[mkoeh]

Hey there,


I'm a new forum member and I would like to ask you, if you could help me out with the following problem:

I have a bcc lattice domain for the stokes equation and I'm trying to set up the domain with gmsh. For all spherical cavitys of the bcc lattice I would like to assign a physical surface to it, such that the FE-solver can handle those surfaces as a noslip cond.

// Gmsh project created on Thu Feb  7 09:15:11 2019
SetFactory("OpenCASCADE");

half_length = 0.5774;
//+
Box(1) = {0, 0, 0, half_length, half_length, half_length};
//+
Sphere(2) = {half_length, half_length, half_length, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(3) = {half_length, half_length, 0, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(4) = {half_length, 0, 0, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(5) = {half_length, 0, half_length, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(6) = {0, 0, half_length, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(7) = {0, half_length, half_length, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(8) = {0, half_length, 0, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(9) = {0, 0, 0, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
Sphere(10) = {half_length/2, half_length/2, half_length/2, 0.25, -Pi/2, Pi/2, 2*Pi};
//+
BooleanDifference{ Volume{1}; Delete; }{ Volume{10}; Volume{8}; Volume{9}; Volume{3}; Volume{4}; Volume{2}; Volume{5}; Volume{7}; Volume{6}; Delete; }
//+

//+
Translate {0, 0, half_length} {
  Duplicata { Volume{1}; }
}
//+
Translate {half_length, 0, 0} {
  Duplicata { Volume{2}; Volume{1}; }
}
//+
Translate {0, half_length, 0} {
  Duplicata { Volume{4}; Volume{3}; Volume{2}; Volume{1}; }
}

Is there a way to get the boundary surface of Spheres 1-10 without using the GUI?


Thanks in advance and kind regards

[mkoeh]

So, since I got frustrated with the Interface of Gmsh, I approached the API, which has a nice and clear documentation. My code to obtain everything marked and seperated.


Maybe it is useful for others

import gmsh

gmsh.initialize()
gmsh.open("Mesh/symmetry_structure_gmsh.geo")
gmsh.model.mesh.generate(3)
gmsh.model.mesh.refine()
gmsh.model.mesh.refine()
gmsh.model.mesh.refine()

entities = gmsh.model.getEntities()

noslipboundary = []
boundary = []
dstuff = []
domain = []
points = []

for entity in entities:
    if gmsh.model.getType(entity[0],entity[1]) == 'Sphere' and entity[0] == 2:
        noslipboundary.append(entity[1])
    elif gmsh.model.getType(entity[0],entity[1]) != 'Sphere' and entity[0] == 2:
        boundary.append(entity[1])
    elif entity[0] == 3:
        domain.append(entity[1])
    elif entity[0] == 1:
        dstuff.append(entity[1])
    elif entity[0] == 0:
        points.append(entity[0])

gmsh.model.addPhysicalGroup(2,noslipboundary,3)
gmsh.model.addPhysicalGroup(3,domain,2)
gmsh.model.addPhysicalGroup(2,boundary,4)
gmsh.model.addPhysicalGroup(1,dstuff,5)
gmsh.model.addPhysicalGroup(0,dstuff,6)
gmsh.model.setPhysicalName(3,1,"Domain")
gmsh.model.setPhysicalName(2,2,"Boundary")
gmsh.model.setPhysicalName(1,4,"1Dstuff")
gmsh.model.setPhysicalName(2,3,"NoSlipBoundary")
gmsh.model.setPhysicalName(0,5,"Points")

gmsh.write("gmsh_api_symmetry_structure_gmsh.msh")
gmsh.finalize()