A mixed finite element method with piecewise linear elements for the biharmonic equation on surfaces.

The biharmonic equation with Dirichlet and Neumann boundary conditions discretized using the mixed finite element method and piecewise linear functions on triangular elements has been well-studied for domains in R2. Here we study the analogous problem on polyhedral surfaces. In particular, we provide a convergence proof of discrete solutions to the corresponding smooth solution of the biharmonic equation. We obtain convergence rates that are identical to the ones known for the planar setting. Our proof relies on a novel bound for the Linf error of the linear FEM for the Poisson equation on curved surfaces, as well as inverse discrete Laplacians to bound the error between discrete solutions on the surface and the polyhedral mesh approximating it.