Vesicles and many biological membranes are made of two monolayers of lipid molecules and form
closed lipid bilayers. The dynamical behaviour of vesicles is very complex and a variety of forms
and shapes appear. Lipid bilayers can be considered as a surface fluid and hence the governing
equations for the evolution include the surface (Navier–)Stokes equations, which in particular take
the membrane viscosity into account. The evolution is driven by forces stemming from the curvature
elasticity of the membrane. In addition, the surface fluid equations are coupled to bulk
(Navier–)Stokes equations.
We introduce a parametric finite element method to solve this complex free boundary problem, and
present the first three dimensional numerical computations based on the full (Navier–)Stokes system
for several different scenarios. For example, the effects of the membrane viscosity, spontaneous
curvature and area difference elasticity (ADE) are studied. In particular, it turns out, that even in
the case of no viscosity contrast between the bulk fluids, the tank treading to tumbling transition
can be obtained by increasing the membrane viscosity. Besides the classical tank treading and
tumbling motions, another mode (called the transition mode in this paper, but originally called the
vacillating-breathing mode and subsequently also called trembling, transition and swinging mode)
separating these classical modes appears and will be studied by us numerically. We also study
how features of equilibrium shapes in the ADE and spontaneous curvature models, like budding
behaviour or starfish forms, behave in a shear flow.