Model-based Optimization of Anguilliform Swimming Gaits for Soft Robotic Applications

2026-06-09

AI Summary

This study addresses the co-design of undulatory gaits and caudal fin morphology for efficient anguilliform swimming in soft robots. By integrating Lighthill’s large-amplitude elongated-body theory with a geometrically and materially nonlinear structural model, the authors develop a high-fidelity fluid–structure interaction framework solved via an implicit second-order Box scheme. For the first time, this nonlinear coupled model is combined with a multi-objective genetic algorithm to simultaneously optimize control patterns and tail fin geometry, achieving high-speed, energy-efficient underwater propulsion. Experiments on the SLIDER pneumatic soft robot demonstrate a tethered swimming speed of 21.7 ± 0.4 cm/s (0.59 body lengths per second) in quiescent water. The work further reveals a transition in propulsion dynamics—from drag-dominated at low frequencies to inertia-dominated at high frequencies—and extends the optimization framework to multimodal aquatic–terrestrial locomotion tasks.

Abstract

In this paper, we introduce the Soft Lamprey-Inspired Dual Environment Robot (SLIDER) and a proper modeling and optimization procedure employed to design the robot. We represent the primary fluid environment actions - inertial effects, vortex forces, and viscous dissipation - using Lighthill's theory for large-amplitude elongated bodies. For structural design parameters such as internal pressure, tail size, and body stiffness, a fast, geometrically and materially nonlinear model is developed and validated. The fluid-structure interaction equations are solved implicitly with an efficient second-order box method. A pneumatic manifold robotic system is employed to actuate SLIDER in a quiescent water tank environment, allowing cross-comparison of computational and experimental results. We find that low-frequency swimming is dominated by resistant environmental forces, whereas higher-frequency swimming is primarily affected by inertial fluid forces. Using our efficient model alongside a genetic algorithm, we co-optimize a swimming control pattern and caudal fin design (subject to SLIDER's climbing morphology) to achieve a tethered swimming speed of 21.7 +/- 0.4 cm/s (0.59 Bl/s). Furthermore, we investigate the optimization procedure for a multimodal robot performing both swimming and climbing tasks.

Problem

• anguilliform swimming
• soft robotics
• gait optimization
• fluid-structure interaction
• multimodal locomotion

Innovation

• fluid-structure interaction
• soft robotics
• gait optimization
• Lighthill's theory
• multimodal locomotion