# [Gmsh] Parallelepiped with hole in the middle

Robert Atanasiu robert.atanasiu29 at gmail.com
Mon Apr 6 19:07:47 CEST 2020

```Hello,

I hope you are all doing well.

I am trying to make an structured mesh having the representation of a
parallelepiped with a hole in the middle of the structure. This "hole" has
the sole purpose of signaling the presence of an obstacle. For some reason,
I get errors regarding the transfinite algo of 2 particular surfaces, while
the other 8 work. Also, how can I ensure the normals are all pointing in
the right convention?

Here is my algorithm:
//
l_ref = 1;

Point(1) = {-0.5, -0.5, 0, l_ref};  Point(2) = {0.5, -0.5, 0, l_ref};
Point(3) = {0.5, -0.5, 4.0, l_ref}; Point(4) = {0.5, 0, 4.0, l_ref};
Point(5) = {0.5, 0, 6.0, l_ref}; Point(6) = {0.5, -0.5, 6.0, l_ref};
Point(7) = {0.5, -0.5, 10.0, l_ref}; Point(8) = {0.5, 0.5, 10.0, l_ref};
Point(9) = {0.5, 0.5, 0, l_ref}; Point(10) = {-0.5, 0.5, 0, l_ref};
Point(11) = {-0.5, -0.5, 4.0, l_ref}; Point(12) = {-0.5, 0, 4.0, l_ref};
Point(13) = {-0.5, 0, 6.0, l_ref}; Point(14) = {-0.5, -0.5, 6.0, l_ref};
Point(15) = {-0.5, -0.5, 10.0, l_ref}; Point(16) = {-0.5, 0.5, 10.0, l_ref};

Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 4};
Line(4) = {4, 5};
Line(5) = {5, 6};
Line(6) = {6, 7};
Line(7) = {7, 8};
Line(8) = {8, 9};
Line(9) = {9, 10};
Line(10) = {10, 16};
Line(11) = {16, 8};
Line(12) = {2, 9};
Line(13) = {10, 1};
Line(14) = {1, 11};
Line(15) = {11, 12};
Line(16) = {12, 13};
Line(17) = {13, 14};
Line(18) = {14, 15};
Line(19) = {15, 16};
Line(20) = {7, 15};
Line(21) = {3, 11};
Line(22) = {14, 6};
Line(23) = {4, 12};
Line(24) = {5, 13};

Line Loop(21) = {1, 12, 9, 13}; Plane Surface(22) = {21};
Line Loop(23) = {2, 3, 4, 5, 6, 7, 8, -12}; Plane Surface(24) = {23};
Line Loop(25) = {7, -11, -19, -20}; Plane Surface(26) = {25};
Line Loop(27) = {-10, 13, 14, 15, 16, 17, 18, 19}; Plane Surface(28) =
{27};
Line Loop(29) = {8, 9, 10, 11}; Plane Surface(30) = {29};
Line Loop(31) = {1, 2, 21, -14}; Plane Surface(32) = {31};
Line Loop(33) = {3, 23, -15, -21}; Plane Surface(34) = {33};
Line Loop(35) = {4, 24, -16, -23}; Plane Surface(36) = {35};
Line Loop(37) = {-5, 24, 17, 22}; Plane Surface(38) = {37};
Line Loop(39) = {6, 20, -18, 22}; Plane Surface(40) = {39};

Surface Loop(40) = {22, 24, 26, 28, 30, 32, 34, 36, 38, 40};
Volume(41) = {40};

Transfinite Line {1, 9, 20, 11} = 10;
Transfinite Line {12, 13, 7, 19} = 20;
Transfinite Line {2, 14} = 20;
Transfinite Line {4, 16} = 60;
Transfinite Line {6, 18} = 40;
Transfinite Line {8, 10} = 120;

Transfinite Surface{22} = {1, 2, 9, 10};
Transfinite Surface{24} = {2, 7, 8, 9};
Transfinite Surface{26} = {7, 8, 16, 15};
Transfinite Surface{28} = {16, 15, 10, 1};
Transfinite Surface{30} = {8, 9, 10, 16};
Transfinite Surface{32} = {1, 2, 3, 11};
Transfinite Surface{34} = {3, 4, 12, 11};
Transfinite Surface{36} = {4, 5, 13, 12};
Transfinite Surface{38} = {5, 6, 13, 14};
Transfinite Surface{40} = {6, 7, 15, 14};

Recombine Surface {22, 24, 26, 28, 30, 32, 34, 36, 38, 40};
Transfinite Volume {41} = {2, 3, 4, 5, 6, 7, 8, 9, 10, 1, 11, 12, 13, 14,
15, 16};

// Physical Surface(200) = {22, 24, 26, 28, 30, 32, 34, 36, 38, 40};
Physical Surface('inlet') = {22};
Physical Surface('periodic_0_r') = {24};
Physical Surface('outlet') = {26};
Physical Surface('periodic_0_l') = {28};
Physical Surface('top') = {30};
Physical Surface('bottom1') = {32};
Physical Surface('bottominclined1') = {34};
Physical Surface('bottom2') = {36};
Physical Surface('bottominclined2') = {38};
Physical Surface('bottom3') = {40};

Physical Volume('fluid') = {41};

//

I would be very grateful if you can answer my question!

Kind regards,
Robert Atanasiu
Imperial College London, Aeronautics Undergraduate Student
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