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Elektromagnetická indukce: 3-D modelování nespojitou Galerkinovou metodou
Čochner, Martin ; Velímský, Jakub (advisor) ; Souček, Ondřej (referee)
This work deals with numerical modeling of electromagnetic induction in 3D environment with heterogeneous conductivity. We develop a program to solve Maxwell's equations in quasistatic approximation by using Continuous and Discontinuous Finite Elements. Their implementation in the numerical library deal.ii is discussed. The obtained numerical results are compared with each other and also with a quasianalytic solution for an environment with 1D heterogeneous conductivity. We discuss different numerical methods, limits of our code for practical use and possible future enhancements.
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A posteriori error estimates of discontinuous Galerkin method for elliptic and parabolic methods
Grubhofferová, Pavla ; Dolejší, Vít (advisor) ; Feistauer, Miloslav (referee)
The presented work deals with the discontinuous Galerkin method with the anisotropic mesh adaptation for stationary convection-diffusion problems. Basic definitions are included in an introduction where we also present the used method. The following parts describe various methods for evaluating a Riemann metric, which is necessary for anisotropic mesh adaptation. The most important part of work follows - numerical experiments carried out with ADGFEM and ANGENER software packages. In these experiments, we compare different approaches for the definition of Riemann metrics and compare their efficiency. The main output of this thesis are subroutines for evaluation of the Riemann metric including its source code.
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A posteriori error estimates for numerical solution of convection-difusion problems
Šebestová, Ivana ; Dolejší, Vít (advisor) ; Sváček, Petr (referee) ; Brandts, Jan (referee)
This thesis is concerned with several issues of a posteriori error estimates for linear problems. In its first part error estimates for the heat conduction equation discretized by the backward Euler method in time and discontinuous Galerkin method in space are derived. In the second part guaranteed and locally efficient error estimates involving algebraic error for Poisson equation discretized by the discontinuous Galerkin method are derived. The technique is based on the flux reconstruction where meshes with hanging nodes and variable polynomial degree are allowed. An adaptive strategy combining both adaptive mesh refinement and stopping criteria for iterative algebraic solvers is proposed. In the last part a numerical method for computing guaranteed lower and upper bounds of principal eigenvalues of symmetric linear elliptic differential operators is presented. 1
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Numerical solution of equations describing the dynamics of flocking
Živčáková, Andrea ; Kučera, Václav (advisor) ; Janovský, Vladimír (referee)
This work is devoted to the numerical solution of equations describing the dynamics of flocks of birds. Specifically, we pay attention to the Euler equations for compressible flow with a right-hand side correction. This model is based on the work Fornasier et al. (2010). Due to the complexity of the model, we focus only on the one-dimensional case. For the numerical solution we use a semi-implicit discontinuous Galerkin method. Discretization of the right-hand side is chosen so that we preserve the structure of the semi-implicit scheme for the Euler equations presented in the work Feistauer, Kučera (2007). The proposed numerical scheme was implemented and numerical experiments showing the robustness of the scheme were carried out. Powered by TCPDF (www.tcpdf.org)
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Adaptivní hp nespojitá Galerkinova metoda pro nestacionární stlačitelné Eulerovy rovnice
Korous, Lukáš ; Feistauer, Miloslav (advisor) ; Dolejší, Vít (referee)
The compressible Euler equations describe the motion of compressible inviscid fluids. They are used in many areas ranging from aerospace, automotive, and nuclear engineering to chemistry, ecology, climatology, and others. Mathematically, the compressible Euler equations represent a hyperbolic system consisting of several nonlinear partial differential equations (conservation laws). These equations are solved most frequently by means of Finite Volume Methods (FVM) and low-order Finite Element Methods (FEM). However, both these approaches are lacking higher order accuracy and moreover, it is well known that conforming FEM is not the optimal tool for the discretization of first-order equations. The most promissing approach to the approximate solution of the compressible Euler equations is the discontinuous Galerkin method that combines the stability of FVM, with excellent approximation properties of higher-order FEM. The objective of this Master Thesis was to develop, implement and test new adaptive algorithms for the nonstationary compressible Euler equations based on higher-order discontinuous Galerkin (hp-DG) methods. The basis for the new methods were the discontinuous Galerkin methods and space-time adaptive hp-FEM algorithms on dynamical meshes for nonstationary second-order problems. The new algorithms...
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Numerical simulation of compressible flows using the parallel computing
Šíp, Viktor ; Dolejší, Vít (advisor) ; Felcman, Jiří (referee)
In the present work we implemented parallel version of a computational fluid dynamics code. This code is based on Discontinuous Galerkin Method (DGM), which is due to its favourable properties suitable for parallelization. In the work we describe the Navier-Stokes equations and their discretization using DGM. We explain the advantages of usage of the DGM and formulate the serial algorithm. Next we focus on the parallel implementation of the algorithm and several particular issues connected to the parallelization. We present the numerical experiments showing the efficiency of the parallel code in the last chapter.
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Use of the hp discontinuous Galerkin method for a simulation of compressible flows
Tarčák, Karol ; Dolejší, Vít (advisor) ; Vejchodský, Tomáš (referee)
Title: Application of hp-adaptive discontinuous Galerkin method to com- pressible flow simulation Author: Karol Tarčák Department: Department of Numerical Mathematics Supervisor: prof. RNDr. Vít Dolejší, Ph.D., DSc. Abstract: In the present work we study an residuum estimate of disconti- nuous Galerkin method for the solution of Navier-Stokes equations. Firstly we summarize the construction of the viscous compressible flow model via Navier-Stokes partial differential equation and discontinuous Galerkin met- hod. Then we propose an extension of an already known residuum estimate for stationary problems to non-stationary problems. We observe the beha- vior of the proposed estimate and modify an existing hp-adaptive algorithm to use our estimate. Finally we apply the modified algorithm on test cases and present adapted meshes from the numerical experiments. Keywords: discontinuous Galerkin method, adaptivity, error estimate 4
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Fluid-structure interaction of compressible flow
Hasnedlová, Jaroslava ; Feistauer, Miloslav (advisor) ; Křížek, Michal (referee) ; Kozel, Karel (referee) ; Rannacher, Rolf (referee)
Title: Fluid-structure interaction of compressible flow Author: RNDr. Jaroslava Hasnedlová Department: Department of Numerical Mathematics, Institute of Applied Mathematics Supervisors: Prof. RNDr. Miloslav Feistauer, DrSc., Dr. h. c., Prof. Dr. Dr. h. c. Rolf Rannacher Supervisors' e-mail addresses: feist@karlin.mff.cuni.cz, rannacher@iwr.uni-heidelberg.de Abstract: The presented work is split into two parts. The first part is devoted to the theory of the discontinuous Galerkin finite element (DGFE) method for the space-time discretization of a nonstationary convection-diffusion initial-boundary value problem with nonlinear convection and linear diffusion. The DGFE method is applied sep- arately in space and time using, in general, different space grids on different time levels and different polynomial degrees p and q in space and time discretization. The main result is the proof of error estimates in L2 (L2 )-norm and in DG-norm formed by the L2 (H1 )-seminorm and penalty terms. The second part of the thesis deals with the realization of fluid-structure interaction problem of the compressible viscous flow with the elastic structure. The time-dependence of the domain occupied by the fluid is treated by the ALE (Arbitrary Lagrangian-Eulerian) method, when the compress- ible Navier-Stokes equations are formulated in...
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Superconvergence for discontinuous Galerkin time discretizations
Roskovec, Filip ; Vlasák, Miloslav (advisor) ; Knobloch, Petr (referee)
The topic of this thesis is the application of the discontinuous Galerkin finite element method (DGFEM) on space-time discretizations of simple nonstationary problems. Unlike the standard finite element method, discontinuous Galerkin method does not require any continuity between neighbouring elements. We apply the DGFEM separately in space and in time. At first, we implement discretization with respect to space variables, whereby we acquire the space semidiscretization. Subsequently we apply Time discontinuous Galerkin method to the problem. We seek the aproximate solution in the space of discontinuous piecewise polynomial functions of degree p in space and degree q in time. This is followed by the error estimates of this scheme. In the end we examine the supercovergence behaviour of the scheme in nodes of the time discretization. The theoretical results are verified by numerical experiments.
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Numerical analysis of approximation of nonpolygonal domains for discontinuous Galerkin method
Klouda, Filip ; Dolejší, Vít (advisor) ; Sobotíková, Veronika (referee)
Title: Numerical analysis of approximation of nonpolygonal domains for discon- tinuous Galerkin method Author: Filip Klouda Department: Department of Numerical Mathematics Supervisor: prof. RNDr. Vít Dolejší, Ph.D., DSc., KNM MFF UK Abstract: In this work we use the discontinuous Galerkin finite element method for the semidiscretization of a nonlinear nonstationary convection-diffusion pro- blem defined on a nonpolygonal two-dimensional domain. Using so called appro- ximating curved elements we define a piecewise polynomial approximation of the boundary of the domain and a space on which we search for a solution. We study the convergence of the method considering a symmetric as well as nonsymmetric discretization of diffusion terms and with the interior and boundary penalty. The obtained results allow us to derive an error estimate for the Discontinuous Galer- kin method employing the approximating curved elements. This estimate depends on the order of the approximation of the solution and also on the order of the approximation of the boundary. We describe one possibility of the construction of the approximating curved elements with the aid of a polynomial mapping given by an interpolation of points on the boundary. We present numerical experiments. Keywords: nonlinear convection-diffusion equation, discontinuous...
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