VIV-induced strain on a lazy wave dynamic marine power cable in a steady current

Abstract

Marine power cables are commonly used to transfer electricity from offshore renewable energy (ORE) devices to shore. Such cables are susceptible to fatigue failure due to flow-induced vibration. We present results from physical model tests conducted at Edinburgh University's FloWave wave-current facility on an instrumented flexible cable in a lazy wave configuration subjected to a steady, unidirectional current. The Reynolds number was subcritical, ranging from 3100 to 24,800. Bending strain was measured at seven locations along the length of the cable and the results are presented in terms of cable curvature. The data analysis shows that, currents propagating normal to the longitudinal axis of the cable caused large local variations in curvature. The maximum variation in curvature occurred near the touchdown zone and at the sag bend. Repeated high-amplitude cyclic loading was observed in currents directed at angles within ±30° normal to the longitudinal axis of the cable. Significant shifts in peak frequency and spectral energy distribution were evident with increasing reduced velocity. At certain locations along the cable, the strain frequency corresponded to a Strouhal number of 0.127–0.144, whereas very low peak strain frequencies occurred elsewhere. The strain behaviour was sensitive to the current speed and direction relative to the orientation of the cable. Mono-frequency strain responses occurred at lower reduced velocity and multi-frequency responses at higher reduced velocity. • Currents perpendicular to the cable's axis cause local curvature variation, especially near the touchdown zone and sag bend. • Strain response is broader band at higher current speed. • Strouhal number ranges between 0.13 and 0.14, with no clear lock-in behaviour observed in these tests. • We believe this is the first comprehensive experimental study of a marine power cable in a lazy wave configuration.

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