On Sat, Sep 12, 2009 at 4:08 PM, Ted Kord <teddy.k...@googlemail.com> wrote: > 2009/9/12 David Knezevic <dk...@mit.edu> > >> Roy Stogner wrote: >> >>> >>> On Sat, 12 Sep 2009, David Knezevic wrote: >>> >>> Ted Kord wrote: >>>> >>> >>> How do I apply a Neumann B.C at an inter-element boundary? >>>>> >>>> >>>> The same way as a usual Neumann BC... the only trick is that you have to >>>> find which internal element to apply it to. One way to do this would be >>>> to set the subdomain_id of elements on one side of the inter-element >>>> boundary to 1 and on the other side to 2, and then search for elements >>>> with subdomain_id = 1 that have a neighbor with subdomain_id = 2, and >>>> apply the Neumann BC to the appropriate side of those elements. >>>> >>> >>> The trouble with this is that you'll still have the entries in your >>> matrix from the shape functions which stretch between the element on >>> one side of the boundary and on the other. If you have a slit in your >>> domain on which you want to weakly impose boundary conditions, you >>> need to make it an actual topologically broken slit, and then it's >>> just another set of exterior boundaries. >>> >> >> I was thinking of imposing an internal flux between internal elements (e.g. >> as a type of forcing, but inside the domain rather than on the boundary). In >> that situation an "internal" Neumann condition does the job --- the >> variational formulation takes care of everything for you... >> >> - Dave >> > > The problem I actually have is that there's a concentrated load at a single > point, say x = 16 (domain: 0 < x < 20) which is represented mathematically > as : > > -0.5 - 30 * dirac-delta(x-16) > > As far as I know, this, i.e., -30 will have to be applied as a Neumann B.C > at that point.
I wouldn't think of a point-load as a boundary condition ... it's not a boundary condition. Assuming the delta function falls on a node in the mesh, you can just modify the load vector entry for the basis function associated to that row. -- John ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
