“…For the case with external force, A. Russo obtained the existence of weak solutions, if is sufficiently small, where α is the total flux from the obstacle defined in (2.14). In particular, if the following outflow condition is satisfied: Next, Galdi [, Section ], A. Russo and Pileckas and R. Russo posed the assumption with a specific coordinate variables , and the external force is assumed to satisfy the condition …”