Generate meshes from .geo files with Gmsh

Meshes are built with gmsh from .geo files then loaded into freshkiss3d.

import os
import numpy as np
import matplotlib.pyplot as plt
import freshkiss3d as fk

Generate meshes from .geo

Meshes are generated with gmsh thanks to a .geo file. The .geo contains all information gmsh needs to generate a Delaunay triangulation. You can specify the number of nodes on boundaries with the Transfinite option.

Note

.geo files can be generated with gsmh and are easy to script for simple geometries. Here is an example of a simple canal geometry:

Lx = 25.0;
Ly = 1.0;
Point(1) = {0, 0, 0, 1};
Point(2) = {Lx, 0, 0, 1};
Point(3) = {Lx, Ly, 0, 1};
Point(4) = {0, Ly, 0, 1};
Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 4};
Line(4) = {4, 1};
Line Loop(5) = {3, 4, 1, 2};
Plane Surface(0) = {5};
Physical Line(1) = {4};
Physical Line(2) = {2};
Physical Line(3) = {3};
Physical Line(4) = {1};
Transfinite Line {3, 1} = 50 Using Progression 1;
Transfinite Line {4, 2} = 3 Using Progression 1;
Physical Surface(0) = {0};

Gmsh can be called via simple commands to generate meshes:

os.system('gmsh -2 -format msh2 inputs/bump0.geo -o inputs/bump0.msh')
os.system('gmsh -2 -format msh2 inputs/bump1.geo -o inputs/bump1.msh')

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Construct a TriangularMesh

triangular_mesh_1 = fk.TriangularMesh.from_msh_file('inputs/bump0.msh')
triangular_mesh_2 = fk.TriangularMesh.from_msh_file('inputs/bump1.msh')

Basic plot

TG = triangular_mesh_1.triangulation
x = np.asarray(TG.x)
y = np.asarray(TG.y)
trivtx = np.asarray(TG.trivtx)

TG_r = triangular_mesh_2.triangulation
x_r = np.asarray(TG_r.x)
y_r = np.asarray(TG_r.y)
trivtx_r = np.asarray(TG_r.trivtx)

plt.rcParams["figure.figsize"]=[20,6]
fig = plt.figure()

# Plot
ax1 = fig.add_subplot(211)
ax1.triplot(x, y, trivtx, color='r')
ax1.set_title("Mesh 1")

# Plot refined mesh
ax2 = fig.add_subplot(212)
ax2.triplot(x_r, y_r, trivtx_r)
ax2.set_title("Mesh 2")

plt.show()

#os.system('rm inputs/bump0.msh')
#os.system('rm inputs/bump1.msh')