Study on the energy capture spectrum (ECS) of a multi-DoF buoy under random waves

Abstract

Energy Capture Spectrum (ECS) and Wave Height Take-Off (WHTO) are two methods for evaluating the energy extraction of a wave energy converter (WEC) by treating energy capture as equivalent wave or wave height loss. This paper demonstrates the relationship between the two in the real sea state and proposed the concept of WHTO under random waves, which is helpful in improving the energy capture evaluation system of WECs. To design and optimize WECs in the preliminary stage, a new ECS calculation method based on potential flow theory is also presented. A case study of a multi-DOF (degree of freedom) buoy was carried out on this method to analyze its ECS characteristics in three main energy-capture DOFs (heave, surge, and pitch). Physical model tests were conducted to measure the initial load and validate the accuracy of the mathematic model. Based on the case study, the characteristics of ECS of the buoy in different DoFs with PTO change were presented and discussed. This paper aims to provide new methods and ideas for the design and optimization of WECs in the real sea state.