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Old   June 21, 2010, 16:00
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Scott
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Hello,

I am just getting started with openFOAM and have found the learning curve to be pretty steep. I am able to generate meshes of my flow volumes and export them as a .UNV (Ideas) format from UG/NX. Its very easy to specify the flow conditions in NX (i.e. velocity, altitude, materials, etc.) I'm not clear on how to do it in openFOAM. It looks like all this would be done in the controlDict file. Also in the tutorials I have seen reference to specifying which patches make up the boundaries, do I have to specify these patches manually? What if I have 1,000,000 elements and thousands of patches on a boundary face? Do I have to manually specify them all? Where do I specify my initial conditions, flow velocity, pressure, material (Air)? Can I measure lift and drag of a protrusion in the flow volume? I suppose this stuff is all in the user guide but it isn't really clear on where it is. I have read through it but still have tons of questions. If anyone can help I would really appreciate it.

Thanks
Scott
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Old   June 22, 2010, 02:17
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Alberto Passalacqua
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Please, read the manual again, go through the tutorials. Many of the questions you asked will find an answer if you go through the tutorials in the User's guide and in the Programmer's guide.

I would suggest you follow the tutorials step by step, and then, if you have questions feel free to ask again.

One suggestion: use one independent thread for each question, and, before opening a thread, use the search function of the forum. Many answers are already there.

You can find also some more information on the wiki: http://openfoamwiki.net/

Thanks
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Old   June 23, 2010, 19:57
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Daniel WEI (老魏)
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Alberto, you are so kind. I found your name every place where people need help.

Your answers are always characterized with Clarity, Well-Organization, and Practical Guidance. They are so helpful.
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Old   June 24, 2010, 00:09
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I just started running my very first OpenFOAM case. And unlike other CFD programs, OpenFOAM doesnt really give a visual representation of whats going on. So I was just wondering if anyone could help me out in figuring out whether the code is going in the right direction.

Code:
DILUPBiCG:  Solving for epsilon, Initial residual = 1.95207e-06, Final residual = 1.95207e-06, No Iterations 0
DILUPBiCG:  Solving for k, Initial residual = 7.29185e-06, Final residual = 7.29185e-06, No Iterations 0
DILUPBiCG:  Solving for Ux, Initial residual = 2.08313e-10, Final residual = 2.08313e-10, No Iterations 0
DILUPBiCG:  Solving for Uy, Initial residual = 2.29687e-10, Final residual = 2.29687e-10, No Iterations 0
DILUPBiCG:  Solving for Uz, Initial residual = 4.2889e-08, Final residual = 4.2889e-08, No Iterations 0
DILUPBiCG:  Solving for h, Initial residual = 5.49913e-06, Final residual = 5.49913e-06, No Iterations 0
DICPCG:  Solving for p, Initial residual = 4.64395e-05, Final residual = 5.84329e-14, No Iterations 1
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 7.35752e-05, global = 5.5069e-05, cumulative = 2.00842
rho max/min : 16.4971 0.00201364
bounding p, min: 306.907 max: 1.34522e+06 average: 106238

Cheers!
T
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Old   June 24, 2010, 00:57
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Alberto Passalacqua
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OF shows you the residuals of each equation and some other information (bound variables, conservation information, ...).

If you want, you can plot residuals in real time with pyFoamPlotRunner, which is part of pyFoam http://openfoamwiki.net/index.php/Contrib_PyFoam

Best,
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Old   June 24, 2010, 01:03
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Hey Alberto!

Thanks for your shifty response! I will give pyFoam a shot soon. But as of today, the senior engineer isnt here and Im unable to work with him with pyFoam. So I was just wondering if you could let me know whether it seems like the calculations are running correctly? If it is, then Im going to let it run through the night. If its not, then I can wait till tomorrow!

Cheers,
T
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Old   June 24, 2010, 11:09
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Quote:
Originally Posted by trex930 View Post
Hey Alberto!

Thanks for your shifty response! I will give pyFoam a shot soon. But as of today, the senior engineer isnt here and Im unable to work with him with pyFoam. So I was just wondering if you could let me know whether it seems like the calculations are running correctly? If it is, then Im going to let it run through the night. If its not, then I can wait till tomorrow!

Cheers,
T
I guess Alberto is busy now watching the ITA VS. SVK game, poor Italy (It's already 2 goals behind), so allow me say something.
  1. I suggest you not wait, you should get your hands as dirty as possible, so keep trying;
  2. Bu that doesn't mean your results are correct, it is hard to judge simply from equation solving information to say your simulation is right or not. Your case description, boundary condition, etc., they are all indispensable to assess the simulation.
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Last edited by lakeat; June 24, 2010 at 11:33.
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Old   June 24, 2010, 12:05
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Quote:
Originally Posted by lakeat View Post
I guess Alberto is busy now watching the ITA VS. SVK game, poor Italy (It's already 2 goals behind), so allow me say something.
Not a bit soccer fan (more a F1 guy ).

About knowing if the simulation is correct or not, well the code is running, and the equations are not diverging, even if some variable is bounded (normal in unsteady runs). I would suggest to save the output in a log and look at the evolution of the initial residuals (you can plot them with pyFoamPlotWatcher.py too) after, when your supervisor is there. In addition, as Daniel said, you've to check the results and the setup. Residuals are just a part of the story.

Best,
A.
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Old   June 26, 2010, 09:04
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Dear Lakeat and Alberto,
Do you have used "directMapped" boundary in tutorials/incompressible/pisoFoam/les/pitzDailyDirectMapped . I have tried the "nearestCell" ,it works fine, but the method "nearestFace" doesn't work for me . I can't find the reason ,and my work can not be going on. Seldom people can give me common, do you have some suggestions ?

Turbulence inflow generation - recycling method

I am sorry to disturb this thread, but I must come here to fine you.
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