Optimal vibration control of Bladeless Wind Turbine

The global energy crisis and growing environmental concerns have intensified the need to transition towards renewable energy sources. Among emerging technologies, bladeless wind energy harvesters have gained significant attention due to their silent operation, low maintenance, and compatibility with urban environments. These systems convert the mechanical energy of vortex-induced vibrations (VIV) generated by wind flow into electrical energy, offering a novel and efficient alternative to conventional rotary-blade wind turbines.

One of the critical challenges in maximizing the efficiency of bladeless wind turbines lies in maintaining the structural natural frequency of the harvester close to the vortex shedding frequency across varying wind conditions. When these two frequencies are matched, the system operates in resonance, significantly amplifying the oscillatory response and, consequently, increasing the harvested power.

To address this issue, the present study proposes a novel frequency-matching mechanism based on stiffness control through geometric adjustment of the structure, specifically by tuning the effective length of the flexible mast. A mathematical model of the bladeless wind turbine is developed that accounts for bending stiffness, distributed and lumped mass, damping effects, and viscoelastic energy dissipation. The governing equations are derived using Euler–Bernoulli beam theory and further simplified into a reduced-order model through Galerkin projection, considering the dominant vibration mode of the system.

An optimization framework is then established to determine the optimal structural length that minimizes the frequency mismatch between the natural frequency and the vortex shedding frequency. The cost function is minimized using gradient-based optimization methods to dynamically update the design parameters under variable wind conditions.

Moreover, to assess the influence of structural material on system performance, a range of core materials with different viscoelastic damping characteristics are evaluated. The simulation results reveal that materials with lower internal damping achieve higher energy harvesting efficiency. Among the tested options, carbon fiber cores offer the best performance, due to their high stiffness-to-weight ratio, low damping, and compatibility with resonant operation.

Finally, the numerical results obtained from solving the coupled nonlinear system of differential equations using time-domain simulations are validated against existing experimental data from the literature. The comparison confirms the effectiveness of the proposed stiffness-based tuning method and material optimization strategy in maintaining resonance and enhancing power output. The proposed approach offers a practical and adaptive solution for real-time operation of bladeless wind harvesters under varying environmental conditions and can be extended to other vibration-based energy harvesting applications.