Can you tell us a bit more about what you have tried? For example, in the
limit of low Re (say Re=0.1 or Re=1) does your non-linear solver converge?
Have you tried making a manufactured solution to get your convergence order
to see if everything is all fine?
RE=200 can be quite heavy for straight-up Newton solver. The linear-search
generally really helps for cases when you are trying to get a steady-state
solution.
On Thursday, January 26, 2023 at 11:15:11 a.m. UTC-5 ggg wrote:
> I already solved the stokes equation and was trying to generalize it to
> solve the steady NS equation.
>
> I saw the step-57 tutorial but I have a mesh from file (while the tutorial
> create in dealii and refine, things that I'm not allowed to do) and also
> uses line search algorithm, which also can't perform.
>
> The general structure of the program is: setup vectors, sparsity and
> matrices (pressure and velocity), newton iteration where first solve the
> stokes problem to get the initial guess for newton (Re will always be < 200
> in my test case, for now), and the start to iterate, at each iteration:
> - assemble the system
> - solve the linearized system
>
> I know the stokes solution is correct. But for the NS solution I have the
> residual decreasing at first 2 steps and then increasing, leading to
> divergence (around step 16 dealii fires the no convergence). The assembly
> is the same as the tutorial at step-57.
>
> It's becoming really frustrating, so if anyone can help I really
> appreciate. I give you the code in case my explanation wasn't clear.
>
>
> https://drive.google.com/drive/folders/1igXMgWq2g6UPRxaRE9Ot1jU5L_eUW9Wk?usp=sharing
>
> PS: the mesh is fine since already used for previous problems.
>
>
>
>
>
>
>
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