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## Re: [ff3d-users] Periodic BCs

**From**: |
Stephane Del Pino |

**Subject**: |
Re: [ff3d-users] Periodic BCs |

**Date**: |
Thu, 6 Jan 2005 23:12:39 +0100 |

**User-agent**: |
KMail/1.7.1 |

Hello.
Le Jeudi 6 Janvier 2005 02:00, Bharat Rangan a écrit :
>* Hi,*
>* Thanks for the detailed reply. As you suggested, I am going through the NS*
>* example and trying my own case. A couple of questions in this are*
>
>* 1. The projection method in the example has -div(eps*grad(p)) + eps*p +*
>* dx(u1)+dy(u2)+dz(u3). The methods that I have come across are*
>* usually -div(grad(p)) + large_number*div(u) =0. Is there a difference in*
>* these implementations.*
Well, I am not a specialist of stabilization, but you can omit the eps*p term
(if you then multiply the equation by 1/eps = large_number you will get back
to your formulation). Obviously you can use your favorite projection
algorithm and couple it with the stabilization procedure of your choice... I
would also be interest in references and feed-back if your algorithm gives
better results. I used the one that is in the documentation during my PhD
thesis, I picked it up from an old freefem+ example, so I do not have precise
reference to give to you...
>* 2. Is there an external way to implement periodic BCs. Like some penalty on*
>* the difference of the solution on the two faces and then iterating ?*
I am not sure if this is possible, and I do not see how to do it this way,
maybe using Robin-Robin like condition as it is done in domain
decomposition ...
But, even if it is possible, to compute Navier-Stokes, you will need it to
work also for convection operator (characteristics method).
Best regards,
Stephane.