Sets specify regions of the geometry as a combination of volumes, surfaces, edges, and nodes. The main usage of sets are to connect regions of elements to a given cross section or apply a boundary condition, though sets can be used for many other things as well.
|[elements #(ia)] [elementranges #(rl)] [allElements]|
|[nodes #(ia)] [noderanges #(rl)] [allNodes]|
|[elementboundaries #(ia)] [elementedges #(ia)]|
Volumes (elements) and nodes can be specified using either a list, elements, nodes, or with a range list elementranges, noderanges. Edges elementedges, and surfaces elementboundaries, are specified in a interleaved list, every other number specifying the element, and edge/surface number (the total length of the list being twice the number of surfaces/edges). The internal numbering of edges/surfaces is available in the Element Library Manual.
Note that edge loads (singular loads given in ``newton per length'' (or equivalent), should be applied to elementedges, surface loads ``newton per area'' on elementboundaries, and bulk loads ``newton per volume'' on elements.
Example 1: A deadweight (gravity) load would be applied to the elements in a set, while a distributed line load would be applied to the midline ``edge'' of the beam element, thus should be applied to a elementedges set. In the latter case, the midline of the beam is defined as the first (and only) ``edge'' of the beam.
Example 2: Axisymmetric structural element analysis: A deadweight load would be applied to elements in a set. A external pressure would be defined as a surface load an be applied to the elementboundaries in a set. The element integrates the load (analytically) around the axis, so the load would still count as a surface load.