Sometimes, particularly with imported geometries, there may be some short edges which are part of the boundary of a face, where the length of the edges is much less than the required mesh spacing in that region of the geometry. Since the mesher will place a minimum of three points on every edge which makes up a face, the presence of these short edges will result in some elements that are of the same size as these short edges, rather than a mesh using the required spacing. This results in an uneven mesh with many more mesh elements than would have been desired.

To get around this problem, CFX-Mesh allows you to remove short edges. To set this up, use the Fix Options item under Geometry in the Tree View. The default is NOT to remove any edges.

If you set Remove Short Edges to Yes, then you will be asked for an Short Edge Tolerance (which must be shorter than the Maximum Spacing set for the Default Body Spacing). All edges shorter than this length will be ignored by the mesher (although they will still show up in the geometry display) and the two ends will collapse to a point. You must make sure that the Short Edge Tolerance specified is shorter than the mesh length scale at any point where edges may be removed, and you must also make sure that removing the edges does not cause any face to collapse (to give a face with zero area).

The pictures below show the effect of short edge removal. The face shown is a square with sides of 1 m. However, the bottom of it is made up from two edges: one is only 2 cm long and the other is 98 cm long. The mesh is shown first without short edge removal, meshed with a length scale of approximately 0.1 m. The short edge has caused a patch of fine mesh which was not required. The magnified inset clearly shows the mesh resolving the short edge.

The second picture shows the mesh after short edge removal. The edge tolerance was set to 0.08 m. The mesh is much smoother since it does not need to resolve the short edge.

Removing short edges in this way does not give you control over individual edges; you can only specify a length and then remove all edges shorter than this length. CFX-Mesh allows you to remove individual short edges in certain circumstances by merging them with adjacent edges to form a Virtual Edge. This is described in Virtual Edges, and a comparison between the Short Edge Removal described in this section and Virtual Edges is given in Virtual Edges and Short Edge Removal.