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www.sname.org/sname/mt October 2012 design approaches. In contrast, the worldwide wind turbine industry has largely settled on a common design?a three-bladed, axial ow turbine. Within that standard design, there is still signicant variation in design details, such as materials, drivetrain, power ratings, control systems, and so forth, but the core design is similar. It is expected that the eld of candidate technologies (measured in the hundreds) will likely be narrowed as time goes on, but it is the subject of some debate whether the MHK industry will reach a similar, worldwide technology downselect and focus on one design. Until then, the solutions are varied and each developer is tailoring its solution to a specic deployment location or resource. With a few exceptions, wave devices fall into several general categories. Point absorber. Point absorbers are most commonly associated with some sort of buoy device. A point absorber seeks to take the ver- tical wave moment (heave) and convert that energy to electrical power. e power take off (PTO) systems for point absorbers are highly varied?some devices use mechani- cal rack and pinion type drivetrains, others use hydraulics, and still others seek a direct connection between the moving parts and the generator. Some point absorber devices can capture not only the heave but also the horizontal component of wave energy (surge). Mooring designs for point absorb- ers are critical: They need to be able to withstand storm loading and depending on the design of the mechanism, either need to have tensioned mooring legs or rely on a slack mooring system that allows the buoy to move but constrains it to a watch circle. One novel wave device being pursued by Oscilla Power involves the use of a buoy tied to ten- sioned mooring legs that have multiple PTO devices connected in series. e PTOs use reverse magnetostriction and convert the change in strain of the mooring lines to elec- trical energy, with no moving parts. Submerged pressure differential. ese submerged devices capture the pres- sure dierential created by a passing wave. Devices of this type are varied in design and orientation, but the reader can imag- ine a bellows type device mounted on the ocean oor whose chambers are alternately lled and expelled by each passing wave. e PTOs for these devices typically rely on an air-driven turbine to power a generator. Oscillating water column (OWC). An OWC uses the principle of a wave pressur- ing the air in a chamber. is pressurized air is then routed to an air turbine to gen- erate electricity. If you were to take a coee can, drill a hole in the bottom of it, and then place it in the water with the small hole fac- ing up, you would have the general idea. Waves passing under the mouth of the coee can will raise the level of the water column, thereby increasing and decreasing the air Wave Category THE EMERGING PLAYER