Veranstaltungen

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Mittwoch, 13.02.2019, 10:00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Professor A. Cohen, Université Pierre et Marie Curie, Paris, France:
Optimal non-intrusive methods in high-dimension
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Motivated by non-intrusive approaches for high-dimensional parametric PDEs, we consider the approximation of an unknown arbirary function in any dimension from the data of point samples, where the approximants are picked from given or adaptively chosen finite dimensional spaces. One principal objective is to obtain an approximation which performs as good as the orthogonal projection using a sampling budget that is linear in the dimension of the approximating space. Using a particular sampling measure, this objective turns out to be met by both least-squares and pseudo-spectral methods in some probabilistic sense, however with some notable distinctions that will be discussed in this talk.

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Mittwoch, 13.02.2019, 11:30 Uhr (WIAS-406)
Seminar Interacting Random Systems
P. Neijjar, Institute of Science and Technology Austria (IST Austria), Österreich:
Product limit laws at shocks in (T)ASEP
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
We consider the asymmetric simple exclusion process (ASEP) on Z with an initial data such that in the large time particle density r a discontinuity at the origin is created, where the value of r jumps from zero to one, but r (resp. 1-r) is strictly positive to the left (resp. right) of the origin. We consider the position of a particle macroscopically located at the discontinuity, and show that its limit law has a cutoff at the origin. Inside the discontinuity region, we show that a discrete product limit law arises, which bounds from above the limiting fluctuations of the particle in the general ASEP, and equals them in the totally ASEP. Sending the size of the shock region to infinity, we recover the product of GUE distributions previously observed at shocks in the totally ASEP.

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Seminar Interacting Random Systems

Veranstalter
WIAS Berlin
Mittwoch, 13.02.2019, 15:15 Uhr (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. A. Mielke, WIAS Berlin:
On similarity solutions for Kolmogorov's two-equation model for turbulence
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Humboldt-Universität zu Berlin
Donnerstag, 14.02.2019, 14:30 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
P. Schroeder, Georg-August-Universität Göttingen:
Building bridges: Pressure-robust FEM, Beltrami flows and structure preservation in incompressible CFD
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
In this talk, an attempt is made to explain why pressure-robust FEM are (by construction) superior when it comes to simulating incompressible flows with a large amount of large-scale/coherent structures. We show that flows with large-scale structures are frequently dominated by large gradient (curl-free) forces. Pressure-robust methods are designed in exactly such a way that they can treat those forces more accurately than non-pressure-robust methods. Furthermore, the class of generalised Beltrami flows is introduced and placed in context with structure preservation and pressure-robustness. Several numerical examples, both in 2D and in 3D, of laminar and turbulent flows, are shown which underline our statements. All pressure-robust computations make us of (high-order) exactly divergence-free H(div)-(H)DG methods.

Veranstalter
WIAS Berlin