I agree with the structured nature of the noise. I did play around with the PetscFV implementation a bit to allow for the computation of different fluxes left and right side of every interface.
Nevertheless it is indeed strange that the problem disappears when I use a PLEX dm. Regards, Mukkund > On 17 Jun 2020, at 22:53, Dave May <dave.mayhe...@gmail.com> wrote: > > > > On Wed 17. Jun 2020 at 21:21, MUKKUND SUNJII <mukkundsun...@gmail.com > <mailto:mukkundsun...@gmail.com>> wrote: > Yes, precisely! I am not sure how I can replicate using the original version > of ex11.c because it does not support bathymetry. > > Regardless, to demonstrate the discrepancy, I have uploaded three plots. The > scenario is a lake at rest. Essentially, you have a varying bathymetry but a > level water surface. If the model is well balanced, then the water surface > height must not change. The description of the files are below > > 1) Bathymetry.png : It shows you the bathymetry profile (z(x)) and the water > surface height (H = h+z(x)) at t = 0. > <Bathymetry.png> > > 2) Plex.png : This is the water surface height after 1 time step (0.007055 > sec) and the dm type is Plex. As you can see, the water surface height is > undisturbed as expected. > <Plex.png> > > 3) P4est.png : This is the result after 1 time step (same final time) if I > set the dm type as p4est. The noise is in the order of 1e-3 to be a little > more specific. Since its not specifically at the boundaries and more or less > spread throughout, it could indeed be noise introduced. But of course I could > be wrong. > <p4est.png> > > > The (wrong) result has seemingly a lot of structure. Have you verified your > code using p4est is valgrind clean? This looks too much like a weird indexing > bug for me to not ask this question. > > Thanks, > Dave > > > Maybe this paints a better picture. > > Regards, > > Mukkund > > For your reference, the Riemann Solver is a modified version of the HLL > solver: A simple well-balanced and positive numerical scheme for the > shallow-water system by Emmanuel Audusse, Christophe Chalons, Philippe Ung. > (https://www.intlpress.com/site/pub/files/_fulltext/journals/cms/2015/0013/0005/CMS-2015-0013-0005-a011.pdf > > <https://www.intlpress.com/site/pub/files/_fulltext/journals/cms/2015/0013/0005/CMS-2015-0013-0005-a011.pdf>) > >> On 17 Jun 2020, at 20:47, Mark Adams <mfad...@lbl.gov >> <mailto:mfad...@lbl.gov>> wrote: >> >> So you get this noise with a regular grid in p4est. So the same grid as will >> Plex, and you are not getting the same results. >> >> I don't know of any difference from p4est on a non-adapted grid. Can you >> reproduce this with ex11? >> >> Matt and Toby could answer this better. >> >> >> On Wed, Jun 17, 2020 at 1:33 PM MUKKUND SUNJII <mukkundsun...@gmail.com >> <mailto:mukkundsun...@gmail.com>> wrote: >> Greetings, >> >> I am a master’s student working on the shallow water model of the TS example >> 'ex11.c' as part of my thesis. Therefore, I am working with DMForest for the >> implementation of adaptive grids. I have a question and an observation. >> >> I am trying to find relevant information about interpolation that takes >> place through the routine DMForestTransferVec. Perhaps it could be my >> inability to find it, but I am unable to locate the implementation of the >> routine >> >> (forest->transfervec)(dmIn,vecIn,dmOut,vecOut,useBCs,time). >> >> Any information on this particular routine is highly appreciated. >> >> Furthermore, I have developed a well balanced Riemann Solver that includes >> topography in the model. In the process of testing both the non-adaptive and >> adaptive version, I found that my results differed when I changed the type >> of DM. For instance, when I run a scenario in a fixed, non-adaptive grid >> with a DM of type 'P4est', I find that the well balanced nature is lost due >> to small perturbations all across the domain. However, this does not occur >> when I use a DM of type ‘plex’. Is there a radical change in the routines >> between the two DM’s? This is not as much of a question as it is an >> observation. >> >> Thank you for all of your suggestions! >> >> Regards, >> >> Mukkund
