FIV induced fatigue damage of two side-by-side flexible cylinders in a uniform flow

Abstract

Flow-induced vibration (FIV) occurs in deep-water engineering when multiple cylinders interact with each other at a closer range and leads to significant fatigue damages. Nevertheless, many studies have focused on the fatigue damage caused by vortex-induced vibration (VIV). Using a group of flexible cylinders is more common in offshore engineering and has attracted extensive concern; however, the features of FIV fatigue damage remain unclear. In this paper, the experimental data of two side-by-side flexible cylinders with high aspect ratios (length to diameter, L/D = 350, where L is the cylinder length and D is the cylinder diameter) and low mass ratios (total structural mass to displaced fluid mass, m* = 1.90) are utilized to calculate fatigue damages based on S-N curves and Miner's rule. Four spacing ratios (centre-to-centre distance to cylinder diameter, S/D = 3.0, 4.0, 6.0 and 8.0, where S is the centre-to-centre distance) are adopted to investigate their effects on fatigue damage. The results are presented in terms of strain responses, fatigue damage distributions and the maximum fatigue damages. The cross-flow (CF) fatigue damages of the two side-by-side cylinders remain almost consistent with that of the isolated cylinder at most of the reduced velocities, while the in-line (IL) fatigue damages are more than 2 times greater than that of the isolated cylinder when S/D = 3.0 and 4.0. In addition, fatigue damage of the two side-by-side cylinders is more serious than that of the isolated cylinder in the IL direction when S/D = 8.0 owing to considerably vigorous interactions.