Compliant Caudal fin

The compliance of a fin affects the thrust of underwater vehicles mimicking the undulatory motion of fish. Determining the optimal compliance of a fin to maximize thrust is an important issue in designing robotic fish using a compliant fin. We present a simple method to identify the condition for maximizing the thrust generated by a compliant fin propulsion system. When a fin oscillates in a sinusoidal manner, it also bends in a sinusoidal manner. We focus on a particular kinematic parameter of this motion: the phase difference between the sinusoidal motion of the driving angle and the fin-bending angle. By observing the relationship between the thrust and phase difference, we conclude that while satisfying the zero velocity condition, the maximum thrust is obtained when compliance creates a phase difference of approximately π/2 at a certain undulation frequency. This half-pi phase delay condition is supported by thrust measurements from different compliant fins (four caudal-shaped fins with different aspect ratios) and a beam bending model of the compliant fin. This condition can be used as a guideline to select the proper compliance of a fin when designing a robotic fish.


Related papers and patents

  • Jeongsu Lee, Yong-Jai Park, Kyu-Jin Cho, Daegyoum Kim, and Ho-Young Kim, “Hydrodynamic advantages of a low aspect-ratio flapping foil,” Journal of Fluids and Structures, Vol. 71, pp. 70–77, May 2017.

  • Hyungmin Park, Yong-Jai Park, Boogeon Lee, Kyu-Jin Cho, and Haecheon Choi, “Vortical structures around a flexible oscillating panel for maximum thrust in a quiescent fluid,” Journal of Fluids and Structures, Vol. 67, pp. 241–260, Nov. 2016.

  • Yong-Jai Park, Tae Myung Huh, Daegeun Park, and Kyu-Jin Cho, “Design of a variable-stiffness flapping mechanism for maximizing the thrust of a bio-inspired underwater robot,” Bioinspiration & Biomimetics, Vol. 9, No. 3, p. 036002, Mar. 2014.

  • Yong-Jai Park, Daegeun Park, and Kyu-Jin Cho, "Design and Manufacturing a Robotic Dolphin to Increase Dynamic Performance," in 2013 10th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), pp. 76–77, Oct. 2013.

  • Yong-Jai Park and Kyu-Jin Cho, “Stabilizing the head motion of a robotic dolphin with varying the stiffness of a caudal fin,” in 2013 13th International Conference on Control, Automation and Systems (ICCAS), pp. 901–904, Oct. 2013.

  • Yong-Jai Park and Kyu-Jin Cho, “Design and Manufacturing a Bio-inspired Variable Stiffness Mechanism in a Robotic Dolphin”, in The 6th International Conference on Intelligent Robotics and Application (ICIRA), pp. 302–309, Sep. 2013.

  • Yong-Jai Park, and Kyu-Jin Cho, "The Effect of a Bio-inspired Variable Stiffness Mechanism in a Robotic Fish," International Symposium on Green Manufacturing and Applications (ISGMA), Jun. 2013.

  • Jeongsu Lee, Yong-Jai Park, Useok Jeong, Kyu-Jin Cho, and Ho-Young Kim, "Wake and thrust of an angularly reciprocating plate," Journal of Fluid Mechanics, Vol. 720, pp. 545-557, Apr. 2013.

  • Hyungmin Park, Yong-Jai Park, Kyu-Jin Cho, and Haecheon Choi, “Mechanism of maximum thrust generation by oscillating compliant caudal-fin model in quiescent fluid,” 66th Annual Meeting of the APS Division of Fluid Dynamics, Vol 58, No. 18, Nov. 2013.

  • Yong-Jai Park, Useok Jeong, Jeongsu Lee, Seok-Ryung. Kwon, Ho-Young. Kim, and Kyu-Jin Cho, “Kinematic Condition for Maximizing the Thrust of a Robotic Fish Using a Compliant Caudal Fin,” IEEE Transactions on Robotics, Vol. 28, No. 6, pp. 1216 –1227, Dec. 2012.

  • Yong-Jai Park, Useok Jeong, Jeongsu Lee, Ho-Young Kim and Kyu Jin Cho, "The effect of compliant joint and caudal fin in thrust generation for robotic fish," 2010 3rd IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics, Tokyo, pp. 528-533, Sep. 2010.