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flow.out - residuals and equations

Hello, 

I am troubleshooting model. I have set MOP(1) = 1 and trying to figure out why my time-stepping continues to get reduced. I have automatic time-stepping turned on. 

My question is the following: 

in flow.out i have the following:

 ...ITERATING... AT [  17892,  1] --- DELTEX =  1.845863E+02   MAX. RES. =  3.294214E-04  AT ELEMENT A5 19  EQUATION   3

What does equation 3 mean here? 

Dr. Finsterle describes a number of steps to take to figure out why your model is not running properly in the link below: 

https://tough.forumbee.com/t/q5yqq6#m231ax

He mentions looking at "which equation causes the problem". 

What does EQUATION 3 or EQUATION 1 mean and where can I learn more about them? 

Thanks,

Majid 

3 replies

null
    • TOUGHREACT Developer
    • Eric_Sonnenthal
    • 4 mths ago
    • Reported - view

    Hi,

     

    The equations solved are basically the primary variables, eg. P, SatGas,T, or for ECO2n P, XNaCl, XCO2, T.

    Regarding automatic timestepping -- that may be ok for some problems, but if injection is taking place or the system is far from steady-state maybe not. There are a lot of things that can cause convergence problems, so you must look at the actual results in the SAVE or other output files to see if they make sense. The flow.out output here says which element is having trouble so you should look at that element using FOFT or in the other output files. There are many reasons why time steps are reduced -- there is a reasonable timestep to solve every problem accurately and stably, and you are exceeding it. That may be due to rock property issues, starting from a problem that is far from steady-state, too large a change in a primary variable in a given step, etc.

    regards,

    Eric

      • Majid_Trf
      • 4 mths ago
      • Reported - view

      Eric Sonnenthal thanks for the explanation. 

      Any chance you could give me feedback on my approach below for reaching steady-state before CO2 injection?

      I created one 1m^3 cell with an area of 1m^2. I proceeded to run my chemical initialization on this one cell. To make sure my chemistry is properly (charge) balanced , I used reaction quotients (in excel) to figure out how many mol/L of each primary species I had (i used chemical.out data to do this). I have provided an excel sheet along with the flow, chemical, and solute input files in the zip folder here: 1 m 3 cell chemical initialization + excel

      I then used the chemistry outputted in chdump for my bigger mesh here: 

      big mesh chemical initialization

      When I use the big mesh chemical initialization outputs (SAVE and chdump chemistry) for my injection simulation, my time-step continues to decrease to sub 1 second levels. Here is my injection zip as well:

      injection

      My hunch says that my chemical.inp file is missing some info and that is what's causing this. Appreciate you looking into this. 

      Thanks,

      Majid

      • TOUGHREACT Developer
      • Eric_Sonnenthal
      • 4 mths ago
      • Reported - view

       

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