Wave-Current Loading on a Lazy Wave Dynamic Power Cable

Abstract This study investigates the dynamic loading experienced by a laboratory-scale model of a lazy wave power cable under combined wave-current conditions. Physical model tests were conducted at the FloWave facility at The University of Edinburgh on a dynamic power cable of outer diameter 31 mm and mass ratio of 1.09, arranged in a lazy wave configuration with both ends fixed. The cable was subjected to irregular waves propagating over uniform currents with flow speeds of 0.3 m/s and 0.5 m/s. The wave direction was perpendicular to the longitudinal axis of the cable, whereas the current direction was parallel (following), opposing, and perpendicular to the waves. Forces and moments at the hang-off point were captured using a 6-axis load cell. The measurements demonstrate that when the cable was subjected to wave loading alone, the dominant load frequency corresponded to the wave frequency, indicating that the primary dynamic response of the cable is governed by direct wave excitation. However, spectral analysis revealed the presence of secondary peaks in the force spectrum at higher frequencies, particularly in the direction perpendicular to the wave action. Under combined wave and current conditions, high-frequency components were observed for both following and opposing currents, with magnitude and vibration frequency increasing progressively as the current speed intensified. The amplification of these dynamic forces resulted in a broadening of the spectral response, with notable energy contributions at higher frequencies (Strouhal number of 0.1 to 0.2) beyond the first-mode vibration corresponding to the wave frequency. The study further shows that, in wave-alone cases, wave force coefficients decrease with significant steepness, whereas, the presence of currents results in an increasing trend in force coefficients based on the ratio of wave to current velocities.