We consider
identical inertialess rigid spherical particles in a Stokes flow in a domain
. We
study the average sedimentation velocity of the particles when an identical force acts
on each particle. If the particles are homogeneously distributed in directions
orthogonal to this force, then they hinder each other leading to a mean
sedimentation velocity which is smaller than the sedimentation velocity of a
single particle in an infinite fluid. Under suitable convergence assumptions of
the particle density and a strong separation assumption, we identify the
order of this hindering as well as effects of small scale inhomogeneities and
boundary effects. For certain configurations we explicitly compute the leading
order corrections.