> On 23 Jun 2023, at 9:39 PM, Alexander Lindsay <alexlindsay...@gmail.com> > wrote: > > Ah, I see that if I use Pierre's new 'full' option for > -mat_schur_complement_ainv_type
That was not initially done by me (though I recently tweaked MatSchurComplementComputeExplicitOperator() a bit to use KSPMatSolve(), so that if you have a small Schur complement — which is not really the case for NS — this could be a viable option, it was previously painfully slow). Thanks, Pierre > that I get a single iteration for the Schur complement solve with LU. That's > a nice testing option > > On Fri, Jun 23, 2023 at 12:02 PM Alexander Lindsay <alexlindsay...@gmail.com > <mailto:alexlindsay...@gmail.com>> wrote: >> I guess it is because the inverse of the diagonal form of A00 becomes a poor >> representation of the inverse of A00? I guess naively I would have thought >> that the blockdiag form of A00 is A00 >> >> On Fri, Jun 23, 2023 at 10:18 AM Alexander Lindsay <alexlindsay...@gmail.com >> <mailto:alexlindsay...@gmail.com>> wrote: >>> Hi Jed, I will come back with answers to all of your questions at some >>> point. I mostly just deal with MOOSE users who come to me and tell me their >>> solve is converging slowly, asking me how to fix it. So I generally assume >>> they have built an appropriate mesh and problem size for the problem they >>> want to solve and added appropriate turbulence modeling (although my >>> general assumption is often violated). >>> >>> > And to confirm, are you doing a nonlinearly implicit velocity-pressure >>> > solve? >>> >>> Yes, this is our default. >>> >>> A general question: it seems that it is well known that the quality of >>> selfp degrades with increasing advection. Why is that? >>> >>> On Wed, Jun 7, 2023 at 8:01 PM Jed Brown <j...@jedbrown.org >>> <mailto:j...@jedbrown.org>> wrote: >>>> Alexander Lindsay <alexlindsay...@gmail.com >>>> <mailto:alexlindsay...@gmail.com>> writes: >>>> >>>> > This has been a great discussion to follow. Regarding >>>> > >>>> >> when time stepping, you have enough mass matrix that cheaper >>>> >> preconditioners are good enough >>>> > >>>> > I'm curious what some algebraic recommendations might be for high Re in >>>> > transients. >>>> >>>> What mesh aspect ratio and streamline CFL number? Assuming your model is >>>> turbulent, can you say anything about momentum thickness Reynolds number >>>> Re_θ? What is your wall normal spacing in plus units? (Wall resolved or >>>> wall modeled?) >>>> >>>> And to confirm, are you doing a nonlinearly implicit velocity-pressure >>>> solve? >>>> >>>> > I've found one-level DD to be ineffective when applied monolithically or >>>> > to the momentum block of a split, as it scales with the mesh size. >>>> >>>> I wouldn't put too much weight on "scaling with mesh size" per se. You >>>> want an efficient solver for the coarsest mesh that delivers sufficient >>>> accuracy in your flow regime. Constants matter. >>>> >>>> Refining the mesh while holding time steps constant changes the advective >>>> CFL number as well as cell Peclet/cell Reynolds numbers. A meaningful >>>> scaling study is to increase Reynolds number (e.g., by growing the domain) >>>> while keeping mesh size matched in terms of plus units in the viscous >>>> sublayer and Kolmogorov length in the outer boundary layer. That turns out >>>> to not be a very automatic study to do, but it's what matters and you can >>>> spend a lot of time chasing ghosts with naive scaling studies.
