Jeudi, 17 Octobre, 14h,  Amphithéatre Pierre-Gilles de Gennes, Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, 75013 Paris.

Soutenance de thèse de Camille Cohen

Caractérisation acoustique de milieux bulleux concentrés

Dirigée par Valentin LEROY (MSC, DOMM, CNRS, Université Paris Cité) et co-encadrée par Tony VALIER-BRASIER (Institut d’Alembert, Sorbonne Université) et Yann DESAILLY (Saint-Gobain Recherche).

Abstract:
This PhD is about acoustical characterization of concentrated bubbly media. In the industrial context of plasterboard production, the presence of air bubbles in the gypsum slurry (liquid gypsum paste) must be monitored to ensure the conservation of plasterboards’ mechanical properties. The fluid medium containing an ensemble of air bubbles that is the slurry is called a multiple scattering medium. Many models allow for the description of the behavior of those media in dilute cases (less than 10% of air). What about the concentrated media that we study in this PhD ? First, the algorithm MuScat is used to numerically simulate the study of a random concentrated monodisperse distribution of air bubbles in water. The results are compared to two multiple scattering models : the Independent Scattering Approximation (ISA) and the Fikioris and Waterman model (FW). This study confirms the agreement between dilute media and the models, and allows us to establish that for more concentrated media, the FW model is in better agreement with the numerical data than the ISA. Finally, the deviation to the ISA is quantified by using the wave number expressions given by the FW model. Secondly, experiments on bubbly gel and foamed slurry, at high volume fractions, are conducted. Different experimental set-ups suited to both media allows for the measurement of the reflection and the transmission coefficients, as well as the calculation of parameters such as the wave number or the acoustical impedance. The deviation to the ISA is again calculated for these polydisperse media. At last, a semi-analytical law established using the ISA is proposed to link the ultrasound results of the studied samples (numerical bubbly water, bubbly gel, foamed slurry) to the bubbles’ size distributions’ parameters : the volume fraction, the median radius and the polydispersity coefficient. This law fits the industrial framework of the PhD to answer the bubble size measurement issue on production lines.

The defence will be in French.