Point zones

Table of Contents

• What are point zones?
• Predefined geometrical shapes
  • Box
  • Sphere
  • Cylinder
• User-defined geometrical shapes
• Using point zones

What are point zones?

Point zones are subsections of the computational domain which are selected based on a given geometrical criterion. A point zone is defined by the point_zone_t abstract type. Each point_zone_t object has a unique name attribute, and a mask containing a list of linear indices referring to the GLL points whose coordinates verify the above-mentioned geometrical criterion. Zones can then be used for different purposes, an example being applying a localized source term or probing a particular zone of interest.

Predefined geometrical shapes

There are three predefined shapes from which to initialize a point zone in the case file: boxes, spheres and cylinders. Each shape is described by its own subtype box_point_zone_t, sphere_point_zone_t and cylinder_point_zone_t, extending the abstract class point_zone_t.

Box

A box is defined from its x,y and z boundaries.

[
    {
        "name": mybox,
        "geometry": "box",
        "x_bounds": [-1.0, 1.0],
        "y_bounds": [-1.0, 1.0],
        "z_bounds": [-1.0, 1.0]
    }
]

Sphere

A sphere is defined by its center and its radius.

[
    {
        "name": "mysphere",
        "geometry": "sphere",
        "center": [0.0, 0.0, 0.0],
        "radius": 0.01
    },
]

Cylinder

A cylinder is defined by its end points and its radius.

[
    {
        "name": "mycylinder",
        "geometry": "cylinder",
        "start": [0.0, 0.0, 0.0],
        "end": [0.0, 0.0, 1.0],
        "radius": 0.01
    },
]

User-defined geometrical shapes

The current version of Neko does not support user-defined shapes from the case file. That said, shapes can be defined manually into new types by extending point_zone_t and implementing the abstract criterion interface.

Using point zones

Point zones defined in the case file are stored in a point zone registry, neko_point_zone_registry. The point zone registry allows for the retrieval of any point_zone_t object when needed. Once a point_zone_t object is retrieved, it can be used for e.g. applying a source term to a localized zone, as demonstrated below:

subroutine forcing(f,t)
  class(fluid_user_source_term_t), intent(inout) :: f
  real(kind=rp), intent(in) :: t
 
  integer :: i
  class(point_zone_t), pointer :: my_point_zone
  
  my_point_zone => neko_point_zone_registry%get_point_zone("myzone")
 
  ! Assign a constant forcing to my_point_zone
  do i = 1, my_point_zone%size
     f%u(my_point_zone%mask(i), 1, 1, 1) = 2.0
  end do
 
end subroutine forcing