unable to use gmsh physical groups in /RBODY and /PART definition

[QiangF]

The /RBODY requires node_id in its definition, which makes problem definition mesh dependent, and makes preprocessing cumbersome.

The problem definition should not mesh size dependent. With meshing software such as gmsh, the node group id can be fixed with physical group, ie. node group id doesn't change if the mesh size changes. And what we get is a decoupling of meshing and physical model.

/RBODY should accept an single-node node group in the current node_id field.

The /PART has a similar situation. https://openradioss.atlassian.net/wiki/spaces/OPENRADIOSS/pages/54624257/Tubes+Contact+Tutorial+Using+Gmsh

BTW, the physical group of single point node should be exported in the gmsh radioss exporter. https://gitlab.onelab.info/gmsh/gmsh/-/issues/3294