Optimization and simulation of a bionic fish tail driving system based on linear hypocycloid with hydrodynamics

Shu-Yan Wang,Jun Zhu,Rui Zhou,Hui-Yun Zhu,Qin-Feng Li,Xin-Guo Wang

doi:10.1177/1687814017694139

Abstract

The tail driving system based on linear hypocycloid has the advantages of adjustable phase difference, no quick-return, and combining speed reducer with transformation mechanism. The plane complex movement of the driving system was realized via a motion triangle with a linear hypocycloid planetary gear train and a linkage. In this article, we approach the question of which kind of parameter design can make this driving system more efficient in swimming from a hydrodynamic perspective. First, dynamic and hydrodynamic models were established with momentum theorem, Lagrange theorem, and two-dimensional foil theory. And then, hydrodynamic optimization on kinematic parameters (i.e. caudal peduncle’s reciprocation velocity and caudal fin swing angle) and structural parameters (i.e. swing amplitude, V planetary carrier’s angle, and sun gear’s radius) for a better propulsive efficiency was developed in detail. Second, influences of structural parameters on vortex ring were further conducted by numerical simulation in FLUENT. Finally, the prototype and experimental platform of the designed driving system were established, and the theoretical derivation of lift and lateral forces was testified by experiment.

Highlights

Instead of using propellers, bionic fish accomplished swimming with body deformation and fin movements has stimulated extensive attention by biologists, mathematicians, and engineers due to its remarkable feats such as speed, efficiency, and agility
Optimal results based on hydrodynamics show that thrust RT, propulsive velocity v2, and propulsive efficiency h increase with the growth of caudal peduncle’s reciprocating velocity vz
Thrust RT increases with the growth of caudal fin’s swing angle u, but propulsive efficiency h will reach a maximum at u = 308

Summary

Introduction

Bionic fish accomplished swimming with body deformation and fin movements has stimulated extensive attention by biologists, mathematicians, and engineers due to its remarkable feats such as speed, efficiency, and agility. The point is that V planetary carrier’s angle f = 08, based on the referred relationship in section ‘‘Structure of the two-joint linear hypocycloid tail driving system,’’ a real phase difference Du of caudal peduncle and caudal fin is equal to 90°, which accorded with other research. In order to reduce the workload of the numerical optimization, fixed parameters such as phase difference Du = 908, flow velocity v0 = 0.4 m/s, and oscillation frequency f = 1 Hz were directly adopted to verify the influences of sun gear’s size and oscillating amplitude to propulsive efficiency. This number between 0.42 and 0.55 achieves a higher propulsive efficiency.[20] lift force RL due to this jet reacted on the caudal fin.

Experiments

Conclusion