Performance variation due to stiffness in a tuna-inspired flexible foil model

Abstract

Tuna are fast, economical swimmers in part due to their stiff, high aspect ratio caudal fins and streamlined bodies. Previous studies using passive caudal fin models have suggested that while high aspect ratio tail shapes such as a tuna's generally perform well, tail performance cannot be determined from shape alone. In this study, we analyzed the swimming performance of tuna-tail-shaped hydrofoils of a wide range of stiffnesses, heave amplitudes, and frequencies to determine how stiffness and kinematics affect multiple swimming performance parameters for a single foil shape. We then compared the foil models' kinematics with published data from a live swimming tuna, to determine how well the hydrofoil models could mimic fish kinematics. Foil kinematics over a wide range of motion programs generally showed a minimum lateral displacement at the narrowest part of the foil, and, immediately anterior to that, a local area of large lateral body displacement. These two kinematic patterns may enhance thrust in foils of

A pressure-based force and torque prediction technique for the study of fish-like swimming

“…For example, understanding how body shape influences swimming specializations [ 5 , 6 ], how material properties of the body dictate swimming performance [ 7 – 11 ], and the relative contributions of individual fins to overall movement [ 12 , 13 ] all remain largely unresolved issues in the study of aquatic locomotion. While many approaches, including computational (e.g., [ 9 , 13 ]), physical modeling (e.g., [ 7 , 11 , 14 , 15 ]), and experimental (e.g., [ 12 , 16 , 17 ]), can be taken to answer these questions, one promising approach is to leverage a detailed understanding of the magnitudes and distributions of the time-varying forces and torques that fishes generate to effect locomotion [ 18 – 21 ]. Despite the value of this information for understanding biological swimming, fish evolution, and developing bioinspired underwater vehicles, the nature of a fish’s fluid environment renders direct measurements of forces and torques impractical.…”

How shape and flapping rate affect the distribution of fluid forces on flexible hydrofoils

“…Many authors have calculated the denominator of (2.8) for pitching fins (input power) as the period-averaged product of torque and angular velocity at the base (Dewey et al 2013;Lucas et al 2015Lucas et al , 2017Quinn et al 2015;Egan, Brownell & Murray 2016;David et al 2017;Floryan et al 2017;Rosic et al 2017;Zhu et al 2017). This efficiency metric is appropriate for hydrodynamic experiments where forces and torque sensors are placed at the attachment rod of the flapping propulsor.…”

Experimental Study of Body-Fin Interaction and Vortex Dynamics Generated by a Two Degree-Of-Freedom Fish Model

“…In the past decade, the field has divided into two groups that focus on either two-dimensional models for parametric studies or three-dimensional models with fewer cases. Within the two-dimensional group, there has been a recent push to understand fish propulsion through nondimensional scaling with a symmetric airfoil representing the caudal fin [10][11][12][13] or a flexible thin foil representing the undulating fish body [14][15][16]. Within the three-dimensional group, there are physical systems that mimic the motions of fish [17][18][19] as well as numerical works that investigate the fluid dynamics around full fish models [20][21][22][23][24].…”

“…The importance of body kinematics has also been shown to be important [14][15][16]22,23,[33][34][35][36]. Wu analytically found that a flexible two-dimensional panel deforming with a transverse traveling wave is preferable to a rigid panel [33].…”

“…Schouveiler et al, noted that the high performance of thunniform swimmers cannot be attributed to the caudal fin only but must also include the interaction between the body and the caudal fin [36]. More recent work has investigated body flexibility using the simplified model of a flexible thin foil [14][15][16]. Numerical full fish simulations by Liu et al, found that the inclusion of the body could increase the thrust produced by the caudal fin by 29.8% when compared to an isolated caudal fin [22].…”