Soutenance de thèse : Florent DUMORTIER

Principle of vibroacoustic subtractive modelling and application to the prediction of the acoustic radiation of partially coated submerged cylindrical shells / Principe de la modélisation vibro-acoustique soustractive et application à la prédiction du rayonnement acoustique des coques immergées partiellement revêtues

Doctorant : Florent DUMORTIER

Laboratoire INSA : LVA

Ecole doctorale : ED162 : Mécanique, Energétique, Génie Civil, Acoustique de Lyon

Modelling the vibroacoustic behavior of submerged cylindrical shells has been a challenging issue for the last decades in the naval industry. The application of viscoelastic coatings on submarine hulls allows reducing the noise radiated and scattered by the shell and is thus of paramount importance for their acoustic furtivity. These coatings can generally be decomposed into two categories. Decoupling coatings isolate the hull from the surrounding medium and reduce the radiated noise, serving as a protection against passive sonars, while anechoic coatings serve as a protection against active sonars by reducing the acoustic scattering from the hull. If fully coated cylindrical shells have been intensively studied in the literature, few works can be found on partially coated cylindrical shells. Modelling the vibroacoustic behavior of such structures may be useful for predicting the impact of missing coating tiles, or for studying cylindrical shells with several kinds of coatings. Compared to fully coated cylindrical shells, partial coating induces a coupling of the circumferential orders of the submerged shell, leading to prohibitive calculation costs for numerical methods and the impossibility of applying classical semi-analytical methods. In this work, a subtractive modelling approach is developed to circumvent this issue. It is based on a reverse formulation of the Condensed Transfer Function method, a substructuring approach that has already proven its ability in dealing with complex vibroacoustic problems. Considering this approach, the partially coated cylindrical shell can be studied considering the model of a fully coated cylindrical shell, from which a model of the missing part of the coating is removed. The theoretical framework of the method is explored for 1-D and 3-D problems before being applied to several test cases to evaluate the method’s accuracy and its sensitivity to model errors. Finally, the partially coated cylindrical shell is studied using this subtractive modelling approach.