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simulating diffusion process in long time (near equilibrium) with TOUGH2

Hi!
I am trying to simulate a simple diffusion poblem with TOUGH2. I am using EOS3, 

I can't get any results for long term (near equilibrium time which is in my problem around 80 days). The simulation stopps after about 3 days, because the program assumed that it has reached steady state. 
As there are two different analytical solutions for diffusion in short time and long time, I am afraid I should change my input file for continuing the simulation up to equilibrium. But I do not know how Tough2 solves diffusion, and which parameters should be changed in long term simulation.

 

can anybody suggest me something?

 

Thanks in advance,

Youhanna

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  • Youhanna,

    In a numerical simulator, there is one formulation for diffusion (see Appendix D of the manual), regardless of whether it is short or long term.

    You state that TOUGH2 stops "because the program assumed that it has reached steady state." What was the precise reason why TOUGH2 stopped. In case you indeed have had 10 time steps that converged on 1 iteration (but I doubt it, because your simulation time would be larger than 3 days), you could try tightening the convergence criterion (RE1) to make sure the simulation continues. Also check that you do not have limited the time step size (DELTMX). Other things could cause early termination (e.g., inappropriate boundary conditions).

    Good luck.

    Stefan

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