CFD Online Discussion Forums - [Gmsh] Gmsh Layers Command

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Gmsh Layers Command

Hi everyone,

I have started learning gmsh and kinda got stuck at one command.

I try to create multiple layers on a particular surface using the command

Code:

Layers { { expression-list }, { expression-list } }

Can someone tell me how exactly should the expression list in the sceond bracket be specified. What does it mean exactly?

The code below is taken from a tutorial case, if someone can please explain what those 0.5 and 1 mean and how to define them, it would be great

Code:

Extrude {0,0,h} {

  Surface{6}; Layers{ {8,2}, {0.5,1} };

}

Thanks once again as always!!!!

Hi,

Did you check documentation?

http://www.geuz.org/gmsh/doc/texinfo...ructured-grids

Quote:

In the first Layers form, expression gives the number of elements to be created in the (single) layer. In the second form, the first expression-list defines how many elements should be created in each extruded layer, and the second expression-list gives the normalized height of each layer (the list should contain a sequence of n numbers 0 < h1 < h2 < … < hn <= 1).

Your question is answered in the second sentence of the quote.

Hi,

I did read the manual but I couldnt understand what they exactly mean by the height of the layer because when I used it in my code shown below to mesh a simple box geometry it gives me an error. I have attached the geometry, error generated and the code.

Can you Please take a look and let me know what is going wrong.

Code:

Point(1) = {0.6, -0.2, 0.1, 1.0};

Extrude {1, 0, 0} {

  Point{1}; Layers{20};

}

Extrude {0, 1, 0} {

  Point{2};Layers{20};

}

Extrude {-1, 0, 0} {

  Point{3};Layers{20};

}

Extrude {0, -1, 0} {

  Point{4};Layers{20};

}

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

Plane Surface(6) = {5};



Extrude {0, 0, 2} {

  Surface{6}; Layers{{10,5}, {0.5,0.5}};

}

Thanks a ton!!

Hi,

I am not quite sure that I have got what you are trying to achieve (i.e. why use extrude instead of just creating straight lines). I did not checked Gmsh sources yet, but I think, the last value in relative heights should be 1 (at least if you put 1 in your case, error disappears). Also see comment in t3.geo before Extrude command.

Hi,

I am trying to create a structured mesh for this geometry but i am just not able to do it. Also, I am unable to create a structured mesh for a geometry which has two blocks sitting next to each other..can you please help because im really stuck at this...:(

Code:

Point(1) = {0.9, -0.2, -0, 1.0};

Point(2) = {1, -0.2, 0, 1.0};

Point(3) = {1, -0.1, -0, 1.0};

Point(4) = {1, 0.1, -0, 1.0};

Point(5) = {0.9, 0.1, -0, 1.0};

Point(6) = {1.4, -0.1, 0, 1.0};

Point(7) = {1.4, 0.1, -0, 1.0};

Point(8) = {1.4, -0.2, 0, 1.0};



Line(1) = {5, 4};

Line(2) = {4, 3};

Line(3) = {3, 2};

Line(4) = {2, 1};

Line(5) = {1, 5};

Line(6) = {7, 6};

Line(7) = {6, 3};

Line(8) = {4, 7};

Line(9) = {8, 6};

Line(10) = {2, 8};



Line Loop(11) = {4, 5, 1, 2, 3};

Plane Surface(12) = {11};

Line Loop(13) = {7, -2, 8, 6};

Plane Surface(14) = {13};



Transfinite Line {7, 8} = 40 Using Progression 1;

Transfinite Line {2, 6} = 40 Using Progression 1;

Transfinite Surface {14} = {7, 6, 3, 4} Left;



Transfinite Line {2, 3, 5} = 40 Using Progression 1;

Transfinite Surface {14} = {4, 3, 6, 7} Right;

Recombine Surface {14};

Transfinite Surface {12} = {1, 2, 4, 5} Right;

Recombine Surface {12};

Transfinite Line {4, 1} = 10 Using Progression 1;

Hi,

I was not able to guess what geometry you are trying to mesh (L-shaped channel?). Please find example mesh of two adjacent blocks attached to the message. If you attach just a sketch of the geometry you are trying to mesh, maybe I will be able to help you.

Hi,

Thank you so much for the example. That really helps. I have a question, for the transfinite algorithm to create structured mesh i.e no rtiangles or tetrahedra is it necessary for the lines being selected have equal number of points distributed?

Hi,

In fact I do not know exactly but in my meshes I keep number of points on opposite lines equal. Guess if number of points is different recombination algorithm may fail.

Hi guys!
What happen if i set Layer >1 and use mesh for 2D simulation in Open Foam,(so set "empty" for the faces that are along 3d dimension)?
Have you got any idea?

Best Regards