# Laboratoire de Mécanique des Fluides et d’Acoustique - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France

## Nos partenaires

Sébastien Aumaître, CEA, SPHYNX\SPEC

## Probing dissipative processes in stationary out-of-equilibrium systems through the fluctuations of injected power

Lundi 3 juin 2019, 13h15, Salle de réunion I11 bas, ECL

In this presentation a tool to study all kinds out—of—equilibrium systems in a stationary state. These systems can be systems in contact with a thermostat pushed out—of—equilibrium or athermal intrinsically dissipative systems. To this purpose, we define an energy, Ec, that characterizes the intrinsic dissipative processes although it is estimated from the fluctuations of the extrinsic injected power. Our definition involves only the two first moments of the injected power smoothed over a large time $\tau$. Hence it is easy to measure it experimentally. Our reasoning lies only on properties of stationary processes. Thus it applies to any kind of dissipative systems. We test our definition on various systems. We show that for Langevin dynamics, we recover some results that are usually given by the fluctuation relation. We also probe this energy experimentally on bending waves in a thin elastic plate. In all these cases, we establish the fact that it coincides with the kinetic energy per degrees of freedom. It is however not always the case as shown on numerical simulations on frictional systems. The puzzling case of turbulent flow will be mentioned to conclude.