Performance analysis of bio-inspired transformable robotic fish tail

We simulate, validate and analyze the performance of a transformable tail of an adaptive robotic fish based on the propulsion of three bio-inspired body deformations similar to those of the big-eye trevally, the butterfish, and the boxfish. The objective is to enable robotic fish operation in rapidly changing underwater environments that may require transitions between swimming modes. The bio-inspired propulsion tail consists of a passive caudal fin attached to three articulated segments each actuated by a servomotor to produce desired deformations. Representing these deformations by analytical functions, the linkage lengths of the three segments are optimized using Simscape. A testing platform, equipped with a load cell and a distance laser sensor, is developed to measure and validate the predicted thrust and forward speed over a range of undulation frequencies and amplitudes of lateral oscillations. Static thrust values are also compared to their theoretical counterparts obtained from Lighthill's theory of elongated bodies' propulsion. The results show that the locomotion modes alone can impact the swimming performance over an unchanging morphology. The experimental results further indicate that synchronicity of locomotion parameters found in nature has a greater effect on the overall thrust than varying a specific parameter.