SMS:Patch

Patch used to define a river channel

Patch used where a culvert will be modeled

The patch method fills polygons that can be defined as topologic rectangles. The method may combine multiple arcs to define a single side of the patch. A bidirectional coons patching method is used to interpolate from the boundary arcs to interior nodes. Typical applications of this method include river channels and regions aligned to channels. The patching method supports transitioning the number of elements across the channel or from one side to another. Transitions in both directions often result in poorer quality elements and should be avoided if possible.

The Rectangular Patch mesh generation method requires a polygon made of exactly four arcs, forming four sides. However, very rarely do exactly four arcs make up a polygon. SMS provides a way to define a rectangular patch from a polygon that has more than four arcs by allowing multiple arcs to act as a single patch side. An example of a rectangular patch made up of four sides is shown below. Note that Side 1 and Side 2 are both made from multiple arcs. Hollow squares represent the beginning and ending points of an arc (feature points). Filled squares represent intermediate points along the arc (feature vertices).

When creating a patch, the number of vertices on parallel arcs should be equal. Often this means aligning vertices on opposite arcs. This can be done using the Redistribute Vertices dialog. Using the "Source Arc" redistribution method is often preferred.

Definition of four sides for a rectangular patch

The basic process to define the meshing attributes for a polygon using the Patch method is to:

1. Switch to the Map module
2. Select the menu Feature Objects | Build Polygons
3. Switch to the Select Polygon tool
4. Select the polygon to set meshing attributes for
5. Select the menu Feature Objects | Attributes
6. Set Mesh Type to Patch
7. Set Bathymetry Type'
8. Set Material Type
9. Set Node Options if the polygon consists of more than four arcs
   1. Switch to the Select Feature Point tool in the dialog
   2. Select the node to "merge"
   3. In the Node Options combo box, change the selection to "merge"
   4. The two arcs meeting at the "merge" node will now be treated as a single arc for the mesh generation within the current polygon.
10. Press OK to exit the dialog and save the polygon attributes

Related Topics

• Paving Meshing Algorithm
• Scalar Paving Density Meshing Algorithm
• Mesh Generation
• 2D Mesh Polygon Properties dialog
• Element Patch Workflow

External Links

• Gonzales, Darren S. (2000). An Automatic Finite Element Mesh Generation Method: the Adaptive Rectangular Coons Patch. Thesis, Brigham Young University. TA 4.02 .G6476 2000