Size matters: Scale effects of an OWC wave energy converter

Models help us understand, assess, predict; but they are limited, uncertain. To better understand limitations and uncertainties due to scale effects in model test experiments of wave energy converters (WECs), we conducted a series of experiments at three model scales of a case study oscillating-water column (OWC) WEC. This paper reports incident waves, power, and loads results across scales, and evaluates the causes and effects of identified scale-dependent parameters. Incident wave profiles varied significantly across scales as they became more nonlinear. These nonlinear wave variations caused and interacted with scale effects associated with capture width ratio and loads, which showed moderate significant differences across scales (10-30%+). Larger models tended to show relatively higher power performance and loads. Key scale-dependent parameters likely contributing most to differences in results across scales were associated with the test environment (incident wave generation and nonlinear waves), the model (deployment position relative to the wavemaker and PTO modelling), and instrumentation and apparatus (force balance). Interacting nonlinearities between waves, OWC hydrodynamics, and power take-off damping exacerbated observed scale effects. Thus, scale effects can be significant and should be accounted for in model test experiments of WECs. Doing so will likely improve experimental outcomes and, hence, a WEC's commercial viability. (C) 2021 Elsevier Ltd. All rights reserved.