[petsc-users] Help with ML/BoomerAMG

[Gaetan Kenway]

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)?
>>
>
>
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