COUPLED FEM-BEM APPROACH FOR MEAN FLOW EFFECTS ON VIBROACOUSTIC BEHAVIOR OF PLANAR STRUCTURES

The originality of the present paper lies in the development of a form ulation accounting for mean flow effects on the forced vibro-acoustic response of a baffled plate. The importance of these effects on the vi brational behavior of the plate, as well as on its acoustic radiation pattern, is investigated for a baffled plate with different kinds of b oundary conditions. The analysis is based on a finite element method f or the calculation of the plate transverse vibrations and the use of t he extended Kirchhoff's integral equation to account for fluid loading with mean flow. A variational boundary element method is used to comp ute the acoustic radiation impedance. The formulation shows explicitly the effects of mean flow in terms of added mass, stiffness, and radia tion damping. Details of the formulation as well as its numerical impl ementation are expounded, and results showing the effect of mean flow in light and heavy fluid on the vibro-acoustic quantities, such as mea n square velocity and radiated acoustic power, are presented. It is se en that the effects of a mean flow amount to a decrease of the natural frequencies of the plate, a small damping effect on the vibrations, a nd a change in the radiated acoustic power when compared with the no-f low case. Besides, these effects increase with the flow speed. The neg ative stiffness added by the flow is shown to be mainly responsible fo r the natural frequency shift effect. The changes in the radiated acou stic power are explained in terms of important changes in the radiatio n efficiencies and modal cross-coupling induced by the flow.