Re: [ff3d-users] Variational form of potential flow with free surface on mesh

[Thomas Ward]

Thanks Stephane, that fixed it.

I thought my formulation was equivalent to the one you wrote,

As I understand it, my formulation includes the natural boundary 
conditions which is unnecessary but I thought that there was no harm 
(other than inefficiency) to include them, anyway thanks for the 
pointers to the wikipedia stuff, I will look through them and try to see 
why including the natural boundary codtions in the surface integral 
won't work.


I'm about to try using periodic BC, I note from the mailing list that 
you were playing around with this a couple of years ago, do you have any 
sample files or other documentation or pointers to the source code?

Do you have any infinite elements? I'm thinking of a radiation condition 
decaying to zero at infinity on an open boundary.

regards,

Tom

Stephane Del Pino wrote:
> Dear Thomas,
> thanks for your interest in ff3d.
>
> In fact, you did not compute the right variational formulation associated to 
> your PDE. You have to be careful in the integration by part
>
> Have a look to
> http://en.wikipedia.org/wiki/Finite_element_method#Variational_formulation
> and to
> http://en.wikipedia.org/wiki/Green%27s_identities
> for some details.
>
> In your case, you should have written:
>
>  solve(phi) in  M
>  {
>     test(w)
>       int(grad(phi)*grad(w))
>       +int[M zmax](w*alpha*phi)
>       =int[M xmin](w*f)
>       -int[M xmax](w*f)
>       =0;
>  };
>
> Do not hesitate to ask me if you get troubles with that.
>
> > PS
> > One small documentation suggestion; the method of defining Robin type
> > boundary conditions be added to the documentation or README file.
> The documentation is far from being completed. I not this on the TODO list.
>
> Best regards,
> Stéphane.
>
>
> _______________________________________________
> ff3d-users mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/ff3d-users