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March 31, 2010, 11:23 
interFoam

#1 
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Andrea Pasquali
Join Date: Sep 2009
Location: Germany
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Hello,
I'd like to simulate a rotating gear system into oil. I choose the solver interFoam. U: I compiled new BC to set a ramp of velocity of rotation (timeVaryingRotatingWallVelocity) for my rotating elements (timeVaryingUniformFixedValue p: I used the totalPressure for the atmosphere patch and zeroGradient for all other walls and rotating element; kepsilon model for the turbulence. First I tried with epsilon = 100 and my simulation died after 0.06 seconds. Then I increased the value of epsilon = 1000 and my simulation died at 0.84 seconds. I attached the plots of residuals and Courant number. You can see that in the end of simulation k and epsilon start increasing very fast and bring the calculation to die in a very little time! Now I'm thinking to run new analysis increasing the value of epsilon, but before I have some question: 1) Is it correct use kepsilon for rotating element? 2) If yes, how can calculate the correct value of k and epsilon without find it by tentative? I try to use the formulas that are in OF user guide but I don't know how can use them with rotating elements or if are correct for rotating elements Thanks anyone for any suggestion Andrea
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Andrea Pasquali 

May 10, 2010, 09:19 

#2  
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Andrea Pasquali
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Location: Germany
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Hello I spent much time about my case,
I think I improved my analysis but I'm still far to obtain the correct solution. The problem is I cannot extend the analysis longer than 1.04 sec. I want explain my problem:  My run looks good until 1.04 sec (it has "just" buonding k from 0.5 sec). I used ramp of velocity until 0.25 sec. You can see the residuals in the pictures I attached.  Suddenly the calculation crash! I can see in the error message the rown "floating point exception".  So, how I found in Problem using single precision in simpleFoam , I commented the row //export FOAM_SIGFPE= in etc/bashrc file.  Then I restart the analysis from 1.04 and this is what I obtain: Quote:
Just in 1 iteration the p equation in the 2^ loop is not solved and in 3^ loop has "solution singulatiy", the time step continuity error grows up and I have "not a number" in k and epsilon!!! Can anyone explain this? Why I have this error? Thanks Andrea
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Andrea Pasquali Last edited by andrea.pasquali; May 10, 2010 at 09:44. 

May 29, 2010, 09:36 

#3 
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Andrea Pasquali
Join Date: Sep 2009
Location: Germany
Posts: 142
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Hello,
I'm still trying with my model and with interFoam. Now I try the BC "buoyantPressure" in p file for each patch, like in interFoam tutorial, instead of "zeroGradient". If you see the alpha1 plot (attached) you can see that for "zeroGradient" alpha1 decrease, for "buoyantPressure" is costant (my model is a closed volume, no inlet no outlet and the liquid can't exit from the atmosphere patch). I can't understand why... The buoyantPressure BC is not for thermal analysis or where the density change? Could anyone help me? Thanks Andrea
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Andrea Pasquali 

May 30, 2010, 08:50 

#4 
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Claus Meister
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The solving for alpha is okay. It is high likely that you face a convectiondominace. Have you tried or even applied flux limiter vor div(rho*phi,U) term? I not try as a guess limitedLinearV 1; Properly, this will avoid the blow up.
cheers 

May 30, 2010, 08:52 

#5 
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Claus Meister
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Addtionally, it seems that you carry out to less PISO loops. At this point in iteration, increase them to five. If you should have an orthogonal mesh then set nonOrthogonalcorrection to zero otherwise 1 and try again.


May 30, 2010, 09:56 

#6 
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Andrea Pasquali
Join Date: Sep 2009
Location: Germany
Posts: 142
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Hi Claus,
thank you very much for your reply! For div(rho*phi,U) I have "Gauss limitedLinearV 1" For PISO loop I have: nCorrectors 3 nNonOrthogonalCorrectors 0 > This check is OK with checkMesh nAlphaCorr 1 nAlphaSubCycles 3 cAlpha 1 Another thing, I saw the solution at 0.5 seconds: with p zeroGradient I have a field from 1850 to +1880 Pa with p buoyantPressure the field goes from 1850 to +3800 Pa I don't know what is the correct way... Can you help me? Thanks Andrea
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Andrea Pasquali 

May 30, 2010, 12:20 

#7 
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Claus Meister
Join Date: Aug 2009
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At now, I don't know it either. Could you please post your p file and alpha1 file; i'd like to take a look!


May 30, 2010, 12:45 

#8  
Senior Member
Andrea Pasquali
Join Date: Sep 2009
Location: Germany
Posts: 142
Rep Power: 9 
Hi Claus,
here "p" Quote:
Quote:
Thank you Andrea
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Andrea Pasquali 

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