The Role of Compliant Joint and Flexibility on the Propulsive Performance of a Self Propelled Caudal Fin

Caudal fin plays an important role in the thrust generation of fish locomotion. Recent studies on the role of body flexibility in propulsion show that fish have a remarkable ability to control or modulate the stiffness of the fin for optimized propulsive performance. Along with the fin stiffness, the stiffness of the joint connecting the caudal peduncle and the fin also plays a major role in the generation of thrust. Since thrust and efficiency are dependent on various parameters, a detailed investigation would be required to understand the combined effect of fin and joint flexibility over a wide range of parameters for optimized performance. The present study provides a parametric study on the effect of flexibility of fin and the compliant joint on propulsive performance. For this investigation, fluid structure interaction of the fin has been modeled considering unsteady slender wing theory coupled with the nonlinear Euler-Bernoulli beam theory. The compliant joint has been modeled as a torsional spring at the leading edge of the fin. A comparison of Self–propelled speed (SPS) and efficiency with parameters such as heaving and pitching amplitude, oscillation frequency, flexibility of the fin and the compliant joint is reported. The model predicts the optimized stiffnesses of the compliant joint and the fin for maximum efficiency. These optimal stiffnesses vary with the motion parameters suggesting the benefits of active stiffness modulation in bio-inspired underwater robotics.