[Gmsh] Gmsh High Order Element Problem

[Kamil ÖZDEN]

Dear All,

I mesh a circular pipe in Gmsh very coarsely as below.


But when I set the order of the element as 2 in Gmsh and convert it into 
.xml and then .vtu file to visualize the spectral mesh in Paraview via 
Nektar, I got error messages like the following:

*/Warning: Level 0 assertion violation/**/
/**/3D deformed Jacobian not positive (element ID = 715) (first vertex 
ID = 388)/*/

/and got the following distorted mesh in Paraview:



I recognized that this is a problem about characteristic length 
parameter. In my .geo files, I set it as 1. However, I didn't understand 
ito which value do I have to increase or decrease this parameter. I read 
the manual of gmsh but couldn't clearly understand the relation between 
characteristic length and mesh. Can you please give a brief information 
about this?

Regards,
Kamil
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