This function is used in the class of ContactRing. Those models calculate friction forces and use the tripleS_Func to do it. The tripleS_Func contains this (s_Func) function.

The purpose of this function is to get a smoother transition when crossing the zero velocity point and to apply the static and dynamic friction coefficient in a good way. If a function like this is not used when calculating friction, the solver might get stuck around velocity close to zero by creating new events at every zero crossing. This might set up a loop of jumping from positive velocity to negative with no actual physical relevance. The s-Func avoids this!