Electromagnetic energy harvesting from 2DOF-VIV of circular oscillators: Impacts of soft marine fouling

Vortex-Induced Vibration (VIV) enhancement through the employment of Two Degrees of Freedom (2DOF) oscillators is an effective approach for bladeless energy harvesting improvement. The effectiveness of this measure in an aquatic environment is questionable since the oscillators are soon inhabited by marine fouling. The fouling affects the vibrations' amplitude and the amount and quality of the energy. In this study, soft marine fouling with coverage ratios of 33, 67, and 100% is physically modeled on a 2DOF circular oscillator. The mechanical system is analytically simulated with a semi-empirical wake oscillator model and is coupled with an optimized electromagnetic transducer to evaluate the performance of the energy converter. The results demonstrate that soft fouling generally suppresses the hydroelastic response of the 2DOF oscillator and reduces the synchronization range of the vibrations. MABAC (Multi-Attributive Border Approximation Area Comparison) analysis based on both the power and efficiency reveals that the soft biofouling, in its early stages of development, only reduces the 2DOF system performance by 21%. Light to medium biofouled oscillators in 2DOF still shows 60% higher performance than 1DOF clean harvester. Soft marine growth, when fully covers the 2DOF oscillator, decreases the energy harvesting performance of the clean system by 60%.