# [Getdp] Multiple natural boundary conditions

**michael.asam at infineon.com**
michael.asam at infineon.com

*Tue Nov 4 17:11:29 CET 2014*

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:
[cid:image001.png at 01CFF852.565D1020]
Then it works ☺
[cid:image002.png at 01CFF852.565D1020]
Cheers,
Michael
From: getdp [mailto:getdp-bounces at ace20.montefiore.ulg.ac.be] On Behalf Of Hamid Badi
Sent: Tuesday, November 04, 2014 1:14 PM
To: getdp-public at googlegroups.com
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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