The effects of marine fouling on the wake-induced vibration of tandem circular cylinders

This paper reports the results of laboratory in-water experiments in which artificially marine-fouled circular cylinders were freely vibrating in the wake of a similar fixed upstream cylinder. Cross-flow vibrations at gaps of 3-7 diameters were examined. The marine fouling was simulated by CNC machining of uniformly distributed single-sized pyramids on the surface of the test cylinders. Depending on the spacing ratio, the smooth tandem cylinder demonstrated both Vortex-Induced Vibration (VIV) and galloping types of response. Interestingly, only the VIV-like response was presented by the artificially marine-fouled cylinder. The maximum amplitude of the oscillations and maximum lift force coefficient of the marine-fouled tandem cylinders were, respectively, around one-third and two-thirds of those in the corresponding smooth tandem cylinders. In the case of tandem circular cylinders, the marine fouling showed two contradictory outcomes. It eliminated the galloping and suppressed the VIV-like response, which is beneficial from structural integrity standpoint. From energy performance point of view, the marine fouling negatively affects the energy harvested in a marine hydrokinetic energy converter.