Dear Christophe,
Thank you! That looks like it has done the trick!
Kind Regards,
[FLOW]
[VUB]
Nathan Ricks | PhD Student
Department of Mechanical Engineering
Thermo and Fluid dynamics (FLOW)
Brussels Faculty of Engineering (BRUFACE<http://bruface.eu/>)
Vrije Universiteit Brussel (VUB<http://www.vub.ac.be>)
________________________________
From: Christophe Geuzaine <[email protected]>
Sent: Thursday, 11 April 2019 9:37 PM
To: Nathan RICKS
Cc: [email protected]
Subject: Re: [Gmsh] Errors when increasing NNodesByEdge on a small edge
> On 11 Apr 2019, at 18:22, Nathan RICKS <[email protected]> wrote:
>
> Sorry for the repeated messages, just trying to sort out the issue and coming
> across new things/information that might help resolve the issue. In the .geo
> file attached, it demonstrates what "I think" is the cause of my errors - if
> you generate the 2D mesh and look at the trailing edge, there are cells/nodes
> crossing over the lines/edges where they obviously shouldn't be. This occurs
> on both Mac and Linux for me at least. Have you seen this issue before by any
> chance?
>
It seems that you ran into a case where the small random perturbation we use in
our 2D initial triangulation is too large. A new version of the algorithm
without any such perturbation will be available in a future release; but in the
meantime you can set e.g. "gmsh -rand 1e-12" (or set Mesh.RandomFactor = 1e-12
in your script), which seems to solve the issue.
Christophe
> Thanks again,
>
> Nathan Ricks
> VUB
>
>
>
>
>
> From: Nathan RICKS
> Sent: Thursday, 11 April 2019 11:41 AM
> To: Christophe Geuzaine
> Cc: [email protected]
> Subject: Re: [Gmsh] Errors when increasing NNodesByEdge on a small edge
>
> I'm not sure if this helps determine the issue, but it seems if I generate
> the mesh using the Delaunay algorithm, there are cells that break through
> boundaries of the surfaces, and if I use Frontal-Delaunay (which I was) these
> correspond to the broken cells shown in the first screenshots. I've attached
> two screenshots showing this, if you compare between the two you can see
> "correspondence of errors".
>
> From: Nathan RICKS
> Sent: Thursday, 11 April 2019 9:00 AM
> To: Christophe Geuzaine
> Cc: [email protected]
> Subject: Re: [Gmsh] Errors when increasing NNodesByEdge on a small edge
>
> Dear Prof. Geuzaine,
>
> Thanks for the response. Indeed, I just tested this using Gmsh on my Mac, and
> the resultant mesh runs fine.
>
> So it seems the problem is restricted to the workstation, which is running
> Linux 64-bit (red hat). I just tried instead compiling from the source code
> and the error persists there also unfortunately. Are you aware of anything
> that may cause this? It's for an optimisation routine, so thousands of meshes
> are generated, so using my Mac isn't feasible unfortunately.
>
> In regards to the boundary layer, I was originally using the BL field
> directly, however ran into issues as I couldn't have a growth rate "around"
> the airfoil spline (to have narrower cells at leading and trailing edges), as
> well as perpendicular to the airfoil. Also, at the trailing edge using the
> fan node resulted in too small cells causing numerical errors, and without it
> the cells were too bad quality, also causing errors. Using the transfinite
> surfaces gave me flexibility in the boundary layers, allowing two different
> growth rates perpendicular to the surface. With that it was running very
> well, until now on trying to include the blunt TE.
>
> Thank you again,
> Kind Regards,
>
> Nathan Ricks.
>
>
>
>
> From: Christophe Geuzaine <[email protected]>
> Sent: Thursday, 11 April 2019 12:09 AM
> To: Nathan RICKS
> Cc: [email protected]
> Subject: Re: [Gmsh] Errors when increasing NNodesByEdge on a small edge
>
>
>
> > On 10 Apr 2019, at 21:57, Nathan RICKS <[email protected]> wrote:
> >
> > Hi all,
> >
> > I have quite a particular problem, but I'm hoping someone can help. I'm
> > meshing an airfoil using transfinite surfaces in the boundary layer.
> >
> > I've just had to add a blunt trailing edge (mesh was working well with
> > sharp trailing edge) to the airfoil, and now I have this one error stopping
> > me, and I just can't figure it out...
> >
> > When I increase the NNodesByEdge on Field[11] from 6 to 15, the mesh ends
> > up bad quality, with cell corners not matching other cells at the boundary
> > of surfaces, and it causes SU2 to diverge instantly. It runs fine with 6,
> > but crashes at 15. I've attached two images showing that it is a mesh issue
> > causing this (nothing else is being changed in the setup).
> >
>
> I cannot seem to reproduce the issue on my Mac. Attached is the mesh
> generated on your .geo file:
>
>
> > Other things such as reducing lcMin on Field[12] can also make it crash for
> > example, however the above has visible errors in the mesh.
> >
>
> Idem... What OS are you running on?
>
> PS: instead of generating the BL by hand, why not using the boundary layer
> field directly? Cf. e.g.
>
> https://gitlab.onelab.info/gmsh/gmsh/blob/master/benchmarks/2d/naca12BL.geo
> https://gitlab.onelab.info/gmsh/gmsh/blob/master/benchmarks/2d/naca12_2d_trailing.geo
>
> > Does anyone have an idea on why I can't use the Distance/Threshold field as
> > normal on this edge?
> >
> > If you can provide any guidance that would be greatly appreciated, it's so
> > close...! I've already tested with the latest release with the same results.
> >
> > Thanks a lot,
> > Kind Regards,
> >
> > Nathan Ricks
> >
> >
> >
> >
> >
> > <NNodes_15.png><NNodes_6.png><airfoil_level1.geo>_______________________________________________
> > gmsh mailing list
> > [email protected]
> > http://onelab.info/mailman/listinfo/gmsh
>
> —
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
>
>
> <airfoil_level1_edit.geo>_______________________________________________
> gmsh mailing list
> [email protected]
> http://onelab.info/mailman/listinfo/gmsh
—
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine
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