Thanks, Wolfgang. Indeed my question is not that clear. The upper panel is actually a 'potential' (phi, solving a Poisson's equation), the lower panel is the x-component of ExB (E=-\nabla phi, B is out of paper), a derivative quantity. This ExB would be used to transport plasma density, (and this plasma density field is then feedback to Poisson's equation through rhs and coef.).
The relevant literatures assume different kinds of BCs, e.g., Neumann for both potential and plasma density in y (one mentioned extrapolation too) and periodic in x. Those simulations usually show a good symmetry in x, but mine shows asymmetry quickly near the top boundary. Although we'll be mainly interested in what'll happen in the interior, this boundary is a nuisance. Don't know how you can enforce \partial rho (density) / \partial y = 0 at the top boundary directly in the transport equation, except modifying the flow field near the boundary? Any suggestions? Thanks again. Houjun On Fri, Apr 14, 2023 at 4:53 PM Wolfgang Bangerth <[email protected]> wrote: > On 4/14/23 14:46, Houjun Wang wrote: > > > > Is there any way to 'extrapolate' the field (from interior to the > boundary) > > such that the lower panel looks like the upper panel near the top > boundary? Or > > enforcing zero normal gradient near the top boundary for the bottom > panel too. > > Houjun, > I understand intuitively what you want, but in the end, in order to > implement > something, you have to specify clearly and unambiguously in mathematical > terms > what it is you want to do. So before we talk about how, can you clarify > what > achieving "looks like the upper panel" would entail? > > As for Neumann boundary conditions: You would first have to tell us how > you > have computed the two panels, and then think about whether it makes sense > from > a modeling perspective to choose one type of boundary conditions over > another. > > Best > Wolfgang > > -- > ------------------------------------------------------------------------ > 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/296t4YJ7NN8/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/c64d2858-142b-0ed1-7dac-8f95413b2b2e%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/CALz2Y39Tw5%3DMgs_AOSVVy1nvdex%2BEQiBbwnGFCLFU5tvZU40%2Bg%40mail.gmail.com.
