BesøksadresseNiels Henrik Abels hus (kart) Moltke Moes vei 35
Foredragene høsten 2018 vil normalt finne sted på fredager 11.15-12.00 i seminarrom B91, 9. etasje i matematikkbygningen.
Programmet annonseres her og per epost til avdeling for mekanikk etterhvert som det blir klart.
Title: Taming nonlinear dynamics using Deep Reinforcement Learning
by: Jean Rabault, Miroslav Kuchta, Ulysse Réglade and Nicolas Cerardi
Abstract: Machine Learning (ML) methods are a promising way to perform optimal control. In a recent book ('Machine Learning Control - Taming Nonlinear Dynamics and Turbulence', Duriez et. al., 2017), several ML methods were presented as well as a couple of benchmarks. One particular benchmark is a small system of ODEs that present features, such as multimodality and cross-talks, that are representative of more complex systems found in Fluid Mechanics.
In this seminar, we present ongoing work about active control of this system of ODEs.
Post doc at Observatoire de la Cote d'Azur, Laboratoire Lagrange
Soft and Wet is Different
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.
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.
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.
When and how surface structure determines the dynamics of partial wetting
Sedimentation-diffusion equilibrium of Quincke rollers
Iceberg drift on dead water
Study of the air-flow very close to the surface of wind-generated water waves Marseille large air-water facility
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.
Bioprocessing of marine and agricultural by-products
Perfeksjon fra bønne til kopp
Hvordan jobber Tim Wendelboe i sin jakt på den perfekte kopp med kaffe?
Tim er både kaffebonde, kaffebrenner og barista og vil gi deg et lite innblikk i alt arbeidet som ligger bak hver kopp kaffe som serveres i hans kaffebar på Grünerløkka.
Large Eddy Simulation of the interaction of water waves with turbulent air flow
Stereolithography - A Powerful Tool to Create almost Everything
Stereolithography or "SLA" printing is a powerful and widely used 3D printing technology for creating prototypes, models, and fully functional parts for production. This additive manufacturing process works by focusing an ultraviolet (UV) laser onto a vat of liquid resin. Layer by layer formation of a polymeric network allows printing parts that are almost impossible to create with other processes.At Formlabs, a startup that originated out of the MIT Media lab in 2011, we work on all aspects of SLA printing; we develop and manufacture 3D printers, resins, and software. In this talk, I will give a detailed overview of the printer technology, the chemistry of the materials, and how to use SLA for lots of exciting applications.
Microfluidics of sugar transport in plants
Plants can rightly be called masters of microengineering. Their survival and successful reproduction depends on their ability to overcome a series of physical challenges during growth and when transporting matter over great distances. In this talk, we focus on the microfluidic network responsible for energy distribution (the phloem). We combine experiments on living plants and biomimetic microfluidic devices to elucidate the basic physical principles that govern sugar transport in plants. We derive a scaling relation between the characteristic sizes of the plant organs, which optimizes the rate of sugar transport. Comparison with experimental data suggests that the pipe network is operating at or near the theoretical optimum. We further consider the coupling between photosynthesis and long-distance transport. While sap with high sugar concentration has the greatest transport potential, viscosity impedes flow, a phenomena analogous to congestion in traffic flows. The optimal sugar concentration for transport in plants is 25%, sweeter than Coke (10%) but much less viscous than maple syrup (65%). Although plants have generally evolved towards the theoretical optimum, a number of unusually sweet plants exist. This group consists primarily of crop plants such as corn (40%) and potato (50%), sugar junkies of the natural world.
Digital signalbehandling og bildeanalyse, UiO and PGS
The effects of moving rough sea surfaces on seismic data.
Enrico Fermi and the birth of modern nonlinear physics
In the early fifties in Los Alamos E. Fermi in collaboration with J. Pasta and S. Ulam investigated a one dimensional chain of equal masses connected by a weakly nonlinear spring. The key question was related to the understanding of the phenomenon of conduction in solids; in particular they wanted to estimate the time needed to reach a statistical equilibrium state characterized by the equipartition of energy among the Fourier modes. They approached the problem numerically using the MANIAC I computer; however, the system did not thermailize and they observed a recurrence to the initial state (this is known as the FPU-recurrence). This unexpected result has led to the development of the modern nonlinear physics (discovery of solitons and integrability). In this seminar, I will give an historical overview of the subject and present the different approaches that have been proposed in the last 60 years for explaining this paradox. Very recent results on the estimation of the time scale and on the explanation of the mechanism of equipartition will also be discussed.
Experimental investigation of linear stability mechanisms in stratified gas-liquid pipe flow
The evolution of interfacial waves on a stratified air water pipe flow is investigated experimentally. An oscillating plate introduced controlled perturbations at the inlet of the pipe. High speed cameras captured the evolution of these perturbations along the pipe by means of a phase-locked shadowgraphy technique. Thereby, it was possible to measure the temporal and the spatial evolution of the disturbances introduced in the flow. Particle image velocimetry was performed further downstream in order to evaluate changes in the base flow.
A relatively large data bank has been gathered with varying air and water flow rates as well as varying amplitudes and frequencies of the inlet perturbations. Some preliminary results contain a qualitative assessment of linear vs. non-linear regimes and momentum transfer into the water layer.