  We consider the derivation and numerical solution of the flow of passive and
active polar liquid crystals, whose molecular orientation is subjected to a
tangential anchoring on an evolving curved surface. The underlying passive
model is a simplified surface Ericksen-Leslie model, which is derived as a
thin-film limit of the corresponding three-dimensional equations with
appropriate boundary conditions. A finite element discretization is considered
and the effect of hydrodynamics on the interplay of topology, geometric
properties and defect dynamics is studied for this model on various stationary
and evolving surfaces. Additionally, we consider an active model. We propose a
surface formulation for an active polar viscous gel and exemplarily demonstrate
the effect of the underlying curvature on the location of topological defects
on a torus.
