  We study the asymptotic limit of solutions to the barotropic Navier-Stokes
system, when the Mach number is proportional to a small parameter $\ep \to 0$
and the fluid is confined to an exterior spatial domain $\Omega_\ep$ that may
vary with $\ep$. As $\epsilon \rightarrow 0$, it is shown that the fluid
density becomes constant while the velocity converges to a solenoidal vector
field satisfying the incompressible Navier-Stokes equations on a limit domain.
The velocities approach the limit strongly (a.a.) on any compact set, uniformly
with respect to a certain class of domains. The proof is based on spectral
analysis of the associated wave propagator (Neumann Laplacian) governing the
motion of acoustic waves.
