  Fluid-structure simulations of slender inextensible filaments in a viscous
fluid are often plagued by numerical stiffness. Recent coarse-graining studies
have reduced the computational requirements of simulating such systems, though
have thus far been limited to the motion of planar filaments. In this work we
extend such frameworks to filament motion in three dimensions, identifying and
circumventing coordinate-system singularities introduced by filament
parameterisation via repeated changes of basis. The resulting methodology
enables efficient and rapid study of the motion of flexible filaments in three
dimensions, and is readily extensible to a wide range of problems, including
filament motion in confined geometries, large-scale active matter simulations,
and the motility of mammalian spermatozoa.
