A Study on Discontinuous Petrov-Galerkin Finite Element Methods in Semi-linear Problems and Adaptivity

A Study on Discontinuous Petrov-Galerkin Finite Element Methods in Semi-linear Problems and Adaptivity
Author: Jor-el Thomas Caparas Briones
Publisher:
Total Pages: 0
Release: 2022
Genre:
ISBN:

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In numerical analysis, finite element methods are a method of approximating solutions to differential equations on a domain. In such methods, the solution function is approximated by partitioning the domain into a mesh of elements, and testing candidate functions in a discrete trial space on that mesh against a discrete space of test functions. We explore certain classes of finite element methods called discontinuous Petrov-Galerkin (DPG) finite element methods, where the test space functions are allowed to be discontinuous across elements, and test spaces are selected specifically to optimize stability. Because we are concerned with the accuracy of our approximation, we place focus on how the error behaves in DPG methods. We explore how DPG methods in semi-linear problems, as well as how DPG problems can interact with adaptive methods, a different framework for finite element methods. In addition, we establish some results about the error of DPG approximations, particularly the error using the subspace dual norms that arise from the construction of the test spaces.

Recent Developments in Discontinuous Galerkin Finite Element Methods for Partial Differential Equations

Recent Developments in Discontinuous Galerkin Finite Element Methods for Partial Differential Equations
Author: Xiaobing Feng
Publisher: Springer Science & Business Media
Total Pages: 289
Release: 2013-11-08
Genre: Mathematics
ISBN: 3319018183

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The field of discontinuous Galerkin finite element methods has attracted considerable recent attention from scholars in the applied sciences and engineering. This volume brings together scholars working in this area, each representing a particular theme or direction of current research. Derived from the 2012 Barrett Lectures at the University of Tennessee, the papers reflect the state of the field today and point toward possibilities for future inquiry. The longer survey lectures, delivered by Franco Brezzi and Chi-Wang Shu, respectively, focus on theoretical aspects of discontinuous Galerkin methods for elliptic and evolution problems. Other papers apply DG methods to cases involving radiative transport equations, error estimates, and time-discrete higher order ALE functions, among other areas. Combining focused case studies with longer sections of expository discussion, this book will be an indispensable reference for researchers and students working with discontinuous Galerkin finite element methods and its applications.

An Adaptive Hybridizable Discontinuous Petrov-Galerkin Method with Selective Stabilization

An Adaptive Hybridizable Discontinuous Petrov-Galerkin Method with Selective Stabilization
Author: Keyi Ni
Publisher:
Total Pages: 0
Release: 2018
Genre:
ISBN:

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An adaptive higher-order partial differential equation solver utilizing hybridizable discontinuous Petrov-Galerkin (HDPG) discretization, coupled with selective stabilization, is presented in this thesis. HDPG method is a higher-order finite element method with a posteriori error estimates available. More importantly, HDPG seeks to improve solution stability in terms of inf-sup constant by computing optimal test spaces. In this work, the elements that require stabilization are selected by a shock sensor. The polynomial degree of the candidate spaces in these elements where the optimal test functions are searched is progressively enriched, yielding an adaptive yet consistent stabilization method. If the adaptive HDPG stabilization could not generate a smooth solution, the more aggressive artificial viscosity is applied. Finally, mesh adaptation guided by goal-oriented dual-weighted residual error estimates is used to quantify output errors and to efficiently achieve user prescribed accuracy.

Least-Squares Finite Element Methods

Least-Squares Finite Element Methods
Author: Pavel B. Bochev
Publisher: Springer Science & Business Media
Total Pages: 669
Release: 2009-04-28
Genre: Mathematics
ISBN: 0387689222

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Since their emergence, finite element methods have taken a place as one of the most versatile and powerful methodologies for the approximate numerical solution of Partial Differential Equations. These methods are used in incompressible fluid flow, heat, transfer, and other problems. This book provides researchers and practitioners with a concise guide to the theory and practice of least-square finite element methods, their strengths and weaknesses, established successes, and open problems.

Adaptive Discontinuous Galerkin Finite Element Methods

Adaptive Discontinuous Galerkin Finite Element Methods
Author: Haihang You
Publisher:
Total Pages: 112
Release: 2009
Genre:
ISBN:

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The Discontinuous Galerkin Method is one variant of the Finite Element Methods for solving partial differential equations, which was first introduced by Reed and Hill in 1970's [27]. Discontinuous Galerkin Method (DGFEM) differs from the standard Galerkin FEM that continuity constraints are not imposed on the inter-element boundaries. It results in a solution which is composed of totally piecewise discontinuous functions. The absence of continuity constraints on the inter-element boundaries implies that DG method has a great deal of flexibility at the cost of increasing the number of degrees of freedom. This flexibility is the source of many but not all of the advantages of the DGFEM method over the Continuous Galerkin (CGFEM) method that uses spaces of continuous piecewise polynomial functions and other "less standard" methods such as nonconforming methods. As DGFEM method leads to bigger system to solve, theoretical and practical approaches to speed it up are our main focus in this dissertation. This research aims at designing and building an adaptive discontinuous Galerkin finite element method to solve partial differential equations with fast time for desired accuracy on modern architecture.

Space-time Discontinuous Petrov-Galerkin Finite Elements for Transient Fluid Mechanics

Space-time Discontinuous Petrov-Galerkin Finite Elements for Transient Fluid Mechanics
Author: Truman Everett Ellis
Publisher:
Total Pages: 364
Release: 2016
Genre:
ISBN:

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Initial mesh design for computational fluid dynamics can be a time-consuming and expensive process. The stability properties and nonlinear convergence of most numerical methods rely on a minimum level of mesh resolution. This means that unless the initial computational mesh is fine enough, convergence can not be guaranteed. Any meshes below this minimum resolution level are termed to be in the ``pre-asymptotic regime.'' This condition implies that meshes need to in some way anticipate the solution before it is known. On top of the minimum requirement that the surface meshes must adequately represent the geometry of the problem under consideration, resolution requirements on the volume mesh make the CFD practitioner's job significantly more time consuming. In contrast to most other numerical methods, the discontinuous Petrov-Galerkin finite element method retains exceptional stability on extremely coarse meshes. DPG is also inherently very adaptive. It is possible to compute the residual error without knowledge of the exact solution, which can be used to robustly drive adaptivity. This results in a very automated technology, as the user can initialize a computation on the coarsest mesh which adequately represents the geometry then step back and let the program solve and adapt iteratively until it resolves the solution features. A common complaint of minimum residual methods by computational fluid dynamics practitioners is that they are not locally conservative. In this thesis, this concern is addressed by developing a locally conservative DPG formulation by augmenting the system with Lagrange multipliers. The resulting DPG formulation is then proved to be robust and shown to produce superior numerical results over standard DPG on a selection of test problems. Adaptive convergence to steady incompressible and compressible Navier-Stokes solutions was explored in Jesse Chan's and Nathan Roberts' dissertations. Space-time offers a natural extension to transient problems as it preserves the stability and adaptivity properties of DPG in the time dimension. Space-time also offers more extensive parallelization capability than problems treated with traditional time stepping as it allows multigrid concurrently in both space and time. A proof of concept space-time DPG formulation is developed for transient convection-diffusion. The robust test norms derived for steady convection-diffusion are extended to the space-time case and proofs of robustness are provided. Numerical results verify the robust behavior and near $L^2$ optimality of the resulting solutions. The space-time formulation for convection-diffusion is then extended to transient incompressible and compressible Navier-Stokes by analogy. Several numerical experiments are performed, but a mathematical analysis is not attempted for these nonlinear problems. Several side topics are explored such as a study of the compressible Navier-Stokes equations under various variable transformations and the development of consistent test norms through the concept of physical entropy.

Adaptive Finite Element Methods for Differential Equations

Adaptive Finite Element Methods for Differential Equations
Author: Wolfgang Bangerth
Publisher: Springer Science & Business Media
Total Pages: 222
Release: 2003-01-23
Genre: Mathematics
ISBN: 9783764370091

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The key issues are a posteriori error estimation and it automatic mesh adaptation. Besides the traditional approach of energy-norm error control, a new duality-based technique, the Dual Weighted Residual method for goal-oriented error estimation, is discussed in detail. This method aims at economical computation of arbitrary quantities of physical interest by properly adapting the computational mesh. This is typically required in the design cycles of technical applications. For example, the drag coefficient of a body immersed in a viscous flow is computed, then it is minimized by varying certain control parameters, and finally the stability of the resulting flow is investigated by solving an eigenvalue problem. `Goal-oriented' adaptivity is designed to achieve these tasks with minimal cost. At the end of each chapter some exercises are posed in order to assist the interested reader in better understanding the concepts presented. Solutions and accompanying remarks are given in the Appendix.

Various Applications of Discontinuous Petrov-Galerkin (DPG) Finite Element Methods

Various Applications of Discontinuous Petrov-Galerkin (DPG) Finite Element Methods
Author: Federico Fuentes (Ph. D.)
Publisher:
Total Pages: 492
Release: 2018
Genre:
ISBN:

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Discontinuous Petrov-Galerkin (DPG) finite element methods have garnered significant attention since they were originally introduced. They discretize variational formulations with broken (discontinuous) test spaces and are crafted to be numerically stable by implicitly computing a near-optimal discrete test space as a function of a discrete trial space. Moreover, they are completely general in the sense that they can be applied to a variety of variational formulations, including non-conventional ones that involve non-symmetric functional settings, such as ultraweak variational formulations. In most cases, these properties have been harnessed to develop numerical methods that provide robust control of relevant equation parameters, like in convection-diffusion problems and other singularly perturbed problems. In this work, other features of DPG methods are systematically exploited and applied to different problems. More specifically, the versatility of DPG methods is elucidated by utilizing the underlying methodology to discretize four distinct variational formulations of the equations of linear elasticity. By taking advantage of interface variables inherent to DPG discretizations, an approach to coupling different variational formulations within the same domain is described and used to solve interesting problems. Moreover, the convenient algebraic structure in DPG methods is harnessed to develop a new family of numerical methods called discrete least-squares (DLS) finite element methods. These involve solving, with improved conditioning properties, a discrete least-squares problem associated with an overdetermined rectangular system of equations, instead of directly solving the usual square systems. Their utility is demonstrated with illustrative examples. Additionally, high-order polygonal DPG (PolyDPG) methods are devised by using the intrinsic discontinuities present in ultraweak formulations. The resulting methods can handle heavily distorted non-convex polygonal elements and discontinuous material properties. A polygonal adaptive strategy was also proposed and compared with standard techniques. Lastly, the natural high-order residual-based a posteriori error estimator ingrained within DPG methods was further applied to problems of physical relevance, like the validation of dynamic mechanical analysis (DMA) calibration experiments of viscoelastic materials, and the modeling of form-wound medium-voltage stator coils sitting inside large electric machinery.

Computational Galerkin Methods

Computational Galerkin Methods
Author: C. A. J. Fletcher
Publisher: Springer
Total Pages: 336
Release: 1984
Genre: Mathematics
ISBN:

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In the wake of the computer revolution, a large number of apparently uncon nected computational techniques have emerged. Also, particular methods have assumed prominent positions in certain areas of application. Finite element methods, for example, are used almost exclusively for solving structural problems; spectral methods are becoming the preferred approach to global atmospheric modelling and weather prediction; and the use of finite difference methods is nearly universal in predicting the flow around aircraft wings and fuselages. These apparently unrelated techniques are firmly entrenched in computer codes used every day by practicing scientists and engineers. Many of these scientists and engineers have been drawn into the computational area without the benefit offormal computational training. Often the formal computational training we do provide reinforces the arbitrary divisions between the various computational methods available. One of the purposes of this monograph is to show that many computational techniques are, indeed, closely related. The Galerkin formulation, which is being used in many subject areas, provides the connection. Within the Galerkin frame-work we can generate finite element, finite difference, and spectral methods.