Introducing virtual topology is a convenient method for creating a clean, well-formed mesh. The emphasis is to ignore small geometric details that result in distorted elements in areas where the analysis results are not of significant interest. Virtual topology relaxes the need for the mesh to conform to every edge or vertex and allows you to obtain a simpler model with less detail. However, virtual topology does not change the underlying geometry of the part instance.

When you combine two faces to form a virtual face, ABAQUS/CAE updates the display to reflect the ignored edge. However, to form a basis for the new virtual face, ABAQUS/CAE maintains the underlying geometry of the faces that were combined. The nodes in the mesh will be placed on the underlying geometry. Therefore, a coarse mesh will interpolate across the virtual face, and a fine mesh will tend to converge to the geometry of the underlying combined faces. Virtual topology allows the mesh definition to be controlled by meshing parameters, such as seed size, and it helps to free meshing from constraints imposed by geometry, such as small faces.

In contrast, you use the Repair toolset to correct minor flaws that are typically introduced when a part is imported from a third-party application. You use the Repair toolset to correct the underlying geometry; for example, to stitch small gaps and to delete self-intersecting faces and recreate a valid replacement face. You also use the Repair toolset to remove redundant topology, such as superfluous vertices and edges. The Repair toolset modifies the actual geometry, and geometric restrictions limit how you can apply the repair tools; for example, you can remove redundant vertices only if the vertex lies on a curve that is common to both edges.

When you export a virtual part instance, the virtual topology is lost because the virtual face, edge, or vertex is not true geometry. For example, a virtual face is an abstracted reference to the underlying collection of combined faces. Therefore, you should use the Repair toolset if you need to remove small details from a part and want to export the part with the changes retained.