AN OPERATOR TOP-DOWN DERIVATION OF "DOUBLY ASYMPTOTIC APPROXIMATIONS"

Some problems involved in fluid-structure interaction in unbounded domains require the computation of the response of an homogeneous acoustic medium to prescribed harmonic motions. The complexity of the submerged structure studied sometimes suggests the use of approximate methods for the numerical analysis of this acoustics problem [1]. The present paper intends to propose a derivation of the so-called "Doubly Asymptotic Approximations" (DAA's). This formal top-down derivation, specialized to steady-state motions, relies on an integral representation of the solution of the Helmholtz equation in an unbounded domain. Two asymptotic expansions of this representation are obtained in the low- and the high-frequency ranges, then these expansions are matched. This procedure allows to point out that some geometrical assumptions underlie the validity of high order continuous forms of the DAA's. It suggests further investigations of some interesting open geometry and numerical analysis problems

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

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

An operator top-down derivation of 'doubly asymptotic approximations'

1er congres francais d'acoustique, Lyon, 10-13 avril 1990SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1990 n.34 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

A contribution to doubly asymptotic approximations : an operator top-down derivation

Tire de : Journal of Vibration and Acoustics, July 1991, vol.113SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1992 n.203 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Reduction of the noise radiated by submerged structures Optimisation of layered coatings

1er congres francais d'acoustique, Lyon, 10-13 avril 1990SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1990 n.35 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc