# Courant-number explodes after a lon while (icoFoam)

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 January 13, 2014, 06:04 #2 New Member   Josh Join Date: Jun 2013 Posts: 14 Rep Power: 5 The best way I've found to debug these errors is to write the output at every time step (use purgeWrite if required) and analyse the 'results'. This should tell you if the courant number is caused by physically high velocities or not.

 January 13, 2014, 07:32 #3 Senior Member     Tobias Holzmann Join Date: Oct 2010 Location: Leoben (Austria) Posts: 1,519 Blog Entries: 6 Rep Power: 27 Additionally I would check the residuals (pyFoam). You will see if any variable is exploding.

 January 14, 2014, 06:34 #4 New Member   Join Date: Jan 2014 Posts: 5 Rep Power: 4 Here are the last iterations: Courant Number mean: 0.00135108479 max: 0.325747809 DILUPBiCG: Solving for Ux, Initial residual = 0.000560602417, Final residual = 4.03296652e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.00015680267, Final residual = 4.9929129e-09, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.000872529694, Final residual = 1.2753294e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0333809278, Final residual = 0.00163371246, No Iterations 99 DICPCG: Solving for p, Initial residual = 0.00664221968, Final residual = 0.000316368199, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.00265865953, Final residual = 0.000131461652, No Iterations 202 time step continuity errors : sum local = 5.62127726e-11, global = 4.85646331e-13, cumulative = 7.05936807e-10 DICPCG: Solving for p, Initial residual = 0.00172637241, Final residual = 8.14285543e-05, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.000829504218, Final residual = 3.89580035e-05, No Iterations 207 DICPCG: Solving for p, Initial residual = 0.000601586018, Final residual = 2.96378233e-05, No Iterations 197 time step continuity errors : sum local = 1.26902051e-11, global = -9.71962381e-14, cumulative = 7.05839611e-10 ExecutionTime = 313815.55 s ClockTime = 316731 s Time = 0.000130464 Courant Number mean: 0.00135142615 max: 0.365206875 DILUPBiCG: Solving for Ux, Initial residual = 0.000624335245, Final residual = 4.49943786e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000173011857, Final residual = 8.25574465e-09, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.000923101222, Final residual = 3.27248077e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0343213889, Final residual = 0.00166055835, No Iterations 193 DICPCG: Solving for p, Initial residual = 0.00707040719, Final residual = 0.000339425603, No Iterations 100 DICPCG: Solving for p, Initial residual = 0.00245047902, Final residual = 0.000120873377, No Iterations 200 time step continuity errors : sum local = 5.52798683e-11, global = 2.32304936e-14, cumulative = 7.05862841e-10 DICPCG: Solving for p, Initial residual = 0.00169495729, Final residual = 8.09930343e-05, No Iterations 101 DICPCG: Solving for p, Initial residual = 0.000876530509, Final residual = 4.18015271e-05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000634705028, Final residual = 3.14877683e-05, No Iterations 102 time step continuity errors : sum local = 1.44976153e-11, global = 1.18459615e-12, cumulative = 7.07047437e-10 ExecutionTime = 313844.61 s ClockTime = 316760 s Time = 0.000130474 Courant Number mean: 0.00135182934 max: 0.413264518 DILUPBiCG: Solving for Ux, Initial residual = 0.000704629111, Final residual = 4.70605141e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.0001940312, Final residual = 1.57881622e-08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.000985879925, Final residual = 1.43045728e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0325267583, Final residual = 0.00158705736, No Iterations 196 DICPCG: Solving for p, Initial residual = 0.00757949401, Final residual = 0.000378785221, No Iterations 108 DICPCG: Solving for p, Initial residual = 0.00280037641, Final residual = 0.000138433166, No Iterations 140 time step continuity errors : sum local = 6.85748798e-11, global = -5.09917634e-12, cumulative = 7.01948261e-10 DICPCG: Solving for p, Initial residual = 0.00193374674, Final residual = 9.46097161e-05, No Iterations 102 DICPCG: Solving for p, Initial residual = 0.00103330869, Final residual = 5.06354596e-05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000753501164, Final residual = 3.73602746e-05, No Iterations 107 time step continuity errors : sum local = 1.86450563e-11, global = 1.84520793e-12, cumulative = 7.03793469e-10 ExecutionTime = 313872.26 s ClockTime = 316787 s Time = 0.000130484 Courant Number mean: 0.00135231156 max: 0.472290254 DILUPBiCG: Solving for Ux, Initial residual = 0.000808944526, Final residual = 4.92679153e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000220969293, Final residual = 2.50528429e-08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00106574013, Final residual = 1.5683862e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0322361377, Final residual = 0.00152126195, No Iterations 198 DICPCG: Solving for p, Initial residual = 0.00820591951, Final residual = 0.000407452729, No Iterations 111 DICPCG: Solving for p, Initial residual = 0.00314755933, Final residual = 0.000155705809, No Iterations 139 time step continuity errors : sum local = 8.46944469e-11, global = -6.48447628e-12, cumulative = 6.97308993e-10 DICPCG: Solving for p, Initial residual = 0.0021942357, Final residual = 0.000101660495, No Iterations 103 DICPCG: Solving for p, Initial residual = 0.00118636758, Final residual = 5.76171022e-05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000863136193, Final residual = 4.25000504e-05, No Iterations 106 time step continuity errors : sum local = 2.33183295e-11, global = 2.26961477e-12, cumulative = 6.99578608e-10 ExecutionTime = 313900.13 s ClockTime = 316815 s Time = 0.000130494 Courant Number mean: 0.00135289441 max: 0.545196474 DILUPBiCG: Solving for Ux, Initial residual = 0.000941724687, Final residual = 5.49792424e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000255768375, Final residual = 3.89239595e-08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00116950018, Final residual = 2.21858032e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0337740886, Final residual = 0.00168285777, No Iterations 198 DICPCG: Solving for p, Initial residual = 0.00916882678, Final residual = 0.000445192936, No Iterations 112 DICPCG: Solving for p, Initial residual = 0.00356657676, Final residual = 0.000174221061, No Iterations 140 time step continuity errors : sum local = 1.05861353e-10, global = -8.43363183e-12, cumulative = 6.91144976e-10 DICPCG: Solving for p, Initial residual = 0.00248973046, Final residual = 0.000117714068, No Iterations 103 DICPCG: Solving for p, Initial residual = 0.00135836735, Final residual = 6.70189108e-05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000989233567, Final residual = 4.88439898e-05, No Iterations 106 time step continuity errors : sum local = 2.99826103e-11, global = 2.88323813e-12, cumulative = 6.94028214e-10 ExecutionTime = 313928.19 s ClockTime = 316844 s Time = 0.000130504 Courant Number mean: 0.00135360692 max: 0.635173148 DILUPBiCG: Solving for Ux, Initial residual = 0.00111241783, Final residual = 6.75475301e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000301108451, Final residual = 5.68671287e-08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00130073141, Final residual = 3.66935785e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0349797822, Final residual = 0.00170827006, No Iterations 200 DICPCG: Solving for p, Initial residual = 0.00970473193, Final residual = 0.000463780216, No Iterations 112 DICPCG: Solving for p, Initial residual = 0.0037789092, Final residual = 0.000183773907, No Iterations 140 time step continuity errors : sum local = 1.26279482e-10, global = -1.0214584e-11, cumulative = 6.8381363e-10 DICPCG: Solving for p, Initial residual = 0.00268332084, Final residual = 0.000132464647, No Iterations 102 DICPCG: Solving for p, Initial residual = 0.00145297631, Final residual = 7.13565785e-05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.00105976862, Final residual = 5.2285137e-05, No Iterations 106 time step continuity errors : sum local = 3.63288792e-11, global = 3.45070742e-12, cumulative = 6.87264337e-10 ExecutionTime = 313963.62 s ClockTime = 316880 s Time = 0.000130514 Courant Number mean: 0.00135448235 max: 0.744505284 DILUPBiCG: Solving for Ux, Initial residual = 0.00132165459, Final residual = 8.89449741e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000357101994, Final residual = 8.05188377e-08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00145279054, Final residual = 6.88082683e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0371526458, Final residual = 0.0018550487, No Iterations 200 DICPCG: Solving for p, Initial residual = 0.00989807886, Final residual = 0.000481242641, No Iterations 110 DICPCG: Solving for p, Initial residual = 0.00380425511, Final residual = 0.000190083233, No Iterations 139 time step continuity errors : sum local = 1.4780888e-10, global = -1.14090625e-11, cumulative = 6.75855275e-10 DICPCG: Solving for p, Initial residual = 0.0027571914, Final residual = 0.000137054566, No Iterations 101 DICPCG: Solving for p, Initial residual = 0.00147465605, Final residual = 7.02733199e-05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.00107328549, Final residual = 5.31538962e-05, No Iterations 106 time step continuity errors : sum local = 4.18094633e-11, global = 4.06678558e-12, cumulative = 6.7992206e-10 ExecutionTime = 313991.65 s ClockTime = 316908 s Time = 0.000130524 Courant Number mean: 0.00135554523 max: 0.870939992 DILUPBiCG: Solving for Ux, Initial residual = 0.00156394584, Final residual = 1.14334821e-07, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000421740246, Final residual = 1.02036997e-07, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00161100897, Final residual = 3.99879114e-07, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.0384808651, Final residual = 0.00179635437, No Iterations 196 DICPCG: Solving for p, Initial residual = 0.00919366901, Final residual = 0.000445499412, No Iterations 101 DICPCG: Solving for p, Initial residual = 0.00331579402, Final residual = 0.000163210372, No Iterations 140 time step continuity errors : sum local = 1.40648799e-10, global = -9.43821672e-12, cumulative = 6.70483844e-10 DICPCG: Solving for p, Initial residual = 0.002405895, Final residual = 0.000117504712, No Iterations 100 DICPCG: Solving for p, Initial residual = 0.00124074764, Final residual = 5.87632053e-05, No Iterations 201 DICPCG: Solving for p, Initial residual = 0.000903733201, Final residual = 4.4399401e-05, No Iterations 106 time step continuity errors : sum local = 3.86305268e-11, global = 3.74852639e-12, cumulative = 6.7423237e-10 ExecutionTime = 314019.16 s ClockTime = 316936 s Time = 0.000130534 Courant Number mean: 0.00135679454 max: 0.998997938 DILUPBiCG: Solving for Ux, Initial residual = 0.00179656253, Final residual = 1.25723893e-07, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000481528948, Final residual = 7.05450051e-08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00172289179, Final residual = 1.35426585e-07, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.0414029784, Final residual = 0.00200185089, No Iterations 31 DICPCG: Solving for p, Initial residual = 0.0083390347, Final residual = 0.000379814079, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.00253898182, Final residual = 0.000115853871, No Iterations 203 time step continuity errors : sum local = 1.03571708e-10, global = -1.46157115e-12, cumulative = 6.72770799e-10 DICPCG: Solving for p, Initial residual = 0.00160164772, Final residual = 7.44660037e-05, No Iterations 193 DICPCG: Solving for p, Initial residual = 0.000650163566, Final residual = 3.19850235e-05, No Iterations 203 DICPCG: Solving for p, Initial residual = 0.000390252354, Final residual = 1.85219341e-05, No Iterations 200 time step continuity errors : sum local = 1.65702356e-11, global = 3.69269402e-14, cumulative = 6.72807726e-10 ExecutionTime = 314051.67 s ClockTime = 316969 s I started the simulation with a program which controls and configure the courant-number (C<0.2), but the solution is also bad after a while. The pressure and the velocity value explodes at the trailing-edge e.g. pressure=9e+156 and velocity=10000 m/s ???

January 14, 2014, 13:56
#5
Senior Member

Tobias Holzmann
Join Date: Oct 2010
Location: Leoben (Austria)
Posts: 1,519
Blog Entries: 6
Rep Power: 27
Quote:
 Originally Posted by joshm The best way I've found to debug these errors is to write the output at every time step (use purgeWrite if required) and analyse the 'results'. This should tell you if the courant number is caused by physically high velocities or not.
Did you do this?
You are using a fixed dt now ?

January 14, 2014, 21:54
#6
New Member

Josh
Join Date: Jun 2013
Posts: 14
Rep Power: 5
Quote:
 Originally Posted by Rody- Here are the last iterations: [I]Courant Number mean: 0.00135108479 max: 0.325747809 DILUPBiCG: Solving for Ux, Initial residual = 0.000560602417, Final residual = 4.03296652e-08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.00015680267, Final residual = 4.9929129e-09, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.000872529694, Final residual = 1.2753294e-06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0333809278, Final residual = 0.00163371246, No Iterations 99 DICPCG: Solving for p, Initial residual = 0.00664221968, Final residual = 0.000316368199, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.00265865953, Final residual = 0.000131461652, No Iterations 202 time step continuity errors : sum local = 5.62127726e-11, global = 4.85646331e-13, cumulative = 7.05936807e-10 DICPCG: Solving for p, Initial residual = 0.00172637241, Final residual = 8.14285543e-05, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.000829504218, Final residual = 3.89580035e-05, No Iterations 207 DICPCG: Solving for p, Initial residual = 0.000601586018, Final residual = 2.96378233e-05, No Iterations 197 time step continuity errors : sum local = 1.26902051e-11, global = -9.71962381e-14, cumulative = 7.05839611e-10 ExecutionTime = 313815.55 s ClockTime = 316731 s I started the simulation with a program which controls and configure the courant-number (C<0.2), but the solution is also bad after a while. The pressure and the velocity value explodes at the trailing-edge e.g. pressure=9e+156 and velocity=10000 m/s ???
Sorry, I meant actually write the data and analyse it with a post-processing tool. This will tell you whether the issue is physical (i.e. fixed time step too large, mesh too large etc.) or not and you can go from there.

I do see now however that your run time is fairly large so you may want to wait for someone who knows a bit more than me to identify your issue without re-running.

 January 29, 2014, 05:27 #7 New Member   Join Date: Jan 2014 Posts: 5 Rep Power: 4 I think the Problem was, that i got velocity over 1000 m/s at the outlet cause of a eddy.... I start the simulation with simpleFoam and use the solution for icoFoam. Now it works fine. Thanks Tobi likes this.

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