VIBRATIONS ET RAYONNEMENT DE PLAQUES COMPLEXES EN FLUIDE LÉGER ET EN FLUIDE LOURD

Mechanical characteristics such as stiffeners, mass inhomogeneities and complex support conditions along the boundaries are known to affect the vibroacoustic behavior and are of interest for passive noise control. An analytical approach is proposed to study the vibrations and sound radiation into a light fluid or a heavy fluid, from baffled rectangular plates showing the above elements of complexity. The method is based on a variational formulation of the structural motion and a procedure of minimization over a functional subspace taking into account arbitrary boundary conditions along the plate contour. The selection of simple polynomials to generate this subspace is shown to have a number of advantages : (i) it is compatible with elastic boundary conditions (deflexion-rotation) along the contour, (ii) it allows the mass and stiffness operators of the structure to be easily calculated, (iii) it allows an analytical solution of the fluid-structure coupling, (iv) it provides a decomposition of the structure into multipoles of radiation. The case of radiation into a light fluid and the case of radiation into a heavy fluid are presented. Numerical results show the incidence on the sond radiation of the boundary conditons, addition of point mass, addition of stiffeners. Comparisons with the Boundary Element Method, and with measurements are also presented. [Work supported by the Defence Research Establishment Atlantic, Canada]