Harvesting more energy from variable-speed wind by a multi-stable configuration with vortex-induced vibration and galloping

Aim at scavenging more energy from the variable-speed wind, a novel multi-stable harvester integrating galloping and vortex-induced vibration is proposed. The harvester includes a cruciform piezoelectric cantilever with a circular cylinder and two square cylinders. The multi-stable characteristic is realized by the interaction between the tip magnet and the fixed magnets. As the wind passes through the harvester, the cylinders could lead to vortex-induced vibration and galloping. Owing to the multi-stability, the harvester will execute snap-through motion, yielding significantly enhanced voltage output. Moreover, altering distance between the magnets could create bi-stability or tri-stability. The potential energy analysis and experimental studies are conducted to investigate the effects of bi-stability and tri-stability on the harvester's performance. It is concluded that the tri-stable configuration outperforms the bi-stable one in wind energy harvesting performance (average 28.6 % improvement). Especially, at the wind speed of 3.0 m s⁻¹, the root-mean-square output voltages of the bi-stable and tri-stable harvesters are 0.70 V and 1.03 V, respectively. Thus, the tri-stable energy harvester promotes the output voltage by about 47 %. Furthermore, the tri-stable configuration could generate large outputs by executing snap-through motions for the wind speed above 1.0 m s⁻¹.