Abstract
The work in this paper focuses on the examination of the effect of variable stiffness distributions on the kinematics and propulsion performance of a tuna-like swimmer. This is performed with the use of a recently developed fully coupled fluid-structure interaction solver. The two different scenarios considered in the present study are the stiffness varied along the fish body and the caudal fin, respectively. Our results show that it is feasible to replicate the similar kinematics and propulsive capability to that of the real fish via purely passive structural deformations. In addition, propulsion performance improvement is mainly dependent on the better orientation of the force near the posterior part of swimmers towards the thrust direction. Specifically, when a variable body stiffness scenario is considered, the bionic body stiffness profile results in better performance in most cases studied herein compared with a uniform stiffness commonly investigated in previous studies. Given the second scenario, where the stiffness is varied only in the spanwise direction of the tail, similar tail kinematics to that of the live scombrid fish only occurs in association with the heterocercal flexural rigidity profile. The resulting asymmetric tail conformation also yields performance improvement at intermediate stiffness in comparison to the cupping and uniform stiffness.
Highlights
Tuna fish, as one of the most derived members of the family Scombridae, has long been thought as an efficient swimmer during high-speed swimming (Donley and Dickson 2000, Fierstine and Walters 1968, Mariel-Luisa et al 2017)
The stiffened fin rays, the hypural plate, and the collagen fibres together form the main structure of the caudal fin, which withstands the majority of resistance fish experiences when it swims
Inspired by the above studies (Lucas et al 2015 and Mariel-Luisa et al 2017), we systematically investigate the effects of non-uniform distributions of flexural stiffness on the kinematics and propulsion performance of a tuna-like swimmer using our recently developed fully coupled fluid-structure interaction (FSI) solver (Luo et al 2020b)
Summary
As one of the most derived members of the family Scombridae, has long been thought as an efficient swimmer during high-speed swimming (Donley and Dickson 2000, Fierstine and Walters 1968, Mariel-Luisa et al 2017) It is streamlined with a tear-drop-shaped body and a narrow caudal peduncle. The stiffened fin rays, the hypural plate, and the collagen fibres together form the main structure of the caudal fin, which withstands the majority of resistance fish experiences when it swims. These intrinsic configurations indicate that tuna tail is a composite structure, similar to the fish body. The non-uniform distribution of vertebrae and caudal fin rays impart anisotropic structural flexibility and contribute significantly to the fish’s swimming behaviour (Affleck 1950 and McHenry et al 1995)
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