The sliding speed V defines the nominal entrainment speed U which is equal to one-half of the sliding speed, U ¼ V =2. However, due to finite deformations, the local velocity v of the points of the layer is equal to v ¼ FV , in steady-state conditions, where F is the deformation gradient. Accordingly, the average velocity u ¼ v=2, which appears in the Reynolds equation, and the local relative (sliding) velocity Δu ¼ v, which is needed to compute the friction stress, are not constant and depend on the solution through F . Actually, for consistency, both u and Δu are projected on the surface S, and the corresponding tangential components are used in the Reynolds equation. The range of nominal entrainment speeds specified in Table 2 corresponds to Uη varying between
0.001 and 1 N/m.