How AutoGEM Uses Existing Elements
You can use AutoGEM commands on curves and surfaces that are already partially covered with elements. AutoGEM recognizes the existing elements and incorporates them as part of the final set of elements it creates.
However, existing elements can overconstrain AutoGEM, resulting in an incomplete set of elements. If you select Modify or Delete Existing Elements on the Settings tab, AutoGEM deletes existing tetrahedral solid and shell elements as required to complete the set of elements.
You can also use AutoGEM on volumes with existing elements. With a volume, AutoGEM recognizes solid elements whose faces are directly or indirectly associated with boundary surfaces. A solid is indirectly associated with a boundary surface when a series of adjacent solids extends from the interior of a volume to its boundary. It is sometimes useful to know the number of solid elements in a volume so that you can compare this number with the number AutoGEM reports.
By default, AutoGEM links the tetrahedral solid faces it creates to existing brick and wedge quad faces.
* 
If you do not want AutoGEM to use existing elements, you must delete the elements before carrying out an AutoGEM command.