[Gmsh] Cylinder (not periodic) meshing problem

[andrew]

Hi,
1. I encountered the same problem when meshing some surfaces like in this
geo file. Since my surfaces are generated randomly even if I scale there
might be always something that is small enough thus generating errors. So
is there a chance of implementing a better implementation that could take
care even very small elements?

2. Also I would like to suggest the addition of a new Boolean command which
will be the combination of two commands
BooleanPartition=BooleanIntersection & BooleanFragments. In the attached
geo file we see that the combination of these two commands gives a new
shape without anything extending outside from the original volume. Since
the arguments of these two commands are almost identical perhaps they could
be combined instead of performing two times a Boolean operation.

3. When I try to select the optimize with NetGen gmsh throws me out. My
guess is that the NetGen tries to move nodes from one side of the internal
baffles without taking care of the cell that is on the other side of the
baffle and shares the node. Since optimization with NetGen produces good
results is there a way to fix this?

4. I guess that you have already thought of that but if on a geometry we
could do a BooleanPartitioning with eg. 4 volumes then we could define the
internal surfaces that are produced as periodic and mesh each volume in a
different thread. After the meshing they could be united and produce a
single final mesh. But meshing in different threads is a way to do
multiprocessing with gmsh thus reducing the time to create a mesh.

kind regards

andrew tsiantis




2017-10-02 16:52 GMT+03:00 Christophe Geuzaine <cgeuzaine at ulg.ac.be>:

>
> Dear Giampiero,
>
> Indeed, there are still some issues with OpenCASCADE models when the
> dimensions are very large (or very small).
>
> For the time being, rescale your model. For example, just dividing all
> lengths by 10 fixes the issue:
>
> SetFactory("OpenCASCADE");
> Mesh.CharacteristicLengthMin = 20;
> Mesh.CharacteristicLengthMax = 20;
>
> //Definisco il cilindro com e coppia di superfici no periodiche
> (altrimenti non posso usare i Boolean)
> Circle(1) = {0,0,0, 905, 0, Pi};
> Extrude{0,0,611}{Line{1};}
>
> You can still save the mesh with another scaling with the
> Mesh.ScalingFactor (e.g. "Mesh.ScalingFactor=10;") option.
>
> Christophe
>
>
> > On 1 Oct 2017, at 19:28, ing. Nobile - OAC Ingegneria <
> gnobile at oacingegneria.com> wrote:
> >
> > Dear all,
> >
> > I have problem meshing an half cylinder.
> >
> > From a first look the mesh seems very good
> >
> > <image.png>
> >
> >
> > But along the upper/lower border there are very deformed and overlapped
> mesh surfaces.
> >
> > <image.png>
> >
> > For example elements 7730 and 7728 in the picture (overlapped, made with
> the same nodes, and very deformed)
> >
> >
> > <image.png>
> >
> >
> > Am I missing something before the 2D meshing process?
> >
> > I attached the script with the geometry.
> >
> > Thanks very much.
> >
> >
> > Giampiero
> >
> >
> > Ing. Giampiero Nobile, PhD   |   OAC Ingegneria
> >
> > Mobile:  +39 3494632155
> > Office:   +39 0108698603
> >
> > www.oacingegneria.com
> >
> >    <24795144.jpg>
> >
> > <half_cylinder.geo>_______________________________________________
> > gmsh mailing list
> > gmsh at onelab.info
> > http://onelab.info/mailman/listinfo/gmsh
>
>
> --
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
> Free software: http://gmsh.info | http://getdp.info | http://onelab.info
>
>
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