# [Getdp] Multiple natural boundary conditions

michael.asam at infineon.com michael.asam at infineon.com
Wed Nov 5 08:49:38 CET 2014

```Hi,

the small dimensions are fine. The problem is located in the definition of the
physical groups: The lines have the same physical numbers as the surfaces,
so GetDP cannot distinguish between them. Just use different numbers like

Physical Line(11) = {1};
Physical Line(12) = {16};
Physical Line(13) = {2,19,15,17,12,8};

Physical Surface(1) = {3};
Physical Surface(2) = {2};
Physical Surface(3) = {4};
Physical Surface(4) = {1};

in the case.geo file and

Interieur = 11;
Exterieur = 12;
Zone1 = 1;
Zone2 = 2;
Zone3 = 3;
Zone4 = 4;

in the case.pro file.

Cheers,
Michael

Sent: Wednesday, November 05, 2014 1:12 AM
To: getdp-public at googlegroups.com
Cc: h.badi at bbs-slama.com; getdp at geuz.org; Asam Michael (IFAG ATV BP D PD DES1)
Subject: Re: [Getdp] Multiple natural boundary conditions

Hi,

Thanks a lot, it works too.

I've an other similar problem, but getdp create a NAN temperature field, I can't explain it. The geometry is different but still with 3 BCs, the main different is that now i define all the dimension of my geometry im meter, so the coordinates are small.

Le mardi 4 novembre 2014 17:12:43 UTC+1, michae... at infineon.com a écrit :
Hi,

the point is that in GetDP it’s not allowed to subtract or add anything from/to
a Dof in a single Galerkin statement. Therefore you have to split your 2nd
Galerkin into two:
[Das Bild wurde vom Absender entfernt.]

Then it works ☺
[Das Bild wurde vom Absender entfernt.]

Cheers,
Michael

From: getdp [mailto:getdp-... at ace20.montefiore.ulg.ac.be<javascript:>] On Behalf Of Hamid Badi
Sent: Tuesday, November 04, 2014 1:14 PM
To: getdp-... at googlegroups.com<javascript:>
Subject: [Getdp] Multiple natural boundary conditions

Hello,

My problem is common, i'd like to solve the heat equation with, for example, 2 natural Robin BC and one adibatique BC : -lambda.dnT = h.(T-Ti) on Gamma_i with i={1,2} and lambda.dnT = 0 on Gamma_3.
I write the weak form with u in Form0 of the heat equation leads to the classical form :

Equation{
Galerkin{ [lambda[] * Dof{Grad u}, {Grad u}];
In Omega; Jacobian JVol; Integration I1;}

Galerkin{ [ h[]* (Dof{u} - T[]), {u}];
In Ambiance; Jacobian JSur; Integration I1;}
}

In my problem there is no essential BC so i do not have Constraint block.
The computation give a 0 temperature field, I do not understand what's wrong.

Moreover :
1 - I wan to store in a file the temperature field respects to the nodes but PostOperation block computes over elements.
2 - How can I compute the integral of the flux over Gamma_i, to do so, I need for each boundary edge : the flux and the normal vector

Best regards.
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