Wave-power absorption from a finite array of oscillating wave surge converters

Abstract

Citation: RENZI, E. ... et al, 2014. Wave-power absorption from a finite array of oscillating wave surge converters. Renewable Energy, 63, Additional Information:• NOTICE: this is the author's version of a work that was accepted for publication in Renewable Energy. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Re- AbstractSemi-analytical and fully numerical modelling is developed in the framework of the inviscid potential flow theory to investigate the dynamics of a wave farm made by flap-type wave energy converters in the nearshore. The hydrodynamic parameters and the efficiency of the system in typical layouts are calculated with both models. Good agreement is shown between the two approaches. Parametric analysis undertaken with the semi-analytical model allows to identify a near-resonant phenomenon which is responsible for increasing the absorbed power by the single elements of the array. Such result could be used as a preliminary design criterion. The numerical model is then applied to analyse a configuration of practical engineering interest, i.e. an array of two staggered converters. The dynamics arising in this more complex system is explained, showing that non-symmetric layouts can be less effective.

Motion-resonant modes of large articulated damped oscillators in waves

“…As mentioned in the Introduction, the flap-type absorber is the mathematical reference model for the OWSC, a large buoyant flap used for wave energy extraction in the nearshore environment Dias, 2012, 2013a,b;Renzi et al, 2014a). Only in-line configurations will be investigated in this paper, as loss of symmetry in small arrays of OWSCs is likely to be accompanied by a reduction in efficiency (Renzi et al, 2014a;Sarkar et al, 2014). The oscillators are set into motion by incident waves of amplitude A ′ I , period T ′ and angular frequency ω ′ = 2π/T ′ incoming along a direction which forms an angle β with the x ′ axis.…”

“…It is assumed that the amplitude of the wave field is small with respect to the width of each device, as it happens in reality for most of the operational life of the system (Gallagher et al, 2013). Hence following the linearised theory of Renzi et al (2014a) and Sarkar et al (2014), the velocity potential Φ ′ (x ′ , y ′ , z ′ , t ′ ) must satisfy the Laplace equation…”

“…, M, where the Heaviside step function assures absence of flux through the foundation. Following Adamo and Mei (2005), Dias (2012, 2013a,b), Renzi et al (2014a) and Sarkar et al (2014), in Eq. (4) the flap thickness is considered immaterial for the calculation of the potential.…”

“…(4) the flap thickness is considered immaterial for the calculation of the potential. The boundary-value problem (1)-(4) has been already studied and solved by Renzi et al (2014a) for an array of flap-type absorbers by employing the Green integral theorem and a series expansion in terms of the Chebyshev polynomials. However, Renzi et al (2014a) did not investigate the system motion-resonant modes, leaving such analysis to further work which is undertaken in this paper.…”

“…Such system has an important application in the field of wave energy extraction, where these oscillators are known as "flap-type absorbers" (Renzi et al, 2014b). The flap-type absorber represents the reference mathematical model used for the design of several wave energy converters (WECs), like for example the Oyster R Oscillating Wave Surge Converter (OWSC, see Whittaker and Folley, 2012;Dias, 2012, 2013a,b;Renzi et al, 2014a) manufactured by Aquamarine Power, with a maximum generating capacity of 800 kW (www.aquamarinepower.com).…”