Description
PTT model for viscoelasticity using the upper-convected time
derivative of the stress tensor with support for multiple modes.
Reference:
\verbatim
Thien, N. P., & Tanner, R. I. (1977).
A new constitutive equation derived from network theory.
Journal of Non-Newtonian Fluid Mechanics, 2(4), 353-365.
\endverbatim
Currently the common exponential form of the PTT model is provided but it could
easily be extended to also support the linear and quadratic forms if the need
arises.