The Fish, the Cat and the WaveTM

Eva Kanso

Caltech

Abstract-
We are interested in the locomotion of aquatic animals due to the coupling between their shape changes and the surrounding fluid dynamics. In this talk, we present a hierarchy of models for describing fishlike swimming in a perfect fluid. The models rely on tools from geometric mechanics similar to those used in studying the falling cat problem where the cat reorients itself by 180 degrees by merely changing its shape. The same approach can be applied to analyze the dynamics of a new skateboard design called the Wave\texttrademark. Indeed, the geometric framework is especially well suited for this class of locomotion problems, that is, locomotion due to shape changes, because the net locomotion is expressed in terms of the shape variables. Further, this approach allows us to address the problem of motion planning or trajectory design as one in optimal control; that is, we seek the most efficient shape changes that achieve a desired net locomotion. For illustration purposes, we show examples of a two-dimensional articulated body propelling and steering itself due to shape changes only. We conclude by discussing the extension of these models to the interaction of the fish with point vortices and other future directions.


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