Abstract
An overtopping model specifically suited for Wave Dragon is needed in order to improve the reliability of its performance estimates. The model shall be comprehensive of all relevant physical processes that affect overtopping and flexible to adapt to any local conditions and device configuration. An experimental investigation is carried out to update an existing formulation suited for 2D draft-limited, low-crested structures, in order to include the effects on the overtopping flow of the wave steepness, the 3D geometry of Wave Dragon, the wing reflectors, the device motions and the non-rigid connection between platform and reflectors. The study is carried out in four phases, each of them specifically targeted at quantifying one of these effects through a sensitivity analysis and at modeling it through custom-made parameters. These are depending on features of the wave or the device configuration, all of which can be measured in real-time. Instead of using new fitting coefficients, this approach allows a broader applicability of the model beyond the Wave Dragon case, to any overtopping WEC or structure within the range of tested conditions. Predictions reliability of overtopping over Wave Dragon increased, as the updated model allows improved accuracy and precision respect to the former version.
Highlights
IntroductionThe Wave Dragon is a floating, offshore Wave Energy Converter (WEC) of the overtopping type
The Wave Dragon is a floating, offshore Wave Energy Converter (WEC) of the overtopping type.Incoming waves are focused by two wing reflectors towards a doubly-curved ramp, by which they surge up into a reservoir placed above the mean water level
Phase 1 was aimed at establishing a reference formulation of the overtopping model as an updated version of Equation (7), which would be suited for the case of Wave Dragon and used as basis for further improvements of the model in the phases of the investigation
Summary
The Wave Dragon is a floating, offshore Wave Energy Converter (WEC) of the overtopping type. Incoming waves are focused by two wing reflectors towards a doubly-curved ramp, by which they surge up into a reservoir placed above the mean water level. The Power Take-Off (PTO) system of the device consists of several variable speed low-head hydro-turbines directly coupled to Permanent. The power production takes place as the water stored in the reservoir is led back to the sea through the turbines (Figure 1). The turbines are of axial type with fixed propeller blades and guide vanes. The rotational speed of the turbines is controlled in accordance to the available pressure head by means of a back-to back frequency converter system. The turbines are activated in a cascade fashion by the control system depending on the water level in the reservoir. The PTO system has been proved to maintain a very high efficiency across the whole span of working conditions
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