A new design for the solo desalination Duck Wave Energy Converter is being studied at the University of Edinburgh. The key innovation is the modification of the profile. A numerical hydrodynamic model showed that similar performance could be obtained by using a circular cylinder with an off-centred axis of rotation. The principle advantage of this new design is the reduction of the cost of the manufacturing process. A 1:33 scale model was built to validate the numerical predictions and has been tested in a wave tank in regular and irregular seas.
The optimisation of the performance of this device requires a systematic investigation of the effect of several variables. In this paper the effect of mass redistribution is analysed. A simplified one degree-of-freedom frequency-domain model with its power-take-off based on linear damping is used and an equation for the position of the ballast mass that maximises the performance of the device for for a certain wave exciting frequency is derived.
It is shown that by relocating the ballast (i.e. changing the inertia of the Duck) a new condition that optimises the performance of the device for a particular wave climate is obtained.