Nonlinear time-domain study of the hydrodynamic performance of a land-based OWC wave energy converter with simplified impulse turbine Modelling

The hydrodynamic performance of a land-based oscillating water column (OWC) wave energy converter is numerically investigated based on an in-house two-dimensional, finite element, fully nonlinear viscous-modified potential flow solver in the time domain, coupled with an impulse turbine pneumatic pressure solver. The study focuses on elucidating the nonlinear dynamic evolution of wave energy absorption and the internal fluid oscillations within the OWC chamber, with particular emphasis on both the initial transient and the final quasi-steady states. The transient hydrodynamic efficiency and fluid oscillations are examined through phase dynamics via the Hilbert transform. Results reveal that the nonlinear energy evolution is fundamentally governed by the relative phase between excitation and response. The critical role of the absorption components of the spatially averaged fluid velocity in determining the energy absorption efficiency is highlighted. Furthermore, the spatial non-uniformity of fluid oscillations within the chamber is characterized through amplitude and phase differences at various locations. The individual effects of viscous and pneumatic damping on amplitude- and phase-frequency responses, hydrodynamic efficiency, and reflected wave energy efficiency are systematically explored. A typical characteristic over-damped response behavior of fluid oscillations is identified. Finally, the energy transfer processes involving wave absorption, reflection, and viscous dissipation are analyzed through detailed examination of wave energy fluxes. The insights gained from this study provide a deeper understanding of the dynamic evolution of energy conversion efficiency and offer valuable guidance for the design and optimization of high-performance OWC wave energy converters.