Piezoelectric energy harvesting from 2DOF flow-induced motion of cylinder in low-velocity flowing water

Purpose This study aims to develop an inertial piezoelectric energy harvester mounted in a cylinder and use the flow-induced motion (FIM) to harvest the abundant water flow energy for powering electronic devices in the ocean. Design/methodology/approach A two-degree-of-freedom (2DOF) structure is designed in the flowing water to excite the FIM. Two vertical columns were placed close to the cylinder in the downstream direction. When the cylinder oscillates in the flowing water, collisions with the columns will be generated and offer a frequency up-conversion mechanism for the inside piezoelectric energy harvester. The system is analyzed theoretically based on the fluid mechanics. A prototype is fabricated for experimental verification. Experiments were explored in a low-speed circulating water channel. The trajectories of the cylinder were experimentally investigated. Parametric studies were carried out regarding the flow speed, the gap distance between the columns and cylinder and the piezoelectric cantilever beam length. Findings The experimental results show that at the flow speed of 0.371 m/s and the gap distance of 17 cm, the maximum power output of the energy harvester is 861.39 µW for one piezoelectric element. Originality/value The 2DOF structure have a larger oscillation amplitude than one-degree-of-freedom structure in the flowing water, which helps to transfer the flow energy into motion energy. A frequency up-conversion mechanism is applied for the inside inertial piezoelectric energy harvester.