Generation of Computational Mesh for Haemodynamics Analysis - Computational Hemodynamics: Theory, Modelling and Applications - page 164

irregular cell distributions near boundaries. For detailed descriptions of quadtrees/
octrees the reader is strongly encouraged to refer to the work by Yerry and Shephard
(1984) and Shephard and Georges (1991).

6.2.7 Advancing Front Connectivity

The advancing front method for an unstructured mesh is created by adding individu-
al elements inwards one at a time from an existing front of generated elements (typi-
cally a boundary or edge). New triangular cells are created by extending the front,
with its growth constituting a stack, and the edges of the stack continuously added
or removed. The process continues until all fronts have merged and the domain is
entirely covered. For three-dimensional grids, a surface grid is first constructed by
generating a two-dimensional triangular mesh on the surface boundaries of the do-
main. This mesh forms the initial front, and is then advanced into the physical space
by placing new points ahead of the front and forming tetrahedral elements. For
detailed descriptions of the advance front method the reader is strongly encouraged
to refer to the work by Lo (1985), and Marcum and Weatherill (1995) (Fig. 6.13 ).

6.2.8 Comparisons Between Structured and Unstructured Mesh

The main advantage of using an unstructured mesh is its ability to conform onto
complex geometries where it may be impossible to apply a structured mesh. With
advances in mesh generation algorithms, combined with a user friendly graphical
interface, an unstructured mesh can be created automatically or with minimal user
interaction. In comparison, a structured mesh requires laying out a single mesh
block that is then split, merged, or have O-, and C- grids applied. This process is
much more difficult to perform and requires experience in the blocking strategy.

Fig. 6.13 Mesh construction based on advance front method on a 90° bend pipe. a Initial front
is established on the edge mesh setting. b New triangular mesh element is added by inserting one
new point to form a triangle and this continues to create a front. c Final completed mesh