Vortex-Induced Vibrations of a 2DOF Rigid Cylinder with Hard Marine Growth in Turbulent Oscillatory Flow

This paper presents a numerical investigation into the vortex-induced vibrations (VIV) of a smooth and a marine-fouled circular cylinder with two degrees of freedom (2DOF), subjected to a turbulent oscillatory flow. The study aims to elucidate the critical influence of the Keulegan-Carpenter (KC) number of 5, 10, and 15 on the vibration response, lock-in regime, frequency synchronization, trajectory patterns and vorticity. Simulations are performed by solving the two-dimensional unsteady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k-ω turbulence model in ANSYS Fluent 2025 R1. An increase in the KC number leads to a significant broadening of the lock-in region, an increase in maximum vibration amplitudes and their emergence at higher reduced velocities. Another key finding is the consistent suppressive effect of biofouling on cross-flow vibrations. The biofouled cylinder exhibits lower cross-flow amplitudes across all KC numbers compared to the smooth cylinder, almost plateauing at around 1.0D for KC = 10 and 15, while the smooth cylinder reaches amplitudes of up to 1.8D and a maximum in-line amplitude of 4.46D. These findings have critical implications for the realistic fatigue life assessment and design of offshore marine structures, highlighting the necessity of incorporating surface roughness effects into VIV prediction models.