Numerical study on coupled heave-pitch motions of multi-body Salter’s duck-WEC with a floating platform in regular and irregular waves

Abstract

The hybrid concept of multi-body Salter’s duck wave energy converter (WEC) provides viable solutions to improve power absorption and reduce the cost of energy. In this paper, the coupled heave-pitch motions of the Salter’s duck combining a floating platform in regular and irregular waves are numerically investigated. The Computational Fluid Dynamics (CFD) based on the Reynolds-averaged Navier-Stokes (RANS) and shear-stress transport $k-\omega$ turbulence model is employed to simulate the whole system under regular and irregular waves generated using the Joint North Sea Wave Project (JONSWAP) wave spectrum, utilizing data gathered from Astara port in the Caspian Sea. We conducted analyses for three distinct scenarios (without platform, fixed platform, and heaving platform) to examine the variations in motion response, power absorption, and performance efficiency. Several significant factors were analyzed, such as differences in wave height, wave period, and angles of incident waves for both fixed and heaving devices. The heaving platform captures maximum power at the wave period of five seconds, while peak performance efficiency is achieved at four seconds. The optimum power take-off (PTO) damping of the single duck under the irregular wave spectrum is found to be 22.5 kN.m.s/rad. The research findings indicate that the heaving platform has a marginally lower wave power capture efficiency than the fixed platform. However, it maintains a consistent pattern in energy absorption from waves and shows reduced sensitivity to fluctuations in wave period, thereby improving its performance reliability.