### ASA 127th Meeting M.I.T. 1994 June 6-10

## 5aSA9. Mean flow effects on the vibroacoustic behavior of a plate backed
by a cavity in light and heavy fluids.

**Franck Sgard
**

**
Noureddine Atalla
**

**
Jean Nicolas
**

**
**
*G.A.U.S., Univ. of Sherbrooke, Sherbrooke, PQ J1K 2R1, Canada
*

*
*
The purpose of this work is to present a general formulation dealing with
the vibroacoustic behavior of a baffled plate, immersed on one side in a mean
flow and coupled on the other side to a rectangular cavity with arbitrary wall
impedances. The plate is excited by a point force, a plane wave convected by
the mean flow, or a turbulent boundary layer. The formulation is based on a
finite element method for the calculation of the transverse vibrations of the
plate. Fluid loading on each side of the plate is taken into account through an
impedance matrix approach. The plate--cavity impedance matrix is calculated
using a boundary element method. The amount of computation is decreased by
using a two indices Green's function for the rigid cavity. The external
impedance matrix accounting for mean flow, is calculated using the extended
form of Kirchhoff's integral equation and a boundary element method. This
formulation is compared with a finite element approach for the calculation of
the acoustic field inside the cavity. The mean flow effects are investigated
through the calculation of different vibroacoustic indicators like the
mean-square velocity of the plate, the internal and external acoustic radiated
power, the radiation efficiency of the plate inside the cavity and the
transmission loss of the plate. Coupling mechanisms are explained in terms of
added mass, stiffness, and damping.