Discussion Forum

Hi everyone, I have recently replicated the Intro to Porous Media tutorial in COMSOL to build a baseline model that I can eventually add modules to and turn it into a model for chloride migration in concrete. The first time I ran the simulation, I did it exactly the way the demonstrator did it in the video tutorial (without NPP equations, only including the Creeping Flow module). The results were a surface velocity plot and contour pressure plot, with a convergence plot that did reach convergence. (screenshots attached of the 2 plots and the convergence plot that belongs to this simulation)

The second time I ran the simulation, I did the exact same simultion in the tutorial, but this time I also added the Nernst-Planck Poisson (NPP) equations from the Chemical Species Transport model because the NPP equations are required for the purposes of my project. This time, when I tried to perform the same studies from the original simulation tutorial, I got an error message and the 'convergence plot' did not reach convergence; the plot was more erratic with multiple peaks and did not converge. I should also mention that the study performed in both of the simulations I did were stationary, so time is not a factor here. (screenshots of the non-converging plot and error message are also attached)

I am confused about why the addition of NPP alone would affect the convergence in this way. I am a new COMSOL user and am not familiar in general with how the NPP equations work in COMSOL or how their convergence should behave. Can anyone explain this or give me tips? It would be greatly appreciated - thanks in advance!