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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 11 to 15 of 15 (0.044 seconds)| 11 |
An efficient high-performance computing based three-dimensional numerical wave basin model for the design of fluid-structure interaction experimentsNimmala, Seshu B. 11 October 2010 (has links)
Fluid-structure interaction (FSI) is an interesting and challenging interdisciplinary area comprised of fields such as engineering- fluids/structures/solids, computational science, and mathematics. FSI has several practical engineering applications such as the design of coastal infrastructure (such as bridges, levees) subjected to harsh environments from natural forces such as tsunamis, storm surges, etc. Development of accurate input conditions to more detailed and complex models involving flexible structures in a fluid domain is an important requirement for the solution of such problems. FSI researchers often employ methods that use results from physical wave basin experiments to assess the wave forces on structures. These experiments, while closer to the physical phenomena, often tend to be time-consuming and expensive. Experiments are also not easily accessible for conducting parametric studies. Alternatively, numerical models
when developed with similar capabilities will complement the experiments very well because of the lower costs and the ability to study phenomena that are not feasible in the laboratory.
This dissertation is aimed at contributing to the solution of a significant component of the FSI problem with respect to engineering applications, covering accurate input to detailed models and a numerical wave basin to complement large-scale laboratory experiments. To this end, this work contains a description of a three-dimensional numerical wave tank (3D-NWT), its enhancements including the piston wavemaker for generation of waves such as solitary, periodic, and focused waves, and validation using large-scale experiments in the 3D wave basin at Oregon State University.
Performing simulations involving fluid dynamics is computational-intensive and the complexity is magnified by the presence of the flexible structure(s) in the fluid domain. The models are also required to take care of large-scale domains such as a wave basin in order to be applicable to practical problems. Therefore, undertaking these efforts requires access to high-performance computing (HPC) platforms and development of parallel codes. With these objectives in mind, parallelization of the 3D-NWT is carried out and discussed in this dissertation. / Graduation date: 2011
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Improved regularity estimates in nonlinear elliptic equations / Improved regularity estimates in nonlinear elliptic equationsDisson Soares dos Prazeres 04 September 2014 (has links)
CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / In this work we establish local regularity estimates for
at solutions to non-convex fully nonlinear elliptic equations and we study cavitation type equations modeled within coef-
icients bounded and measurable. / Neste trabalho estabelecemos estimativas de regularidade local para soluÃÃes "flat" de equaÃÃes elÃpticas totalmente nÃo-lineares nÃo-convexas e estudamos equations do tipo cavidade com coeficientes meramente mensurÃveis.
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[en] REGULARITY THEORY FOR NONLINEAR PARTIAL DIFFERENTIAL EQUATIONS / [pt] TEORIA DA REGULARIDADE PARA EQUAÇÕES DIFERENCIAIS PARCIAIS NÃO LINEARESMIGUEL BELTRAN WALKER URENA 31 January 2024 (has links)
[pt] Primeiro examinamos soluções de viscosidade Lp para equações elípticas
totalmente não lineares com ingredientes de fronteira mensuráveis. Ao
considerar p0 < p < d, focamos nas estimativas da regularidade dos gradientes
derivadas de potenciais não lineares. Encontramos condições para
Lipschitz-continuidade local das soluções e continuidade do gradiente. Examinamos
avanços recentes na teoria da regularidade decorrentes de estimativas
potenciais (não lineares). Nossas descobertas decorrem de – e são
inspiradas por – fatos fundamentais na teoria de soluções de Lp-viscosidade,
e resultados do trabalho de Panagiota Daskalopoulos, Tuomo Kuusi e Giuseppe
Mingione (DKM2014). Na segunda parte provamos a regularidade
parcial de mapas harmônicos com peso fracamente estacionários com dados
de fronteira livre em um cone. Como ponto de partida, damos uma
olhada na teoria da regularidade parcial interior para mapas harmônicos
fracionários de minimização de energia intrínseca do espaço euclidiano em
variedades Riemannianas compactas e suaves para potências fracionárias
estritamente entre zero e um. Mapas harmônicos fracionários intrínsecos
podem ser estendidos para mapas harmônicos com peso, então provamos
regularidade parcial para mapas harmônicos minimizantes locais com dados
de fronteira (parcialmente) livres em meios-espaços, mapas harmônicos
fracionários então herdam essa regularidade. / [en] We first examine Lp-viscosity solutions to fully nonlinear elliptic equations
with bounded measurable ingredients. By considering p0 < p < d, we
focus on gradient-regularity estimates stemming from nonlinear potentials.
We find conditions for local Lipschitz-continuity of the solutions and continuity
of the gradient. We survey recent breakthroughs in regularity theory
arising from (nonlinear) potential estimates. Our findings follow from – and
are inspired by – fundamental facts in the theory of Lp-viscosity solutions,
and results in the work of Panagiota Daskalopoulos, Tuomo Kuusi and Giuseppe
Mingione (DKM2014). In the second part we prove partial regularity
of weakly stationary weighted harmonic maps with free boundary data on
a cone. As a starting point we take a look at the interior partial regularity
theory for intrinsic energy minimising fractional harmonic maps from
Euclidean space into smooth compact Riemannian manifolds for fractional
powers strictly between zero and one. Intrinsic fractional harmonic maps
can be extended to weighted harmonic maps, so we prove partial regularity
for locally minimising harmonic maps with (partially) free boundary data
on half-spaces, fractional harmonic maps then inherit this regularity.
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Free surface flow simulation in estuarine and coastal environments : numerical development and application on unstructured meshes / Simulation des écoulements à la surface libre dans des environnements côtiers et estuariens : développement numérique et application sur des maillages non-structurésFilippini, Andrea Gilberto 14 December 2016 (has links)
Over the last decades, there has been considerable attention in the accurate mathematical modeling and numerical simulations of free surface wave propagation in near-shore environments. A physical correct description of the large scale phenomena, which take place in the shallow water region, must account for strong nonlinear and dispersive effects, along with the interaction with complex topographies. First, a study on the behavior in nonlinear regime of different Boussinesq-type models is proposed, showing the advantage of using fully-nonlinear models with respect to weakly-nonlinear and weakly dispersive models (commonly employed). Secondly, a new flexible strategy for solving the fully-nonlinear and weakly-dispersive Green-Naghdi equations is presented, which allows to enhance an existing shallow water code by simply adding an algebraic term to the momentum balance and is particularly adapted for the use of hybrid techniques for wave breaking. Moreover, the first discretization of the Green-Naghdi equations on unstructured meshes is proposed via hybrid finite volume/ finite element schemes. Finally, the models and the methods developed in the thesis are deployed to study the physical problem of bore formation in convergent alluvial estuary, providing the first characterization of natural estuaries in terms of bore inception. / Ces dernières décennies, une attention particulière a été portée sur la modélisation mathématique et la simulation numérique de la propagation de vagues en environnements côtiers. Une description physiquement correcte des phénomènes à grande échelle, qui apparaissent dans les régions d'eau peu profonde, doit prendre en compte de forts effets non-linéaires et dispersifs, ainsi que l'interaction avec des bathymétries complexes. Dans un premier temps, une étude du comportement en régime non linéaire de différents modèles de type Boussinesq est proposée, démontrant l'avantage d'utiliser des modèles fortement non-linéaires par rapport à des modèles faiblement non-linéaires et faiblement dispersifs (couramment utilisés). Ensuite, une nouvelle approche flexible pour résoudre les équations fortement non-linéaires et faiblement dispersives de Green-Naghdi est présentée. Cette stratégie permet d'améliorer un code "shallow water" existant par le simple ajout d'un terme algébrique dans l'équation du moment et est particulièrement adapté à l'utilisation de techniques hybrides pour le déferlement des vagues. De plus, la première discrétisation des équations de Green-Naghdi sur maillage non structuré est proposée via des schémas hybrides Volume Fini/Élément Fini. Finalement, les modèles et méthodes développés dans la thèse sont appliqués à l'étude du problème physique de la formation du mascaret dans des estuaires convergents et alluviaux. Cela a amené à la première caractérisation d'estuaire naturel en terme d'apparition de mascaret.
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Fully linear elliptic equations and semilinear fractionnal elliptic equationsChen, Huyuan 10 January 2014 (has links)
Cette thèse est divisée en six parties. La première partie est consacrée à l'étude de propriétés de Hadamard et à l'obtention de théorèmes de Liouville pour des solutions de viscosité d'équations aux dérivées partielles elliptiques complètement non-linéaires avec des termes de gradient, ... / This thesis is divided into six parts. The first part is devoted to prove Hadamard properties and Liouville type theorems for viscosity solutions of fully nonlinear elliptic partial differential equations with gradient term ...
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