# the problem about"Max(gamma)>1"

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 March 10, 2010, 01:50 the problem about"Max(gamma)>1" #1 Member   jingjing Join Date: Mar 2009 Location: shanghai,China Posts: 30 Rep Power: 9 Hello everyone, I use a flap-type wavemaker to make wave, during the calculation, I find the Max(gamma)>1, is this a serious problem which will affect the accuracy of the result? ... Courant Number mean: 0.001894994 max: 0.4794407 Time = 1.005 DICPCG: Solving for cellMotionUx, Initial residual = 1, Final residual = 8.496246e-07, No Iterations 397 DICPCG: Solving for cellMotionUy, Initial residual = 1, Final residual = 8.863253e-07, No Iterations 58 Execution time for mesh.update() = 1.61 s time step continuity errors : sum local = 4.29361e-09, global = 1.803651e-10, cumulative = -1.818315e-08 DICPCG: Solving for pcorr, Initial residual = 1, Final residual = 9.335962e-11, No Iterations 222 DICPCG: Solving for pcorr, Initial residual = 2.391854e-11, Final residual = 2.391854e-11, No Iterations 0 DICPCG: Solving for pcorr, Initial residual = 2.391854e-11, Final residual = 2.391854e-11, No Iterations 0 time step continuity errors : sum local = 5.333407e-19, global = -6.352097e-21, cumulative = -1.818315e-08 MULES: Solving for gamma Liquid phase volume fraction = 0.5000393 Min(gamma) = -1.77805e-30 Max(gamma) = 1.02632 MULES: Solving for gamma Liquid phase volume fraction = 0.5000393 Min(gamma) = -1.712193e-30 Max(gamma) = 1.02593 DICPCG: Solving for pd, Initial residual = 0.01384289, Final residual = 0.00065049, No Iterations 18 DICPCG: Solving for pd, Initial residual = 0.009080314, Final residual = 0.0003433817, No Iterations 20 DICPCG: Solving for pd, Initial residual = 0.0005947545, Final residual = 2.57424e-05, No Iterations 20 time step continuity errors : sum local = 5.215714e-08, global = 1.521795e-08, cumulative = -2.965199e-09 DICPCG: Solving for pd, Initial residual = 0.07757173, Final residual = 0.003759144, No Iterations 11 DICPCG: Solving for pd, Initial residual = 0.003940919, Final residual = 0.0001762634, No Iterations 16 DICPCG: Solving for pd, Initial residual = 0.0001668971, Final residual = 8.316119e-06, No Iterations 19 time step continuity errors : sum local = 1.606884e-08, global = 1.689781e-10, cumulative = -2.796221e-09 DICPCG: Solving for pd, Initial residual = 0.06889182, Final residual = 0.002239976, No Iterations 11 DICPCG: Solving for pd, Initial residual = 0.0022981, Final residual = 0.0001148254, No Iterations 14 DICPCG: Solving for pd, Initial residual = 0.00011941, Final residual = 8.745692e-08, No Iterations 38 time step continuity errors : sum local = 1.69809e-10, global = 6.533056e-12, cumulative = -2.789688e-09 ExecutionTime = 320.99 s ClockTime = 322 s Courant Number mean: 0.006729381 max: 0.5210432 Time = 1.01 DICPCG: Solving for cellMotionUx, Initial residual = 0.0005103467, Final residual = 9.866497e-07, No Iterations 16 DICPCG: Solving for cellMotionUy, Initial residual = 0.9999998, Final residual = 8.860694e-07, No Iterations 58 Execution time for mesh.update() = 0.49 s time step continuity errors : sum local = 1.69809e-10, global = 6.533055e-12, cumulative = -2.783155e-09 DICPCG: Solving for pcorr, Initial residual = 1, Final residual = 9.21361e-11, No Iterations 229 DICPCG: Solving for pcorr, Initial residual = 2.966365e-11, Final residual = 2.966365e-11, No Iterations 0 DICPCG: Solving for pcorr, Initial residual = 2.966365e-11, Final residual = 2.966365e-11, No Iterations 0 time step continuity errors : sum local = 1.638706e-19, global = -2.329411e-22, cumulative = -2.783155e-09 MULES: Solving for gamma Liquid phase volume fraction = 0.5000523 Min(gamma) = -1.193101e-31 Max(gamma) = 1.02555 MULES: Solving for gamma Liquid phase volume fraction = 0.5000523 Min(gamma) = -1.149855e-31 Max(gamma) = 1.025178 DICPCG: Solving for pd, Initial residual = 0.282985, Final residual = 0.006764506, No Iterations 3 DICPCG: Solving for pd, Initial residual = 0.006902246, Final residual = 0.000315175, No Iterations 17 DICPCG: Solving for pd, Initial residual = 0.0003561435, Final residual = 1.441456e-05, No Iterations 19 time step continuity errors : sum local = 2.345417e-08, global = 2.280152e-09, cumulative = -5.030029e-10 DICPCG: Solving for pd, Initial residual = 0.1002033, Final residual = 0.004059263, No Iterations 11 DICPCG: Solving for pd, Initial residual = 0.003998678, Final residual = 0.0001579902, No Iterations 14 DICPCG: Solving for pd, Initial residual = 0.0001502544, Final residual = 7.512438e-06, No Iterations 19 time step continuity errors : sum local = 1.186638e-08, global = -3.455044e-10, cumulative = -8.485073e-10 DICPCG: Solving for pd, Initial residual = 0.08480317, Final residual = 0.002404498, No Iterations 11 DICPCG: Solving for pd, Initial residual = 0.002482414, Final residual = 0.000107671, No Iterations 15 DICPCG: Solving for pd, Initial residual = 0.0001129264, Final residual = 7.94363e-08, No Iterations 40 time step continuity errors : sum local = 1.263819e-10, global = 3.338986e-12, cumulative = -8.451684e-10 ExecutionTime = 322.76 s ClockTime = 323 s ... what can I do? I modify the write precision or change the nNonOrthogonalCorrectors from 0 to 2, or increase nGammaCorr But it seems no use. Any help will be appreciated! Jingjing

 March 10, 2010, 04:52 #2 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,713 Rep Power: 27 Hi My experience with moving mesh and interFoam-type solvers is that having mesh-movement courant numbers larger than 1 results in overshooting of gamma. I do not know if that could be the source of your problem? Best regards, Niels

March 10, 2010, 06:12
#3
Member

jingjing
Join Date: Mar 2009
Location: shanghai,China
Posts: 30
Rep Power: 9
Quote:
 Originally Posted by ngj Hi My experience with moving mesh and interFoam-type solvers is that having mesh-movement courant numbers larger than 1 results in overshooting of gamma. I do not know if that could be the source of your problem? Best regards, Niels
Hi Niels,

The courant number is just around 0.5,never beyond 1.Even after I limit the maxCo below 0.2, Max(gamma) is still beyond 1, sometines even 1.2....I wonder whether I set the boundary condition correctly. I set the flow velocity at the flap in U the same as the velocity of the flap in pointMotion, and set the gamma "zeroGradient" at the flap. Is there any problem?
The abnormal phenomonen didn't happen when I use piston-type wavemaker, it happened when I use flap-type. I don't know whether the result is acceptable.

 March 11, 2010, 06:35 #4 Senior Member   Kathrin Kissling Join Date: Mar 2009 Location: Besigheim, Germany Posts: 134 Rep Power: 9 Hi zhajingjing, what discretisation scheme are you using for the convective term of the gammaEqn? Can you try to use a first order upwind scheme and check whether the unboundedness still appears? If the error comes from the discretisation of the convective term, this should work. Best Kathrin

 March 11, 2010, 08:18 #5 Member   jingjing Join Date: Mar 2009 Location: shanghai,China Posts: 30 Rep Power: 9 Hi Kathrin, I use this :" div(phi,gamma) Gauss vanLeer;" after I change to "div(phi,gamma) Gauss upwind", I find this problem still exist. I find that the unbounded gamma comes out the area where the flap contacts with the free surface.

 April 4, 2010, 23:29 gamma>1 also happen in my piston type wavemaker #6 Member   jingjing Join Date: Mar 2009 Location: shanghai,China Posts: 30 Rep Power: 9 Hi, In fact, in my piston type wavemaker cases, the maximum gamma value also reach to 1.004. Why, is it the reason of the singularity at the intersection of the wavemaker and free surface?

 April 5, 2010, 02:33 #7 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,910 Rep Power: 27 You said you limited Co at 0.2. Was this limit strictly respected? Try to plot a contour of Co and check where it is large. Also, keep an eye on the convergence of the pd equation. Switch to GAMG linear solver, and tighten that tolerance to very low (10^-15 or less). You have 10^-8 the correction steps, which might indicate a problem there. Best __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

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