Two-degrees-of-freedom vortex-induced vibration of cylinders covered with hard marine fouling

Marine fouling quickly covers the submerged surfaces of the man-made structures and affects the flow regime around them. Many important studies have already been conducted on the Vortex-Induced Vibration (VIV) of bluff bodies, but the two-Degree-of-Freedom (2-DoF) VIV of marine-fouled cylinders has received no previous attention. The current towing tank experimental study tries to fill this gap in the context of mechanical sciences. A Poisson Cluster Process (PCP) is used to model aggregated spatial distributions of artificial marine fouling on test cylinders. The Reynolds number ranges between 6.4 x 103 and 5.2 x 104. The results show that in the fouling presence, the super-upper branch disappears from the 2-DoF VIV response of the cylinders. The maximum oscillation amplitudes in the in-line and cross-flow DoFs are reduced up to 37% and 50%, respectively, as compared to those of the smooth cylinder. Marine fouling moderately reduces the maximum lift force coefficient, whereas remarkably decreases the maximum drag force coefficient, the "lock-in "range, the lower branch length, and the reduced velocity (U*) marking the beginning of the lower branch. The highest mitigation occurs with the most sparsely marine-fouled cylinder examined (33% coverage). The aforementioned fouling effects generally reduce as the fouling coverage ratio increases.