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 formulation accounting for mean flow effects on the forced vibro-acoustic response of a baffled plate. The importance of these effects on the vibrational behavior of the plate, as well as on its acoustic radiation pattern, is investigated for a baffled plate with different kinds of boundary conditions. The analysis is based on a finite element method for the calculation of the plate transverse vibrations and the use of the extended Kirchhoff's integral equation to account for fluid loading with mean flow. A variational boundary element method is used to compute the acoustic radiation impedance. The formulation shows explicitly the effects of mean flow in terms of added mass, stiffness, and radiation damping. Details of the formulation as well as its numerical implementation are expounded, and results showing the effect of mean flow in light and heavy fluid on the vibro-acoustic quantities, such as mean square velocity and radiated acoustic power, are presented. It is seen 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, and a change in the radiated acoustic power when compared with the no-flow case. Besides, these effects increase with the flow speed. The negative stiffness added by the flow is shown to be mainly responsible for the natural frequency shift effect. The changes in the radiated acoustic power are explained in terms of important changes in the radiation efficiencies and modal cross-coupling induced by the flow.