An ultrasonic transmission thickness measurement system for study of water rivulets characteristics of stay cables suffering from wind–rain-induced vibration

Water rivulets will appear on the inclined cables of cable-stayed bridges and oscillate around the cable surface when rain–wind-induced vibration (RWIV) occurs. This paper develops an ultrasonic transmission thickness measurement system (UTTMS) capable of measuring time-dependent spatial distribution of water rivulets around the surface of the stayed cable suffering from the RWIV. Consequently, the geometry and oscillation of water rivulets around the cable can be obtained, providing valuable information for investigating the dynamics of RWIV phenomenon. The mechanism, layout, and measurement accuracy of UTTMS are first illustrated in detail. A wind tunnel test of the RWIV of an inclined cable model incorporated with the UTTMS is then carried out. The measurement results indicate that a lower rivulet and upper rivulet form on the surface of the test cable. The lower rivulet is more or less fixed, while the upper rivulet oscillates along the circumferential direction of the test cable. The thickness and width of rivulet are statistically analyzed. The amplitude, dominant frequency and equilibrium position of upper rivulets along the circumferential direction of the cable are also presented in this paper.