Box Refinement

The box refinement section allows for a specific region in the grid to be finer before the simulation starts. To do so, a box refinement can be added with the following parameters and their appropriate values:

subsection box refinement
set number of refinement boxes = 0
  subsection box 0
    subsection mesh
      set type                   = dealii
      set grid type              = hyper_cube
      set grid arguments         = -1 : 1 : true
      set initial refinement     = 0
      set scale                  = 1
      set initial translation    = 0, 0, 0
      set initial rotation axis  = 1, 0, 0
      set initial rotation angle = 0
    end
    set additional refinement = 0
  end
end

• The number of refinement boxes corresponds to the number of refinement boxes we want to introduce.

  Attention

  At the moment, the software only supports up to \(5\) different boxes.

• The subsection box 0 includes information regarding the 1st refinement box.

  Note

  When number of refinement boxes = 2, the 2nd refinement box will be described in the subsection box 1. We increment the last digit of the subsection name to describe a new refinement box.

• The mesh subsection allows to define the region in which the fluid mesh needs to be uniformly refined. A cell will be refined if at least one of its degrees of freedom (DoFs) is located within the outer boundaries of the box specified in the grid arguments. Therefore, in the 3D example above, every cell of the fluid mesh that has at least one of its DoFs located in the hexahedron defined by the corners (-1, -1, -1) and (1,1,1) will be refined.

  Note

  The used mesh can be of any type and any grid type. Additionally, box refinement meshes support scaling, translation, and rotation, applied in the listed order.

  See also

  For more information on meshes, see the mesh documentation.

  Tip

  The initial refinement of the hyper_cube should be as small as possible, since the initial refinement of the box mesh itself will not have any impact on the definition of the refinement zone. However, in the case of a curved shape such as a hyper_sphere, increasing the initial refinement of the box refinement mesh improves the geometry resolution of the box boundary.

• The additional refinement parameter in the box refinement subsection indicates the number of times the cells inside the box will be refined in addition to the ones prescribed in the simulation mesh subsection.

  Warning

  This number is not the level of refinement of the cell, but the number of additional refinements applied within the region defined by the box at the initial condition. For instance, let us consider a simulation mesh with an initial refinement of \(1\) and a box refinement mesh with an additional refinement of \(2\). The level of refinement of cells within the box refinement region becomes: \(1 + 2 = 3\). However, the mesh resolution within this region, may change dynamically if adaptive mesh refinement is enabled.