[Getdp] Second order element peculiarity
David Colignon
David.Colignon at ulg.ac.be
Thu Aug 24 16:19:54 CEST 2006
Hi,
the condition on the coefficients associated to the second order basis functions must be homegeneous ( 0 value ) otherwise the imposed condition considers a boundary condition other than constant ( with second degree variation ). This is due to the fact that the second order elements are built with hierarchical basis functions.
So with
{ Name ElectricScalarPotential_d2 ; Type Assign ;
Case {
{ Region Ground; Value 0. ; }
{ Region electrode ; Value 0. ; }
}
}
in con_cyl.pro it works very well
Cheers,
Dave
--
David Colignon, Ph.D.
ELAP - Service d'Electricité Appliquée
Institut Montefiore B28
Université de Liège
4000 Liège - BELGIQUE
Tél: +32 (0)4 366 37 32
Fax: +32 (0)4 366 29 10
http://elap.montefiore.ulg.ac.be
Jim Davis wrote:
> Hello getdp aficionados,
>
> I am having trouble using second order elements in the solution of an
> electrostatics problem and I was hoping someone could tell me what I am
> doing wrong. It seems that when I have a region surrounded by
> constrained surfaces (Dirichlet and homogeneous Neumann) the solution
> getdp gives me for second order elements contains nodal potentials
> higher than any of the constrained potentials in the grid.
>
> As an example, I have attached the input files for a concentric cylinder
> problem. The inner radius is 0.1 and is set to 0 volts while the outer
> radius is 0.5 and is set to 100 v. The endcaps have no boundary
> conditions set and therefore default to the natural b.c. (homogeneous
> Neumann), right? Looking at the solution generated by getdp, there is a
> distinct rise in potential (117 v) prior to the outer radius. If I use
> linear elements, I do not see this behavior. That is, the potential
> increases monotonically from the inner radius to the outer radius as
> expected for linear elements.
>
> In going to second order elements, I took the following steps:
>
> 1. Increased the number of Gaussian integration points for
> triangles from 4 to 6.
> 2. Increased the fill-in parameter in solver.par to cover
> the max bandwidth
> 3. Added the basis functions associated with element edges
> and added the corresponding constraints.
>
> What am I missing?
>
> Thanks very much for any insight you can provide on this problem.
>
>
> Jim
>
>
> ----------------------------------------------------------------------------
>
>
> Jim Davis Telephone: (404) 894-7231
> Signature Technology Laboratory Fax: (404) 894-8515
> Georgia Tech Research Institute email: jd4 at prism.gatech.edu
> Georgia Institute of Technology
> Atlanta, GA 30332-0800
>
>
> ------------------------------------------------------------------------
>
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