[petsc-users] GAMG parallel convergence sensitivity

[Mark Lohry]

>
> It depends what you're trying to resolve.  Sounds like maybe you're
> stepping toward steady state.  The paper is wishing to resolve vortex
> and baroclinic dynamics while stepping over acoustics and barotropic
> waves.


Yeah, I'm usually working towards steady state or with fairly large time
steps, but with the highly stretched meshes typical in aerodynamics
applications even with pretty accurate time resolution fully implicit is
advantageous. Doubly so with the nasty explicit stability limits in DG --
I've been playing with DNS setups (taylor-green vortex) and getting
considerable efficiency advantages using ILU+gmres with a CFL ~100 with no
noticeable resolution losses compared to explicit.

On Thu, Mar 14, 2019 at 9:45 AM Jed Brown <jed at jedbrown.org> wrote:

> Mark Lohry <mlohry at gmail.com> writes:
>
> > It seems to me with these semi-implicit methods the CFL limit is still so
> > close to the explicit limit (that paper stops at 30), I don't really see
> > the purpose unless you're running purely incompressible? That's just my
> > ignorance speaking though. I'm currently running fully implicit for
> > everything, with CFLs around 1e3 - 1e5 or so.
>
> It depends what you're trying to resolve.  Sounds like maybe you're
> stepping toward steady state.  The paper is wishing to resolve vortex
> and baroclinic dynamics while stepping over acoustics and barotropic
> waves.
>
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