  It is known that a finite-size homogeneous granular fluid develops an
hydrodynamic-like instability when dissipation crosses a threshold value. This
instability is analyzed in terms of modified hydrodynamic equations: first, a
source term is added to the energy equation which accounts for the energy
dissipation at collisions and the phenomenological Fourier law is generalized
according to previous results. Second, a rescaled time formalism is introduced
that maps the homogeneous cooling state into a nonequilibrium steady state. A
nonlinear stability analysis of the resulting equations is done which predicts
the appearance of flow patterns. A stable modulation of density and temperature
is produced that does not lead to clustering. Also a global decrease of the
temperature is obtained, giving rise to a decrease of the collision frequency
and dissipation rate. Good agreement with molecular dynamics simulations of
inelastic hard disks is found for low dissipation.
