Generation of Computational Mesh for CFPD Simulations - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 73

Fig. 4.1 Mesh topology hierarchy from lowest ( left ) to the highest ( right ). a Topology heirachy.
b 2D and 3D mesh element types

4.1.1 Mesh Topology

A computational mesh topology has a hierarchical system whereby higher topol-
ogy assumes the existence of the topologies beneath it (Fig. 4.1 ). For example, the
creation of a volume cell automatically inherits the lower topologies (i.e. a volume
cell contains face, line and vertex structures). For a 2D mesh, all nodes (discrete
points) lie in a given plane with its resulting 2D mesh elements being quadrilater-
als or triangles. For a 3D mesh, nodes are not constrained to a single plane with
its resulting 3D mesh elements being hexahedra, tetrahedra (tets), square pyramids
(pyramids, extruded triangles, wedges or triangular prisms) or polyhedra. Since all
3D elements are bounded by 2D faces, it is obvious that 3D meshes are constructed
with 2D elements at boundaries. Typically many meshing algorithms start by mesh-
ing the enclosed surface before filling the interior with 3D elements. In this case,
care should be taken to generate a good quality surface.

4.2 Structured Mesh Systems

4.2.1 Structured Mesh Properties

By definition, a structured mesh is a mesh containing cells having either a regular-
shape element with four-nodal corner points in two dimensions or a hexahedral-shape
element with eight-nodal corner points in three dimensions. It is characterised by
regular connectivity that is a straightforward prescription of an orthogonal (90 ◦ )
mesh in a Cartesian system. The use of a structured mesh brings certain benefits
in CFPD computations. Being relatively easy to construct, it allows novel ideas or