A Class of Stable, Globally Noniterative, Nonoverlapping Domain Decomposition Algorithms for the Simulation of Parabolic Evolutionary Systems.

Parabolic systems are governed by time dependent partial differential equations. To obtain a high simulation quality that captures important features of a parabolic system requires solving the governing equation to an adequate accuracy, which necessitates a large sampling size in the spatial and temporal dimensions, and hence a large amount of simulation data and high computing cost. Domain decomposition is an effective method of divide-and-conquer paradigm that divides the problem domain into several subdomains, reducing the original problem into several smaller interdependent problems which can be solved in parallel. In this dissertation, we propose a class of stabilized explicit-implicit time marching (SEITM) domain decomposition algorithms for parabolic equations. Explicit-implicit time marching (EITM) algorithms are globally non-iterative nonoverlapping domain decomposition methods, which, when compared with Schwartz algorithm based parabolic solvers, are both computationally and communicationally efficient for each time step simulation but suffer from small time step size restrictions due to conditional stability. The proposed stabilization techniques in the SEITM algorithms retain the time-stepwise efficiency in computation and communication of the EITM algorithms but free the algorithms from small time step size restrictions, rendering SEITM algorithms excellent candidates for large scale parallel simulation problems. Three algorithms of the SEITM class are presented in this dissertation, which are mathematically analyzed and experimentally tested to show excellent numerical stability, computation and communication efficiencies, and high parallel speedup and scalability

Computational fluid dynamics: science or toolbox?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76112/1/AIAA-2001-2520-552.pd

Postprocessing the Galerkin method: the finite-element case

A postprocessing technique, developed earlier for spectral methods, is extended here to Galerkin nite-element methods for dissipative evolution partial di erential equations. The postprocessing amounts to solving a linear elliptic problem on a ner grid (or higher-order space) once the time integration on the coarser mesh is completed. This technique increases the convergence rate of the nite-element method to which it is applied, and this is done at almost no additional computational cost. The numerical experiments presented here show that the resulting postprocessed method is computationally more e cient than the method to which it is applied (say, quadratic nite elements) as well as standard methods of similar order of convergence as the postprocessed one (say, cubic nite elements). The error analysis of the new method is performed in L2 and in L1 norms.DGICYT PB95-21

Measurements, Models, Systems and Design

531 s.

Decoupled, Linear, and Energy Stable Finite Element Method for the Cahn-Hilliard-Navier-Stokes-Darcy Phase Field Model

In this paper, we consider the numerical approximation for a phase field model of the coupled two-phase free flow and two-phase porous media flow. This model consists of Cahn—Hilliard—Navier—Stokes equations in the free flow region and Cahn—Hilliard—Darcy equations in the porous media region that are coupled by seven interface conditions. The coupled system is decoupled based on the interface conditions and the solution values on the interface from the previous time step. A fully discretized scheme with finite elements for the spatial discretization is developed to solve the decoupled system. In order to deal with the difficulties arising from the interface conditions, the decoupled scheme needs to be constructed appropriately for the interface terms, and a modified discrete energy is introduced with an interface component. Furthermore, the scheme is linearized and energy stable. Hence, at each time step one need only solve a linear elliptic system for each of the two decoupled equations. Stability of the model and the proposed method is rigorously proved. Numerical experiments are presented to illustrate the features of the proposed numerical method and verify the theoretical conclusions. © 2018 Society for Industrial and Applied Mathematics

Computational Electromagnetism and Acoustics

It is a moot point to stress the significance of accurate and fast numerical methods for the simulation of electromagnetic fields and sound propagation for modern technology. This has triggered a surge of research in mathematical modeling and numerical analysis aimed to devise and improve methods for computational electromagnetism and acoustics. Numerical techniques for solving the initial boundary value problems underlying both computational electromagnetics and acoustics comprise a wide array of different approaches ranging from integral equation methods to finite differences. Their development faces a few typical challenges: highly oscillatory solutions, control of numerical dispersion, infinite computational domains, ill-conditioned discrete operators, lack of strong ellipticity, hysteresis phenomena, to name only a few. Profound mathematical analysis is indispensable for tackling these issues. Many outstanding contributions at this Oberwolfach conference on Computational Electromagnetism and Acoustics strikingly confirmed the immense recent progress made in the field. To name only a few highlights: there have been breakthroughs in the application and understanding of phase modulation and extraction approaches for the discretization of boundary integral equations at high frequencies. Much has been achieved in the development and analysis of discontinuous Galerkin methods. New insight have been gained into the construction and relationships of absorbing boundary conditions also for periodic media. Considerable progress has been made in the design of stable and space-time adaptive discretization techniques for wave propagation. New ideas have emerged for the fast and robust iterative solution for discrete quasi-static electromagnetic boundary value problems