Stability of a trilinear-trilinear approximation for the Stokes equations

The choice of mixed finite element approximations for fluid flow problems is a compromise between accuracy and computational efficiency. Although a number of finite elements are found in the literature only few low-order approximations are stable. This is particularly true for three-dimensional flow problems. These elements are attractive because of their simplicity and efficiency, but can suffer though poor rate of convergence. In this paper the stability of a continuous trilinear-trilinear approximation is being analysed for general geometries. Using the macroelement technique, we prove the stability of the approximation. As a result, optimal rates of convergence are obtained for both the velocity and pressure approximations.