  Many vesicles have a spherical resting shape and exposure to fluid flows
induces an exchange between sub-optical area and visible (systematic)
deformation, while the total area is conserved. The dynamics which controls the
exchange between sub-optical and visible area depends on membrane properties
such as bending rigidity and initial tension. Conversely, observation of these
dynamics can be used to determine the membrane properties. The goal of this
work is to create a general numerical model which accounts for the exchange
between sub-optical and visible area. Unlike prior modeling efforts, the model
does not pre-assume a shape type, such as nearly-spherical, or applied flow
field, allowing the model to capture a wider variety of flow conditions. Based
on implicit interface tracking and using a volume-preserving multiphase
Navier-Stokes solver, the model is compared to several experimental results,
showing excellent agreement. It is used to explore regimes not possible with
previously published models, such as the variable viscosity case, and how these
system properties influence experimentally measurable parameters such as
deformation parameter. By creating a more generalized framework for the
modeling of vesicles with sub-optical area, it will now be possible to make
predictions on vesicle material properties from a wider variety of experimental
results.
