Thin water film around a cable subject to wind

Cables of cable-stayed bridges can experience rain-wind-induced vibrations (RWIV). This instability involves lower frequencies and higher amplitudes than classical vortex-induced vibrations. Furthermore, RWIV is restricted to a certain range of wind velocities, unlike linear 1 dof galloping. When flowing along the cables, the water gathers near the separation points to form one or two rivulets. Former studies which have described the coupling between the rivulets' motion and the cable motion assume the existence of at least one rivulet. In this paper, we address the conditions for the formation of the rivulets. A two-dimensional model is developed within the lubrication theory, describing the evolution of a thin film subjected to gravity, surface tension, wind and motion of the cylinder. Numerical simulations show the appearance of the rivulets that are reputedly responsible for the instability. The position at which the rivulets appear is found to vary with the wind speed and the predictions of the model are in good agreement with new experimental data.