demo04 of writeMesh

Mesh with quadratic elements
Cite as: Ma, J., & Li, Y. (2025). Im2mesh: A MATLAB/Octave package for generating finite element mesh based on 2D multi-phase image (2.1.5). Zenodo. https://doi.org/10.5281/zenodo.14847059
Jiexian Ma, mjx0799@gmail.com. Project website.
Table of Contents
Initialize Load mesh Plot mesh Convert linear elements to quadratic elements Plot mesh Export as inp file (Abaqus) Export as bdf file (Nastran bulk data) Export as msh file (Gmsh mesh file)

Initialize

clearvars
Set default image size.
x = 250; y = 250; width = 250; height = 250;
set(groot, 'DefaultFigurePosition', [x,y,width,height])
% To reset:
% set(groot, 'DefaultFigurePosition', 'factory')

Load mesh

Let's load the mesh data from "mesh_data_1.mat"
load("mesh_data_1.mat")
We will see 2 variables.
vert
vert = 96×2
44.5000 48.5000 52.5000 98.5000 76.5000 158.5000 84.5000 96.5000 100.5000 156.5000 104.5000 17.5000 104.5000 47.5000 105.5000 205.5000 105.5000 222.5000 109.5000 214.5000
ele
ele = 135×3
36 17 86 49 77 58 77 84 88 57 82 92 45 71 22 4 73 40 87 67 66 52 28 46 86 35 36 5 82 64
'ele' has 3 column so it is a triangular mesh with linear elements.

Plot mesh

Use function plotMeshes to plot mesh.
plotMeshes(vert,ele);

Convert linear elements to quadratic elements

We use function insertNode to convert the linear elements to quadratic elements.
% vert2, ele2 define quadratic elements
[vert2, ele2] = insertNode(vert, ele);
Let check the size of them
size(vert)
ans = 1×2
96 2
size(vert2)
ans = 1×2
326 2
size(ele)
ans = 1×2
135 3
size(ele2)
ans = 1×2
135 6
We saw that 'ele2' has 6 column so it is a triangular mesh with quadratic elements.

Plot mesh

Use function plotMeshes to plot mesh.
plotMeshes(vert2,ele2);

Export as inp file (Abaqus)

We use function printInp2d to write 2d mesh to inp file.
The exported inp file would have a model with one part, which contains one section.
We can specify element type, precision_nodecoor and file name.
ele_type = 'CPS6';
precision_nodecoor = 8;
file_name = 'test.inp';
printInp2d( vert2, ele2, [], ele_type, precision_nodecoor, file_name );
printInp2d Done! Check the inp file!

Export as bdf file (Nastran bulk data)

Function printBdf2d currently does not work for quadratic element. We will see error message.
precision_nodecoor = 8;
file_name = 'test.bdf';
printBdf2d( vert2, ele2, [], [], precision_nodecoor, file_name );
Error using printBdf2d (line 228)
Function printBdf2d do not support quadratic elements.

Export as msh file (Gmsh mesh file)

Function printMsh currently does not work for quadratic element. Mesh element will be proceesed as linear elements.
precision_nodecoor = 8;
file_name = 'test.msh';
printMsh( vert2, ele2, [], [], precision_nodecoor, file_name );
Warning: Mesh elements will be processed as linear trangles.
printMsh Done! Check the msh file!
% reset image size
set(groot, 'DefaultFigurePosition', 'factory')
% end of demo