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1
Galvin, Brian Russell. "Numerical studies of localized vibrating structures in nonlinear lattices". Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28408.
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Zhang, Botao. "Design of Variable-Density Structures for Additive Manufacturing Using Gyroid Lattices". University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535374427634743.
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Brown, Stephen A. "The response of polyhedra in close packed structures to temperature and pressure". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-11102009-020124/.
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Damon, François. "Sonder des structures complexes avec des ondes de matière". Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30342/document.
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Ce manuscrit présente les travaux que j'ai effectués au Laboratoire de Physique Théorique durant ma thèse. Ils portent sur l'interaction d'ondes de matière avec des réseaux optiques modulables en temps et en espace. L'utilisation de ces réseaux a permis de contrôler de manière cohérente les propriétés dynamiques d'un gaz d 'atomes ultra-froids. Cette étude théorique a été réalisée en collaboration avec le groupe Atomes Froids du Laboratoire LCAR. Les variations spatiales de l'enveloppe d u réseau créent, localement, des gaps spatiaux créant une cavité de Bragg pour onde de matière, dont nous avons étudié en détail les propriétés et qui a fait l'objet d'une réalisation expérimentale impliquant la propagation d'un condensat de Bose-Einstein de rubidium 85 dans un guide d'onde. Nous avons également étudié la propagation d'un nuage d 'atomes dans un réseau bichromatique qui permet de réaliser un simulateur quantique du modèle de Harper. Le spectre du hamiltonien de ce système a une dimension fractale pouvant être caractérisée nu mériquement. Nous avons montré, par ailleurs, qu'il est possible d'exploiter les interactions inter-atomiques répulsives d'un condensat de Bose-Einstein afin d'amplifier les corrélations position-vitesse lors de sa pro pagation dans un guide. Notre étude montre qu'une mesure des grandeurs dynamiques locales du nuage atomique permet de sonder expérimentalement les résonances d'un potentiel optique jusqu'à l'échelle du picoKelvin. Enfin, un nuage d'atomes en interaction attractive admet une solution d'équilibre : le soliton. Nous avons démontré, numériquement, que celui-ci peut être utilisé pour sonder des états liés d'un poten tiel de taille finie, en peuplant ces états lors d'une expérience de diffusion comme, par exemple, des états de surfaceThis thesis presents the studies that I did at the Laboratoire de Physique Théorique. It concerns the interaction between matter waves and time and space depandant optical lattices. Using such lattices allows one to manipulate coherently the dynamical properties of ultra cold atoms. This theoretical study has been done in collaboration with the Cold Atoms group at the LCAR laboratory. The spatial variations of the lattice envelope locally create spatial gaps which create a Bragg cavity for matter waves. We have st udied in detail their properties and the cavity has been realized experimentally by using a Ru bid ium 85 Bose-Einstein condensate in a wave guide. We have also studied the propagation of an atomic cloud in a bichromatic optical lattice which allows us to make a quantum simulator of the Harper madel. The spectrum of the system Hamiltonian· posseses a fractal dimension which can be numerically characterized. We have also shawn that it is possible to use the repulsive interatomic interaction of a Bose-Einstein condensate in arder to amplify the momentum-position correlation during propagation in a guide. Our st udy shows that a mesure of local dynamical quantities of the atomic cloud enables one to experimentally probe resonances of an optical potential down to the picoKelvin scale. At last, an atomic cloud with attractive interactions admit a stable solution, the soliton. We have numerically demonstrated that this soliton can be used to probe bound states of a potential by populating those states through a scattering experiment, for example surface states
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Reid, Robert. "Propagation and period-doubling of coherent structures in coupled lattice maps". Thesis, University of Warwick, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369417.
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Leo, James Lewis. "The transport properties of semiconductor super-lattices and multiple quantum well structures". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47153.
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Holder, Jonathan Paul. "Resonant tunnelling spectroscopy of vertical GaAs/AlGaAs structures". Thesis, University of Exeter, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312281.
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Stay, Justin L. "Multi-beam-interference-based methodology for the fabrication of photonic crystal structures". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31783.
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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.Committee Chair: Thomas K. Gaylord; Committee Member: Donald D. Davis; Committee Member: Gee-Kung Chang; Committee Member: Muhannad S. Bakir; Committee Member: Phillip N. First. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Refai, Khalil. "Effet de la méso-architecture sur le comportement en fatigue des structures lattices optimisées obtenues par fabrication additive". Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE028.
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Une approche numérique est proposée pour évaluer la résistance en fatigue à grand nombre de cycles des structures cellulaires périodiques produites par SLM sous des chargements multiaxiaux. Le modèle est basé sur un schéma général d'homogénéisation numérique et une description explicite de la cellule élémentaire combinée à une analyse des valeurs extrêmes utilisant un paramètre indicateur de fatigue basé sur le critère de Crossland. De plus, l'écart géométrique et la rugosité de surface sont caractérisés expérimentalement et prisent en compte dans le modèle numérique en utilisant trois méthodes qui sont comparées à la résistance en fatigue expérimentale. L'optimisation topologique (OT) repousse encore plus loin les limites de la liberté de conception. Dans notre étude, l'OT a été développée pour prévenir les défaillances dues à la fatigue en utilisant la méthode SIMP reformulée dans le cadre mathématique des fonctions NURBS (Non-Uniform Rational BSpline)A numerical approach is proposed to assess the high cycle fatigue strength of periodic cellular structures produced by SLM under multiaxial loads. The model is based on a general numerical homogenisation scheme and an explicit description of the Elementary Cell combined to an extreme values analysis making use of a fatigue indicator parameter based on Crossland’s criterion. Also, geometric discrepancy and surface roughness are experimentally characterised and considered in the numerical model using three methods which are compared to the experimental fatigue strength. Topology optimisation (TO) pushes the boundaries of design freedom even further. In our study, Topology Optimisation was developed to prevent fatigue failure using SIMP method revisited and reformulated within the mathematical framework of Non-Uniform Rational BSpline functions
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Chen, Li. "A quasicontinuum approach towards mechanical simulations of periodic lattice structures". Doctoral thesis, Universite Libre de Bruxelles, 2020. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/314314.
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Thanks to the advancement of additive manufacturing, periodic metallic lattice structures are gaining more and more attention. A major attraction of them is that their design can be tailored to specific applications by changing the basic repetitive pattern of the lattice, called the unit cell. This may involve the selection of optimal strut diameters and orientations, as well as the connectivity and strut lengths. Numerical simulation plays a vital role in understanding the mechanical behavior of metallic lattices and it enables the optimization of design parameters. However, conventional numerical modeling strategies in which each strut is represented by one or more beam finite elements yield prohibitively time consuming simulations for metallic lattices in engineering scale applications. The reasons are that millions of struts are involved, as well as that geometrical and material nonlinearities at the strut level need to be incorporated. The aim of this thesis is the development of multiscale quasicontinuum (QC) frameworks to substantially reduce the simulation time of nonlinear mechanical models of metallic lattices. For this purpose, this thesis generalizes the QC method by a multi-field interpolation enabling amongst others the representation of varying diameters in the struts’ axial directions (as a consequence of the manufacturing process). The efficiency is further increased by a new adaptive scheme that automatically adjusts the model reduction whilst controlling the (elastic or elastoplastic) model’s accuracy. The capabilities of the proposed methodology are demonstrated using numerical examples, such as indentation tests and scratch tests, in which the lattice is modeled using geometrically nonlinear elastic and elastoplastic beam finite elements. They show that the multiscale framework combines a high accuracy with substantial model reduction that are out of reach of direct numerical simulations.Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished
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Hassaine, Daouadji Valentin. "Caractérisation et modélisation de structures lattices obtenues par fabrication additive : application aux équipements sportifs absorbeurs de chocs". Thesis, Centrale Lille Institut, 2020. http://www.theses.fr/2020CLIL0005.
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L’émergence des techniques de fabrication additive permet de réaliser des structures lattices de géométries complexes. Leur potentiel, en termes de légèreté, d’absorption des chocs, de personnalisation et de design attise l'intérêt de l'équipementier sportif DECATHLON, qui envisage ces méso-structures pour des applications casques et chaussures. Ce travail étudie le comportement de différentes géométries de lattices soumises à des chargements de compression.Dans une première partie, la faisabilité technique de produits sportifs en lattices a été évaluée par des compressions statiques et des impacts dynamiques adaptés aux normes casques et chaussures. Cette étude préliminaire a permis de mettre en évidence l’intérêt des lattices dans les applications sportives.La deuxième phase de ce travail a consisté à développer des modèles et méthodes de dimensionnement de lattices. Le comportement mécanique de lattices octets réalisées en deux matériaux (PA12 et TPU) a été caractérisé. La géométrie et le respect dimensionnel de ces structures ainsi que la quantification des champs cinématiques sous sollicitations ont été analysés par micro-tomographie.Un modèle numérique réalisé sous un code éléments finis a ensuite été proposé. Une confrontation aux observations expérimentales a permis d'évaluer la pertinence du modèle. Pour une meilleure représentativité des zones de jonction des poutres (les vertices), et donc une meilleure exploitation des modélisations, une rigidification locale aux vertices est étudiée par un plan d'expérience numériqueAdditive manufacturing enables the production of complex parts such as lattice structures. Their potential, in terms of lightness, improved impact performances, customization and design, draws the attention of the sports equipment manufacturer DECATHLON, who is considering these meso-structures for helmets and shoes applications. This study focuses on the behaviour of several lattices subjected to compressive loading.A preliminary experimental phase identified the behaviour of two materials (PA12 and TPU) produced by a laser sintering process (SLS). The technical feasibility of lattices structures in sports products was then evaluated using static compressions and dynamic impacts adapted to helmet and footwear standards.The second stage of the study consists in developing numerical tools for the design of lattices structures. Several lattices were produced. There mechanical behaviour was characterized in several aspects: the static response under compressive loadings was compared to foams conventionally used for energy absorption; the dimensional stability of the structures and the quantification of the kinematic fields under stress were assessed by micro-tomography.Thanks to these observations, the relevance of a numerical lattice model realized under a finite element code was evaluated. Its lack of representativeness of the junction zones of the beams (the vertices) limits its use. Nevertheless, a local stiffening at the vertices, studied by a numerical design of experiment, greatly improved the modeling
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Hassaine, Daouadji Valentin. "Caractérisation et modélisation de structures lattices obtenues par fabrication additive : application aux équipements sportifs absorbeurs de chocs". Thesis, Ecole centrale de Lille, 2020. http://www.theses.fr/2020ECLI0005.
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L’émergence des techniques de fabrication additive permet de réaliser des structures lattices de géométries complexes. Leur potentiel, en termes de légèreté, d’absorption des chocs, de personnalisation et de design attise l'intérêt de l'équipementier sportif DECATHLON, qui envisage ces méso-structures pour des applications casques et chaussures. Ce travail étudie le comportement de différentes géométries de lattices soumises à des chargements de compression.Dans une première partie, la faisabilité technique de produits sportifs en lattices a été évaluée par des compressions statiques et des impacts dynamiques adaptés aux normes casques et chaussures. Cette étude préliminaire a permis de mettre en évidence l’intérêt des lattices dans les applications sportives.La deuxième phase de ce travail a consisté à développer des modèles et méthodes de dimensionnement de lattices. Le comportement mécanique de lattices octets réalisées en deux matériaux (PA12 et TPU) a été caractérisé. La géométrie et le respect dimensionnel de ces structures ainsi que la quantification des champs cinématiques sous sollicitations ont été analysés par micro-tomographie.Un modèle numérique réalisé sous un code éléments finis a ensuite été proposé. Une confrontation aux observations expérimentales a permis d'évaluer la pertinence du modèle. Pour une meilleure représentativité des zones de jonction des poutres (les vertices), et donc une meilleure exploitation des modélisations, une rigidification locale aux vertices est étudiée par un plan d'expérience numériqueAdditive manufacturing enables the production of complex parts such as lattice structures. Their potential, in terms of lightness, improved impact performances, customization and design, draws the attention of the sports equipment manufacturer DECATHLON, who is considering these meso-structures for helmets and shoes applications. This study focuses on the behaviour of several lattices subjected to compressive loading.A preliminary experimental phase identified the behaviour of two materials (PA12 and TPU) produced by a laser sintering process (SLS). The technical feasibility of lattices structures in sports products was then evaluated using static compressions and dynamic impacts adapted to helmet and footwear standards.The second stage of the study consists in developing numerical tools for the design of lattices structures. Several lattices were produced. There mechanical behaviour was characterized in several aspects: the static response under compressive loadings was compared to foams conventionally used for energy absorption; the dimensional stability of the structures and the quantification of the kinematic fields under stress were assessed by micro-tomography.Thanks to these observations, the relevance of a numerical lattice model realized under a finite element code was evaluated. Its lack of representativeness of the junction zones of the beams (the vertices) limits its use. Nevertheless, a local stiffening at the vertices, studied by a numerical design of experiment, greatly improved the modeling
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Balthazar, Matthis. "Conception d’outillage de mise en forme des composites à haute dynamique thermique via l’utilisation de structures lattices à porosité contrôlée". Electronic Thesis or Diss., Nantes Université, 2024. http://www.theses.fr/2024NANU4031.
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La mise en forme des matériaux composites nécessite un apport et une évacuation contrôlés de la chaleur dans la pièce afin de garantir sa qualité tout en permettant une productivité maximale. Dans les procédés nécessitant un outillage pour le formage des matériaux, la régulation thermique est assurée par des canaux où circule un fluide à débit et température contrôlés. Ces canaux doivent être proches de la surface de la cavité moulante pour une réponse thermique rapide, mais leur distance est limitée par la résistance mécanique et le risque de marquage thermique des pièces. Une alternative aux approches classiques est l'utilisation d’un milieu poreux constitué de structures lattices dans lequel un fluide de régulation va circuler. Ces structures poreuses peuvent être intégrées dans les outillages au plus près de la surface car elles apportent un renfort structurel, et évitent le marquage thermique grâce à un écoulement sous forme de « nappe ». L’inertie thermique peut alors être fortement réduite. Cette solution a pour objectif de réduire au maximum le temps de réponse thermique de l'outillage lorsqu'il est soumis à des variations de température, de réduire la consommation énergétique du procédé, mais aussi de pouvoir concentrer localement les puissances à évacuer ou apporter en adaptant spatialement la porosité de la structure. Ce travail de thèse s’interesse à l’analyse des transferts thermiques couplés à l’écoulement du fluide au sein de l’outillage. Pour cela, le travail comporte une étude numérique et une expérimentale. Les résultats fournissent une compréhension des paramètres de conception sur la performance de l’outillage et démontrent la pertinence de l’utilisation de telles structures pour la gestion thermiqueThe forming of composite parts requires a controlled supply and release of heat to and from the part, in order to guarantee quality while maximizing productivity. In processes requiring tooling for material forming, thermal regulation is ensured by channels through which a fluid circulates at a controlled flow rate and temperature. These channels need to be close to the surface of the mold cavity for rapid thermal response, but their distance is limited by mechanical strength and the risk of thermal marking of the parts. An alternative to conventional approaches is to use a porous medium consisting of lattice structures in which a fluid will circulate. These porous structures can be integrated into tooling as close as possible to the surface, as they provide structural reinforcement and avoid thermal marking thanks to a "sheet" flow. Thermal inertia can thus be greatly reduced. The aim of this solution is to minimize the thermal response time of the tooling when subjected to temperature variations, to reduce the energy consumption of the process, and to locally concentrate the power to be evacuated or supplied by spatially adapting the porosity of the structure. This research focuses on the analysis of heat transfer coupled with fluid flow within the tooling. To this end, the work includes a numerical and an experimental study. The results provide an understanding of the impact of design parameters on tooling performance, and demonstrate the relevance of using such structures for thermal management
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Jeong, Sang Min. "Analysis of Vibration of 2-D Periodic Cellular Structures". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7122.
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The vibration of and wave propagation in periodic cellular structures
are analyzed. Cellular structures exhibit a number of desirable
multifunctional properties, which make them attractive in a variety of
engineering applications. These include ultra-light structures, thermal
and acoustic insulators, and impact amelioration systems, among others.
Cellular structures with deterministic architecture can be considered
as example of periodic structures. Periodic structures feature unique
wave propagation characteristics, whereby elastic waves propagate only
in specific frequency bands, known as "pass band", while they are
attenuated in all other frequency bands, known as "stop bands". Such
dynamic properties are here exploited to provide cellular structures
with the capability of behaving as directional, pass-band mechanical
filters, thus complementing their well documented multifunctional
characteristics.
This work presents a methodology for the analysis of the dynamic
behavior of periodic cellular structures, which allows the evaluation
of location and spectral width of propagation and attenuation regions.
The filtering characteristics are tested and demonstrated for
structures of various geometry and topology, including cylindrical
grid-like structures, Kagom and eacute; and tetrhedral truss core lattices.
Experimental investigations is done on a 2-D lattice manufactured out
of aluminum. The complete wave field of the specimen at various
frequencies is measured using a Scanning Laser Doppler Vibrometer
(SLDV). Experimental results show good agreement with the methodology
and computational tools developed in this work. The results demonstrate
how wave propagation characteristics are defined by cell geometry and
configuration. Numerical and experimental results show the potential of
periodic cellular structures as mechanical filters and/or isolators of
vibrations.
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Chan, Eric J. "Structural systematics of complexes of lanthanoid picrates with unidentate O-donor ligands and other related arrays". University of Western Australia. School of Biomedical, Biomolecular and Chemical Sciences, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0075.
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Structures as determined by single crystal X-ray methods for lanthanoid(III) compounds for series of simple homoleptic species with diverse ligands frequently display variations entailing a diminution in coordination number (‘C.N.’), a consequence of the variation in the size of the atoms/ions due to the ‘lanthanoid contraction’. A change from C.N. nine to eight is common, clearly separating compounds of the light/‘early’ or heavy/‘later’ metal atoms. Earlier work on the complexes of the lanthanoid(III) picrates arose out of the exploration of simple reagents which might usefully exploit lanthanoid ion properties for purposes such as solvent extraction. They are also of potential synthetic utility because of their relatively high solubility in apolar solvents. This thesis encompasses a systematic structural study of hydrated lanthanoid picrate complexes (including those of yttrium) with a selection of dipolar aprotic solvent ligands, namely trimethylphosphate (‘tmp’), dimethylsulfoxide (‘dmso’), hexamethylphosphoramide (‘hmpa’), N,N´-dimethylacetamide (‘dma’), N-methylpyrrolidinone (‘nmp’) and octamethylpyrophosphoramide (‘ompa’), all liquids at room temperature and all unidentate, with the exception of ompa which can be considered in some cases to behave as the equivalent of two unidentate ligands, in others as a chelate. Structures of adducts of these ligands with scandium picrate are also included in order to gain further insight into the coordination behavior of the totality of the group ‘3’ transition metals, and, for similar reasons, a study of the structures of complexes of Eu(dipivaloylmethanide)3 with the same (solvent) ligands as a ‘baseline’. In the course of these studies, hydrolysis of the aprotic solvent trimethylphosphate was found to lead to novel adducts of the dimethylphosphate (‘dmp’) ligand; the introduction of polycyclic aromatic nitrogen base ligand complexes resulted in further novel mixed ligand compounds, supplemented by a study of protonated base picrate salts. This work aims not only to establish structural ‘domains of existence’ with a concomitant consideration of the associated stereochemistry for these related series of rare earth complexes, but, also, to enhance our understanding of metal ion solvation and the interactions of aromatic groups within these types of crystal structures.
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Guy, Philippe. "Contribution à l’étude et à la caractérisation des propriétés mécaniques de structures lattices métalliques obtenues par Fabrication Additive (fusion sur lit de poudre)". Electronic Thesis or Diss., Toulouse, ISAE, 2025. http://www.theses.fr/2025ESAE0005.
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La fabrication additive s’est beaucoup développée ces dernières années dans l’industrie, notamment dans le secteur spatial. Cette technologie permet de concevoir et de fabriquer des pièces de géométrie complexe souvent impossible à obtenir par les procédés conventionnels. C’est le cas en particulier des structures lattices qui restent à ce jour difficiles à dimensionner et qui sont encore délicates à maîtriser en matière de stabilité de fabrication.Cette thèse avait pour objectifs d'améliorer la compréhension et la prédiction du comportement mécanique des structures lattices, structures qui sont de plus en plus présentes dans les satellites. Des éprouvettes sandwiches avec âme lattice de type BCC ou Dode-Thin (DT) ont été mises à disposition par Thales Alenia Space – France. Ces éprouvettes en aluminium AS7G06 ou en titane TA6V ont été fabriquées par fusion laser sur lit de poudre. De nombreux essais statiques et dynamiques ont été réalisés ainsi que différents calculs prédictifs analytiques et numériques.Les propriétés mécaniques équivalentes de cellules parfaites sans défauts ont été déterminées par Éléments Finis (EF) et ont été comparées à la théorie des poutres. Un modèle théorique de la poutre DT a été particulièrement développé permettant de modéliser par EF les cellules DT comme un ensemble d’éléments poutres 1D ou un matériau homogénéisé équivalent. Les essais mécaniques ont permis de mesurer la rigidité des éprouvettes sandwiches. Des mesures complémentaires par microscopie optique, MEB et microtomographie RX ont permis de mesurer la géométrie réelle des sections des poutres.Les rigidités mesurées sont le plus souvent inférieures à celles prédites par calculs. Les écarts observés sont dus aux imperfections géométriques des poutres réellement fabriquées, à la présence de porosités internes et aussi au fait que les matériaux imprimés ont des propriétés moindres que celles des matériaux de fonderie, notamment des modules de Young plus faibles. Un outil informatique de post-traitement des images de la tomographie a été développé pour quantifier les différences de rigidité et de masse et les comparer aux valeurs nominales. Les modèles mis à jour suite à ces observations ont conduit à une nette amélioration de la corrélation entre essais et calculs.À l’issue de ces travaux, les ingénieurs et les chercheurs bénéficient maintenant de méthodes et de formules permettant de modéliser simplement des structures BCC et Dode-Thin. Grâce aux nombreuses mesures et observations expérimentales, ces travaux ont aussi contribué à une meilleure compréhension du comportement des structures lattices.D’autres axes de recherche peuvent être envisagés pour continuer à développer et à améliorer leur dimensionnement. Il faudrait continuer à étudier l’influence de la non rectitude des fibres moyennes et du désalignement des nœuds d’intersection. Il serait aussi intéressant de réaliser des mesures et essais supplémentaires pour observer la qualité de fabrication actuelle. Le développement d’outils informatiques de traitement des images de tomographie RX rend possible la création de modèles EF 3D représentatifs de la géométrie réelle des poutres fabriquées et aussi la construction à terme de jumeaux numériques en s’appuyant sur l’intelligence artificielleAdditive manufacturing technology has created new possibilities in design for aerospace components, particularly using lattice structures. The industrial challenge remains to size these structures within a reasonable lead time.This research aimed to improve the understanding and prediction of the mechanical performance of lattice structures that are increasingly used in spacecraft components.Thales Alenia Space – France provided lattice core sandwich beams manufactured by the powder bed laser beam melting process. The mechanical properties of two types of cell, BCC and Dode-Thin, were investigated for two metal alloys, AS7G06 aluminium and TA6V titanium. We performed a number of static and vibration tests and predicted the mechanical behaviour of the specimens using both analytical and numerical calculations.Various Finite Element (FE) models were developed to calculate the effective mechanical properties of a defect-free structure and compared with the beam theory. In particular, we established a theory of cross-sectional properties for the specific Dode-Thin strut. This allowed the Dode-Thin lattice cell to be modelled as a set of 1D beam elements or an equivalent 3D-orthotropic homogenised material. Tests were also carried out to measure the stiffness of the sandwich beams. Optical and SEM observations and X-ray computed tomography (CT) determined the actual cross-sectional properties of the struts.The experiments in this study generally showed that theoretical and numerical predictions significantly overestimated the stiffnesses. Porosity rate and geometrical imperfections were the main causes of the discrepancy between the prediction and the as-built parts. In addition, the 3D-printed materials exhibited a lower Young’s modulus. An in-house code was developed to calculate the cross-sectional properties directly from the CT data and compare them with the nominal properties. These observations and results helped to explain the differences in stiffness and mass and were used to update the predictive models, resulting in a better correlation with the experimental results for static and dynamic behaviour.Finally, this study provided the engineer with a simple method for replacing BCC and Dode-Thin cells with equivalent beams of solid circular cross-section, or with homogenised mechanical properties. This study also deepened the knowledge of the as-built lattice structures and their mechanical behaviour.Further research should explore the effect of strut waviness and the misalignment of the junction centres. Additional tests with other samples manufactured more recently and benefiting from developments in the SLM technique could be conducted. The in-house code we have started to develop for post-processing digital CT images could be enhanced with new functions. We could envisage the construction of a full FE tetrahedral volumetric mesh capturing the geometric imperfections of each strut. This could make it possible to identify the true effective stiffness of the strut geometry. This approach could pave the way for the creation of a digital twin consisting of a FE lattice model constructed directly from CT data
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Bitar, Diala. "Collective dynamics of weakly coupled nonlinear periodic structures". Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD002/document.
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Bien que la dynamique des réseaux périodiques non-linéaires ait été investiguée dans les domainestemporel et fréquentiel, il existe un réel besoin d’identifier des relations pratiques avec lephénomène de la localisation d’énergie en termes d’interactions modales et topologies de bifurcation.L’objectif principal de cette thèse consiste à exploiter le phénomène de la localisation pourmodéliser la dynamique collective d’un réseau périodique de résonateurs non-linéaires faiblementcouplés.Un modèle analytico-numérique a été développé pour étudier la dynamique collective d’unréseau périodique d’oscillateurs non-linéaires couplés sous excitations simultanées primaire et paramétrique,où les interactions modales, les topologies de bifurcations et les bassins d’attraction ontété analysés. Des réseaux de pendules et de nano-poutres couplés électrostatiquement ont étéinvestigués sous excitation extérieure et paramétrique, respectivement. Il a été démontré qu’enaugmentant le nombre d’oscillateurs, le nombre de solutions multimodales et la distribution desbassins d’attraction des branches résonantes augmentent. Ce modèle a été étendu pour investiguerla dynamique collective des réseaux 2D de pendules couplés et de billes sphériques en compressionsous excitation à la base, où la dynamique collective est plus riche avec des amplitudes de vibrationplus importantes et des bandes passantes plus larges. Une deuxième investigation de cettethèse consiste à identifier les solitons associés à la dynamique collective d’un réseau périodique etd’étudier sa stabilitéAlthough the dynamics of periodic nonlinear lattices was thoroughly investigated in the frequencyand time-space domains, there is a real need to perform profound analysis of the collectivedynamics of such systems in order to identify practical relations with the nonlinear energy localizationphenomenon in terms of modal interactions and bifurcation topologies. The principal goal ofthis thesis consists in exploring the localization phenomenon for modeling the collective dynamicsof periodic arrays of weakly coupled nonlinear resonators.An analytico-numerical model has been developed in order to study the collective dynamics ofa periodic coupled nonlinear oscillators array under simultaneous primary and parametric excitations,where the bifurcation topologies, the modal interactions and the basins of attraction havebeen analyzed. Arrays of coupled pendulums and electrostatically coupled nanobeams under externaland parametric excitations respectively were considered. It is shown that by increasing thenumber of coupled oscillators, the number of multimodal solutions and the distribution of the basinsof attraction of the resonant solutions increase. The model was extended to investigate the collectivedynamics of periodic nonlinear 2D arrays of coupled pendulums and spherical particles underbase excitation, leading to additional features, mainly larger bandwidth and important vibrationalamplitudes. A second investigation of this thesis consists in identifying the solitons associated tothe collective nonlinear dynamics of the considered arrays of periodic structures and the study oftheir stability
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Mokhtari, Hossein. "Transmission electron microscopy of defects and internal fields in GaN structures". Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368206.
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Ngapasare, Arnold. "Waves in disordered and nonlinear mechanical structures". Thesis, Le Mans, 2020. http://www.theses.fr/2020LEMA1036.
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Ce travail est consacré à l’ étude théorique et numérique de la propagation des ondes élastiques dans les structures mécaniques désordonnées. L’ objectif principal est d’ étudier comment la localisation induite par le désordre est affectée par la non-linéarité et par la présence de mouvements de rotations. Nous étudions d’abord une chaîne granulaire finie et montrons que non seulement la localisation d’ Anderson est rompue mais aussi que l’ équipartition de l’ énergie est réalisée grâce à la non-linéarité discontinue propre aux chaînes granulaires. De plus, nous étendons nos études à un reseau micropolaire qui supporte les ondes de rotation. Nous montrons que, dans la limite linéaire, la repartition de l’ énergie est facilitée à la fois par des ondes étendues à basse fréquence et par un ensemble de modes quasi-étendus à haute fréquence. Nous identifions aussi un cas où l’ énergie est complètement localisée en réglant la rigidité. Enfin, pour une chaîne LEGO architecturée non linéaire présentant un movement à la fois transversal et rotatif, nous étudions comment la non-linéarité rompt, dans ce système polarisé, la localisation d’ Anderson. Il s’avère que la dynamique de ce système a un caractère unique qui ressemble à une combinaison des modèles Fermi-Pasta-Ulam-Tsingou et Klein Gordon pour le comportement asymptotique et chaotiqueThis work is devoted to the theoretical and numerical study of elastic wave propagation in disordered mechanical structures. The main goal is to investigate how the localization induced by disorder is affected by nonlinearity and by the presence of rotational motion. Firstly, we study a finite granular chain and show that not only Anderson localization is broken but also energy equipartition is achieved due to the discontinuous nonlinearity which is particular to granular chains. Furthermore, we extend our studies to a micropolar lattice that supports rotational waves. We show that in the linear limit the energy spreading is facilitated both by low frequency extended waves and a set of high frequency quasiextended modes. Also, we identify a case where energy is completely localized by tuning the stiffness. Finally, for a nonlinear architected LEGO chain featuring both transverse and rotational motion we study how nonlinearity breaks Anderson localization in this polarized system. The dynamics is found to have a unique character resembling a combination of the Fermi-Pasta-Ulam Tsingou and Klein-Gordon models regarding the asymptotic dynamical behavior and chaoticity
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Vassaux, Maxime. "Comportement mécanique des matériaux quasi-fragiles sous sollicitations cycliques : de l’expérimentation numérique au calcul de structures". Thesis, Cachan, Ecole normale supérieure, 2015. http://www.theses.fr/2015DENS0010/document.
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Les modèles de comportement mécanique, dits macroscopiques, sont développés à la fois pour leur légèreté, permettant le calcul d’éléments structuraux pouvant atteindre d’importantes dimensions, et pour leur finesse de représentation des phénomènes mécaniques observés par le matériau à des échelles plus fines. Le développement de tels modèles est ici effectué dans le cadre de la sollicitation sismique, donc des chargements cycliques alternés, appliquée à des ouvrages en matériaux quasi-fragiles, et plus précisément en béton. À ce jour, les modèles macroscopiques, effectivement applicables au calcul de structures, et représentatifs du comportement cyclique du béton sont encore rares. En conséquence de la complexité du problème de fissuration à homogénéiser, les modèles macroscopiques existants affichent une robustesse limitée ou ne permettent pas de reproduire l’ensemble des phénomènes mécaniques observés par le matériau. Une des barrières à la résolution de ces deux problématiques est le manque de données expérimentales relatives aux phénomènes à modéliser. En effet, en cause de la difficulté technique de les réaliser, peu de résultats d’essais cycliques alternés sur du béton sont disponibles dans la littérature.
Une démarche d’expérimentation numérique a donc été élaborée sur la base d’un modèle fin du matériau, dit microscopique, capable de fournir les résultats nécessaires à la formulation et à l’identification d’un modèle macroscopique. Dans le modèle microscopique le matériau est considéré comme une structure à part entière, il a été développé afin de ne nécessiter qu’une quantité réduite de résultats d’essais, maîtrisés, pour être mis en oeuvre. Le modèle microscopique, un modèle particulaire lattice, a été développé sur la base d’un modèle lattice existant, enrichi pour être en mesure de simuler le comportement des matériaux quasi-fragiles sous chargements multi-axiaux et cycliques. Le modèle microscopique a alors été validé en tant qu’outil d’expérimentation numérique, et exploité afin d’établir les équations constitutives du modèle macroscopique fondées sur les théories de l’endommagement et de la plasticité. La régularité de la relation de comportement proposée, intégrant un effet unilatéral progressif, a notamment été garantie par l’utilisation d’un modèle d’élasticité non-linéaire. Le modèle macroscopique a finalement été calibré, entièrement, à l’aide du modèle microscopique, et mis à l’oeuvre dans la simulation de la réponse d’un voile en béton armé soumis à un chargement de cisaillement cyclique alterné. Cette simulation a permis de mettre en avant la robustesse numérique du modèle développé, ainsi que la contribution significative du comportement uni-axial cyclique alterné du béton à l’amortissement de telles structuresMacroscopic mechanical behavior models are developed for their light computational costs, allowing the simulation of large structural elements, and the precise description of mechanical phenomena observed by the material at lower scales. Such constitutive models are here developed in the seismic solicitation framework, therefore implying cyclic alternate loadings at the material scale, and applied to civil engineering buildings, often made of concrete, or more generally of quasi-brittle materials. To date, macroscopic models applicable to structural computations, while representing the cyclic mechanical behavior are rare. In consequence of the intricacy of the fracture processes to homogenize, macroscopic constitutive models either do not present sufficient robustness or miss on important phenomena. One of the limitations to the resolution of this issue is the lack of experimental data. Indeed, because of the complexity of the experiments to set up, few results on alternate cyclic tests on concrete are available in the literature.A virtual testing approach has therefore been established on a microscopic model of the material, able to provide results needed to the formulation and the calibration of a macroscopic model. In the microscopic model, the material is considered as structure itself, it is developed so as to only necessitate a reduced amount of results from controlled experimental tests, in order to be used. The microscopic model, a lattice discrete element model, has been developed on the basis of an existing lattice model and extended to the simulation of multi-axial and cyclic loadings. The microscopic model has then been validated as a virtual testing tool and used to establish equations of the macroscopic model, on the basis of damage and plasticity theories. The consistency of the proposed constitutive relation, embedding progressive unilateral effect, has been achieved using non-linear elasticity. The macroscopic model has finally been calibrated, entirely with the microscopic model, and employed to simulate the response of a reinforced concrete wall under alternate shear loading. This simulation has served to showcase the numerical robustness of the proposed model, as well as the significant contribution of the uni-axial alternate behavior of concrete to the structural damping of such structures
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ASHOK, RAMYA. "A DATABASE SYSTEM TO STORE AND RETRIEVE A CONCEPT LATTICE STRUCTURE". University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1130552767.
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O'Connor, Joseph. "Fluid-structure interactions of wall-mounted flexible slender structures". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/fluidstructure-interactions-of-wallmounted-flexible-slender-structures(1dab2986-b78f-4ff9-9b2e-5d2181cfa009).html.
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The fluid-structure interactions of wall-mounted slender structures, such as cilia, filaments, flaps, and flags, play an important role in a broad range of physical processes: from the coherent waving motion of vegetation, to the passive flow control capability of hair-like surface coatings. While these systems are ubiquitous, their coupled nonlinear response exhibits a wide variety of behaviours that is yet to be fully understood, especially when multiple structures are considered. The purpose of this work is to investigate, via numerical simulation, the fluid-structure interactions of arrays of slender structures over a range of input conditions. A direct modelling approach, whereby the individual structures and their dynamics are fully resolved, is realised via a lattice Boltzmann-immersed boundary model, which is coupled to two different structural solvers: an Euler-Bernoulli beam model, and a finite element model. Results are presented for three selected test cases - which build in scale from a single flap in a periodic array, to a small finite array of flaps, and finally to a large finite array - and the key behaviour modes are characterised and quantified. Results show a broad range of behaviours, which depend on the flow conditions and structural properties. In particular, the emergence of coherent waving motions are shown to be closely related to the natural frequency of the array. Furthermore, this behaviour is associated with a lock-in between the natural frequency of the array and the predicted frequency of the fluid instabilities. The original contributions of this work are: the development and application of a numerical tool for direct modelling of large arrays of slender structures; the characterisation of the behaviour of slender structures over a range of input conditions; and the exposition of key behaviour modes of slender structures and their relation to input conditions.
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Hou, An. "Strength of composite lattice structures". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12475.
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Obiedat, Mohammad. "Incrementally Sorted Lattice Data Structures". Thesis, The George Washington University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3732474.
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Data structures are vital entities that strongly impact the efficiency of several software applications. Compactness, predictable memory access patterns, and good temporal and spacial locality of the structure's operations are increasingly becoming essential factors in the selection of a data structure for a specific application. In general, the less data we store and move the better for efficiency and power consumption, especially in infrastructure software and applications for hand-held devices like smartphones. In this dissertation, we extensively study a data structure named lattice data structure (LDS) that is as compact and suitable for memory hierarchies as the array, yet with a rich structure that enables devising procedures with better time bounds.
To achieve performance similar to the performance of the optimal O(log(N)) time complexity of the searching operations of other structures, we provide a hybrid searching algorithm that can be implemented by searching the lattice using the basic searching algorithm when the degree of the sortedness of the lattice is less than or equal to 0.9h, and the jump searching algorithm when the degree of the sortedness of the lattice is greater than 0.9h. A sorting procedure that can be used, during the system idle time, to incrementally increase the degree of sortedness of the lattice is given. We also provide randomized and parallel searching algorithms that can be used instead of the usual jump-and-walk searching algorithms.
A lattice can be represented by a one-dimensional array, where each cell is represented by one array element. The worst case time complexity of the basic LDS operations and the average time complexity of some of the order-statistic operations are better than the corresponding time complexities of most of other data structures operations. This makes the LDS a good choice for memory-constrained systems, for systems where power consumption is a critical issue, and for real-time systems. A potential application of the LDS is to use it as an index structure for in-memory databases.
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Kouach, Mona. "Methods for modelling lattice structures". Thesis, KTH, Hållfasthetslära (Avd.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-260498.
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The application of lattice structures have become increasingly popular as additive manufacturing (AM) opens up the possibility to manufacture complex configurations. However, modelling such structures can be computationally expensive. The following thesis has been conducted in order for the department of Structural Analysis, at SAAB in Järfälla, to converge with the future use of AM and lattice structures. An approach to model lattice structures using homogenization is presented where three similar methods involving representative volume element (RVE) have been developed and evaluated. The stiffness matrices, of the RVEs, for different sizes of lattice structures, comprising of BCC strut-based units, have been obtained. The stiffness matrices were compared and analysed on a larger solid structure in order to see the deformational predictability of a lattice-based structure of the same size. The results showed that all methods were good approximations with slight differences in terms of boundary conditions (BCs) at the outer edge. The comparative analyses showed that two of the three methods matches the deformational predictability. The BCs in all methods have different influences which makes it pivotal to establish the BCs of the structure before using the approach presented in this thesis.Ökad implementering av gitterstrukturer i komponenter är ett resultat av utvecklingen inom additiv tillverkning. Metoden öppnar upp för tillverkning av komplexa strukturer med färre delmoment. Dock så uppkommer det svårigheter vid simulering av dessa komplexa strukturer då beräkningar snabbt tyngs ner med ökad komplexitet. Följande examensarbete har utförts hos avdelningen Strukturanalys, på SAAB i Järfälla, för att de ska kunna möta upp det framtida behovet av beräkningar på additivt tillverkade gitterstrukturer. I det här arbetet presenteras ett tillvägagångsätt för modellering av gitterstrukturer med hjälp av represantiva volymselement. Styvhetsmatriser har räknats fram, för en vald gitterkonfiguration, som sedan viktats mot tre snarlika representativa volymselement. En jämförelseanalys mellan de olika styvhetsmatriserna har sedan gjorts på en större och solid modell för att se hur väl metoderna förutsett deformationen av en gitterstruktur i samma storlek. Resultaten har visat att samtliga metoder är bra approximationer med tämligen små skillnader från randeffekterna. Vid jämförelseanalysen simulerades gitterstrukturen bäst med två av de tre metoder. En av slutsatserna är att det är viktigt att förstå inverkan av randvillkoren hos gitterstrukturer innan implementering görs med det tillvägagångssätt som presenterats i det här examensarbetet.
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Dashyan, Ruben. "Représentations de groupes fondamentaux en géométrie hyperbolique". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066242/document.
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Deux méthodes de construction de représentations de groupes sont présentées. La première propose une stratégie essayant de déterminer les représentations de groupes libres de type fini à valeurs dans tout réseau de groupes de Lie réel. La seconde, après avoir revu une construction d'une surface hyperbolique complexe, c'est-à-dire le quotient du plan hyperbolique complexe par un réseau, et examiné soigneusement ses propriétés, produit une infinité de représentations non-conjuguées, à valeurs dans un réseau du groupe des isométries du plan hyperbolique complexe, de groupes fondamentaux de variétés hyperboliques fermées de dimension 3, obtenues comme des fibrés en surfaces sur le cercleTwo construction methods of group representations are presented. The first one proposes a strategy to try to determine the representations of finitely generated free groups into any lattice in real Lie groups. The second, after reviewing a construction of a complex hyperbolic surface, that is the quotient of the complex hyperbolic plane by a lattice, and examining its properties carefully, yields infinitely many non-conjugate representations into a lattice in the group of isometries of the complex hyperbolic plane, of fundamental groups of closed hyperbolic 3-dimensional manifolds, obtained as surface bundles over the circle
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Goel, Archak. "Design of Functionally Graded BCC Type Lattice Structures Using B-spline Surfaces for Additive Manufacturing". University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1552398559313737.
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Jenkins, Sarah Nield Morrish. "Mechanical properties and structural evaluation of diamond structure Ti6Al4V lattices made by Electron Beam Melting". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/20954/.
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Banihashemi, Amir H. "Decoding complexity and trellis structure of lattices". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22189.pdf.
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Burns, D. "Factorisability, group lattices, and Galois module structure". Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335599.
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Pugh, David John Rhydwyn. "Topological structures in lattice gauge theory". Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279896.
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Papachristou, Petros G. "Probabilistic relaxation for square lattice structures". Thesis, University of Surrey, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241395.
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AGUILERA, JEAN RODRIGO FERREIRA. "LIGHT LATTICE STRUCTURES UNDER WIND ACTION". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=10538@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONo projeto de estruturas treliçadas esbeltas, um ponto relativamente em aberto é quanto à resposta dinâmica dessas torres sob ação do vento. Já foram observadas várias ocorrências de queda de torres por tais efeitos no Brasil e ultimamente, essas incidências vêm aumentando, trazendo diversos transtornos e prejuízos significativos à sociedade e às empresas concessionárias. Nesse contexto, brotam dois aspectos centrais: a modelagem da estrutura e a discretização da ação do vento. A montagem desses dois cenários é feita com base em um modelo numérico, no SAP2000, de uma torre de 73,75 m de altura da linha de transmissão LT - 103, na Amazônia, e uma torre de TV com 192 m de altura, localizada em Brasília-DF, ambas no Brasil. Para avaliação da excitação do vento, é utilizada a norma brasileira NBR 6123. Em estudo preliminar, propõe-se uma forma de representação simplificada das forças do vento sobre a torre, de modo a serem utilizadas resultantes por módulos, convenientemente distribuídas por seus nós principais, visando-se quer a resposta estática, quer a dinâmica. A torre de TV é ensaiada sob a ação de pulsos isolados do vento de projeto e por sucessões diversas desses pulsos com o intuito de simular rajadas de vento. Investiga-se também, para a ação de ventos normalizados extremos, a resposta linear e não-linear P-Delta do sistema. Em consequência, identificam-se pontos de insuficiência estrutural e, para as ações extremas, ensaiam-se recursos mecânicos para controle dos deslocamentos e esforços máximos produzidos pela ação estática e dinâmica do vento.
The dynamic response of slender latticed tower structures under wind excitation is still an open point in the design of such systems. In Brazil, an expressive number of accidents have been registered, in the last few decades, and a large number of material and financial losses have been equally reported, for both people and industrial plant owners. In the structural analysis scenario, two central points dominate the structural engineer concerns: the modeling of the structure and of the wind action. Two tower models are used, a 73,75m high transmission line trussed structure, LT 103, settled in the Brazilian Amazon Basin and a 193m tall trussed TV tower, built in Brasilia-DF. The wind action on the tower members is computed according to the brazilian recommendation, NBR- 6123. In a preliminary study, a simplified procedure is proposed to evaluate the wind forces on the LT-103 tower sections and to conveniently distribute them on the main tower model nodes (joints). The TV Tower is evaluated under the static and dynamic action of the wind forces, either by isolated pulses or by a train of them to model a wind gust. The tower response is computed under a linear and non-linear P-Delta behavior; some faulting spots are identified in the response reports and a combined vibration control solution is proposed incorporating steel tendons conjugated with multiple tuned mass absorbers. A comparison is also made with the NBR 15307 recommendation and a couple of comments are addressed to those who may intend to apply this regulation to investigate the behavior of slender trussed tower structures.
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Leung, Anthony Chi Hin. "Actuation properties of kagome lattice structures". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613328.
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Dinter, Simon. "Nucleon structure from lattice QCD". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16629.
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In dieser Arbeit berechnen wir mit Hilfe der Gitter-QCD Observablen, die in Beziehung zur Struktur des Nukleons stehen. Ein Teil dieser Arbeit beschäftigt sich mit Momenten von Parton-Verteilungsfunktionen. Solche Momente sind wichtig für das Verständnis der Nukleon-Struktur und werden durch globale Analysen von tief-inelastischen Streuexperimenten bestimmt. Eine theoretische, nicht-perturbative Rechnung der Momente in der Gitter-QCD ist möglich. Allerdings existiert, seit solche Gitter-QCD Rechnungen vorliegen, eine Diskrepanz zwischen diesen Rechnungen und den Ergebnissen globaler Analysen experimenteller Daten. Wir untersuchen, ob systematische Effekte für diese Diskrepanz verantwortlich sind, dabei studieren wir insbesondere die Effekte angeregter Zustände. Zudem führen wir eine erste Rechnung mit vier dynamischen Quark-Flavors durch. Ein weiterer Aspekt dieser Arbeit ist eine Machbarkeitsstudie zur Berechnung des skalaren Quark-Inhalts des Nukleons in der Gitter-QCD. Dieser bestimmt den Wirkungsquerschnitt der durch ein skalares Teilchen (z.B. ein Higgs-Teilchen) vermittelten Wechselwirkung eines schweren Teilchens mit einem Nukleon und kann somit einen Einfluss bei der Suche nach Dunkler Materie haben. Bisherige Gitter-Rechnungen dieser Größe besitzen große Unsicherheiten und sind daher von geringer Signifikanz für phenomenologische Anwendungen. Wir benutzen eine Varianz-Reduktions-Methode zur Auswertung von unverbundenen Diagrammen um ein präzises Ergebnis zu erhalten. Des Weiteren stellen wir eine neue stochastische Methode zur Berechnung von Nukleon-Dreipunkt-Korrelationsfunktionen vor, die für die Berechnung von Observablen der Nukleon-Struktur benötigt werden. Wir testen die Konkurrenzfähigkeit dieser neuen Methode gegenüber der Standard-Methode. In allen Rechnungen benutzen wir Wilson twisted-Mass Fermionen mit maximalem Twist, so dass die hier berechneten Observablen nur O(a^2) Diskretisierungsfehler aufweisen.In this thesis we compute within lattice QCD observables related to the structure of the nucleon. One part of this thesis is concerned with moments of parton distribution functions (PDFs). Those moments are essential elements for the understanding of nucleon structure and can be extracted from a global analysis of deep inelastic scattering experiments. On the theoretical side they can be computed non-perturbatively by means of lattice QCD. However, since the time lattice calculations of moments of PDFs are available, there is a tension between these lattice calculations and the results from a global analysis of experimental data. We examine whether systematic effects are responsible for this tension, and study particularly intensively the effects of excited states by a dedicated high precision computation. Moreover, we carry out a first computation with four dynamical flavors. Another aspect of this thesis is a feasibility study of a lattice QCD computation of the scalar quark content of the nucleon, which is an important element in the cross-section of a heavy particle with the nucleon mediated by a scalar particle (e.g. Higgs particle) and can therefore have an impact on Dark Matter searches. Existing lattice QCD calculations of this quantity usually have a large error and thus a low significance for phenomenological applications. We use a variance-reduction technique for quark-disconnected diagrams to obtain a precise result. Furthermore, we introduce a new stochastic method for the calculation of connected 3-point correlation functions, which are needed to compute nucleon structure observables, as an alternative to the usual sequential propagator method. In an explorative study we check whether this new method is competitive to the standard one. We use Wilson twisted mass fermions at maximal twist in all our calculations, such that all observables considered here have only O(a^2) discretization effects.
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Kahn, Giacomo. "A structural study of lattices, d-lattices and some applications in data analysis". Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC066/document.
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Nous nous intéressons à un cadre théorique de l'analyse de données : l'analyse formelle de concepts. Le formalisme de l'analyse formelle de concepts permet d'exprimer les notions centrales de la fouille de données telles que les implications ou les ensembles fermés, avec au centre la notion de treillis qui décrit la structure et les relations que ces objets ont entre eux. Pour les données multidimensionnelles, une proposition de formalisme existe en tant que généralisation de l'analyse formelle de concepts : l'analyse polyadique de concepts. Dans cette thèse, nous étudions certains problèmes de combinatoire et d'algorithmique dans le cas de l'analyse polyadique de concepts. Nous approchons aussi un cadre plus appliqué à l'analyse de données en proposant des approches de navigation conceptuelle et de classificationWe are interested in formal concept analysis, a theoretical framework for data analysis.This formalism allows to express some central notions of data mining such as implications or closed itemsets, and is centered around lattices, as the description of the relational structure that those objects can have.For multidimensional data, a formalism exists as a generalisation of formal concept analysis : polyadic concept analysis.In this document, we study some combinatorial and algorithmic problems that arose in polyadic concept analysis.We also introduce more applied data analysis techniques of conceptual navigation and classification
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Čambalová, Kateřina. "Volné algebraické struktury a jejich využití pro segmentaci digitálního obrazu". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231711.
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The thesis covers methods for image segmentation. Fuzzy segmentation is based on the thresholding method. This is generalized to accept multiple criteria. The whole process is mathematically based on the free algebra theory. Free distributive lattice is created from poset of elements based on image properties and the lattice members are represented by terms used by the threshoding. Possible segmentation results compose the equivalence classes distribution. The thesis also contains description of resulting algorithms and methods for their optimization. Also the method of area subtracting is introduced.
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Hammetter, Christopher Ian. "Designing pyramidal lattice structures for energy absorption". Thesis, University of California, Santa Barbara, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3602080.
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Applications for energy absorption materials range from athletic equipment, to vehicle crumple zones, to blast protection for military vehicles and personnel. Many energy absorption structures employ stochastic foams because of their plateau-like stress-strain response that allows for the absorption of large amounts of energy at relatively low stresses over large compressive strains. Periodic lattice structures, when properly designed, provide the same capabilities as stochastic systems, but with a more tailorable response that provides potential for improved specific strength and energy absorption. The present dissertation provides an in-depth study of the pyramidal lattice: one particular periodic structure that strikes a good compromise between performance and manufacturability. Through finite element and analytical modeling, this study identifies key parameters of the geometry, boundary conditions, and parent material properties that determine the compressive stress-strain response of the structure. In conjunction with experimental investigations, these models are used to understand and determine the potential for improving the response of the as-manufactured polymeric pyramidal lattice structures through additional heat treatment and filling the lattice void-space with stochastic foam. Finally, additional models are developed to understand and predict the structural rate effects that arise from inertial stabilization of strut buckling during dynamic loading. Particular emphasis is given to the effects of yield strain and density of the parent material on failure modes and dynamic response. In addition to providing a strong basis for the design of pyramidal lattice materials, this work provides useful insight into the design of energy absorption materials in general.
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Novak, Jurica. "Simulated mesoscopic structures in a ferroelastic lattice". Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621535.
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Craig, Adam Patrick. "Novel structures for lattice-mismatched infrared photodetectors". Thesis, Lancaster University, 2016. http://eprints.lancs.ac.uk/82854/.
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Using the interfacial misfit (IMF) array growth mode, GaSb p-i-n diodes were grown on Si and GaAs lattice-mismatched substrates by molecular beam epitaxy (MBE) under optimised growth conditions. For the sample grown on Si, an AlSb nucleation layer was used to reduce the occurrence of twinning defects. In addition to the samples grown on mismatched substrates, an equivalent structure was further grown on a native GaSb substrate, for comparison. X-ray diffraction (XRD) was used to demonstrate that the layers were fully relaxed, and transmission electron microscopy (TEM) imaging showed arrays of 90° misfit dislocations with measured periodicities in agreement with atomistic modelling. However, after processing, device dark current densities of 0.9 Acm^-2 and 0.18 Acm^-2 were recorded for the sample grown on Si and the sample grown on GaAs, respectively, at -1.0 V and 300 K. These were compared to the sample grown on native GaSb, which had a dark current density of 0.01 Acm^-2 under the same conditions. Furthermore, TEM analysis revealed relatively high threading dislocation densities (TDDs) of ~10^8 cm^-2. It was proposed that not all the interfacial strain could be accommodated by the IMF arrays, since the array periods (9:8 for AlSb/Si and 13:14 for GaSb/GaAs) were not in exact agreement with ratio of the lattice constants (of AlSb to Si and GaSb to GaAs), i.e. a population of 60° misfit dislocations was still formed. It was therefore decided to investigate the use of nBn detector structures as lattice mismatched photodetectors. Using a design based on an InAsSb bulk-material absorber, a comparison was again drawn between two samples, one grown on mismatched GaAs and a second grown on native GaSb. This time, device dark current densities were found to be relatively similar when comparing the two samples (1.6×10^-5 Acm^-2 vs 3×10^-6 Acm^-2 at 200 K). D^* performance figures were also found to be within one order of magnitude (1.5×10^10 cmHz^1/2 W^-1 vs 9.8×10^10 cmHz^1/2 W^-1 at 200 K). Furthermore, diffusion limited performance was exhibited at all temperatures tested, so that the effects of Shockley Read Hall (SRH) generation were established to be absent (or at least much less significant). It was also found that absorption layer doping of around ~4×10^17 cm^-3 was necessary to ensure diffusion limited performance for the sample grown on GaAs and that, with this modification, diffusion limited performance was achieved even for a sample with a highly lattice-mismatched absorption layer (with higher Sb content and longer cut-off wavelength).While nBn detector structures offer very low dark currents, it will sometimes be necessary to have a detector which is sensitive to very weak signals. In telecoms applications, avalanche photodiode (APD) structures are often used as receivers for long-haul fibre optic systems. However, relatively few avalanche photodiode designs exist for wavelengths beyond 1.55 μm. Two novel separate-absorption-and-multiplication (SAM) APD structures were therefore demonstrated based on the IMF growth mode. In particular, by transitioning the lattice from 5.65 Å to 6.09 Å, it was possible to combine GaSb absorption layers with GaAs and (for improved noise performance) Al0.8Ga0.2As multiplication layers. Multiplication profiles were established using capacitance voltage modelling (together with ionisation coefficients from the literature) and excess noise measurements were then carried out. Through the presence of 1.55 μm photocurrent, it was confirmed that absorption took place in the GaSb regions, with transport to the p-n junction (in the multiplication region) taking place by diffusion. Through measurements showing 0.2
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Melpal, Gopalakrishna Ranjan. "Conformal Lattice Structures in Additive Manufacturing (AM)". University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535382325233769.
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Huff, Cheryl Rae. "Countable Additivity, Exhaustivity, and the Structure of Certain Banach Lattices". Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc278330/.
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The notion of uniform countable additivity or uniform absolute continuity is present implicitly in the Lebesgue Dominated Convergence Theorem and explicitly in the Vitali-Hahn-Saks and Nikodym Theorems, respectively. V. M. Dubrovsky studied the connection between uniform countable additivity and uniform absolute continuity in a series of papers, and Bartle, Dunford, and Schwartz established a close relationship between uniform countable additivity in ca(Σ) and operator theory for the classical continuous function spaces C(K). Numerous authors have worked extensively on extending and generalizing the theorems of the preceding authors. Specifically, we mention Bilyeu and Lewis as well as Brooks and Drewnowski, whose efforts molded the direction and focus of this paper. This paper is a study of the techniques used by Bell, Bilyeu, and Lewis in their paper on uniform exhaustivity and Banach lattices to present a Banach lattice version of two important and powerful results in measure theory by Brooks and Drewnowski. In showing that the notions of exhaustivity and continuity take on familiar forms in certain Banach lattices of measures they show that these important measure theory results follow as corollaries of the generalized Banach lattice versions. This work uses their template to generalize results established by Bator, Bilyeu, and Lewis.
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Renner, Dru Bryant 1977. "Exploring proton structure using lattice QCD". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/29448.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.Includes bibliographical references (leaves 219-222).
We calculate moments of the generalized parton distributions of the nucleon using lattice QCD. The generalized parton distributions determine the angular momentum decomposition of the nucleon and the transverse distributions of partons within the nucleon. Additionally, the generalized parton distributions reduce to the elastic form factors and ordinary parton distributions in particular kinematic limits. Thus by calculating moments of the generalized parton distributions in lattice QCD we can explore many facets of the structure of the nucleon. In this effort, we have developed the building block method to determine all the lattice correlation functions which con- tribute to the off forward matrix elements of the twist two operators. These matrix elements determine the generalized form factors of the nucleon which in turn give the moments of the generalized parton distributions. Thus we use our building block method to calculate all the matrix elements of the lowest twist two operators. Fur- thermore, we use our method to construct an overdetermined set of matrix elements allowing a more accurate calculation of the generalized form factors.
by Dru Bryant Renner.
Ph.D.
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Ayers, James T. "Hydrodynamic Drag and Flow Visualization of IsoTruss Lattice Structures". Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd782.pdf.
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Taylor, Lesley. "Structural investigations of novel liquid crystals". Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358364.
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Felderhoff, Joël. "Difficultés de Problèmes de Réseaux Structurés pour la Cryptographie Post-Quantique". Electronic Thesis or Diss., Lyon, École normale supérieure, 2024. http://www.theses.fr/2024ENSL0059.
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La sécurité des protocoles cryptographiques repose sur la difficulté présumée de problèmes algorithmiques. Parmi ceux qui ont été identifiés jusque-là, les meilleurs problèmes pouvant servir de fondation à une cryptographie résistante aux ordinateurs quantiques sont issus des réseaux euclidiens. Les réseaux euclidiens sont une structure mathématique définie comme un ensemble de vecteurs de l’espace générés par les combinaisons entières d’un nombre fini de vecteurs réels linéairement indépendants (sa base). Un exemple typique de problème de sécurité relié est le Shortest Vector Problem (SVP). Étant donné une base d’un réseau euclidien en dimension n, trouver un vecteur court non nul. Pour des raisons d’efficacité, ces problèmes sont restreints à des réseaux issus de la théorie des nombres, dit structurés. Les hypothèses de sécurité relatives à ces réseaux particuliers étant différentes de celles des réseaux non structurés, il est nécessaire de les étudier spécifiquement, c’est l’objet de cette thèse. Nous avons étudié le cas des modules NTRU et uSVP en rang 2, prouvant que le problème SVP est équivalent sur ces deux familles de réseaux. Nous montrons également une réduction pire-cas vers cas-moyens pour les réseaux uSVP en rang 2. Ensuite nous avons démontré que résoudre SVP sur un idéal premier de petite norme n’était pas plus facile que de résoudre SVP sur n’importe quel idéalThe security of cryptographic protocols is based on the presumed difficulty of algorithmic problems. Among those identified so far, some of the best problems to serve as a foundation for quantum-proof cryptography come from lattices. Lattices are a mathematical structure defined as a set of space vectors generated by integer combinations of a finite number of linearly independent real vectors (its basis). A typical example of a related security problem is the Shortest Vector Problem (SVP). Given a base of an n-dimensional lattice, find a non-zero short vector. For efficiency reasons, these problems are restricted to lattices arising from number theory, known as structured lattices. As the security assumptions for these particular lattices are different from those for unstructured lattices, it is necessary to study them specifically, which is the aim of this thesis.We have studied the case of NTRU and uSVP modules in rank 2, proving that the SVP problem is equivalent on these two families of lattices. We also show a worst-case to average-case reduction for rank-2 uSVP lattices. Then we show that solving SVP on a prime ideal of small norm is no easier than solving SVP on any ideal
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Bailey, S. J. "Cathodoluminescence of quantum well structures". Thesis, University of Bristol, 1987. http://hdl.handle.net/1983/b02b03a2-c0d8-401d-a94e-8bd26b52b953.
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Farley, Jonathan David. "The structure of function lattices : automorphisms, congruences, and ideals". Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282346.
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Cox, Jennifer Jane. "Structure of organic molecular thin films vapour deposited on III-V semiconductor surfaces". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327025.
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Tornatore, Dario. "Damping Capability of Lattice Structures: a Numerical Study". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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Lattices are recognized as ultra-lightweight materials with high specific stiffness and high specific strength. The applications of this architectural material range from the aerospace and automotive industry up to the biomedical one.
In the literature, most of the studies address the mechanical responses of lattice structures under static, dynamic (impact) and fatigue loading conditions while only few works deal with the damping capabilities of such structures.
This study focuses on the damping capability of classical lattice configurations whose architecture is made of struts (i.e. CC, CBCC, ACC, Octet, Rhombic dodecahedron). The influence of three aspects has been investigated: the geometrical parameters defining the structure of the lattice cell, the introduction of a compressive pre-stress field within the cell and the plastic constitutive behaviour of the material used for the struts. A broad sensitivity campaign has been performed in order to evaluate the amount of dissipated energy for the different cell architectures according to the variation of the strut diameter and to the presence of local instabilities (post-buckling behaviour of the struts).
The numerical results highlight how the damping capability of the considered cell, for the same loading condition, is strongly related to the topology of the cell and to its relative density. By smartly tailoring these parameters, the damping capability without pre-stress can be increased up to 23% and, if the pre-stress is introduced within the cell, the damping effects can be ulteriorly intensified .