Events - Page 10

In recent years there have been numerous studies on floating films of non-Newtonian fluids due to their application to model the stability of floating ice shelves. Sayag & Worster (2019) showed theoretically that expanding cylinders of shear-thinning fluids can become non-axisymmetrical at the advancing fluid edge, driven by their non-Newtonian rheology. This instability carries over to radially spreading, thinning films of the same material when that fluid floats on a deeper bath of less viscous, but denser, Newtonian fluid.

Experimentally validating these theoretical results has, however, been challenging. Initial experimental exploration using Xanthan gum floating on a dense bath of salt solution shows dramatic non-axisymmetrical patterns. These patterns have their origin in interfacial effects, rather than Sayag & Worster's instability, with the expanding film appearing to fracture under extensional stresses at the fluid edge (Ball et al., 2022).

In this talk, I will present a new set of experiments exploring the instability, in which spreading films of aqueous suspensions of Carbopol and Xanthan gum are floated on a bath of more dense perfluorinated oil. The immiscibility between the bath and floating film prevents the failure of the material under tension and allows comparison against theoretical predictions from a shallow film model (Ball & Balmforth, 2021; Ball & Balmforth 2025).

The Tien Mai is currently a postdoc at FHI. He has held postdoc positions in statistics at NTNU (Trondheim) and in biostatistics at UiO (OCBE). His research spans statistics and machine learning, with a particular interest in PAC-Bayesian analysis. He holds a PhD in Statistics from CREST-ENSAE-ParisTech/Paris Saclay and University College Dublin.

Doctoral candidate Boxue Zheng at the Department of Mathematics will be defending the thesis Soft wetting phenomena:
exploring the effects of substrate geometry and poro-viscoelasticity for the degree of Philosophiae Doctor.

Mauro Di Nasso, University of Pisa, will give a talk in the Logic Seminar

Doctoral candidate Anna Piterskaya at the Department of Mathematics will be defending the thesis Plasma Instabilities and Turbulence with Magneto-Hydrodynamics and Spectral Numerical Simulations for the degree of Philosophiae Doctor.

Anders Kvellestad is a Researcher in theoretical physics at the Department of Physics and head of the GAMBIT Collaboration. His research focuses on how to test new theories against results from the Large Hadron Collider and other experiments, using both frequentist and Bayesian approaches, and the computational challenges related to this work. Anders completed his PhD at the University of Oslo in 2015 and has since held postdoctoral positions at Nordita (Stockholm), Imperial College London and UiO.

Since 2021 he has lead the GAMBIT Collaboration, an international collaboration of physicists working on global fit analyses. He is also part of the PLUMBIN’ project at UiO, which aims to develop new computational and statistical tools for particle physics and beyond.

Multiphase flow in pipes is very complex due to the large number of parameters involved. Differences in phase combinations (e.g. gas-liquid-liquid) and inclination angle can significantly affect the flow regime within the pipe. This in turn can lead to differences in demand on pressure support systems or other facilities. Therefore, accurate estimation of the flow behaviour is crucial for equipment design and operational safety of the production. In this talk, various experimental measurement techniques for monitoring multiphase flow in pipes will be discussed that are currently in use at the Well Flow Loop installation at IFE, Kjeller. In addition, some results from the ongoing research project focusing on flow in steeply inclined pipes will be shown.

Based on the preprint Bhatt, Iyengar, Ma - Regular rings and perfectoid algebras. Notes for the lecture here.

Doctoral candidate Anders Dahl Hjort at the Department of Mathematics will be defending the thesis Advances in predictive modeling with tree-based machine learning: applications to automated valuation models for the degree of Philosophiae Doctor.

QOMBINE seminar by Håkon R. Fredheim (University of Oslo)

Qombine presentation by Delphine Martres (UiO): postponed to 5 March 2025

Recent advances in experimental techniques have enabled remarkable discoveries and insight into how the dynamics of thin gas/vapour films can profoundly influence the behaviour of liquid droplets: drops impacting solids can “skate on a film of air” [1], so that they can “bounce off walls” [2,3]; reductions in ambient gas pressure can suppress splashing [4] and initiate the merging of colliding droplets [5]; and evaporating droplets can levitate on their own vapour film [7] (the Leidenfrost effect). Despite these advances, the precise physical mechanisms governing these phenomena remain a topic of debate.  A theoretical approach would shed light on these issues, but due to the strongly multiscale nature of these processes brute force computation is infeasible.  Furthermore, when films reach the scale of the mean free path in the gas (i.e. ~100nm) and below, new nanoscale physics appears that renders the classical Navier-Stokes paradigm inaccurate.

In this talk, I will overview our development of efficient computational models for the aforementioned droplet dynamics in the presence of gas nanofilms into which gas-kinetic, van der Waals and/or evaporative effects can be easily incorporated [8,9].  It will be shown that these models can reproduce experimental observations – for example, the threshold between bouncing and wetting for drop impact on a solid is reproduced to within 5%, whilst a model excluding either gas-kinetic or van der Waals effects is ~170% off!  These models will then be exploited to make new experimentally-verifiable predictions, such as how we expect drops to behave in reduced pressure environments.  Finally, I will conclude with some exciting directions for future work.

[1] JM Kolinski et al, Phys. Rev. Lett.  108 (2012), 074503. [2] JM Kolinski et al, EPL.  108 (2014), 24001. [3] J de Ruiter et al, Nature Phys.  11 (2014), 48. [4] L Xu et al, Phys. Rev. Lett. 94 (2005), 184505. [5] J Qian & CK Law, J. Fluid. Mech. 331 (1997), 59.  [6] KL Pan J. Appl. Phys. 103 (2008), 064901. [7] D Quéré, Ann. Rev. Fluid Mech. 45 (2013), 197.  [8] JE Sprittles, Phys. Rev. Lett.  118 (2017), 114502.  [9] MV Chubynsky et al, Phys. Rev. Lett.. 124 (2020), 084501.
Much of this work is based on a recent Annual Review: JE Sprittles, Ann. Rev. Fluid Mech. 56 (2024), 91.

Doctoral candidate Ola Sande at the Department of Mathematics will be defending the thesis Hyperétale Framed Correspondences for the degree of Philosophiae Doctor.

The internal waves in consideration are generated locally in combination by:
1) the North Atlantic Current (NAC) that flows along the Norwegian shelf (average speed 0.3 m/s),
2) the local tide (dominant 24 hr mode),
3) the particular shelf geometry,
4) the seasonal pycnocline (at 20 m depth). The typical amplitude is 50 m. The local depth where they exist is 100 m (approx.).
The local internal wave speed of 0.4 m/s is comparable to the current speed.

The wave generation process occurs in a sequence of:
A) locally large depressions of the internal tide occurring at the lee side of two shallow ridges,  
B) the depressions are orthogonal to the current,
C) the depressions move slowly against the current, and
D) eventually fission into nonlinear-dispersive wave groups,
E) they propagate upstream against the current,
F) they are recorded on satellite images and is visible by eye.
 

In a recent RCN-funded project (ECOPULSE) 2020-2023 including research groups at UiO, the Norwegian Meteorological Institute and the Institute of Marine Research in Bergen, field experiments of the mother wave in points A) and C) were undertaken during July-September 2021 and 2022. The measurements show that the waves break and mix in the entire water column by convective breaking in the upper part of the water column, shear instability within the pycnocline, and by a variant of a shear instability near the bottom. The field measurements document the local wave properties and the initial phase of the fission process. The Vesterålen-Lofoten area is of immense political interest because of a) its traditional fisheries and breeding ground for the North Atlantic and Barents Sea Cod and other species, where also a cold water coral reef is located right where these waves are generated.  The waves do also extend across NORDLAND VII, an oil / gas field which may be considered for exploitation. Preliminary results will be presented.

C*-algebra seminar by David Jaklitsch (University of Oslo).

Doctoral candidate Lars Henry Berge Olsen at the Department of Mathematics will be defending the thesis What’s in the Black Box?
Improving the Shapley Value Explanation Methodology for the degree of Philosophiae Doctor.