Abstract
Point absorbers utilize the relative motion between the floating body and the submerged body to harvest the wave energy. This paper presents the parametric study of a two-body wave energy point absorber to investigate the influence of key design factors. The targeting point absorber employs a slotless Halbach linear generator as the power take-off system to improve the energy conversion efficiency. In this work, we have linearized our developed nonlinear time domain model and presented it in frequency domain to improve the simulation efficiency, where the results of the time domain model and the frequency domain model have been compared. The stochastic linearization method is employed for the first time to linearize the nonlinear dragging effect of a point absorber. The case study suggests that the stiffness of the power take-off system and viscous floater dragging coefficient should be as small as possible and the optimal mass of the bodies should be adopted to achieve the maximum power output. Under the irregular wave condition, the power matrix against the wind speed and the damping coefficient of the power take-off system shows that the optimal damping coefficient is determined by the local weather and geographic condition. Regarding the determinants of the damping coefficient, the factors that affect the power take-off system is investigated. The Halbach PM array length and the coil width should be specially optimized to obtain the desired damping coefficient of the power take-off system at a given point absorber dimension. Lastly, a test-rig has been developed to validate the magnetic domain model.
Highlights
To date, various kinds of wave energy converters (WEC) have been proposed to harness wave energy and several designs have been put into sea tests (Hong et al, 2016; Lehmann et al, 2017)
As a step of our on-going project, we aim to demonstrate the potential of the stochastic linearization method on the frequency domain modeling of the Self-reacting Two-body Point Absorber (STPA)
In order to apply the Halbach PM linear generator in the STPA, we have studied the dependence of the power take-off (PTO) damping coefficient on the above listed parameters
Summary
Various kinds of wave energy converters (WEC) have been proposed to harness wave energy and several designs have been put into sea tests (Hong et al, 2016; Lehmann et al, 2017). Among different types of the WECs, the point absorber is the most suitable design to power the standalone devices because of its structural simplicity. Point absorbers typically consist of one or two heaving bodies that extract the wave energy from the heaving motion by a power take-off (PTO) system. For one-body point absorbers, the motion refers to the relative displacement between a floater and a fixed frame. For the two-body point absorbers, the input motion is the relative displacement between the floater and a submerged oscillating body caused by the difference. The experimental study conducted by Beatty et al (2019) has proven that the point absorber with a heaving plate will yield a higher power production by 41%. The heaving plate of the submerged body reacts to the wave-brought oscillation so that the stability of the WEC can be increased. It is favorable to employ the Self-reacting Two-body Point Absorber (STPA) for powering the offshore devices
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