whitejd
Aerospace
- Apr 19, 2004
- 9
I am using NX NASTRAN's glue element approach for connecting element surfaces with dissimilar meshes. They seem to be working out well in static stress models, but for unconstrained frequency extraction models I am having a lot of trouble getting the necessary 6 rigid body modal frequencies of zero. I am working with shell elements including offsets, and some half of the frequencies are on the order unity (1 Hz).
Sanity checks with a small test model 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 mode frequencies is drop the compressive-based penalty factor to a point at which the glue/bond effect is not accurately captured in the non-rigid body modes. Any advice? I've taken the test model and excluded the glue surfaces via node-to-node rigid links, and that version behaves as expected (6 rigid body modes with 0 frequency).
FYI - Literature (release notes) state that the internally generated glue elements are essentially very stiff springs, but really does not explain the inner workings further.
Sanity checks with a small test model 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 mode frequencies is drop the compressive-based penalty factor to a point at which the glue/bond effect is not accurately captured in the non-rigid body modes. Any advice? I've taken the test model and excluded the glue surfaces via node-to-node rigid links, and that version behaves as expected (6 rigid body modes with 0 frequency).
FYI - Literature (release notes) state that the internally generated glue elements are essentially very stiff springs, but really does not explain the inner workings further.
