### ASA 125th Meeting Ottawa 1993 May

## 5aSA7. Acoustic radiation from a coupled planar semicomplex structure in
heavy fluid.

**Noureddine Atalla
**

**
Alain Berry
**

**
**
*GAUS, Mech. Eng., Univ. of Sherbrooke, Sherbrooke, PQ J1K 2R1, Canada
*

*
*
A mathematical model is derived to address the vibrations and sound
radiations into a dense fluid, of a coupled system consisting of two
semicomplex plates (i.e., supporting added mass, stiffeners, and having
arbitrary elastic boundary conditions) linked in four points through multistage
suspensions elements. The top plate is subjected to point, line, or surface
harmonic excitation, while the radiating plate is excited through the
suspensions. Both plates are assumed to be baffled, and the radiating plate is
fluid loaded. The model is based on a variational approach for the plates, and
a matrix transfer approach is used to handle the coupling between the two
plates. The solution is sought using a Rayleigh--Ritz expansion in terms of
polynomial trial functions which are shown to allow for the arbitrary elastic
boundary conditions and to facilitate the calculation of the radiation
impedance matrix. The vibrations and noise design of the system is discussed.
The main design indicators are the force transmissibilities between the
different excitation and attachment points, the ratio of mean-square velocities
of the two plates, the mean-square velocity, the radiated power, and the
radiation efficiency of the radiating plate. Numerical examples are presented
to show the effects of different design parameters (plates thickness, boundary
conditions, added mass, stiffeners,...) on the radiated sound. [Work supported
by DREA.]