This did exactly what I needed. Thanks!! On Saturday, March 16, 2019 at 5:48:14 PM UTC, Jean-Paul Pelteret wrote: > > There’s a function to compute the bounding box in GridTools: > > https://www.dealii.org/current/doxygen/deal.II/namespaceGridTools.html#ae1ec55abefa31cf001fd29d8d4d993f1 > > > On 16 Mar 2019, at 18:36, jane...@jandj-ltd.com <javascript:> wrote: > > Thanks for your suggestions. > > BoundingBox should for now be sufficient, but I am having some trouble > using it properly. > > I am unsure what to put in to use it? triangulation? cell? > > I think i need something like > BoundingBox<dim> mybox; > mybox.get_boundary_points(); > > but I'm a little unsure where I put my argument and what that is - I can't > seem to find any examples either. Sorry if this is very basic! > > On Friday, March 15, 2019 at 11:40:28 PM UTC, Wolfgang Bangerth wrote: >> >> >> > Yes, what you put into much better words than mine is exactly what I am >> > needing - For a given quadrature point at >> > (x,y), find how far the domain extends above (x,y) in y-direction? >> > >> > So I am looking to find the y-coordinate of the point which is directly >> > above the (x,y) in question, so that I can find how far it extends >> above >> > it (by subtracting it from what I am trying to find) >> >> As Jean-Paul already mentioned, this is easy enough if your top surface >> is level (i.e., at the same y value). It is, in general, difficult to >> figure this out on unstructured meshes if the top surface is not level. >> >> The way to do this then is to define a "depth" variable D(x,y). You know >> that D(x,y)=0 at the top surface, and that it grows linearly with depth >> y. So D(x,y) satisfies a differential equation of the form >> >> d/d(-y) D(x,y) = 1 >> >> or equivalently >> >> d/dy D(x,y) = -1 >> >> which you can also write as follows: >> >> (0,-1) . nabla D(x,y) = 1 >> >> So it is an advection equation with the advection velocity being the >> vector pointing straight down. The boundary condition at the "inflow" >> boundary -- which here is the top boundary) is D(x,y)=0. >> >> Then, if you need to know the depth at a given point (x_q,y_q), for >> example at a quadrature point when assembling your linear system, all >> you need to do is evaluate the depth field D(x_q,y_q) that you have >> previously computed. >> >> Best >> W. >> >> -- >> ------------------------------------------------------------------------ >> Wolfgang Bangerth email: bang...@colostate.edu >> 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+un...@googlegroups.com <javascript:>. > For more options, visit https://groups.google.com/d/optout. > > >
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