Jed Brown writes:
Michael Werner <[email protected]> writes:
>> > It uses unpreconditioned GMRES to estimate spectral
>> > bounds for
>> > the operator before using a Chebychev smoother.
It is GMRES preconditioned by the diagonal.
Moreover, in the incompressible limit, the compressible
formulation can
become very stiff,
leading to failure of solvers. That is why you get the
slightly
compressible (adiabatic?) formulations.
Ah, too bad, I was already expecting something like that,
because
most of the applications I found so far were FEM/ elasticity
problems. Then I'll have to see if I can find some other
suitable
solution.
You can implement a low-Mach preconditioner that would use
multigrid.
If you're working in conservative variables, then it requires a
nonlinear change of variables to isolate the pressure space.
A low-Mach preconditioner might help with the current test cases,
however I also intend to apply this code to high-Mach number
flows, so I need to find a more general solution. Actually, the
high-Mach number applications are more important, since so far all
the low-Mach cases are small enough to be solved with direct
solvers.
I was also thinking about using a geometric multigrid approach via
DMPlex. As far as I understood, hyperbolic problems are difficult
to solve with AMG because the solver isn't aware of the underlying
structure of the problem. Therefore I would think that a geometric
multigrid approach should produce better results, right? Do you
think it would be worthwile to implement a DMPlex, or would I
still run into the same problems?
Kind regards,
Michael
