Hi Wolfgang, step-20: Yes indeed I do agree that that is what I am doing. I guess I'm trying now to find out what else it could be that is producing: the correct boundary points as in the Dirichlet condition when local_rhs=0 is done again (overwriting), but the wrong boundary points when it isn't.
For the u_t=0 condition, I had been imposing weak. So basically, I have separated a Neumann boundary condition into: n.[pI-2e] = (n.[pI-2e]n)n + (n.[pI-2e]t)t and saying that the second term on the rhs is 0 so disappears, and the first term is known weakly imposed into topstress_values[q_point]*fe_face_values.normal_vector[q_point] etc. Is this not a valid way? (PS apologies - earlier, i had said my boundary condition is partial but i've imposed it in a Neumann sense. sorry for any confusion) On Monday, March 18, 2019 at 5:17:08 PM UTC, Wolfgang Bangerth wrote: > > > Jane, > > > Ok, re the first step-20 bc issue, I'll have another think, but I still > am not > > sure why then it isn't giving me the exact figure, whilst my suggestion > is (I > > understand your point here and I would have said I agreed with you, but > my > > implementation does work). I've verified this part of the code using > exact > > solutions so I really have no idea what the issue is, but I guess i'll > have to > > have another think. > > In your exact solution, you may simply have had zero boundary conditions > on > parts of the boundary, so removing these contributions again made no > difference. > > I don't know if that rings any kind of bell, but if you're in 2d and you > have > a rectangular geometry, you first visit the left and right boundaries of > cells, and then the bottom and top boundaries. So if you do local_rhs=0 > before > every boundary face, in essence you are overwriting everything you've done > for > the left/right boundaries if you are on a cell that also has a bottom or > top > boundary. > > > > On the second, step-22 issue, i don't have u.n=0 conditions. I have > partial > > boundary conditions in the form of that stated in the tutorial (1st in > the > > fourth set of Bc explanations) of: > > u_t = 0 > > n.(n.(pI-2*epsilon)) = nonzero value. > > So this is imposed weakly, and no strong conditions are set on that > boundary > > at all, and that nonzero value equals the topstress_value I had before > in the > > weak form. > > But u_t=0 is a strong boundary condition. Are you not calling a function > that > imposes it? > > Best > W. > > > -- > ------------------------------------------------------------------------ > Wolfgang Bangerth email: bang...@colostate.edu > <javascript:> > 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 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. For more options, visit https://groups.google.com/d/optout.
