Porous Polygons
Porous Polygon objects are used as part of the mesh generation process carried out when undertaking 2D Modelling. The polygons represent enclosed walls with a specified porosity and height which are taken into account during the 2D simulation process. Note that a porous polygon collinear with the boundary of a 2D zone, will override the boundary condition of the 2D zone along the coincident portion of the boundary. The coincident portions of the polygon are considered infinitely high, regardless of any crest level specified.
Porous Polygon objects can be imported via the Open Data Import Centre or, for InfoWorks networks, from AutoCad DWG. Polygons can also be digitised directly on the GeoPlan Window.
Porous Polygon parameters are edited in the Porous Polygon Grid Window of the Polygons Grid or the Porous Polygon Property Sheet. For further information on creating and editing polygons, see the Digitising Network Objects section.
Collapsing walls
It is possible to set parameters for the Porous Polygon object which will result in the full or partial removal of the wall during a simulation depending on criteria based on the results of 2D mesh elements adjacent to the polygon edge. The removal of the wall represents the collapse of the wall.
Collapsing walls criteria
The criteria to trigger a collapse are defined in fields in the Definition section of the Porous Polygon Property Sheet.
See the Porous Polygon Data Fields (InfoWorks) or Porous Polygon Data Fields (SWMM) topic for full details.
Remove wall during simulation
The Remove wall during simulation option can be set to either Full or Partially.
- Full: if collapse of the wall is triggered, the entire Porous Polygon object will be removed from the simulation.
- Partially: if collapse of the wall is triggered, only the edge of the Porous Polygon object adjacent to the mesh elements triggering the collapse will be removed from the simulation.
Wall removal trigger
The Wall removal trigger field is used to select the variable to be used to determine whether the wall has collapsed. The trigger variable relates to the results in 2D mesh elements adjacent to the Porous Polygon edge; for example, the Depth option uses depth of water in adjacent elements as the trigger for wall collapse.
Threshold fields
The threshold field values to be specified will depend on the trigger variable selected in the Wall removal trigger field.
By default, if the trigger variable in a mesh element adjacent to the Porous Polygon edge exceeds the defined threshold, the wall will collapse.
If the Use difference across wall option is selected, collapse of the wall will be triggered when the difference between the trigger variable values in the adjacent mesh elements either side of the polygon edge exceeds the defined threshold.
