Thanks for the kindly suggestions. Best regards!! Dr. Rongwei Yang (杨荣伟) School of Civil Engineering, Tianjin University, 135 Yaguan Rd, Jinnan District, Tianjin 300350, China P.R. Email: [email protected] *http://jgxy.tju.edu.cn/teachers.asp?id=221 <http://jgxy.tju.edu.cn/teachers.asp?id=221>*
Wolfgang Bangerth <[email protected]> 于2024年9月10日周二 23:41写道： > > Rongwei: > > > Maybe I had not make my question clear. I dont think the question we > > encountered is not graphical output, instead, I think the the problem we > > encountered is numerical issue in Deal II. For example, when we take > thermal > > conductivity as 1e6 (the real value of the problem), there always > > exhibit erroneous results in the figure (see the figure below), in > temperature > > distribution, as high as 24 degree centigrate in the figure, but as > > theoretical calculation, all the temperatures within the figure should > range > > between 0 and -50 degree. > > I see. Here are two thoughts: > * Just because something is true for the solution of the exact PDE does > not > mean that it is true for the discrete solution. This is most apparent for > hyperbolic conservation laws -- think, the simple advection equation > beta.grad u=f > For these, the exact solution may have discontinuities but not over- or > undershots. But the *discrete* solution has over- and undershots unless > you do > something specific about it. The same is true for other equations: Just > because you know that the exact solution should be between -50 and 0 > degrees > does not mean that the discrete solution needs to satisfy the same > property > (although one would hope that at least in the limit h->0 it should). > > * One of the things that happens when you have large jumps in the > conductivity > is that you lose coercivity of the bilinear form. A consequence is that > the > matrix becomes ill-conditioned. You might want to see whether choosing a > smaller tolerance in the linear solver helps, or perhaps using a direct > solver. > > > > On the contrary, when thermal conductivity was > > taken as 1e2, the simulation results work well. Moreover, when we make > the > > simulation via Matlab, the simulation results work well even thermal > > conductivity was taken as 1e6. So we suspect that the high magnitude of > > thermal conductivity in coupled equation significantly affects the > simulation > > results. But we are really not sure where is the problem and how to fix > it, > > any other suggestions? > > If you find that it works with Matlab, then you might want to compare the > matrix and right hand side you get from both implementations, on a very > coarse > mesh. If they are different, you should find out why they are. > > Best > W. > -- > ------------------------------------------------------------------------ > Wolfgang Bangerth email: [email protected] > 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 a topic in the > Google Groups "deal.II User Group" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/dealii/NeV2zRU_aVY/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/0d27bfc5-be8a-4f16-805c-6f96589a5dd0%40colostate.edu > . > -- 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/CAGJ%2BbAFynCr2OvLe0B5BO293WkX67XrzUXSkJnGVdtM9JFKd2A%40mail.gmail.com.
