[aspect-devel] cylindrical rigid body rotation

[Wolfgang Bangerth]

> Sure, but that is not enough. For the Krylov method to converge, the
> right-hand side needs to be compatible (be in the image of the
> operator). This means we can only generate net rotation in the order
> of the Krylov residual (so something like 1e-8), because GMRES will
> stay in the nullspace we start with (and u=0 and t=0).
> This explains why using adaptive mesh refinement produces non
> negligible rotation quicker than a fixed mesh (it produces small
> round-off).
>
> So, I don't see a way to generate a significant difference in net
> rotation and net angular momentum that is still compatible. Producing
> a fake rotational component (for example a tangential gravity) means
> that the linear solver won't converge (unless we make it compatible
> which involves removing the rotational part again :-) ).
>
> The only way I can see to create a significant difference is to
> initialize our initial guess for the velocity with something with a
> large rotational component (which is in the nullspace).

Ah, I see. But then, why would one want to do that :-)

Cheers
  W.


-- 
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Wolfgang Bangerth               email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/