You may encounter a situation in your model when the geometry appears to connect and meet up, but is actually discontinuous. Consider this simple model for example, two surfaces that appear to meet and share a common interface or line. However, when we go to mesh them, the resulting mesh is discontinuous and there are free edges still at the interface of the surfaces.
However, we can fix that in Femap with the NonManifold Add command, which is located in the Geometry | Surface | NonManifold Add menu. When we select this the entity selection dialog appears and we can pick both of the surfaces.
Femap then connects the two surfaces together so that if we go back and remesh them, this time you see that a continuous mesh is created.
NonManifold Add can be used to connect up two or more surfaces that share a common interface.