Abstract
Bio-inspired long-based undulating fin propulsion is commonly employed in biological autonomous underwater vehicles (BAUVs), while the hydrodynamic characteristics of various undulating patterns are different. To investigate what kind of undulating pattern has outstanding propulsion or braking performance for BAUVs in directional maneuvers, undulations with four basic undulating patterns are numerically examined under the Open-source Field Operation And Manipulation environment at the Reynolds number of 5 × 102, 5 × 103, and 5 × 104, corresponding to viscous, transitional, and inertial flow regimes, respectively. The study is conducted at various non-dimensional phase speeds c (0.5–2.0, normalized by incoming flow speed) at a constant maximum amplitude of 0.08 and a wavelength of 0.5 (both are normalized by the fin cord length) to imitate the long-based fin. The numerical results indicate that the undulating fin motion with the amplitude envelope gradually increasing from the anterior part to the posterior (conical sinusoidal wave) part may be preferable for thrust generation; undulating with the amplitude envelope increasing from the anterior part to the mid part and decreasing toward the posterior (fusiform sinusoidal wave) presents the superior braking performance when the phase speed is low enough. Moreover, the influence of undulating patterns on the wake structure is analyzed. Through further comparative analysis for propulsion and braking performances, the results obtained here may have instructional significance to the propulsion mechanism in bionic design.
Highlights
With the gradual development of ocean explorations, engineering practice has a much higher requirement of autonomous underwater vehicles (AUVs), which has received considerable attention
Two typical dimensionless wave speeds were selected to investigate how each undulating pattern contributes to the propulsion and braking performances of the fin, respectively
The upper vortex layer is still shed to the upper side of the wake, eventually forming the von Kármán vortex street
Summary
With the gradual development of ocean explorations, engineering practice has a much higher requirement of autonomous underwater vehicles (AUVs), which has received considerable attention. Bio-inspired undulating fin propulsion, inspired by the locomotion of aquatic species, such as stingray and cuttlefish, has some unique advantages, such as enhanced propulsive efficiency, greater maneuverability and agility, and stability in high-energy environments, which has potential enormous applications in the design of more maneuverable underwater vehicles.. Biologists and engineers have long been captivated by the grace and fluidity of undulatory swimmers and are trying to identify optimal solutions for undulatory swimming in terms of speed and efficiency. The optimal shape and motion of undulatory swimming organisms can be obtained by optimizing locomotive performance measures. van Rees, Gazzola, and Koumoutsakos reverse-engineered scitation.org/journal/adv undulatory self-propelled swimmers to maximize the speed or efficiency as a function of both their morphology and gait. Based on the conditions for optimal undulatory propulsion, the imposed deformation of carangiform swimming can increase the efficiency to 50% by the optimized motion.
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