Дисертації з теми "Numerical Limit Analysis"
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Visram, Abeed. "Asymptotic limit analysis for numerical models of atmospheric frontogenesis." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/23219.
Повний текст джерелаDegwitz, Fernando G. (Fernando Guillermo) 1980. "Numerical upper and lower bound limit analysis for braced excavations." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/30131.
Повний текст джерелаIncludes bibliographical references (leaves62-63).
This thesis reviews limit theorems and their applications for stability problems in geotechnical engineering. Rigorous numerical solutions of limit analyses can be obtained through finite element discretization of the soil mass and formulation of the limit theorems within a linear programming framework. The current research uses a formulation proposed by Sloan et al. (1988) and extended in a recent Ph.D. thesis by Ukritchon (1998) to include soil-structure interactions. The thesis details the input and output required for numerical limit analysis and presents an example application for the stability of a broad excavation for the MUNI Metro Turnback project in San Francisco. This well documented case study involves a 13 M deep excavation within a deep deposit of May Mud that was supported by an SPTC wall with three levels of cross-lot bracing. The numerical limit analyses calculate factors of safety, FS = 1.03 - 1.36, against basal instability. The factor of safety used in the original design (FS = 1.2) is contained in this range. The results illustrate that numerical limit analysis offers a practical alternative to limit equilibrium methods in evaluating the stability of braced excavations.
by Fernando G. Degwitz.
M.Eng.
ARAUJO, LUIZ GONZAGA DE. "NUMERICAL STUDIES OF THE STABILITY OF GEOTECHNICAL MATERIALS THROUGH LIMIT ANALYSIS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=2084@1.
Повний текст джерелаO presente trabalho apresenta um estudo de problemas de estabilidade, freqüentemente,encontrados, em Engenharia Geotécnica, através da técnica da Análise Limite associada ao Método dos Elementos Finitos (MEF).Inicialmente, faz-se uma revisão das formulações da Análise Limite, via MEF,encontradas, com maior freqüência, na literatura técnica especializada.Uma formulação mista que é descrita em detalhe na tese foi escolhida para implementação. Extensões das formulações da Análise Limite de meios contínuos são propostas para contemplar características de maciços rochosos fraturados. É proposto,também, um procedimento numérico para tratar de problemas de estabilidade de meios que exibem fluxo plástico não associado.As implementações realizadas foram validadas através de problemas cujas soluções podem ser obtidas por via analítica.Finalmente, um número considerável de problemas de interesse em Engenharia Geotécnica é estudado utilizando a implementação realizada. Os resultados destes estudos sugerem a viabilidade da utilização da técnica estudada na solução de problemas práticos de Engenharia Civil.
This work presents a study of stability problems often encountered in Geotechnical Engineering, through the use of Limit Analysis in conjunction with the Finite Element Method (FEM).Initially, a literature survey of the most often found formulations in Limit Analysis through the FEM is carried out.A mixed formulation of Limit Analysis was chosen for implementation and its details are fully described. Extensions of the formulation to deal with stability problems in fractured rock media are also proposed and described. A numerical procedure to take into account the effect of non associative plastic flow is proposed.The implementations carried out were validated through problems to which analytical solutions could be found.Finally, a considerable number of problems of interest to Geotechnical Engineering is studied with the implemented formulation. The results of these studies suggest that Limit Analysis can be considered as a viable tool in the solution of practical problems in Geotechnical Engineering.
Prasad, Anamika 1979. "Development of user interface for numerical limit analysis of geotechnical stability problems." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/85751.
Повний текст джерелаLe, Canh. "Novel numerical procedures for limit analysis of structures : mesh-free methods and mathematical programming." Thesis, University of Sheffield, 2010. http://etheses.whiterose.ac.uk/856/.
Повний текст джерелаAlves, Vian Marina. "Funicular solutions for masonry vaults: a review of recent and past numerical methods." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Знайти повний текст джерелаROJAS, JHONATAN EDWAR GARCIA. "NUMERICAL LIMIT ANALYSIS USING SEMIDEFINITE AND SECOND ORDER CONIC PROGRAMMING WITH APPLICATION IN STABILITY OF SHALLOW TUNNELS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36904@1.
Повний текст джерелаCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Nesse trabalho é avaliada a solução numérica do colapso na frente de escavação em túneis rasos, através da teoria de análise limite numérico, usando o teorema do limite inferior, a partir da condição de equilíbrio para as condições plásticas, além de considerar o comportamento do material rígido perfeitamente plástico. O teorema de limite inferior implica em maximizar o fator multiplicador na carga atuante, por isso a análise limite se torna um problema de otimização, nele tem que se usar a programação matemática para ser resolvido. É avaliada a solução numérica tridimensional da análise limite através do método dos elementos finitos, usando malha de elementos hexaédricos de oito nós, a análise dos elementos finitos é feita com o próprio código gerado na linguagem de programação do MATLAB 2017.As metodologias de programação matemática empregadas são: programação cônica de segunda ordem e programação semidefinida. Antes deve-se adaptar os critérios de ruptura de Drucker Prager à programação cônica de segunda ordem e Mohr-Coulomb tridimensional à programação semidefinida. Para a otimização se usa o algoritmo comercial MOSEK Aps 7.1 baseado no método do ponto interior em grande escala, na linguagem do MATLAB 2017. Além disso, obteve-se o mecanismo de colapso através da propriedade da dualidade do problema de otimização, dualidade que é cumprida pelos teoremas de limite superior e inferior.
In this work the numerical solution of the collapse in the front of excavation in shallow tunnels is evaluated through the theory of numerical limit analysis, using the lower limit theorem, from the equilibrium condition for the plastic conditions, considering the behavior of the perfectly plastic rigid material. The lower limit theorem implies maximizing the multiplier factor in the acting load, so that the limit analysis becomes an optimization problem. The three-dimensional numerical solution of the limit analysis using the finite element method is evaluated using a mesh of eight-node hexahedral elements. The finite element analysis is done using the code generated in the MATLAB 2017 programming language. The mathematical programming methodologies used are: second order conic programming and semidefinite programming. The Drucker-Prager three-dimensional criteria should be adapted to the conic programming of the second order and Mohr-Coulomb three-dimensional to the semidefinite programming. For the optimization, the MOSEK Aps 7.1 commercial algorithm based on the large-scale interior point method is used in the MATLAB 2017 language. In addition, the collapse mechanism was obtained through the duality property of the optimization problem, duality that is fulfilled by the upper and lower limit theorems.
Antocheviz, Rafael Bugs. "Metodologia para determinação do procedimento a ser utilizado em uma análise de estabilidade de taludes : ruptura circular." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/184854.
Повний текст джерелаAnalysis of slope stability in mining is one of the most important activities of the process of obtaining a mineral resources. Ensuring the excavation stability and the safety of the project are vital to the extraction process. The choice of the form of analysis (2D, quasi-threedimensional or 3D) or of the method (limit equilibrium or numerical analysis) more suitable for this type of study is of paramount importance since, the responsible engineer often end up basing the analysis on familiarity with a particular methodology or on the availability of a particular program, to the detriment of technical factors and relevance to the study. Thus, in order to fill this existing gap and facilitate the selection of the best methodology to be used, the present study brings together the main known methods, their advantages and disadvantages and, therefore, presents a methodology for such a choice to be based on relevant technical parameters. The proposed methodology is somewhat restrictive in the choice of procedures that will be considered, since it has been tried to use methods that have proven applicability, that have considerable advantages over other methods and that are rigorous, satisfying all equilibrium conditions (forces and moments). In order to corroborate the proposed methodology, four different practical situations were presented, demonstrating the applicability of the methodology.
Franca, Paulo Ricardo Behrens da. "Analysis of slope stability using limit equilibrium and numerical methods with case examples from the Águas Claras Mine, Brazil." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20637.pdf.
Повний текст джерелаJanssen, Arend. "Order book models, signatures and numerical approximations of rough differential equations." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:264e96b3-f449-401b-8768-337acab59cab.
Повний текст джерелаPan, Qiujing. "Deterministic and Probabilistic Assessment of Tunnel Face Stability." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI044.
Повний текст джерелаIn the contemporary society, the utilization and exploitation of underground space has become an inevitable and necessary measure to solve the current urban congestion. One of the most important requirements for successful design and construction in tunnels and underground engineering is to maintain the stability of the surrounding soils of the engineering. But the stability analysis requires engineers to have a clear ideal of the earth pressure, the pore water pressure, the seismic effects and the soil variability. Therefore, the research aimed at employing an available theory to design tunnels and underground structures which would be a hot issue with high engineering significance. Among these approaches employed to address the above problem, limit analysis is a powerful tool to perform the stability analysis and has been widely used for real geotechnical works. This research subject will undertake further research on the application of upper bound theorem to the stability analysis of tunnels and underground engineering. Then this approach will be compared with three dimensional analysis and experimental available data. The final goal is to validate new simplified mechanisms using limit analysis to design the collapse and blow-out pressure at the tunnel face. These deterministic models will then be used in a probabilistic framework. The Collocation-based Stochastic Response Surface Methodology will be used, and generalized in order to make possible at a limited computational cost a complete parametric study on the probabilistic properties of the input variables. The uncertainty propagation through the models of stability and ground movements will be evaluated, and some methods of reliability-based design will be proposed. The spatial variability of the soil will be taken into account using the random field theory, and applied to the tunnel face collapse. This model will be developed in order to take into account this variability for much smaller computation times than numerical models, will be validated numerically and submitted to extensive random samplings. The effect of the spatial variability will be evaluated
Raithatha, Ankor Mahendra. "Incremental sheet forming : modelling and path optimisation." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:89b0ac1e-cab4-4d80-b352-4f48566c7668.
Повний текст джерелаCaër, Typhaine. "Interprétation structurale et équilibre mécanique : La calcul à la rupture appliqué aux chaînes d'avant-pays. Cas du Jura." Thesis, Cergy-Pontoise, 2016. http://www.theses.fr/2016CERG0812/document.
Повний текст джерелаFold-and-thrust-belts form in a compressive geological context and represent the external part of orogens.They are composed of numerous folds and thrusts generally rooted in a shallow décollement level located in the basal part of the sedimentary cover.These belts have been studied extensively during the XX century. They have been modeled kinematically, analogically and mechanically.The mechanical aspect of deformation must be taken into account in structural geology, but yet, mechanical models remain underused by the structural geologist.The objective of this thesis is to show how to bring mechanical constraints to the study of geological structures with a mechanical theory easily usable in structural geology, the Limit Analysis.This theory represents a good compromise between the kinematic models and the finite element mechanical models, very complete but relatively complicated to use.We study here examples from the Jura fold-and-thrust belt and use the softwares Optum G2 and SLAMTec.We proceed with two different approaches.The first one is presented in the first part of this manuscript and consists in studying the past deformation.We focus on Saint-Ursanne area, in the North-East Switzerland Jura.We construct first a 2D geological cross section of the Mont Terri structure and then we extend this work in 3D by a series of cross sections that scan the whole Saint Ursanne area.These cross-sections are drawn using kinematical rules, mechanical modeling with Limit Analysis and analog sandbox modeling.We show the importance of the tectonic inheritance on the onset of structures in the studied region and we mechanically model the influence of a décollement offset due to an inherited normal fault during a subsequent compressive episode.We show that this offset represents a “fault generator” and a catching point that slows the propagation of the deformation front and furthermore controls the orientation of the structure that develops.We also show that the topography plays a major role in the establishment of geological structures.In the second part of the manuscript we follow a second approach that consists in studying the current deformation.We change of scale and study the current tectonics of the entire Jura.Our models predict that this belt, formed in thin-skin tectonics, is currently partially affected by thick-skin tectonics.The western Jura would be still affected by a thin-skin tectonics, but the basement should be involved in the deformation in the north-east Jura.However, we show that a thick-skin tectonics does not preclude the simultaneous activation of the shallower décollements contained by the sedimentary cover (Triassic evaporites, in the Jura).Practical interest of these methods is illustrated by industrial questions: the last chapter presents a study of geological cross-sections from a studied area of Nagra in the eastern Jura.We look at the current mechanical answer under compression of the proposed structural interpretations.The numerical tools used in this work have been the subject of a tutorial made during a mission at Total company
Outada, Nisrine. "Complex Systems in Biology and Soft Sciences : Modeling by Hyperbolic and Kinetic Equations, Analytic and Numerical Problems A critical analysis towards research perspectives Reply to comments on “Modeling human behavior in economics and social science” A critical analysis towards research perspectives Reply to comments on “Modeling human behavior in economics and social science”." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS448.
Повний текст джерелаThis thesis tackles the challenging aim of developing a mathematical theory of living systems with focus on hyperbolic and kinetic equations, to multicellular systems in biology, crowd dynamics, and social sciences and economy viewed as behavioral sciences, occasionally called soft sciences. In more details, the following topics have been tackled: 1) Development of the theory and application of the kinetic theory of the scalled active particles, with the main objective of deriving a general mathematical structure, consistent with the complexity features of living systems, where the dynamics are developed over the space variable. This structure offers the conceptual background for the derivation of specific models corresponding to well-defined classes of systems and substitutes the field theories, which classically offers the natural support in the sciences of the inert matter that cannot be applied in the case of living systems. Applications have also motivated development of simulation tools. 2) Mathematical methods to derive macroscopic tissue equations, of Keller– Segel and Cattaneo type, from the underlying description at the microscopic scale delivered by kinetic type models and development of computational schemes towards simulations both of kinetic transport models and hyperbolic macroscopic models. In more details, finite volume methods for hyperbolic conservative laws equations have been developed for the simulations of macroscopic models. 3) Applications to modeling, qualitative analysis, and simulations of social systems. Applications have been addressed to social systems and behavioral crowd dynamics with a special focus on evacuation dynamics from venues with complex geometry with special focus to a dy- namics, where panic propagates. Simulations have been obtained by a suitable developments of the socalled Monte Carlo particle methods. 4) Analytical problems generated by the convergence of the Hilbert approach to the derivation of macroscopic equations from the kinetic theory approach, and a qualitative analysis related to existence and uniqueness of the solutions of the initial value problems of the kinetic systems
Bader, Philipp Karl-Heinz. "Geometric Integrators for Schrödinger Equations." Doctoral thesis, Universitat Politècnica de València, 2014. http://hdl.handle.net/10251/38716.
Повний текст джерелаBader, PK. (2014). Geometric Integrators for Schrödinger Equations [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/38716
TESIS
Premiado
Ukritchon, Boonchai 1970. "Evaluation of numerical limit analyses by finte elements and linear programming." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11199.
Повний текст джерелаUkritchon, Boonchai 1970. "Application of numerical limit analyses for undrained stability problems in clay." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9591.
Повний текст джерелаIncludes bibliographical references.
This thesis describes the development and application of numerical limit analyses for planar, undrained stability problems in geotechnical engineering. The proposed analyses formulate upper and lower bound theorems for perfectly plastic, cohesivefrictional soils as linear programming problems, with spatial variations of the unknown velocities and stresses approximated by standard finite element interpolation functions. The thesis includes three substantial modifications of the pre-existing software: l) inclusion of structural beam and joint elements, that enable the program to model failure in combined bending, shear and axial loading; 2) implementation of functions to represent the undrained strength anisotropy of soft clays; and 3) representation of pore water pressures and effective stress strength parameters for stability analyses that include free draining soil layers. In all of the examples presented in this thesis, the proposed numerical limit analyses are able to bracket the true collapse load within ±5%. The stability of surface footings under combined effects of vertical, horizontal and moment (V, H, M) loading is solved in the form of three-dimensional failure envelopes, that include effects of underbase suction and non-homogeneous undrained strength profiles. Existing empirical bearing capacity factors for inclined, eccentric loading are shown to be conservative, often underestimating the exact collapse solutions for footings on homogeneous clay by more than 25%. However, the same correction factors can become completely unreliable when there is a significant undrained strength gradient. The numerically-derived failure envelope for footings on homogeneous clay is described approximately by curve fitting techniques using relatively simple functions that can be used to update the existing bearing capacity factors. The undrained (short-term) pullout capacity of a single caisson cell in clay is initially investigated as a planar problem. Limit analyses show that the capacity can be presented as a normalized function of the undrained strength gradient in the clay, and interior surface area of the caisson. The results show that there are significant errors in limit equilibrium calculations which assume mechanisms of reverse end-bearing. Pullout predictions are compared with measured data from 1) small scale laboratory element tests on miniature caissons, 2) centrifuge models and 3) field tests on a four-cell caisson unit. These comparisons introduce approximations in the scaling of the planar solutions to axisymmetric cell geometries, and inclined loading cases. Good agreement is obtained with all three sets of experiments, and confirms that the proposed limit analyses are at least comparable in predictive capability to the limit equilibrium calculations currently used in practice. The limit analyses represent the undrained strength anisotropy of soft clays using a yield function originally proposed by Davis and Christian ( 1970). Undrained strength anisotropy is found to have a major influence on the stability and failure mechanisms for unbraced vertical cuts in clay. In contrast, there is minimal effect on the failure mechanisms for kinematically constrained problems such as the lateral load capacity of deeply embedded pile or pipe sections. Applications of limit analyses for braced excavations show important errors in existing calculations of basal stability. The analyses also provide the first theoretical solutions that quantify effects of wall embedment and bending strength on the stability of well-braced cuts. The results have also been compared with previous displacement-based finite element calculations based on the anisotropic MIT-E3 soil model. Good matching is obtained using the limit analyses together with anisotropic strength parameters mobilized at shear strains, y = 0.6 - 1.0%, corresponding to failure conditions in the finite element solutions. Limit analyses have been used to re-assess the stability of tied-back walls at Bird Island Flats in East Boston. Detailed analyses were carried out for two cases l) estimated excavation and support geometry at an unstable section; and 2) at final excavated grade after placement of a remedial buttress constructed by deep soil-mixing and jet grouting. Reliability analyses show that uncertainties in the undrained strength profile represent the major factor affecting predictions of stability. Successful performance of the improved cross-section is not consistently explained by strength parameters derived from the unstable cross-section. Additional calculations compare the stabilizing effects of different designs for the wall, tiebacks and remedial buttress. The failure of an offshore breakwater in Brazil was analyzed extensively using conventional slope stability methods in a recent Ph.D thesis by Lee ( 1995). Limit analyses, using the same soil parameters, shows similar mechanisms of failure controlled by the undrained shear strength of the underlying Sergipe clay. However, the factors of safety computed by Spencer's method are shown to be unrealistically low due to the assumed directions of interslice forces in the overlying sand and rockfill layers.
by Boonchai Ukritchon.
Sc.D.
Sahlaoui, Ramzi. "Panneaux en maçonnerie renforcés à l'aide de matériaux composites : approche de type calcul à la rupture et étude expérimentale." Phd thesis, Université Paris-Est, 2011. http://pastel.archives-ouvertes.fr/pastel-00672356.
Повний текст джерелаFogelklou, Oswald. "Computer-Assisted Proofs and Other Methods for Problems Regarding Nonlinear Differential Equations." Doctoral thesis, Uppsala universitet, Analys och tillämpad matematik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-161314.
Повний текст джерелаDJILALI, BERKANE LAIEB ZOHRA. "Evaluation numérique d'un coefficient de sécurité cinématique pour les barrages et les ouvrages en terre." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10193.
Повний текст джерелаJohnson, Tomas. "Computer-aided Computation of Abelian integrals and Robust Normal Forms." Doctoral thesis, Uppsala universitet, Matematiska institutionen, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-107519.
Повний текст джерелаStloukal, Štěpán. "Zesílení ŽB sloupu pomocí ocelové bandáže." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-265384.
Повний текст джерелаMansouri, Lotfi zoher. "Analyse des instabilités plastiques dans les matériaux ductiles endommageables : application à la prédiction de la striction et de la formabilité des tôles métalliques." Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0059/document.
Повний текст джерелаDiffuse and localized necking are precursors to ductile fracture, and represent one of the main causes of metal parts rejection during forming operations. The implementation of theoretical and computational tools to predict the occurrence of these defects turns out to be necessary for economic and environmental reasons. These tools require in part the introduction of an appropriate behavior model in order to reproduce the physical phenomena involved during forming operations. Such a behavior model is then coupled to a plastic instability indicator providing the ability to reliably predict diffuse and localized necking. In the present work, we considered a micromechanical damage models based on Gurson's approach, which were coupled to different plastic instabilities criteria, based on Bifurcation Analysis. The numerical implementation of these models was carried within the implicit finite element code Abaqus/Standard. With regard to the damage models, several integration schemes were tested to analyze their performance and robustness when the behavior exhibits softening effect. The approach combining the Gurson's damage model and necking criteria has been applied for the prediction of formability limits of several metallic materials. The obtained results allowed establishing a theoretical and numerical classification between the necking criteria used in this work
Hafiene, Yosra. "Continuum limits of evolution and variational problems on graphs." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC254/document.
Повний текст джерелаThe non-local p-Laplacian operator, the associated evolution equation and variational regularization, governed by a given kernel, have applications in various areas of science and engineering. In particular, they are modern tools for massive data processing (including signals, images, geometry), and machine learning tasks such as classification. In practice, however, these models are implemented in discrete form (in space and time, or in space for variational regularization) as a numerical approximation to a continuous problem, where the kernel is replaced by an adjacency matrix of a graph. Yet, few results on the consistency of these discretization are available. In particular it is largely open to determine when do the solutions of either the evolution equation or the variational problem of graph-based tasks converge (in an appropriate sense), as the number of vertices increases, to a well-defined object in the continuum setting, and if yes, at which rate. In this manuscript, we lay the foundations to address these questions.Combining tools from graph theory, convex analysis, nonlinear semigroup theory and evolution equa- tions, we give a rigorous interpretation to the continuous limit of the discrete nonlocal p-Laplacian evolution and variational problems on graphs. More specifically, we consider a sequence of (determin- istic) graphs converging to a so-called limit object known as the graphon. If the continuous p-Laplacian evolution and variational problems are properly discretized on this graph sequence, we prove that the solutions of the sequence of discrete problems converge to the solution of the continuous problem governed by the graphon, as the number of graph vertices grows to infinity. Along the way, we provide a consistency/error bounds. In turn, this allows to establish the convergence rates for different graph models. In particular, we highlight the role of the graphon geometry/regularity. For random graph se- quences, using sharp deviation inequalities, we deliver nonasymptotic convergence rates in probability and exhibit the different regimes depending on p, the regularity of the graphon and the initial data
Loiseau, Jean-Christophe. "Dynamics and global stability analysis of three-dimensional flows." Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0016/document.
Повний текст джерелаUnderstanding, predicting and eventually delaying transition to turbulence in fluid flows have been challenging issues for scientists ever since the pioneering work of Osborne Reynolds in 1883. These problems have mostly been addressed using the hydrodynamic linear stability theory. Yet, due to limited computational resources, linear stability analyses have essentially relied until recently on strong simplification hypotheses such as the “parallel flow” assumption. In this framework, known as “local stability theory”, only the stability of flows with strong academic interest but limited practical applications can be investigated. However, over the course of the past decade, simplification hypotheses have been relaxed from the “parallel flow” assumption to a two-dimensionality assumption of the flow resulting in what is now known as the “global stability theory”. This new framework allows one to investigate the instability and transition mechanisms taking place in more realistic flows. More particularly, the stability of strongly non-parallel flows exhibiting separation, a common feature of numerous flows of practical interest, can now be studied. Moreover, with the continuous increase of computational power available and the development of new iterative eigenvalue algorithms, investigating the global stability of fully three-dimensional flows, for which no simplification hypothesis is necessary, is now feasible. Following the work presented in 2008 by Bagheri et al., the aim of the present thesis is thus to develop the tools mandatory to investigate the stability of 3D flows. Three flow configurations have been chosen to illustrate the new investigation capabilities brought by global stability theory when it is applied to realistic three-dimensional flows: i) the flow within a cuboid lid-driven cavity, ii) the flow within an asymmetric stenotic pipe and iii) the boundary layer flow developing over a cylindrical roughness element mounted on a flat plate. Each of these flows have different practical applications ranging from purely academic interests to biomedical and aerodynamical applications. They also allow us to put in the limelight different aspects and possible limitations of the various tools developed during this PhD thesis
Franck, Emmanuel. "Construction et analyse numérique de schéma asymptotic preserving sur maillages non structurés. Application au transport linéaire et aux systèmes de Friedrichs." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00735956.
Повний текст джерелаRodriguez, Miranda Juan Carlos 1984. "Estudio y análisis de sistemas lineales generados en problemas de contorno con frontera discontínua a partir de métodos espectrales/hp = Estudo e análise de sistemas lineares gerados nos problemas de contorno com fronteira descontinua a partir de métodos espectrais/hp." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/306347.
Повний текст джерелаDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Científica
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Resumo: O Método dos Elementos Finitos representou nos últimos anos uma ferramenta fundamental no estudo de problemas de contorno. A evolução desde sua formulação fundamental a partir do Método de Galerkin clássico até sua versão com refinamento hp, se tornou na base dos métodos numéricos mais avançados como é o Método de Galerkin Descontinuo. O Método dos Elementos Finitos de Alta Ordem juntamente com os Métodos Espectrais usados na obtenção de soluções numéricas para problemas de contorno com fronteira descontinua, serão nosso objeto de estudo nesta Dissertação. Desde sua formulação matemática fundamental, por intermédio da escolha apropriada das funções hierárquicas que compõem os espaços de aproximação, assim como a montagem dos sistemas lineares locais e sua respectiva utilização no sistema linear global esparso, cuja solução é obtida pelo método iterativo de Gradiente Conjugado usando diversos Precondicionadores, será o caminho a seguir
Abstract: The Finite Element Method developed in the last decades has been the most important tool in the study of Boundary Value Problems. Your evolution from its fundamental formulation using the Galerkin Method to the hp-adaptive finite element methods (hp-FEM), provided the necessary foundation for more advanced Numerical Methods like the Galerkin Discontinuous Method. The Finite Element Method of Higher Order, together with the Spectral formulation as a numerical method to solve Boundary Problems with Discontinuous Boundary, is the objective of study to this dissertation. The fundamental mathematical formulation of the finite element methods, passing through of to choose of hierarchical basis functions, also the assembly of local linear systems and it posteriorly use to construct a Sparse Linear System, whose solution is obtained for an iterative Preconditioner Gradient Method
Mestrado
Matematica Aplicada
Mestre em Matemática Aplicada
Gu, Qilong. "Solutions globales, limite de relaxation, contrôlabilité et observabilité exactes, frontières pour des systèmes hyperboliques quasi-linéaires." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2009. http://tel.archives-ouvertes.fr/tel-00725524.
Повний текст джерелаRenard, Nicolas. "Simulations numériques avancées et analyses physiques de couches limites turbulentes à grand nombre de Reynolds." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066041/document.
Повний текст джерелаBetter understanding the specificities of the dynamics of high-Reynolds number boundary layers despite metrological constraints and its numerical simulation cost is crucial. For instance, this dynamics can determine more than half of the drag of a cruising aircraft. Describing wall turbulence can guide the numerical resolution of some of the fluctuations at a limited cost by WMLES strategies (wall-modelled large eddy simulation). The present physical analyses of zero-pressure gradient incompressible turbulent boundary layers at high Reynolds number rely on advanced numerical simulations. After validating a database, mean skin friction is decomposed by means of the FIK identity (Fukagata et al. (2002)), whose application despite the spatial growth is discussed. A spectral analysis shows that the large scales (\lambda_x > \delta) contribute approximately half of the friction near Re_\theta = 10^4. The limitations of the FIK identity motivate the derivation of a physical decomposition of the generation of friction whose asymptotic behaviour is then related to turbulent kinetic energy production in the logarithmic layer. In order to better reconstruct spatial spectra, a new method to estimate the turbulent convection velocity as a function of the wavelength of the fluctuations, adapted to spatial growth and to temporal signals of finite duration, is derived, interpreted, and assessed at Re_\theta = 13000. Some of the conclusions enlighten modifications to a WMLES strategy, mode III of the ZDES method
Imbert-Gérard, Lise-Marie. "Analyse mathématique et numérique de problèmes d'ondes apparaissant dans les plasmas magnétiques." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00870184.
Повний текст джерелаFerria, Hakim. "Contribution to Numerical and Experimental Studies of Flutter in Space Turbines. Aerodynamic Analysis of Subsonic or Supersonic Flows in Response to a Prescribed Vibratory Mode of the Structure." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00677648.
Повний текст джерелаPaditz, Ludwig. "Beiträge zur expliziten Fehlerabschätzung im zentralen Grenzwertsatz." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-115105.
Повний текст джерелаIn the work the asymptotic behavior of suitably centered and normalized sums of random variables is investigated, which are either independent or occur in the case of dependence as a sequence of martingale differences or a strongly multiplicative system. In addition to the classical theory of summation limiting processes are considered with an infinite summation matrix or an adapted sequence of weighting functions. It will be further developed the method of characteristic functions, and especially the direct method of the conjugate distribution functions to prove quantitative statements about uniform and non-uniform error estimates of the remainder term in central limit theorem. The investigations are realized in the Lp metric, 1
Szubert, Damien. "Physics and modelling of unsteady turbulent flows around aerodynamic and hydrodynamic structures at high Reynold number by numerical simulation." Phd thesis, Toulouse, INPT, 2015. http://oatao.univ-toulouse.fr/15129/2/szubert_1.pdf.
Повний текст джерелаMéndez, Margio González. "Simulations numériques de la transition de la couche limite sur une surface concave : application à la conception des éoliennes à axe vertical de type Savonius Heat-transfer analysis of a transitional boundary layer over a concave surface with Görtler vortices by means of direct numerical simulations Boundary layer transition over a concave surface caused by centrifugal instabilities." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR05.
Повний текст джерелаDirect numerical simulations (DNS) are computed in order to study the complete laminar-to-turbulent transition process of a boundary layer developing over a concave surface. It is found that the flow passing through such geometry is prone to develop centrifugal instabilities in the form of Görtler vortices. Transition is triggered by means of wall-roughness elements that are also utilized to preset the spanwise wavelength of the Görtler vortices. The different regions encountered in the transition process, i.e. linear, nonlinear, transition, and fully turbulent, are identified and characterized. Primary and secondary (varicose and sinuous) instabilities are identified and analyzed as well. Parametric studies showing the effect of several physical parameters (radius of curvature, the vortices wave-length, the perturbation amplitude and streamwise location, and the wall-roughness perturbation geometry) on the transition starting point are presented. Furthermore, thermal analyses are conducted in order to study the modification of the thermal boundary layer due to the Görtler vortices swirl motion. The streamwise evolution of the surface heat transfer is investigated finding that it is considerably enhanced in the non-linear region surpassing the turbulence-region values. It is also found that the Reynolds analogy between streamwise-momentum and heat transfer is followed throughout the whole transition process
Marly, Arthur. "Analyse mathématique et numérique d'écoulements de fluides à seuil." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN034/document.
Повний текст джерелаThis thesis is devoted to the flow of yield stress (or viscoplastic) fluids in pipes.Analytical and numerical difficulties lie in the multivaluation of the stress tensor in the plastic regions and in the non-differentiability of the associated minimization problem. This manuscript is organized following two main axes.First, very accurate numerical simulations were carried out using duality methods and parallel multifrontal solvers. Thus, experimental observations were recovered, namely the existence of a slip line for the flow over an obstacle and the Poiseuille-like behaviour of the velocity above this line. Moreover, the viscoplastic boundary layer theory defined by Oldroyd (1947 at high Bingham numbers) was revisited at moderate Bingham numbers in confined areas. This study provided an opportunity to go back and forth between these simulations and the physical measures of Luu et al. from IRSTEA and to perform a theoretical derivation. The boundary layer approximation is valid up to a certain extent in the cavity. An adaptation of the viscoplastic boundary layer definition is then given and allows to generalize the scalings shown by Oldroyd (1947) and Balmforth et al. (JFM 2017). These scalings are also generalized to the Herschel-Bulkley case. Then, an asymptotic analysis of the velocity and stress fields for thin layer (ε) flows is presented. A velocity development up to ε2 lets us find a Reynolds equation of same accuracy. This Reynolds equation extends the already existing results, on the one hand in the newtonian case and on the second hand for free surface flows
De, Moor Sylvain. "Limites diffusives pour des équations cinétiques stochastiques." Electronic Thesis or Diss., Rennes, École normale supérieure, 2014. http://www.theses.fr/2014ENSR0001.
Повний текст джерелаThis thesis presents several results about stochastic partial differential equations. The main subject is the study of diffusive limits of kinetic models perturbed with a random term. We also present a result about the regularity of a class of stochastic partial differential equations and a result of existence and uniqueness of invariant measures for a stochastic Fokker-Planck equation.First, we give three results of approximation-diffusion in a stochastic context. The first one deals with the case of a kinetic equation with a linear operator of relaxation whose velocity equilibrium has a power tail distribution at ininity. The equation is perturbed with a Markovian process. This gives rise to a stochastic fluid fractional limit. The two remaining results consider the case of the radiative transfer equation which is a non-linear kinetic equation. The equation is perturbed successively with a cylindrical Wiener process and with a Markovian process. In both cases, we are led to a stochastic Rosseland fluid limit.Then, we introduce a result of regularity for a class of quasilinear stochastic partial differential equations of parabolic type whose random term is driven by a cylindrical Wiener process.Finally, we study a Fokker-Planck equation with a noisy force governed by a cylindrical Wiener process. We prove existence and uniqueness of solutions to the problem and then existence and uniqueness of invariant measures to the equation
Sheng-Horng, Shiau. "Numerical methods for shakedown analysis of pavements under moving surface loads." Thesis, 2001. http://hdl.handle.net/1959.13/1312942.
Повний текст джерелаFailure of pavements associated with moving repeated traffic loads are typically caused by gradual deterioration rather than sudden collapse. This type of failure behaviour is mostly due to the accumulation of plastic strains under repeated loadings. There are different from the geotechnical engineering solution of the stability problems of soil masses under simple loading programs. It can be shown theoretically that there is a load magnitude below which a protective residual stress will develop in the road, and above which the pavement will undergo an incremental failure. This load is known as the 'shakedown limit load' and the protective residual stresses associated with this shakedown limit load are the optimal residual stresses for the life of the pavement. This thesis thus aims at describing a general numerical method for the shakedown solutions of pavements subjected to repeated moving traffic loads. To achieve this goal, a novel numerical formulation based on Bleich-Melan shakedown theorem is developed by making use of finite element techniques and mathematical programming. The proposed numerical procedure can be used to solve for the shakedown limit load and the associated developed residual stresses for both two- and three- dimensional continua under complex load distribution and boundary geometry, layered material, and inhomogeneous soil deposit.
Chiwaye, Henry Tonderai. "A comparison of the limit equilibrium and numerical modelling approaches to risk analysis for open pit mine slopes." Thesis, 2010. http://hdl.handle.net/10539/8376.
Повний текст джерелаChuang, Hsien-Cheng, and 莊憲政. "using the numerical analysis to conclude the deviation for upper and under limit of Gerretsen - inequality and simply proof." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/26621085846935682375.
Повний текст джерела國立臺中教育大學
數學教育學系
96
Due to Gerretsen - inequality always can solve many tough question in proving effectively. So, this research use method of primary substitution operation and arithmetic average greater than geometry average to conclude Gerretsen -inequality as below: 16Rr-5r^2le s^2 le 4R^2+4Rr+3r^2. And then, using the numerical analysis to conclude the deviation for upper and under limit of Gerretsen - inequality. The research found : 1.Gerretsen- inequality only use the character of arithmetic average greater than geometry average to prove the inequality . The rest is just routine primary substitution operation. 2.Using Excel to calculate upper limit of Gerretsen - inequality, the difference of inequality inclines to 0.33333. 3.Using Excel to calculate under limit of Gerretsen - inequality, the difference of inequality inclines to 0.33333.
MISSERI, GIULIA. "Seismic vulnerability of pointed arches under rigid body assumption. Numerical and experimental evaluations." Doctoral thesis, 2017. http://hdl.handle.net/2158/1079986.
Повний текст джерелаKanda, Mpoyi Jacques. "Limit equilibrium and numerical modelling approaches in slope stability analyses with regard to risk assessment for open pit mining." Thesis, 2016. http://hdl.handle.net/10539/20094.
Повний текст джерелаThe planning of open pit mines, and road and rail cuttings constitutes one of the activities usually undertaken by geotechnical engineers. However, this endeavour faces major challenges such as the correct design of rock slopes, the evaluation of their stability and the risk associated with them. Two main analytical methods are used in this process: the Limit Equilibrium (LE) analysis and the Numerical Modelling (NM) method; Slide and Phase2 programmes will be used respectively in this regard. Previous studies have shown some discrepancies between their results in assessing the probabilities of slope failure and the consequent economic risks. This research project aims to understand the reasons behind these divergences and possibly to find some ways of reducing them. To attain these objectives, a homogeneous slope model was adopted. It required a detailed validation study depending on the analytical method, such that the settings would carefully be calibrated to avoid any further misinterpretation of the results. For Phase2, attention was given with regard to the number of mesh elements and their type, and for Slide, the number of slices. In addition, for both methods, attention was given to the adequate distribution of rock mass variables, the adequate failure criterion, etc. Deterministic and probabilistic assessments were performed to better interpret the differences to be found from these methods and results. The response surface methodology (RSM) facilitated the probabilistic studies, to avoid the constraints of long computer run times and to ease the study of the influence of the rock mass parameters on the slope stability. For the considered model, 25 slices and 1500 mesh elements were found adequate to better assess the probability of failure (POF), while 1000 slices and 50 000 mesh elements provided results of estimated failure volumes. Well defined distributions of rock mass variables have proven indispensable to better assess the POF as well as the risk associated with the slope failure. Application of the Hoek Brown criterion resulted in the LE analysis predicting higher failure volumes than when Mohr Coulomb criterion was used. With the NM method, cares were taken not to under or overestimate the resultant failure volume when extracting the path of the failure surface. Deterministic assessments showed that the risk determined from NM analyses is not always greater than that from LE analyses. The addition of rock mass parameters not taken into account in LE analyses results does not sensibly influence the POF and the failure volume outcomes, but can in some conditions influence the behaviour of the outcome risk of slope failure. In essence, LE and NM methods can be relied on for probabilistic studies, or even for risk assessments conditioned by carefully setting the models, and in case of LE being adopted to assess the risk, it is recommended to introduce a multiplying factor for cases similar to those that have already been analysed.
Abdollahzadehsangroudi, Mohammadmahdi. "Analysis and development of numerical methodologies for simulation of flow control with dielectric barrier discharge actuators." Doctoral thesis, 2014. http://hdl.handle.net/10400.6/4238.
Повний текст джерелаO objetivo deste trabalho visa a investigação e desenvolvimento de diferentes métodos numéricos para modelação de actuadores a plasma de Descarga em Barreira Dieléctrica, (DBD), tendo em vista o controlo do escoamento na camada limite. Esta modelação numérica foi abordada de duas formas diferentes, uma baseada num modelo de “plasma-fluid” e outra fundamentada num modelo fenomenológico. Neste trabalho é usado um modelo “plasma-fluid” de três componentes que é baseado numa equação de transporte para as partículas electricamente carregadas. Este foi implementado no software OpenFOAM fazendo uso de diversas técnicas para minimização de problemas numéricos que ocorriam na resolução das equações. O cálculo de um problema com acoplamento entre plasma e fluido envolve uma gama diversa de escalas, tanto temporais como dimensionais, trata-se então de uma simulação numérica delicada. Como tal, e por forma a obter resultados estáveis e precisos num tempo de cálculo considerado razoável, foram implementados diversos procedimentos numéricos, tais como o tratamento semiimplícito do acoplamento da equação de Poisson com a equação da densidade de carga, o super-passo-tempo e ainda um algoritmo do tipo divisão de operador. Foi considerado o caso de uma diferença de potencial positiva, constante, e testada a dependência da densidade de corrente com os diferentes esquemas numéricos. Apesar de não existir atualmente uma base de dados, de tipo numérica ou experimental, com casos de teste para actuadores a plasma tipo DBD, o modelo computacional desenvolvido para calcular o plasma foi validado qualitativamente, bem como quantitativamente, usando os vários trabalhos numéricos disponíveis na literatura. Após esta validação inicial, a metodologia numérica desenvolvida foi utilizada para explorar a possibilidade de influenciar um escoamento de maior velocidade, através de actuadores a plasma tipo DBD com impulsos de tensão da ordem de nano-segundos (NS). Desta forma foi simulada a interacção entre um escoamento transónico e o efeito dos actuadores a plasma tipo DBD sobre o escoamento, usando pulsos de nano-segundos. O efeito térmico do gás, assim como a força resultante, foram calculados usando o modelo numérico para cálculo de plasmas desenvolvido neste trabalho. O resultado obtido é acoplado ao modelo de cálculo para a dinâmica de gases, o que torna possível simular as condições do escoamento resultante. Adicionalmente, os resultados do modelo de “plasma-fluid” foram reaproveitados para desenvolver um modelo de deposição de energia. Este demonstrou ter a capacidade de capturar correctamente as características principais do efeito de actuadores de plasma, de tipo NS-DBD, com um tempo de computação menor. Foi demonstrada que uma rápida transferência de energia, do plasma para o fluido, leva à formação de micro-ondas de choque que alteram localmente as características do escoamento transónico. Apesar da eficiência numérica do modelo de “plasma-fluid” ter sido melhorada, o seu custo computacional para a simulação de actuadores a plasma tipo DBD à escala real continua bastante elevado. Neste sentido, a partir de uma escala de propulsão gerada pelo actuador plasma DBD, foi desenvolvido um modelo mais simples para a descarga do plasma e para determinar os seus efeitos sobre o escoamento. O modelo inicial previa correctamente uma dependência não-linear entre a força propulsiva gerada e a diferença de potencial aplicada. Estas escalas foram então introduzidas num modelo fenomenológico mais simples para estimar, e simular, a distribuição de forças geradas pelo actuador a plasma. Apesar de o modelo incluir algumas correlações experimentais, este não requer qualquer parâmetro de afinação. O modelo foi validado com resultados experimentais, demonstrando melhores resultados quando comparado com outros modelos de plasma . Utilizando um modelo fenomenológico simplificado, que foi desenvolvido no presente trabalho, foi feito um estudo numérico com o objetivo de investigar, e comparar, os efeitos que uma actuação estacionária e não-estacionária exibe sobre o controlo do escoamento a números de Reynolds relativamente elevados. Foi demostrado que a dimensão da bolha de separação é reduzida em muito e que a estrutura do escoamento é sensível à frequência da modulação “burst” do actuador a plasma tipo DBD. Os resultados também confirmaram que, para o caso de actuação não-estacionária, a frequência de “burst” e o “burst ratio”, são parâmetros cruciais para influenciar a capacidade de controlo do escoamento por parte dos actuadores a plasma. Determinou-se que as frequências “burst”, semelhantes às frequências naturais do sistema, são capazes de excitar as estruturas do escoamento num modo de ressonância. Esta observação confirma igualmente que, com frequências de excitação apropriadas, a estrutura de um escoamento de camada limite consegue ser correctamente modificada, e que as perdas no escoamento são reduzidas. Por fim, os actuadores a plasma foram utilizados para o controlo do escoamento sobre uma superfície Coanda de uma tubeira. Quando nesta foi aplicado um plasma, tornou-se possível retardar a separação do escoamento e aumentar o ângulo de deflexão do jacto gerado pelo propulsor. Por forma a encontrar a posição óptima para os actuadores, sete actuadores de tipo DBD foram distribuídos ao longo da superfície Coanda, tendo em consideração os pontos de separação do escoamento na camada limite obtidos numericamente. Os resultados mostram que quando o actuador DBD é colocado ligeiramente antes do ponto de separação do escoamento, há um aumento da capacidade de controlo e vectorização do jacto gerado. Os resultados preliminares das experiências efectuadas estão de acordo com o ângulo de deflexão do jacto previsto pelo modelo computacional.
Paditz, Ludwig. "Beiträge zur expliziten Fehlerabschätzung im zentralen Grenzwertsatz." Doctoral thesis, 1988. https://tud.qucosa.de/id/qucosa%3A26930.
Повний текст джерелаIn the work the asymptotic behavior of suitably centered and normalized sums of random variables is investigated, which are either independent or occur in the case of dependence as a sequence of martingale differences or a strongly multiplicative system. In addition to the classical theory of summation limiting processes are considered with an infinite summation matrix or an adapted sequence of weighting functions. It will be further developed the method of characteristic functions, and especially the direct method of the conjugate distribution functions to prove quantitative statements about uniform and non-uniform error estimates of the remainder term in central limit theorem. The investigations are realized in the Lp metric, 1
De, Moor Sylvain. "Limites diffusives pour des équations cinétiques stochastiques." Phd thesis, 2014. http://tel.archives-ouvertes.fr/tel-01010825.
Повний текст джерела