#fluiddynamics
"Tractor beam" from water waves. "Tractor beam" of course being a Star Wars reference. If you increase the amplitude of water waves enough, they become what he calls "3D" waves, and instead of pushing floating objects (e.g. boats) away from the wave source, they pull objects in. The mechanism for this (which doesn't have a rigorous mathematical model) is called modulation instability and it happens because the periodic waveforms created are non-linear this leads to an instability that eventually breaks up the waves into "a train of pulses that create vortices and these vortices can group together to create large flow in one direction."
Tractor beam waves (waves that pull you in) - The Action Lab