This paper deals with the numerical and experimental work carried out as part of the development of a new wave energy converter device suggested by Aker Solutions. The device consists of one catenary moored platform hinged to several smaller buoys. Energy is extracted through the relative rotation in the hinges. Model tests have been carried out in a towing tank with the aim to verify the use of linear hydrodynamic theory as a mean to predict the annual mean power production. The mathematical model of the device relies on linear hydrodynamic theory, and the commercial BEM code WAMIT is used to obtain the hydrodynamic coefficients. The equation of motion is formulated using generalized coordinates and Lagrange equation. The non-linear characteristics of the pneumatic cylinders, used to represent the power take-off forces in the model tests, necessitate the use of a time domain model. The convolution integral representing the radiation forces is replaced by an approximate state-space model, which is obtained using an frequency domain identification method.
The results show that the simulation model overpredicts the mean absorbed power by approximately 20% in sea states that result in moderate hinge response, whereas in one particular sea state that produce large hinge response, and consequently large power absorption, the overprediction is as large as 49%. This trend is expected, since large hinge response imply that the linear assumption is violated.
