On 2/14/20 5:34 AM, Richard Schussnig wrote:
Could the observed behaviour be caused by applying an iterative solver*?
(using ReductionControl and a reduction factor of 1e-13 which is really low)
* Block-triangular Schur-complement-based approach, similar as in
step-55 suggested in the further possibilities for extension, basically
using S~-(1/viscosity)*Mass_pressure giving 20-40 iterations up to 3mio
dofs tested.
I have been checking the code for a week now, and i really doubt, that
the integration of just tau*grad(p)*grad(p) is wrong (again, the laplace
drops out for a rectangular grid).
Just to check, i used a manufactured solution from Poisuille flow and
added the laplacian from PSPG to the rhs, giving me the exact (linear)
solution in the pressure and quadratic convergence in the velocity, thus
I assume, that the grad(p)grad(q) term added is correctly implemeted.
(exact solution meaning, that i get an L2 error of err<1e-9 for any
number of elements used)
Anyone has ever experienced this or has anyone some tipps for further
debugging?
We have all spent much time trying to figure out these sorts of issues
:-) My usual approach is to switch to a direct solver to eliminate the
possibility that the problem lies with the solver. Just speaking about,
say, step-22, there is also the issue that the iterative solver actually
just ignores the pressure-pressure block of the matrix (I think that we
put a mass matrix in there as that is used in the preconditioner -- or
at least that's what we used to do). So it's useful to just remove
everything that could be problematic, and the iterative solvers are
definitely a point in case.
The other thing I usually check is what happens if I increase the order
of quadrature.
Best
W.
--
------------------------------------------------------------------------
Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
--
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see
https://groups.google.com/d/forum/dealii?hl=en
---
You received this message because you are subscribed to the Google Groups "deal.II User Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/dealii/ed9ba448-aa41-217f-38c7-9a0a64ed8e02%40colostate.edu.
