Andreas Koutras
Ansys Employee

TIED_SURFACE_TO_SURFACE is constraint-based while TIED_SURFACE_TO_SURFACE_OFFSET is penalty based. If there no rigid bodies or other constraints involved, TIED_SURFACE_TO_SURFACE would be more advantageous because it won't affect the stability of the explicit scheme. On the other hand, if the penalty stiffness of TIED_SURFACE_TO_SURFACE_OFFSET is scaled up (to reduce any relative displacement), the stability may be compromised and the explicit time step may need to be reduced.