Adding voids to exclude areas from the 2D mesh

Step-by-step guide

Voids are polygon mesh objects that can be used for excluding areas from the 2D mesh. A common use of voids is to represent buildings within the 2D area.

The advantage of using voids is that they reduce the overall number of mesh elements and therefore simulation time. The disadvantage is that they represent an infinitely high impermeable barrier, which is unrealistic.

To add voids to a 2D mesh, polygons are created and associated with a common category name. In this example model, there are several polygons already created to represent buildings.

To associate a common category, so that the mesh engine knows which polygons to use:

1. From the Windows toolbar, Grid windows drop-down, select New polygons window.

2. In the grid window, switch to the Polygon tab.
3. Click the Category column header to select the column.
4. Right-click the column and select Current cell(s) Value > Set new value(s) for cell(s).

5. In the New Cell Value popup, enter a value of “Voids”.
6. Click OK.

7. Close the window.

Now, re-mesh the 2D zone to include these changes in the mesh:

8. On the GeoPlan, select the 2D zone.
9. From the Model menu, select Meshing > Mesh 2D zones.

10. In the Mesh 2D Zones dialog box, under Voids, select Polygons.
11. From the drop-down, select the Voids category.

12. From the Database, drag the Ground model into the Mesh 2D Zones dialog box, and drop it into the Ground Model box.
13. Click OK to mesh the 2D zone.
14. In the Schedule Job(s) popup, click OK.
15. In the Job Control window, under Status, click Mesh ready.
16. In the Manage mesh results dialog box, click Load mesh.
17. Click Close.

When the mesh loads, the polygon areas are excluded from the mesh generation, as they have no internal 2D elements. Therefore, the boundaries are treated as an infinitely high impermeable barrier by the 2D engine.

To view these excluded areas within the mesh, turn off the display of polygons:

18. In the GeoPlan, right-click and select Properties & Themes.
19. On the Layers and Themes tab, for the Polygons layer, deselect Display.
20. Click OK.

Now, the areas excluded by the polygon voids are visible within the 2D mesh.