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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 flaptype 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 = 8.496246e07, No Iterations 397 DICPCG: Solving for cellMotionUy, Initial residual = 1, Final residual = 8.863253e07, No Iterations 58 Execution time for mesh.update() = 1.61 s time step continuity errors : sum local = 4.29361e09, global = 1.803651e10, cumulative = 1.818315e08 DICPCG: Solving for pcorr, Initial residual = 1, Final residual = 9.335962e11, No Iterations 222 DICPCG: Solving for pcorr, Initial residual = 2.391854e11, Final residual = 2.391854e11, No Iterations 0 DICPCG: Solving for pcorr, Initial residual = 2.391854e11, Final residual = 2.391854e11, No Iterations 0 time step continuity errors : sum local = 5.333407e19, global = 6.352097e21, cumulative = 1.818315e08 MULES: Solving for gamma Liquid phase volume fraction = 0.5000393 Min(gamma) = 1.77805e30 Max(gamma) = 1.02632 MULES: Solving for gamma Liquid phase volume fraction = 0.5000393 Min(gamma) = 1.712193e30 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 = 2.57424e05, No Iterations 20 time step continuity errors : sum local = 5.215714e08, global = 1.521795e08, cumulative = 2.965199e09 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 = 8.316119e06, No Iterations 19 time step continuity errors : sum local = 1.606884e08, global = 1.689781e10, cumulative = 2.796221e09 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 = 8.745692e08, No Iterations 38 time step continuity errors : sum local = 1.69809e10, global = 6.533056e12, cumulative = 2.789688e09 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 = 9.866497e07, No Iterations 16 DICPCG: Solving for cellMotionUy, Initial residual = 0.9999998, Final residual = 8.860694e07, No Iterations 58 Execution time for mesh.update() = 0.49 s time step continuity errors : sum local = 1.69809e10, global = 6.533055e12, cumulative = 2.783155e09 DICPCG: Solving for pcorr, Initial residual = 1, Final residual = 9.21361e11, No Iterations 229 DICPCG: Solving for pcorr, Initial residual = 2.966365e11, Final residual = 2.966365e11, No Iterations 0 DICPCG: Solving for pcorr, Initial residual = 2.966365e11, Final residual = 2.966365e11, No Iterations 0 time step continuity errors : sum local = 1.638706e19, global = 2.329411e22, cumulative = 2.783155e09 MULES: Solving for gamma Liquid phase volume fraction = 0.5000523 Min(gamma) = 1.193101e31 Max(gamma) = 1.02555 MULES: Solving for gamma Liquid phase volume fraction = 0.5000523 Min(gamma) = 1.149855e31 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 = 1.441456e05, No Iterations 19 time step continuity errors : sum local = 2.345417e08, global = 2.280152e09, cumulative = 5.030029e10 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 = 7.512438e06, No Iterations 19 time step continuity errors : sum local = 1.186638e08, global = 3.455044e10, cumulative = 8.485073e10 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 = 7.94363e08, No Iterations 40 time step continuity errors : sum local = 1.263819e10, global = 3.338986e12, cumulative = 8.451684e10 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: 1,702
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Hi
My experience with moving mesh and interFoamtype solvers is that having meshmovement 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:
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 pistontype wavemaker, it happened when I use flaptype. 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: 1,907
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
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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 opensource implementation of quadraturebased moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. 

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