[Gmsh] integration, spikes

[Christophe Geuzaine]

> On 5 Aug 2020, at 10:12, t.eschner at dokom.net wrote:
> 
> Dear all,
> 
> trying to get acquainted with gmsh/getdp, I stumbled upon two problems that I am not able to resolve.
> 
> I am trying to model a simple conductive cell with two electrodes, a simple one and a structured one. To me, the results look quite realistic so far (I am still in the stage of checking), with two exceptions:
> 
> The first: When I try to calculate the overall current by calling plugin(Integrate) on views slightly above the simple electrode, I get two different results (for the vector view -8,88 and the x-component view -39,9), and neither is close enough to the expected value of -2x(4,94..4,99).

Be careful with brute-force integration. If you use GetDP would recommend using global quantities, which define such integrals in the "variationally correct" way: see e.g. https://gitlab.onelab.info/doc/tutorials/-/wikis/Electrostatics-with-floating-potentials

> 
> The second: The current density field has few spiky values that I do not know how to cure. Their position seems to be constant, the values seem to change with the grid parameters, and it might be getdp-related. 

With a (scalar) potential formulation your current density is defined through the gradient, whose accuracy will depend quite strongly on the mesh quality. You can give the new "HXT" 3D algorithm a try, whose optimizer produces slightly better elements, and see if this improves things.

Christophe

> 
> Please, have a look and give me a hint on how to correct/proceed. Thank you.
> 
> Kind regards, Thomas
> 
> 
> 
> 
> 
> <porous_electrode.zip>_______________________________________________
> 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