Extreme Loads on the Mooring Lines and Survivability Mode for the Wave Dragon Wave Energy Converter

One of the main challenges Wave Energy Converters have to face on the road towards commercialization is to ensure survivability in extreme condition at a reasonable capital costs. For a floating device like the Wave Dragon, a reliable mooring system is essential. The control strategy of the Wave Dragon aims at optimizing the power production by adapting the floating level to the incoming waves and by activating the hydro-turbines and regulating their working speed. In extreme conditions though, the control strategy could be changed in order to reduce the forces in the mooring system, lowering the design requirements with almost no added cost. The paper presents the result of the tank testing of a 1:51.8 scale model of a North Sea Wave Dragon in extreme wave conditions of up to 100 years of return period. The results show that the extreme loads in the main mooring line can be reduced by approximately 20-30% by lowering the crest level and balancing the device to lean a little towards the front.