Seminars

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Time and place: May 7, 2021 12:15 PM1:00 PM, 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.

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).

Time and place: Apr. 9, 2021 12:15 PM1:00 PM, 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...

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).

Time and place: Mar. 26, 2021 12:15 PM1:00 PM, 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.

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).

Time and place: Mar. 12, 2021 12:15 PM1:00 PM, 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.

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).

Time and place: Feb. 26, 2021 12:15 PM1:00 PM, 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.​

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).

Time and place: Jan. 15, 2021 12:15 PM1:00 PM, Zoom

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.

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).

Time and place: Dec. 4, 2020 12:15 PM1:00 PM, Zoom

Abstract: Intraluminal vesicle (ILV) formation plays a crucial role in the attenuation of growth factor receptor signaling. The endosomal sorting complex required for transport (ESCRT-0 to -III/VPS4) mediates this process. The general dogma has been that upstream ESCRTs (0 to II) sequester receptors at the surface of endosomes and the downstream ESCRTs (III/VPS4) remodel the endosome membrane leading to the abscission and formation of receptor-containing ILVs. We now show that upstream ESCRTs not only sequester cargo, but in addition play a crucial role for the initiation of membrane shape remodeling in ILV budding. Through a combination of mathematical modeling and experimental measurements we show that upstream ESCRTs facilitate ILV budding by crowding with a high density in the membrane neck region.

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).

Time and place: Nov. 20, 2020 12:15 PM1:00 PM, Zoom

Abstract: Due to the fluid nature of biological membranes, proteins are able to diffuse along the membrane surface. Additionally, several processes of vesicle formation require protein recruitment.  We discuss, on one hand, the implications of fixed membrane shapes in protein diffusion, and on the other hand, the effects of protein diffusion and recruitment in membrane shape transformation. 

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).

Time and place: Nov. 13, 2020 12:15 PM1:00 PM, Zoom

Abstract: Magnetic Resonance Elastography (MRE) is an emerging technique to measure the bio-mechanical properties of tissue in vivo. We present measurements of the shear modulus in healthy subjects, and in patients with brain cancer.

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).

Time and place: Nov. 6, 2020 12:15 PM1:00 PM, Zoom

Abstract: Upon burst, air bubbles release droplets that transfer biological and chemical materials from water bodies to the atmosphere. This mechanism is one of the main sources of cloud condensation nuclei and participates to airborne contamination when the bulk water contains pathogens. Predicting the size and composition of droplets emitted by bubbles requires a fundamental understanding of their dynamic at the surface, yet a consistent physical picture is lacking. Relying on experimental data from bubbles generated in various environments and using scaling analysis, I will show that surface tension gradients control the drainage of bubbles. I will also explain how local perturbations of surface tension can explain their seemingly stochastic burst mechanism. Consequences for application purposes will be mentioned throughout the presentation: I will notably take the examples of bubbles in saltwater and in water contaminated with bacteria.

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).

Time and place: Oct. 23, 2020 12:15 PM1:00 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

 

Registration Link: https://nettskjema.no/a/167852 

Abstract: Frailty is a multi-system dysregulation leading to a loss of physiological reserve known to predict dementia. However, its link with neurodegenerative alterations of the central nervous system (CNS) is not well understood at present. We investigated the association between the biomechanical response of the CNS and frailty in older adults suspected of normal pressure hydrocephalus (NPH) presenting markers of multiple comorbid neurodegenerative pathologies, including pathologies of Alzheimer’s Disease. The biomechanical response of the CNS was characterized from phase contrast magnetic resonance imaging and intracranial pressure monitoring during a lumbar infusion test. Frailty was assessed with an index of health deficit accumulation. We found a significant association between the CNS biomechanical response and frailty, with an effect size comparable to that between frailty and age, the latter being the strongest known risk factor of frailty. The CNS biomechanical characterization may help to understand how frailty is related to neurodegeneration and detect the shift from normal to pathological brain ageing.

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

Time and place: Oct. 9, 2020 12:00 PM12:45 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

I will present some of my work on the solid-electrolyte interface. There, so-called electric double layers (EDLs) can form that consist of electrons on the solid screened by a diffuse cloud of ions in the adjacent liquid. EDLs are of paramount importance to many processes in physical chemistry, soft matter and biophysics, as well as in EDL capacitors and modern "supercapacitors". My work on EDLs focused on their (out-of-equilibrium) formation through questions like: 'On what timescale does an electrolyte respond to an applied temperature or voltage difference?', 'How does the (local) temperature in an electrolyte react to an applied electric field?', and 'How is the EDL affected by a change in temperature or salt concentration?'. I will show how answers to these questions suggest new methods for harvesting sustainable energy, for instance, from the controlled mixing of seawater and river water.

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

Registration Link:  https://nettskjema.no/a/161232

 

Time and place: Sep. 18, 2020 12:00 PM12:45 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

DuMux  (short for "Dune for Multi- {Phase, Component, Scale, Physics,…} flow and transport in porous media") is  a free and open-source simulator for flow and transport processes in porous media. DuMux is modern C++ code based on the scientific software framework Dune (Distributed and Unified Numerics Environment) and has a focus on modularity and reusability. 

The main features and ideas behind DuMux will be introduced with several examples from recent research projects.

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

Registration Link:  https://nettskjema.no/a/161230

 

Time and place: Aug. 9, 2018 11:15 AM12:00 PM, NHA 919

Christophe Henry

Post doc at Observatoire de la Cote d'Azur, Laboratoire Lagrange

Time and place: Feb. 14, 2018 3:15 PM4:00 PM, End of the line, Ullevål Stadion

Soft and Wet is Different

Time and place: Jan. 9, 2018 1:15 PM2:00 PM, Ullevål End of the Line

Emerging instabilities and bifurcations from deformable fluid interfaces in the inertialess regime 

In this talk, I will present two studies regarding the dynamics of droplets in the creeping flow, focusing on the arising instability and bifurcation phenomena. The first work investigates a buoyancy-driven droplet translating in a quiescent environment and the second a particle-encapsulating droplet in shear flow. There-dimensional simulations based on versatile boundary integral methods were employed to explore the intriguing instability and bifurcation phenomena in the inertialess flow. In the first work, a non-modal stability analysis was performed to predict the critical condition of instability; and in the second, a dynamic system approach was adopted to model and characterize the interacting bifurcations.

Time: Nov. 24, 2017 11:30 AM12:00 PM

Andreas Carlson og Jean Rabault

Nature has invented ingenious aerodynamic design solutions, some of which are critical for plants as wind dispersal of seeds and fruits is coupled to their flight performance. This formulates into an optimization problem for plants: large seed wings can lead to increased lift and more efficient dispersion, but are costly for the tree to build and can more easily be trapped in the canopy. Double winged seeds/fruits separate from their tree when a specific level of dessication is reached, and autorotate as they descend to the ground. This leads to the question: how is the wing curvature of seeds/fruits linked to their flight performance? To answer this, we develop a theoretical model that suggests the existence of an optimal wing curvature that yields maximal lift. To further understand the interplay between the flow and the wing geometry, we perform a synthetic seed adaptation by deploying 3D printing of double winged fruits that we use in flight experiments, where we span the phase space of aerial dynamics by changing the of wing curvature and seed/fruit weight. Experiments confirm that there is a sweet-spot in curvature to maximise the flight time consisted with geometrical measurements from a wide range of seeds in Nature. Our results highlights the importance of not curving too much or too little for helicopter fruits to have an optimal flight performance.

Time: Nov. 24, 2017 11:00 AM11:30 AM

Elisabeth Seland

In my job as research adviser, I receive a lot of questions about rights, possibilities and problems in connection with scientific publishing and open access. Both EU and the Norwegian Research Council have rules about this, and there is also a UiO policy in place that is relevant for all employees. I will give a short presentation to try to clear up what you have to, must, may, could and should related to Open access. In my experience many of you have the same questions about these issues, so I hope you bring your questions with you and we can address them in the seminar.

Time and place: Nov. 2, 2017 10:15 AM11:00 AM, Gates of Eden

When and how surface structure determines the dynamics of partial wetting  

Time and place: Oct. 30, 2017 3:15 PM4:00 PM, Hurricane

Sedimentation-diffusion equilibrium of Quincke rollers  

Time and place: Oct. 27, 2017 1:00 PM2:00 PM, hurricane

Iceberg drift on dead water

Time and place: Oct. 20, 2017 11:15 AM12:00 PM, Hurricane

Reyna Ramirez

Time and place: Sep. 15, 2017 11:15 AM12:00 PM, Hurricane
Time and place: May 12, 2017 11:15 AM12:00 PM, NHA bygget 9 etg B91

Study of the air-flow very close to the surface of wind-generated water waves Marseille large air-water facility

Time and place: Apr. 28, 2017 11:15 AM12:00 PM, NHA bygget 9 etg B91

Activity at IFE Wind Energy: numerical modeling of offshore wind turbines

IFE (Institutt for Energiteknikk) is a research center located in Kjeller. The wind group at IFE mainly works with the development and analysis of new cost effective concepts for offshore wind energy, both concerning innovative rotor designs and new concepts for substructures. The group main investigation tool is the in-house software 3DFloat, an aero-elastic code which can simulate the whole wind turbine structure when exposed to the associated environmental loads (wind loads, hydrodynamic loads, soil loads if bottom-fixed).

In the presentation, an insight into the wave kinematics and wave loads modeling tools that are currently included in 3DFloat will be provided.