Mesh#

The mesh subsection of DEM simulations is almost identical to the CFD in Lethe. There are two additional parameters mainly used in DEM and CFD-DEM simulations. These parameters are check diamond cells and expand particle-wall contact search.

subsection mesh
   set check diamond cells                 = false

   set expand particle-wall contact search = false
end

  • check diamond cells parameter enables searching for diamond-shaped boundary cells and adding them to particle-wall contact search cells. The following image shows a diamond-shaped boundary cell colored in red. A diamond cell is defined as a cell that has a vertex or an edge on the boundary, but no face lying on the boundary.

Schematic

  • expand particle-wall contact search extends the boundary walls in a cell by appending the boundary walls of the neighboring cells to the particle-wall contact list. This adds the boundary faces of the neighboring cells and allow particles to collide with boundary walls that are not faces of the cell in which they reside. Only neighboring boundary faces that form a convex boundary with the current cell are added; boundary faces forming a non-convex boundary are excluded. The following figure illustrates this concept. When a particle is located in a boundary cell (shown in red), the boundary faces of neighboring cells that form a convex boundary with the current cell (neighboring cells shown in green) are also considered during the particle-wall contact search. This is necessary because a particle whose centroid lies within the red cell can simultaneously contact both the boundary face of the current cell and the boundary face of a neighboring cell when the two faces form a convex boundary. In contrast, boundary faces of neighboring cells that form a concave boundary (neighboring cells shown in orange) are not considered during the particle-wall contact search.

Schematic