Collapse Faces
The operation collapses a face by removing it, merging its adjacent opposite edges or collapsing all adjacent edges, and reconnecting the adjacent faces to the resulting merged edges. A small face with sides of similar length will typically be collapsed into a vertex, while a sliver face is more often collapsed into an edge, as shown in Figure 7-17.
Figure 7-17: Collapsing two faces, highlighted in blue. The smaller triangular face is collapsed into a vertex (indicated with arrow in the right image) while the rectangular face is collapsed into the upper of its two longer edges.
Which edge to keep is decided based on geometrical and topological criteria. For example, if the tangent is continuous for two faces over an edge, that edge is more likely to be removed than one with noncontinuous tangent.
It is recommended to use this operation to remove faces that are significantly smaller or narrower than the desired local mesh element size. For more control over which edge to keep, refer to the Merge Edges operation. An alternative is to use the Ignore Edges operation. The Remove Details operation provides a fully automated way to detect and remove small and sliver faces within the whole geometry or a selection of entities.
To use the operation, in the Geometry toolbar, from the Virtual Operations menu (), select Collapse Faces (). Then enter the properties of the operation using the following sections:
Input
Select the faces that you want to collapse in the Graphics window. They then appear in the Faces to collapse list. If the geometry sequence includes user-defined selections above the Collapse Faces node, choose Manual to select faces, or choose one of the selection nodes from the list next to Faces to collapse.
Click the Active button to toggle between turning ON and OFF the Faces to collapse selections.
Select the Ignore merged entities check box to ignore the resulting merged edges or vertices (if possible). A vertex will be kept if there are more than two edges connected to the vertex.
Figure 7-18: Collapsing the same two faces, highlighted in blue, as in Figure 7-17, but this time with the check box Ignore merged entities selected. The small triangular face is still collapsed into a vertex (indicated by the upper-left arrow in the image to the right). As there are more than two ingoing edges into this vertex, it is kept. The rectangular face is collapsed into the upper of the two longer edges, which is then ignored. Note that the vertex on the edge in the lower-right corner has been ignored as there are only two ingoing edges (position indicated by lower-right arrow).
The Collapse to vertex tolerance controls if a sliver face is collapsed into an edge or a vertex. By default, it is set to Automatic. The default tolerance used is 0.001 times the length of the longest edge of the geometry’s bounding box. For more control, select Manual to enter a value in the Maximum face perimeter field that appears. The default value is 0.001. This tolerance is the maximum perimeter of a face to be collapsed into a vertex. If you build the operation with Automatic and then switch to Manual, the Maximum face perimeter field shows the value of the parameter that was used when the operation was built.
In the case of a face being collapsed into a vertex, it is typically collapsed into the vertex with the most ingoing edges. If that number is the same for all vertices, the face is collapsed to the vertex with the lowest index. With the default Automatic setting a sliver face is more likely to be collapsed into an edge, in which case the tolerance value is set to a value smaller than the face perimeter. For a face that is collapsed to a vertex the tolerance value is larger than the face perimeter.
Figure 7-19: The face is collapsed into an edge when the Maximum face perimeter tolerance is set to 0.45 mm. With the tolerance set to 0.55, mm the face is collapsed into a vertex.
With the Mixer Module, see Free Surface Mixer: Application Library path Mixer_Module/Tutorials/free_surface_mixer
With the Molecular Flow Module, see Evaporator: Application Library path Molecular_Flow_Module/Industrial_Applications/evaporator
With the Subsurface Flow Module, see Geothermal Doublet: Application Library path Subsurface_Flow_Module/Heat_Transfer/geothermal_doublet