Spelling suggestions: "subject:"burgers"" "subject:"burgersi""
81 |
Estudo de esquemas de alta resolução em algoritmos simultaneos e sequenciaisMenezes, Luiz Augusto Pretti de January 1996 (has links)
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnologico / Made available in DSpace on 2016-01-08T21:07:33Z (GMT). No. of bitstreams: 1
103916.pdf: 3688429 bytes, checksum: 7eb414d2824d20a2c8544d4868002676 (MD5)
Previous issue date: 1996 / Estudo dos fundamentos dos esquemas de alta resolução TVD e NVD. Revisa os principais aspectos matemáticos de leis de conservação hiperbólicas cujas soluções podem envolver descontinuidades. As características dissipativas e oscilatórias dos principais esquemas numéricos, usados no desenvolvimento dos esquemas de alta resolução, são analisadas e testadas na equação de Burgers invícida. Os esquemas TVD são testados para as Eq. de Euler nos problemas de tubo de choque e bocal divergente. Os esquemas NVD são testados para as equações de Navier-Stokes no problema de convecção forçada em uma cavidade quadrada. É utilizado o método de volumes finitos e o sistema de equações é resolvido segregadamente ou via características locais (simultâneamente). Os esquemas NVD foram utilizados para gerar esquemas de interpolação de alta resolução, que foram implementados num procedimento geral com o uso de limitadores. Os resultados obtidos são comparados com soluções analíticas, benchmark e entre si.
|
82 |
Analysis and Implementation of High-Order Compact Finite Difference SchemesTyler, Jonathan G. 30 November 2007 (has links) (PDF)
The derivation of centered compact schemes at interior and boundary grid points is performed and an analysis of stability and computational efficiency is given. Compact schemes are high order implicit methods for numerical solutions of initial and/or boundary value problems modeled by differential equations. These schemes generally require smaller stencils than the traditional explicit finite difference counterparts. To avoid numerical instabilities at and near boundaries and in regions of mesh non-uniformity, a numerical filtering technique is employed. Experiments for non-stationary linear problems (convection, heat conduction) and also for nonlinear problems (Burgers' and KdV equations) were performed. The compact solvers were combined with Euler and fourth-order Runge-Kutta time differencing. In most cases, the order of convergence of the numerical solution to the exact solution was the same as the formal order of accuracy of the compact schemes employed.
|
83 |
Sustainable Communication or Communicating Sustainability? : A qualitative research studying sustainable marketing practices at IBM, Max Burgers & H&MOhlsson, Caroline, Riihimäki, Jessica January 2015 (has links)
The demand for sustainability initiatives is increasing by both consumers and organizations (Gittell, et al. 2013). It changes the way businesses are operating and communicating, hence the interest for sustainable marketing has increased. Sustainable marketing should not only be about initiatives to appear more environmental friendly or socially conscious, but rather about a more substantive and meaningful levels of commitments (ibid). Alongside these practical ideas of sustainable marketing, consumers’ requirements for sustainability have sometimes been used as a strategy to create sustainable communication, although companies are lacking initiatives of sustainability. The idea of marketing as a strategy to create desire and needless spending along with sustainability goals has been criticized as being in direct contradictories (Meller & Magaš 2014, Pettie 2001, Pettie & Belz 2010). Thus, the problematics compose of the discussed oxymoron between sustainability and marketing together with the difference between sustainable communication and communicating sustainability. This qualitative study has been done with a starting position from the idea of addressing how sustainable marketing is practiced, why it is practiced and how the future outlook of the concept is perceived from a company perspective. The chosen theories for this study compose mainly of basic marketing theories and models with a sustainability adaption. A qualitative study addressing this issue from a company perspective has not been discovered in previous researches, which resulted in the idea of highlighting different companies’ opinions and practices of sustainable marketing. The findings have discovered the usage of sustainable marketing today and potentially in the future, together with reasons for why it is practiced. Sustainability has become a well-known concept with a lot of business scandals associated to it, which has been mentioned in this study as one of the reasons for the predictions of a future demand of real sustainable marketing practices.
|
84 |
EXPERIMENTALLY VALIDATED CRYSTAL PLASTICITY MODELING OF TITANIUM ALLOYS AT MULTIPLE LENGTH-SCALES BASED ON MATERIAL CHARACTERIZATION, ACCOUNTING FOR RESIDUAL STRESSESKartik Kapoor (7543412) 30 October 2019 (has links)
<p>There is a growing need to understand the
deformation mechanisms in titanium alloys due to their widespread use in the
aerospace industry (especially within gas turbine engines), variation in their
properties and performance based on their microstructure, and their tendency to
undergo premature failure due to dwell and high cycle fatigue well below their
yield strength. Crystal plasticity finite element (CPFE) modeling is a popular
computational tool used to understand deformation in these polycrystalline alloys.
With the advancement in experimental techniques such as electron backscatter
diffraction, digital image correlation (DIC) and high-energy x-ray diffraction,
more insights into the microstructure of the material and its deformation
process can be attained. This research leverages data from a number of
experimental techniques to develop well-informed and calibrated CPFE models for
titanium alloys at multiple length-scales and use them to further understand
the deformation in these alloys.</p>
<p>The first part of the research utilizes
experimental data from high-energy x-ray diffraction microscopy to initialize
grain-level residual stresses and capture the correct grain morphology within
CPFE simulations. Further, another method to incorporate the effect of grain-level
residual stresses via geometrically necessary dislocations obtained from 2D
material characterization is developed and implemented within the CPFE
framework. Using this approach, grain level information about residual stresses
obtained spatially over the region of interest, directly from the EBSD and
high-energy x-ray diffraction microscopy, is utilized as an input to the model.</p>
<p>The second part of this research involves
calibrating the CPFE model based upon a systematic and detailed optimization routine
utilizing experimental data in the form of macroscopic stress-strain curves
coupled with lattice strains on different crystallographic planes for the α and
β phases, obtained from high energy X-ray diffraction experiments for multiple
material pedigrees with varying β volume fractions. This fully calibrated CPFE
model is then used to gain a comprehensive understanding of deformation
behavior of Ti-6Al-4V, specifically the effect of the relative orientation of
the α and β phases within the microstructure.</p>
<p>In the final part of this work, large and highly
textured regions, referred to as macrozones or microtextured regions (MTRs),
with sizes up to several orders of magnitude larger than that of the individual
grains, found in dual phase Titanium alloys are modeled using a reduced order
simulation strategy. This is done to overcome the computational challenges
associated with modeling macrozones. The reduced order model is then used to
investigate the strain localization within the microstructure and the effect of
varying the misorientation tolerance on the localization of plastic strain
within the macrozones.</p>
|
85 |
Kolmogorov Operators in Spaces of Continuous Functions and Equations for MeasuresManca, Luigi 17 March 2008 (has links) (PDF)
La thèse est consacrée à étudier les relations entre les Équations aux Derivées Partielles Stochastiques et l'operateur de Kolmogorov associé dans des espaces de fonctions continues.<br />Dans la première partie, la théorie de la convergence faibles des fonctions est mis au point afin de donner des résultats généraux sur les semi-groupes des Markov et leur générateur.<br />Dans la deuxième partie, des modèles de semi-groups de Markov associés à des équations aux dérivées partielles stochastiques sont étudiés. En particulier, Ornstein-Uhlenbeck, réaction-diffusion et équations de Burgers ont été envisagées. Pour chaque cas, le semi-groupe de transition et son générateur infinitésimal ont été étudiées dans un espace de fonctions continues.<br />Les résultats principaux montrent que l'ensemble des fonctions exponentielles fournit un Core pour l'opérateur de Kolmogorov. En conséquence, on prouve l'unicité de l'équation de Kolmogorov de mesures (autrement dit de Fokker-Planck).
|
86 |
Approche probabiliste des particules collantes et système de gaz sans pressionMoutsinga, Octave 16 June 2003 (has links) (PDF)
A chaque instant $t$, nous construisons la dynamique des particules collantes dont la masse est distribuée initialement suivant une fonction de répartition $F_0$, avec une vitesse $u_0$, à partir de l'enveloppe convexe $H(\cdot,t)$ de la fonction $m\in (0,1)\mapsto \int_a^m\big( F_0^(-1)(z) + tu_0\big(F_0^(-1)(z)\big)\big)dz$. Ici, $F_0^(-1)$ est l'une des deux fonctions inverses de $F_0$. Nous montrons que les deux processus stochastiques $X_t^-(m)= \partial_m^-H(m,t),\; X_t^+(m) = \partial_m^+H(m,t)$, définis sur l'espace probabilisé $([0, 1], (\cal B), \lambda)$, sont indistinguables et ils modélisent les trajectoires des particules. Le processus $X_t:= X_t^- = X_t^+$ est une solution de l'équation $(EDS): \; \frac(dX_t)(dt) =\E[ u_0(X_0)/X_t]$, telle que $P(X_0 \leq x) = F_0(x)\,\,\forall x$. L'inverse $M_t:= M(\cdot,t)$ de la fonction $m\mapsto \partial_mH(m,t)$ est la fonction de répartition de la masse à l'instant $t$. Elle est aussi la fonction de répartition de la variable aléatoire $X_t$. On montre l'existence d'un flot $(\phi(x,t,M_s, u_s))_( s < t)$ tel que $X_t= \phi(X_s,t,M_s,u_s)$, où $u_s(x) = \E[ u_0(X_0)/X_s = x]$ est la fonction vitesse des particules à l'instant $s$. Si $\frac(dF_0^n)(dx)$ converge faiblement vers $\frac(dF_0)(dx)$, alors la suite des flots $\phi(\cdot,\cdot,F_0^n,u_0)$ converge uniformément, sur tout compact, vers $\phi(\cdot,\cdot,F_0,u_0)$. Ensuite, nous retrouvons et étendons certains résultats des équations aux dérivées partielles, à savoir que la fonction $(x,t)\mapsto M(x,t)$ est la solution entropique d'une loi de conservation scalaire de donnée initiale $F_0$, et la famille $\big(\rho(dx,t) = P(X_t\in dx),\, u(x,t) = \E[ u_0(X_0)/X_t = x]\big)_(t >0)$ est une solution faible du système de gaz sans pression de données initiales $\frac(dF_0(x))(dx), u_0$. Cette thèse contient aussi d'autres solutions de l'équation différentielle stochastique $(EDS)$ ci-dessus.
|
87 |
Dynamique de trafic dans les réseaux microfluidiques modèles : Embouteillages, chocs et avalanches.Champagne, Nicolas 06 October 2011 (has links) (PDF)
Filtration, récupération assistée du pétrole, flux sanguin... La compréhension des écoulements dans ces exemples repose sur la connaissance du transport de particules en milieu confiné. Plus généralement, dans ces situations se pose la question de l'influence des intéractions entre particules sur le comportement général de l'écoulement. Pour répondre à cela, une approche expérimentale originale est proposée, basée sur la création de nouveaux outils microfluidiques. Dans une première partie, nous étudions la dynamique du trafic de gouttes (suspension diluée) dans des réseaux d'obstacles microfluidiques. La présence des interactions hydrodynamiques entre particules rend cet écoulement non linéaire et il peut alors être parfaitement décrit par une équation dynamique de Burgers, rationalisant ainsi la présence des chocs de densité observés expérimentalement. Nous avons aussi fait ressortir de notre étude des paramètres généraux qui, non seulement sont utiles en microfluidique, mais s'avèrent pertinents à l'étude des différents domaines de trafic (voiture, piétons, ...). Ce travail est poursuivi par l'étude du transport d'une suspension concentrée 2D. Cet écoulement, gouverné par une dynamique intermittente, a été compris à travers une approche numérique, rendant compte de la phénoménologie d'avalanche constatée. Ce code s'avère ainsi efficace quant à l'interprétation de l'écoulement de particules dans des réseaux de tubes, modèle simple des milieux poreux.
|
88 |
Méthodes de sous-espaces de Krylov matriciels appliquées aux équations aux dérivées partiellesHached, Mustapha 07 December 2012 (has links) (PDF)
Cette thèse porte sur des méthode de résolution d'équations matricielles appliquées à la résolution numérique d'équations aux dérivées partielles ou des problèmes de contrôle linéaire. On s'intéressen en premier lieu à des équations matricielles linéaires. Après avoir donné un aperçu des méthodes classiques employées pour les équations de Sylvester et de Lyapunov, on s'intéresse au cas d'équations linéaires générales de la forme M(X)=C, où M est un opérateur linéaire matriciel. On expose la méthode de GMRES globale qui s'avère particulièrement utile dans le cas où M(X) ne peut s'exprimer comme un polynôme du premier degré en X à coefficients matriciels, ce qui est le cas dans certains problèmes de résolution numérique d'équations aux dérivées partielles. Nous proposons une approche, noté LR-BA-ADI consistant à utiliser un préconditionnement de type ADI qui transforme l'équation de Sylvester en une équation de Stein que nous résolvons par une méthode de Krylox par blocs. Enfin, nous proposons une méthode de type Newton-Krylov par blocs avec préconditionnement ADI pour les équations de Riccati issues de problèmes de contrôle linéaire quadratique. Cette méthode est dérivée de la méthode LR-BA-ADI. Des résultats de convergence et de majoration de l'erreur sont donnés. Dans la seconde partie de ce travail, nous appliquons les méthodes exposées dans la première partie de ce travail à des problèmes d'équations aux dérivées partielles. Nous nous intéressons d'abord à la résolution numérique d'équations couplées de type Burgers évolutives en dimension 2. Ensuite, nous nous intéressons au cas où le domaine borné est choisi quelconque. Nous établissons des résultats théoriques de l'existence de tels interpolants faisant appel à des techniques d'algèbre linéaire.
|
89 |
Eulerian Droplet Models: Mathematical Analysis, Improvement and ApplicationsKeita, Sana 23 July 2018 (has links)
The Eulerian description of dispersed two-phase flows results in a system of
partial differential equations describing characteristics of the flow, namely volume
fraction, density and velocity of the two phases, around any point in space over
time. When pressure forces are neglected or a same pressure is considered for both
phases, the resulting system is weakly hyperbolic and solutions may exhibit vacuum
states (regions void of the dispersed phase) or localized unbounded singularities (delta shocks) that are not physically desirable. Therefore, it is crucial to find a physical way for preventing the formation of such undesirable solutions in weakly hyperbolic Eulerian two-phase flow models.
This thesis focuses on the mathematical analysis of an Eulerian model for air-
droplet flows, here called the Eulerian droplet model. This model can be seen as the
sticky particle system with a source term and is successfully used for the prediction
of droplet impingement and more recently for the prediction of particle flows in air-
ways. However, this model includes only one-way momentum exchange coupling, and develops delta shocks and vacuum states. The main goal of this thesis is to improve this model, especially for the prevention of delta shocks and vacuum states, and the adjunction of two-way momentum exchange coupling. Using a characteristic analysis, the condition for loss of regularity of smooth solutions of the inviscid Burgers
equation with a source term is established. The same condition applies to the droplet
model. The Riemann problems associated, respectively, to the Burgers equation with
a source term and the droplet model are solved. The characteristics are curves that
tend asymptotically to straight lines. The existence of an entropic solution to the
generalized Rankine-Hugoniot conditions is proven. Next, a way for preventing the
formation of delta shocks and vacuum states in the model is identified and a new
Eulerian droplet model is proposed. A new hierarchy of two-way coupling Eulerian
models is derived. Each model is analyzed and numerical comparisons of the models
are carried out. Finally, 2D computations of air-particle flows comparing the new
Eulerian droplet model with the standard Eulerian droplet model are presented.
|
90 |
Finite Element Solutions to Nonlinear Partial Differential EquationsBeasley, Craig J. (Craig Jackson) 08 1900 (has links)
This paper develops a numerical algorithm that produces finite element solutions for a broad class of partial differential equations. The method is based on steepest descent methods in the Sobolev space H¹(Ω). Although the method may be applied in more general settings, we consider only differential equations that may be written as a first order quasi-linear system. The method is developed in a Hilbert space setting where strong convergence is established for part of the iteration. We also prove convergence for an inner iteration in the finite element setting. The method is demonstrated on Burger's equation and the Navier-Stokes equations as applied to the square cavity flow problem. Numerical evidence suggests that the accuracy of the method is second order,. A documented listing of the FORTRAN code for the Navier-Stokes equations is included.
|
Page generated in 0.0541 seconds