Error: CSysSolve linear solver diverged

mdsar · November 19, 2020, 08:39

Hello everybody, I am trying to run a turbulent simulation with RANS solver and the same error keeps showing up:

Error in "void CSysSolve<ScalarType>::ModGramSchmidt(int, su2matrix<ScalarType>&, std::vector<CSysVector<ScalarType> >&) const [with ScalarType = double; su2matrix<ScalarType> = C2DContainer<long unsigned int, double, (StorageType)0, 64, 0, 0>]

FGRMES orthogonalization failed, linear solver diverged

I have already tried to change the CFL number, the slope limiter, the type of linear solver, convergence criteria and all the other parameters, but nothing works.

Does anyone have an idea of what might be happening here?
Thanks in advanced

aero_amit · November 29, 2020, 00:43

Is it happening at the start or after few iterations ?

Make sure that your mesh is of acceptable quality and boundary conditions are correctly applied (at times mesh quality causes such divergence issue). Having said that, give a try to -

LINEAR_SOLVER= BCGSTAB
LINEAR_SOLVER_PREC= ILU
LINEAR_SOLVER_ITER= 5 or 10 (if needed) (In one case, these setting helped me to overcome the similar issue)

You can also try first order simulation followed by second order (restart from first) and see if it helps. Also switch off the multigrid (if turned on).

November 19, 2020, 08:39	Error: CSysSolve linear solver diverged	#1
mdsar New Member Join Date: Nov 2020 Posts: 1 Rep Power: 0	Hello everybody, I am trying to run a turbulent simulation with RANS solver and the same error keeps showing up: Error in "void CSysSolve<ScalarType>::ModGramSchmidt(int, su2matrix<ScalarType>&, std::vector<CSysVector<ScalarType> >&) const [with ScalarType = double; su2matrix<ScalarType> = C2DContainer<long unsigned int, double, (StorageType)0, 64, 0, 0>] FGRMES orthogonalization failed, linear solver diverged I have already tried to change the CFL number, the slope limiter, the type of linear solver, convergence criteria and all the other parameters, but nothing works. Does anyone have an idea of what might be happening here? Thanks in advanced

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November 29, 2020, 00:43		#2
aero_amit Member Amit Join Date: May 2013 Posts: 85 Rep Power: 13	Is it happening at the start or after few iterations ? Make sure that your mesh is of acceptable quality and boundary conditions are correctly applied (at times mesh quality causes such divergence issue). Having said that, give a try to - LINEAR_SOLVER= BCGSTAB LINEAR_SOLVER_PREC= ILU LINEAR_SOLVER_ITER= 5 or 10 (if needed) (In one case, these setting helped me to overcome the similar issue) You can also try first order simulation followed by second order (restart from first) and see if it helps. Also switch off the multigrid (if turned on).