# Gmsh 3D Boundary layer

 Register Blogs Members List Search Today's Posts Mark Forums Read

 March 17, 2016, 08:09 Gmsh 3D Boundary layer #1 New Member   Join Date: Mar 2016 Posts: 8 Rep Power: 10 Hi everyone! First time I post a question here, hope it's not a stupid one! I am trying to mesh a 3D geometry imported in STEP format and I would like to control the size of the first cell on the boundary. I found the "Boundary Layer" in the "Size fields" menu so I tried to fill the Edges list and to choose the size with the parameters (hwall_n, ratio, thickness...). But then, nothing happens. I tried to remesh but there is no difference... Obviously I do not use it correctly but I don't understand how I am supposed to use it. So, could anyone tell me how to use "Size field" and/or how to choose the thickness of the first cell? Thank you! (Sorry for the bad English, this is not my mother tongue). EDIT : Here is my .geo file : --------------------------------------------------------------------------------- lc = 1; fflc = 4000; Merge "demie_voile_v2.step"; Transfinite Line { 6, 8} = 191 Using Progression 1; Transfinite Line {12, 19} = 2 Using Progression 1; Transfinite Line {13, 16} = 91 Using Progression 1; Transfinite Line {14, 20} = 90 Using Progression 1; Transfinite Line { 9, 11} = 94 Using Progression 1; Mesh.CharacteristicLengthFactor = lc; Mesh.CharacteristicLengthMax = fflc; Physical Line(0) = {9,11,10,14,20,18,13,16,17,12,19,5,6,8,7}; Physical Surface(1) = {1,2,3,4,5,6,7,8}; Field[4] = BoundaryLayer; Field[4].FacesList = {1,2,3,4,5,6,7,8}; Field[4].hfar = fflc; Field[4].hwall_n = 0.1; Field[4].hwall_t = 0.5; Field[4].thickness = 0.01; Field[4].ratio = 1.1; BoundaryLayer Field = 4; --------------------------------------------------------------------------------- I don't know exactly what values I should use. But now it is simply useless. I can take the Boundary layer part off without any difference. Last edited by Ambroise; March 18, 2016 at 08:09.

 March 28, 2016, 03:38 #2 Member   Peter Join Date: Feb 2015 Location: New York Posts: 73 Rep Power: 11 Hi, Have a look at the Gmsh documentation. In this specific case, you've set your desired layer thickness at the wall larger than the desired thickness of your entire boundary layer. Also worth noting, Gmsh 2.12+ doesn't seem to generate boundary layers. I would suggest using version 2.10 or 2.11. Good luck! Kind regards, Peter

 March 29, 2016, 09:49 #3 New Member   Join Date: Mar 2016 Posts: 8 Rep Power: 10 Indeed, version 2.11 do create a boundary layer once I changed the settings as you said! The mesh is not perfect yet but I have a boundary layer! Thanks for your help!

 Tags boundary cell, boundary layer, boundary layer thickness, gmsh, mesh 3d