> On 23 Jun 2023, at 10:06 PM, Pierre Jolivet <pierre.joli...@lip6.fr> wrote: > > >> 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
Oops, sorry for the noise, looks like it was done by me indeed in 9399e4fd88c6621aad8fe9558ce84df37bd6fada… Thanks, Pierre > (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. >
