I apologize that it took so long to respond Jean-Paul, as some things came up that kept me away from working on this.
I was going through the code and attempted to integrate it within Step-44 as appropriate. I appreciate your willingness to share it with me, but I have some questions concerning error messages that were made when I tried to implement it. The last portion of the code was commented as ``source''. Am I correct to assume you intended for this to be it's own header file to be included in the Step-44 introduction? What was the type of ``first_cycle_refinement''? It appears to only show up once in the file you sent. More errors than the two above occur in the code, but I want to try and work through them before asking for additional help... Bruno, I do appreciate your suggestion, but since Jean-Paul was willing to share a portion of his code I'm going to try not to re-invent the wheel. James On Thursday, October 15, 2020 at 2:44:01 PM UTC-4 Jean-Paul Pelteret wrote: > Dear James, > > > I've got some snippets of code that I'll post below to show you how this > can be done within the framework of step-44. The basic concept that I > implemented is as follows: > > > - The nonlinear solver is called by some function who's job it is to solve > for a single timestep. Collectively, they return a status that says what > happened within the nonlinear solver. Essentially, the nonlinear solver > declares that it took the optimal number of steps to converge (according to > its settings), too few steps, too many steps (i.e. we stopped it at some > maximum number of iterations), or it diverged completely. This is returned > to the main function that performing the loop that steps through time. > > - From within that loop, it now decides what to do. If the nonlinear > solver converged, but took either the optimal number of steps (say, 3-6) or > too few then it accepts the timestep (too few = still converged). If it > took too many but still converged, then it will accept the step but the TS > size should be adjusted. If the maximum number of iterations are hit > without convergence or the solver diverged then we reject the timestep and > will have to restart it completely (since this tutorial uses an implicit > scheme, linearised about the current timestep, you basically have to reject > anything that you've done in that time iterate and start the iterate > again). > > - It the nonlinear solver status is then converted to a message for the > time stepper. If too few nonlinear iterations were performed, then it tells > the time stepper that the timestep size was too small. If the optimal > number of steps were taken then it says that the TS size is adequate. If > too many steps were taken or the solver diverged then it informs the time > stepper that the step size was too large; if no convergence was achieved > during that step then it must be performed again after adjustment. (Without > employing some sophisticated nonlinear solver, such as the arc length > method, then hope is that reducing the timestep size will circumvent the > conditions that lead to divergence.) > > - The time stepper would then decide how it adjusts the time step size. A > simple scheme would be to halve (or scale by some factor) the timestep size > each time its declared to be too large, with some minimum value enforced. > Similarly, if the time step size is too large then you could scale the time > increment by a constant factor. This would be the most simple approach to > try to implement first. > > > I think that those are the most important details. Attached is some code > for you to peruse. I extracted it from a project of mine that used step-44 > as its base, so if it looks like I cropped out anything important then just > let me know and I'll try to fill in the gaps. Granted, it's not the easiest > to understand but hopefully it, in conjunction with my summary, will give > you some idea as to how you could move forward. > > > Best, > > Jean-Paul > > > On 14.10.20 02:39, James Gorman wrote: > > deal.ii users, > > I'm learning deal.ii with the goal of using it to non-linear solid > mechanics problems. In many of these problems (such as Step-44), a time > step is used to move a calculation from the initial condition to the final > loaded state. > > Step-44 uses a uniform time-step, but there are instances where an > adaptive time step would be helpful. Using the initial parameter settings > in 2-D, I found that a time-step of 0.7 was too large (the residual was on > the order of 10^3) for the calculation to converge. > > I modified Step-44 to allow the time increment to increase the time > increment when the number of Newton-Raphson iterations for two consecutive > increments is small enough. I used global variables to make this happen. > > I am, however, at a loss for how to efficiently make it so that Step-44 > (or any other script) will automatically decrease a time-step. The only > idea I had at the moment was to use a ``for'' loop and run a certain number > of iterations, and each time the solution did not converge would be to > multiply the time-step by some fraction. However, I am not sure this > solution would work well with my previous solution > > Has anyone done this before, or have thoughts on how one might modify > Step-44 to automatically increase and decrease based on the number of > iterations required for Newton-Raphson convergence or divergence? Thank you > for your help. > > James > > -- > 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+un...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/e0ec0522-510f-475c-bb9a-a615bd9b0800n%40googlegroups.com > > <https://groups.google.com/d/msgid/dealii/e0ec0522-510f-475c-bb9a-a615bd9b0800n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- 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. 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