Optimal Energy Harvesting from Vortex-Induced Vibrations of Cables

TL;DR

This study explores optimal placement of energy harvesters on flexible cables experiencing vortex-induced vibrations, demonstrating that end-positioning maximizes energy transfer and enhances robustness to flow variations.

Contribution

It introduces a numerical optimization approach for positioning energy harvesters on VIV cables, revealing a systematic end-placement strategy and improved flow velocity robustness.

Findings

Optimal harvesters are best placed at cable ends.

End-positioned harvesters leverage deformation waves for energy transfer.

Cable-based systems are more robust to flow variations than rigid cylinders.

Abstract

Vortex-induced vibrations (VIV) of flexible cables are an example of flow-induced vibrations that can act as energy harvesting systems by converting energy associated with the spontaneous cable motion into electricity. This work investigates the optimal positioning of the harvesting devices along the cable, using numerical simulations with a wake oscillator model to describe the unsteady flow forcing. Using classical gradient-based optimization, the optimal harvesting strategy is determined for the generic configuration of a flexible cable fixed at both ends, including the effect of flow forces and gravity on the cable's geometry. The optimal strategy is found to consist systematically in a concentration of the harvesting devices at one of the cable's ends, relying on deformation waves along the cable to carry the energy toward this harvesting site. Furthermore, we show that the performance of systems based on VIV of flexible cables is significantly more robust to flow velocity variations, in comparison with a rigid cylinder device. This results from two passive control mechanisms inherent to the cable geometry : (i) the adaptability to the flow velocity of the fundamental frequencies of cables through the flow-induced tension and (ii) the selection of successive vibration modes by the flow velocity for cables with gravity-induced tension.