Nonlinear analysis of an actuated seafloor-mounted carpet for a high-performance wave energy extraction

Abstract

It is known that muddy seafloors can extract significant energy from overpassing surface waves via engaging them in strong interaction processes. If a synthetic seabed can respond to the action of surface gravity waves similar to the mud response, then it too can take out a lot of energy from surface waves. Analysis of the performance of a mud-resembling seabed carpet in harvesting ocean wave energy is the subject of this article. Specifically, and on the basis of the field measurements and observations of properties/responses of seafloor mud, we focus our attention on an artificial viscoelastic seabed carpet composed of (vertically acting) linear springs and generators. We show that the system of sea/synthetic-carpet admits two propagating wave solutions: the surface mode and the bottom mode. The damping of a surface-mode wave is proportional to its wavelength and hence is classic. However, the damping of a bottom-mode wave is larger for shorter waves, and is in general stronger than that of the surface-mode wave. To address the effect of (high-order) nonlinear interactions as well as to investigate the performance of our proposed carpet of wave energy conversion (CWEC) against a spectrum of waves, we formulate a direct simulation scheme based on a high-order spectral method. We show, by taking high-order nonlinear interactions into account, that the CWEC efficiency can be significantly higher for steeper waves. We further show that the bandwidth of high performance of the CWEC is broad, it yields minimal wave reflections and its theoretical efficiency asymptotically approaches unity within a finite and (relatively) short extent of deployment.

Hydrodynamic modelling of marine renewable energy devices: A state of the art review

“…At early stages of device development, numerical models can allow rapid estimates of the energy capture performance of a device (Pizer, 1992;Josset et al, 2007;Payne et al, 2008;Kurniawan et al, 2011;Babarit et al, 2012), and provide powerful tools to gain insight in the behaviour of novel device configurations (Renzi and Dias, 2012;Alam, 2012;Farley et al, 2011;Lovas et al, 2010). The use of efficient numerical models allows extended parametric studies and optimization to be performed more rapidly than can be achieved experimentally (Malmo and Reitan, 1985;Babarit et al, 2005;Folley et al, 2007a,b;Vicente et al, 2009;Gomes et al, 2011;Oskamp and Ozkan-Haller, 2012;Falcao et al, 2012).…”

Real time hybrid modeling for ocean wave energy converters

“…Under simplifying assumptions of an infinitely long, twodimensional and linear visco-elastic carpet with uniformly distributed actuation under the action of the overpassing waves (assuming inviscid and irrotational flow), we showed that [12,13] the linearized form of the governing equations admits two modes of motion: a surface-mode and a bottom-mode. While damping of surface-mode waves is higher for longer waves, the damping of a bottom-mode wave is higher for shorter waves.…”

“…We have investigated mud theoretically and computationally in the linear and weakly nonlinear regimes [12,13], and experimentally with the purpose of providing a proof of the concept [14]. Under simplifying assumptions of an infinitely long, twodimensional and linear visco-elastic carpet with uniformly distributed actuation under the action of the overpassing waves (assuming inviscid and irrotational flow), we showed that [12,13] the linearized form of the governing equations admits two modes of motion: a surface-mode and a bottom-mode.…”

“…This concept is the idea behind the Wave Carpet [12][13][14], which is a mud-resembling synthetic compliant seabed-mounted mat, composed of springs and generators, that can be used as an efficient wave energy absorption device. The idea has several advantages over previously considered ideas:…”

“…As a case study, we consider a newly developed wave energy convertor called "Wave Carpet" that is a seabed mounted pressuredifferential wave energy harvester [12][13][14]. The Wave Carpet is a flexible mat that is fully submerged and connected to the seabed by reciprocating fluid pumps working as power takeoffs.…”