(Translational) linear spring and linear damper in parallel.
Parameters:
c : spring constant in [N/m]
s0: length in [m], at which the spring force is zero
d : damping constant in [N*s/m]
Note: Both cuts of a force element have ALWAYS to be connected at the cut
of a joint, of a body or of the inertial system. It is not possible
to e.g. connect two force elements in series.