Submodeling is based on the St. Venant's principle.
The St. Venant's principle states that the stresses on a boundary reasonably distant from an applied load are not significantly altered if this load is changed to a statically equivalent load. The distribution of stress and strain is altered only near the regions of load application.
You may cut a portion of the model, refine the mesh, and run analysis only for the selected portion provided that displacements are properly prescribed at the cut boundaries. If displacement results from the parent study are accurate, then these displacements
are considered as boundary conditions at the cut boundaries for the submodeling study.
The boundaries of the submodel must be adequately far from stress concentration areas.