At : salle Conf IV - Département de Physique, Ecole Normale Supérieure, 24 Rue Lhomond, 75005 Paris , on 14:00

In this thesis, we study the impact of solid boudaries on surface waves. We first consider the dissipation caused by dynamical wetting. We experimentally show how the damping of surface waves evolves with the size of the meniscus and demonstrate that in perfect wetting it leads to a nonlinear behavior as soon as the meniscus oscillation amplitude compares to the thickness of the boundary layer. Secondly, we investigate energy exchanges through scales occuring when a surface wave reflects on an oscillating wall, the so-called generalized Doppler effect. We evidence the creation of Doppler-shifted waves, compute their amplitudes and illustrate how the continuous bouncing of surface waves on wave-makers may lead to self-similar spectra competing with the ones of wave turbulence. Finally, we focus on nonlinear interaction between surface waves. We prove that gravity waves can undergo triad resonances in confined geometry. Going beyond the consequencies of solid boundaries, we perform experiments on four-wave interactions in the gravity regime and describe large scales in capillary wave turbulence.

At : UPD

At : UPMC , on 15:00

At : IPhT - Orme des Merisiers - Salle Claude Itzykson, Bât. 774 , on 14:00

2016-07-27

At : Diderot , on 14:00

At : Auditorium ou Salle des conseils de l'IPN - Bâtiment 100, 15 Rue Georges Clemenceau, 91405 Orsay, France , on 14:00

Many systems that are somehow characterized by a degree of disorder share a similar structure: the energy landscape has many sample-dependent local energy minima. When a small external perturbation is applied to the system at low temperature, it is reasonable to expect that the dynamics will lead the system from a minimum to another, thus displaying a random and jerky response. The discontinuous jumps that one observes are called avalanches, and the focus of this work is the computation of their distribution. One of the results is indeed the development of a framework that allows the computation of this distribution in infinite-dimensional systems that can be described within a replica symmetry breaking ansatz. We apply the results to one of the simplest models of structural glasses, namely dense packings of (harmonic) soft spheres, either at jamming or at larger densities, subject to a shear transformation that induces jumps both in the total energy and in the shear stress of the system. We argue that, when the shear strain is small enough, the avalanche distribution develops a power-law behavior, whose exponent can be directly related to the functional order parameter of the replica symmetry breaking solution. This exponent is also related to the distribution of contact forces (or at least of the contact forces between some of the spheres), whose asymptotic behavior is known not to depend strongly on the spatial dimension; for this reason, we compare the infinite-dimensional prediction with three dimensional simulations of the same systems and, remarkably, we find a good agreement. In the rest of the thesis we compare our results with previous works, and we also discuss some of the consequences that the avalanche distribution lead to, concerning the statistical elastic properties of dense granular media.

At : Conf IV - Dpt de Physique de l'ENS - 24 rue Lhomond 75005 Paris , on 10:00