  Motivated by the experimental development of quasi-homogeneous Bose-Einstein
condensates confined in box-like traps, we study numerically the dynamics of
dark solitons in such traps at zero temperature. We consider the cases where
the side walls of the box potential rise either as a power-law or a Gaussian.
While the soliton propagates through the homogeneous interior of the box
without dissipation, it typically dissipates energy during a reflection from a
wall through the emission of sound waves, causing a slight increase in the
soliton's speed. We characterise this energy loss as a function of the wall
parameters. Moreover, over multiple oscillations and reflections in the
box-like trap, the energy loss and speed increase of the soliton can be
significant, although the decay eventually becomes stabilized when the soliton
equilibrates with the ambient sound field.
