The upper rivulet movement was also measured when the cable vibration was very small. Fig. 14 shows the spatial distribution of the upper rivulet when the standard deviation of the cable vibration amplitude was 4.2 mm. The distribution along the cable was non-uniform, and the rivulet oscillation was non-harmonic. Fig. 15(a) and (b) show the time history and PSD of the cable vibration, respectively. The dominant frequency of the cable vibration was 1.27 Hz, while a higher frequency occurred as well. Fig. 15(c) and (d) show the time history and PSD of the averaged upper rivulet oscillation, respectively. The averaged upper rivulet oscillated unsteadily between 20° and 37°. Although a peak at 1.27 Hz was observed, the upper rivulet exhibited a uniform frequency band between 0 and 5 Hz.