[Gmsh] sharp edges between surfaces in the 3d meshing of an ellipsoid

[valentina carapella]

Hi,

I am new to gmsh and I'm trying to use it to generate a tetrahedral finite
element mesh of a thick-walled truncated ellipsoid. To do so I have created
a scaffold of elliptic arcs and then connected them to make an inner
half-ellipsoidal surface and an outer one and then generated a volume and
meshed it. I added the code at the end of the email.
My problem is that in this way I get kinks where the different surfaces
meet and this affects the simulations I then do with such mesh. I get
indeed on a xy-plane cut a couple of rhomboid-like rather than concentric
ellipses. I then mesh using
Mesh Adapt <-- 2D algorithm
Delaunay <-- 3D algorithm
Standard <-- recombination algorithm

None <-- Subdivision algorithm
No split <-- Remeshing algorithm
Harmonic <-- remeshing parametrization

1<-- Smoothing steps
1.00 <-- Element size factor
0-1e+22 <-- Min/Max element size

I don't know if its a matter of meshing settings or the way I've defined
the scaffold. I've tried a few different settings but didn't succeed. Is
there a way to make the connection between surfaces smoother?

Best

Valentina


-----------------------------------------
-----------------------------------------
lc = 0.09;
b0=0.5;
a0=0.4;
c0= 1;
rad_ax=0.1;

//CENTRE POINT

Point(1) = {0.0,0.0,0.0,lc};

//OUTER ELLIPSOID

Point(2) = {a0,0.0,0.0,lc};
Point(3) = {0.0,b0,0.0,lc};
Point(4) = {0.0,rad_ax,0.0,lc};

Ellipse(1) = {2,1,4,3};

Point(5) = {-a0, 0.0, 0.0, lc};

Ellipse(2) = {3,1,4,5};

Point(6) = {0.0,-b0, 0.0, lc};
Point(7) = { 0.0, -rad_ax,0.0, lc};

Ellipse(3) = {2,1,7,6};
Ellipse(4) = {6,1,7,5};

Point(8) = {0.0,0.0,-c0,lc};
Point (9) = {0.0,0.0, -rad_ax,lc};

Ellipse(5) = {3,1,9,8};
Ellipse(6) = {2,1,9,8};
Ellipse(7) = {6,1,9,8};
Ellipse(8) = {5,1,9,8};

Line Loop(9) = {1,5,-6};
Ruled Surface(10) = {9};

Line Loop(11) = {3,7,-6};
Ruled Surface(12) = {11};

Line Loop(13) = {4,8,-7};
Ruled Surface(14) = {13};

Line Loop(15) = {2,8,-5};
Ruled Surface(16) = {15};

// INNER ELLIPSOID

d=0.15;
a1=a0-d;
b1=b0-d;
c1=c0-d;
Point(10) = {a1,0.0,0.0,lc};
Point(11) = {0.0,b1,0.0,lc};
Ellipse(17) = {10,1,4,11};

Point(12) = {-a1, 0.0, 0.0, lc};

Ellipse(18) = {11,1,4,12};

Point(13) = {0.0,-b1, 0.0, lc};


Ellipse(19) = {10,1,7,13};
Ellipse(20) = {13,1,7,12};

Point(14) = {0.0,0.0,-c1,lc};


Ellipse(21) = {11,1,9,14};
Ellipse(22) = {10,1,9,14};
Ellipse(23) = {13,1,9,14};
Ellipse(24) = {12,1,9,14};

Line Loop(25) = {17,21,-22};
Ruled Surface(26) = {25};

Line Loop(27) = {19,23,-22};
Ruled Surface(28) = {27};

Line Loop(29) = {20,24,-23};
Ruled Surface(30) = {29};

Line Loop(31) = {18,24,-21};
Ruled Surface(32) = {31};

//BORDERS


Line(33)={2,10};
Line(34)={6,13};
Line(35)={5,12};
Line(36)={3,11};

Line Loop(37) = {33, 17, -36, -1};
Plane Surface(38) = {37};
Line Loop(39) = {36, 18, -35, -2};
Plane Surface(40) = {39};
Line Loop(41) = {35, -20, -34, 4};
Plane Surface(42) = {41};
Line Loop(43) = {34, -19, -33, 3};
Plane Surface(44) = {43};

Surface Loop(45) = {10,12,14,16,26,28,30,32,38,40,42,44};
Volume(46) = {45};
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