Mesh Generation with Feature Objects. (a) Feature Objects (b) Resulting Mesh.
The simplest and most powerful method for generating a mesh is to use feature objects and the Map -> 2D Mesh command. This command can be used for both the SEEP2D and FEMWATER conceptual models. The process of constructing a mesh from feature objects is illustrated in the following figure:
Mesh Generation with Feature Objects. (a) Feature Objects (b) Resulting
Mesh.
The types of feature objects that are used to guide the construction of the mesh are shown in part (a) and the resulting mesh is shown in part (b). The polygons shown in part (a) represent material zones and also define the domain of the region to be meshed. The spacing of the edges (defined by the arc vertices) of arcs is used to guide the number and size of elements that are generated. One element is generated adjacent to each arc edge. The elements in the interior of the mesh domain are generated in a manner that gradually transitions the element sizes between arcs with small edges and arcs with large edges. This allows the user to control the mesh density and ensure that higher mesh density is used where necessary. Both arcs on polygons and arcs representing interior boundaries such as rivers are honored in the meshing process.
An element size can be assigned to individual points in the interior of the mesh. As the mesh is constructed, the element sizes are gradually transitioned so that the elements adjacent to the point have the specified size. In most cases, this element size is relatively small and is intended to cause the mesh to be refined about the point.
Properties are assigned to feature objects by selecting the object(s) and selecting the Properties command in the Feature Objects menu. Properties can also be assigned by double-clicking on an object. When the active coverage is a SEEP2D or FEMWATER type coverage, Properties can be assigned to polygons and points.
Polygons in a SEEP2D or FEMWATER type coverage can be assigned a mesh type and material type. When the Properties command is selected, the attribute table for the coverage appears. Select the Mesh opts button to enter the 2D Mesh Polygon Properties dialog. This dialog allows users to preview the result of different meshing techniques for a single or set of polygons. After selecting a mesh type and specifying the nodes on the arcs, selecting the Preview button will display the resulting mesh. The mesh is not generated until the Map -> 2D Mesh command in the Feature Objects menu is selected.
Points in a SEEP2D or FEMWATER type coverage can be assigned an element size. When the Properties command is selected, a dialog with a single edit field appears prompting the user for the element size. The size represents an edge length. When the mesh is generated, the elements just adjacent to the point are equilateral triangles with the designated edge length.
If an element size is not assigned to a point in a SEEP2D or FEMWATER coverage, the point will still be honored in the mesh. A node will be created at the exact location of the node. However, the sizes of the elements in the vicinity will depend on the transitioning required by other objects in the coverage.
Once a set of feature objects has been created for a SEEP2D or a FEMWATER coverage, the Map -> 2D Mesh command can be used to generate a 2D finite element mesh from the objects.
Related Links:
Feature Objects
Coverages