Mesh a cube with a sphere on the side

General Discussion
1

Dear All

I’d like to mesh a cube with a sphere on the side.

i use" tetgen".

There is the code FreeFem++

load “msh3”
load “TetGen”
load “medit”
include “MeshSurface.idp”

// Parameters
real hs = 0.1; //mesh size on sphere
int r= 0.5;
int[int] M = [20, 20, 20];
real [int,int] B = [[-1, 1], [-1, 1], [-1, 1]];
int [int,int] L = [[1, 2], [3, 4], [5, 6]];

// Meshes
meshS ThH = SurfaceHex(M, B, L, 1);
meshS ThS = Sphere(0.5, hs, 7, 1);

meshS Th1S= movemesh(ThS, [x+1, y+1, z+1]);

meshS ThHS = Th1S + ThH ;
medit(“Hex-Sphere”, ThHS);

real voltet = (hs^3)/6.;
cout << "voltet = " << voltet << endl;
real[int] domain = [0, 0, 0, 1, voltet, 1, 1, 1, 2, voltet];
mesh3 Th = tetg(ThHS, switch=“pqaAAYYQ”, nbofregions=2, regionlist=domain);

medit(“Cube with ball”, Th);

plot(Th, wait=true,fill=true);

I have this error bellow:

Loading data file(s)
End of mesh
Input seconds: 0.00

medit1()

Building scene(s)
Creating scene 1
Loading default options
Scene seconds: 0.36

Rendering scene(s)

Total running seconds: 10.16
Thank you for using Medit.
voltet = 0.000166667
3D RemplissageSurf3D:: Vertex triangle2 border 3208 6408 240
tetgenio: vertex
tetgenio: facet
tetgen: before tetrahedralize( , &in, &out);
numberof regions 10
numberof hole 0
PLC Error: A segment and a facet intersect at point (0.562503,1,0.762503).
Segment: [2021,2041] #-1 (4)
Facet: [287,282,312] #7
Strange catch exception ???
at exec line 94 , mpirank 0

Thank you in advance to the help

2

Maybe you could use Gmsh instead.

SetFactory('OpenCASCADE');
Box(1) = {-1.0,-1.0,-1.0, 2, 2, 2};
Sphere(2) = {0.9999,1,1, 0.5};
BooleanFragments{ Volume{1,2}; Delete; }{}
Characteristic Length{ PointsOf{ Volume{1}; } } = 0.1;
Characteristic Length{ PointsOf{ Volume{3}; } } = 0.1;
Characteristic Length{ PointsOf{ Volume{2}; } } = 0.1;

Then, to do the actual meshing.

gmsh -3 cube-sphere.geo -format mesh

Finally, the .edp.

// gmsh -3 cube-sphere.geo -format mesh

load "msh3"
load "medit"

mesh3 Th = readmesh3("cube-sphere.mesh");
fespace Vh(Th, P1);
Vh u = x + y + z;

medit("Th", Th, u);

Screenshot 2020-05-22 at 10.09.41 AM
Screenshot 2020-05-22 at 10.09.41 AM594×600 107 KB

1 Like
3

Ok i will try with Gmsh.

Thank you for your help

4

i try with Gmsh and i got this error:

read mesh ok 1Mesh3, num Tetra:= 0, num Vertice:= 0 num boundary Triangles:= 0
– Mesh3::Mesh3 Erreur opening cube.mesh
current line = 6
Assertion fail : (0)
line :161, in file …/femlib/Mesh3dn.cpp
Assertion fail : (0)
line :161, in file …/femlib/Mesh3dn.cpp
err code 6 , mpirank 0
try getConsole C:\Users\aboubakiri.diaw\Desktop\tr\test.edp
save log in : ‘C:\Users\aboubakiri.diaw\Desktop\tr\test.log’
wait enter ?

can you help me to fix it, i never use Gmsh before
thank you in advance

5

What .geo did you mesh, how did you mesh it, how do you load it? It seems there is no cube.mesh in your folder.

6

I tried to mesh with the code you wrote above. I first wrote the code on a notepad and then saved it as a .geo file. Then I tried to open it with FreeFem++. is this correct?

7

No. You need to actually mesh the .geo using Gmsh.

8

okay, i was able to mesh it using Gmsh.
How can i add a sphere in the middle and a quarter sphere on the side?
what is the syntax in this case with gmsh?

Thank you in advance for you response

9

Here is a pretty good Gmsh tutorial. You can also look at the numerous Gmsh examples.

10

I finally done it.

thanks for all