Development and analysis of a numerical model for a two-oscillating-body wave energy converter in shallow water

The Energy Double System (EDS) is a two-degree-of-freedom (2DOF), nearshore, point absorber wave energy converter (WEC). It is composed of a heaving float and a surging paddle, which are interconnected and each one has its own Power Take-Off (PTO). In this work, a numerical model of the EDS was developed on the basis of the existent laboratory model, which had already been the object of several studies at the Politecnico di Milano. Firstly, a general mechanical scheme of the EDS was developed, which is simplified with respect to the laboratory model. This is a mass-spring-damper 2DOF system, described by a couple of equations linearized around the equilibrium position. Once that the mechanical equivalence with the laboratory model was established, the simplified EDS geometry was set in a Computational Fluid Dynamics (CFD) model, together with the experimental boundary conditions: the EDS is placed in shallow water depth along a sloping beach, undergoing regular waves. Numerical results fairly agree with the experimental ones, although slightly overestimate the energy absorption of the float (+20%) and the paddle (+10%). Finally, new cases were simulated: different values of PTO damping and random waves were tested.