Meshing a volume into tetrahedrons

I am trying to mesh a simple volume (into tetrahedrons. I obtained the 3D geometry by extruding a 2-D geometry. From what I understand I can only mesh a volume by first writing an stl-file, then importing it into MATLAB and then meshing the volume. But how do I export my 3-D geometry to an stl-file?

I somehow managed successfully to mesh the brick without the hole using the function Delaunay, triangulation and stl-write.

Below is some code.

Thank you so much for any help you could offer

Ansgar

%exterior boundary
x = [-4 4 4 -4];
y = [-4 -4 4 4];
%interior boundary
x1 = [0  -2 0 2];
y1 = [-2 0 2 0];
R1 = [2;4;x';y'];
R2 = [2;4;x1';y1'];
gm =[R1 R2];
sf = 'R1-R2';
ns = char('R1','R2')'

ns = 2×2 char array
    'RR'
    '12'

g = decsg(gm,sf,ns)

g = 7×8

2 2 2 2 2 2 2 2 4 4 0 -2 0 2 -4 -4 4 -4 -2 0 2 0 -4 4 -4 4 -2 0 2 0 -4 -4 4 4 0 2 0 -2 4 -4 1 1 1 1 1 1 0 1 0 0 0 0 0 0 1 0

model = createpde;
g1=geometryFromEdges(model,g)

g1 = 
  AnalyticGeometry with properties:

       NumCells: 0
       NumFaces: 1
       NumEdges: 8
    NumVertices: 8
       Vertices: [8×2 double]

%meshing the area works fine
mesh=generateMesh(model,'GeometricOrder','linear','Hmax',1,'Hmin',.3)

mesh = 
  FEMesh with properties:

             Nodes: [2×88 double]
          Elements: [3×132 double]
    MaxElementSize: 1
    MinElementSize: 0.3000
     MeshGradation: 1.5000
    GeometricOrder: 'linear'

pdeplot(model)

g2=extrude(g1,1)

g2 = 
  DiscreteGeometry with properties:

       NumCells: 1
       NumFaces: 10
       NumEdges: 24
    NumVertices: 16
       Vertices: [16×3 double]

figure 
pdegplot(g2,'FaceLabels','on','facealpha',.2)

%***********************
%where do I go from here
%***********************
%stlwrite, delaunay ?????? 

Answer 1

[Tushar]

Hi Ansgar,

I understand that you are looking for meshing the volume into tetrahedrons. But tetrahedron triangulation is not supported by 'stlwrite'. However, you can follow the steps below to get started:

• Extract the vertices from the 3D model, using the Vertices property of 'DiscreteGeometry' object:

X_=g2.Vertices(:,1);
Y_=g2.Vertices(:,2);

• Use the 'delaunayTriangulation' object to create a 2-D or 3-D 'Delaunay triangulation' from the set of vertices as follows:

DT=delaunayTriangulation([X_,Y_]);

• Explore the 'ConnectivityList' Property of the object DT.
• (optional step) Using the connectivity list as stated above, create a 'triangulation' object:

tri=triangulation(DT.ConnectivityList,X_,Y_);

• Finally, using the 'stlwrite' function, output this geometry into an STL file:

stlwrite(tri,"output.stl");