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**.