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.
