Figure 2.5 Avoid Midside-to-Corner Node Connections Between Elements For elements having midside nodes, it is generally preferred that each such node be located at the straight-line position halfway between the corresponding corner nodes. There are, however, situations where other locations may be more desirable:
Nodes following curved geometric boundaries will usually produce more accurate analysis results - and all ANSYS meshers place them there by default.
Even internal edges in some meshes may have to curve to prevent elements from becoming inverted or otherwise overly distorted. ANSYS meshers sometimes produce this type of curvature.
It is possible to mimic a crack-tip singularity with "quarter point" elements, with midside nodes deliberately placed off-center. You can produce this type of specialized area mesh in ANSYS by using the KSCON command (Main Menu> Preprocessor> Meshing> Size Cntrls> Concentrat KPs> Create).