Seminarer - Side 4
Abstract: It is known that a sessile drop subject to a forced vibration will vibrate in different shapes depending on the frequency of the forcing, the drop’s liquid properties and the liquid/solid/gas system. So the question then becomes, what can these vibrating drops help us understand? Here we find that we can use the motion of these drops to understand the constitutive law relating the drop’s apparent dynamic contact angle to its contact line velocity. We find we are able to extract mobility parameters like those described by the Davis-Hocking model, and that mobility parameters extracted in this fashion can be used in simulations of drop-drop coalescence to accurately predict post-coalescence dynamics.
This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting and bring-your-own-lunch.
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).
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).
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).
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.
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: 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).
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.
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: 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).
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).
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).
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).
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).
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).
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.
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
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
Title: Recent advances in Deep Reinforcement Learning applied to Active Flow Control, by Jean Rabault
Title: Numerical studies of rheology and elasticity, by Prof Luca Brandt, Linnè FLOW Centre and SeRC (Swedish e-Science Research Centre), Department of Engineering Mechanics, KTH, Stockholm.
Title: Experimental investigation of droplet trajectories and airflow above breaking waves, by Reyna Guadalupe Ramirez de la Torre
Abstract: Within the marine boundary layer the interaction between air and water is constant and takes different forms. An interesting example is the artic ocean spray, generated by wave impact and wind, which can cause severe icing on vessels. Understanding this phenomenon is important for the safety of people, ships and installations that operate in the arctic environment.
In this study we performed lab-scale experiments of breaking waves, to describe the trajectories of the droplets in the spray generated by wave impact and wind. Focusing waves generated by a wavemaker provided highly repeatable wave breaking events. A fan was used to produce wind within a closed section above the waves. The airflow over breaking waves was measured using Particle Image Velocimetry, while 3D Particle Tracking Velocimetry was used to reconstruct the droplets trajectories. The main objective is to understand the dynamics and characteristics of the spray cloud under different wind conditions. The results of these experiments can be an important input for simulations, and in the future assist the the development of accurate models which can be used to reduce the risk associated with icing of arctic structures.
Prof S. Balachandar, Department of Mechanical and Aerospace Engineering, University of Florida
Title Center for Compressible Multiphase Turbulence and An Improved Point-Particle Approach that Captures Fully-Resolved Physics
Title: The role of perception in models of movement, by Dr. Renaud Bastien, Max Planck Institute
Title: Modeling the drift and radar backscatter signature of icebergs, by Ron Saper, Carleton University, Canada.
Abstract: Icebergs are a source of wonder and mystery, and hide many mysteries that remain to be solved. In the quest to observe icebergs remotely and predict their behaviour, many difficulties are encountered and, at every turn, we find the expectations of engineers and researchers are frustrated. In this wide-ranging talk the many misconceptions and fallacies about icebergs are surveyed and analyzed, and their impact on scientific research and practice are explained and reflected upon. Examples are drawn from iceberg drift forecasting, remote sensing, and iceberg tracking studies.