====== Sides ======

===== Definition =====

{{ doc:user:doc-faces.png |}}

A ''Side'' is a set of ''[[doc:user:geometry:user:contours|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 ''[[doc:user:geometry:user:peaux]]'' for the definition of the boundaries of ''Volumes'' in 3D.

  side = sideset.add( Side(number, [wire1, wire2, wire3, ...]) )
  side.setSurface(surface)
with
| ''number''                | user number (unique among Sides and $\ge 1$) |
| ''wire1''                 | external ''[[contours|Wire]]'' (boundary)    |
| ''wire2'', ''wire3''      | internal ''[[contours|Wires]]'' (holes)     |
| ''surface''               | associated ''[[surfaces|Surface]]''         |

===== Notes =====

  * 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'').