1,721,124 research outputs found
On the numerical approximations of stiff convection-diffusion equations in a circle
No full textOur aim in this article is to study the numerical solutions of singularly perturbed convection-diffusion problems in a circular domain and provide as well approximation schemes, error estimates and numerical simulations. To resolve the oscillations of classical numerical solutions due to the stiffness of our problem, we construct, via boundary layer analysis, the so-called boundary layer elements which absorb the boundary layer singularities. Using a P1 classical finite element space enriched with the boundary layer elements, we obtain an accurate numerical scheme in a quasi-uniform mesh.close0
Boundary layer analysis for the stochastic nonlinear reaction diffusion equations
No full textSingularly perturbed stochastic (and deterministic) nonlinear reaction-diffusion equations are considered. We first study the governing problem posed in the channel domain with lateral periodicity and extend the results to general smooth domains. Introducing corrector functions, which correct the boundary values discrepancies, we are able to develop the convergence analysis. For the analysis, we make use of the maximum principle to estimate the corrector functions. The stochastic problems also rely on the deterministic corrector functions, which lead to simpler computations than those of the stochastic version of the correctors
Numerical Simulations of the Two-Dimensional Inviscid Hydrostatic Primitive Equations with Humidity and Saturation
No full textThe two-dimensional inviscid hydrostatic primitive equations of the atmosphere with humidity and saturation are considered in the presence of topography. The model studied here describes the dynamics of the air or water in order to approximate global atmospheric flows. The heart of the paper is to derive a new set of transformed inviscid primitive equations using a version of the terrain-following coordinate systems and to develop an accurate numerical scheme to the equations. In this regard, a fully discrete numerical algorithm based on a Godunov-type finite volume method is proposed and its convergence tested. We then use this algorithm to simulate the flows above a mountain using the terrain-following coordinate system with a dynamic bottom pressure.
Singular perturbation analysis of time dependent convection-diffusion equations in a circle
No full textWe study singularly perturbed time dependent convection-diffusion equations in a circular domain. Considering suitable compatibility conditions, we present convergence results and provide as well approximation schemes and error estimates. To resolve the oscillations of classical numerical solutions due to the stiffness of our problem, we construct, via a specific boundary layer analysis, the so-called boundary layer elements which absorb the boundary layer singularities. Using a P1 classical finite element space enriched with the boundary layer elements, we obtain an accurate numerical solution using a quasi-uniform mesh, that is without refinement of the mesh in the boundary layer. ??? 2014 Elsevier Ltd. All rights reservedclose0
Analysis of a Penalty Method
No full textIn this article we study the simplest one-dimensional transport equation u (t) +au (x) =f and study the implementation of the boundary condition using a penalty method combined with a P1 finite element discretization. We discuss the convergence of the method when both the penalty parameter I mu and the mesh size h go to zero, in sequence or simultaneously. Some numerical simulations are reported also showing the efficiency of the method. Numerical simulations are also made for the similar problem in space dimension 2.
Navier–Stokes–Voigt Equations with Memory in 3D Lacking Instantaneous Kinematic Viscosity
Get PDFWe consider a Navier–Stokes–Voigt fluid model where the instantaneous kinematic viscosity has been completely replaced by a memory term incorporating hereditary effects, in presence of Ekman damping. Unlike the classical Navier–Stokes–Voigt system, the energy balance involves the spatial gradient of the past history of the velocity rather than providing an instantaneous control on the high modes. In spite of this difficulty, we show that our system is dissipative in the dynamical systems sense and even possesses regular global and exponential attractors of finite fractal dimension. Such features of asymptotic well-posedness in absence of instantaneous high modes dissipation appear to be unique within the realm of dynamical systems arising from fluid models
Enriched numerical scheme for singularly perturbed barotropic Quasi-Geostrophic equations
No full textSingularly perturbed barotropic Quasi-Geostrophic (QG) models are considered. A boundary layer analysis is presented and the convergence of solutions is studied. Based on the rigorous analysis of the underlying boundary layer problems, an enriched spectral method (ESM) is proposed to solve the QG models. It consists of adding to the Legendre basis functions, analytically-determined boundary layer elements called “correctors”, with the aim of capturing most of the complex behavior occurring near the boundary with such elements. Through detailed numerical experiments, it is shown that high-accuracy is often reached by the ESM scheme with only a relatively low number N of basis functions, when compared to approximations based on spectral elements which typically display non-physical oscillations throughout the physical domain, for such values of N. The key to success relies on our analytically-based boundary layer elements, which, due to their highly nonlinear nature, are able to capture most of the steep gradients occurring in the problem's solution, near the boundary. Our numerical results include multi-dimensional as well as time-dependent problems.
Infinite-dimensional dynamical systems in mechanics and physics
No full textIn this book the author presents the dynamical systems in infinite dimension, especially those generated by dissipative partial differential equations This book attempts a systematic study of infinite dimensional dynamical systems generated by dissipative evolution partial differential equations arising in mechanics and physics and in other areas of sciences and technology This second edition has been updated and extende
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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