Internally-resonant broadband point wave energy absorber

Abstract

Motivated by the need for broadband point wave energy absorbers (PWAs) whose response is insensitive to the frequency of the incident waves, this work exploits a two-to-one internal resonance energy pump to design a PWA with improved response capabilities. The proposed PWA consists of two elastically-coupled nonlinear oscillators in the form of a partially-submerged buoy and an auxiliary mass suspended inside it by a nonlinear restoring force element. The auxiliary oscillator is designed such that its modal frequency is tuned to the peak frequency in the incoming waves spectrum and to half the modal frequency of the buoy. When the buoy is subjected to low-frequency wave excitations near half its natural frequency, the auxiliary mass resonates with the waves and starts to move. Energy is then channeled to the buoy via a two-to-one nonlinear internal resonance energy pump. This results in reasonably large-amplitude buoy’s displacements over a relatively wide spectrum of incoming waves frequencies. Numerical simulations were presented to evaluate the behavior of the proposed PWA under regular and irregular incident waves. It was shown that the PWA can be designed to have a broad bandwidth, which is insensitive to variations in the incoming waves frequency. It was also shown that, with the proper choice of the PWA’s design parameters, its frequency response can be made almost flat without the clear resonance peak typically shown in the response of the traditional linear PWAs. A proof-of-concept experimental study was also performed on an equivalent prototype using an electrodynamic shaker to simulate the sea waves. Experimental results were shown to corroborate the numerical findings.