Creating a Simple Structure With Tetgen

The documentation and source code for TetGen can be found at the following location:

http://tetgen.berlios.de

When compiling the program is it best to disable the gnu library timer to avoid downloading the gnu libraries. This can be disabled in one of the #define statements.

There are two ways of defining a structure in TetGen, using either the .poly or .smesh file. The .poly format allows the creation of volumes containing holes, and other more complex features. It is usually sufficient to use the .smesh format where the surface meshes are defined, and a mesh is generated, bound by these surfaces. Here we describe the procedure for defining an IPS structure, including a dielectric region between the LC and the electrodes. Neumann or periodic boundary conditions should be applied to the sides of the structure.

It is essential that each surface is fully defined, even if a section of it has no boundary condition. All surfaces MUST be defined in a clockwise fashion.

To begin with it is necessary to define each node. The definitions can either be placed at the top of the .smesh or .poly file, or defined separately in a .node file, as has been done here

# Cube.node
8 3 0 0 # number of nodes, dimension (always 3), …don’t want a material number for nodes
1 0 0 0
2 0 2 0
3 2 2 0
4 2 0 0
5 0 0 10
6 0 2 10
7 2 2 10
8 2 0 10
0
0

Each surface is defined in the file below. Multiple surfaces may be defined on each face, but if the .smesh format it used, the created volumes cannot contain holes. The first number on each line gives the number of nodes that defines the surface, which are subsequently listed. The final number is the material number of the surface. The final region section of the file allows a material number to be applied to volumes by defining a point at the centre of the volume, and providing the material number.

# Cube.smesh
0 # A zero indicates the node list should read from file *.node
6 1 # number of surfaces, 1=material numbers given
4 1 2 3 4 2112# FixLC-1_Electrode-1
4 5 6 7 8 4224 # FixLC-2_Electrode-2
4 1 2 6 5 3 # Periodic
4 4 3 7 8 3 # Periodic
4 1 5 8 4 3 # Periodic
4 2 6 7 3 3 # Periodic
0
# region
1 # Number of regions
# region number, {x,y,z} region centre, material number
1 2 2 2 4 # Domain-1

To generate the mesh the following command should be used:

tetgen IPS.smesh -g -A -a2

The number that follows the –a indicated the volume of the elements that you want to generate. It is possible to adapt the mesh, and details of how to do so are given in the TetGen manual. Rename the output file IPS.1.mesh to meshin.txt and then run:

ConvTet.exe

This converts the format of the output into the standard GID form, as used by the modelling program, producing mesh.txt

This page last modified 2 June, 2006 by r.james