Le 4 septembre 2023
Benjamin Apffel (Ecole Polytechnique Fédérale de Lausane, Suisse)
In this talk, I aim to show two different effects that can happen when one shakes a fluid at a given frequency. In a first part, I will focus on the case where the excitation frequency is twice the typical response frequency of the system. In this case, parametric instability occurs and large waves oscillating at half the excitation frequency appear at the surface of the fluid (Faraday instability). The phase of those waves can take two distinct values depending on the initial condition. I will discuss how one can switch on demand from one phase state to the other by introducing a temporal defect in the excitation. Interestingly, such transition of phase has a simple topological interpretation that will be discussed. In a second part, I will show that when the shaking frequency is large enough with respect of the typical frequency response of the system, one can dynamically stabilize some unstable behavior of the system. An experimental illustration of this principle is the stabilization of a liquid layer above an air layer, as well as the possibility for small objects to float under the liquid layer. I will conclude with some perspective for future experiments and applications of those concepts.
Contact: Philippe Marmottant