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Monday, July 8 • 11:00 - 11:20
ACOUSTIC DEVICES FOR STEALTH AND DISCRETION

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The optimization of stealth (response to an active sonar) and discretion (noise radiated from the vehicule) performance for underwater vehicules at very low frequencies is currently an important research topic in underwater acoustics. One classical way to improve acoustic performance is to cover the hull with specific acoustic coatings. This talk focuses on another approach, which is to introduce slight modifications of the hull internal structure. The results that are presented have been obtained in the frame of a project with the ANR French agency, supported by the french DGA. Classically, in order to withstand hydrostatic pressure, the hulls of underwater vehicles support periodically distributed rib stiffeners, which give rise to typical phenomena of acoustic diffraction at low frequencies and thus allow the detection and identification of these vehicles (Bloch-Floquet waves and Bragg diffractions). To overcome these problems, we propose to attach to a part of the stiffeners resonant systems whose characteristics vary randomly from one stiffener to the next. The frequency signature created by the network of stiffeners equipped with resonators is thus jammed and attenuated, improving stealth at low and very low frequencies This paper first presents analytical, numerical and experimental results obtained on a plate equipped with simple rib stiffeners, associated or not with resonators. Stealth performance diagrams highlight the usefulness of the proposed rib attachments. Then, optimization algorithms are used to choose the parameters of the resonators and their distribution in order to minimize a given objective function. The extension of this concept to the discretion problem is finally discussed.


Monday July 8, 2019 11:00 - 11:20 EDT
Westmount 5
  T12 Underwater & marit. noise, SS01 … underwater snd measur & monit