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ABSTRACT:
Superconvergent and divergence-free finite element methods
for the Stokes equation are developed. The velocity and pressure are
discretized using $H(\mathrm{div})$-conforming vector elements and
discontinuous piecewise polynomials. The discrete formulation employs
a weak deviatoric gradient operator built with tangential-normal
continuous finite elements for traceless tensors, requiring no
stabilization. Optimal and superconvergent error estimates are
established. The method connects to nonconforming virtual element and
pseudostress-velocity-pressure mixed formulations. Numerical
experiments verify the theory.