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Date Time Venue Talk
02/20/20 01:15 pm Room H - SBC5 - H0.03 Novel Space-Time Finite Element Discretizations*
Prof. Dr. Marek Behr, Chair for Computational Analysis of Technical Systems (CATS), RWTH Aachen University

Moving-boundary flow simulations are an important design and analysis tool in many areas, including civil and biomedical engineering, as well as production engineering. Interface-capturing offers flexibility for complex free-surface motion, while interface-tracking is very attractive due to its mass conservation properties at low resolution. We focus on these alternatives in the context of flow simulations based on stabilized finite element discretizations of Navier-Stokes equations, including space-time formulations that allow extra flexibility concerning grid design at the interface.

Space-time approaches offer some not-yet-fully-exploited advantages; among them, the potential to allow some degree of unstructured space-time meshing. A method for generating simplex space-time meshes has been developed, allowing arbitrary temporal refinement in selected portions of space-time slabs. The method increases the flexibility of space-time discretizations, even in the absence of dedicated space-time mesh generation tools. The resulting tetrahedral and pentatope meshes are being used in the context of cavity filling flow simulations, such as those necessary to design injection molding processes.
01/23/20 02:00 pm TBA Einblicke in die Modellierung des Materialverhaltens von Elastomerwerkstoffen
Nils Hendrik Kröger, Deutsches Institut für Kautschuktechnologie e.V., Hannover, Eupener Straße 33, 30519 Hannover, Deutschland

Im Maschinen- und Automobilbau werden für mechanisch extrem beanspruchte, temperatur- und chemikalienbeständige Bauteile Elastomerwerkstoffe benötigt. Typische Beispiele sind Reifen, Zahn- und Keilriemen, Motor- und Aggregatelager, Luftfedern und Fahrwerkbuchsen sowie statisch und dynamisch beanspruchte Dichtungen. Die Anforderungen bezüglich Zuverlässigkeit und Leistungsdichte sind speziell in Verbindung mit den hochsensiblen, sicherheitsrelevanten Funktionen der Bauteile besonders hoch.
Insbesondere im Rahmen der Digitalisierung in der Produktion gewinnen Simulationsmodelle verstärkt an Bedeutung. Viele Verarbeitungsschritte in der Herstellung von Elastomerbauteilen beginnend mit dem Mischen, dem Walzen und der Extrusion oder des Spritzgießens, über die Vulkanisation beeinflussen die endgültigen mechanischen Eigenschaften. Im Laufe ihres Einsatzlebens verändern sich diese Eigenschaften auf Grund von thermo-oxidativer Alterung, so dass auch Lebensdauervorhersagen zur einer Herausforderung werden. Die zuverlässige Erstellung von „Digitalen Zwillingen“ für Elastomerbauteile bedarf so einer Beschreibung vieler auch untereinander gekoppelter Effekte.
Dieser Vortrag bietet Einblicke in verschiedene Modellierungsansätze einzelner Abschnitte des Leben von Elastomeren. Hauptfokus ist hierbei die Beschreibung der mechanischen Eigenschaften unter Berücksichtigung der Vernetzung und Alterung.
01/16/20 02:00 pm TBA TBA
Sara Krause-Solberg, Institut für Mathematik (E-10), Lehrstuhl Angewandte Analysis
01/09/20 04:30 pm Am Schwarzenberg-Campus 3 (E), Room 3.074 TBA
Kristof Albrecht
12/19/19 02:00 pm Am Schwarzenberg-Campus 3 (E), Room 3.074 Parallel-in-Time PDE-constrained Optimization*
Dr. Sebastian Götschel, Zuse Institut Berlin (ZIB)

Large-scale optimization problems governed by partial differential equations (PDEs) occur in a multitude of applications, for example in inverse problems for non-destructive testing of materials and structures, or in individualized medicine. Algorithms for the numerical solution of such PDE-constrained optimization problems are computationally extremely demanding, as they require multiple PDE solves during the iterative optimization process. This is especially challenging for transient problems, where methods working on the reduced objective functional are often employed to avoid a full spatio-temporal discretization of the associated optimality system. The evaluation of the reduced gradient then requires one solve of the state equation forward in time, and one backward-in-time solve of the adjoint equation. In order to tackle real-life applications, it is not only essential to devise efficient discretization schemes, but also to use advanced techniques to exploit computer architectures and decrease the time-to-solution, which otherwise is prohibitively long.

One approach is to utilize the increasing number of CPU cores available in current computers. In addition to more common spatial parallelization, time-parallel methods are receiving increasing interest in the last years. There, iterative multilevel schemes such as PFASST (Parallel Full Approximation Scheme in Space and Time) are currently state of the art and achieve significant parallel efficiency. In this talk, we investigate approaches to use PFASST for the solution of parabolic optimal control problems. Besides enabling time parallelism, the iterative nature of the temporal integrators within PFASST provides additional flexibility for reducing the cost of solving nonlinear equations, re-using previous solutions in the optimization loop, and adapting the accuracy of state and adjoint solves to the optimization progress. We discuss benefits and difficulties, and present numerical examples.

This is joint work with Michael Minion (Lawrence Berkeley National Lab).
12/16/19 01:00 pm Am Schwarzenberg-Campus 3 (E), Room 3.074 Präkonditionierer für lineare Systeme aus RBF-FD diskretisierten partiellen Differentialgleichungen (Bachelorarbeit)
Henrik Wyschka
12/12/19 02:00 pm Am Schwarzenberg-Campus 3 (E), Room 3.074 Molecular-Continuum Flow Simulation with MaMiCo: Where HPC and Data Analytics Meet
Prof. Dr. Philipp Neumann, Helmut-Schmidt-Universität

Molecular-continuum methods, as referred to in my talk, employ a domain decomposition and compute fluid flow either by means of molecular dynamics (MD) or computational fluid dynamics (CFD) in the sub-domains. This enables multiscale investigations of nano- and microflows beyond the limits of validity of classical CFD.

In my talk, I will focus on latest developments in the macro-micro-coupling tool (MaMiCo). MaMiCo enables the coupling of arbitrary CFD and MD solvers, hiding the entire coupling algorithmics from the actual single-scale solvers. After a brief discussion of the limits of the MD method, I will focus on various aspects of the molecular-continuum coupling and its realization in MaMiCo, including parallelization, multi-instance sampling for MD (that is ensemble averaging) and filtering methods that extract smooth responses from the fluctuating MD description to enhance consistency on the side of the continuum solver. I will further present preliminary results from a study which aims to generate open boundary force models for MD using machine learning.
12/05/19 02:00 pm Am Schwarzenberg-Campus 3 (E), Room 3.074 A new approach to the QR decomposition of hierarchical matrices
Vincent Griem

All existing QR decompositions for hierarchical matrices suffer from numerical drawbacks that limit their use in many applications. In this talk, I will present a new method based on the recursive WY-based QR decomposition by Elmroth and Gustavson. It is an extension of an already existing method for a subclass of hierarchical methods developed by Kressner and Susnjara.

I will try to keep things as simple as possible and give a short introduction to hierarchical matrices as well. Previous knowledge of hierarchical matrices is not necessary to understand the basic ideas and main obstacles of the new algorithm.
11/26/19 05:00 pm Am Schwarzenberg-Campus 5 (H), Room H0.10 Two-scale convergence for evolutionary equations
Marcus Moppi Waurick, Department of Mathematics and Statistics, University of Strathclyde, Livingstone Tower, 26 Richmond Street, Glasgow G1 1XH, Scotland, Room number: LT1007

In the talk, we shall develop a general framework for the treatment of both deterministic and stochastic homogenisation problems for evolutionary equations. The versatility of the methods allow the unified treatment of static, dynamic as well as mixed type problems.
11/21/19 02:00 pm Am Schwarzenberg-Campus 3 (E), Room 3.074 Parallel-in-time integration with PFASST: from prototyping to applications
Robert Speck, Jülich Supercomputing Centre, Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428 Jülich

The efficient use of modern supercomputers has become one of the key challenges in computational science. New mathematical concepts are needed to fully exploit massively parallel architectures. For the numerical solution of time-dependent processes, time-parallel methods have opened new ways to overcome scaling limits. With the "parallel full approximation scheme in space and time" (PFASST), multiple time-steps can be integrated simultaneously. Based on spectral deferred corrections (SDC) methods and nonlinear multigrid ideas, PFASST uses a space-time hierarchy with various coarsening strategies to maximize parallel efficiency. In numerous studies, this approach has been used on up to 448K cores and coupled to space-parallel solvers with finite differences, spectral methods or even articles for discretization in space. Yet, since the integration of SDC or PFASST into an existing application code is not straightforward and the potential gain is typically uncertain, we will present in this talk our Python prototyping framework pySDC. It allows to rapidly test new ideas and to implement first toy problems more easily. We will also discuss the transition from pySDC to application-specific implementations and show recent use cases.

* Talk within the Colloquium on Applied Mathematics