Yes, en and es are normal and tangential coefficients of restitution
(ratio of velocities after and before the 'impact': vf/vi).
I wanted to say that the parameters in
SimpleViscoelasticBodyParameters could be the stiffnesses and
restitution coefficients. Then, the effective mass together with the
viscous constants could be determined in
SimpleViscoelasticRelationships (maybe with the equations you
showed me).
I do not quite understand the idea. At this point,
SimpleViscoelasticBodyParameters contains the viscoelastic
parameters of
a single body, i.e. its stiffnesses and viscosity.
SimpleViscoelasticRelationships defines the effective parameters of
interaction between two different viscoelastic bodies (by analogy with
the effective Young's modulus).
