A novel pipeline VIV-based synergetic hybrid renewable energy harvesting system for sustainable underwater WSN and IoT applications

Flow-induced motion of underwater pipelines could beneficially serve as an excellent host for energy extraction in the modern information-based offshore and deep ocean environments that are reluctant towards the conventional means of external power supply. In this paper, a novel dual-functional hybrid tandem electromagnetic-piezoelectric (EM/PVDF) energy harvesting and VIV mitigation configuration is suggested and computationally implemented that is particularly suitable for powering large scale underwater wireless sensor networks (UWSNs), subsea installations, and Internet of Underwater Things (IoUTs). Furthermore, the key characteristics of major state-of-the-art energy harvesting technologies for powering UWSNs in the deep ocean monitoring applications are succinctly reviewed, while the basic practical design, implementation, and deployment issues and challenges of similarly adopted EM- and PVDF-based energy harvesting devices in the realistic ocean environment are briefly scrutinized. The proposed hybrid EM/PVDF hydrokinetic energy harvesting device is comprised of a linearly sprung EM-based near-bottom horizontal circular cylinder (as a representative of seabed pipeline) that is set in tandem arrangement within the close hydrodynamic interaction range near a downstream wall-mounted cantilever bimorph piezo-plate (PVDF) energy harvester. Detailed numerical simulations reveal the significantly enhanced synergetic energy extraction capability of the hybrid assembly by virtue of the flow field coupling effects between the two energy harvesting mechanisms over a relatively broad range of turbulent Reynolds numbers $\left(5\times {10}^3\le Re\le 3\times {10}^4\right).$ In particular, the time-averaged harvested power at the peak VIV-lockin Reynolds number $(Re={10}^4)$ of the hybrid system $\left(P_{EM/PVDF}^{avg\ast }\right)$ is upgraded about 66 % in comparison to the virtual sum of the single-alone EM- and PVDF-based harvesters $\left(P_{EM}^{avg\ast }+P_{PVDF}^{avg\ast }\right),$ progressively increasing to about 92 % at the highest Reynolds number considered $\left(Re=3\times {10}^4\right).$ Also, the EM-based (PVDF-based) energy component of the hybrid EM/PVDF harvester promptly decays (progressively increases) in the second desynchronization region ($\mathrm{Re}\ge {1.5\times 10}^4$) owing to the consecutive high frequency interactions of a highly asymmetric and intensive 2S-type vortex street emanating from the upstream cylinder.