[Gmsh] Broken mesh for coarser mesh size at centre of circle

[Christophe Geuzaine]

> On 8 Feb 2020, at 20:14, Rohracker, Maurice <mau.rohracker at fau.de> wrote:
> 
> Dear GMSH user and developer,
> 
> I have a small example where some weird things are going on. We have a quadric box with a circle inside and interphase around it. For the FE simulation, it's sufficient to have a coarser mesh at the centre point of the circle. We increase here the computed mesh size by a factor (centreMeshFactor in the .geo-file). For some reasons, the resulting mesh has for the factor = 10 and > 15 not a good shape anymore and the elements kind of stretch up.
> Could you please tell me why this happens and how the mesh sizes are interpolated between two specified points. Our goal is here to understand the issue or interpolation.
> I agree that for an increasing factor the mesh size gets unproportional in comparison to the other mesh sizes on the circle, but why does this occur, that at some point the mesh breaks. It seems that the mesh generator could not interpolate the mesh sizes in a correct way at some point anymore, or am I wrong?
> 

The frontal-based algorithms can indeed exhibit this behavior. Since with large mesh size variations the regularity (orthogonality) of the mesh will be poor anyway, I would  simply select e.g. a simple Delaunay for the center surface:

MeshAlgorithm Surface {24} = 5;

Here's the result for centreMeshFactor = 30 :



Christophe


> Thank you very much in advance.
> 
> Best regards,
> Maurice Rohracker
> Master Student, FAU Erlange-Nürnberg<bubble_interphase_layers.geo>_______________________________________________
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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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