Numerical Simulation for Blood Flow - Microsurgery: Advances, Simulations, and Applications - page 188

5.3.2 Approximation Using Regular Grids

The simplest approach uses orthogonal grids (Cartesian or polar-
cylindrical). To apply such a grid to solution domains with inclined
or curved boundaries, the boundaries have to be approximated by
staircase-like steps. This approach has been used, but it raises two
kinds of problems:
1. The number of grids points (or CVs) per grid line is not
constant, as it is in a fully regular grid. This requires either
indirect addressing, or special arrays have to be created that
limit the index range on each line. The computer code may
need to be changed for each new problem.
2. The steps at the boundary introduce errors into the solution,
especially when the grid is coarse. The treatment of the
boundary conditions at stepwise walls also requires special
attention. This approach is a last resort, to be used when an
existing solution method cannot be quickly adapted to a grid
that its boundary better. It is not recommended, except when
the solution algorithm allows local grid reinement near the
wall.
Figure 5.25 shows example of trimmer mesh applied to vessel 3D
data of internal carotid artery (ICA). This method is the derived from
stepwise approximation.

Figure 5.17 Trimmer mesh.