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Use of AMG blockSolver on blockCoupledScalarTransportFoam |
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October 21, 2021, 10:14 |
Use of AMG blockSolver on blockCoupledScalarTransportFoam
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#1 |
Member
Join Date: Mar 2021
Posts: 39
Rep Power: 5 |
Hello to all,
I am trying to run the tutorial case from foam-extend 4.1 called blockCoupledSwirlTest. By default the tutorial is solved with a BiCGStab solver. I would like to use an AMG solver. I copied the parameters from /incompressible/pUCoupledFoam/backwardFacingStepLaminar/ Code:
solver AMG; cycle W-cycle; coarseningType SAMG; norm componentNorm; normComponent 3; minGroupSize 4; maxGroupSize 6; nPreSweeps 2; nPostSweeps 2; groupSize 2; minCoarseEqns 4; nMaxLevels 100; scale on; smoother ILUC0; minIter 0; maxIter 100; tolerance 1e-7; relTol 0.0; Code:
Courant Number mean: 10 max: 39 velocity magnitude: 0.975 Time = 1 --> FOAM FATAL ERROR: index out of range From function VectorSpace<Form, Cmpt, nCmpt>::component(direction) const in file /home/pc/foam/foam-extend-4.1/src/foam/lnInclude/VectorSpaceI.H at line 75. |
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October 21, 2021, 16:28 |
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#3 | |
Member
Join Date: Mar 2021
Posts: 39
Rep Power: 5 |
Quote:
AMG works in pUCoupledFoam (4x4 block matriX). GAMG works in standard scalarTransportFoam.
I would say AMG should on this system too. Is there any reason why it does not work ? Best Regards |
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October 22, 2021, 10:29 |
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#4 |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
Rep Power: 15 |
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October 22, 2021, 14:51 |
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#5 |
Senior Member
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The pressure-velocity coupled formulation leads to linear systems with coefficient matrices of the form [A B; B^T C]. These saddle point linear systems are hard to solve. Developing multigrid solvers that outperform single-grid solvers for these systems is challenging.
I was not aware of GAMG for the pUCoupledFoam for the backwardStep to converge. I wonder to what extend GAMG outperforms single level solvers and how the mesh affects the convergence of GAMG. The question that started this thread remains. A non-block-structured mesh should not be the cause of an out-of-range error. |
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October 23, 2021, 10:45 |
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#6 | |
Member
Join Date: Mar 2021
Posts: 39
Rep Power: 5 |
Quote:
All solvers listed for asymmetric matrices work with the exception of AMG. If you can also replicate this, I would say it is a bug in the implementation of AMG for block matrices. |
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