Swimming Under Constraints: A Safe Reinforcement Learning Framework for Quadrupedal Bio-Inspired Propulsion

Fuente: arXiv
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Autori principali: Cui, Xinyu, Han, Fei, Xu, Hang, Zeng, Yongcheng, Sun, Luoyang, Zhang, Ruizhi, Zhao, Jian, Zhang, Haifeng, Li, Weikun, Chen, Hao, Wang, Jun, Fan, Dixia
Natura: Preprint
Pubblicazione: 2026
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author Cui, Xinyu
Han, Fei
Xu, Hang
Zeng, Yongcheng
Sun, Luoyang
Zhang, Ruizhi
Zhao, Jian
Zhang, Haifeng
Li, Weikun
Chen, Hao
Wang, Jun
Fan, Dixia
author_facet Cui, Xinyu
Han, Fei
Xu, Hang
Zeng, Yongcheng
Sun, Luoyang
Zhang, Ruizhi
Zhao, Jian
Zhang, Haifeng
Li, Weikun
Chen, Hao
Wang, Jun
Fan, Dixia
contents Bio-inspired aquatic propulsion offers high thrust and maneuverability but is prone to destabilizing forces such as lift fluctuations, which are further amplified by six-degree-of-freedom (6-DoF) fluid coupling. We formulate quadrupedal swimming as a constrained optimization problem that maximizes forward thrust while minimizing destabilizing fluctuations. Our proposed framework, Accelerated Constrained Proximal Policy Optimization with a PID-regulated Lagrange multiplier (ACPPO-PID), enforces constraints with a PID-regulated Lagrange multiplier, accelerates learning via conditional asymmetric clipping, and stabilizes updates through cycle-wise geometric aggregation. Initialized with imitation learning and refined through on-hardware towing-tank experiments, ACPPO-PID produces control policies that transfer effectively to quadrupedal free-swimming trials. Results demonstrate improved thrust efficiency, reduced destabilizing forces, and faster convergence compared with state-of-the-art baselines, underscoring the importance of constraint-aware safe RL for robust and generalizable bio-inspired locomotion in complex fluid environments.
format Preprint
id arxiv_https___arxiv_org_abs_2603_04073
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Swimming Under Constraints: A Safe Reinforcement Learning Framework for Quadrupedal Bio-Inspired Propulsion
Cui, Xinyu
Han, Fei
Xu, Hang
Zeng, Yongcheng
Sun, Luoyang
Zhang, Ruizhi
Zhao, Jian
Zhang, Haifeng
Li, Weikun
Chen, Hao
Wang, Jun
Fan, Dixia
Robotics
Bio-inspired aquatic propulsion offers high thrust and maneuverability but is prone to destabilizing forces such as lift fluctuations, which are further amplified by six-degree-of-freedom (6-DoF) fluid coupling. We formulate quadrupedal swimming as a constrained optimization problem that maximizes forward thrust while minimizing destabilizing fluctuations. Our proposed framework, Accelerated Constrained Proximal Policy Optimization with a PID-regulated Lagrange multiplier (ACPPO-PID), enforces constraints with a PID-regulated Lagrange multiplier, accelerates learning via conditional asymmetric clipping, and stabilizes updates through cycle-wise geometric aggregation. Initialized with imitation learning and refined through on-hardware towing-tank experiments, ACPPO-PID produces control policies that transfer effectively to quadrupedal free-swimming trials. Results demonstrate improved thrust efficiency, reduced destabilizing forces, and faster convergence compared with state-of-the-art baselines, underscoring the importance of constraint-aware safe RL for robust and generalizable bio-inspired locomotion in complex fluid environments.
title Swimming Under Constraints: A Safe Reinforcement Learning Framework for Quadrupedal Bio-Inspired Propulsion
topic Robotics
url https://arxiv.org/abs/2603.04073