Submodeling is a finite element technique used to get more accurate results in a region of your model.
Often in finite element analysis, the finite element mesh may be too coarse to produce satisfactory results in a region of interest, such as a stress concentration region. The results away from this region, however, may be adequate. To obtain more accurate results in such a region, you have two options:
Re-analyze the entire model with greater mesh refinement (Ex. If in a 100.000 solid elements welded structure there's the need to better analyze a critical weld, actually the only action a Simulate user can do is to refine the mesh locally and re-run the whole model with a huge waste of time).
Use submodeling technique to generate an independent, more finely meshed model of only the region of interest and analyze it (Impossible for a Simulate user so far).
Submodeling is also known as the cut-boundary displacement method or the specified boundary displacement method and it is based on St. Venant's principle. The cut boundary is the boundary of the submodel which represents a cut through the coarse model. Displacements calculated on the cut boundary of the coarse model are specified as boundary conditions for the submodel.
The majority of high-end FEM codes allow this technique; use the following link to see an example: