# [Gmsh] surface from extrude in volume

John Daily John.Daily at lemmasoftware.org
Fri Feb 5 20:47:11 CET 2016

```I am trying to embed an extruded object within another volume for the
generation of a 3D mesh. Below is my .geo file. However, when I do 3D mesh,
I get an error "no tetrahedra in region 1 0", which occurs regardless of
how many toroid segments I add to the volume. I would appreciate any help?
I am at a loss here?

Thanks

/////////////////////////
// Geometric Inputs

ts = 1;         // height of toroid
tx = radius;    // radial width of toroid, measured in centre of ring
tl = 0;         // centre of rotation

/////////////////////////////////////
// Large Bounding box
X0 = -Box;
X1 =  Box;
Y0 = -Box;
Y1 =  Box;
Z0 = -Box;
Z1 =  Box;

pp = newp;
Point(pp)    = {X0, Y0, Z0, blc};
Point(pp+1)  = {X1, Y0, Z0, blc};
Point(pp+2)  = {X1, Y1, Z0, blc};
Point(pp+3)  = {X0, Y1, Z0, blc};

lv = newl;
Line(lv) = {pp,pp+1};
Line(lv+1) = {pp+1,pp+2};
Line(lv+2) = {pp+2,pp+3};
Line(lv+3) = {pp+3,pp};
Line Loop(lv+4) = {lv, lv+1, lv+2, lv+3};

bs = news;
Plane Surface(bs) = {lv+4};
v[] = Extrude {0, 0, Z1-Z0} { Surface{bs}; };

/////////////////////////////////////////
// Make a toroid
tpp = newp;
Point(tpp  ) = {    tx,    0, 0,  lc};
Point(tpp+1) = { ts+tx,    0, 0,  lc};
Point(tpp+2) = {    tx,   ts, 0,  lc};
Point(tpp+3) = {    tx,  -ts, 0,  lc};
Point(tpp+4) = {-ts+tx,    0, 0,  lc};

cc = newc;
Circle(cc  ) = {tpp+1, tpp, tpp+2};
Circle(cc+1) = {tpp+2, tpp, tpp+4};
Circle(cc+2) = {tpp+4, tpp, tpp+3};
Circle(cc+3) = {tpp+3, tpp, tpp+1};

ll = newll;
Line Loop(ll) = {cc, cc+1, cc+2, cc+3};
rs = news;

ps = news;
Plane Surface(ps) = {ll};

tv1[] = Extrude {{0, 1, 0},{-tl,0,0}, 2*Pi/3} { Surface{ps}    ;};
tv2[] = Extrude {{0, 1, 0},{-tl,0,0}, 2*Pi/3} { Surface{tv1[0]};};
tv3[] = Extrude {{0, 1, 0},{-tl,0,0}, 2*Pi/3} { Surface{tv2[0]};};

// Not correct?
Surface{tv1[0]} In Volume{v[1]};
Surface{tv2[0]} In Volume{v[1]};
Surface{tv3[0]} In Volume{v[1]};

Physical Volume(1) = {v[1]};
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```