Chen: I'm not sure anyone still active in the project knows the program well, so I asked the author of the program, Abner Salgado, about the issue and this was his answer:
> What happens is that the pressure update equation, written right above > the implementation of > > update_pressure > > is understood in "weak" form. We multiply by a test function in the > pressure space and the divergence term is integrated by parts (hence the +). > > This is so because div u is not in the pressure space and so we cannot > simply add the corresponding coefficient vectors. > > It involves solving a mass matrix problem, as it can be seen in the > implementation. > > Hope this clarifies things. I hope this helps! Best Wolfgang On Monday, August 21, 2023 at 2:30:37 AM UTC-6 hkch...@gmail.com wrote: > Dear all, > > I have a question on the step-35 > <https://dealii.org/current/doxygen/deal.II/step_35.html> when I learn > it. the step use project method to solve NS equation. And for updating the > pressure step, there is a Rotational Form > <https://dealii.org/current/doxygen/deal.II/step_35.html#:~:text=Incremental%20Method%20in%20Rotational%20Form.%20In%20this%20case>. > > In the function of update_pressure(const bool reinit_prec), it seem it > plus the rotational term(+1/Re*div u), while the formula is minus(-1/Re*div > u), the pres_tmp is calculated at projection_step > <https://dealii.org/current/doxygen/deal.II/step_35.html#:~:text=%C2%A0%20%20%20%20%20for%20(unsigned%20d%20%3D%200%3B%20d%20%3C%20dim%3B%20%2B%2Bd)-,pres_Diff%5Bd%5D.Tvmult_add(pres_tmp%2C%20u_n%5Bd%5D)%3B,-phi_n_minus_1%20%3D%20phi_n%3B>, > > and is pres_tmp is (div u). > > I want to know why here is plus not minus. Maybe the minus sign was > included in the original code I didn't notice or understand. > > Could anyone help me out? > > Best, > Chen > -- 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/6ccc6ad8-2cf6-4dde-a529-b61617721ddfn%40googlegroups.com.
