A modal synthesis method to solve the elastoacoustic vibration problem
is analyzed. A two-dimensional coupled fluid-solid system is considered;
the solid is described by displacement variables, whereas displacement
potential is used for the fluid. A particular modal synthesis leading to
a symmetric eigenvalue problem is introduced. Finite element discretizations
with Lagrangian elements are considered for solving the uncoupled problems.
Convergence for eigenvalues and eigenfunctions is proved,
error estimates are given, and numerical experiments exhibiting the good
performance of the method are reported.