As marine energy technology continues to move rapidly from laboratory to reality, the first generation of commercial wave and tidal energy converters now feed into electricity networks in the UK and Europe. The UK enjoys some of the world's best marine energy resources and is a world leader in the research, development, demonstration and deployment of wave and tidal energy systems. To increase that lead, we must be able to develop ever more accurate models of these and future systems before entering the sea, if we are to optimise their behaviour and performance under realistic combinations of waves and tidal currents. This demands a combined wave and current test tank. Such a tank will also extend our understanding of the effects of environmental features such as islands and coastlines on wave and tidal energy devices. Conversely, we would also better understand the impacts of these devices on the environment and the tank would have wider applications in optimising maritime and coastal defence. To mimic reality in full, waves and currents in the tank must be able to act in any combination, in any relative direction. The realistic wave and tidal tank (RealWATT) described below will create wave and tidal conditions that represent, at scale, any prospective marine energy or coastal site in the UK. It will be able to model conditions equivalent to years at sea in a few hours and will create normal and extreme conditions reliably and repeatedly. There is no combined test tank in the UK or Europe that can do this.The marine renewable industry is developing rapidly. However, most types of wave energy converters are vulnerable to currents and most tidal current energy converters are vulnerable to waves. Although wave tanks and current flow facilities do exist, there are no facilities which can create the necessary wide spectral wave conditions, in terms of both spatial and frequency parameters, coincident with robust current conditions at laboratory scales necessary to give confidence in the research and developmental testing necessary to support the next generation of marine energy converters. Marine currents are rarely simple or unidirectional and usually have complex variations of velocity texture and gradient. Ocean waves are also multi-directional and their height, period, steepness and spectral content vary in equally complex ways. The design of this new test facility takes this into account.The overarching objective of SuperGen Marine Phase 2 is to understand the device-sea interactions across the range of scales from the laboratory to the open sea, when subject to the combined effects of waves and tidal currents and this has give us considerable insight into the need for this tank. Early device deployments have been at tidal sites which are sheltered from waves and wave sites in which currents were expected to be low. Many of the first generation of full scale wave energy prototypes have experienced operational difficulties due to current effects on moorings, with consequent effects on stability and performance. Even in the absence of tidal currents, wave induced currents in coastal waters can have an influence on behaviour. Tidal developers have avoided sites exposed to large waves. The European Marine Energy Centre (EMEC) tidal test site at the Fall of Warness in Orkney was chosen as it is partly sheltered from wave action as was the Strangford Narrows site in Northern Ireland, where SeaGen is deployed. Many of the most energetic tidal current sites are not, however, so sheltered. The Pentland Firth, which is recognised as one of the most significant sites for long term development, and is now the subject of a Crown Estate licensing round, is exposed to significant Atlantic swell. If the industry is to develop and exploit the most energetic sites, research must continue to understand device behaviour in controllable combined waves and currents at model scale in laboratories.
The All-Waters Combined Current and Wave Test Facility (FloWaveTT) is a unique marine device test facility to allow testing in any combination of current and wave environments, generated in any relative direction.
The tank is built in a 30m diameter 5m deep circular concrete tank and equipped with 168 absorbing wave makers and 28 1.7m diameter 48kW impellers (from Edinburgh Designs Ltd). We can generate 0.7 meter high waves and 0.8 m/s currents which at scales of between 1:20 and 1:40 equate to the most energetic conditions found in UK coastal waters.