Results from previous tests in a wave channel with a heaving axisymmetric floating body, connected to the piston of a pump, are compared with a new time-domain mathematical model, for which model parameters have been chosen to obtain reasonable fit with experimental results. Comparisons are made for heave response and also for absorbed wave power as well as for converted useful hydraulic power. For sub-resonant frequencies, enhanced heave response and larger produced power are achieved by application of a latching-control method.
Already many years ago, an axisymmetric heaving body was considered as a means for extraction of wave energy (McCormick, 1974; Ambli et al., 1977; Bergdahl et al., 1979; Budal & Falnes, 1980; Hicks & Pleass, 1986; Hopfe & Grant, 1986; Nielsen, 1986).
If a piston pump is connected between the body and some forceresisting reference, such as an anchor on the sea bed, a hydraulic machinery may be applied to convert the extracted wave energy into useful energy.
In order to increase energy capture by a power buoy, a control method ("latching control") has been proposed, where the relative motion of the buoy with respect to the said reference is kept latched during certain time intervals of the oscillation cycle (Budal & Falnes, 1980; Falnes & Lillebekken, 2005). An object of the control is to achieve an oscillatory velocity that is in phase with the excitation force from the incident wave.
More recently, an experimental laboratory test has been reported on a reduced-scale model of a heaving axisymmetric body in a wave channel, using sinusoidal incident waves (Bjarte-Larsson & Falnes, 2006). The body was shaped as a cylinder with hemispherical bottom. The diameter was 2rb = 0.14 m and its equilibrium draft l+rb = 0.16 m. The channel width was d = 0.33 m.
