Generation of Computational Mesh for CFPD Simulations - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 91

4.4.4 Mesh Generation Software

Mesh generation is a research field in itself, whereby new algorithms are constantly
being developed in order to provide significant benefites in mesh generation. This
includes producing algortihms that provide higher quality connectivity between the
nodal points, improved data structures, and more efficient storage and data handling.
Typically commercially available software will have general capability to generate
both structured and unstructured meshes. A graphical user interface is used to start
the automated mesh generation, and therefore these software requires the user to
become familiar with the tools and functions of the software. Open source software
are typically more specialised in their functionality. They tend to produce either
one type of mesh such as triangular/tetrahedral quadrilateral or hexahedral. These
software are normally available as source codes which need to be run and compiled
under the programming language it is available in.

4.5 Examples

4.5.1 Meshing the Nasal Cavity

After extracting the nasal cavity airway by segmentation, the computational file
should be saved as an IGES, STL, or STEP in order to be cross-compatible with a
range of 3D modelling and meshing programs. Typically the meshing procedure can
begin by applying a simple unstructured tetrahedral mesh all over which produces a
single contiguous mesh. However for easier post processing of local flow variables
and particle deposition fractions, the computational model may be split into smaller
sub-regions during the CAD surface and volume generation stage, prior to meshing.
While the process of subdividing the computational model into smaller regions can
be performed within some CFD packages, it is not always an easy task; therefore it
is recommended that the division be performed in CAD packages that have NURBS
functionality. Figure 4.19 shows a nasal cavity subdivided into ten sections.

Fig. 4.19 Nasal geometry
subdivided into ten sections
and labelled with S and a
number representing the
section. S1 - S3 represents the
anterior , S4 - S7 the middle ,
and S8 - S10 the posterior
nasal cavity. An artificial
extension is added after S10
to assist in the simulation