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The Surface section allows users to define surfaces. These surfaces can then later be used to define the boundary conditions and contact definitions. A surface definition is followed by a list of surface elements, following the format described below.

<Surface name="named_surface">
  <quad4 id="1">1,2,3,4</quad4>
  <...>
</Surface>

The Surface takes one required attribute, namely the name. This attribute sets the name of the surface. This name will be used later to refer back to this surface.

The value for the surface element is the nodal connectivity:

<quad4 id="n">n1,n2,n3,n4</quad4>
<tri3 id="n">n1,n2,n3</tri3>

Surface elements cannot overlap element boundaries. That is, the surface element must belong to a specific element. Surface elements do not contribute to the total number of elements in the mesh. They are also not to be confused with shell elements.