Wolfang is right. Negligible values of diffusion or thermal coefficients lead to a compete change in the physics of the problem. In that case if there are source terms the solution might become negative and if there is no source it will become steady. Things might get worse if advection term is involved.
On Mon, May 27, 2019, 21:59 Wolfgang Bangerth <bange...@colostate.edu wrote: > On 5/27/19 11:01 AM, Muhammad Mashhood wrote: > > I am working with deal.ii step-26 to implement > temperature > > dependent thermal diffusivity. Currently for thermal diffusivity values > > > > order of 1e-2 the results are quit satisfactory but if I use the low > thermal > > diffusivity values like the order of 1e-6 to 1e-3, I get temperature > > oscillations (temperature going to -ve value even with all positive > > temperature initial and boundary conditions in domain and at boundaries). > > If anyone has faced the same issue in thermal conduction simulations or > knows > > the criteria to keep simulation stable in terms of thermal diffusivity, > time > > step and mesh size then kindly suggest and share the opinion. Thank you > in > > advance! > > In the limit of no thermal diffusivity, your equation ends up as an > ordinary > differential equation and that means that you lose stability in the H^1 > norm > -- in other words, you will get oscillations. That's just part of the > nature > of the equation. > > What is the situation you are trying to model that leads to such a small > diffusivity? > > Best > W. > > > -- > ------------------------------------------------------------------------ > Wolfgang Bangerth email: bange...@colostate.edu > www: http://www.math.colostate.edu/~bangerth/ > > -- > The deal.II project is located at http://www.dealii.org/ > For mailing list/forum options, see > https://groups.google.com/d/forum/dealii?hl=en > --- > You received this message because you are subscribed to the Google Groups > "deal.II User Group" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to dealii+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/84cc645b-9b75-79ec-8c3b-53d428ab8fc8%40colostate.edu > . > For more options, visit https://groups.google.com/d/optout. > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/CAAUzbWMfZNUO1Fs2uWx_%3DOfz_6PR05%3DtGgUtEu%2Bvj4q4yibjNw%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
