Brilliant! Thanks a lot. -Lei Li On Friday, June 5, 2020 at 4:49:56 AM UTC-7, Simon Sticko wrote: > > Hi, > I suspect that the condition you have would be easier to enforce weakly by > adding terms to the weak formulation, as is done in e.g. discontinuous > Galerkin. > > Nevertheless, if you still want the normals at the nodes you can create a > "dummy" quadrature which has the nodes on the face as quadrature points: > > const FiniteElement<dim> &fe = ... // some element > > const Quadrature<dim - 1> quadrature(fe.get_unit_face_support_points()); > > You can then use this quadrature in FEFaceValues to get the normals. Here, > the weights of the dummy quadrature are inf, but if the normals are > everything you need that isn't a problem. > > Best, > Simon > > On Thursday, June 4, 2020 at 8:09:08 PM UTC+2, Lex Lee wrote: >> >> Hello Deal.II Users, >> >> >> I am working on setting a constraint: (V - v_s ) \cdot n = \phi_f (v_f - >> v_s) \cdot n on three vector variables at the interface with affine >> constraint class in Deal.II's library. >> >> (Where, V, v_s, and v_f are velocity vectors on two different domains, >> and they are coupled with each other at the interface; n is the normal >> vector; \phi_f is the volume fraction.) >> >> >> I decided to constrain either V_x= -(...) / n_x or V_y= -(...) / n_y >> depending on the absolute values of n_x or n_y (n_x and n_y are the >> components at x, y directions of the normal vector n). >> >> Now, I have a problem with getting the normal vectors *at nodes *when >> playing with affine constraint within the fe_nothing and hp:finite element >> framework. The relevant function/class I have found in Deal.II's library >> all return the normal vector *at quadrature points,* not at nodes. >> >> Have you ever encountered a problem like this? Could you kindly share me >> your idea of handling this problem? Thousand of thanks. >> >> >> Best, >> >> Lei Li >> >> >>

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