### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 5aSA2. A 3-D finite element model for sound transmission through a
double-plate system with isotropic elastic porous materials.

**Raymond Panneton
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Noureddine Atalla
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*G.A.U.S., Dept. Genie Mecanique, Univ. de Sherbrooke, Sherbrooke, PQ J1K
2R1, Canada
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**J.-F. Allard
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*Univ. du Maine, Le Mans, France
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The prediction of sound transmission through multilayer structures is of
utmost importance in aircrafts, buildings, and other engineering applications.
In view of optimizing the transmission loss, the finite element method is an
interesting mean to model such structures since it permits one to account for
complex structure geometries and to model accurately the boundary conditions.
In this paper, a 3-D-finite element model is developed to evaluate the normal
incidence transmission loss through a double-plate system with cavity
absorption. The cavity is filled with an air-saturated isotropic elastic porous
materials. The model uses a two-field finite element procedure for the porous
medium based on the Biot theory. Since the Biot theory considers only the
energy dissipation due to the viscous effects, the frequency-dependent bulk
modulus of the air, worked out by Champoux and Allard [J. Appl. Phys. 70,
2182--2191 (1991)], is adopted to account for the energy dissipation due to
thermal exchanges. Also, two sets of field variables are considered: the u-U
and the u-P sets, where u and U are the solid and fluid displacements and P is
the pore-fluid pressure. Both approaches are developed and compared through
numerical simulations. [Work supported by Bombardier, Inc., Canadair, and
N.S.E.R.C.]