From: li pan <li76pan@ya...>  20070424 10:26:06

Hallo Roy, Maybe, I didn't explain my question clearly. I need the grad_displacemet at each node point but not at quadrature point. In this case, I think the only thing to do is like in MeshFunction::gradient(), go over each element and node_fe_value.reinit(elem,node); Node is each node of the element. thanx pan  Roy Stogner <roystgnr@...> wrote: > On Mon, 23 Apr 2007, li pan wrote: > > > I have found it. MeshFunction::gradient(). Is it > > right? > > Not if you want to perform these calculations > efficiently. If your > displacement and velocity spaces are expressed in > the same basis (and > probably even if they aren't) the most efficient > thing to do is to > manually sum the local degrees of freedom times > basis gradients at > each quadrature point. See the construction of > grad_u, grad_v, etc. > in example 13. > > You're *already* going to "go over all elements, > nodes again" when > you're assembling the displacement equation matrix > and right hand > side. You might as well calculate the grad(u) > contributions at the > same time. >  > Roy > > >  li pan <li76pan@...> wrote: > > > >> Hallo, > >> I'm calculating a kind of NavierStokes equation. > >> After one "solve", I get the velocity vector. > Then > >> I'll evaluate displacement. Here, I have to > >> transform > >> the velocity vector from Euler coordinates to > >> Lagrange > >> coordinates, because of convective derivative: > >> vel: velocity at time t > >> u: displacement at time t > >> I : identity matrix > >> vel(t) = d_u/d_t + grad(u,t)*vel(t). > >> I need to do something like: > >> d_u/d_t = (I+grad(u,t))vel(t) > >> > >> My question is, how to do it effectively? I don't > >> want > >> to go over all elements, nodes again, to > calculate > >> the > >> deformation gradient. > >> Do you have good idea ? > >> > >> pan > >> > >> > >> > __________________________________________________ > >> Do You Yahoo!? > >> Tired of spam? Yahoo! Mail has the best spam > >> protection around > >> http://mail.yahoo.com > >> > > > > > > __________________________________________________ > > Do You Yahoo!? > > Tired of spam? Yahoo! Mail has the best spam > protection around > > http://mail.yahoo.com > > > > >  > > This SF.net email is sponsored by DB2 Express > > Download DB2 Express C  the FREE version of DB2 > express and take > > control of your XML. No limits. Just data. Click > to get it now. > > http://sourceforge.net/powerbar/db2/ > > _______________________________________________ > > Libmeshusers mailing list > > Libmeshusers@... > > > https://lists.sourceforge.net/lists/listinfo/libmeshusers > > > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com 