Artificial lateral line based longitudinal separation sensing for two swimming robotic fish with leader-follower formation

Lateral line system (LLS) is a sensory organ system which serves functions in varieties of flow-relative fish behaviors. Inspired by excellent performances of LLS in fish behaviors, multiple artificial lateral line systems (ALLSs) have been designed and applied to promote underwater robot technology. In this article, we focus on using ALLS for longitudinal separation sensing between two adjacent swimming robotic fish whose tails oscillate, and meanwhile the two fish are towed with a precisely controlled speed which equals to the rectilinear speed of freely-swimming robotic fish with the same oscillating parameters. Flow visualizations based on dye injection technique, hydrogen bubble technique, and computational fluid dynamics simulation are conducted to study the distribution characteristics of the vortices caused by the robotic fish. In addition, towing tank experiments are conducted for investigating the qualitative relationships between the longitudinal separations and the ALLS-measured HPVs of the two robotic fish. This work provide a guidance for the application of ALLS in relative states sensing of underwater robot group composed of two or more individuals, which has been rarely explored.