Vol 78 No 1 78102

Abstract

Unmanned surface vehicles (USVs) increasingly support long-duration ocean observation, yet their mission endurance remains constrained by limited onboard energy storage. Wave energy offers a continuous, weather-independent supply, although most pendulum-based harvesters respond to only a single motion axis. This study presents a horizontal-plane pendulum-based inertial wave energy harvester integrated within the USV hull, with the pendulum configured parallel to the XY-plane to simultaneously exploit pitch and roll excitation. A sprag-clutch mechanical rotation rectifier (MRR), a three-stage planetary gearbox, a hypoid stage, and a Halbach-array permanent magnet generator are used to convert the irregular, bidirectional motion of the pendulum into stable, unidirectional electrical output. A Lagrangian-based dynamic model, partitioned into torque-transmitting and freewheeling states, was developed and validated against motion-platform experiments under sinusoidal, swept-frequency, and JONSWAP irregular-wave excitation. The system delivers 13.0 W under matched-load conditions (f = 0.51 Hz, Φ₀ = 15°), exhibits a monotonic increase in output across the principal ocean-wave band (0.10-0.70 Hz), reaches 91 W at Φ₀ = 30°, and yields a fourfold power gain over single-axis operation under in-phase pitch-roll excitation. Under JONSWAP excitation (Hₛ = 1.5 m, Tₚ = 7 s), the mean experimental output is 7.21 W, corresponding to a motion-to-electric conversion efficiency of approximately 43 % under matched-load conditions.