Can not change Mesh size.

OCCUser
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5 years 3 months ago #1733 by OCCUser

Can not change Mesh size. was created by OCCUser

Hello,
I load my geometry using LoadOCCGeometry and when I am trying to mesh it I have the same number of elements for different values of maxh parameter.

Code:

from netgen.NgOCC import *
geo = LoadOCCGeometry("brick.step")
mp = MeshingParameters(maxh=1, grading=0.3)
ngmesh = geo.GenerateMesh(mp=mp)

Output: 17 elements were created

Code:

from netgen.NgOCC import *
geo = LoadOCCGeometry("brick.step")
mp = MeshingParameters(maxh=0.1, grading=0.3)
ngmesh = geo.GenerateMesh(mp=mp)

Output: 17 elements were created

Code:

ngmesh = geo.GenerateMesh(maxh=0.1, segmentsperedge=20)

Tried with segments meshing - > 17 elements were created.

Do you have experience with this? Is it a bug of python interface?
Thanks

christopher
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5 years 3 months ago #1744 by christopher

Replied by christopher on topic Can not change Mesh size.

Hi,
you are right, the meshing parameters from Python were ignored for the occ geometry. This is fixed in the upcoming nightly release. We have included some further changes/improvements/syntactic sugar:

The occ module should now be included using netgen.occ, geometries constructed by the constructor taking the filename as argument.

Code:

from netgen.occ import *
geo = OCCGeometry("brick.step")

This constructor now understands .brep, .iges, .step and .stp files.
One can now use meshing parameters as given in the gui, by the helper variable meshsize:

Code:

geo.GenerateMesh(meshsize.very_fine)

you can give additional meshsize parameters as kwargs as well:

Code:

geo.GenerateMesh(meshsize.coarse, maxh=0.2)

There is a docstring about available meshing and optimization parameters if you query GenerateMesh for its help:

Code:

help(geo.GenerateMesh)

Hope that helps and let us know if you run into problems.

Best
Christopher

The following user(s) said Thank You: OCCUser

OCCUser
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5 years 3 months ago #1761 by OCCUser

Replied by OCCUser on topic Can not change Mesh size.

Thanks a lot, now it works good

Could you, please, tell me if netgen has MPI support. Can I create mesh in parallel?

joachim
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5 years 3 months ago #1762 by joachim

Replied by joachim on topic Can not change Mesh size.

Hi,
no, you cannot generate a mesh mpi-parallel. But you can distribute a mesh for parallel computations, and also refine a mesh in parallel.

Here is a simple example for that::

Code:

from ngsolve import *
from netgen.csg import unit_cube
import netgen.meshing


if mpi_world.rank == 0:
    ngmesh = unit_cube.GenerateMesh(maxh=0.2).Distribute(mpi_world)
else:
    ngmesh = netgen.meshing.Mesh.Receive(mpi_world)

for l in range(2):
    ngmesh.Refine()

mesh = Mesh(ngmesh)
fes = H1(mesh, order=3)
print ("ndof-local =", fes.ndof, "ndof-global =", fes.ndofglobal)

Joachim

OCCUser
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5 years 3 months ago - 5 years 3 months ago #1784 by OCCUser

Replied by OCCUser on topic Can not change Mesh size.

Hello joachim,
Could you please tell me if RestrictH() method works with occ geometries?
I try to run the code like this(Cube properties 10x10x10, starting point (0,0,0) ):

Code:

from netgen.occ import *
from netgen.meshing import MeshingParameters
mp = MeshingParameters()
n = 100
for i in range(n+1):
    loc_h = 10/n
     mp.RestrictH(x=0,y=i*loc_h,z=0,h=loc_h)
geo = OCCGeometry("cube.step")
mesh = geo.GenerateMesh(mp=mp)
mesh.Export("output.msh", "Gmsh2 Format")

But it does not mesh my edge. When I use CS Geometry it works good.
Could you please help me?
Thanks

Last edit: 5 years 3 months ago by OCCUser.

christopher
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5 years 2 months ago - 5 years 2 months ago #1818 by christopher

Replied by christopher on topic Can not change Mesh size.

Fixed in github.com/NGSolve/netgen/commit/13c17ad...768f001776390b343fa8
Will be in coming nightly release
Thanks for reporting

Best
Christopher

Last edit: 5 years 2 months ago by christopher.

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