Open Access

REVIEW

Hydrodynamic Mechanisms, Fluid–Structure Interaction, and Material Selection in Underwater Bio-Inspired Robots: A Review

Hao Jiang¹, Lucheng Sun², Liguo Shuai^1,*, Zhihan Li^3,*

1 School of Mechanical Engineering, Southeast University, Nanjing, China
2 School of Information Engineering, Yangzhou University, Yangzhou, China
3 Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

* Corresponding Authors: Liguo Shuai. Email: ; Zhihan Li. Email:

(This article belongs to the Special Issue: Advanced Aerodynamics and Fluid–Structure Interactions for Next-Generation Engineering Systems)

Fluid Dynamics & Materials Processing 2026, 22(6), 3 https://doi.org/10.32604/fdmp.2026.082152

Received 11 March 2026; Accepted 11 June 2026; Issue published 30 June 2026

Abstract

Underwater bio-inspired robots have emerged as a promising alternative to conventional propeller-driven autonomous underwater vehicles and remotely operated vehicles because of their potential for high propulsive efficiency, superior maneuverability, reduced acoustic signatures, and enhanced environmental adaptability. Unlike rigid propellers operating under approximately steady inflow conditions, bio-inspired propulsion relies on strongly unsteady hydrodynamic mechanisms, including vortex generation and shedding, added-mass effects, boundary-layer evolution, and flexible fluid–structure interaction (FSI). These processes fundamentally govern thrust production, energy conversion, and maneuvering performance, yet a systematic synthesis connecting hydrodynamic mechanisms with engineering implementation remains limited. This review addresses that gap from a hydrodynamic perspective. First, the major propulsion modes of aquatic organisms, including body and caudal fin (BCF), median and paired fin (MPF), and jet propulsion, are summarized together with their characteristic wake structures. Key unsteady flow mechanisms are then discussed, including reverse Kármán vortex streets, leading-edge vortex dynamics, dynamic stall, boundary-layer behavior, wake instabilities, and biomimetic drag-reduction strategies. Particular attention is given to flexible FSI, including modeling frameworks, passive deformation–active actuation coupling, stiffness and morphology effects, and energy-transfer pathways. Representative studies report propulsive efficiencies of approximately 50–70% for optimized flexible flapping foils and above 70% for phase-tuned dual-foil systems, while biomimetic surface designs have achieved approximately 5–10% drag reduction under specific flow conditions. However, these gains remain strongly condition-dependent, and their practical transfer is still limited by scale effects, propulsor interference, model uncertainty, material degradation, biofouling and insufficient marine validation. Future directions are proposed in real-environment hydrodynamics, multi-robot flow coordination, interdisciplinary modeling, and advanced materials. This review provides a mechanism-to-design framework for understanding, designing, and optimizing next-generation underwater bio-inspired robots.

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