Browsing by Author "Mehl, Miriam (Prof. Dr. rer. nat. habil.)"

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Open Access
Data transfer in partitioned multi-physics simulations : interpolation & communication
(2019) Lindner, Florian; Mehl, Miriam (Prof. Dr. rer. nat. habil.)
Partitioned multi-physics simulations allow to reuse existing solvers and to combine them to multi-physics scenarios. This provides not only greater flexibility and improved time-to-solution, but also helps to manage the increasing complexity of modern scientific software. This thesis sees itself as a continuation of the works of B. Gatzhammer and B. Uekermann who developed a comprehensive tool to couple independent simulation codes. I focus on the two important aspects of interpolation between non-matching grids as well as communication between several parallel codes and conclude with aspects of software development of the coupling library preCICE. The interpolation part puts special emphasis on radial-basis function interpolation. It starts with a thorough review of existing interpolation methods with special consideration of the black-box approach to multi-physics simulations and explores promising enhancements to RBF interpolation. Numerical experiments provide a rigorous testing for accuracy, stability and scaling behavior of different variants of RBF implementations. Following the insights gained from the numerical experiments, a highly-optimized parallel implementation for preCICE is developed, containing various measures to improve accuracy and stability of the interpolation. The communication part first defines the requirements for partitioned simulations in terms of communication. A new technique for peer-to-peer communication networks between distinct MPI domains is developed and evaluated against existing approaches. Furthermore, a fast method to establish connections via the file system is presented. Both measures optimize the initialization phase and achieve a considerable speedup. Finally, a strategy to fully decouple algorithmically independent participants on the communication protocol level is implemented and tested. In the last part, the software-related challenges in developing a parallel scientific application involving multiple independent solvers are outlined. I show how the preCICE project handles testing, profiling and integration of a large parallel scientific software with multiple participants. A profiling library for distributed applications has been developed and is extensively used in preCICE and potentially other projects.
Open Access
Modeling and simulation of cabin air filtration with focus on electrostatic effects
(2019) Schober, Carolin; Mehl, Miriam (Prof. Dr. rer. nat. habil.)
Cabin air filters serve to remove harmful pollutants from the air flow supplied to the car passenger compartment. Electrostatic charges on cabin air filter media significantly improve the degree of particle separation without compromising the air permeability, thus achieving superior filtration performance. In order to optimize the performance metrics, a basic understanding of electrostatic filtration effects is required. However, these effects are largely unexplored due to limited experimental measurement options. Numerical simulations allow a deeper insight into fundamental physical processes than the measurement of macroscopic quantities. However, the uni-directionally coupled status quo simulation approach leads to results deviating from experimental observations for electrostatically charged systems. Numerous unknown parameters such as the charge distribution on filter fibers and dust particles and the lacking implementation of all simultaneously effective electrostatic separation mechanisms cause these differences. This dissertation provides an enhanced fully-coupled modeling approach to simulate specific electrostatic filtration effects. The new simulation model includes the interaction of highly bipolar charged dust particles with each other, with filter fibers, and with the background air flow. Extensive studies demonstrate the necessity of this high level of detail in order to dissolve electrostatic agglomeration effects in the inflow area. In addition, combined numerical and experimental test scenarios provide qualitative results allowing to observe the effect of induced dipoles and mirror charges. A combination of the fully-coupled modeling approach with the status quo simulation method in a two-step procedure is highly recommended for further research studies.