Abstract
We study stationary Stokes equations in an unbounded domain of ℝ3, with periodicity conditions on one part of the boundary, Dirichlet conditions on the other and a transmission condition. We show the existence and uniqueness of a solution which decays exponentially fast at infinity. We introduce an approximation process by solutions in bounded subdomains and establish asymptotically precise estimates for the truncation error. This gives rise to a practical numerical approximation method.