[Gmsh] integration, spikes
cgeuzaine at uliege.be
Mon Aug 17 14:42:43 CEST 2020
> 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.
> Please, have a look and give me a hint on how to correct/proceed. Thank you.
> Kind regards, Thomas
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Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
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