Power Takeoff Optimization to Maximize Wave Energy Conversions for Oscillating Water Column Devices

Abstract

This paper presents an investigation on how to optimize the power takeoffs (PTOs) to maximize the mean wave energy conversion from seas for floating oscillating water column (OWC) devices. For this purpose, the linear air turbine PTOs are first analytically optimized to maximize the mean energy conversion for regular waves, based on which a simple and fast-turnaround assessment method is proposed to optimize the linear PTO damping coefficient for maximizing the mean energy conversion for the given sea states. Further on, the focus is on how we can reliably assess the maximized mean wave energy conversions if the OWCs are equipped with nonlinear air-turbine PTOs, as frequently seen in practical OWC plants. Conventionally, the time-consuming time-domain analysis is employed for searching the optimized nonlinear damping coefficients which may be both wave-height- and wave-period-dependent for the given sea state. This may not be suitable in the early design stages of the device when many different options may be compared and checked for optimizing the device itself. As such, a reliable fast-turnaround assessment is very desirable for the device performance and for the assessment of energy conversion for the sea states in the deployment site. From the examples in the study, it is shown that the OWC wave energy converters with the optimized linear PTOs have the same energy capture capacities as those with optimized nonlinear PTOs. As such, it can be suggested that the OWC wave energy capture capacity can be analyzed using the fast-turnaround frequency-domain analysis, regardless of whether the linear or nonlinear PTO is used in the wave energy converter.