Generation of Computational Mesh for CFPD Simulations - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 93

4.5.2 Meshing the Trachea and Primary Bronchi

The trachea and primary bronchi conducting airway are extracted via the segmenta-
tion stage as shown in Fig. 4.22 . Here we present a different method to reconstruct the
airway, by exporting the bounding airway surface location data as discrete coordinate
points (point clouds). This is a common procedure referred to as reverse engineering.
The point clouds form the basis for developing the surface using B-Spline or NURBS
algorithms where the actual surface wraps around the object by effectively joining up
the cloud points. After the CAD reconstruction, the domain is subdivided into smaller
regions for local analysis. Meshing of the airway is achievable because the primary
bronchi are large enough that the mesh does not need to become too small and pro-
hibitive. However as the bronchial airway bifurcates, the next generation airway's
diameter decreases. For example, in the trachea the diameter is approximately 18 mm
while the third generation branch diameters are approximately 5-7 mm (Inthavong
et al. 2010). Further downstream these diameters become even smaller and often this
leads to a loss of resolution. In this case the small airways which do not resemble
a coherent tubular shape are cut, and an artificial extension is applied to the outlets.
This allows the meshing to be more manageable. Using a meshing program, an au-
tomatic unstructured mesh is initially applied to create both the surface and volume
mesh. Mesh refinements were applied in a similar manner to that of the nasal cavity
discussed earlier.

Fig. 4.22 Mesh generation from the trachea and primary bronchi