Mechanism and sensitivity for broadband energy harvesting of an adaptive bistable point absorber wave energy converter

Highlights: • The broadband feature is due to the introduction of both positive and negative stiffness. • The broadband feature can be explained by an "inherent" phase control capability. • The broadband performance is not sensitive to the floater's initial conditions. • The broadband performance can be realized by different combinations of springs' stiffness. • The broadband performance is affected by wave amplitude. -- Abstract: The adaptive bistable point absorber wave energy converter (WEC) concept proposed by Zhang et al. (Applied Energy 2018(228), pp. 450–467) is further investigated by exploring the underlying mechanism and sensitivity related to the broadband energy harvesting of this device. The mechanism can be explained in two different ways: (i) the broadband power capture is due to the fact that the adaptive bistable mechanism introduces both negative (at low wave frequencies) and positive (at high wave frequencies) stiffness to the device; and (ii) an inherent 'phase control' feature is observed especially at low wave frequency region. The variation of initial conditions of floater motion only has an observable influence at intermediate wave frequencies corresponding to chaotic response of the floater. The broad frequency bandwidth can be realized through different combinations of main and auxiliary springs' stiffness. The effects of wave amplitude on broadband energy harvesting can be categorized according to an optimum amplitude (if existing) into a gradual reduction for a larger wave amplitude and a quick drop for a smaller amplitude.