Meeting Abstract
Despite significant importance, compliance of fish fins has not yet been investigated with live, freely-swimming fish. This is partly due to the challenges of interrogating a live fish during free swimming and the lack of adequate experimental devices and methodologies to measure the stiffness of the fin. The objective of this work was to validate a perturbation technique by predicting a known change in the stiffness of a physical system. A physical model of known stiffness was built and perturbed with a vortex ring, and its response was measured using high speed video. A second-order model was used to predict how the response of the system changes with compliance and those changes were compared to those observed experimentally. Comparison of the predicted and measured responses suggested that the displacement and the rate of displacement from unperturbed state can be enough to assess the compliance change. For the technique to be applicable to a fish, changes in displacement in the initial 20 – 100 ms due to a change in compliance were compared. This was done to ensure that the technique can work on the live fish by only looking at the passive response in the fin. The proposed technique of applying a known force to the fin and predicting compliance changes by looking at the displacement in the fin, was successful in estimating a known compliance change in a physical system. As the stiffness increases, the displacement at a given time can be expected to decrease and the rate of change from unperturbed state to that displacement at a given time can be also be expected to decrease. These trends hold true within 20 – 100 ms. Future work will involve studying the interaction of the vortex ring with flexible structures under water, so the force estimate of the vortex ring can be better validated for the biological studies.
