Meshing of volumes algorithms
Introduction
Flux provides three generators for automatic meshing of volumes: the Delaunay mesher, the Netgen mesher and the MeshGems mesher.
The three meshers are presented in the blocks below.
Delaunay mesher: process
The mesh generation by the Delaunay mesher is carried out in two phases, as presented in the table and figure below.
Stage  Description 

1  Generation of boundary mesh 
2  Insertion of internal nodes into border mesh elements 
MeshGems mesher: process
MeshGems, by its module MGTetra it is a generator of tetrahedral mesh of volume from a mesh of surface triangular. It is marketed by Distene http://www.distene.fr/
Comparison between Delaunay and MeshGems is presented in the table below.
Delaunay  MeshGems  

Characteristics 


Advantages / disadvantages 


* Reminder: In 3D, in case of a mixed meshing (mapped mesh /automatic mesh) with the Delaunay mesher, certain nodes must be inserted on the faces during the generation of the mesh front. This insertion is forbidden on the mapped faces, which generates the failure of the Delaunay mesher. The Netgen mesher is better suited to this problem.
Netgen mesher: process
The mesh generation by the Netgen mesher is an iterative process that is carried out in several phases, as presented in the table and figure below.
Stage  Description 

1  Initialization of front on the domain boundary 
2  The front becomes the border between the meshed region and the nonmeshed region 
3 
At each iteration:

4  Stop the process when the domain is entirely meshed 
Note: This mesher will not be available in future versions
Mesh optimization
Independent of the choice of mesher, Flux equally provides an algorithm for the optimization of the automatic volume meshing.
The optimization enables:
 to improve the mesh quality
 to reduce the number of elements
Optimization of the process
The mesh optimization is an iterative process of partition and/or fusion of the volume elements in function by certain predefined criteria. The global goal is the improvement of the mesh quality and the reduction of the number of elements.
The number of iterations influences over the quality of the result and the process time:
 Optimization of average quality and rapid: one iteration
 Optimization of good quality and slow: five iterations
The default number of iterations is set to 3, a value permitting to obtain a good quality/time ratio.