Theoretical and Experimental Studies of the Rain Load for Transmission Tower Based on Single-Raindrop Impinging Force

Abstract

Rain load has a substantial effect on the dynamic response of transmission tower-line systems, and studying the impinging force imparted by a single raindrop can provide a better understanding of the acting mechanism of rain load on these systems. In this study, a theoretical analysis of the impinging force of a raindrop is conducted, and a piezoelectric transducer has been developed to measure the impinging force versus time. Based on the principle of conservation of momentum, a formula for the force is derived under ideal conditions. However, the form of the equation is so complex that the force can only be obtained by numerical methods for non-spherical raindrop shapes. Then, the formula of raindrop impinging force was derived by considering the raindrop acceleration, the raindrop splashing, the water film, and the flow velocity of the impinged raindrop, of which the form is so complex that it cannot be solved directly. At last, a single-raindrop impinging experiment was carried out, and the results reveal that the raindrop impinging process exhibits both positive and negative forces and that the peak values are of the same order of magnitude. The negative force is caused primarily by the rebound of the raindrop. The positive force acts for only a short time, while the negative force acts much longer. When the transducer surface is wet, the positive force is greater than that under dry conditions, and the force acts for a longer period of time. This study is expected to expand the understanding of the rain load mechanism for transmission towers.