Submodeling is based on the St. Venant's principle which states that the stresses reasonably distant from an applied load on a boundary 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 and run analysis only for the selected portion provided that displacements are properly prescribed at the boundaries of the cut. If displacements at the boundaries of the cut are calculated accurately at the first run, then these displacements
may be considered as boundary conditions for the submodel run.
The cut boundary of the submodel cannot cut through a bonded contact defined by either beam-to-beam joints or shell edge-to-shell edge joints.
The boundaries of the submodel must be adequately far from stress concentration areas.