flow.out  residuals and equations
Hello,
I am troubleshooting model. I have set MOP(1) = 1 and trying to figure out why my timestepping continues to get reduced. I have automatic timestepping turned on.
My question is the following:
in flow.out i have the following:
...ITERATING... AT [ 17892, 1]  DELTEX = 1.845863E+02 MAX. RES. = 3.294214E04 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

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 steadystate 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 steadystate, too large a change in a primary variable in a given step, etc.
regards,
Eric