tet_mesh_l2q, an Octave code which converts a 4-node tetrahedral mesh ("tet mesh") into a 10-node tet mesh.
In particular, the code reads information describing a set of 3D points, and a 4 node ("linear") tet mesh of those points. It creates a "quadratic" tet mesh, which has the same number of tetrahedrons, but in which each tetrahedron is defined by 10 nodes. In the process, it adds just enough nodes, at the midsides of the edges of the original mesh, to define the new mesh. The data defining the new mesh is written out to files for further use.
The refinement of a single tetrahedron is easy. Every pair of nodes generates a new node whose location is the average of the locations of the original two nodes. The problem is that many tetrahedrons may share the same edge. The new node needs to be generated exactly once, and assigned a unique index, which all the tetrahedrons will share. The tricky part of this calculation is thus figuring out whether it is time to generate a new node, or whether the node has already been generated, in which case the appropriate index must be retrieved.
tet_mesh_l2q ( 'prefix' )where
The input and output files use the simple TABLE format; comment lines begin with a "#" character. Otherwise, each line of the file contains one set of information, either the coordinates of a node (for a node file), or the indices of nodes that make up a tetrahedron, (for a tetrahedron file).
The input file prefix_nodes.txt contains the coordinate information for the 4-node tet mesh. Each data line contains the X and Y coordinates of a single node.
The input file prefix_elements.txt contains the tetrahedron information for the 4-node tet mesh. Each data line contains the indices of four nodes that form a tetrahedron.
The output file prefix_l2q_nodes.txt contains the coordinate information for the 10-node tet mesh. The data lines begin with the node information from nodes.txt, followed by the coordinates of the new nodes.
The output file prefix_l2q_elements.txt contains the tetrahedron information for the 10-node tet mesh. There are exactly as many tetrahedrons as before, but now each tetrahedron uses 10 nodes. Each line of the file contains the indices of 10 nodes that form the tetrahedron, listed in a particular order. The first four node indices are the same as for the linear tet mesh. The next six node indices may be thought of as being obtained as averages of pairs of the first four nodes. Symbolically, this may be thought of as:
1 2 3 4 (1+2) (1+3) (1+4) (2+3) (2+4) (3+4)
The computer code and data files described and made available on this web page are distributed under the MIT license
tet_mesh_l2q is available in a C++ version and a Fortran90 version and a MATLAB version and an Octave version.
tet_mesh, an Octave code which includes a variety of routines for working with tetrahedral meshes.
tet_mesh_boundary, an Octave code which returns the nodes and faces of the boundary of a tetrahedral mesh, which themselves form a 3d triangular mesh or "tri_surface".
tet_mesh_display, an Octave code which can read in the node and tetra files defining a tet mesh and display a wireframe image.
tet_mesh_order4, a directory which contains a description and examples of a tet mesh using order 4 elements.
tet_mesh_order10, a directory which contains a description and examples of a tet mesh using order 10 elements.
tet_mesh_q2l, an Octave code which takes a 10-node tet mesh and makes a 4-node tet mesh.
tet_mesh_quality, an Octave code which takes a 4-node tet mesh and computes the "quality" of the mesh.
tet_mesh_rcm, an Octave code which takes a tet mesh and relabels the nodes to reduce the bandwidth of the corresponding adjacency matrix.
tet_mesh_refine, an Octave code which can refine a tet mesh.
tet_mesh_tet_neighbors, an Octave code which computes the tetrahedral adjacency information.
tet_mesh_volumes, an Octave code which computes the volume of each tetrahedron in a tet mesh;