Can not change Mesh size.

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1

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.

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

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

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

2

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.

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:

geo.GenerateMesh(meshsize.very_fine)

you can give additional meshsize parameters as kwargs as well:

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

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

help(geo.GenerateMesh)

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

Best
Christopher

3

Thanks a lot, now it works good :slight_smile:
Could you, please, tell me if netgen has MPI support. Can I create mesh in parallel?

4

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::

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

5

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) ):

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

6

Fixed in restricth for occ and stl geometries · NGSolve/netgen@13c17ad · GitHub
Will be in coming nightly release
Thanks for reporting

Best
Christopher