Discussion Forum

Hello. I´m starting using Comsol to sove a coupled electromagnetic-thermal problem. I have an underground cable buried inside a PVC pipe. I want to solve the temperature field taking into account conduction and natural convection inside the pipe. I have followed the coffee thermos example to model the free convection. This example says that this kind of models usually have convergence problems, so gives some instructions about that. But, I don´t know why, even following those instructions, my problem some times shows this message:"Failed to find a solution: No convergence, even when using the minnimun damping factor ". I have tried to change mesh size, but the only thing I get is an "out of memory during LU factorization" message. Some times I don´t have this problem when I change some dimensions of the problem. I suppose that the solver has to be better tuned, but I don´t know how to do it yet. Could any one help me to fix this situation?

As a comment, I also tried to implement radiation inside the pipe, but I have a strange message saying that there is a complex value evaluating J. I don´t know why, but it seems that the temperature T has become a complex number, because when evaluating air properties (rho, Cp, etc.) I have to use abs(T) to avoid errors evaluating those parameters. This problem only appears when I have a multiphysics model. Using only General Heat transfer module without any other module there is no problem. What it is happening?

Thanks for your help.