Veranstaltungen

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Donnerstag, 20.02.2020, 14:00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Prof. Wolfgang Dreyer, WIAS Berlin:
Classical tests of electro-chemistry
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Volume changes, heat of dilution, osmosis, saturation pressure decrease and boiling temperature increase of electrolytes are classical phenomena that can be used to test and adjust parameter of electrochemical modeling. In this lecture we apply the electrolyte model developed at WIAS to these phenomena in order to critically examine the underlying assumptions. The observations require generalizations of the notions of incompressibility and surface tension.

Veranstalter
WIAS Berlin
Dienstag, 25.02.2020, 15:00 Uhr (WIAS-405-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Prof. Dr. Håkon Hoel, RWTH Aachen:
Multilevel ensemble Kalman filtering algorithms
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

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Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics

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WIAS Berlin
Donnerstag, 27.02.2020, 11:00 Uhr (WIAS-ESH)
Seminar Nichtglatte Variationsprobleme und Operatorgleichungen
Dr. Axel Kröner, WIAS Berlin:
Optimal control of a semilinear heat equation subject to state and control constraints
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
Donnerstag, 27.02.2020, 14:00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Dr. Philip Lederer, TU Wien, Österreich:
Divergence-free tangential finite element methods for incompressible flows on surfaces
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
In this work we consider the numerical solution of incompressible flows on twodimensional manifolds. Whereas the compatibility demands of the velocity and the pressure spaces are known from the flat case one further has to deal with the approximation of a velocity field that lies only in the tangential space of the given geometry. Abandoning H1-conformity allows us to construct finite elements which are -- due to an application of the Piola transformation -- exactly tangential. To reintroduce continuity (in a weak sense) we make use of (hybrid) discontinuous Galerkin techniques. To further improve this approach, H(div Γ)-conforming finite elements can be used to obtain exactly divergence-free velocity solutions. We present several new finite element discretizations. On a number of numerical examples we examine and compare their qualitative properties and accuracy.

Veranstalter
WIAS Berlin
Donnerstag, 27.02.2020, 15:00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Dr. Anton Stephan, Institut für Physik der Atmosphäre:
Modeling Navier--Stokes equations for high Reynolds number flows and complex geometries in aerodynamic applications
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
The flight of an aircraft through a turbulent environment presents a difficult numerical problem. Though it can be easily described by the Navier-Stokes equations, it is impossible to perform a direct numerical simulation resolving all physically relevant scales. For several decades, numerous different models have been developed which perform very well for very specific problems. However, since the aircraft flight includes complex geometries as well as large spatial dimensions these models fail to capture all important features of the problem.
The vision of establishing a simulation system for virtual flight in a realistic environment is addressed by the coupling of two separate flow solvers in a bi-directional manner. This enables for example the simulation of a flight through gusts, trailing vortices and clear air turbulence, including the effects on the aircraft and the roll-up of trailing vortices and their further development until final decay. A compressible Reynolds-Averaged Navier-Stokes (RANS) solver resolves the near-field around an aircraft model. An incompressible Large-Eddy Simulation (LES) solver is used to model the atmosphere around the aircraft with its wake footprint in the LES domain. This hybrid simulation setup is used to investigate complex physical problems occurring in different flight scenarios.

Veranstalter
WIAS Berlin
Donnerstag, 05.03.2020, 14:00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Dr. Alexander Linke, WIAS Berlin:
Gradient-robustness: A new concept assuring accurate spatial discretizations for vector-valued PDEs
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Vector-valued PDEs like the incompressible Navier--Stokes equations (in primitive variables velocity and pressure) describe the time evolution of a vector-valued quantity like the momentum density. For vector-valued PDEs it is quite natural to derive formally on the continuous level a derived time evolution of the vorticity and the divergence. Accordingly, any space discretization for a vector-valued PDE (implicitly) delivers a discrete vorticity and discrete divergence equation.
While the celebrated inf-sup stability will be shown to assure an accurate discrete divergence equation, the talk will actually focus on the question, which structural properties allow for an implicitly defined accurate discrete vorticity equation. The key observation is that the L^2-orthogonality of divergence-free vector fields and gradient fields is the weak equivalent to the vector calculus identity $nabla times nabla psi = mathbf0$ for arbitrary smooth scalar fields $psi$.
In the context of the incompressible Navier-Stokes equations, the concept of pressure-robustness was introduced in 2016, in order to discriminate between space discretizations with accurate and inaccurate discrete vorticity equations. H(div)-conforming finite element spaces have been found as an important means to realize the L^2-orthogonality between discretely divergence-free vector fields and (arbitrary) gradient fields. Further, it is shown that spatial discretizations that are not pressure-robust may suffer from i) a degradation of the (preasymptotic) convergence rate, and ii) large, parameter-dependent constants in error estimates. Typical flows that benefit from pressure-robustness are quasi-hydrostatic flows, quasi-geostrophic flows and vortex-dominated high Reynolds number flows.
Last but not least, the talk shows how to extend the concept of pressure-robustness to more general vector-valued PDEs, leading to the concept of gradient-robustness. Gradient robustness assures that dominant and extreme gradient fields in a vector-valued PDE will not lead to inaccuracies in the discretization. The talk will show examples from linear elasticity and compressible (Navier--)Stokes flows at low Mach numbers and in stratified flows. Thus, connections to well-balanced schemes and WENO schemes will be drawn.

Veranstalter
WIAS Berlin
12. – 13. März 2020 (WIAS-ESH)
Workshop/Konferenz: International Workshop: Uncertainty and Fluctuations in Thermodynamics
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Mittwoch, 10.06.2020, 15:15 Uhr (WIAS-HVP-3.13)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Pierluigi Colli, Università di Pavia, Italien:
Optimal control of a tumor growth model with chemotaxis and singular potentials
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
17. – 19. Juni 2020 (WIAS-ESH)
Workshop/Konferenz: Junior Female Researchers in Probability
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
The goal of the workshop is to offer junior female researchers in stochastics a platform to talk about their own research work and to get acquainted with important research topics presented by well-established female researchers. To cover various topics in probability and its applications, two keynote talks by outstanding female probabilists and four invited talks are planned. Moreover, a number of contributed talks will be chosen by the organizing committee among the submitted abstracts.

Veranstalter
Technische Universität Berlin
Humboldt-Universität zu Berlin
WIAS Berlin
2. – 4. November 2020 (WIAS-ESH)
Workshop/Konferenz: Workshop on Stochastic Geometry and Communications
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin