  The density stratification in an incompressible fluid is responsible for the
propagation of internal waves. In domains with topography, these waves exhibit
interesting features. In particular, numerical and lab experiments show that,
in two dimensions, for generic forcing frequencies, these waves concentrate on
attractors. The goal of this paper is to analyze mathematically this behavior,
using tools from spectral theory and microlocal analysis. The same results
apply also to inertial waves in rotating fluids.
