# [Getdp] Multiple natural boundary conditions

**Hamid Badi**
h.badi at bbs-slama.com

*Wed Nov 5 01:02:34 CET 2014*

Thanks a lot
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:
*>*
*>*
*>*
*>* Then it works J
*>*
*>*
*>*
*>* 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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