Growing demand for underwater interventions puts the focus on novel Autonomous Underwater Vehicle (AUV) designs. Bio-inspired AUVs aim to replicate the efficient and highly manoeuvrable swimming capabilities of fish and other natural swimmers. To better understand the underlying mechanism of Body Caudal Fin (BCF) swimming, this study conducts CFD multibody simulations coupled with control to study the effect of body curvature envelopes on the turning trajectory and power expenditure as well as comparing powered and unpowered turns.

To investigate the manoeuvring performance of a body-caudal fin robot fish, a numerical framework combining computational fluid dynamics and multi-body dynamics with a closed-loop control algorithm was established in this study. Within this framework, we modelled a body-caudal fin swimmer as a multi-body system with the shape of a NACA0012 hydrofoil. The manoeuvring performance was investigated by using different curvature magnitudes and distributions along the centre line (the curvature is defined by means of a curvature envelop function as part of the general body undulation equation). To characterize the turning performance, a new parameter named cost of manoeuvring (CoM) is proposed. This parameter provides a combined assessment of the turning radius, linear and angular velocity components, and power. It is found that when the body curvature is introduced, the swimmer switches from straight-line swimming to quasi-steady turning at a constant speed. Further investigations were conducted to study contributions of head and tail deformations on the turning performance by comparing predominantly head and tail curved envelopes. Results reveal that a tail-dominated envelope improves performance, whereas a head-dominated envelope has a negative effect.

This paper describes the design and construction of a magnetically coupled modular bio-inspired underwater robot named the Modular Magnetic Bio-Inspired Underwater Vehicle (MMBAUV). Designed to form a traveling wave to mimic efficient Body Caudal Fin (BCF) swimming and manoeuvring, its modularity allows for flexible system setup and offers an opportunity for redundancy and cost reduction through a common design structure. The specific feature of this design presents a novel application of a permanent synchronous magnetic coupling between neighbouring modules with a rotational degree of freedom (DoF). The actuated magnetic coupling provides a reliable and low maintenance solution to the fundamental issues of water tightness of flexible underwater structures. When encountering extreme conditions, the magnetic coupling allows the safe decoupling of the modules increasing the survivability of the robotic system. Presented lab testing results demonstrate the function of the design and provide initial evidence of its thrust generation and manoeuvrability.

To reduce human risk and maintenance costs, Autonomous Underwater Vehicles (AUVs) are involved in subsea inspections and measurements for a wide range of marine industries such as offshore wind farms and other underwater infrastructure. Most of these inspections may require levels of manoeuvrability similar to what can be achieved by tethered vehicles, called Remotely Operated Vehicles (ROVs). To extend AUV intervention time and perform closer inspection in constrained spaces, AUVs need to be more efficient and flexible by being able to undulate around physical constraints. A biomimetic fish-like AUV known as RoboFish has been designed to mimic propulsion techniques observed in nature to provide high thrust efficiency and agility to navigate its way autonomously around complex underwater structures. Building upon advances in acoustic communications, computer vision, electronics and autonomy technologies, RoboFish aims to provide a solution to such critical inspections. This paper introduces the first RoboFish prototype that comprises cost-effective 3D printed modules joined together with innovative magnetic coupling joints and a modular software framework. Initial testing shows that the preliminary working prototype is functional in terms of water-tightness, propulsion, body control and communication using acoustics, with visual localisation and mapping capability.

For the design of a bio-inspired, fish-like robot with caudal fin, a Fluid Structure Interaction (FSI) analysis has been conducted to investigate the influence of material properties and undulation kinematics on hydrodynamic performance and efficiency. This supports the design process with focus on practical prototype build up.

An innovative magnetic joint design has been developed as part of the construction of a bio-inspired Autonomous Underwater Vehicle (AUV) for wind farm inspection. This paper presents our design solutions for a jointed watertight AUV body made using current 3D printing techniques to achieves watertightness and resilient composite metal-polymer bonding. The design avoids dynamic interfaces and the need for rotary seals yet achieves robustness and strength. Test results prove a successful implementation of the magnetic connection between a freely rotating inner shaft and a driven outer shaft in a fish-like jointed AUV body.