Chris Quan
Ansys Employee

In Autodyn, the feature "Import -> Convert IJK Parts to Unstructured" will convert the IJK-based parts (mesh) created from Autodyn GUI to unstructured parts (mesh). Unstructured mesh doesn't use IJK indexes to generate mesh and is the same type of mesh as generated from Workbench Meshing.

Comparing with IJK-based (structured) mesh, unstructured mesh runs faster and uses less memory.

"Interactions -> Lgrange/Lagrange -> External Gap" requires a non-zero visible gap present between parts that are in contact. When "Calculate" is clicked, Autodyn will calculate the best gap size for use with External Gap contact. When "Check" is clicked, Autodyn will check if the gap size entered is appropriate to the analysis. When "Create" is clicked, Autodyn will create such visible gap automatically (use this with caution!).

If you encounter difficulties with determining the best gap size to your model, you can click on "Trajectory" to switch the contact type. "Trajectory" contact doesn't require visible non-zero gap between parts in contact. However, "Trajectory" contact only works with unstructured parts (mesh) so you need to use Import options to convert the IJK parts (mesh) to unstructured parts (mesh) first.