If the mesh on either side of an interface is moving, then all nodes on that interface are marked as overlap. ‘Overlap’ simply means that a node (and it’s associated mesh faces) is a candidate for interface re-intersection. This is required since, with moving mesh, we never know a-priori where (or how) the mesh on each side of the interface will actually intersect; we must presume that point ‘A’ on one side of the interface could intersect with *any* point on the other side of the interface. Although the memory usage will be increased due to the high overlap, there shouldn’t be too large a hit in terms of the CPU time required for the solution.