Manuel Valera <mvaler...@sdsu.edu> writes: > Yes, all of that sounds correct to me, > > No I haven't tried embedding the column integral into the RHS, right now I > am unable to think how to do this without the solution of the previous > intermediate stage. Any ideas are welcome,
Do you have some technical notes on your present formulation? I think it just amounts to performing the integration and then evaluating the differential operator using results of that integral. > Thanks, > > On Wed, Oct 9, 2019 at 4:18 PM Jed Brown <j...@jedbrown.org> wrote: > >> Manuel Valera <mvaler...@sdsu.edu> writes: >> >> > Sorry, I don't follow this last email, my spatial discretization is >> fixed, >> > the problem is caused by the choice of vertical coordinate, in this case >> > sigma, that calls for an integration of the hydrostatic pressure to >> correct >> > for the right velocities. >> >> Ah, fine. To phrase this differently, you are currently solving an >> integro-differential equation. With an explicit integrator, you should >> be able to embed that in the RHS function. With an implicit integrator, >> that causes the Jacobian to lose sparsity (the column integral is dense >> coupling) so it's sometimes preferable to add pressure as an explicit >> variable (or transform your existing variable set as part of a >> preconditioner), in which case you get a differential algebraic equation >> (the incompressible limit). >> >> Have you tried embedding the column integral into the RHS function to >> make a single unsplit formulation? >> >> > I had RK3 working before and SSP is much more stable, i can use way >> bigger >> > DTs but then i get this asynchronous time integration. With RK3 I can >> > operate in the intermediate states and thus I can advance everything in >> > synchronization, but bigger DTs are not viable, it turns unstable >> quickly. >> > >> > On Wed, Oct 9, 2019 at 3:58 PM Jed Brown <j...@jedbrown.org> wrote: >> > >> >> Is it a problem with the spatial discretization or with the time >> >> discretization that you've been using thus far? (This sort of problem >> >> can occur for either reason.) >> >> >> >> Note that an SSP method is merely "preserving" -- the spatial >> >> discretization needs to be strongly stable for an SSP method to preserve >> >> it. It sounds like yours is not, so maybe there is no particular >> >> benefit to using SSP over any other method (but likely tighter time step >> >> restriction). >> >> >> >> Manuel Valera <mvaler...@sdsu.edu> writes: >> >> >> >> > To correct for the deformation of the sigma coordinate grid... without >> >> this >> >> > correction the velocity become unphysical in the zones of high slope >> of >> >> the >> >> > grid. This is very specific of our model and probably will be solved >> by >> >> > updating the equations transformation, but that's not nearly close to >> >> > happening right now. >> >> > >> >> > On Wed, Oct 9, 2019 at 3:47 PM Jed Brown <j...@jedbrown.org> wrote: >> >> > >> >> >> Manuel Valera <mvaler...@sdsu.edu> writes: >> >> >> >> >> >> > Thanks, >> >> >> > >> >> >> > My time integration schemes are all explicit, sorry if this a very >> >> >> atypical >> >> >> > setup. This is similar to the barotropic splitting but not >> exactly, we >> >> >> > don't have free surface in the model, this is only to correct for >> >> sigma >> >> >> > coordinates deformations in the velocity field. >> >> >> > >> >> >> > From how i see it this could be solved by obtaining the >> intermediate >> >> >> stages >> >> >> > and then updating them accordingly, is this not possible to do ? >> >> >> >> >> >> Why are you splitting if all components are explicit and not >> subcycled? >> >> >> >> >> >>