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November 7, 2013, 10:01 |
p_rgh residuals
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#1 |
New Member
Join Date: Aug 2013
Posts: 1
Rep Power: 0 |
Hi,
I have a problem with compressibleInterFoam (probably also with the other solvers). In my case I have a rectangular mesh and set all fields to fixedValue (U to zero, p_rgh to 1e5, alpha to 1) on the boundary (same as internal value), such that actually each solver has nothing to do. However the output looks like MULES: Solving for alpha1 Liquid phase volume fraction = 1 Min(alpha1) = 1 Min(alpha2) = 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for T, Initial residual = 0.2561283, Final residual = 6.2762823e-15, No Iterations 1 GAMG: Solving for p_rgh, Initial residual = 0.61205684, Final residual = 0.64939008, No Iterations 1000 max(U) 1.6479872e-15 min(p_rgh) 100000 GAMGPCG: Solving for p_rgh, Initial residual = 0.48389343, Final residual = 1.2801586e-08, No Iterations 7 max(U) 2.6078623e-15 min(p_rgh) 100000 ExecutionTime = 1.97 s ClockTime = 2 s If I look into the solution for each time step, the values actually do not change. Except for the velocity, which looks like random noise with amplitude of 1e-13. When I change the solver from p_rgh { solver GAMG;} to p_rgh { solver PCG;} i get now MULES: Solving for alpha1 Liquid phase volume fraction = 1 Min(alpha1) = 1 Min(alpha2) = 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for T, Initial residual = 0.2561283, Final residual = 6.2762823e-15, No Iterations 1 GAMGPCG: Solving for p_rgh, Initial residual = 0.61205684, Final residual = 8.4709971e-08, No Iterations 5 max(U) 1.8399522e-15 min(p_rgh) 100000 GAMGPCG: Solving for p_rgh, Initial residual = 0.48273501, Final residual = 1.2982136e-08, No Iterations 7 max(U) 2.4301619e-15 min(p_rgh) 100000 ExecutionTime = 0.34 s ClockTime = 0 s Does anybody know why the "Initial residual" is always so large and why are so many iterations are required to basically do nothing? How are residuals computed and how to avoid this behavior? |
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September 10, 2019, 13:46 |
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#2 | |
Member
Join Date: Mar 2019
Posts: 81
Rep Power: 7 |
Quote:
Last edited by mm66; September 10, 2019 at 15:05. |
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December 7, 2021, 03:32 |
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#3 |
New Member
lee wei
Join Date: Dec 2020
Posts: 11
Rep Power: 5 |
Another two years later, I also face the same problem as the former encountered. Any idea? thanks.
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December 7, 2021, 10:55 |
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#4 | |
Member
Join Date: Mar 2019
Posts: 81
Rep Power: 7 |
Quote:
Please make sure of a good mesh quality. If no help, then try something like: Code:
p_rgh { solver PCG; preconditioner { preconditioner GAMG; smoother DICGaussSeidel; tolerance 1e-6; } tolerance 1e-6; } Cheers, MJ Last edited by mm66; December 7, 2021 at 15:13. |
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December 9, 2021, 07:36 |
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#5 | |
New Member
lee wei
Join Date: Dec 2020
Posts: 11
Rep Power: 5 |
Quote:
thanks for your help, it works well when I changed the solver as you mentioned, but the simulation runs slower than before, can you tell me why if you do not mind. |
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