[Gmsh] Symetry : when it is become explicit ?

[Geordie McBain]

2013/2/6 Adrien Girard <cassel.girard at gmail.com>:
>
> Hello,
>
> I just finish university and I am now working as a mechanical engineer and I
> am still confused with some points of FEM theory.
>
> I have to make the complete thermal analysis of a rectangular box, I decided
> to use the symetry of the problem and thus modelise only 1/8 of the box. But
> now, I wonder when I have to add the symetry to the problem.
>
> - 1) to the mechanical model ? (before the simulation)
> - 2) at the simulation phase ?
> - 3) only for the post process, to visualise the result ?

The finite element has what are called "natural boundary conditions"
so that for each partial differential equation, doing nothing on a
boundary has a definite physical significance.  Generally in thermal
problems this means no conduction, i.e. an adiabatic condition.  This
is appropriate to a plane of symmetry, so the answer to your question
is most likely (3), although even that could be omitted, displaying
just the nonredundant octant; this would have the advantage that the
insides would be visible on the symmetry planes.