A Floating Unit for Wave Power Driven Desalination of Seawater: The Hydrodynamics of the Ocean Oasis Buoy

Abstract The Ocean Oasis buoy is a floating wave energy converter (WEC) which utilizes the relative motion between the buoy and a disc floating in a central deep moonpool to pressurize seawater and run it through a standard reverse osmosis (RO) process. A combined flow control and energy recovery unit has been developed to ensure that the seawater provided to the RO membranes has a steady flow and pressure and that the remaining energy in the brine is utilized before the brine is discharged. Fresh water is led to shore using inexpensive hoses on the seabed. The buoy is floating freely anchored to the seabed using a conventional catenary mooring system. The moving parts in the power take-off (PTO) system are easily accessible above water, protected in the central part of the buoy above the disc, and designed for easy replacement using small maintenance vessels. In adverse weather conditions, or for maintenance, the disc is lifted and locked securely to the buoy so that the system behaves as a single buoy unit with no moving parts. The present paper describes the model testing and hydrodynamic analysis of the Ocean Oasis concept in production and survival conditions. It is documented that the PTO can be reliably predicted by relatively simple analysis models and the analysis models used to investigate the behaviour in the survival cases are described.