States which ones from the list of dof's in which nodes get prescribed nodal forces. The item node_range represents a range of node numbers. In stead of a node range also, by example, -geometry_line 1 can be used, indicating that the nodes on line 1 get the prescribed nodal forces. The items unknown_0 etc. can be one of the items listed at dof_label. However, neither -dis and -scal can be used.
For a specific index, only one of bounda_force and bounda_unknown can be specified; thus, either Neumann conditions or Dirichlet conditions can be applied to a particular node, but nor both.
Attention: with this option you get the same nodal force on all the specified nodes. If you want to apply a distributed force on a edge, however, you should use force_element_edge. That option gives forces consistent with the displacement field, so not necessarily the same for all nodes. By example the nodes on the side of linear elements on a edge get only half the force.
See also: bounda_time, bounda_sine and force_element_edge.