Not to butt-in, but just to confirm, I also compute this "manually" as John suggests for things like normal pressure on membranes, etc. I don't believe there's a canned function for it.
On Tue, May 15, 2018 at 10:38 AM, John Peterson <jwpeter...@gmail.com> wrote: > On Tue, May 15, 2018 at 8:31 AM, Griffith, Boyce Eugene < > boy...@email.unc.edu> wrote: > > > > > > > On May 15, 2018, at 10:23 AM, John Peterson <jwpeter...@gmail.com> > wrote: > > > > > > > > On Tue, May 15, 2018 at 8:17 AM, Griffith, Boyce Eugene < > > boy...@email.unc.edu> wrote: > > > >> > >> > >> On May 15, 2018, at 10:13 AM, John Peterson <jwpeter...@gmail.com> > wrote: > >> > >> > >> > >> On Tue, May 15, 2018 at 5:37 AM, Griffith, Boyce Eugene < > >> boy...@email.unc.edu> wrote: > >> > >>> Folks -- > >>> > >>> Is there an easy way in the library to get normal vectors on surface > >>> meshes (e.g. 2D elements in 3D space, 1D elements in 2D space, etc)? > It > >>> seems like most of the support for this assumes that these are only > needed > >>> for doing surface integrals on volumetric meshes, but I am sure I am > >>> overlooking something. > >>> > >> > >> The "simplest" way is to build an FE object and only pre-request the > >> normals by calling: > >> > >> const std::vector<Point> & face_normals = fe_face->get_normals(); > >> > >> > >> I may be making a blunder here, but this doesn't seem to work if the > >> dimension of the quadrature rule is equal to the dimension of the mesh > --- > >> the normals do not appear to be computed. > >> > > > > > > Hmm... yes generally you would use a dim-1 dimensional quadrature rule in > > this context, e.g. the following (from adaptivity_ex4) should work: > > > > std::unique_ptr<FEBase> fe_face (FEBase::build(dim, fe_type)); > > std::unique_ptr<QBase> qface(fe_type.default_quadrature_rule(dim-1)); > > fe_face->attach_quadrature_rule (qface.get()); > > const std::vector<Point> & face_normals = fe_face->get_normals(); > > fe_face->reinit(elem, s); > > > > > > I need to integrate on a surface mesh (for instance, a boundary mesh > > extracted from a volumetric mesh --- although it could simply be a > surface > > that is not derived from a volumetric mesh) and to get the normals --- > > something like: > > > > std::unique_ptr<FEBase> fe_surface(FEBase::build(dim, fe_type)); > > std::unique_ptr<QBase> quad_surface(fe_type.default_ > quadrature_rule(dim)); > > fe_surface->attach_quadrature_rule (quad_surface.get()); > > const std::vector<Point> & face_normals = fe_surface->get_normals(); > > fe_surface->reinit(elem); > > > > > I see now what you are saying. Yeah, the normals are only computed during > *side* reinits, since they are outward normals relative to > higher-dimensional element. > > So, for a 2D element I would compute them manually by computing dx/d(xi) > \cross dx/d(eta), (those two quantities are available from the FE object to > help you). > > -- > John > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Libmesh-users mailing list > Libmesh-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/libmesh-users > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
