Gmsh Mesh

Geometry

We construct the geometry by first creating points, then connecting the points into curves, and finally the curves into surfaces. Fig. 87 shows the geometry and variables names of the vertices and curves.

Fig. 87 Geometry created in Gmsh for generating the finite-element mesh. We construct curves from points (p_*) and surfaces from the curves (c_*). The arrows indicate the direction (orientation) of the curves.

Meshing using Python Script

We use the Python script generate_gmsh.py to create the geometry and generate the mesh. The script is structured identically to the one we used in examples/strikeslip-2d and examples/reverse-2d. We create a class App that implements the functionality missing in gmsh_utils.GenerateMesh. We must implement the create_geometry(), mark(), and generate_mesh() methods that are abstract in the GenerateMesh base class. In this case the geometry is significantly more complex with arrays of points defining the top surface (topography and bathymetry) and the geometry of the slab.

We use the Gmsh MeshSize options to define a discretization size the grows slowly at a geometric rate with distance from the main fault.

Listing 127 Run the generate_gmsh.py Python script to generate the mesh.

# Generate a mesh with triangular cells and save it to `mesh_tri.msh` (default filename).
$ ./generate_gmsh.py --write

# Save as above but start the Gmsh graphical interface after saving the mesh.
$ ./generate_gmsh.py --write --gui

# Create only the geometry and start the Gmsh graphical interface.
$ ./generate_gmsh.py --geometry --gui

By default the Python script will generate a finite-element mesh with triangular cells and save it to the file mesh_tri.msh. You can view the mesh using Gmsh either by using the --gui command line argument when you generate the mesh or running Gmsh from the command line and opening the file.

Listing 128 View the Gmsh mesh file mesh_tri.msh using Gmsh.

gmsh -open mesh_tri.msh

Fig. 88 Finite-element mesh with triangular cells generated by Gmsh.