devido á sua flexibilidade, apresenta também características parecidas às de leito móvel. Nesse novo tipo de concepção de leito, a biomassa aderida às fibras flexíveis adquirem forma de longos filamentos, os quais, devido ao próprio escoamento do esgoto e à rotação do eixo em que as fibras são fixadas, permanecem estendidos de modo a proporcionar elevada relação volume/superfície. Essa biomassa na forma de finos filamentos permanece firmemente aderida ás fibras flexíveis, reduzindo o potencial de perda de biomassa juntamente com o efluente e também de possíveis obstruções de poros, comum em leitos granulares. Para o estudo, foi projetada, construída, operada e avaliada durante 458 dias, uma instalação piloto constituída de seis reatores na forma de colunas verticais com escoamento contínuo e ascendente, operando em paralelo. Nesses reatores foram variados parâmetros de configuração e operação, como: i) a densidade de fibras flexíveis que compuseram o leito de fibras flexíveis; ii) a rotação do eixo vertical onde foram fixadas as fibras do leito; iii) o tempo de detenção hidráulica (nas etapas de 1 a 4 foram testados TDH de 9; 6; 4 e 3 horas, respectivamente); iv) a interrupção da rotação em reator em andamento. Foram analisadas as eficiências de remoção de carga orgânica e do perfil vertical dos reatores, assim como foi realizada a avaliação da composição da biomassa encontrada no biofilme, com análise de imagem e microscopia. Os resultados demonstram que a configuração dos reatores forneceram excelentes resultados de remoção de carga orgânica e também se mostraram aptos para se adaptar as variações de vazões aplicadas ao longo do trabalho, sendo observados os melhores resultados na Etapa 1 da fase 1, onde o Reator 2 apresentou eficiência de remoção de 91% de DQO total, 96% de DQO filtrada, 86% de DBO e 60% de SST. Também foi possível observar que os reatores com maiores densidades de fibras apresentaram melhores eficiências e permaneceram mais estáveis em face às características investigadas. Quanto à aplicação de rotação foi possível observar sua interferência positiva sobre a eficiência de remoção dos reatores, principalmente para as densidades de fibras inferiores e que o aumento de sua rotação também trazia melhorias na remoção de carga orgânica. Já para a avaliação da interrupção da rotação foi possível observar a redução de eficiência para os parâmetros avaliados. Também foram analisados três pós-tratamentos do efluente do reator anaeróbio por flotação, sedimentação (com e sem coagulante) e filtração em filtro de fibras flexíveis. O pós-tratamento mais adequado para ser aplicado em conjunto ao reator anaeróbio de fibras flexíveis foi a flotação, por separação (sem adição de coagulante), que apresentou remoção de 71%de turbidez, 51% de cor aparente, 40% de DQO, 25% de DQO filtrada, 34% de fósforo total e 52% de SST. Na avaliação do pós-tratamentos físico-químico mais adequado, a flotação por ar dissolvido apresentou melhores resultados utilizando o coagulante PAC em dosagem de 14 mg.L-1 do princípio ativo de Al2O3, com eficiência de remoção do sistema de 84% de turbidez, 73% de cor aparente, 50% de DQO total e 31% de DQO filtrada, 45% de fosforo total e 62% SST.
In the last decades, many different types of support media have been proposed for improving the efficiency and / or increasing the compactness of biological reactors treating domestic sewage. The results obtained in the application of a new type of up flow anaerobic bioreactor with flexible fibers bed applied to synthetic wastewater treatment are presented in this PhD thesis. Its design was motivated by the difficulties observed in some types of expanded bed reactors, which may lose their initial hydrodynamic characteristics during operation time, due to the biomass accumulation, leading to inhomogeneous bed expansion. The proposed nylon fiber is used as the support media due to its ability to operate as flexible bed - when it is fixed at only one end - which, due to its flexibility, also has characteristics similar to the moving bed. In this new type of bed design, the biomass attached to the flexible fibers acquire the form of long filaments, which, due to the sewage flow and the rotation axis in which the fibers are fixed, remain extended in order to provide high volume /surface ratio. This biomass in the form of fine filament remains firmly attached to the flexible fibers, thereby reducing the potential loss of biomass along with the effluent, as well as possible pore clogging, which are common in granular beds. For this study, a pilot installation consisted of six parallel reactors in the form of vertical columns with continuous upflow was designed, constructed, operated and evaluated for 458 days. In these reactors were varied configuration settings and operation as: i) the density of flexible fibers that composed the bed of flexible fibers; ii) the rotation of the vertical axis where the bed fibers were fixed; iii) the hydraulic retention time (in steps 1 to 4, HDTs of 9, 6, 4 and 3 hours were tested, respectively); iv) interruption of the rotation in the reactor in progress. The organic load removal and the reactors vertical profile efficiencies were analyzed, as well as the biomass composition found in biofilm, with image analysis and microscopy. The results demonstrate that the configuration of reactors provided excellent results of organic load removal and also proved to be able to adapt to variations in flow rates applied during the tests. The best results were observed in Step 1 in phase 1, where the reactor 2 presented removal efficiency of 91% of total COD, 96% of filtered COD, 86% of BOD and 60% of SST. Reactors with higher fiber density presented improved efficiencies and remained more stable, considering the investigated characteristics. The application of rotation was proved to cause a positive interference on the efficiency of the reactors removal, mainly for lower fiber density, and the increase of this rotation also brought improvements in the organic load removal. The rotation interruption caused en efficiency reduction for the evaluated parameters. Three post-treatments of the effluent of anaerobic reactor were analyzed: flotation, sedimentation (with and without coagulant) and filtration on flexible fibers filter in phase 2. The most suitable post-treatment to be applied along with the anaerobic reactor with flexible fibers was the flotation by separation (without addition of coagulant), which presented removal of 71% of turbidity, 51% of apparent color, 40% of COD, 25% of filtered COD, 34% of total phosphorus and 52% of SST. In the evaluation of the most appropriate chemical-physical post-treatment, the dissolved air flotation presented better results when using the PAC coagulant in the dosage of 14 mg.L-1 of the active principle of Al2O3, with removal efficiency of 84% of turbidity, 73% of apparent color, 50% of total COD, 31% of filtered COD, 45% of total phosphorus and 62% of TSS.

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26

Rodríguez, Razón Uriel Antonio. "DESARROLLO DE UN DETECTOR FLEXIBLE DE FOTONES GAMMA BASADO EN FIBRAS ÓPTICAS PLÁSTICAS." Tesis de maestría, Universidad Autónoma del Estado de México, 2019. http://hdl.handle.net/20.500.11799/105966.

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Se desarrolló un detector de fotones gamma con características técnicas competitivas similar a los detectores que incluyen los materiales más usados para imagen nuclear. Asimismo, se desarrolló un sistema que basado en fibras ópticas centellográficas, el cual puede dar lugar a un sistema de sonda de detección de blancos moleculares de dimensiones pequeñas.
Introduction: Nuclear imaging is based on the principle of detection of radionuclides integrated in specific recognition molecules in patients. Detection devices such as positron emission tomography and single photon emission tomography (PET, SPECT for their acronym in English) are made up of scintillating materials, mostly of the inorganic type, such as NaI(Tl) and the transducer known as a photomultiplier tube (PMT). The purpose of this work was to implement the novel options, which are analogous to the main components of the detecting devices for nuclear imaging studies. In addition to improvements in the acquisition of images for targets of small dimensions (<3 mm), reduce operating times, as well as study costs. The main materials proposed to achieve these objectives are, the scintillating plastic optical fibers and the avalanche photodiode
CONACYT, Instituto Nacioal de Investigaciones Nucleares, Universidad Autónoma del Estado de México

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27

Boiyo, Duncan Kiboi, and Romeo Gamatham. "Optimization of flexible spectrum in optical transport networks." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/14609.

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The ever-increasing demand for broadband services by end-user devices utilising 3G/4G/LTE and the projected 5G in the last mile will require sustaining broadband supply from fibre-linked terminals. The eventual outcome of the high demand for broadband is strained optical and electronic devices. The backbone optical fibre transport systems and techniques such as dense wavelength division multiplexing (DWDM), higher modulation formats, coherent detection and signal amplification have increased both fibre capacity and spectrum efficiency. A major challenge to fibre capacity and spectrum efficiency is fibre-faults and optical impairments, network management, routing and wavelength assignment (RWA). In this study, DWDM and flexible spectrum techniques such as wavelength assignment and adjustment, wavelength conversion and switching, optical add and drop multiplexing (OADM) and bitrate variable transmission have been experimentally optimized in a laboratory testbed for short- and long-haul optical fibre networks. This work starts by experimentally optimising different transmitters, fibre-types and receivers suitable for implementing cost effective and energy efficient flexible spectrum networks. Vertical cavity surface-emitting lasers (VCSELs) and distributed feedback (DFB) lasers have been studied to provide up to 10 Gb/s per channel in 1310 nm and 1550 nm transmission windows. VCSELs provide wavelength assignment and adjustment. This work utilises the non-return-to-zero (NRZ) on-off keying (OOK) modulation technique and direct detection due to their cost and simplicity. By using positive intrinsic negative (PIN) photo-receivers with error-free BER sensitivity of -18±1 dBm at the acceptable 10-9-bit error rate (BER) threshold level, unamplified transmission distances between 6 km and 76 km have been demonstrated using G.652 and G.655 single mode fibres (SMFs). For the first time, an all optical VCSEL to VCSEL wavelength conversion, switching, transmission at the 1550 nm window and BER evaluation of a NRZ data signal is experimentally demonstrated. With VCSEL wavelength conversion and switching, wavelength adjustments to a spectrum width of 4.8 nm (600 GHz) can be achieved to provide alternative routes to signals when fibre-cuts and wavelength collision occurs therefore enhancing signal continuity. This work also demonstrates a technique of removing and adding a wavelength in a bundle of DWDM and flexible channels using an OADM. This has been implemented using a VCSEL and a fibre Bragg grating (FBG) providing a wavelength isolation ratio of 31.4 dB and ~0.3 𝑑𝐵 add/drop penalty of 8.5 Gb/s signal. As a result, an OADM improves spectrum efficiency by offering wavelength re-use. Optical impairments such as crosstalk, chromatic dispersion (CD) and effects of polarization mode dispersion (PMD) have been experimentally investigated and mitigated. This work showed that crosstalk penalty increased with fibre-length, bitrate, interfering signal power and reduced channel spacing and as a result, a crosstalk-penalty trade-off is required. Effects of CD on a transmitted 10 Gb/s signal were also investigated and its mitigation techniques used to increase the fibre-reach. This work uses the negative dispersion fibres to mitigate the accumulated dispersion over the distance of transmission. A 5 dB sensitivity improvement is reported for an unamplified 76 km using DFB transmitters and combination of NZDSF true-wave reduced slope (TW-RS) and submarine reduced slope (TW-SRS) with + and – dispersion coefficients respectively. We have also demonstrated up to 52 km 10 Gb/s per channel VCSEL-based transmission and reduced net dispersion. Experimental demonstration of forward Raman amplification has achieved a 4.7 dB on-off gain distributed over a 4.8 nm spectral width and a 1.7 dB improvement of receiver sensitivity in Raman-aided 10 Gb/s per wavelength VCSEL transmission. Finally, 4.25-10 Gb/s PON-based point to point (P2P) and point to multipoint (P2MP) broadcast transmission have been experimentally demonstrated. A 10 Gb/s with a 1:8 passive splitter incurred a 3.7 dB penalty for a 24.7 km fibre-link. In summary, this work has demonstrated cost effective and energy efficient potential flexible spectrum techniques for high speed signal transmission. With the optimized network parameters, flexible spectrum is therefore relevant in short-reach, metro-access and long-haul applications for national broadband networks and the Square Kilometre Array (SKA) fibre-based signal and data transmission.

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28

Reader-Harris, Peter. "Flexible membranes for nanoplasmonic applications." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7451.

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Nanoplasmonics has provided a way to control light with extremely high precision, into nanoscale volumes. In many circumstances, the nanoplasmonic devices which can be realised are fabricated using processing techniques which rely on planar technologies. This thesis provides a general method to make nanoplasmonic devices on a flexible membrane structure, which can be free standing, extremely thin (less than the wavelength of visible light), but retains the ability to be manipulated without loss of optical function. These devices are very pliant and conformable. Flexibility allows the integration of nanoplasmonic devices into many new applications where curved surfaces or the ability to conform to another object is required, as well as providing a route for post-fabrication tunability. Two specific applications are considered: lab-on-fibre technology and surface enhanced Raman spectroscopy. Lab-on-fibre technologies have been advancing the ability to miniaturise experiments which would normally require a whole laboratory. Fabricating a membrane and then later applying it to the fibre decouples the choice of fibre from the design of the device. Surface enhanced Raman spectroscopy is a powerful diagnostic tool which can uniquely identify an optical fingerprint of different molecules. The technique has been held back from widespread clinical adoption because of the difficulty of reproducibility of the substrates used. A repeatable and reliable rigid substrate is demonstrated, which can identify the concentration of a three component mixture of physiologically relevant biomolecules. This same design is then shown in a flexible form factor, which is applied to a non-planar landscape where it can identify the locations where a molecule of interest has been deposited. This thesis details the development of the fabrication protocol, the construction of experimental apparatus for characterisation, and the use of numerical modelling to advance the flexible nanoplasmonic membrane platform.

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Zhao, Wei. "Flexible Transparent Electrically Conductive Polymer Films for Future Electronics." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1297888558.

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Reichard, Karl Martin. "Distributed-effect modal domain optical fiber senors for flexible structure control." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39420.

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Souza, João Carlos Perbone de. "Fibras de carbono modificadas com a álcool desidrogenase para o estudo da bioeletroxidação do etanol utilizando espectrometria de massas diferencial eletroquímica (DEMS)." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-16012018-102941/.

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Para a bioeletrocatálise de oxidação de etanol, a alteração da superfície eletródica e a otimização do processo de imobilização enzimática se fazem necessárias. Neste cenário, as fibras flexíveis de carbono (FFC) merecem destaque, pois além de sua superfície ser facilmente modificada devido à presença de carbono sp2, as mesmas possuem alta resistência mecânica e elasticidade, combinadas com a alta condutividade elétrica e térmica. Nesta tese de doutorado, apresenta-se como obter bioeletrodos de FFC modificadas com a enzima álcool desidrogenase (ADH) NAD-dependente, visando também aprimorar a oxidação da coenzima NADH (dinucleotídeo de nicotinamida e adenina). Os resultados mostram que quando as FCF são previamente submetidas a um tratamento oxidativo em meio ácido (KMnO4/H2SO4), obtém-se bioeletrodos estáveis, robustos e com alta área superficial. Além disso, observou-se que esses eletrodos possuem grupos funcionais contendo oxigênio que auxiliam na bioeletrocatálise de oxidação do etanol. Presume-se que presença de grupos quinonas seja responsável por facilitar a regeneração da coenzima, ou seja, estes grupos atuam decisivamente na oxidação do NADH. A alta qualidade dos bioeletrodos possibilitou manter a atividade catalítica da ADH por longo prazo, propriedade essa crucial para o estudo da oxidação do etanol acoplada à espectrometria de massas (DEMS). Devido a este estudo, foi possível observar concomitantemente a regeneração da coenzima (NADH -> NAD+) e a geração de acetaldeído como produto de bioeletroxidação do etanol, ambos em estado estacionário. Em suma, o estudo aqui apresentado introduz uma abordagem que combina não só o desenvolvimento de fibras de carbono tratadas quimicamente para aplicação em bioeletrocatálise, mas também um foco inédito no acoplamento entre a espectrometria de massas e a bioeletroquímica para a resolução de mecanismos enzimáticos.
Regarding the bioelectrocatalysis of the ethanol oxidation, the electrodic surface modification and the optimization of enzymatic immobilization are necessary. In this scenario, the flexible carbon fibers (FCF) are noteworthy, because besides their surface can be modified in an easy way due the presence of carbon sp2, they have high mechanical resistance and elasticity, combined with high electrical and thermal conductivity. In this doctoral thesis, it is presented how to obtain bioelectrodes of FFC modified with the enzyme alcohol dehydrogenase (ADH) NAD-dependent, as well as to improve the oxidation of the coenzyme NADH (nicotinamide adenine dinucleotide). The results show that when FCF is previously submitted to an oxidative treatment in acidic medium (KMnO4/H2SO4), stable, robust and high surface area bioelectrodes are obtained. In addition, it was observed that these electrodes have oxygen-containing functional groups that improve the bioelectrocatalysis of ethanol oxidation. There is proposed that the presence of quinone groups is responsible for facilitating the regeneration of the coenzyme, i. e., these groups act decisively in the oxidation of NADH. The high quality of the bioelectrodes allowed it to maintain the catalytic activity of the ADH for long term, property crucial for the study of the oxidation of ethanol coupled to mass spectrometry (DEMS). By using DEMS, there were possible to observe coenzyme regeneration and the generation of acetaldehyde as a bioelectrooxidation product of ethanol, both at steady state, which were simultaneously observed. In summary, the present study introduces an to an approach that combines not only the development of chemically treated carbon fibers for application in bioelectrocatalysis, but also an unprecedented focus on the coupling between mass spectrometry and bioelectrochemistry for the resolution of enzymatic mechanisms.

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32

Zhang, Ruirong. "A study of flexible supercapacitors : design, manufacture and testing." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/13426.

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Supercapacitors have attracted great attention because of their high power density, long life cycle and high efficiency. They can be generally classified into two types: electrical double-layer capacitors (EDLCs) and pseudocapacitors. Compared with pseudocapacitors, EDLCs have a very fast charge/discharge rate, higher power density, higher coulombic efficiency and longer cycle life. Recently, in order to meet the requirements of portable and wearable electronics, supercapacitor development is moving towards flexible and stretchable solutions. This thesis presents the design, fabrication, performance testing and optimisation of flexible strip and fibre EDLCs. In this research, a sandwich structured strip EDLC was designed and manufactured. Experimental design was utilised to optimise the operation parameters of the EDLC in order to improve its capacity for energy storage. The flexibility of the strip EDLCs was studied extensively by mechanical tests under static and dynamic loading conditions, and the correlation between the electrochemical performance of the EDLCs and the mechanical testing process was investigated. Novel coaxial fibre EDLCs have also been studied and developed in this study. Fibre supercapacitors showed a good flexibility and weavability. The activated carbon produced by ball-milling method with optimum specific capacitance was mixed with commercial ink to produce active material to optimise the electrochemical performance of fibre EDLCs. The flexible EDLCs were applied into different appliances to demonstrate the stability of performance and the usability of EDLCs developed in this study. The electrical current and potential range can be altered by connecting multiple strip or fibre EDLCs in parallel or in series to meet the power and energy requirements. It has been proved that the flexible EDLCs developed have a great potential to be used as energy storage devices for smart electronics. This thesis makes original contributions to knowledge, including using an advanced test method to study the electrochemical performance of flexible supercapacitors under static and dynamic mechanical testing, investigation of the effect of key parameters in the manufacturing process on the performance of strip supercapacitors using experimental design method to optimise the supercapacitors’ performance, and optimisation of the performance of fibre supercapacitors by improving the structure and using a new active material with higher specific capacitance.

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33

Schulmann, Nava. "Du polymère à la fibre : Conformations et élasticité de chaines à deux dimensions." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE014/document.

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Cette thèse de doctorat est consacrée à l’étude analytique et numérique de systèmes de polymères et de fibres à deux dimensions. Des systèmes de polymères confinés en films ultra-minces présentent un très grand intérêt technologique et expérimentale et posent de nombreux défis théoriques en raison de leur fort comportement non-champ moyen qui se manifeste par divers exposants critiques non triviaux. Nous nous concentrons sur la limite strictement 2D où le croisement des chaînes est interdit et nous étudions, en fonction de la densité et de la rigidité des chaînes, les propriétés élastiques et conformationnelles de trois classes de systèmes: polymères flexibles et semi flexibles à température finie et polymères macroscopiques athermiques (fibres) à courbure spontanée imposée. Pour les polymères flexibles, il est démontré que bien que les polymères auto-évitant denses adoptent des configurations compactes avec un exposant de Flory ν = 1/2, ils ne se comportent pas comme des chaines gaussiennes. En particulier un exposant de contact non-nul θ2 = 3/4 implique une dimension fractale de périmètre dp = 5/4. Par conséquence, en accord avec la loi généralisée de Porod, le facteur de structure intramoléculaire F(q) révèle un comportement non-gaussien et la température de démixion des mélanges de polymères 2D devrait être réduite. Nous étudions également les effets de la rigidité des chaînes sur les systèmes de polymères à 2D et constatons que le comportement universel n’est pas modifié lorsque la longueur de persistance est beaucoup plus petite que la longueur de confinement. La nature de la transition de phase nématique à haute rigidité, qui est dans le cas 2D l’objet d’un débat de longue date, est également explorée. Des résultats préliminaires semblent indiquer une transition du premier ordre. Enfin, motivés par un travail théorique récent sur les modules élastiques de faisceaux de fibres, nous étudions les effets de la courbure spontanée sur l’élasticité d’ensembles de fibres. Nous montrons que en jouant sur le désordre des amplitudes des modes de Fourier de l’état fondamental il est possible de régler le module de compression, en accord qualitatif avec la théorie
This PhD thesis is devoted to a theoretical study of polymer and ’polymer like’ systems in strictly two dimensions. Polymer systems in reduced dimensions are of high experimental and technological interest and present theoretical challenges due to their strong non-mean-field-like behavior manifested by various non-trivial universal power law exponents. We focus on the strictly 2D limit where chain crossing is forbidden and study as function of density and of chain rigidity conformational and elastic properties of three system classes: flexible and semiflexible polymers at finite temperature and macroscopic athermal polymers (fibers) with imposed quenched curvature. For flexible polymers it is shown that although dense self-avoiding polymers are segregated with Flory exponent ν = 1/2 , they do not behave as Gaussian chains. In particular a non-zero contact exponent θ2 = 3/4 implies a fractal perimeter dimension of dp = 5/4. As a consequence and in agreement with the generalized Porod law, the intramolecular structure factor F(q) reveals a non-Gaussian behavior and the demixing temperature of 2D polymer blends is expected to be reduced. We also investigate the effects of chain rigidity on 2D polymer systems and found that universal behavior is not changed when the persistence length is not too large compared to the semidilute blob size. The nature of the nematic phase transition at higher rigidities, which is in the 2D case the subject of a long standing debate, is also briefly explored. Preliminary results seem to indicate a first order transition. Finally, motivated by recent theoretical work on elastic moduli of fiber bundles, we study the effects of spontaneous curvature at zero temperature. We show that by playing on the disorder of the Fourier mode amplitudes of the ground state, it is possible to tune the compression modulus, in qualitative agreement with theory

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34

Chang, Sheau-Miin. "Critical evaluation of strong organic fibers vis-a-vis mechanical performance in flexible structures." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/8479.

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Sharma, Varunesh. "Mechanical properties of high performance fibers vis-a-vis applications in flexible structural composites." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/9188.

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36

Cakici, Murat. "Highly flexible carbon fibre fabric based nanostructured hybrids for high performance energy storage systems." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/18123.

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Electrochemical supercapacitors (ES), or ultracapacitors, store energy using either reversible adsorption of electrolyte ions (electrochemical double layer capacitors) or fast surface redox reactions on its electrodes (pseuodocapacitors). Currently, they are used together with batteries or fuel cells when high-power delivery or uptake is required. They have exceptional features such as high power density, high cycle efficiency, fast charging-discharging rate, long lifecycle, and safe operation. Therefore, they have attracted tremendous interest as next generation energy conversion and storage systems, ranging from portable wearable electronics to hybrid electric vehicles. However, low energy density is the main drawback to use ES as a stand-alone energy storage system. Thus, their performance should be improved to fulfil the requirements of ever-growing energy demands of progressing global economy and industry. In addition, most of the ES electrodes are fabricated from powders which makes them unsuitable for their potential use as wearable lightweight flexible devices in the future. Considering the requirements of future industrial applications of ES, this thesis focuses on synthesizing high performance, flexible, mechanically stable, lightweight, eco-friendly, and low cost ES electrodes using green, scalable, and inexpensive fabrication methods. To develop highly efficient electrode materials suitable for practical applications in a flexible design, novel synthesis procedures were explored to incorporate pseudocapacitive materials (metal oxides and electrically conductive polymers) into three-dimensional and flexible conductive carbon materials to obtain multicomponent hybrid materials. Therefore, hybrid materials reported in this thesis are binder-/conductive agent-free and also have enhanced three-dimensional nanostructures which promote energy storage. Simplicity of the fabrication methods also enable large scale and economical production of flexible and mechanically stable materials which can be directly used as ES electrodes. First, electrode materials with a unique nanostructure was developed for supercapacitor applications based on carbon fibre fabric (CFF) / MnO2 hybrid materials, in which MnO2 was uniformly coated on the surface of CFF. A green hydrothermal method was used to functionalize CFF with coral-like MnO2 nanostructures to improve the electrochemical performance of the hybrid composites. The morphological, structural, and crystalline properties of composites were analysed by using various techniques to confirm the deposition of coral-like MnO2 on CFF. The electrochemical performance was examined in a three-electrode system and cyclic voltammetry results reveal the superior specific capacitance of 467 F g-1 at a scan rate of 5 mV s-1. The cycling performance test revealed that the capacitance retention was 99.7% and the coulombic efficiency remained as high as 99.3% after 5000 cycles, demonstrating an outstanding electrochemical stability of the coral-like MnO2/CFF composite electrode. Second, synthesis method used in the first study was optimised to obtain three novel nanostructured MnO2 layers on flexible CFF substrates. It was observed that different morphologies of MnO2 could be grown on carbon fibres by adjusting the concentration of precursor solution. The morphological, structural, and crystalline properties of the composites were analysed by using various techniques to confirm that MnO2 nanostructures were successfully anchored on CFF. The electrochemical performances of the nanostructured MnO2/CFF composites were examined in two-electrode symmetric cell configuration in 1 M Na2SO4 electrolyte. Among three different morphologies, nanoplate type MnO2/CFF electrode had the best electrochemical performance (528 F g-1 at 0.5 A g-1 current density). In addition, binder and conductive agent free, flexible MnO2/CFF composite electrode had excellent cycling stability and coulombic efficiency. Finally, activated CFF (ACFF) / reduced graphene oxide (RGO)/polyaniline (PANI) composite flexible electrodes were prepared by in-situ polymerization method. Polymerization of aniline was optimized by adjusting aniline concentration to obtain PANI nanowire arrays on the three-dimensional flexible carbon based substrate. Electrochemical performance of ACFF/RGO/PANI composite was compared with ACFF and ACFF/RGO electrodes in two-electrode symmetrical cell configuration in 1 M H2SO4 electrolyte. The results indicated that ACFF/RGO/PANI exhibited outstanding area normalized capacitance due to synergistic effect between ACFF, RGO, and PANI. The facile synthesis method of the composite electrode using textile based substrate enables the possibility for fabrication of high-performance flexible energy storage devices.

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Semin, Benoît. "Intercation d'une fibre et d'un écoulement en géométrie confinée." Palaiseau, Ecole polytechnique, 2010. http://pastel.archives-ouvertes.fr/docs/00/55/93/59/PDF/these_BSemin.pdf.

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Le déplacement d'objets allongés dans un fluide se retrouve dans de nombreux domaines tels que la récupération du pétrole, la production du papier ou la nage de micro-organismes. Dans ce travail, nous étudions le comportement d'une fibre cylindrique longue dans un écoulement en géométrie confinée (fracture, canal microfluidique). Dans un premier temps, les forces de trainée exercées sur la fibre ont été déterminées expérimentalement et numériquement en fonction de son orientation et de sa position dans l'ouverture. Lorsque la fibre est parallèle à l'écoulement, elle le perturbe faiblement et une modélisation 2D est suffisante ; au contraire, lorsqu'elle est perpendiculaire, l'écoulement devient 3D quand le blocage est incomplet. Pour cette orientation, la portance est suffisante pour maintenir l'objet au centre de l'écoulement. Pour un nombre de Reynolds de l'ordre de 20, cette position devient instable : le cylindre oscille entre les deux parois. Le seuil de l'instabilité est inférieur au seuil d'émission des tourbillons de Bénard-Von Kármán. La position du cylindre est modélisée par une équation de Van der Pol qui prédit quantitativement la bifurcation de Hopf du système. Une interprétation hydrodynamique des coefficients de cette équation est présentée. Nous présentons et validons ensuite une méthode de traitement d'image, qui détermine de manière analytique la forme d'une fibre avec une précision sub-pixel. De plus, l'angle du vecteur tangent et la courbure de la fibre - essentielle car reliée à son moment fléchissant - sont mesurés avec précision
The motion of elongated objects in a fluid is encountered in many scientific fields, ranging from oil recovery and paper production to microorganism swimming. In the present thesis we study the behavior of a long cylindrical fiber in a confined flow (fracture, microfluidic channel). We first determine both experimentally and numerically the drag on this object as a function of its orientation and position in the aperture. A fiber parallel to the flow only slightly perturbs the flow, and the force on it can be estimated using 2D models. On the contrary, if it is perpendicular to the flow, the latter becomes 3D if blockage is partial. In this configuration, the lift is sufficient to keep the cylinder in the middle of the flow. For Reynolds numbers higher than 20, this position becomes unstable and the cylinder oscillates between the walls. The threshold of this instability is lower than that of Bénard-Von Kármán vortex shedding. The position of the cylinder satisfies a Van der Pol equation, which allows for a quantitative prediction of the Hopf bifurcation of the system. A hydrodynamic interpretation of the coefficients of this equation is given. We also develop and validate a new image processing method, which give the shape of the fiber with a sub-pixel precision. Moreover, the tangent vector angle and the curvature, of interest because it is related to the bending moment, are accurately measured

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Fagundes, Thalita Salgado. "Emprego de filtro de fibras flexíveis constituído de fibras de algodão mercerizado e poliéster na clarificação de água para abastecimento." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18138/tde-22062015-145737/.

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Os filtros de fibras flexíveis são módulos de filtração direta cujo leito filtrante é formado por micro fibras de poliamida, permitindo altas eficiências de remoção de sólidos suspensos, e aplicação de altas taxas de filtração. O presente estudo avaliou tal configuração de filtro utilizando fibras de algodão mercerizado e poliéster na forma de fios. Foram realizados testes de resistência dos fios a meios com características químicas distintas - alcalino, ácido e com cloro residual. Foi realizada caracterização das fibras estudadas através de Microscopia Óptica e Microscopia Eletrônica de Varredura. Foram construídos 4 filtros com diâmetro interno de 28 mm, e porosidade 67% (algodão), e 75% (poliéster), sendo 2 filtros constituídos de fibras de algodão mercerizado - comprimento de leito 60 e 100 cm; e 2 filtros constituídos de fibras de poliéster - comprimento de leito 60 e 100 cm. Foi utilizada para alimentação dos filtros água sintética de turbidez 7,7 ± 0,3 uT, e cor aparente 97 ± 5,0 uC, e realizada coagulação in-line com 22,5mg/L e 15 mg/L (este último valor somente para os filtros de 100 cm) de sulfato de alumínio. Foram avaliadas taxas de filtração de 40, 60, 80, 100 e 120 m/h. Os limites de turbidez estabelecidos para o filtrado foram de 1 e 2 uT. Os filtros de fibras flexíveis de algodão mercerizado e poliéster de leito 60 cm só conseguiram atingir os limites de turbidez até taxa de 80 m/h. Os filtros de leito 100 cm atingiram os limites satisfatoriamente em todas as taxas de filtração. Os filtros de poliéster obtiveram carreiras de filtração mais longas do que as obtidas pelos filtros de algodão, além de apresentarem perdas de carga menores. Exceto para taxa 40 e 60 m/h para o filtro de algodão mercerizado, todas as outras taxas em ambos os filtros obtiveram desempenhos melhores (carreiras de filtração longas, e filtrado de melhor qualidade) com dosagem menor de coagulante. Esse estudo mostrou potencial no uso das fibras de algodão mercerizado e poliéster nos filtros de fibras flexíveis aplicados em tratamento de água para abastecimento. Sugere-se estudos avançados para aplicação no Brasil de tal tecnologia.
The flexible fiber filters are direct filtration modules which filter media is made of polyamide micro fibers, obtaining high solids removal efficiency, and high filtration rates. This study evaluated the performance of the filter using mercerized cotton and polyester fibers. Tests of fibers resistance due to alkaline, acid and chlorinated environments were realized at the present research. The fibers were also analyzed by means of Optic and Scanning Electronic Microscopy. Four field-scale filters with an internal diameter of 28mm, porosity of 67% (cotton), and 75% (polyester) were installed; two of them made of mercerized cotton fiber- high of 60 and 100 cm; and two made of polyester fiber - high of 60 and 100 cm. A synthetic water was used as influent - turbidity 7,7 ± 0,3 uT, and color 97 ± 5,0 uC. In-line coagulation was used with 22,5 mg/L and 15 mg/L (this last value was only applied on 100cm length filters) of aluminium sulfate. The filtration rates studied were 40, 60, 80, 100 e 120 m/h. The turbidity limits were 1 e 2 uT. The 60 cm high flexible fiber filter made of mercerized cotton and polyester only could work under the established turbidity limits until 80 m/h. The 100 cm high flexible fiber filter could work well in all the filtration rates. The flexible fiber filter made of polyester obtained longer filtration times, and lower pressure drop comparing to the flexible fiber filter made of mercerized cotton. Except for filtration rates of 40 e 60 m/h which mercerized cotton filter, in all the rates for both fiber filters, the lower coagulant dosage demonstrated better results - longer filtration times, and better quality in the effluent. This study indicated the potential of using flexible fiber filter made of mercerized cotton and polyester in water treatment. It is suggested advanced studies for this technology application in Brazil.

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39

Galperin, Inna. "A numerical model of the motion of a curved flexible fibre in a shear flow." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ29375.pdf.

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40

Wang, Wenhu. "Hierarchical Hybrid Materials from Flexible Fabric Substrates." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1590083299625317.

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41

Saadat-Sarmadi, Mozafar. "Investigation of the machining processes of flexible fibrous materials for applications in industrial automation." Thesis, Durham University, 1992. http://etheses.dur.ac.uk/1124/.

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42

Cox, David E. "Active control of flexible structures using fiber optic modal domain sensors." Thesis, Virginia Tech, 1990. http://hdl.handle.net/10919/42074.

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43

Farfán, Gonzales Fabrizio Jesús, and Díaz José Luis Huaquía. "Análisis de la influencia de las fibras de basalto y lignina en las propiedades mecánicas de mezclas asfálticas en caliente de pavimentos flexibles." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/654546.

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La capa superficial del pavimento está expuesta a diversos agentes externos que desafían sus propiedades. Si estos agentes no son previstos en el diseño de mezcla, se generan distintas deformaciones. Las deformaciones excesivas en la capa de rodadura brindan bajos niveles de servicialidad. Este problema genera, además, una inversión adicional de costo y tiempo en mantenimiento. La presente investigación, estudia los efectos que tienen las fibras de basalto y lignina en la mezcla de asfalto para mejorar sus propiedades mecánicas y así, reducir las deformaciones en la carpeta asfáltica. En este trabajo se utilizó 0.3% de fibras de basalto y lignina, según investigaciones previas. Se diseñaron dos mezclas asfálticas. La primera muestra representa una mezcla convencional elaborada con agregados de la zona sur de Lima, Conchán. La segunda muestra fue elaborada con los mismos componentes, y con la adición de fibras de basalto y lignina. Ambas muestras fueron sometidas a los ensayos de estabilidad y flujo de Marshall, y al ensayo de resistencia a compresión. De los resultados obtenidos, se observa que la incorporación de basalto y lignina, aumenta la estabilidad de la mezcla en 6.45%, el índice de rigidez de Marshall en 5.8% y la resistencia a compresión en 4%. Las propiedades mencionadas, permiten tener una mezcla con mayor resistencia y mayor durabilidad.
The surface layer of the pavement is exposed to various external agents that challenge its properties. If these agents are not foreseen in the mix design, different deformations are generated, including permanent deformation. Excessive tread deformations provide low levels of serviceability. This problem also generates an additional investment of cost and time in maintenance. The present research studies the effects that basalt and lignin fibers have in the asphalt mix to improve its mechanical properties and thus reduce the deformations in the asphalt mat. Previous research indicated that the suggested percentages of basalt and lignin fibers are 0.3% of the total weight of the sample each. Two asphalt mixes were designed. The first sample represents a conventional mixture made with aggregates from the southern area of Lima, Conchán. The second was made with the same components, but with the addition of the indicated percentages of basalt fibers and lignin. Both samples were subjected to the Marshall stability and flow tests, and the compressive strength test. From the results obtained, it is observed that the incorporation of basalt and lignin increases the stability of the mixture in 6.45%, the Marshall stiffness index in 5.8% and the compressive strength in 4%. The properties allowed, allow to have a mixture with greater resistance and greater durability.
Trabajo de investigación

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Sá, Aline Beatriz Carvalho de. "Influência da porosidade do leito e do diâmetro das fibras na eficiência da filtração com filtro de fibras flexíveis aplicado ao tratamento de água." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18138/tde-21032017-104634/.

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Os filtros de fibras flexíveis são unidades de filtração direta, compostos por leito de microfibras. São operados com altas taxas de filtração, garantindo alta eficiência de remoção de sólidos suspensos. Neste estudo avaliou-se a influência dos diâmetros das fibras, da porosidade do leito e da taxa de filtração na eficiência de clarificação de uma água sintética, utilizando filtro de fibras de poliamida. Foram construídos três filtros com diâmetro interno de 28mm e porosidade de 84%, cada um com leito de 100 cm de comprimento e diâmetro de fibra de 0,03, 0,11 e 0,32 mm e um filtro de mesmo diâmetro e comprimento, composto por fibras de 0,03 mm e porosidade 93%. A distribuição de água na entrada do filtro foi composta por 4 orifícios periféricos de 3,5 mm e um orifício central de 8 mm (Fundo de filtro Tipo 1 – FTipo1). Essa mesma entrada foi utilizada para a distribuição de água e ar na lavagem. Em um segundo momento, avaliou-se outra distribuição de água na entrada do filtro, com apenas quatro orifícios periféricos (Fundo de filtro Tipo 2 – FTipo2). Nessa nova configuração de filtro, foram avaliados os filtros de fibras de 0,03 mm, em duas porosidades: 84% e 93%. A água sintética possuía turbidez de 9,51 ± 0,22 uT e cor aparente de 86,4 ± 4,5 uC. A coagulação foi realizada in-line com sulfato de alumínio na dosagem de 22,5 mg.L-1. Em todos os filtros foram avaliadas três taxas de filtração: 60, 80 e 100 m h-1 e estabeleceu-se os limites de turbidez na água filtrada de 0,5 e 2,0 uT para o final da carreira de filtração. A distribuição de água na entrada do filtro mostrou-se de extrema importância para o bom funcionamento do mesmo, pois, dependendo da sua configuração, podem ocorrer emaranhamentos das fibras, comprometendo a eficiência de remoção de cor e turbidez. O filtro com fundo FTipo1 apresentou qualidade satisfatória para o filtro de fibras com diâmetro 0,11 mm, produzindo água filtrada com turbidez abaixo de 2,0 uT. O filtro de fibras de 0,03 mm de diâmetro conseguiu produzir qualidade dentro do limite estabelecido em alguns ensaios, entretanto não houve repetibilidade devido ao emaranhamento ocorrido no leito. Já o filtro de fibras de diâmetro 0,32 mm não atingiu turbidez satisfatória. Os dois filtros de fibras com fundo FTipo2 e porosidades 93% e 84%, respectivamente, conseguiram atingir os valores impostos para a turbidez da água filtrada em todas as taxas estudadas (60, 80 e 100m h-1) , com exceção do filtro de 93% de porosidade que não atingiu a turbidez mínima de 0,5 uT quando operado uma taxa de 100 m h-1. Ao final estimou-se os volumes de água filtrada produzidos no intervalo de um dia (24h) para cada filtro que atingiu os limites de turbidez pré-estabelecidos. Dentre as variações testadas em FTipo1 e FTipo2, concluiu-se que o volume diário de água produzida aumenta proporcionalmente ao aumento da taxa de filtração. Esse estudo demonstrou que o diâmetro da fibra, a porosidade e o fundo do filtro são características essenciais para o bom funcionamento do filtro, influenciando na eficiência de remoção de turbidez e cor aparente da água afluente.
The flexible fiber filters are direct filtration module, made of microfibers filter media. They are operated with high filtration rates ensuring high solids removal efficiency. This study evaluated the influence of diameters of fibers, porosity and filtration rates in the clarification efficiency of synthetic water. Three filters have been constructed with internal diameter of 28 mm and porosity of 84%, each with a filter medium of 100 cm length and fiber diameter of 0.03, 0.11 and 0.32 mm, and a filter of the same diameter and length, comprises fibers of 0.03 mm and porosity of 93%. The water distribution at the filter inlet was composed by four peripheral holes of 3.5 mm and a central hole of 8 mm (filter bottom Type 1 - FType1). That same input was used for water and air distribution in the wash. In a second step, was evaluated other water distribution in the filter inlet, with only four peripheral holes (filter bottom Type 2 - FType2). In this new filter configuration were evaluated 0.03 mm fiber filters with two porosity values: 84% and 93%. The synthetic water had turbidity of 9.51 ± 0.22 NTU and apparent color of 86.4 ± 4.5 uC. The coagulation was performed in-line with aluminum sulfate at a dosage of 22.5 mg.L-1. In all three filters were evaluated three filtration rates: 60, 80 and 100 m / h and fixed the limits of the filtered water turbidity of 0.5 and 2.0 NTU at the end of the career filter. The water distribution in the filter inlet proved to be extremely important for the proper functioning of the same, because, depending on your configuration, entanglements can occur, compromising the color and turbidity removal efficiency. The bottom filter FType1 presented a satisfactory quality for the fiber filter diameter 0.11 mm, producing filtered water with turbidity below 2.0 NTU. The filter of 0.03 mm diameter fibers could produce water quality within the limit in some tests, however there was no repeatability due to entanglement occurred in the bed. Other way, the 0.32 mm diameter fiber filter has not reached satisfactory turbidity. The two fibers filters FType2 and porosity 93% and 84%, respectively, were able to achieve values imposed to the turbidity of the filtered water in all studied rates (60, 80 and 100 m.h-1), except 93% porosity filter witch not reached the minimum turbidity of 0.5 NTU when operated a 100 m.h-1 rate. At the end was estimated the volumes of the filtered water produced within one day (24h) for each filter that has reached the limits of predetermined turbidity. Among the variations tested FType1 and FType2, can be concluded that the daily water volume produced increases with the filtration rate increasing. This study demonstrated that the fiber diameter, porosity and filter bottom characteristics are essential for the proper functioning of the filter, influencing the apparent color and turbidity removal efficiency of influent water.

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Herrington, Kevin D. "Factors Affecting Fiber Orientation and Properties in Semi-Flexible Fiber Composites Including the Addition of Carbon Nanotubes." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/56655.

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Within this research, factors affecting the orientation of injection molded long fiber composites in an end-gated plaque were investigated. Matrix viscosity was found to have a small effect on fiber orientation. The impact matrix viscosity had on orientation was dependent on fiber loading. At lower fiber loadings, the higher viscosity material had a more asymmetric orientation profile throughout the samples and less of a shell-core-shell orientation. At higher fiber loadings, there were few differences in orientation due to matrix viscosity. Fiber concentration was found to have a larger influence on fiber orientation than matrix viscosity. Increased fiber concentration led to a lower degree of flow alignment and a broader core region at all locations examined, following the trend previously reported for short fiber composites. The orientations of three different fiber length distributions of glass fiber (GF) were compared. The longer fibers in the fiber length distribution were shown to have a disproportionate effect on orientation, with weight average aspect ratio being better than number average aspect ratio at indicating if the GF and CF samples orientated comparably. To improve properties transverse to the main flow direction, the super critical carbon dioxide aided deagglomeration of multi-walled carbon nanotubes (CNTs) was used to create injection molded multiscale composites with CNT, CF, and polypropylene. The addition of CNTs greatly improved the tensile and electrical properties of the composites compared to those without CNTs. The degree of improvement from adding CNTs was found to be dependent on CF concentration, indicating that the CNTs were most likely interacting with the CF and not the polymer. A CNT concentration of 1 wt% with a tenfold degree of expansion at 40 wt% CF proved to be optimum. A large improvement in the tensile properties transverse to the flow direction was found implying that the CNTs were not highly flow aligned. Tensile and electrical properties began to fall off at higher CNT loadings and degrees of expansion indicating the importance of obtaining a good dispersion of CNTs in the part.
Ph. D.

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46

Semin, Benoît. "Interaction d'une fibre et d'un écoulement en géométrie confinée." Phd thesis, Ecole Polytechnique X, 2010. http://pastel.archives-ouvertes.fr/pastel-00006340.

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Le déplacement d'objets allongés dans un fluide se retrouve dans de nombreux domaines tels que la récupération du pétrole, la production du papier ou la nage de micro-organismes. Dans ce travail, nous étudions le comportement d'une fibre cylindrique longue dans un écoulement en géométrie confinée (fracture, canal microfluidique). Dans un premier temps, les forces de trainée exercées sur la fibre ont été déterminées expérimentalement et numériquement en fonction de son orientation et de sa position dans l'ouverture. Lorsque la fibre est parallèle à l'écoulement, elle le perturbe faiblement et une modélisation 2D est suffisante ; au contraire, lorsqu'elle est perpendiculaire, l'écoulement devient 3D quand le blocage est incomplet. Pour cette orientation, la portance est suffisante pour maintenir l'objet au centre de l'écoulement. Pour un nombre de Reynolds de l'ordre de 20, cette position devient instable : le cylindre oscille entre les deux parois. Le seuil de l'instabilité est inférieur au seuil d'émission des tourbillons de Bénard-Von Kármán. La position du cylindre est modélisée par une équation de Van der Pol qui prédit quantitativement la bifurcation de Hopf du système. Une interprétation hydrodynamique des coefficients de cette équation est présentée. Nous présentons et validons ensuite une méthode de traitement d'image, qui détermine de manière analytique la forme d'une fibre avec une précision sub-pixel. De plus, l'angle du vecteur tangent et la courbure de la fibre - essentielle car reliée à son moment fléchissant - sont mesurés avec précision.

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47

McKnight, Thomas Kevin. "An Improved Flexible Neutron Detector For Powder Diffraction Experiments." BYU ScholarsArchive, 2005. https://scholarsarchive.byu.edu/etd/463.

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Large amounts of money are being applied to the construction of the next generation of spallation sources for neutron scattering. Neutron powder diffraction instruments will be an important element of these facilities and the incorporation of detectors into these instruments with a high neutron capture efficiency is desirable. A new detector design named the Flexible Embedded Fiber Detector (FEFD) has been developed and tested for this thesis. This detector is based on wavelength shifting fibers embedded in a zinc-sulfide lithium-fluoride based scintillator. The virtue of this design is that the detecting surface can be curved around the Debye-Scherrer rings. This virtue is lacking in other detector designs, making them more complex and poorer in performance than our FEFD detectors. Monte Carlo calculations were performed to determine the neutron capture efficiencies of our FEFD detectors, which proved to be much higher than those of the proposed powder diffractometer design for the Spallation Neutron Source and about equal with the efficiency for the ISIS powder diffractometer design. Four FEFD detector prototypes were then fabricated and tested at the Intense Pulsed Neutron Source at Argonne National Laboratory. We find that our measured and calculated relative efficiencies are in good agreement.

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Stenhammar, Philip, and Patrik Hård. "Optimering av flexibel transmissionslänk till vinschbaserat vågkraftverk." Thesis, KTH, Maskinkonstruktion (Inst.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-230618.

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Detta projekt undersöker olika alternativ av design utav transmissionskedja för ett vågkraftverk. Designen av koncepten kan delas in i två grupper, en grupp med styva länkar och rörliga leder och en annan grupp med stela leder och böjflexibla länkar. Analysen genomförs genom att undersöka olika tvärsnitt och olika material. De material som länkarna undersöks för är kolstål, rostfritt stål, aluminium, glas- och kolfiberkomposit. Analyserna utförs analytiskt för transmissioner med stela leder och böjflexibla länkar och för styva länkar med rörliga leder används Solidworks tillsammans med Ansys Workbench. En transmission med rörliga leder togs fram och idén baserades på en rullkedja. Denna design klarar de ställda kraven men det skapas problem i kontakteringen mellan kedjelederna där det blir koncentrationsspänningar och mycket slitage. I nuläget finns det inte några bussningar eller lager som klarar kraven som ställs på kedjan. I den andra gruppen med stela leder och böjflexibla länkar togs det fram två koncept. Den första har ett rektangulärt tvärsnitt och den andra ett runt. Den med det runda tvärsnittet klarar inte kraven då både böj- och dragspänningarna inte kan hållas tillräckligt låga samtidigt.Konceptet med det rektangulära tvärsnittet, som liknar ett band, klarar alla krav förutom utmattningskravet. Då bandet är tillverkat i stål blir bandets bredd för stor för bojen. Då bandet är tillverkat i aluminium uppfylls inte utmattningskravet. Fiberkompositer tappar mer än 50 % av sin styrka efter 10 miljoner repetitioner vilket gör att de måste bytas ut med jämna mellanrum för att undvika brott.
This project examines different options of designs of transmission chains for a wave power plant. The different designs can be divided into two groups, one group that contains chains with stiff links and moving joints and another group with stiff joints and bend flexible links. The analysis is carried out by examining different cross sections and different materials. The links are evaluated with carbon steel, stainless steel, aluminum, glass and carbon fiber composite. The analyses are preformed analytically for the group with stiff joints and bend flexible links and the group with stiff links and moving joints are examined with Solidworks together with Ansys workbench. One transmission with stiff links and moving joints was made inspired by a roller chain. This design meets the requirements, but problems occur in the contact between the links, where it appears concentration stresses and a lot of wear. At present there are no bearings that meet the demands on the chain.In the second group with stiff joints and bend flexible links, two designs were developed. The first one has a rectangular cross section and the other one has a round. The circular cross section does not meet the requirements, since both bending and tensile stresses cannot be kept low enough at the same time. The design with the rectangular cross section meets all the requirements except the fatigue requirement. After 10 million repetitions the fiber composites loses more than 50 % of its strength, which means that they needs to be replaced periodically to avoid fracture.

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Morita, Alice Kimie Martins. "Emprego de filtro de fibra flexível constituído de sisal e de polipropileno na clarificação de água para abastecimento." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18138/tde-31072013-114421/.

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Os filtros de fibra flexível são módulos de filtração recentemente desenvolvidos cujo leito é constituído de fibras de poliamida, o que permite a obtenção de altas eficiências de remoção de sólidos associadas a altas taxas de filtração. Este estudo objetivou avaliar o desempenho deste tipo de filtro utilizando-se como meio filtrante fibras flexíveis de sisal e de polipropileno. Com isso se buscou aprofundar o entendimento da técnica de filtração em leito de fibras flexíveis, além de propor e avaliar leitos com fibras diferentes daquelas citadas na literatura (constituídas de poliamida), neste caso fibras naturais (sisal) e fibras de polipropileno. A superfície das fibras em estudo foi analisada por meio de microscopia óptica e eletrônica de varredura e através de ensaios de solubilidade em ácido clorídrico e hidróxido de sódio, com a finalidade de investigar as características superficiais dos materiais filtrantes e sua solubilidade. Foram construídos 6 filtros com diâmetro interno de 28 mm e porosidade de leito de 93%, sendo 3 constituídos de fibras de sisal com comprimentos de leito de 25,60 e 100 cm, e 3 constituídos de fibras de polipropileno, também nos comprimentos de 25,60 e 100 cm. Em um segundo momento foi avaliado o desempenho de filtros constituídos de sisal nos mesmos comprimentos citados, no entanto com porosidade de leito de 85%. Foi utilizada para alimentação dos filtros água sintética com 8,19 ± 0,85 uT e 14,47 ± 5,25 uC e foi realizada coagulação in-line por meio da adição de 22,5 mg/L de sulfato de alumínio. Foram avaliadas taxas de filtração desde 5 m/h até 80 m/h no caso dos filtros do sisal com diferentes comprimentos e porosidades, e desde 20 m/h até 80 m/h no caso dos filtros de polipropileno. O limite de turbidez estabelecido para o filtrado foi de 1 uT. Puderam operar dentro do limite de turbidez estabelecido os filtros de polipropileno de 25,60 e 100 cm com taxa de 20 m/h e de 60 e 100 cm com taxas de até 80 m/h, e o filtro de sisal de 100 cm e 85% de porosidade com taxas de 20 e 40 m/h. Os maiores volumes de filtrado foram obtidos para filtro de polipropileno de 100 cm operando com taxa de 20 m/h, no entanto estes foram associados a maior perda de carga. Por outro lado, o filtro de sisal de 100 cm produziu menor quantidade de filtrado, porém com perda de carga associada consideravelmente baixa. Os melhores índices de filtrabilidade foram obtidos para o filtro de sisal de 100 cm de comprimento e 85% de porosidade de leito, o que indica seu potencial de aplicação, especialmente em ocasiões em que a carga hidráulica disponível seja restrita e a turbidez exigida do filtrado não seja demasiadamente baixa (inferior a 0,5 uT). Sugere-se a utilização de filtros constituídos de fibras de sisal como unidades de pré-filtração ou a construção de leitos com menor porosidade e maior comprimento de leito do que os utilizados neste estudo, caso se objetive aplicação em tratamento de água para abastecimento. Este estudo mostrou que é possível utilizar fibras de sisal e de polipropileno em filtros de fibras flexível, e a escolha dos diferentes tipos de fibras, comprimentos e porosidades de leito dependeria da disponibilidade no local, da qualidade do efluente exigida e da carga hidráulica disponível.
The flexible fiber filter is a filtration module recently developed whose filter media is made of polyamide fibers, what permits to obtain high solids removal efficiency associated to high application rates. The objective of this study was to evaluate the performance of this kind of filter using as filter media flexible fibers of sisal and polypropylene. With this it was intended to deepen the understanding of the filtration technique using flexible fibers as media and to propose and evaluate filter medias made of fibers different from the ones found in the literature: natural fibers (sisal) and polypropylene fibers. The fibers in study were analysed by means of optic and scanning electronic microscopy and through solubility essays in chloridric acid and sodium hydroxide, with the intention to characterize the filtering materials and find if there are restrictions of their use. Six filters with 28 mm of intern diameter and 93% of porosity were constructed, three being made of sisal fibers with 25, 60 and 100 cm of length, and three being made of polypropylene fibers, with 25,60 and 100 cm of length, too. In a second moment three other sisal fibers were constructed and evaluated, with the same lengths studied before, but with porosity of the filter medium of 85%. The filtration system was fed with synthetic water with 8,19 ± 0,85 uT and 14,47 ± 5,25 uC, and in-line coagulation was applied by the addition of 22,5 mg/L of aluminium sulfate. In the case of the sisal filters, made of different lengths and porosities, rates from 5 m/h to 80 m/h were evaluated; in the case of polypropylene filters, rates from 20m/h and 80m/h were evaluated. It was established as the turbidity limit the value of 1 uT. The filters that worked within the established turbidity limit were the polypropylene filters of 25,60 and 100 cm for the rate of 20 m/h and of 60 and 100 cm for rates until 80m/h, and the sisal filter of 100 cm and 85% of porosity for rates of 20 and 40 m/h. The biggest filtrate volumes were obtained for polypropylene filter of 100 cm working with the rate of 20 m/h; however this one was associated to the biggest values of pressure drop. On the other hand, the filter made of sisal with 100 cm produced a smaller quantity of filtrate, but associated to a considerably low value of pressure drop. The best filterability indexes were obtained for the filter made of sisal with 100 cm of length and 85% of porosity, what indicates its application potential, mainly to situations when there is not enough hydraulic charge and when the requested turbidity of the filtrate is not too low (less than 0,5 uT). It is suggested that the filters made of sisal are used as pre-filtration units or that they are built with smaller values of porosity and/or with a longer filter length than the ones used in this study, in the case that water treatment application is aimed. This study showed that it is possible to use sisal and polypropylene fibers in flexible fiber filters, and that the choice of different types of fibers, lengths and porosities depends on de availability of materials in the local, on the required quality of the filtrate and on the available hydraulic charge.

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Samur, Algan. "Flexible piezoelectric composites and concepts for bio-inspired dynamic bending-twisting actuation." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47680.

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