Acknowledgement
This work has been partially supported by the National Science
Centre (NCN) in Poland under Grant no. 2011/01/B/ST8/07434.
Appendix A. Surface gradient and surface divergence
The Reynolds equation has been formulated in Section 3.2 on the surface S which is, in general, a two-dimensional manifold immersed in a three-dimensional Euclidean space. Accordingly, the surface gradient and surface divergence operators appear in the formulation, and the corresponding definitions are provided below, for the details see, e.g., [30].