Enhanced power absorption of a point absorber wave energy converter using a tuned inertial mass

Abstract

A novel point absorber wave energy converter with a tuned inertial mass (TIM), which is capable of significantly increasing the energy absorption and broadening the effective bandwidth, is proposed in this paper. The mechanism of the TIM has originally been introduced in the field of civil engineering as a passive energy absorber for structures subjected to external loadings such as earthquakes. It relies on attaching an additional tuning spring and a rotational inertial mass to the primary system, to improve the energy absorption performance by amplifying the displacement of the damper. Thus, considering typical point absorbers modeled as a mass-spring-dashpot system similar way to civil structures, the application of the TIM to wave energy converters can be expected to have a significant effect. In this paper, numerical investigation on the power generation performance of a point absorber with the TIM is conducted under random sea waves. The amplitude response and power generation performance are compared with the conventional point absorber, considering both non-resonant and resonant buoy cases. It is shown that by properly designing the tuning spring stiffness and generator damping, the rotation of the generator can be amplified compared to the buoy, increasing the power absorption drastically.

Wave flume testing of an oscillating-body wave energy converter with a tuned inerter

“…Therefore, the proposed WEC with the TI becomes a two-degree-of-freedom (2DOF) system and the power generation by the motor can be improved by designing the tuning spring stiffness and the rotational mass appropriately based on the frequency of the external wave input [14].…”

“…First, the power generated in the wave flume testing is simulated using the models developed in the previous section by the method proposed in [14]. In this reference, a DC motor is assumed for generating power, so the threephase motor employed in the prototype is approximated by the technique introduced in [27,32] as the circuit shown in Figure 10.…”

“…The details of this derivation are not described in this paper. However, the outline of the method can be found in [14]. Additionally, to investigate the dependence of the power generation performance on the input wave frequency ω, sinusoidal waves emulating the regular waves measured in the wave flume testing, which is given by a(t) = a 0 sin ωt (24) are input into the system expressed by Eqs.…”

“…To address this problem, the authors proposed the oscillating-body WEC with a tuned inerter (TI) [14]. The concept of the inerter was originally proposed by Smith [15] and the inerter generates force proportional to the relative acceleration by using gears or flywheels.…”

Wave flume testing of an oscillating-body wave energy converter with a tuned inerter

“…In the second decay test, u P = 40.8 mm, u Q = 26.0 mm are measured, leading to ζ = 0.086 by Eq. (14). Also, ω d = 7.22 rad/s is obtained with t P = 6.81 s, t Q = 7.68 s by Eq.…”