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Bio-inspired thruster designs encompass significant potential for developing a new generation of underwater vehicles with enhanced propulsion and maneuvering abilities, to address the needs of a growing number of underwater applications. Undulatory fin propulsion, inspired by the locomotion of cuttlefish and of certain electric eel species, is one...
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... main parameters of the propulsive wave in un- dulating median/paired fins are illustrated in Fig. 2. The velocity V at which the propulsive waveform propagates along the fin depends on its wavelength and the oscillation frequency of the fin rays, and is always greater than the overall swimming speed U of the fish. In fact, the ratio γ = U/V (often termed "phase velocity" or "wave efficiency") is commonly used as a metric for the ...
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... The thrust generation mechanisms and the performance characteristics of undulatory fin propulsion have been investigated through analysis of kinematic data from live animals, 11,12 theoretical models, 13,14 computational fluid dynamics (CFD) studies, 15,16 and experiments with robotic prototypes. [16][17][18][19][20][21][22][23][24] However, despite the progress that has been achieved, there are still gaps in our understanding of the effect of the fin undulations' parameters on the generated thrust, particularly for developing appropriate propulsion control strategies. ...
... For the selected data sets, Fig. 10(a) shows the average steady state velocity U attained by the prototype, as a function of the undulation frequency f and the inter-ray phase shift φ 0 (the corresponding number of waves w is also provided in the upper x-axis of these plots). In line with previous studies, 11,22,24,36 the attained velocity was found to increase with A and f , while its dependence on w is considerably more complicated. It can be seen that, with the oscillation amplitude and frequency held constant, as the number of waves increases from zero, U goes up to a maximum value and is then reduced as w is further increased. ...
... The existence of an optimal number of waves with regard to the swimming velocity has also been observed in prior experimental studies. 20,24,36 However, the detailed sampling of the parameter space adopted in the present work further suggests a dependency on both f and A of the φ 0 value that optimizes swimming velocity. More specifically, the peak in U can be seen to progressively shift towards higher φ 0 values as the undulation frequency increases (with A held constant), or as the amplitude is decreased (with f held constant). ...
Undulatory fin propulsion, inspired by the locomotion of aquatic species such as electric eels and cuttlefish, holds considerable potential for endowing underwater vehicles with enhanced propulsion and maneuvering abilities, to address the needs of a growing number of applications. However, there are still gaps in our understanding of the effect of the fin undulations' characteristics on the generated thrust, particularly within the context of developing propulsion control strategies for such robotic systems. Towards this end, we present the design and experimental evaluation of a robotic fin prototype, comprised of eight individually-actuated fin rays. An artificial central pattern generator (CPG) is used to produce the rays' undulatory motion pattern. Experiments are performed inside a water tank, with the robotic fin suspended from a carriage, whose motion is constrained via a linear guide. The results from a series of detailed parametric investigations reveal several important findings regarding the effect of the undulatory wave kinematics on the propulsion speed and efficiency. Based on these findings, two alternative strategies for propulsion control of the robotic fin are proposed. In the first one, the speed is varied through changes in the undulation amplitude, while the second one involves simultaneous adjustment of the undulation frequency and number of waves. These two strategies are evaluated via experiments demonstrating open-loop velocity control, as well as closed-loop position control of the prototype.
Stable, quiet, and efficient propulsion methods are essential for underwater robots to complete their tasks in a complex marine environment. However, with a single propulsion method, such as propeller propulsion and bionic propulsion, it is difficult to achieve high efficiency and high mobility at the same time. Based on the advantages of the high-efficiency propulsion of a bionic undulating fin and the stable control of the propeller, an underwater robot based on the hybrid propulsion of a quadrotor and undulating fin is proposed in this paper. This paper first introduces the mechanical implementation of the underwater robot. Then, based on kinematic modeling and theoretical derivation, the underwater motion and attitude of the robot are analyzed and the 6-DOF dynamic equation of the robot is established. Finally, the underwater motion performance of the robot is verified through field experiments. The experimental results show that the robot can realize the heave motion, surge motion, and in-situ steering motion independently and can hover stably. When the undulating frequency is 6 Hz, the maximum propulsion speed of the robot can reach up to 1.2 m/s (1.5 BL/s).
This article proposes a locomotion controller inspired by black Knifefish for undulating elongated fin robot. The proposed controller is built by a modified CPG network using sixteen coupled Hopf oscillators with the feedback of the angle of each fin-ray. The convergence rate of the modified CPG network is optimized by a reinforcement learning algorithm. By employing the proposed controller, the undulating elongated fin robot can realize swimming pattern transformations naturally. Additionally, the proposed controller enables the configuration of the swimming pattern parameters known as the amplitude envelope, the oscillatory frequency to perform various swimming patterns. The implementation processing of the reinforcement learning-based optimization is discussed. The simulation and experimental results show the capability and effectiveness of the proposed controller through the performance of several swimming patterns in the varying oscillatory frequency and the amplitude envelope of each fin-ray.
Bio-inspired undulatory fin propulsion holds considerable potential for enhancing the low-speed manuever-ability and hovering performance of unmanned underwater vehicles. Robotic fins typically comprise a number of serially arranged and individually actuated 'fin rays', interconnected by a membrane-like flexible surface, where appropriately timed ray oscillations lead to the propagation of an undulatory wave along the mechanism. In this context, we present an analytical model for the torques arising at the mechanism's revolute joints specifically from the elastic deformation of the membrane. The developed model, which considers the effect of various parameters, related to the fin's geometry, the membrane material properties, and the kinematics of the undulatory wave, is validated through comprehensive experimental studies with a two-ray testbed operating in air.
