Hi Again I did try running LU instead of ILU on the sub-domains. (This is the result of a RANS simulation at M=0.85, SA model, frozen turbulence and 96768 cells or matrix dimension or 483840). However, the ILU does not seem to be the cause of the issue. I've attached a plot of the two convergence histories. Both take 426 iterations of full GMRES (restart was set at 600). Column F is ASM(1), ILU(1) Column L is ASM(1), LU. This is right preconditioning and a check of the residual after the solver has completed confirms the actual residual has reduced by 6 orders of magnitude.
Any thoughts? Thank you, Gaetan Kenway On Mon, Apr 29, 2013 at 11:19 AM, Gaetan Kenway <gaetank at gmail.com> wrote: > It is possible the information provided by the discrete adjoint here is > somewhat less meaningful, but I need to analyze them for > off-design conditions for optimizations. I am using > a centered discretrization plus scalar JST dissipation. I have not tried > using LU on the subdomains, that is certainly something to try. > > Thank you for your help, > > Gaetan > > > On Mon, Apr 29, 2013 at 10:51 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote: > >> Gaetan Kenway <gaetank at gmail.com> writes: >> >> > It is an SA turbulence model and the discrete adjoint computed exactly >> with >> > AD. Certainly the grids are highly stretched in the BL since the grids >> are >> > resolving the viscous sublayer (y+ < 1) and the Reynolds numbers are on >> > the order of 10's of millions. I tend only to see this behaviour at >> > higher mach numbers when stronger shocks start to appear. For example, >> the >> > adjoint system may solve fine at M=0.80, and fail to converge at >> M=0.85. >> >> How meaningful is the information provided by the discrete adjoint here? >> Limiters and even just upwind discretizations on non-uniform grids lead >> to inconsistent discretizations of the adjoint equations. If the >> adjoint equation is full of numerical artifacts, it can cause the linear >> problem to lose structure, resulting in singular sub-problems, negative >> pivots, and other badness. What happens when you use a direct solve for >> subdomain problems (ASM+LU; use smaller subdomains if necessary)? >> > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130429/93aa2f9f/attachment-0001.html> -------------- next part -------------- A non-text attachment was scrubbed... Name: convergence.pdf Type: application/pdf Size: 24237 bytes Desc: not available URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130429/93aa2f9f/attachment-0001.pdf>
