Mario Ohlberger
University of Münster
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Publication
Featured researches published by Mario Ohlberger.
Computing | 2008
Peter Bastian; Markus Blatt; Andreas Dedner; Christian Engwer; Robert Klöfkorn; Ralf Kornhuber; Mario Ohlberger; Oliver Sander
In a companion paper (Bastian et al. 2007, this issue) we introduced an abstract definition of a parallel and adaptive hierarchical grid for scientific computing. Based on this definition we derive an efficient interface specification as a set of C++ classes. This interface separates the applications from the grid data structures. Thus, user implementations become independent of the underlying grid implementation. Modern C++ template techniques are used to provide an interface implementation without big performance losses. The implementation is realized as part of the software environment DUNE (http://dune-project.org/). Numerical tests demonstrate the flexibility and the efficiency of our approach.
Computing | 2008
Peter Bastian; Markus Blatt; Andreas Dedner; Christian Engwer; Robert Klöfkorn; Mario Ohlberger; Oliver Sander
We give a mathematically rigorous definition of a grid for algorithms solving partial differential equations. Unlike previous approaches (Benger 2005, PhD thesis; Berti 2000, PhD thesis), our grids have a hierarchical structure. This makes them suitable for geometric multigrid algorithms and hierarchical local grid refinement. The description is also general enough to include geometrically non-conforming grids. The definitions in this article serve as the basis for an implementation of an abstract grid interface as C++ classes in the framework (Bastian et al. 2008, this issue).
Mathematics of Computation | 2000
Dietmar Kröner; Mario Ohlberger
In this paper we shall derive a posteriori error estimates in the L 1 -norm for upwind finite volume schemes for the discretization of nonlinear conservation laws on unstructured grids in multi dimensions. This result is mainly based on some fundamental a priori error estimates published in a recent paper by C. Chainais-Hillairet. The theoretical results are confirmed by numerical experiments.
Mathematical and Computer Modelling of Dynamical Systems | 2011
Bernard Haasdonk; Markus Dihlmann; Mario Ohlberger
Modern simulation scenarios require real-time or many-query responses from a simulation model. This is the driving force for increased efforts in model order reduction for high-dimensional dynamical systems or partial differential equations. This demand for fast simulation models is even more critical for parameterized problems. Several snapshot-based methods for basis construction exist for parameterized model order reduction, for example, proper orthogonal decomposition or reduced basis methods. They require the careful choice of samples for generation of the reduced model. In this article we address two types of grid-based adaptivity that can be beneficial in such basis generation procedures. First, we describe an approach for training set adaptivity. Second, we introduce an approach for multiple bases on adaptive parameter domain partitions. Due to the modularity, both methods also can easily be combined. They result in efficient reduction schemes with accelerated training times, improved approximation properties and control on the reduced basis size. We demonstrate the applicability of the approaches for instationary partial differential equations and parameterized dynamical systems.
Computing | 1997
Mario Ohlberger; Martin Rumpf
Modern numerical methods are capable to resolve fine structures in solutions of partial differential equations. Thereby they produce large amounts of data. The user wants to explore them interactively by applying visualization tools in order to understand the simulated physical process. Here we present a multiresolution approach for a large class of hierarchical and nested grids. It is based on a hierarchical traversal of mesh elements combined with an adaptive selection of the hierarchical depth. The adaptation depends on an error indicator which is closely related to the visual impression of the smoothness of isosurfaces or isolines, which are typically used to visualize data. Significant examples illustrate the applicability and efficiency on different types of meshes.
Mathematical and Computer Modelling of Dynamical Systems | 2011
Bernard Haasdonk; Mario Ohlberger
We address the problem of model order reduction (MOR) of parametrized dynamical systems. Motivated by reduced basis (RB) methods for partial differential equations, we show that some characteristic components can be transferred to model reduction of parametrized linear dynamical systems. We assume an affine parameter dependence of the system components, which allows an offline/online decomposition and is the basis for efficient reduced simulation. Additionally, error control is possible by a posteriori error estimators for the state vector and output vector, based on residual analysis and primal-dual techniques. Experiments demonstrate the applicability of the reduced parametrized systems, the reliability of the error estimators and the runtime gain by the reduction technique. The a posteriori error estimation technique can straightforwardly be applied to all traditional projection-based reduction techniques of non-parametric and parametric linear systems, such as model reduction, balanced truncation, moment matching, proper orthogonal decomposition (POD) and so on.
Archive | 1999
Dietmar Kröner; Mario Ohlberger; Christian Rohde
An Introduction to Kinetic Schemes for Gas Dynamics.- An Introduction to Nonclassical Shocks of Systems of Conservation Laws.- Viscosity and Relaxation Approximation for Hyperbolic Systems of Conservation Laws.- A Posteriori Error Analysis and Adaptivity for Finite Element Approximations of Hyperbolic Problems.- Numerical Methods for Gasdynamic Systems on Unstructured Meshes.
Multiscale Modeling & Simulation | 2005
Mario Ohlberger
In this paper, we derive a new approach for the numerical analysis of the heterogeneous multiscale finite element method (HM-FEM) for elliptic homogenization problems. The HM-FEM was introduced in ...
Numerische Mathematik | 2009
Patrick Henning; Mario Ohlberger
In this contribution we analyze a generalization of the heterogeneous multiscale finite element method for elliptic homogenization problems in perforated domains. The method was originally introduced by E and Engquist (Commun Math Sci 1(1):87–132, 2003) for homogenization problems in fixed domains. It is based on a standard finite element approach on the macroscale, where the stiffness matrix is computed by solving local cell problems on the microscale. A-posteriori error estimates are derived in L2(Ω) by reformulating the problem into a discrete two-scale formulation (see also, Ohlberger in Multiscale Model Simul 4(1):88–114, 2005) and using duality methods afterwards. Numerical experiments are given in order to numerically evaluate the efficiency of the error estimate.
Numerische Mathematik | 2001
Mario Ohlberger
Summary. This paper is devoted to the study of a posteriori and a priori error estimates for the scalar nonlinear convection diffusion equation