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Soutenance de Thibault Lestang

When Sep 25, 2018
from 02:00 to 04:00
Where Salle Fontaine
Contact Name Thibault Lestang
Attendees Thibault Lestang
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This thesis discusses the numerical simulation of extreme fluctuations of the drag force acting on an object immersed in a turbulent medium.

Because such fluctuations are rare events, they are particularly difficult to investigate by means of direct sampling. Indeed, such approach requires to simulate the dynamics over extremely long durations. In this work an alternative route is introduced, based on rare events algorithms. The underlying idea of such algorithms is to modify the sampling statistics so as to favour rare trajectories of the dynamical system of interest. These techniques recently led to impressive results for relatively simple dynamics. However, it is not clear yet if such algorithms are useful for complex deterministic dynamics, such as turbulent flows. This thesis focuses on the study of both the dynamics and statistics of extreme fluctuations of the drag experienced by a square cylinder mounted in a two-dimensional channel flow. This simple framework allows for very long simulations of the dynamics, thus leading to the sampling of a large number of events with an amplitude large enough so as they can be considered extreme. Subsequently, the application of two different rare events algorithms is presented and discussed. In the first case, a drastic reduction of the computational cost required to sample configurations resulting in extreme fluctuations is achieved. Furthermore, several difficulties related to the flow dynamics are highlighted, paving the way to novel approaches specifically designed to turbulent flows.