NASTRAN Surface-to-Surface Gluing (AKA Glue Elements)

[whitejd]

Anybody have experience with NASTRAN's glue element approach of connecting surfaces with dissimilar meshes? They seem to be working out well in static stress models, but for dynamic models, I am having a lot of trouble getting 6 rigid body modes. I am working with shell elements, and some of my frequencies that should be zero are on the order of 0.1. Sanity checks show that even if the surfaces are right on top of each other and nodes are coincident, this still happens. All I've been able to do to produce thee sought near-zero rigid body frequencies is drop the penalty factor to a point at which the glue effect is not accurately captured in the non-rigid body modes. Any advice?

Literature states that the internally generated glue elements are essentially very stiff springs, but does not explain further.