# <boundary_conditions>

This category specifies parameters for special types of boundaries.

## <boundary_conditions> - <rotating>

This category contains all regions where a rotating wall velocity should be applied to the surface. It can have an arbitrary number of children named <rotating_instance>, each with the following parameters:

<name>
Name of the instance (optional).
<rpm>
Rotational speed of the instance in [rpm] (revolutions per minute).
<center>
Center of the rotation, specified via the child parameters <x_pos>, <y_pos> and <z_pos> in $\left[\text{m}\right]$.
<axis>
Rotational axis of the instance, its direction (right-hand rule applies) must be specified via the child parameters <x_dir>, <y_dir> and <z_dir>.
<parts>
The parts to which the rotating wall velocity should be applied must be specified via the child parameter <name> within the <parts> category, several parts can be specified via repeated usage of <name> to assign the rotating wall velocity to all of them. The specified names must exactly match the respective part names in the STL file.

## <boundary_conditions> - <belt>

This category contains all regions where a moving wall velocity should be applied to the wind tunnel ground (if <moving_ground> is set to true, see above), it can have an arbitrary number of children named <belt_instance>, each with the following parameters:
<name>
Name of the instance (mandatory).
<include_force>
If set to true, aerodynamic forces that act on the belt instance are included in the force evaluation.
Default = false
<bounding_box>
Bounding box of the instance, must be specified via the child parameters <x_min>, <x_max>, <y_min> and <y_max> in $\left[\text{m}\right]$. The z-coordinate is omitted because the belt is always located on the wind tunnel ground.

## <boundary_conditions> - <periodicity>

Via the child parameters <x_dir>, <y_dir>, and <z_dir>, periodic <boundary_conditions> can be activated.
Note: At least eight voxels in periodic direction have to be used.

The default value for all three children is false.

## <boundary_conditions> - <static>

This category contains all regions where a no-slip <boundary_condition> with non-default wall model settings should be applied to the surface. It can have an arbitrary number of children named <static_instance>, each with the following parameters:
<name>
Name of the instance (optional).
<wall_model_variant>
Name of the non-default wall model variant to be applied, must be specified in <simulation> - <wall_model_variant>.
<parts>
The parts to which the properties should be applied must be specified via the child parameter <name> within the <parts> category. Several parts can be specified via repeated usage of <name> to assign the properties to all of them. The specified names must match the respective part names in the STL file.
Note: Static parts use the globally specified wall model settings by default. They must be specified separately, if settings other than global settings are applied locally.