文摘
We consider the P1/P1 or P1b/P1 finite element approximations to the Stokes equations in a bounded smooth domain subject to the slip boundary condition. A penalty method is applied to address the essential boundary condition \(u\cdot n = g\) on \(\partial \Omega \), which avoids a variational crime and simultaneously facilitates the numerical implementation. We give \(O(h^{1/2} + \epsilon ^{1/2} + h/\epsilon ^{1/2})\)-error estimate for velocity and pressure in the energy norm, where h and \(\epsilon \) denote the discretization parameter and the penalty parameter, respectively. In the two-dimensional case, it is improved to \(O(h + \epsilon ^{1/2} + h^2/\epsilon ^{1/2})\) by applying reduced-order numerical integration to the penalty term. The theoretical results are confirmed by numerical experiments.