Multi-stage wave energy conversion and electric power estimation of a chamber-breakwater integrated system with a U-shaped impulse turbine

To facilitate a comprehensive exploration of the wave energy conversion process of a full-scale Oscillating Water Column (OWC), encompassing primary -stage (from wave energy to pneumatic power), secondary -stage (from pneumatic power to mechanical power), and third -stage (from mechanical power to electric power) conversions, together with an estimation on the electric power output, a fully coupled model aimed at an OWC-turbine-generator-breakwater integrated system is established, in which an impulse turbine with a Ushaped air duct is employed. Owing to the superior steady-state characteristics (working independently) of the U-shaped air duct turbine, the transient -state (characterized by reciprocating airflow induced by incident waves and embedded into an OWC-breakwater system) characteristics is further explored across a wide spectrum of external excitation conditions. The integration of the chamber -turbine -generator system into a vertical breakwater reveals that an increase in the load torque coefficient corresponds to a consistent rise in the primary -stage conversion efficiency. Opting for a medium load torque coefficient maintains a satisfactory overall efficiency and results in a maximum electric power output of 11.59 kW. In addition, the height of guide vanes significantly influences airflow through the air duct, impacting primary -stage conversion efficiency. Optimal turbine efficiency is attainable under the medium guide vane height, with electric power output ranging from 4.08 kW to 11.66 kW. Moreover, in both free -spinning and forced -spinning modes, the adoption of the U-shaped air duct turbine surpasses the I -shaped turbine in overall conversion efficiency of the integrated system, indicating its superior potential for the utilization of wave energy in nearshore areas. The coupled analysis and power generation prediction model of the OWC-turbine-generator-breakwater integrated system established in this study can serve as a basis for the array deployment of such devices and the scalable development of wave energy.