| Since 2006, as part of projects funded by the Office of Naval Research (SBIRs and STTRs) and the State of Rhode Island (STAC, RI Alliance), the Department of Ocean Engineering at the University of Rhode Island (OCE) and Electro Standard Laboratories (ESL) have worked on the design, modeling (both computer and laboratory), construction, and testing of a series of small point absorber, multi-directional buoys for wave energy conversion. At full scale, these systems target up to 1kW of power per unit, mostly to power ocean instrumentation systems. Initially 4 design concepts were proposed. From these, two design concepts were selected for further examination. Design concept 2 (DC2) has a spherical float, to which a cylindrical canister is rigidly attached, and which houses a Linear Electric Generator (LEG; made of a permanent magnet, suspended to a spring, oscillating within a (two-phase) coil). A rod, attached to the generator's magnetic armature, exits through the bottom of the canister and connects to a resistance platform. Differential movement between the float and the platform drives the generator oscillations. Design concept 3 (DC3) is comprised of a self-contained resonating multiple-spar buoy. A long central spar contains an LEG and is surrounded by four shallower satellite spars (satellite spars reduce draft, increase stability and help achieve proper resonance characteristics). The LEG has a large ballast attached to its bottom which oscillates as a result of buoy heave through coupled resonance. Hence, LEG oscillations are maximized by matching buoy heave and LEG natural periods to the targeted sea state peak spectral period. Successful prototype testing at the 1:10 scale (in the URI-OCE wavetank) and the 1:4 scale (in field tests performed in Narragansett Bay) have been performed for both buoys. These scale model experiments are used to calibrate parameters of a pre-existing numerical model (viscous drag coefficients) and select buoy characteristics to maximize energy production. |
