A Side is a set of Wires, to which is associated a Surface. The first Wire is the external boundary, the next Wires define optional holes. These Sides are used directly in 2D modelling, or gathered in Skins for the definition of the boundaries of Volumes in 3D.

side = sideset.add( Side(number, [wire1, wire2, wire3, ...]) )
side.setSurface(surface)

with

• In contact problems, the normal of a Side is the normal defined by its Surface.
• For rigid contact, the normal must point towards the interior of the material (as for curves in 2D).
• For Sides defined by their Surface only (surface of revolution for example), it is allowed to define the Side without any Wire (the Side has an implicit boundary: it is limited by the parameters $(u,v) = (0,0) \rightarrow (1,1)$ of the Surface).