Elastic snap-through instabilities are governed by geometric symmetries.
Orateur : Basile Radisson
Abstract : While shape transitions in elastic structures are known to be related to the type of bifurcation the system undergoes \citegomez2017, sano2018, there is no general understanding of the mechanisms that select these bifurcations. In this work, we analyze numerically and analytically a set of simple systems in which an elastic strip is initially maintained in a buckled state and driven through shape transitions by either translating or rotating its boundaries. We first identify the relevant frame of reference to analyze this kind of problem and extract three configurations that illustrate the entire range of shape transitions described by previous authors. For each of these systems, we establish the nature of the bifurcation they undergo using reduction order methods and provide the evidence that the selection of these standard bifurcation forms is governed only by the geometrical symmetries of the system. Being based solely on the universal concept of symmetry, these findings are likely expandable to more complex systems and could be applied to design new metamaterials that can change their shapes on demand.
There’s a bug in my supercomputer : what numerical simulation can teach us about insect flight.
Orateur : Thomas Engels
Abstract : Flying insects, spectacular little flapping machines with enormous evolutionary success, are an invaluable source of inspiration for a large, interdisciplinary community of scientists. The aerodynamic mechanisms they use for propulsion are quite different from human-designed flying machines, and many aspects of their locomotion are not yet understood. In this talk, I will present my work on numerical modeling and simulation of the aerodynamics of flapping insects using national-scale supercomputers. I will elaborate where this research is located in the pluridisciplinary landscape of insect flight, illustrate what insight numerical simulations can contribute to our knowledge and discuss why such simulations are highly challenging. Results on bumblebees flying in heavy turbulence will be shown, demonstrating that flapping flight in turbulence is a problem for flight control, but not for force production. I will conclude with the latest results on the peculiar flight of some of the smallest insects. They often feature bristled wings that have lost almost their entire membrane. Yet, those animals fly surprisingly well, and I discuss what trade-offs they made.
Date et lieu : le jeudi 17/03 10h00, en ligne sur Zoom.