Nonlinear ocean wave energy harvester: A novel mooring-based design for enhanced energy conversion

Abstract

This study presents a novel mooring-based ocean wave energy harvesting system, named the Nonlinear Ocean Wave Energy Harvester (NOWEH). Unlike conventional designs, NOWEH addresses a widely overlooked nonlinear behavior inherent in moored buoys, caused by variable-mass chain dynamics, without imposing any additional economic or structural load on the system. The design integrates a spherical buoy with a compact mechanical power take-off (PTO) unit, including a mechanical rectifier, generator, and spring-based dynamic balancer. A dynamic model of the mooring system is developed using energy principles and validated with a real-world 65 cm buoy. Both harmonic and random wave excitations are considered to evaluate system performance. Parametric studies on non-dimensional mooring mass ratio, buoy mass ratio, and stiffness ratio reveal that the optimized configuration enhances hidden relative motion by up to 42 % and improves resonance characteristics. This also led to a redesign of the PTO architecture to better exploit these nonlinear dynamics. The proposed approach offers practical design guidelines for developing efficient, low-cost ocean wave energy harvesters and demonstrates how nonlinear mooring effects, often ignored, can be strategically optimized to improve energy output in real-world sea conditions.