A broad-band vortex-induced vibration energy harvester with adjustable stiffness

This study presents a vortex-induced vibration (VIV)-based energy harvesting system that consists of a cantilevered cylindrical beam with surface-mounted piezoelectric patches. A follower-type compressive tip force is applied to dynamically tune the beam's stiffness in accordance with the vortex shedding frequency, with the goal of maintaining the frequency lock-in in a broader fluid-speed range and hence enhancing energy harvesting efficiency. The proposed model incorporates wake oscillator coupling and piezoelectric interactions to model the response of the energy harvester. A dynamic control strategy is introduced to smoothly alter the compressive force, ensuring continuous frequency matching and maximization of vibration amplitude. A parametric study is also conducted to identify optimal electrical resistance values of the piezoelectric circuit across varying flow velocities and compression levels. Results demonstrate that tuning the mechanical stiffness can widen the lock-in region by 43 % and further simultaneous tuning of electrical resistance can account for 46 % increase in power output.