PhD DEFENSE BY YVES PAQUETTE

This PhD project started in 2014 was supervised by Marc Fivel (SIMAP) and Giovanni Ghigliotti (LEGI).

Yves has also been selected for the finals of the "Ma thèse en 180 secondes" contest.

The defense will take place at 2:30 pm in room K118 at the LEGI.

Abstract

His numerical work focuses on the collapse of a single air bubble close to adeformable wall generated by the impact of an incident high-pressure wave. A CFD code was fully coupled to a FEM solid code in order to compute the bubble collapse and the subsequent plastic deformation in the material. The CFD code was developed from the numerical model of Johnsen et al. (University of Michigan). A mobile mesh capability was added in order to account for the displacement of the fluid-structure interface. An ALE (Arbitrary LagrangianEulerian) method was implemented to switch from an Eulerian description in a fixed mesh to an Eulerian description in a moving mesh. The solid response to bubble collapse was computed with the FEM software CAST3M (developed by CEA) assuming an elastic-plastic constitutive law for the material. The communication between the two codes is achieved through the MPI library.For the CFD code, bubble collapse dynamics was validated by comparison with two others codes: research software CaviFlow and commercial software Ansys Fluent. The coupling between the CFD and the FEM code was validated on the case of the impact of a wave on an elastic medium.The paper will present a detailed analysis in 2D of both the dynamics of bubble collapse and solid behaviour for various conditions. They were obtained by changing the amplitude of the incident shock wave, the standoff distance and the material properties. Special attention will be given to the shock wave that forms when the microjet hits the bubble interface and to the impact of this shock wave on the material surface. In particular, the damping of the impactpressure with respect to a perfectly rigid wall was computed as well as the plastic deformation of the material surface. These final data gave us crucial information about the requirement of taking account of fluid-structure interaction in numerical modeling of cavitation erosion.