[petsc-users] Help with ML/BoomerAMG

[Gaetan Kenway]

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)?
>
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