Wave-energy Absorption by a Rotating Electric-power Generator Set inside an Asymmetric Floating Body

摘要

This paper deals with the performance in the wave-energy absorption over a wide range of wave frequencies by using a rotating pendulum-type electric-power generator installed inside an asymmetric floating body. In the present model, an electric-power generator is supposed to be set at the center of a smaller cylinder which rotates without sliding on the interior circular surface with larger radius of an asymmetric floating body. The floating body responds in roll to the action of incident wave, and due to coupling effects between the floating body and smaller cylinder inside, the smaller cylinder rotates and then the electric-power generator installed in the smaller cylinder generates electricity. When only the roll motion is allowed for the floating body, the conditions for maximizing the wave-energy absorption efficiency can be derived analytically. It is also shown analytically that if an asymmetric floating body has a special feature that no wave generates on the lee side of the floating body, the maximum wave-energy absorption efficiency becomes 1.0 only with a single mode of roll motion. This result implies that the present device can absorb the wave power perfectly provided the special conditions are satisfied. Numerical computations are performed to confirm the results obtained analytically. It is also shown by numerical computations that the wave-energy absorption efficiency becomes higher around the two resonant frequencies in the swing motion of smaller cylinder and in the roll motion of floating body, and that the total wave power absorbed, which is the integrated value of the absorption efficiency over the wave frequency, can be large by tuning the geometric parameters of the device and the damping coefficient of an electric-power generator.