Global Attractor and Omega-Limit Sets Structure for a Phase-Field Model of Thermal Alloys

In this paper, the existence of weak solutions is established for a phase-field model of thermal alloys supplemented with Dirichlet boundary conditions. After that, the existence of global attractors for the associated multi-valued dynamical systems is proved, and the relationship among these sets is established. Finally, we provide a more detailed description of the asymptotic behaviour of solutions via the omega-limit sets. Namely, we obtain a characterization–through the natural stationary system associated to the model–of the elements belonging to the omega-limit sets under suitable assumptions

Solidificação de ligas binarias : existencia de soluções de modelos do tipo campo de fase

Orientador : Jose Luiz BoldriniTese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação CientificaResumo: Neste trabalho apresentamos resultados de existência de soluções para alguns modelos matemáticos do tipo campo de fase para a solidificação de ligas binárias. Inicialmente, consideramos um modelo composto por um sistema de equações diferenciais parciais altamente não lineares degenerado e parabólico, com três variáveis independentes: o campo de fase, a temperatura e a concentração. Depois incluímos termos convectivos para levar em consideração o fluxo nas regiões não sólidas. Estudamos alguns modelos desse tipo. A característica comum nesses modelos é que na equação da velocidade é utilizado um termo de penalização do tipo Carman-Kozeny para modelar o efeito mushy. Utilizamos técnicas de aproximação que envolvem regularização, o método de Faedo-Galerkin e o Teorema de Ponto Fixo de Leray-SchauderAbstract: In this work we present results of existence of solutions for some mathematical models of phase- field type for solidification of binary alloys. Firstly, we consider a model based on a highly non-linear degenerate parabolic system of partial differential equations, with three independent variables: phase-field, solute concentration and temperature. After that, we include convective terms in order to consider the flow in the non-solid regions. We study some models of this sort. All of them have the characteristic of modeling the mushy effect with a Carman- Kozeny penalization term added to the velocity equation. The proofs are based on an approximation technique which includes regularization, Faedo-Galerkin method and Leray-Schauder Fixed Point TheoremDoutoradoDoutor em Matemática Aplicad

Gradient-like nonlinear semigroups with infinitely many equilibria and applications to cascade systems

We consider an autonomous dynamical system coming from a coupled system in cascade where the uncoupled part of the system satisfies that the solutions comes from −∞ and goes to ∞ to equilibrium points, and where the coupled part generates asymptotically a gradient-like nonlinear semigroup. Then, the complete model is proved to be also gradient-like. The interest of this extension comes, for instance, in models where a continuum of equilibrium points holds, and for example a Lojasiewicz-Simon condition is satisfied. Indeed, we illustrate the usefulness of the theory with several examples.Fundação de Amparo à Pesquisa do Estado de São PauloConselho Nacional de Desenvolvimento Científico e TecnológicoCoordenação de aperfeiçoamento de pessoal de nivel superiorMinisterio de Ciencia e InnovaciónJunta de AndalucíaMinisterio de Educació

Decay rates for the 4D energy-critical nonlinear heat equation

In this paper we address the decay of solutions to the four-dimen\-sional energy-critical nonlinear heat equation in the critical space $\dot{H}^1$. Recently, it was proven that the $\dot{H}^1$ norm of solutions goes to zero when time goes to infinity, but no decay rates were established. By means of the Fourier Splitting Method and using properties arising from the scale invariance, we obtain an algebraic upper bound for the decay rate of solutions.Comment: 13 pages. arXiv admin note: text overlap with arXiv:2206.0944

Algebraic decay rates for 3D Navier-Stokes and Navier-Stokes-Coriolis equations in H˙12 \dot{H}^{\frac{1}{2}}

An algebraic upper bound for the decay rate of solutions to the Navier-Stokes and Navier-Stokes-Coriolis equations in the critical space $\dot{H} ^{\frac{1}{2}} (\mathbb{R} ^3)$ is derived using the Fourier Splitting Method. Estimates are framed in terms of the decay character of initial data, leading to solutions with algebraic decay and showing in detail the roles played by the linear and nonlinear parts.Comment: 20 pages. Title changed. Emphasis placed on new estimates in critical spac

Asymptotic Behaviour of a Phase-Field Model with Three Coupled Equations Without Uniqueness

AbstractWe prove the existence of weak solutions for a phase-field model with three coupled equations with unknown uniqueness, and state several dynamical systems depending on the regularity of the initial data. Then, the existence of families of global attractors (level-set depending) for the corresponding multi-valued semiflows is established, applying an energy method. Finally, using the regularizing effect of the problem, we prove that these attractors are in fact the same

Attractors for a Double Time-Delayed 2D-Navier-Stokes Model

In this paper, a double time-delayed 2D-Navier-Stokes model is considered. It includes delays in the convective and the forcing terms. Existence and uniqueness results and suitable dynamical systems are established. We also analyze the existence of pullback attractors for the model in several phase-spaces and the relationship among them