Hydrodynamics of Wave-Induced Flapping Foil Propulsion in Irregular Ocean Waves

The wave glider is a type of watercraft that harnesses wave energy for propulsion using a series of oscillating hydrofoils. Its performance can vary significantly between sinusoidal and irregular ocean wave conditions, and under different pitch constraint mechanisms. To better understand its dynamics and optimize performance in irregular seas, we conduct a computational study of flow-induced pitch oscillations of elliptic foils undergoing irregular heave motions at a chord-based Reynolds number of 10,000, across three sea states. Irregular waves are modeled using the Bretschneider spectrum, a commonly used representation of ocean wave energy distribution across frequencies. Our results show that the flapping foil generates greater thrust under irregular wave conditions compared to sinusoidal waves with equivalent energy. Furthermore, we observe that a spring-based pitch limiter yields higher thrust than an angle-based limiter. To uncover the mechanisms behind the enhanced thrust, we apply the Force Partitioning Method, revealing key interactions between flow structures and foil motion under irregular wave forcing.