Open Postdoctoral Positions in Scientific Computing and Machine Learning

In the framework of the new project on “Cultural Evolution in Changing Climate: Human and Earth System Coupled Research (HESCOR)”, we invite applications for postdoctoral research associate positions in the area of Earth system modeling, Human system modeling, applied numerical mathematics, scientific computing and/or machine learning, among many others.

The job descriptions, duty statement and qualification requirements for each of these positions can be found on the websites:
https://imfess.uni-koeln.de/hescor/positions and
https://ufg.phil-fak.uni-koeln.de/hescor

The research associate RA6 (RA in Scientific Computing) will be hosted at the Numerical Simulation Research Group of the University of Cologne.

We provide a collaborative and friendly environment for cutting edge research and ensure measures are in place to promote early-career researchers.

 

New Open Position: Postdoc in Scientific Computing

The Numerical Simulation group of Professor Gassner invites applications for a 2.5 year (possibility for extensions afterwards available) postdoc position in scientific computing (pay grade 100% TVL-13).

Deadline for applications is 10.2.2023.

For details, please have a look at the job ad: click here

For questions, please contact Professor Gassner via Email (ggassner@uni-koeln.de).

Talk: Gregor Gassner (UoC) with Robust Split-Form DGSEM for Hydro- and Magnetohydrodynamics

In this talk, we present the class of split form discontinuous Galerkin methods. The notion of split form refers to different interpretations of the non-linear terms in the fluid dynamics equations. For instance the advective part of the momentum flux can be cast in analytically equivalent forms such as the advective form, or the conservative form, or convex combinations of both forms. While these forms are analytically equivalent for smooth solutions, it is interesting to understand that their discrete forms might have strongly different properties. It turns out that specific underlying split forms of the fluid equations give discontinuous Galerkin (DG) approximations with special favourable properties such as, kinetic energy preservation, energy consistency, pressure equilibrium preservation and even entropy conservation/stability. The most important improvement that can be observed is drastically increased non-linear robustness of the DG discretization, in particular when simulating under-resolved turbulence. A necessary ingredient to retain fully discrete conservation when using split formulations is the so-called summation-by-parts (SBP) property of the discrete derivative and integral operator. It turns out hat specific DG discretizations, such as the Legendre-Gauss-Lobatto (LGL) spectral element method, satisfy the SBP property. We will further discuss in this talk that it is possible to construct compatible low-order finite volume discretizations on the LGL subcell grid, such that a convex blending of the high-order DG method with the robust low-order method is feasible. This allows to construct provably positive hybrid discretizations that enable simulations of problems with strong shock waves, such as e.g. an astrophysical jet with Ma=2000.

Link to the Talk: https://cassyni.com/events/VrFL7HmR9YjHyFJvFcZNjP

Workshop: Novel Adaptive Discontinuous Galerkin Approaches for the Simulation of Atmospheric Flows

On November 30th and December 1st, the workshop on “Novel Adaptive Discontinuous Galerkin Approaches for the Simulation of Atmospheric Flows” will take place at the Department of Mathematics and Computer Science with researchers from the German Aerospace Center (DLR) Cologne, Deutscher Wetterdienst (DWD), and University of Cologne (UoC). This workshop is supported by and embedded into the Center for Earth System Observation and Computational Analysis (CESOC).

The idea of the workshop is to discuss novel developments for discontinuous Galerkin methods applied to atmospheric flow simulations, with a focus on implicit time integration, meshing of the sphere, adaptivity, efficient implementations, benchmark test cases for atmospheric flows, entropy-stable split formulations of the nonlinear partial differential equations, and bounds-preserving numerical schemes.

A detailed program with abstracts is available here.

Talk: Deniz Bezgin (TUM) and Aaron Buhendwa (TUM) about Differentiable Fluid Dynamics in JAX: Challenges and Perspectives, Friday, 26th August 2022, 10am CEST

JAX-FLUIDS is a CFD solver written in Python, which uses the JAX framework to enable automatic differentiation (AD). This allows one to easily create applications for data-driven simulations or other optimization problems.The talk is based on the recent preprint “JAX-FLUIDS: A fully-differentiable high-order computational fluid dynamics solver for compressible two-phase flows” (arXiv:2203.13760).

To obtain the Zoom link for this online talk, please get in touch with Gregor Gassner or Michael Schlottke-Lakemper.

Start of new Research Project: Klaus-Tschira-Stiftung funded Project “HiFiLab: A High-Fidelity Laboratory for the Simulation of Celestial Bodies with their Space Environment” (2022 – 2025)

In this project, we focus on generating a novel computational simulation framework to describe the interaction of plasma with celestial bodies. Understanding the interaction of celestial bodies with their space environment is very important, as it often reveals information about their inner structure and the existence/composition of their atmospheres. Of fundamental importance is the question about liquid water under the icy surface of some moons of the solar system, as water is considered to be one of the essential ingredients for life as we know it.In the last years, we have successfully designed a high-order accurate 3D unstructured discontinuous Galerkin (DG) open source solver with fully parallel adaptive mesh refinement for single-fluid magnetohydrodynamics. DG methods are famous for their high accuracy, their high flexibility and extreme parallel scaling capabilities and are thus perfectly suited for complex plasma interaction simulations. We plan a major step forward regarding the physical modeling fidelity of our computational plasma framework, by extending our high-order DG solver to multi-ion MHD models that account for the interaction of electrons, ions, and neutrals. We will further apply the resulting novel computational plasma framework to simulate the Jovian moon Europa and compare our results with data taken by space missions during flybys of the moon and observations from the Hubble Space Telescope to gain insight and better understanding of the complex plasma interactions.

New Open Position: PostDoc in Scientific Computing

The Numerical Simulation group of Professor Gassner invites applications for a 2 year (possibility for extensions afterwards available) postdoc position in scientific computing (pay grade 100% TVL-13).

Deadline for applications is 28.2.2022.

For details, please have a look at the job ad:

German version (click here)
English version (click here)

For questions, please directly contact Professor Gassner via Email (ggassner@uni-koeln.de).

JuliaCon 2021: Adaptive and extendable numerical simulations with Trixi.jl

Trixi.jl is a numerical simulation framework for adaptive, high-order discretizations of conservation laws. It has a modular architecture that allows users to easily extend its functionality and was designed to be useful to experienced researchers and new users alike. In this talk, we give an overview of Trixi’s current features, present a typical workflow for creating and running a simulation, and show how to add new capabilities for your own research projects.

This talk was given on July 30th, 2021 by Michael Schlottke-Lakemper and Hendrik Ranocha as part of JuliaCon 2021.

Talk on YouTube: https://www.youtube.com/watch?v=hoViWRAhCBE
Repository: https://github.com/trixi-framework/talk-2021-juliacon
Conference agenda entry: https://live.juliacon.org/talk/VAGFD7

Talk on 2021-07-02: On Wave Propagation Characteristics, Upwind SBP Properties and Energy Stability of DG Viscous Flux Discretizations

Speaker: Dr. Sigrun Ortleb, University of Kassel, Germany
Date & time: Friday, 2nd July 2021, 10 am (CEST)
Venue: Please request the Zoom meeting link from Michael Schlottke-Lakemper

Abstract:
Regarding accuracy and stability of numerical schemes for computational fluid dynamics, the investigation of diffusion/dispersion errors depending on the wave number is of utmost importance. Especially for high order methods, a desired small numerical dissipation competes with robustness and thus has to be carefully analyzed. This wave propagation analysis is often based on pure advection problems. In the literature, various approaches to discretize diffusion terms within a DG scheme have been introduced since the discretization of higher order spatial derivatives within the DG framework is less natural than in case of first order derivatives. In this talk, we will address significant differences in the disspation/dispersion properties for linear advection-diffusion, depending on the specific DG viscous flux discretization which is employed. In addition, results on energy stability of DG viscous flux formulations are dealt with and we show how to formulate the well-known LDG and BR1 fluxes in terms of global upwind SBP operators which complements the derivation and analysis regarding element level SBP properties of the DG scheme.