Re: [Gmsh] Transfinite 3D meshing

Bruno Tue, 06 Oct 2020 11:35:26 -0700

Dear Christophe and Max,


Thank you very much for your fast answer.

Yes indeed Christophe's advice works perfectly and this is clearlyexplained in the provided link.


Sorry for bringing up such a trivial issue!


Best regards

Bruno




On 06.10.20 19:39, Christophe Geuzaine wrote:

Hi Bruno and Max,

There is nothing mysterious about the "gmsh.model.geo.synchronize()" and "gmsh.model.occ.synchronize()" calls 
:-) They serve a single purpose: to synchronize the topological Gmsh model (the model manipulated by the "gmsh.model" 
functions) with the internal CAD representations in each of the supported CAD kernels (the representations manipulated by the 
"gmsh.model.geo" functions for the built-in kernel, or the "gmsh.model.occ" functions for the OpenCASCADE 
kernel).

In Bruno's case the issue is not linked to a missing sync. It is simply that the script merges a BREP file 
(the OpenCASCADE CAD file format, which thus creates an internal occ representation and is synced with the 
gmsh model) but tries to set transfinite constraints on the built-in internal CAD representation - using 
"gmsh.model.geo.setTransfiniteSurface()". The transfinite constraint should simply be set on the 
Gmsh model using "gmsh.model.setTransfiniteSurface()" (without the ".geo"!).

I encourage you to read the introduction of the API chapter in the user's guide 
(http://gmsh.info/dev/doc/texinfo/gmsh.html#Gmsh-API): it explains the Gmsh 
data model and all the underlying concepts.

Cheers,

Christophe

On 6 Oct 2020, at 18:46, Max Orok <[email protected]> wrote:

Hi Bruno,

At a quick glance, it's possible you require some more synchronize calls 
between the different API calls.
It's good practice to call synchronize when you move from one part of the API 
to another (e.g. from gmsh.model.geo to gmsh.model.geo.mesh).
This is a somewhat common issue (see e.g. 
https://gitlab.onelab.info/gmsh/gmsh/-/issues/987, 
https://gitlab.onelab.info/gmsh/gmsh/-/issues/986).

I see you have a single sync call at the end but it possibly comes too late to 
register the transfinite settings.
I would suggest trying to minimize your script further (maybe a single geometry 
and a single transfinite call) to dig in further.

Sincerely,
Max

On Tue, Oct 6, 2020 at 10:43 AM Bruno <[email protected]> wrote:
Dear Gmsh community,

I have a 3 dimensional square duct here attached that I wish to mesh
using the transfinite option in Gmsh, which seems very powerful.

I wish to have on each side of the inlet and outlet square of the duct
20 meshing points

To this end I wrote the script below, but it does the meshing without
taking into account the transfinite points.

Any clue what I am doing wrong here? I could not find the answer in the
mail archive.

Python script:

import gmsh

dcell = Wd = Hd = 2.8
tol = dcell / 100
Ld = 18.46

gmsh.initialize()
gmsh.option.setNumber("General.Terminal", 1)
gmsh.option.setNumber("Mesh.MshFileVersion", 4.1)
gmsh.option.setString("Geometry.OCCTargetUnit", "MM")
gmsh.option.setNumber("Mesh.Optimize",1)
#gmsh.option.setNumber("Mesh.Optimize",1)

gmsh.merge("SquareDuct.brep")
model = gmsh.model
model.mesh.removeDuplicateNodes()


# CREATE PHYSICAL GROUPS

# WALLS
s = []
s_bot = model.getEntitiesInBoundingBox(-Hd/2-tol, -Wd/2-tol, -Ld/2-tol,
-Hd/2+tol, Wd/2+tol, Ld/2+tol, dim = 2)
s_top = model.getEntitiesInBoundingBox(Hd/2-tol, -Wd/2-tol, -Ld/2-tol,
Hd/2+tol, Wd/2+tol, Ld/2+tol, dim = 2)
s_left = model.getEntitiesInBoundingBox(-Hd/2-tol, -Wd/2-tol, -Ld/2-tol,
Hd/2+tol, -Wd/2+tol, Ld/2+tol, dim = 2)
s_right = model.getEntitiesInBoundingBox(-Hd/2-tol, Wd/2-tol, -Ld/2-tol,
Hd/2+tol, Wd/2+tol, Ld/2+tol, dim = 2)
s = s + s_bot + s_left + s_top + s_right
s_no_slip = [s[i][1] for i in range(len(s))]
p = model.addPhysicalGroup(2, s_no_slip)
model.setPhysicalName(2, p, "noslip")
print("noslip = ", len(s))

# FLUID INLET CURVE
c_in = model.getEntitiesInBoundingBox(-Hd/2-tol, -Wd/2-tol, -Ld/2-tol,
Hd/2+tol, Wd/2+tol, -Ld/2+tol, dim = 1)
# FLUID INLET
s = model.getEntitiesInBoundingBox(-Hd/2-tol, -Wd/2-tol, -Ld/2-tol,
Hd/2+tol, Wd/2+tol, -Ld/2+tol, dim = 2)
p = model.addPhysicalGroup(2, [s[i][1] for i in range(len(s))])
model.setPhysicalName(2, p, "inlet")
print("inlet = ", len(s))
for ci in c_in:
      gmsh.model.geo.mesh.setTransfiniteCurve(ci[1], 20)
p = model.addPhysicalGroup(1, [c_in[i][1] for i in range(len(c_in))])
model.setPhysicalName(1, p, "inlet_curve")

# FLUID OUTLET CURVE
c_out = model.getEntitiesInBoundingBox(-Hd/2-tol, -Wd/2-tol, Ld/2-tol,
Hd/2+tol, Wd/2+tol, Ld/2+tol, dim = 1)
# FLUID OUTLET
s = model.getEntitiesInBoundingBox(-Hd/2-tol, -Wd/2-tol, Ld/2-tol,
Hd/2+tol, Wd/2+tol, Ld/2+tol, dim = 2)
p = model.addPhysicalGroup(2, [s[i][1] for i in range(len(s))])
model.setPhysicalName(2, p, "outlet")
print("outlet = ", len(s))
for co in c_out:
      gmsh.model.geo.mesh.setTransfiniteCurve(co[1], 20)
p = model.addPhysicalGroup(1, [c_out[i][1] for i in range(len(c_out))])
model.setPhysicalName(1, p, "outlet_curve")

for si in s_no_slip:
      gmsh.model.geo.mesh.setTransfiniteSurface(si)

# VOLUME
s = model.getEntities(3)
p = model.addPhysicalGroup(3, [s[i][1] for i in range(len(s))])
model.setPhysicalName(3, p, "air")

for vi in [s[i][1] for i in range(len(s))]:
      gmsh.model.geo.mesh.setTransfiniteVolume(vi)

gmsh.model.geo.synchronize()

# MESH 3D
model.mesh.generate(3)
#model.mesh.recombine()

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


Best regards

Bruno Agostini


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--
Max Orok
Contractor
www.mevex.com


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—
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine


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Re: [Gmsh] Transfinite 3D meshing

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