Performance variation due to stiffness in a tuna-inspired flexible foil model

Area of Science:

• * Biomechanics and Hydrodynamics
• * Robotics and Animal-Inspired Design

Background:

• * Tuna's efficient swimming is linked to stiff, high aspect ratio caudal fins and streamlined bodies.
• * Previous passive models suggest tail shape alone doesn't determine performance, necessitating dynamic analysis.

Purpose of the Study:

• * To investigate how varying stiffness and kinematics affect swimming performance parameters in tuna-tail-shaped hydrofoils.
• * To compare hydrofoil model kinematics with live tuna swimming data.
• * To assess the utility of hydrofoil models in biomechanical studies.

Main Methods:

• * Analysis of tuna-tail-shaped hydrofoils across a range of stiffnesses, heave amplitudes, and frequencies.
• * Comparison of hydrofoil kinematics with published data from live swimming tuna.
• * Evaluation of different motion control programs for foil models.

Main Results:

• * Intermediate stiffness foils showed enhanced thrust at high heave amplitudes and frequencies.
• * Specific kinematic patterns (minimum lateral displacement at foil's narrowest point) may enhance thrust.
• * Stiffness and kinematics interact subtly, with no single stiffness optimizing both thrust and efficiency.
• * Tuna motion is better mimicked by zero angle of attack foil motion programs without pitch.

Conclusions:

• * Hydrofoil models are valuable for biomechanics research when model characteristics and control programs are appropriately chosen.
• * Accurate replication of fish swimming requires refined motion control programs and physical models, including variable stiffness.
• * Understanding the interplay between stiffness and kinematics is crucial for optimizing bio-inspired propulsion systems.