CONTROL OF THE ACOUSTIC RADIATION USING RESONANT SYSTEMS – RAMSES

Acoustic discretion is an important problem in the field of naval operations for new ships as well as in the air domain, for example for planes, rail cars... More particularly, the RAMSES project deals with the noise radiated by periodically stiffened metallic structures when they are excited either by pressure fluctuations of the turbulent boundary layer or by mechanical vibrations (in a frequency range below 2kHz, for a typical submarine). The purpose is to eliminate or reduce significantly the radiation of the Bloch-Floquet waves created by the stiffener periodicity. Several solutions are proposed: (1) classical solution based on resonant systems, made of viscoelastic materials and additional masses, as those considered in the ASTRID FARAON project (Acoustic stealth by resonating stiffeners, 04/2014-09/2016, handled by Mr. Tran Van Nhieu from Thales RT) with the aim of controlling the stealth of stiffened plates or shells, (2) solution with passive metamaterials to allow for resonance frequency tuning on a wide range by simply modifying the effective properties of the metamaterials constituting the resonant systems, (3) solution with piezoelectric materials connected to a very simple electronic circuit (short circuit, open circuit or positive capacitance) with the aim of modifying by a simple external electric command the properties of each resonant system independently, (4) semi-active solutions with piezoelectric materials connected to a complex electronic circuit with a negative capacitance or a blind switch damping for instance, usually used for vibration damping or energy harvesting. The last two solutions are innovative strategies for the control of the acoustic radiation in break with the previously proposed solutions because they will allow variable jamming by modifying in real time the electric connections of the active materials.
The developed analytical and numerical models will be implemented to design and optimize systems for acoustic radiation control corresponding to realistic configurations in line with naval concerns. Four plates equipped with stiffeners and resonant systems will be manufactured at the 1/100 scale and tested, in connection with each of the proposed solutions. The project will also aim at adapting the proposed solutions to periodically stiffened cylindrical shells.
The skills linked with the project are analytical, numerical, as well as experimental with measurements in air and in water to estimate both plate vibration and far-field acoustic radiation reductions. Moreover, the proposed solutions present the advantage of handling both discretion and stealth simultaneously in the range of low frequencies, where the usual hull coating solutions are generally less efficient.
This project is part of research topics n°3 " acoustic and radio waves" and n°2 " Fluids, structures ", and in the research priority for 2016: "new materials to optimize the radiation of antennas and stealth".
The project is handled by IEMN (UMR 8520 CNRS) which has an internationally recognized expertise in passive and active metamaterials, as well as in modelling, with the help of Thales RT for the study, the choice and the manufacturing of the resonant structures, the LOMC for the manufacturing of scale models and the acoustic tests in water tank and Thales US for the finite element numerical models and for its expertise in underwater acoustics.