Effect of variable current on vortex-induced vibrations

Experiments are described whose objective was to investigate the combined effect of current and waves by studying an elastically mounted circular cylinder in a time-varying flow. This is relevant for risers subjected to both current and wave-induced motion. The rigid cylinder section was 75 mm in diameter and 2 meters long and mounted horizontally in a towing tank. The time-varying flow consisted of a constant and a harmonic velocity component. The general conclusion from the experiments is that both the amplitude and acceleration response of a cylinder subjected to constant + harmonic current is smaller than for constant current only.