# Tidligere arrangementer

C*-algebra seminar talk by Ulrich Pennig

**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.

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).

C*-algebra seminar talk by Rufus Willett

**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...

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).

**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.

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).

**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).

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

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

**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).

C*-algebra seminar talk by Amine Marrakchi (Lyon)

C*-algebra seminar talk by Yoshimichi Ueda (Nagoya)

C*-algebra seminar talk by Olof Giselsson

**Abstract:** Physics-informed neural networks (PINNs) are a new and promising methodology to combine deep learning with partial differential equations (PDE). PINNs extend deep neural networks by regularizing their output to fulfill any given PDE, allowing to solve both forward and inverse PDE problems utilizing high-performance machine learning libraries such as Tensorflow and PyTorch. This talk will give a short introduction to PINNs and provide a detailed, tutorial-style code demonstration on their implementation in PyTorch.

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

C*-algebra seminar talk by Siegfried Echterhoff (Muenster)

You are welcome to attend a two days online workshop on the topic

**"Rough Paths and Stochastic Partial Differential Equations". **

William Robert Paul Denault (Department of Genetics and Bioinformatics, Norwegian Institute of Public Health) will give a talk on December 8th at 14:15 ~~(held with restricted attendance in the Erling Sverdrups plass, Niels Henrik Abels hus, 8th floor and streamed~~ in Zoom - the link will be sent by mail one day in advance).