Vesicles in linearly forced motion

We study the shape of vesicles being dragged through their viscous environm ent by a homogeneous force, using a numerical method to treat Stokes hydrod ynamics around the vesicle. Due to the mobile boundaries, the uniqueness th eorem does not apply here, and we have obtained a catalog of the various st ationary solutions. Vesicles can be bean-like and pear-like, the latter bei ng unstable with respect to perturbations breaking their axisymmetry. Oblat e ellipsoids are stabilised by a sufficiently strong drag. A 2d flow of lip ids in the membrane is induced for non-axisymmetric shapes. As the drag for ce becomes too strong, no more stationary solutions exist. For very deflate d vesicles, an "S"-shaped solution appears, coupling rotational and transla tional motion.