This paper presents the results of an experimental test programme and theoretical analysis of the hydrodynamic design of wave powered axi-symmetric navigation buoys. A two degree of freedom system with power extraction damping the relative motion of the two heave modes is considered. Results are presented for a theoretical model which has been verified experimentally.
It is concluded that the power extraction efficiency and frequency bandwidth of the current design of wave powered. navigation buoy can be considerably improved. Peak capture factor increases proportionally with the tube diameter for tube / buoy diameter ratios of up to 75%. Increased tube length widens the frequency bandwidth response. The level of applied damping has considerable effect on peak performance and frequency bandwidth response. With this two degree of freedom system, the levels of applied damping which produce maximum capture factor are approximately 20 times greater than the optimum values for the isolated water columns. Also the radiation damping associated with the two heave modes should be similar so that the damping applied by the power extraction system is matched at both natural response frequencies. The work has general application to the design of wave powered buoys with a central cylindrical water column.
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