OPTIMIZATION OF GALLOPING-BASED ENERGY HARVESTER USING NON-LINEAR MAGNETIC FORCE

Abstract

This study compares the performance of a galloping-based energy harvester working in both bi-stable and mono-stable conditions. For this reason, an axially attached prismatic body having a square cross-section is considered at the free end of an overhanging cantilever beam. Two mutually attractive magnets are used to provide the axial compressive force. The magnetic separation distance can change the amplitude of the compressive force, which in turn dictates the shift between mono-stable and bi-stable conditions. For a detailed comparison, a numerical model has been established that incorporates the dynamics of the bluff body under galloping force as well as the influence of non-linear magnetic force. An analysis of the static behavior was performed to find the bifurcation point at which the system shifts from a mono-stable state to the bi-stable state. The buckling point is re-confirmed using the coupled frequency analysis. Furthermore, frequency graph provides a basis for selecting pairs of datasets where the system operates at the same coupled frequency in both regimes. A Galerkin discretization-based reduced order model has been developed, followed by different parametric studies exploring the impact of magnetic distance, beam amplitude, coupled frequency, electrical power, and ambient wind speed. In the end, increasing and decreasing wind speeds are used to investigate the nonlinear response and hysteresis regions for both configurations. Performance graphs for bi-stable and mono-stable conditions are presented for the same coupled frequency for better comprehension. Additionally, a minimal gap between the magnets in a bi-stable setup is employed to understand the system's behavior at the system's highest achievable coupled frequency. Few phase diagrams and time histories are also included for illustration. The results show that for the same coupled frequency, the power harvested for the bi-stable condition is comparable to the mono-stable condition despite lower amplitudes which is beneficial for the extended life of the harvester.