[FLASH-USERS] [EXTERNAL] Re: Adaptive timestep

[Ann Almgren]

The two "difficulties" in going to subcycling are typically:

1) how to accumulate mismatches over the subcycled time steps in order to
do the right sync at the end of the coarse time step (straightforward if
everything is purely explicit, can get complicated if elliptic pieces)

2)  "level solves" -- Poisson solves that don't coarsen down to the
coarsest AMR level



On Tue, Oct 1, 2019 at 9:33 AM Ricker, Paul Milton <pmricker at illinois.edu>
wrote:

> It would be good to come up with a strategy for developing this feature in
> FLASH 5. It's been a desired feature for a long time, but it has
> essentially been triaged out of development since it is not easy and not
> the most urgent feature for most developers' science. The transition to
> AMReX is a good opportunity to revisit the question of how hard it would be
> to implement.
>
> I'll just put that on my to-do list... :)
>
> Paul
>
>
> Paul M. Ricker
> Professor of Astronomy
> University of Illinois
> http://sipapu.astro.illinois.edu/~ricker
>
> On October 1, 2019 11:03:41 AM "Messer II, Bronson" <bronson at ornl.gov>
> wrote:
>
> > Hi Sean, Matuesz, et al.,
> >
> > Sean is right both about not having sub-cycling in the current solvers
> and about the desire to change that in the future for FLASH5.
> >
> > So, I guess I didn’t have a different opinion at all, just felt the need
> to chime in. :)
> >
> > Bronson
> >
> >> On Oct 1, 2019, at 11:33 AM, Sean M. Couch <couch at pa.msu.edu> wrote:
> >>
> >> Hi Mateusz,
> >>
> >> I will venture my view of this and others can chime in if they have a
> different opinion. Also, I’m assuming by adaptive timestep you mean
> sub-cycling in time where different refinement levels take different time
> steps?
> >>
> >> For FLASH5, we are transitioning to the AMReX package. AMReX is built
> on the idea of time sub-cycling so in principle, we could utilize that. For
> that matter, PARAMESH was also built to allow time sub-cycling, we just
> never used it. As of now, for the solvers we are porting to FLASH5/AMReX we
> are still making the assumption of a single global time step. This
> simplifies things considerably. But I am of the opinion that, eventually,
> we should implement time sub-cycling and take advantage of what AMReX
> offers in that regard. This, however, will not likely be a feature
> available from the outset.
> >>
> >> Now, what might speed things along is capable developers willing to
> lend a hand in the implementation ;)
> >>
> >> Sean
> >>
> >> ----------------------------------------------------------------------
> >> Sean M. Couch, Ph.D.
> >> Assistant Professor
> >> Department of Physics and Astronomy
> >> Department of Computational Mathematics, Science, and Engineering
> >> Facility for Rare Isotope Beams
> >> Michigan State University
> >> 567 Wilson Rd, 3260 BPS
> >> East Lansing, MI 48824
> >> (517) 884-5035 --- couch at pa.msu.edu --- www.pa.msu.edu/~couch
> >> On Sep 30, 2019, 7:55 PM -0400, Mateusz Ruszkowski <mateuszr at umich.edu>,
> wrote:
> >>>
> >>>
> >>>
> >>>
> >>> Hi all,
> >>>
> >>>
> >>> Does anyone know if there a plan to extend FLASH to include adaptive
> timestep or if users would be interested in such a code feature?
> >>> Myself and a number of my collaborators would definitely be interested
> in using such a code capability.
> >>>
> >>>
> >>> Cheers,
> >>> Mateusz
>
>
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