## Besøksadresse

Niels Henrik Abels hus (kart)Moltke Moes vei 35

0851 OSLO

English version of this page
# Gjesteforelesninger og seminarer

## Tidligere

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Tid og sted:
25. juni 2021 12:15–13:00,
Zoom

**Abstract:** *Efficient and parameter robust solvers for multiscale/multiphysics systems, where the coupling is enforced by the Lagrange multipliers, rely on operators in fractional Sobolev spaces defined over the interface. Arguably, this feature is not unexpected as there is explicit coupling/an interfacial variable in the system. However, in this talk we show that even for coupled problems free of Lagrange multipliers the fractional operators are a crucial component for constructing robust preconditioners. Stokes-Darcy/Biot systems will be discussed.*

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
18. juni 2021 12:15–13:00,
Zoom

**Abstract:** *New estimates of heat loss from Earth's interior (the mantle) suggest that the Pacific side of the planet has been losing heat at a much higher rate compared to the African side. The difference in heat loss amounts to almost 50 degrees more cooling of the Pacific side over the past 400 million years.*

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
11. juni 2021 12:15–13:00,
Zoom

**Abstract:** Magmatic intrusions into the earth's crust lead to geological formations such as sills, laccholites and volcanoes. The conventional approach is to threat the intrusive fluid as Newtonian and viscous, while the host-rock is assumed to behave purely elastic. However, Magma is known to have non-Newtonian properties. In addition, field studies indicate that visco-elastic deformation of the host rock is an important effect in the propagating fracturing. We thus want to investigate the effect of introducing a yield-stress fluid in the intrusion process. We perform an experiment based on the elasto-hydro-dynamical approach, but where we change the injected fluid from a viscous (glycerol) to a yield-stress fluid (carbopol). We are interested in seeing how this potentially can change the dynamics of the intrusion compared with the viscous case.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
25. mai 2021 14:00–15:00,
Zoom

C*-algebra seminar talk by Magnus Goffeng

Florian Arbes: Non-intrusive reduced order modelling of parameterized partial differential equations

Tid og sted:
21. mai 2021 12:15–13:00,
Zoom

**Abstract:** In computational mechanics, high fidelity simulations of a parameterized partial differential equation (PDE) are often computational expensive, which make them impractical for real-time predictions. Non-intrusive reduced order modelling aims to address this problem with a fast low rank approximation. This is usually done in two phases: the model is built in the *offline* phase and the prediction is done in the *online* phase. In the offline phase, data points, or so-called snapshots, are collected from simulations or measurements. The reduced basis space can then be obtained from the dataset using Proper Orthogonal Decomposition. In the online phase, the solution for a new set of parameters is obtained by first recovering the expansion coefficients for the reduced basis and then projecting them back into the uncompressed real-life space. The non-intrusive approach relies on a statistical mapping between the coefficients and the parameters. Various methods have been proposed to do so, this seminar will discuss radial basis function interpolations and dynamic mode decompositions.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
11. mai 2021 14:00–15:00,
Zoom

C*-algebra seminar talk by Ulrich Pennig

Tid og sted:
7. mai 2021 12:15–13:00,
Zoom

**Abstract:** Graphics processing units, or GPUs, offer significantly increased performance for some scientific computing workloads. But in the case of finite element simulations on unstructured meshes, the benefits of using GPUs are still the subject of an ongoing discussion for which there is no clear conclusion. We describe our work on improving the GPU acceleration of a finite element solver framework called FEniCS, where code is automatically generated for the user from a high-level description of their finite element problem. We use automated code generation to offload the assembly of linear systems to a GPU, while taking care that data transfers between CPU and GPU do not become a performance bottleneck. We provide examples to show that GPUs and automated code generation can be used to accelerate finite element solvers. Even though more work is needed to find efficient GPU-based linear solvers, our improvements to FEniCS can be used as a starting point for exploring the potential of GPU acceleration for finite element simulations.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
27. apr. 2021 21:00–22:00,
Zoom

C*-algebra seminar talk by Rufus Willett

Tid og sted:
9. apr. 2021 12:15–13:00,
Zoom

**Abstract:**Due to their large mass and small aspect ratio, icebergs pose a threat to boats and offshore structures. Small icebergs and bergy bits can cause harm to platform hulls and are more difficult to discover remotely. When there is a risk of collision between icebergs and platforms, it is necessary to deflect its drifting course to ensure safe human operations in polar offshore regions. In this talk, I will present iceberg towing experiments carried out on Svalbard in September 2020...

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
26. mars 2021 12:15–13:00,
Zoom

**Abstract:** We report on the observation of gravity-capillary wave turbulence on the surface of a fluid in a high-gravity environment. By using a large-diameter centrifuge, the effective gravity acceleration is tuned up to 20 times Earth’s gravity. The transition frequency between the gravity and capillary regimes is thus increased up to one decade as predicted theoretically. A frequency power-law wave spectrum is observed in each regime and is found to be independent of the gravity level and of the wave steepness. While the timescale separation required by weak turbulence is well verified experimentally regardless of the gravity level, the nonlinear and dissipation timescales are found to be independent of the scale, as a result of the finite size effects of the system (large-scale container modes) that are not taken currently into account theoretically.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
12. mars 2021 12:15–13:00,
Zoom

**Abstract:** I will present a Biot-Stokes formulation created by Ricardo Ruiz-Baier. The formulations consists of a fluid-structure interaction model for flow of a Newtonian fluid, coupled with Biot consolidation equations through an interface, and incorporates total pressure as an unknown in the poroelastic region. I will also present a preconditioner for this system which is robust in all parameters and apply the model to a third circulation process to show the velocity fields in the brains subarachnoid space.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Tid og sted:
10. mars 2021 11:00–12:00,
Zoom

C*-algebra seminar talk by Bram Mesland (Leiden)

Tid og sted:
3. mars 2021 11:00–12:00,
Zoom

C*-algebra seminar talk by Karen Strung (Prague)

Tid og sted:
26. feb. 2021 12:15–13:00,
Zoom

**Abstract:** If a droplet smaller than the capillary length is placed on a substrate with a conical shape, it spreads by itself in the direction of growing fibre radius. We describe this capillary spreading dynamics by developing a lubrication flow approximation on a cone and by using the perturbation method of matched asymptotic expansions. The droplet velocity is found to increase with the cone angle but decrease with the cone radius. We show that a film is formed at the receding part of the droplet, much like the classical Landau–Levich–Derjaguin film. By using the approach of matching asymptotic profiles in the film region and the quasi-static droplet, we obtain the same film thickness as the results from the lubrication approach. Our results show that manipulating the droplet size, the cone angle and the slip length provides different schemes for guiding droplet motion and coating the substrate with a film.

**Zoom: **To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).