Tractor beam by water waves
Gregory Falkovich, Weizmann Institute

The ability to send a wave to fetch an object from a distance would fulfill many dreams. It was known since Stokes that propagating small-amplitude potential waves only push particles in the direction of propagation. I describe the experiments which show that when waves become three-dimensional as a result of the modulation instability, a floater can be forced to move towards the wave source. The mechanism for this is the generation of surface vortices by waves propagating away from vertically oscillating plungers. That introduces a new conceptual framework for understanding
wave-driven flows, which enables us to engineer inward and outward surface jets, stationary vortices, and other complex flows. The results form a new basis for the remote manipulation of objects on fluid
surfaces and for a better understanding of the motion of floaters in the ocean, the generation of wave-driven jets, and the formation of Lagrangian coherent structures.