Artificial lateral line based longitudinal separation sensing for two swimming robotic fish with leaderfollower formation * Lateral line system (LLS) is a sensory organ system which serves functions in varieties of flowrelative 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 freelyswimming 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 ALLSmeasured 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.

Obstacle Avoidance Control Strategy of a Biomimetic Wiredriven Robot Fish * Fish has attracted the attentions of researchers because of its excellent swimming performance in water, and biomimetic robot fish was then developed. For robot fish, it is quite significant to perceive its surroundings and then take actions automatically due to the unexpected obstacles. In this paper, a wiredriven robot fish, which can detect obstacles, is designed. We adopt Central Pattern Generator (CPG) for motion control of the robot fish which is capable for smooth transitions among different swimming modes. Moreover, an obstacle avoidance control strategy based on a rule base and a closed loop control structure based on PID algorithm are proposed, which can improve the robot fishxe2x80x99s perception and reaction abilities to the surrounding environment. Finally, experiments are carried out to examine the feasibility of the proposed control strategy.