In this work, we present a nonlinear system identification method, modeling the pressure fluctuation inside the chamber of an oscillating water column wave energy converter (OWC–WEC) under monochromatic excitation. The systemic scheme, upon which the identification is based, is a Wiener–Hammerstein cascade and thus the functional analogue of the model is a truncated Volterra series.
The Fourier spectrum of the fully nonlinear thermodynamic equations investigated for various combinations of excitation amplitudes and frequencies revealed that the first three harmonics are the most significant ones and explain adequately the response, while the relative significance of second and third harmonics varies strongly with respect to the excitation parameters.
To tame such nonlinear characteristics, a novel approach is developed for the systemic modeling and identification of the OWC system. The key concept is the construction of filter banks and static-polynomial coefficient banks, associated with the excitation properties (amplitude and frequency) resulting in an accurate and robust systemic model sensitive to the inherent nonlinear characteristics of the actual system.
Furthermore, we present how this novel systemic concept can be appropriately extended in order to be able to treat multi-chromatic excitations. This extension will be fully developed in a forthcoming work.