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Old   November 3, 2005, 20:08
Default Computation time
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I still wonder if I am doing something wrong or the computations are really so demanding and time consuming. Can you present here some details about some of your experiences?

I start with this:

Platform: Win2003, AMD64 3200, 2GB RAM dual PC400


- unsteady simulation,

- rushton turbine (240 rpm) in a 20x20cm tank with 4 baffles,

- sliding mesh,

- VOF (air-water),

- k-epsilon,


- pressure: Body Force Weighted,

- under-relaxation factors - all 0.1,

- about 31000 cells of mesh.

Time: 1 second is computed in about 10 hours

I think its quite long, maybe I make some mistake?
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Old   November 4, 2005, 05:00
Default Re: Computation time
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Your settings sound quite good. Typical VOF unsteady application. Anyway your computational time is actually quite large (never did a serious benchmark, but it takes me approximately the same time, 1 second flow time in about 8 hours, for 400k cells model on a Linux machine).

How long does it take you 1 iteration? Which is your time step? How many iterations are required for a time step?

Reading back your post: maybe you're URFs are too low...try something like:

-pressure: 0.6

-momentum: 0.8

-others: 1

Hope this can help

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Old   November 4, 2005, 08:29
Default Re: Computation time
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1- Check the swap area 2- Check the performance of the microprocessor (Right click on the bottom of the screen, select the task manager then the performance tab)
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Old   November 5, 2005, 07:16
Default Re: Computation time
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Swap file is probably not used as system disposes 2GB RAM memory and fluent takes about 150MB also processor works at 99%.

I found the problem existing rather in simulation settings than in system settings.

I changed the under relaxation factors and simulation speed increased 5 times - quite good. I set the urfs very rigorously because at the initial stage the integration bacame unstable - so it's worth to "loose" the urfs a little after the simulation has already passed that troublesome initial stage.

reagrds Maciej
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