Modeling and analysis of a swimming tincaeus with bio-inspired stiffness profile

Resulted from the complex interactions among the muscle actuation, body's properties and surrounding fluid, tincaeus fish has great capability to propel itself fast and efficiently. In this study, swimming tincaeus was modeled as a multi-joint dynamic mechanism to explore body's mechanical property. It was actuated at only one joint, and several passive joints were followed with almost arbitrary stiffness profile. Specifically, the stiffness profile was obtained from experiments using the anatomical-cine measuring method. Besides, the reactive fluid force is considered according to Lighthill's elongate theory. To simulate its steady swimming, we built a SimMechanics model, and investigated how swimming performances changed with stiffness distribution, driving frequency and amplitude. And the results show that when driving amplitude is 0.5e-4 N-m, the virtual fish with measured stiffness outperformed at 0.2 Hz, in producing forward speed and tail amplitude, and its velocity was increased with driving amplitude. Besides, after increasing actuation condition by times, we varied the stiffness profile multiplied of the measured values, and found a fish-like swimming through increasing body stiffness by a factor of the square of driving frequency. All these swimming behaviors were closely matched with biological observations. This work illustrated the potential to optimize swimming by changing body stiffness along with driving conditions, and provided a new sight to design robotic fish with various body stiffness.

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