Inertial effects on the mechanical efficiency of a semi-passive oscillating hydrofoil energy harvester
Abstract
Oscillating-foil-based energy harvesters have demonstrated strong potential for low-speed hydrokinetic energy extraction; however, the actuator-level mechanical energy balance associated with prescribed pitching motion remains poorly understood. The present work experimentally characterizes how foil mass ratio, pitching-axis location, and reduced frequency jointly govern the hydrodynamic and mechanical efficiencies of a semi-passive oscillating hydrofoil. Results show that rotational inertia redistributes actuator demand through phase-dependent torque exchange, while heave-pitch coupling can partially cancel this demand when favorably phased. Pitching-axis location modifies the phase and direction of the fluid torque through changes in the effective hydrodynamic moment arm. Reduced frequency governs the balance between enhanced unsteady loading and inertia-amplified actuator demand. Optimal performance is achieved within reduced frequency region of 0.125-0.16 using quarter-chord to one-third-chord pitching axes and relatively low foil mass ratios from about 0.5 to 2.0, yielding a peak mechanical efficiency of 33.96% -- which can diverge from the hydrodynamic efficiency by approximately 38.16% depending on configuration. Torque-loop analysis and PIV measurements show that this synchronization is a key mechanism governing the observed efficiency trends.
Versions
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BibTeX
@misc{zhang2026inertial,
title = {{Inertial effects on the mechanical efficiency of a semi-passive oscillating hydrofoil energy harvester}},
author = {Zihan Zhang and Qimin Feng and Yuanhang Zhu and Qiang Zhong},
howpublished = {arXiv},
year = {2026},
month = jun,
doi = {10.48550/arxiv.2606.11126},
eprint = {2606.11126},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.11126},
}
RIS
TY - UNPB
TI - Inertial effects on the mechanical efficiency of a semi-passive oscillating hydrofoil energy harvester
AU - Zihan Zhang
AU - Qimin Feng
AU - Yuanhang Zhu
AU - Qiang Zhong
PY - 2026
DA - 2026/06/09
PB - arXiv
DO - 10.48550/arxiv.2606.11126
UR - https://arxiv.org/abs/2606.11126
AB - Oscillating-foil-based energy harvesters have demonstrated strong potential for low-speed hydrokinetic energy extraction; however, the actuator-level mechanical energy balance associated with prescribed pitching motion remains poorly understood. The present work experimentally characterizes how foil mass ratio, pitching-axis location, and reduced frequency jointly govern the hydrodynamic and mechanical efficiencies of a semi-passive oscillating hydrofoil. Results show that rotational inertia redistributes actuator demand through phase-dependent torque exchange, while heave-pitch coupling can partially cancel this demand when favorably phased. Pitching-axis location modifies the phase and direction of the fluid torque through changes in the effective hydrodynamic moment arm. Reduced frequency governs the balance between enhanced unsteady loading and inertia-amplified actuator demand. Optimal performance is achieved within reduced frequency region of 0.125-0.16 using quarter-chord to one-third-chord pitching axes and relatively low foil mass ratios from about 0.5 to 2.0, yielding a peak mechanical efficiency of 33.96% -- which can diverge from the hydrodynamic efficiency by approximately 38.16% depending on configuration. Torque-loop analysis and PIV measurements show that this synchronization is a key mechanism governing the observed efficiency trends.
ER -