An approach for non-linear stochastic analysis of U-shaped OWC wave energy converters

This paper analyzes the dynamics of a U-Oscillating Water Column (U-OWC) wave energy harvester. The geometrical configuration of this device comprises: an air mass enclosed into a pneumatic chamber and connected to the atmosphere through a duct containing the Power-Take-Off device; and a U-shaped water column connecting the air mass to the open wave field. The dynamics of the U-OWC is described by a set of two coupled nonlinear integro-differential equations which have no obvious exact analytical solution. In this context, the paper addresses the problem of estimating efficiently and reliably, albeit approximately, the dynamic response of the U-OWC system given a certain power spectrum-compatible wave excitation. For this purpose, an equivalent linear model describing the dynamic response of the system is derived by the technique of statistical linearization, and used to determine iteratively the statistics of the harvester response. Further, two specific U-OWC configurations are considered: the full-scale U-OWC prototype equipped with a linear Wells turbine in the port of Civitavecchia (Rome, Italy); and a U-OWC small scale model which comprises a non-linear orifice, only, and is installed in the benign basin of the NOEL laboratory (Reggio Calabria, Italy). Relevant Monte Carlo data are used to demonstrate the efficiency and reliability of the proposed approach.