[Gmsh] How to make a hole in a volume?

[Christophe Geuzaine]

Hengjin Liu wrote:
> Hello,
>  
> I am trying to create a simple block with an internal hole (a smaller 
> block) using GUI.
>  
> I select the external boundary surfaces to create the volume and then 
> select the internal surfaces as the hole following the message in the 
> GUI windows. However, when I am trying to generate the volume mesh, I 
> get an error message saying that an edge 6 is multiple time in surface mesh.
>  
> I attached the .geo file with this e-mail. Should the internal hole be 
> explicitly defined as a volume? or the characteristic length I choose is 
> not good for the model.    
>  
> Is there a way to visualize the volume mesh to make sure that there is 
> no elements generated inside the hole?
>  
> Thanks in advance!
>  

Hi Henry - your model works fine here with the default algorithm.

The message you mention ("edge 6 multiple times in surface mesh") comes
from the netgen algorithm, right? Remember that if you want to use this
algorithm, you need to orient the boundary surfaces such that their
normals all point outside of the volume. (This is not insured
automatically right now, so you need to take care of this by hand.)

PS: it is also usually better to keep the surface loops separate (one
for the external shell, one for the hole). I know that the "brutal" way
works, but by keeping the surface loops separate you can keep track (or
change) the orientations much more easily.


> henry
> 
> 
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-- 
Christophe Geuzaine
Assistant Professor, Case Western Reserve University, Mathematics
http://www.case.edu/artsci/math/geuzaine