Events

Here you can find upcoming and past events organized by our group.

  • Thu
    29
    Oct
    2020
    Thu
    11
    Feb
    2021

    Prof. Dr. Nicolas Gauger, Chair for Scientific Computing (SciComp), TU Kaiserslautern

    SciComp Seminar Series

    Please contact Prof. Gauger, if you want to register for an online talk in our SciComp Seminar Series or just to register for the seminar.

    A list with the already scheduled talks you’ll find here.

  • Thu
    21
    Jan
    2021

    16:00Online

    Dr. Roy Charles Swanson, NASA Langley Research Center

    Title: On boundary value problems for RANS equations and two-equation turbulence models – Talk 2

    Abstract:

    Currently, in engineering computations for high Reynolds number turbulent flows, turbulence modeling continues to be the most frequently used approach to represent the effects of turbulence. Such models generally rely on solving either one or two transport equations along with the Reynolds-Averaged Navier-Stokes (RANS) equations. The solution of the boundary-value problem of any system of partial differential equations (PDEs) requires the complete delineation of the equations and the boundary conditions, including any special restrictions and conditions. In the literature, such a description is often incomplete, neglecting important details related to the boundary conditions and possible restrictive conditions, such as how to ensure satisfying prescribed values of the dependent variables of the transport equations in the far field of a finite domain. In these two lectures, which build on each other, we consider the following topics:

    Talk 2:

    In this work, we address the issue of a properly defined boundary-value problem, what we call a well-defined problem. To obtain a unique numerical solution for the well-defined problem, well-posedness is required. The basic requirements of a well-posed problem are reviewed, and the current status of proving well-posedness, including the relevance of the boundary data and a bounded solution, is briefly discussed. This sets the stage for the focus on well-posedness as it pertains to considering the RANS equations and the transport equations for modeling the effects of turbulence as a weakly coupled system. Emphasis is placed on the equations of the turbulence model, and how turbulence modeling can be interpreted as a parameter identification problem, specificaly an inverse
    problem. A compelling argument (although not a proof) for ill-posedness is made for both direct and inverse problems. This argument is based on using surface pressure and skin-friction data that produces very different results for the distribution of the turbulent viscosity. Numerical examples for the RANS equations and two-equation turbulence models are presented that confirm the theoretical findings.

    How to join:

    The talk is held online via Jitsi. You can join with the link https://jitsi.uni-kl.de/SciCompSeminar_11. Please follow the rules below:

    • Use a chrome based browser (One member with a different browser can crash the whole meeting).
    • Mute your microphone and disable your camera.
    • If you have a question, raise your hand.

    More information is available at https://www.rhrk.uni-kl.de/dienstleistungen/netz-telefonie/konferenzdienste/jitsi/.

  • Thu
    28
    Jan
    2021

    16:00Online

    Prof. Qiqi Wang, Massachusetts Institute of Technology (MIT), USA

    Title: The climatic butterfly effect — do numerical simulations capture the statistics of chaotic systems?

    Abstract:

    The butterfly effect is a well-known phenomenon in fluid dynamics. A small perturbation can lead to large differences later in a chaotic dynamical system, such as turbulent flows. Lorenz famously posed the question, does the flap of a butterfly’s wings in Brazil set off a tornado in Texas? The answer is now widely accepted to be yes. This result has significant consequences to simulations that resolve chaotic dynamics, e.g., in fluid flows.

    Whereas a tiny perturbation can change the state of a chaotic system, it is unclear whether it can change the long-time statistics. Statistics of many turbulent flows are known to be stable, insensitive to initial conditions. Ergodic theory provided a foundation for such stability. Indeed, for many unsteady flow simulations to be meaningful, we must believe that their statistics are not super sensitive to perturbations such as numerics. Many researchers rationalize his belief with the concept and theory of shadowing in dynamical systems.

    Having dedicated a decade of research into the theory of shadowing, the speaker has found problems in this theory. Even systems that satisfy the most idealized assumptions in the shadowing theory can be arbitrarily sensitive to parameter perturbations. This question thus resurfaces: do numerical simulations capture the statistics of chaotic systems? In this talk, we will illustrate why the theory of shadowing cannot answer this question. We will then construct a simple mathematical model in which arbitrarily small perturbations can significantly influence the statistics of a stable, ergodic system. In Lorenz’s analogy, an intelligent butterfly could control the climate. Engineers must construct numerical simulations more meticulously to predict the statistics of chaotic fluid flows.

    How to join:

    The talk is held online via Jitsi. You can join with the link https://jitsi.uni-kl.de/SciCompSeminar_12. Please follow the rules below:

    • Use a chrome based browser (One member with a different browser can crash the whole meeting).
    • Mute your microphone and disable your camera.
    • If you have a question, raise your hand.

    More information is available at https://www.rhrk.uni-kl.de/dienstleistungen/netz-telefonie/konferenzdienste/jitsi/.

  • Thu
    04
    Feb
    2021

    11:30Online

    Mitesh Mittal, TU Kaiserslautern

    Title: TBA

    Abstract:

    TBA

    How to join:

    The talk is held online via Jitsi. You can join with the link https://jitsi.uni-kl.de/SciCompSeminar_13. Please follow the rules below:

    • Use a chrome based browser (One member with a different browser can crash the whole meeting).
    • Mute your microphone and disable your camera.
    • If you have a question, raise your hand.

    More information is available at https://www.rhrk.uni-kl.de/dienstleistungen/netz-telefonie/konferenzdienste/jitsi/.

  • Thu
    11
    Feb
    2021

    11:30Online

    Michael Sendhoff, TU Kaiserslautern

    Title: TBA

    Abstract:

    TBA

    How to join:

    The talk is held online via Jitsi. You can join with the link https://jitsi.uni-kl.de/SciCompSeminar_14. Please follow the rules below:

    • Use a chrome based browser (One member with a different browser can crash the whole meeting).
    • Mute your microphone and disable your camera.
    • If you have a question, raise your hand.

    More information is available at https://www.rhrk.uni-kl.de/dienstleistungen/netz-telefonie/konferenzdienste/jitsi/.

  • Thu
    18
    Feb
    2021

    11:30Online

    Michaela Schmitt, TU Kaiserslautern

    Title: TBA

    Abstract:

    TBA

    How to join:

    The talk is held online via Jitsi. You can join with the link https://jitsi.uni-kl.de/SciCompSeminar_15. Please follow the rules below:

    • Use a chrome based browser (One member with a different browser can crash the whole meeting).
    • Mute your microphone and disable your camera.
    • If you have a question, raise your hand.

    More information is available at https://www.rhrk.uni-kl.de/dienstleistungen/netz-telefonie/konferenzdienste/jitsi/.