Civil Engineering Reference
In-Depth Information
(a)
(b)
Medial axis
Quadrilaterals
Largest circles
Figure 5.101
Mesh generation by means of medial axis construction: (a) medial axis of an object; (b) object
divided using medial axis as a guide.
surface method (Price and Armstrong 1995, 1997) involves an initial decomposition of the
volume into sub-regions.
The decomposition of the volume by medial surfaces will define regions to be meshed by
means of a mapping procedure. A set of templates for the expected topology of the regions
formed by the medial surfaces are employed to fill the volume with hex mesh. Linear and
integer programming is used to ensure that element divisions match from one region to
another (Li et al. 1995). This method, while proving useful for some geometry, has been
less than reliable for meshing general 3D objects with irregular non-smooth boundaries.
Robustness issues in generating medial surfaces, as well as in providing, for all cases, regions
that are readily defined for simple hexahedral meshing, appear to be rather difficult issues.
5.8.10 Plastering method
The paving method introduced by Blacker and Stephenson (1991) and Blacker et al. (1991)
offers a simple way to form complete rows of quads, starting from the boundary and work-
ing inwards, as shown in Figure 5.102a (Thompson and Soni 1999). Front closure remains
a major issue when the offset contour intersects itself, and very often, poor quads have to
be used to fill up the interior just for building up a quad mesh of correct topological struc-
ture, as shown in Figure 5.102b. White and Kinney (1997) proposed an improvement to the
paving procedure, suggesting individual placement of quads rather than a complete row.
Plastering is an attempt to extend the paving method in 2D to generate hex meshes in 3D
(Canann 1991; Johnston and Sullivan 1993; Cass et al. 1996; Meyers et al. 1998). Within a
(a)
(b)
Offset from
the boundary
Figure 5.102
Quadrilateral mesh generated by the paving method: (a) layer of quadrilaterals generated along
the boundary; (b) irregular quadrilaterals are found at the interior of the domain.
