Re: [ff3d-users] how to use an external mesh

[Pierre Michaud]

I Stephane,
thanks for your answer

Stephane Del Pino wrote:

> Hello Pierre,
>
> At first reading I did not noticed any mistake in your ff3d's file ...
>
> This might be a bug in ff3d, but I am not sure about that (this is a quite 
> basic test case, but one never knows ...). What does happen when your mesh is 
> more refined along the Z-axis? Is it converging?
> The difference with the structured case could be explained by the fact that 
> structured discretization uses Q1 (hexahedra) finite element, which is exact 
> for tri-affine functions ((a+x)*(b+y)*(d+z)+e) and P1 is only exact for 
> affine functions (ax+by+cz+d) functions ...
>
> Please let me know if this converges.
>  

I have tried with a much finer mesh (>200000 tetrahedra), but I obtain 
the same wrong value
as with the coarse mesh.

> By the way I have a few remarks concerning your ff3d's command file:
> - you should use cg instead of bicgstab: your problem is symetric, so it is 
> more efficient, and you can use the ichol preconditionner if you use the 
> sparse matrix storage (default is no preconditionner);
> - since you are consumming to much memory you could use the 
> 'memory(matrix=none)' option. It is a bit slower but requires few memory. 
>  

Actually, in the more complex (and asymetric) problems I am studying, I 
am using the fictitious domain method
because my geometry is not a simple box, and I use the "extract" command 
to define boundaries.
I reach the memory limit during the initial phase, before the solver 
launches.

Pierre