  We study the problem of finding strain-minimising stream surfaces in a
divergence-free vector field. These surfaces are generated by motions of seed
curves that propagate through the field in a strain minimising manner, i.e.,
they move without stretching or shrinking, preserving the length of their
arbitrary arc. In general fields, such curves do not exist. However, the
divergence-free constraint gives rise to these 'strain-free' curves that are
locally arc-length preserving when infinitesimally propagated. Several families
of strain-free curves are identified and used as initial guesses for stream
surface generation. These surfaces are subsequently globally optimised to
obtain the best strain-minimising stream surfaces in a given divergence-free
vector field.
  Our algorithm was tested on benchmark datasets, proving its applicability to
incompressible fluid flow simulations, where our strain-minimising stream
surfaces realistically reflect the flow of a flexible univariate object.
