Fin Ray Stiffness and Fin Morphology Control Ribbon-Fin-Based Propulsion

Area of Science:

• Robotics and biomechanics
• Fluid dynamics
• Bio-inspired engineering

Background:

• Ribbon-fin propulsion offers advanced mobility for underwater vehicles in complex environments.
• Bony fishes utilize traveling waves along flexible fins for locomotion.

Purpose of the Study:

• To investigate the impact of flexible rays and fin morphology on ribbon-fin propulsion performance.
• To analyze thrust generation, power consumption, and propulsive efficiency.

Main Methods:

• Developed a physical model with 15 interconnected flexible rays and an elastic membrane.
• Tested variations in ray flexural stiffness and fin aspect ratios.
• Measured fin kinematics, net surge forces, and power consumption in a flume.

Main Results:

• Thrust generation correlated linearly with swept area and the square of relative velocity; thrust coefficient plateaued around 0.5.
• Power consumption scaled with the cube of effective tangential velocity.
• Decreased stiffness reduced thrust and power, but flexible rays improved propulsive efficiency.
• Aspect ratio 1:6.5 showed higher efficiency than 1:3.25.

Conclusions:

• Flexible rays can enhance propulsive efficiency compared to rigid counterparts.
• Fin morphology, specifically aspect ratio, significantly affects propulsive efficiency.
• Optimal morphology and flexible rays can improve performance for ribbon-fin propulsion systems.