A numerical study of the benefits of driving jellyfish bells at their natural frequency. (7th June 2015) - Hoover, Alexander
Abstract: A current question in swimming and flight is whether or not driving flexible appendages at their resonant frequency results in faster or more efficient locomotion. It has been suggested that jellyfish swim faster when the bell is driven at its resonant frequency. The goal of this study was to determine whether or not driving a jellyfish bell at its resonant frequency results in a significant increase in swimming velocity. To address this question, the immersed boundary method was used to solve the fully coupled fluid structure interaction problem of a flexible bell in a viscous fluid. Free vibration numerical experiments were used to determine the resonant frequency of the jellyfish bell. The jellyfish bells were then driven at frequencies ranging from above and below the resonant frequency. We found that jellyfish do swim fastest for a given amount of applied force when the bells are driven near their resonant frequency. Nonlinear effects were observed for larger deformations, shifting the optimal frequency to higher than the resonant frequency. We also found that the benefit of resonant forcing decreases for lower Reynolds numbers. Abstract : Highlights: Driving the model jellyfish bell at or slightly below the resonant frequency led to a high amplitude of bell oscillation. The model jellyfish bell swam fastest at periodic steady state when driven at frequencies at or slightly above the resonant frequency. The optimal driving frequency for forward swimming was dependent upon the magnitude of the driving force. The advantage of driving the bell at its resonant frequency was reduced when additional fluid damping is introduced.