Hi Prof. Wolfgang! Thank you for the response. Indeed the solution is quite reasonable and validated with analytical solution if diffusivity is kept bigger. Actually in my case I am using the metals and metallic alloys where the thermal diffusivity are of the range of 1e-5 to 1e-4 m^2/s (I wonder there might be an alternative way to simulate with these physical properties values). Just as a further explanation, the approach to vary the diffusivity is also in a way that it is calculated from U_old temperature vector and remains same for current time step.
On Monday, May 27, 2019 at 10:58:59 PM UTC+2, Wolfgang Bangerth 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: [email protected] > <javascript:> > 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/d85f0475-87d1-420e-930f-ad27e6eff6a7%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
