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These seminars (unless otherwise stated) will take place on Wednesdays at 4pm in Maths Room 707 (25 Gordon Street) on a bi-weekly basis - see the map for further details.
24 Oct 2018
Speaker: Jurriaan Gillissen (UCL)
Title: Contact Forces and Normal Stresses in Particle Suspensions
Abstract:
A model is presented for particle suspension microstructure and stress, that includes hydrodynamic and contact interaction forces. The model provides an explanation for experimental observations of the first normal stress difference in shear thickening suspensions.
31 Oct 2018
NO SEMINAR
07 Nov 2018
Speaker: Tom Grylls (Imperial College London)
Title: Towards an integrated large-eddy simulation model for urban pollution dispersion
Abstract:
Air quality is the largest single environmental health risk globally. Computational modelling presents an integral tool in understanding and facing the challenge of urban air quality as cities continue to grow and become more dense. The unsteady and turbulent nature of the urban flow field alongside the range of temporal and spatial scales associated with the urban environment result in a complex and computationally demanding modelling problem.
The large-eddy simulation model, DALES, has been adapted and simulation capabilities have been developed to investigate the dominant factors determining local air quality within a city (e.g. urban morphologies, atmospheric stability, chemistry and trees) at the highest possible resolutions. Progress to date is presented including 1) a methodology to produce steady-state non-neutral planetary boundary layers, 2) a minimal tree model with which to investigate the role of vegetation (e.g. drag, evapotranspiration, deposition) within the urban canopy layer and 3) an evaluative case study over South Kensington, London against the operational street network model SIRANE.
14 Nov 2018
NO SEMINAR
21 Nov 2018
Speaker: Sean Jamshidi (UCL)
Title: Steady states in geostrophic adjustment
Abstract:
One of the classical questions in ocean and atmospheric dynamics is; given an initially unbalanced pressure distribution (due to a gradient in density, height, temperature etc) how does fluid adjust to a balanced state under the influence of the Earth’s rotation? In this talk, I will present some simple models that have been used to answer this question in an ocean setting. I will outline the basic principles and philosophy that direct the approach (balance of forces, conserved quantities, reduction to an algebraic system), and then discuss steady states for a number of particular cases including: the creation of capped eddies, the structure of the thermocline in a lake, and how topography and coastal geometry can affect adjustment.
28 Nov 2018
Speaker: Liam Escott (UCL)
Title: Particle migration induced by quadratic flow in non-Newtonian fluid.
Abstract:
It seems self evident to say that upon placing a solid particle in a stream with parallel walls, under uni-directional flow, the particle will simply flow downstream. Its position relative to both walls will remain constant. However, all I have to do is state that the fluid is no longer water, and such assurances become dubious at best. In this talk, I shall show that a particle in Second Order fluid (non-Newtonian) does not follow the streamlines exactly, that is to say migrates in a direction other than that of the flow. In the proceedings, I will outline the tensorial method used, and display results in a particular quadratic background flow, which may be found in flows past a corner, and in plate-plate rheometers.
05 Dec 2018
Speaker: Laura Cope (University of Cambridge)
Title: Variability of Stochastically Forced Zonal Jets
Abstract:
Turbulent flows on a beta-plane lead to the spontaneous formation and equilibration of persistent zonal jets. However, the equilibrated jets are not steady and the nature of the time variability in the equilibrated phase is of interest both because of its relevance to the behaviour of naturally occurring jet systems and for the insights it provides into the dynamical mechanisms operating in these systems. Variability is studied within a barotropic model, damped by linear friction, in which stochastic exogenous forcing generates a kind of turbulence that in more complicated systems would be generated by internal dynamical instabilities such as baroclinic instability. This nonlinear (NL) system is used to investigate the variability of zonal jets across a broad range of parameters. Comparisons are made with a reduced quasilinear (QL) system, where eddy-eddy interactions are neglected, permitting only nonlocal interactions between eddies and the zonal mean flow. Both systems reveal a rich variety of jet variability. In particular, the NL model is found to admit the formation of systematically migrating jets, a phenomenon that is observed to be robust in subsets of parameter space. Jets migrate north or south with equal probability, occasionally changing their direction of migration.