3.2 Bending Spring
Our method is most similar to the elastic rods model [Bergou et al.
2008; Bergou et al. 2010], which computes the material frame as the
minimizer of elastic energy of the curve. They use these material
frames to compute the bending and twisting energies along the rod.
However, this formulation introduces rotation during simple motion
of a curl, such as a walk cycle, shown in Figure 2 top. This rotation
can be removed by increasing the material’s stiffnesses, but this
change leads to wire-like behavior (see video).
This type of rotation in the curl, while physically accurate, is undesired
for our hair model. We instead introduce a novel method
to stably generate the material frame by parallel transporting the
root frame of the hair along a smoothed piecewise linear curve (see
Section 3.2.1). The result of using our smoothed curve is a series