Research WG Applications of PDEs - Prof. Dr. Christian Engwer

  • Overview and focus

    Many of our applications origin from porous media or biological systems, which exhibit very different kinds of complexity. Complexity can origin from a complicated geometric shapes, which poses a challenge for the numerical solution of PDEs in the complex shaped domain. The other kind of complexity is complexity of the system itself, due to complex couplings between different physical, biological & chemical processes.

    Complex Geometries

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     When solving of PDEs on time dependent domains or domains with a complex shape, classic Finite Element Methods pose many problems regarding the construction of the mesh. During the last decade a range of different methods have been developed to decouple the construction of a finite element mesh, i.e. the finite element discretization, from the geometrical details of the domain.

    One approach, our group is working on, is the Unfitted Discontinuous Galerkin method. It offers the possibility to compute simulations with a fine structures on a relatively coarse mesh and was used for the solution of elliptic, parabolic and hyperbolic problems. Using the UDG approach it is easily possible to run simulations directly on image data, e.g. micro-CT images, or to combine it with level-set or phase-field methods to handle moving interfaces.

    Multi-Physics Problems

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    In the course of multi-physics applications the efficient coupling of different PDEs on different sub-domains is getting more important. We are working on different aspects of domain decomposition methods and their implementation, either for parallelization and preconditioning, or for the coupling in a multi-physics setting. The latter also includes heterogenous coupling of sub-domains of different dimension.

    Efficient PDE Software

    Dune
    Dune
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    We set high value on the development of efficient FEM software. Reusability and interoperability of and with existing software are very important. In this course we are actively participating in the development of the C++ FEM framework DUNE.

    Programming with C++ and using generic programming techniques, allows us to use fine grained interfaces and still employ optimization techniques, like inlining and loop-unrolling. This is the basis for sustainable and efficient software development.

    High Performance Computing

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    The speed of a single processor stopped growing in the last years, instead modern chips include many cores to increase the performance. At the same time the architecture of high performance computers like the BlueGene is changing, they include acceleration processors which leaves us with a heterogeneous hardware system. Modern scientific software must cope with these changing requirements. As it is too much a burden to expect scientist to rewrite their code for each new hardware, the software design and the numerical algorithms must be adopted in a way that allows us to port our software with as small work as possible, while still retaining a reasonable performance boost.

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    Latest Publications

    • Engwer, Christian; Ohlberger, Mario; Renelt, Lukas. . ‘Model order reduction of an ultraweak and optimally stable variational formulation for parametrized reactive transport problems.’ SIAM Journal on Scientific Computing 46, № 5: A3205–A3229. doi: 10.1137/23M1613402.
    • Engwer, Christian; Ohlberger, Mario; Renelt, Lukas. . ‘Construction of local reduced spaces for Friedrichs' systems via randomized training.’ Contributed to the Central-European Conference on Scientific Computing, ALGORITMY, Podbanské.

    • Medani, Takfarinas; Garcia-Prieto, Juan; Tadel, Francois; Antonakakis, Marios; Erdbrügger, Tim; Höltershinken, Malte; Mead, Wayne; Schrader, Sophie; Joshi, Anand; Engwer, Christian; Wolters, Carsten H.; Mosher, John C.; Leahy, Richard M. . ‘Brainstorm-DUNEuro: An integrated and user-friendly Finite Element Method for modeling electromagnetic brain activity.’ NeuroImage 267: 119851. doi: 10.1016/j.neuroimage.2022.119851.
    • Erdbrügger, T.; Westhoff, A.; Höltershinken, M.; Radecke, J.-O.; Buschermöhle, Y.; Buyx, A.; Wallois, F.; Pursiainen, S.; Gross, J.; Lencer, R.; Engwer, C.; Wolters, C.H. . ‘CutFEM forward modeling for EEG source analysis.’ Frontiers in Human Neuroscience 17: 1216758. doi: 10.3389/fnhum.2023.1216758.
    • Renelt, Lukas; Ohlberger, Mario; Engwer, Christian. . ‘An optimally stable approximation of reactive transport using discrete test and infinite trial spaces.’ In Finite Volumes for Complex Applications X—Volume 2, Hyperbolic and Related Problems, edited by Franck, Emmanuel; Fuhrmann, Jürgen;, Michel-Dansac, Victor; Navoret, Laurent, 289–298. Heidelberg: Springer. doi: 10.1007/978-3-031-40860-1_30.

    • Bastian P, Blatt M, Dedner A, Dreier N, Engwer C, Fritze R, Gräser C, Kempf D, Klöfkorn R, Ohlberger M, Sander O. . ‘The DUNE Framework: Basic Concepts and Recent Developments.’ Computers & Mathematics with Applications 81: 75–112. doi: 10.1016/j.camwa.2020.06.007.
    • Streitbürger Florian, Engwer Christian, May Sandra, Nüßing Andreas. . ‘Monotonicity considerations for stabilized DG cut cell schemes for the unsteady advection equation.’ Contributed to the ENUMATH2019, Egmond aan Zee, The Netherlands.
    • Dreier Nils-Arne, Engwer Christian. . ‘Strategies for the vectorized Block Conjugate Gradients method.’ Contributed to the ENUMATH2019, Egmond aan Zee, The Netherlands.
    • Schrader S, Westhoff A, Piastra MC, Miinalainen T, Pursiainen S, Vorwerk J, Brinck H, Wolters CH, Engwer C. . ‘DUNEuro- A software toolbox for forward modeling in bioelectromagnetism.’ PloS one 2021. doi: 10.1371/journal.pone.0252431.
    • Dreier Nils-Arne. . Hardware-Oriented Krylov Methods for High-Performance Computing Dissertation thesis, WWU Münster. N/A: Selbstverlag / Eigenverlag. doi: 10.48550/arXiv.2104.02494.

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