A time-domain non-linear potential-flow model has been developed in order to predict the large-amplitude motions of the SEAREV device in a prescribed or arbitrary sea state. The floating body three-dimensional, undergoing six degree-of-freedom motions. The fluid is considered homogeneous, incompressible, inviscid and with an irrotational flow. Surface tension is not taken into account and the depth is considered infinite. The incident wave field is given by a higher-order spectral method. This spectral method permits the simulation of very steep wave field.