Hi Lorenzo,
regarding your point (3): Let us consider the mass balance equation for one of the phases. Then, for outflow BCs the flux across the boundary is computed by using the current pressure gradients. For a darcy flux this would mean -(K*gradP)*normal is evaluated on the boundary. Afterwards, the flux is turned into a mass flux by multiplying with the mobility and the density, for which we typically use a simple upwind scheme. Thus, these values are obtained from inside the domain, which means that this only works well as long as you really have a flux leaving the domain. If the sign flips (essentially an inflow boundary), mobility and density are not defined. With respect to your question what the difference is: you could achieve the same thing manually by implementing the above mentioned stuff into the neumann() function: But note that especially for cell-centered schemes the outflow BCs are rather tricky to realize and personally I would try to avoid them and restrict myself to Neumann and/or Dirichlet BCs where you actually know what exactly happens. Best wishes, Dennis ________________________________ Von: Dumux <[email protected]> im Auftrag von lc <[email protected]> Gesendet: Montag, 3. Dezember 2018 12:37:19 An: [email protected] Betreff: [DuMuX] on IMPES, grid adaptation and BCs Hello, I have the following questions: 1) Is it possible to run IMPES algorithm in sequential (not implicit) mode without considering capillarity forces (pressure)? 2) Is it possible to do some sort of grid adaptation, for example locally refine the (unstructrured) mesh where the water saturation front becomes steeper? If yes, how, is there any example? 3) What actually the Outflow BC does? What is the difference with Neumann? Thank you very much! Kind regards, Lorenzo _______________________________________________ Dumux mailing list [email protected] https://listserv.uni-stuttgart.de/mailman/listinfo/dumux
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