REDUCTION OF THE NOISE RADIATED BY SUBMERGED STRUCTURES : OPTIMISATION OF LAYERED COATINGS

Abstract
We propose an optimization process in order to design optimal viscoelastic (isotropic or transverse-isotropic) layered coatings for submerged structures. These coatings are optimized in order to reduce the far-field pressure radiated by the structure when subjected to time-harmonic prescribed forces or displacements. These coatings have to satisfy three inequality constraints, maximum thickness, maximum and minimum mean value mass density, maximum mean value compressibility. In order to define a fast and efficient optimization process, we have considered the structure to be an infinite plate radiating in a semi-infinite fluid and the coating to be an infinite layered medium. The optimization has to provide coatings feasible with respect to the constraints and inducing the maximum far-field radiated noise attenuation in the largest frequency range. We present the software named OPTIMASQ we have developped for this purpose and some of the results we have obtained which prove the efficiency of the optimization process even for severe constraints.