States which unknowns in which nodes get prescribed values by adjustment of the node_dof records. 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 boundary values. The items unknown_0 etc. are one of the primary unknowns listed at dof_label.
For a specific index, only one of bounda_force and bounda_unknown can be specified (thus either Neumann conditions or Dirichlet conditions).
Example for discrete node forces in y-direction on the nodes on a line:
bounda_unknown 0 -geometry_line 1 -vely
bounda_time 0 0. 0. 1. 1. 100. 1.
Normally you only should specify boundary conditions on principal unknowns (like velocity, temperature, etc.) and not on strain, stresses, etc.!
Specially for velocity (displacement) unknowns, you can prescibe a rotation around either the x-axis, y-axis or z-axis. In 1D you cannot use this record. In 2D you can only specify a rotation around the z-axis. In 3D you can specify each of the three axis.
Example of an x-axis rotation of node 12 with angular velocity of 0.33 [degrees per unit time]:
For the rotation 0.33 the rotation vector points in the positive x-axis direction.
bounda_unknown 0 12 -rotation_x_axis
bounda_time 0 0.33
See also: bounda_time, bounda_sine, force_element_edge and force_element_volume.