Meeting Abstract

P1.205  Friday, Jan. 4  Resonance in fish swimming to minimize muscle tension KOHANNIM, S; IWASAKI, T*; UCLA; UCLA tiwasaki@ucla.edu

This research provides analytical support for the hypothesis that swimming fish exploit resonance, using a simple body/hydrodynamic interaction model and optimal gait analysis. Carangiform locomotion of fast-swimming saithe is modeled using three rigid bodies with two rotational joints, representing a large head and undulating pre-caudal and caudal regions, subject to resistive and reactive fluid forces. An optimal periodic body movement (gait) is defined through the minimization of muscle tension, or bending moment, subject to a constraint on average locomotion velocity. Results prove that the gait is optimized when the undulation frequency coincides with the resonance frequency that maximizes the ratio of the tail-tip velocity to bending moment. Numerical results of the optimal gait quantitatively match data gathered from observed swimming, illustrating that live fish are exploiting resonance to minimize muscle tension. Optimal locomotion of fish with active anterior muscles and passive tail muscles explains the tendency of live fish to increase flexural stiffness and undulation frequency with increased speed, while maintaining a constant tail-beat amplitude and Strouhal number. If both anterior and posterior muscles are activated, and there is no body flexibility, resonance still exists purely from body-fluid interactions. This result agrees with previous studies suggesting the existence of hydrodynamic wake resonance. Additional analysis demonstrates a direct relationship between steady-state swimming speed and tail-tip velocity for carangiform swimmers. With this relationship, the Strouhal number can be determined based only on the drag coefficient and the ratio of wetted to tail area.