Vortex-Induced Strumming Vibrations of Marine Cables With Attached Masses

Abstract

Twenty full-scale test runs were conducted during the cable strumming experiments reported in this paper. These consisted of ten pairs of equivalent tests conducted in air and in water with a cable fitted with arrays of attached masses. The measured in-air natural frequencies are in good agreement with computed code predictions for the second and higher (up to n = 5) cable modes. The first mode frequency apparently was influenced by the sag of the cable. The measured mode shapes of the cable vibrations in water also are in agreement with the computed mode shapes. For the experiments in water the computed and measured natural frequencies are in good agreement. Drag coefficients in the range CD = 2.4 to 3.2 were commonly observed when the cable-attached mass system was strumming due to the water flow past it.