Wave–current interaction effects on marine energy converters

Abstract

Many countries have significant interests in generating electricity using waves and tidal current technologies. In energetic areas, waves and tidal currents interact for modifying the energy resource and impacting on the design conditions. Changes to the wave climate depend on the strength of the current and the relative wave direction. SWAN simulations of the wave climate around the Orkney Islands, with and without currents, show that considerable changes in the wave climate occur near sites of interest to wave and tidal energy project developers. Using circular statistics the effect of the relative angle between the waves and the current can be investigated. Local effects can lead to 150-200% increases in wave height when the waves oppose the current. These dramatic changes lead to an increase in wave power of over 100kWm −1 . The complex nature of the tides in the channels also leads to large changes in wave power during the so-called slack water period. Wave amplification diagrams are proposed to provide a convenient summary of wave-current effects at a particular site and allow a statistical analysis to be made. When performing resource analysis and site selection work for marine energy projects, wave-current interaction must be considered.

The impact of sea surface currents in wave power potential modeling

“…This outcome reconfirms previous works (see for example Saruwatari et al 2013;Belibassakis and Athanassoulis 2014;Hashemi and Neill 2014) performed over different areas and under different points of view on the necessity of taking into account wavecurrent interaction processes for wave energy assessment studies and underlines the added value of advanced/ integrated modeling systems for resource assessment, designing, and operational relevant activities. …”

“…On the other hand, when waves propagate along with the sea current field, the individual waves lengthen and their amplitudes are reduced. This results to a decrease, both in surface elevation and spectral density (Peregrine 1976, Rusu and Soares 2011, Saruwatari et al 2013.…”

“…Despite the above-mentioned efforts in analyzing the wave power over different areas worldwide and although it is well known that sea surface currents have a non-trivial impact on the wave properties and local wave climatology (see for example Huang et al, 1972;Hedges 1987;Jonsson 1990;Soares and de Pablo 2006;Haus 2007;Mellor 2008;Brown and Davies 2009;JoãoTeles et al 2013), only a few wave resource assessment studies have encountered wave-current interaction impact: Saruwatari et al (2013) show that considerable changes in the wave climate may occur due to tidal impacts on waves leading even to 150-200 % in wave height and to a subsequent increase in wave power of over 100 kW/m. Belibassakis and Athanassoulis (2014) studied the transformation of the directional spectrum of an incident wave system over a region of strongly varying three-dimensional bottom topography and the corresponding impact to wave energy dissipation, Hashemi and Neill (2014) suggested that the impact of tides may exceed 10 % in some areas, while Barbariol et al (2013) provide a wave energy assessment study in the Adriatic Sea based on a wave-ocean coupled system.…”

The cumulative impact of tidal stream turbine arrays on sediment transport in the Pentland Firth

“…The wave climate to the west of the region is one of the most energetic in Europe and mean significant wave heights in the Pentland Firth are 2 m [18]. Sheltering via the islands and wave blocking by the strong currents mean that wave heights in the east are lower [19]. The PF is arguably the most promising area for tidal stream development in the world: resource assessments have predicted power potential between 1 and 18 GW [20].…”

The Effect of the Leeuwin Current on Offshore Surface Gravity Waves in Southwest Western Australia

“…A numerical model study by Hashemi and Neill () examined the role of tidal currents on waves on the northwest European shelf and found the wave energy flux was altered by up to 10% in areas with strong tidal currents. On smaller scales, around the Orkney Islands, wave heights were found to increase by up to 150–200% due to strong local tidal effects and (Saruwatari et al, ). Whilst effects of tidal currents on wave fields are most predominant in shallow water regions, in open ocean areas the main contribution to variations in offshore and shelf wave regimes comes from the major current systems.…”