Wave Energy Extraction by Flexible Floaters

Abstract

We present a novel mathematical model to investigate the extraction of wave power by flexible floaters. The model is based on the method of dry modes, coupled with a matched eigenfunction expansion. Our model results compare satisfactorily with preliminary data obtained from a demonstrator device, developed at the University of Groningen. We show that the role of elasticity is to increase the number of resonant frequencies with respect to a rigid body, which has a positive effect on wave power output. The mathematical model is then extended to irregular incident waves, described by a JONSWAP spectrum. Our results show that the peak capture factors decrease in irregular waves, as compared to the monochromatic case. However, the system becomes more efficient at non-resonant frequencies. This work highlights the need to scale-up experimental investigations on flexible wave energy converters, which are still a small minority, compared to those on rigid converters.

Niche Applications and Flexible Devices for Wave Energy Conversion: A Review

“…Loughborough University, in collaboration with Dutch company Ocean Grazer BV have recently proposed an innovative wave energy converter made by a floating flexible membrane, and connected to a multi-pump, multi-piston power take off system (MP 2 PTO). Michele et al [98] developed a novel mathematical model of the system, based on a potential-flow approach. Figure 17 shows a sketch of the conceptual model, where the floater has length 2L, submergence d, thickness h p and is connected to a series of linear PTO mechanisms (each with power take-off constant ν PTO ), over an ocean of depth h, above a platform of height c. Michele et al [98] showed that the bending elastic modes of the flexible floater enhance the energy extraction efficiency of the converter, with respect to the case of a rigid plate of the same dimensions.…”

“…Michele et al [98] developed a novel mathematical model of the system, based on a potential-flow approach. Figure 17 shows a sketch of the conceptual model, where the floater has length 2L, submergence d, thickness h p and is connected to a series of linear PTO mechanisms (each with power take-off constant ν PTO ), over an ocean of depth h, above a platform of height c. Michele et al [98] showed that the bending elastic modes of the flexible floater enhance the energy extraction efficiency of the converter, with respect to the case of a rigid plate of the same dimensions. As an example, Figure 18 shows the behaviour of the Capture Factor versus the frequency of the incident waves, for an elastic and a rigid floater-Figure 18a,b, respectively.…”

“…An experimental demonstrator of the technology was also developed and tested in the wave tank at the University of Groningen (The Netherlands), see Figure 19. The demonstrator was made of two layers of red silicone sheets, attached to a 10piston MP 2 PTO system and tested in several configurations (see [98] for details). The power output of the device was not measured directly, rather the discharge of each piston was used as a proxy for power.…”

Wave power extraction from a floating elastic disk-shaped wave energy converter

“…Michele et al. (2020) considered a 2-D flexible plate floating on the sea surface connected to a series of linear PTO units under the water. To investigate the wave power extraction by the device, a 2-D theoretical model was proposed based on the dry modes and eigenfunction matching method, and each PTO unit was modelled as a linear damper.…”

Extending limits for wave power absorption by axisymmetric devices

“…Very recently, Michele et al. (2020) have used a distributed power take-off system connecting a floating elastic plate to the bed to generate power.…”