Optimisation of heaving buoy wave energy converter using a combined numerical model

Abstract

This optimisation study focused on the mass, dimension, hydrodynamic response, and power take-off (PTO) damping for heaving buoy wave energy converters (WEC). A numerical model, consisting of a potential flow (PF) model and a computational fluid dynamics (CFD) model, is designed and applied to address numerical errors caused by liquid viscosity after physical validations. Comparing results from the PF and CFD models, it is evident that the liquid viscosity will produce additional radiation damping for the oscillator near its resonance frequency, leading the decrease of the device's energy absorption. Optimisations based on the combined model were conducted, including non-PTO and PTO cases with both regular and irregular incident waves. The results of non-PTO cases indicate that a buoy with a relatively larger mass is more sensitive to the liquid viscosity, but it still can obtain a better optimal hydrodynamic performance with a higher wavelength-to-diameter ratio. The PTO cases compare the energy absorption caused by the linear PTO and the Coulomb PTO. The comparison results demonstrate that the Coulomb PTO can reduce the effects of viscosity and absorb more energy under identical wave conditions. This paper presents the methods and considerations for working towards the overall optimisations of the heaving buoy WEC. The work will be useful for practitioners and researcher working on wave energy utilization.