  We present a two dimensional model of hydrodynamic interaction between a
circular swimmer and a circular post at low Reynolds number, using a point
singularity description of the swimming activity. We derive a nonlinear
dynamical system fully describing the motion and discuss the generic features
of the phase portrait and typical trajectories for a variety of squirmer modes.
Contractile swimmers exhibit stable bound orbits arising from the contrasting
nature of monopolar and dipolar squirmer modes, which are robust with respect
to swimmer size and the inclusion of higher squirmer modes. The behaviour of
extensile swimmers is related through time reversal and their orbits are
unstable, in qualitative agreement with experimental observations.
