Session: 06-11-01 Ocean Engineering Technology - I

Submission Number: 174707

Performance Optimization of Glider Hydrofoils for Wave-Powered Mobile Platforms 

Flapping hydrofoils convert wave energy into thrust by generating foil forces and creating a reverse von Kármán vortex street through combined heaving and pitching motions. This propulsion method has been extensively studied recently. Autonomous wave gliders employ tandem hydrofoils to maximize thrust within constrained spaces, resulting in closely spaced foils with overlapping vortex streets. In these configurations, each flapping foil experiences a unique flow field and thus exhibits different performance compared to its single-foil counterpart. Therefore, optimizing each foil is essential for maximizing overall thrust and propulsive efficiency. However, a significant research gap remains in the optimization of individual foils within wave glider systems. This work aims to address this challenge by systematically examining how pivot position and spring stiffness, known to exert a substantial impact on flapping foil performance and are more straightforward to modify than the hydrofoil cross-section, affect the thrust and efficiency of each foil and the overall system. The findings can provide new insights for wave glider design.

To investigate these effects, a series of simulations is conducted on a tandem flapping hydrofoil system. Two NACA 0012 foils are arranged in tandem, spaced 1.5 times the chord length c between their leading edges. The pitch and heave foil motions are prescribed by the wave glider floating body, which travels at 0.2 m/s in regular waves of 0.1 m amplitude and 2.5 s period. The glider unit, located in deep water, is rigidly attached to the float below significant wave orbitals, and therefore cannot pitch freely. Simulations are performed in Simcenter STAR CCM+ utilizing an unsteady, two-equation Reynolds-averaged Navier-Stokes (RANS) approach with the k-ω Shear Stress Transport (SST) turbulence model. A set of pivot positions, {0.09c, 0.16c, 0.25c, 0.33c}, is applied to each foil, resulting in 16 study cases. Average thrust and propulsive efficiency, the evaluation metrics, are calculated from the forces and moments acting on the foils. The performance of each individual foil and the tandem configuration is assessed and compared to corresponding single-foil cases. After identifying the optimal pivot positions, spring stiffnesses, with dimensionless values K* = {0.69, 1.19, 2.19, 2.69} defined relative to foil and flow properties, are applied to each foil at the optimal pivot setting. Performance is evaluated in the same manner.

The results show that the front foil in a tandem system always achieves higher average thrust and propulsive efficiency than its single-foil counterpart across all pivot positions, with this improvement becoming more pronounced as both tandem foil pivot positions increase. The rear foil exhibits a global optimum but can perform worse than a single-foil structure (with the same properties as the front foil) at high pivot positions; however, this negative impact is reduced when the front foil pivot position is also large. The optimal rear pivot position for maximizing system-average thrust is between [0.16c, 0.25c], regardless of front foil pivot position, while total average thrust reaches its highest value at a front foil position of 0.25c. Generally, overall propulsive efficiency decreases as the pivot positions of both foils increase.

For spring stiffness investigations, the front foil depicts improved performance over the single-foil system and remains unaffected by changes in the rear foil spring stiffness. In contrast, the rear foil reveals a global optimum and can underperform relative to the single-foil structure using the front foil properties, but rear foil performance relative to the single-foil system improves as front foil spring stiffness increases. Average system thrust generally increases with rear foil spring stiffness and obtains a maximum when both foils utilize springs with a stiffness of 2.19. Propulsive efficiency is optimized at a rear spring stiffness of 1.19 for any front foil spring stiffness, and the global propulsive efficiency is achieved when the front foil stiffness is set to 0.69.

These findings highlight the distinct hydrodynamic behaviors of tandem versus single-foil systems and emphasize the benefit of optimizing individual parameters to enhance wave glider performance.

Presenting Author: Sirawit Shimpalee University of Michigan

Presenting Author Biography: Sirawit Shimpalee is a current Master's student of the University of Michigan's Naval Architecture and Marine Engineering program. Mr. Shimpalee obtained his Bachelor's degree from the University of Michigan in the Department of Naval Architecture and Marine Engineering in 2025. He has been conducting research for nine years, investigating various topics such as ship hydrodynamics, vortex-induced vibration, piezoelectric generators, tsunami breakwater design, hydrokinetic turbines, and platform mooring design. Currently, Mr. Shimpalee is working on wave glider design under the supervision of Dr. Binh Truong and Prof. Lei Zuo.

Authors:

Sirawit Shimpalee University of Michigan
Binh Truong University of Michigan
Lei Zuo University of Michigan